Imagine™ I51-2 High- Performance Mobile Audio

Imagine™ I51-2 High- Performance Mobile Audio
Imagine™ I51-2 HighPerformance Mobile Audio
Speaker System
User’s Manual and
Mobile Audio
Reference Handbook
Table of Contents
(Use your mouse and click to advance to various sections below)
Welcome and Introduction .................................................................................................................. 3
Imagine Individual Component Parameters ................................................................................. 4
Midbass Speakers (Imagine I5)............................................................................................................. 4
Tweeter Speakers (Imagine I1) ............................................................................................................ 5
Imagine System Specifications .......................................................................................................... 6
Midbass Thiele/Small Parameters (incl. mounting dimensions) ............................................ 7
Unpacking/Inventory ............................................................................................................................. 7
How to Use This Manual ........................................................................................................................ 8
Section I - Getting Started – Basic System Installation ............................................................ 9
Coaxial / Component Set Conversion ..................................................................................................11
Installation ...............................................................................................................................................11
Section II - Moving Forward – Advanced System Installation ..............................................14
Lessons Learned .....................................................................................................................................14
Lesson One: Off-Axis Response.......................................................................................................14
Lesson Two: Equalization of Pathlength Differences ...................................................................14
Lesson Three: The Effect of HRTF, ITD, and IID .........................................................................16
Lesson Four: Point-Sourcing ............................................................................................................17
Lesson Five: Reference .....................................................................................................................18
Advanced Installation of the Imagine Component Systems ............................................................18
Mounting Baffle Considerations ..........................................................................................................18
Acoustic Treatment ..............................................................................................................................19
Advanced Installation Conclusions .......................................................................................................20
Warranty ....................................................................................................................................................21
Thank You! ................................................................................................................................................22
Welcome and Introduction
Congratulations on your purchase of high performance Imagine-series mobile audio
component loudspeakers, and welcome to the world of Hybrid Audio Technologies, where
high-end mobile audio loudspeaker development is our passion! When installed and set-up
properly, the Imagine component system you have purchased will make a remarkable
improvement in the sound quality of virtually any mobile audio sound system and give years of
superior performance.
Thank you for going “on line” to read and download your User’s Manual. Our offices are
located amongst the evergreens in North Georgia USA, and we happen to like trees. Aside
from the obvious aesthetic benefits, trees improve our air, protect our water, save energy, and
improve economic sustainability. Additionally, it is expensive to print and distribute thousands
of copies of an owner’s manual; we’d rather invest our production dollars into an incredible
line-up of speaker systems for your listening pleasure. With online resources becoming the
main source of information for more and more people, we are pleased that you’re here,
reading this manual on line, verses having a print copy which might get read once and put
back into the gift box, or worse yet, discarded.
With the publication of this user’s manual and reference guide, it is our goal to assist the “do it
yourself” enthusiast and professional installer alike in getting the highest level of performance
out of Imagine 2-way convertible coaxial and component set using straight-forward installation
advice and practical application of timeless acoustic principles. As you begin to read this
document, you will quickly realize that this is not your typical user’s manual. This manual has
been written to be more or less a miniature mobile audio reference guide that can be used to
better any sound system, and in particular, a system that utilizes the Imagine component
speaker systems. It is an introductory primer to the world of high-end mobile audio; we hope
this user’s manual is not only informative, but motivating. Keep it handy throughout your
installation process, and any time you go to improve your audio system with other Hybrid
Audio Technologies products. We are confident that if the principles explained in this manual
are exercised in your own installation, you will be ecstatic with the sound quality outcome!
We realize that you have a choice in loudspeakers, and are thrilled that you have chosen the
Imagine-series. For more information about Hybrid Audio Technologies, our philosophies
regarding high-end mobile audio, and for information about our other products, please visit us
online at
Thank you, and happy listening!
Scott E. Buwalda
Founder – Hybrid Audio Technologies
© Hybrid Audio Technologies, 2010
Page 3 of 22
Imagine Individual Component Parameters
Your Imagine system contains speaker drivers and a tweeter passive crossover network that
were developed and assembled with a significant effort in research and development,
materials science engineering, an exhaustive level of sampling and prototyping, real-world
testing, and obsessive attention to detail. The specifications and parameters of your Imagine
component system is detailed as follows:
Midbass Speakers (Imagine I5)
Frame: Cast ABS
Cone: Pressed paper
with water proof
Phase Plug: Cast
ABS plastic.
Surround: Inverted
high-loss rubber
Spider: Phenolicized
fabric and tinned
tinsel leads.
The basket is a high-quality cast ABS design, which plays a critical role in
aligning the voice coil in the magnetic circuit. Additionally, the cast ABS
frame allows for better clamping strength verses typical stamped steel
frames, and ensures that the voice coil remains centered in the former.
Hybrid Audio Technologies believes that the pressed paper cone is the best
marriage of lightness, stiffness, and ability of the cone to damp unwanted
cone and edge modes and resonances (read: distortion). All of our designs
use pressed paper cones. The paper cone, known for its excellent sonic
attributes, is water proof, thanks to a polymer developed exclusive and is
proprietary to Hybrid Audio Technologies. The treatment does not change
the look and parameters of the driver like old-fashioned “glossy” polymers
which added an appreciable amount of moving mass and significantly
colored the sound. No, the Imagine cones look like any “normal” paper
cone, but in reality are likely the only high-performance water proof paper
cone car audio speaker systems on the market. The treatment protects the
cone from periodic drips (such as inside a door panel), as well as accidental
splashes to the front of the cone.
When using the midbass in component set mode, the tweeter pole piece is
replaced with an ABS extended phase plug pole piece. The extended phase
plug pole piece is critical for focusing high-frequency information at the
center of the cone. This design ensures the speaker’s response remains
linear into the lower- to mid-treble frequencies.
The inverted high-loss rubber surround (in concert with the spider, detailed
below), helps to provide the compliance and “restorative force” needed for
the Imagine drivers to play effectively into the lower midbass, and even
upper subbass frequencies (depending on in-car cabin gain and other
factors). You'll also know a Hybrid Audio midrange and midbass design by
its inverted surround; this design feature allows for the use of a smaller
height grille, better clearance with OEM panels, and more flexibility in
mounting options.
The spider is the brownish/yellow corrugated (rippled) fabric that attaches
the cone and voice coil. The spider for the Imagine designs was the subject
of a considerable amount of our research and development. The spider is a
phenolic symmetrically-rolled fabric which provides excellent restorative force
during excursion. The spider is vented courteous of the speaker frame; a
design element not typically found in this price range of speaker system.
The spider venting increases the thermal power handling of the I5 driver.
The tinsel leads are connected to real epoxy PCB, not flimsy cardboard.
© Hybrid Audio Technologies, 2010
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Voice Coil and
Motor System:
The voice coil used in the I5 midbass is a 2-layer aluminized copper wire
coils on a round former. An “overhung” voice coil was selected to improve
sensitivity while still keeping distortion to a minimum.
Tweeter Speakers (Imagine I1)
Dome: Small
impregnated silk
textile dome with
high-loss rubber
Voice Coil and
Motor System:
Tweeter Passive
Crossover: LowTolerance Mylar
The I1 has an impregnated fine cloth silk dome diaphragm for a linear,
smooth sound, with a high-loss rubber suspension to damp edge modes and
resonances. The dome is of extremely low mass and is much less
susceptible to mechanical deformation than other designs, and yet yields a
smooth response over the extent of its range. At Hybrid Audio Technologies,
we feel larger diaphragm tweeters sound heavy and unremarkable, lack
detail in the upper treble frequencies, have undesirable polar response, and
are difficult to install. Additionally, we find metal dome tweeters to be harsh,
brittle, and sound unrealistic. As a small diameter, soft-dome tweeter, the I1
is the antithesis of large diaphragm and metal-dome tweeters, for the
effective and convincing reproduction of treble frequencies.
The motor assembly is “conventional dynamic”, with a compact neodymium
magnet structure to ensure a small footprint size and shallow depth. A
perforated grille protects the dome. The voice coil is ferrofluid cooled and
damped, and the tweeter housing consists of extruded plastic with three
different mounting options in component set mode, giving the end-user
flexibility in not only placement of the I1 but also in physical installation.
The tweeter’s protection circuit and crossover filter is a very high-quality,
low-tolerance Mylar capacitor that has been affixed to the midbass frame.
The set ships as a coaxial set, and is ready to install. Should the end-user
want to connect the tweeter in component set mode, simply unscrew the
tweeter, remotely mount the tweeter, and extend wiring back to the midbass
terminals for re-connection to the tweeter output posts. Refer to Page 10
for more details on how to convert from coaxial to component set.
© Hybrid Audio Technologies, 2010
Page 5 of 22
Imagine System Specifications
Efficiency at 2.83
volts / 1 meter
Continuous Power
Handling (RMS)
Peak Power
Power Range
Discussion for
Imagine Midbass
60 Hz – 22,000 Hz, ± 3 dB
Typically, in-car response including vehicular “cabin gain”, or the gain
expected with midbass installed in the vehicle, will result in an extended
midbass and upper subbass response. This is a result of these frequencies
being below the lowest resonance in the vehicle (typically around 50-125 Hz
in most vehicles, described in more detail on page 17). In more practical
terms, install the Imagine midbass into your vehicle and you will see a
dramatic improvement in midbass and upper subbass output, much more so
than just simply listening to the Imagine in a large room, or worse yet, “free
air” (we don’t recommend even trying the Imagine speakers in “free air”
without some form of enclosure or infinite baffle for the midbass).
93.5 dB
100 watts (musical input)
230 watts (musical input)
20 – 150 watts (musical input)
4 ohms
The mechanical and electrical parameters of the Imagine I5 midbass are
amenable to a variety of different installations and speaker locations. The
high Qms (Q factor of mechanical system) and Qts (Q factor of total system),
coupled with the driver’s Fs (resonance frequency) allow it to be used in an
“infinite baffle” configuration. In more practical terms, install the Imagine
midbass such that the front and back waves don’t “meet” (as detailed in
Section I – Getting Started - Basic System Installation), including in a door or
kick panel (using only the airspace behind the speaker as a pseudo
enclosure), with no need for a real enclosure or “box.” The design goes hand
in hand with fool-proof, high-end sound quality with minimal work.
For more advanced users, please reference the Thiele/Small Parameters,
listed on the following page. Note also the mounting diameter and depth for
the I5 midbass.
© Hybrid Audio Technologies, 2010
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Midbass Thiele/Small Parameters (incl. mounting dimensions)
**please note, the following parameters are for the midbass drivers only**
Overall Diameter
Mounting Depth
Mounting Hole
Recommended Minimum Crossover Frequency
Pnom Rated Power Input (No Crossover)
Pmax Rated Power Input (No Crossover)
Pmax (With Recommended Minimum Crossover)
Frequency Range
Voice Coil Diameter
DC Resistance
5 ¼-inch Midbass
6-inch (150 mm)
2.75-inch (70 mm)
4.85-inch (123 mm)
65 Hz
25 watts (AES Standard)
50 watts (AES Standard)
175 watts
55 – 11,000 Hz +/- 4.5 dB
91 dB at 2.83 V/1meter
8.9 g
489 µM/N
5.5 T*m
25 mm (1-inch)
3.4 Ω
76 Hz
9 mm (two way)
5.2 L
8.659 mM2
Carefully unpack the Imagine carton, and verify that the following parts are included in the
box (CAUTION: use care to remove the midbass speakers with two hands, and avoid pressing
your thumb or fingers against the cone of the midbass1):
Two Imagine I5 (5 ¼-inch / 150mm) midbass speakers with integrated tweeter crossover;
Two Imagine I1 (1” / 25mm) tweeter speakers pre-installed in coaxial mode;
Two midbass grilles with anodized aluminum Hybrid Audio Technologies nameplates and
ABS grille mounting flanges;
Nine small packages located underneath the midbass drivers, which contain parts for use
as a component system:
• Two tweeter surface-mount cups;
• Two tweeter flush-mount cups;
• Two tweeter angle-mount cups;
• Tweeter and midbass mounting hardware including two silver plain steel tweeter
retainer clips (attaches to the back side of the flush-mount tweeter cup to keep the
In addition to being careful unpacking the midbass speakers, NEVER test the speaker’s excursion manually with your fingers by pressing the
cone down. This can cause a critical misalignment of the voice coil within the former, and may permanently damage your speakers.
© Hybrid Audio Technologies, 2010
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cup solidly installed), machine screws and set screws for the retainer clips, and
hardware needed to install the midbass speakers, including high-quality black oxide
Philips head screws black anodized screws to mount the midbass speakers; and
A pair of replacement magnet decals.
Should you be missing parts, please contact your authorized Hybrid Audio Technologies dealer
for replacement parts, or contact us directly at [email protected]
How to Use This Manual
As mentioned in the Welcome and Introduction, this is not your typical car stereo speaker
owner’s manual. It is a mobile audio reference manual for not only your impending Imagine
installation, but also to act as a guide to get the most out of your audio system.
Generally speaking, this manual is divided into two parts. The first part focuses on a typical,
basic installation of the Imagine product, and follows in general what you’d expect from a
mobile audio component system owner’s manual. The second part delves into more advanced
topics on optimized speaker placement, “lessons learned” (a topical discussion of real-world
applications), use of sound damping products and acoustic absorption materials, and fine
tuning. Most users will stop at the conclusion of the first section once the basic installation is
complete, and this is perfectly acceptable. But for those with an intrinsic desire to learn more
about how to make their mobile audio systems better, we invite you to continue reading
through the latter half of the manual as well. Our goal is to not only build the best-performing
mobile audio systems in the world, but to also educate consumers and professional installers
alike on how to achieve reference-grade audio system playback in the mobile audio
© Hybrid Audio Technologies, 2010
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Section I - Getting Started – Basic System Installation
Now that you have unpacked the Imagine box and have verified that all of the parts are
included, it is time to evaluate the vehicle for the impending installation. If you feel the least
bit uncomfortable about the installation, have the Imagine speakers installed by an authorized
Hybrid Audio Technologies dealer. The Imagine speakers are an incredible high-end speaker
system, but will only be as good as the installation; a poor installation can negatively affect the
performance of the Imagine speakers.
Should you decide that you can handle the installation yourself and feel confident that the end
result will be adequate to reap the performance benefits of the Imagine component system,
you will need to have certain hand tools available to you for the installation. These include,
but may not be limited to:
Cordless drill/driver with a 1/8” drill bit and a Phillips head and a few assorted Torx
screw driver bits with an attachment (a hand-operated screw driver and/or torx driver
will also likely work);
Certain vehicles may require an assortment of Allen wrenches to remove the old
speakers and/or panel screws;
A panel-popping tool (retaining clip removal tool) to remove panels in the vehicle (such
as door panels). In a pinch, a large flat-head screwdriver does work, but damage to
panels or retaining clips can result;
A wire cutter and wire stripper;
Electrical tape; and
If you plan to use the vehicle’s existing speaker wire, you will need to know which wire
is positive and which is negative at each proposed speaker location. If you’re unsure,
we highly recommend the use of Installation Excellence, an on-line resource for
wire colors, wire locations, fit guides, and technical support. To access the Installation
Excellence site, click your mouse on the blue-highlighted text above.
In a basic system, the Imagine midbass speakers were designed to be installed in the original
factory speaker locations, most often in the vehicle’s doors (more advanced locations that
provide an additional level of performance are discussed in Section II of this manual, if you’re
interested in learning more). The Imagine midbass drivers are infinite baffle-capable
speakers, and must be mounted in a “large enclosure”, or as close to it as possible, with
unrestricted access to airspace to ensure the speaker’s ability to effectively reproduce its wide
frequency bandwidth. The reason why the speaker was designed in this way is highly
empirical. When a speaker is mounted in a small closed box, it radiates as much energy
forward of the cone as it does rearward of the cone. All speaker cones (diaphragms) are a
weak sound barrier at best, and the result of the high amount of energy being “pushed” into a
small enclosure is the energy transmitting through to the outside of the cone (an additive
phenomenon to the incidental wave). Consequently, Hybrid Audio has designed the Imagine
midbass to work well without an enclosure, and as such, should not be significantly prone to
enclosure back-pressure and sound coloration when placed infinitely baffled. The “infinitely
© Hybrid Audio Technologies, 2010
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large” enclosure, such as one might find in a door panel, improves spectral response and
power response variation between high and low frequencies.
In a basic system, like the Imagine midbass, the Imagine tweeters were designed to be
installed coaxially with the midbass, or as a component system in the original factory tweeter
locations, such as those typically found in many newer-generation vehicles, most often at the
top of the door, or in the “a-pillar.” The obvious “path of least resistance” is to leave the
Imagine speakers in their coaxial mode. If you do decide to use the Imagine set as a
component system, and if your vehicle is older, or did not come with factory tweeter locations,
you may need to install the tweeters in a bit of a custom fashion. Not to fear though – we
have included several different options for easily mounting the tweeters, so you can decide
which will work the best for your application. Since the tweeters are a sealed-back design,
they can be placed anywhere without having to provide airspace or any type of enclosure.
Hybrid Audio Technologies highly recommends that the tweeter placement be the subject of
your own experimentation. This can be accomplished by leaving some excess wire length for
the tweeter, and experimenting with different potential mounting locations by temporarily
attaching the tweeter using double stick tape, Velcro®, etc.
An important learning note! Hybrid Audio Technologies designed the Imagine-series to be
used predominantly as a coaxial, as we can effectively mitigate anticipated environmental
conditions and reduce the number of variables in this type of installation. When used as a
coaxial, the relative amplitudes (volumes) of the midbass and tweeter are equalized to each
other and the speaker will perform as intended. There is much less amplitude control of the
tweeter amplitude with respect to the midbass amplitude when the set is converted into
component set mode. This is due to simple physics. If the midbass drivers are placed low in
the door, for example, and the tweeter is placed high in the dashboard, sail panels, or apillars, there WILL be a notable amplitude difference between the two speakers. This is
because the midbass are installed further from you, and are likely aimed into your leg,
carpeting, and other soft furnishings in the vehicle, while the tweeter is located likely closer to
you, likely aimed more “ox-axis”, and is near hard, reflective surfaces, such as window glass,
hard plastic interior panels, and etc. In many cases, converting to component set will cause
the tweeter to be notably louder than the midbass. This is not a speaker malfunction; it is a
simple acoustical phenomenon playing out in your vehicle. Hybrid Audio Technologies usually
recommends that the Imagine sets be left as a coaxial, but encourage the end-user to test the
Imagine systems in both formats to evaluate what suits the end-user’s listening habits best.
Finally, just because there is a factory tweeter pod location in the dashboard, a-pillars, or sail
panels in your vehicle doesn’t mean you have to use it! Because our ears are on the left and
right sides of the human head, human hearing is much less susceptible to hearing height cues
as it is hearing width and depth cues (please reference Lesson 3 and Lesson 4 later in this
manual). Please don’t be fooled into thinking that the tweeters MUST be placed high in order
to establish a good stage height! Alas, as the end-user, it is up to you to take the time and
test the set to see what orientation is to your liking, and certainly, as students of acoustics, we
at Hybrid Audio Technologies encourage that learning exercise.
© Hybrid Audio Technologies, 2010
Page 10 of 22
Coaxial / Component Set Conversion
At this juncture, you must decide if you want to install the Imagine set as a coaxial, or as a
component system. If you opt to continue on as a coaxial, you can disregard this section. If
installing as a component system, read on.
Here are a few very simple steps to convert your coaxial into a component set:
1. Remove both midbass’ from the Imagine carton and flip them upside down on a clean,
non-abrasive surface such as a kitchen table.
2. Peel the Imagine decals off of both of the midbass magnets. You will now see a small
screw in the dead center of the magnet. This screw is holding the tweeter and the tweeter
pole piece (the “platform” the tweeter is attached to) in place.
3. Disconnect the tweeter’s wires from the midbass’ terminals. Note that red is positive and
black is negative.
4. Put the midbass in your hand and softly cup the tweeter in the palm of your hand. Use a
3mm hex wrench (alan-head wrench) to remove the screw and allow the tweeter pole
piece to drop out from the front of the midbass into your hand. Pull the speaker wire
through the midbass’ magnet. DO NOT DISCARD THE SCREW!
5. Locate the extended phase plug pole piece in the kit (looks like a bullet), and insert the
bullet into the magnetic gap the same way the tweeter pole piece used to be inserted.
Secure the extended phase plug pole piece bullet with the screw you just removed.
Tighten securely, but don’t over-tighten. Note, the screw is the perfect length to snug the
pole piece to the former. DO NOT shorten the screw or use a different screw! The last
several turns of the hex key actually “cut” threads into the phase plug, ensuring that it
does not come loose over time. Keep turning the screw until the phase plug is secure.
Please read here for more details:
6. Locate the magnet decal in the Imagine carton and replace the decal to the magnet of the
midbass. The decal doesn’t need to be installed if you want to skip this step.
7. Extend some speaker wire length (not included) between your tweeter location back to the
midbass, and re-connect (red to positive and black to negative).
Once you have determined the mounting locations for the Imagine separates, and have
evaluated the circumstances by which the Imagine speakers will need to be installed, it is time
to dismantle the vehicle to access the old speakers. Most dashboard-mounted speakers are
easily accessed by removing their grilles, which are usually attached to the dashboard with
screws or retaining clips. A-pillars are usually accessed by pulling firmly at a right angle to the
panel. Door speakers are usually easy to access as well, either from the front by prying off
the OEM grille, or by physically removing the entire door panel. In all cases, it may be
prudent to reference your vehicle’s factory service manual. If you don’t have a factory service
manual, you can go to the Installation Excellence website for downloadable resources with
© Hybrid Audio Technologies, 2010
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respect to not only wiring but disassembly of your vehicle, and the procedures to access your
OEM speakers.
With the OEM speakers removed, we HIGHLY recommend the use of a self-adhesive damping
product, such as brand names Dynamat®, B-Quiet®, and others. The reason for the use of
damping material is to quiet buzzes and rattles that will be exposed by the high-performance
Imagine midbass speakers, but more importantly to seal up door accesses and cavities,
thereby creating a pseudo “enclosure” for the Imagine midbass. If the midbass are installed
immediately adjacent to a large access hole or opening in the door panel, there will be an
acoustic “short circuit” (as described later in “Frequency Response”) where the front and back
waves of the speaker meet, and cancellation will occur, seriously effecting midbass output.
The use of a good damping product is the single-biggest installation-related improvement you
can do to enhance the performance of your Imagine audio system. And since the Imagine
midbass require an “infinite baffle”, it is intuitive to seal up the mounting area as best as
possible, such as in the door, allowing the speaker to “see” a large enclosure in the door
cavity, kick panel, dashboard, or wherever you decide to mount the Imagine midbass.
If you plan to use the OEM speaker wiring, you will likely need to cut off the OEM speaker
plug, and strip back approximately 3/8” (10mm) of insulation to expose the bare wire. It is
recommended that you then install slide-style terminals on the wire, for easy connection to the
Imagine midbass.
In a basic installation, the Imagine midbass were designed to install directly into the factorysupplied speaker baffles or speaker openings. The speaker should fit snug to the baffle
without air gaps; do not force the speaker into a baffle that is too small, as this will damage
the speakers. If the factory-supplied mounting baffle is too small, refer to Section II for
advice on how to build custom baffles. When tightening your speakers to the baffle, alternate
the tightening of the screws, just as if you were changing a tire on your vehicle, by alternating
in a pattern around the speaker until all screws are hand-tight. DO NOT INSTALL THE
SPEAKERS WITH A DRILL OR DRILL-DRIVER, as the drill-drive will put considerably more
torque on the speaker basket than what is required, and can easily damage the frame of the
In the event a component set mounting topology is chosen, the same procedure can be
followed for the tweeter installation observing the precautions mentioned in the midbass
installation, above. Once a suitable location is found for the tweeters, mounting options can
be evaluated. The Imagine kit comes standard with three tweeter mounting options, including
a swivel flush-mount cup, a surface-mount cup, and an angle-mount cup. The tweeter fits
first into the surface-mount cup, and then can be installed as one unit into the flush-mount
cup. Conversely, the surface-mount cup can be attached to the angle cup as well. In all
cases, the tweeter is fitted into the surface-mount cup first, and in then either installed as-is,
or is further encased in the flush-mount cup, or is attached to the angle-mount cup. Decide
which mounting strategy works the best for your installation, and permanently mount the
tweeters. Route the wiring from the underside of the tweeter to an accessible location and
connect to the tweeter connections (small diameter slide terminals) on the midbass frame.
© Hybrid Audio Technologies, 2010
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Once all four speakers are installed, you will need to do a brief listening test with CD-quality
music that you are intimately familiar with to determine if the tweeter seems to be linear in
amplitude with the midbass, or seems to be too muted. If the tweeter seems too muted, or if
you prefer a louder tweeter sound, simply reverse the black and red wires on the tweeter
terminals located on the frame of the midbass. You will be changing the polarity of the
tweeter, and will be increasing the loudness of frequencies between approximately 6,000 –
10,000 Hz by doing this.
Once all four speakers have been installed and the level set as per the above, the sound
damping cropped so as to allow for the re-installation of door panels and/or interior panels,
and all wiring neatly wire-tied away from heat and noise sources, or from abrasion and areas
where the wires may be accidentally sliced or cut, the vehicle can be re-assembled. Sit back
and enjoy the music.
This is the end of Section I: Basic Installation. If you’re happy with the end product, stop
reading here. If you want to learn more about advanced techniques for achieving great
mobile audio sound quality, flip the page!
© Hybrid Audio Technologies, 2010
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Section II - Moving Forward – Advanced System Installation
The previous section detailed a typical, basic installation of the Imagine product. In this
section, Hybrid Audio Technologies has prepared a more advanced topical discussion of
Imagine I51-2 installation techniques, concepts, and principals, where a little bit of additional
installation work can net immense gains in overall sound quality.
There are certainly many things you can do to improve your mobile audio system, such as
addition of amplification, a dedicated subwoofer system, higher-gauge speaker wire, and
higher-end passive crossovers, and active crossovers. All of these things require an additional
amount of monetary investment into your audio system, and may not net the immediate gains
that other, more elementary installation items can net.
The following discussion is pertinent to easy and cost-effective enhancements you can do for
your audio system, particularly as it relates to the installation of Imagine component speakers.
In any mobile audio system, the weakest link will always be the speaker systems, followed
closely by installation techniques (sometimes its vice-versa). Since the Imagine component
system you have purchased has solved the first issue, where speakers are the weakest link in
your audio system, the second issue, that being installation techniques, can see a significant
improvement as well by understanding and incorporating some or all of the techniques in the
following sections.
Lessons Learned
We like to call this our “Lessons Learned” section, where we expose some critical lessons that
we have learned through thousand upon thousands of hours of trial and error:
Lesson One: Off-Axis Response
When a speaker system like the Imagine I51-2 is placed in an automotive environment, we
hear the direct (shortest path) and reflected (longer path) sounds, such as resonances and
reverberations. The two sounds are processed by the brain as one sound, and this influences
our perception of height, width, and depth of soundstage, as well as rearward ambience. For
this reason, the off-axis radiation pattern of any speaker in a vehicular environment has a
significant influence on how natural the music sounds.
The lesson to learn here is that most mobile audio sound systems benefit greatly from having
the front stage speakers at least partially “off-axis.” Off-axis means that the speakers are not
pointing at you, but rather at some angle less than 90 degrees away from you.
Lesson Two: Equalization of Pathlength Differences
Quite possibly the most important functional consideration that a do-it-yourself enthusiast or
professional installer should give to the Imagine speaker placement is to optimize, as best as
possible, pathlength differences (PLD’s) in the vehicle. PLD’s are defined mathematically as
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follows (this example assumes a right-hand driven vehicle---PLD’s are always a positive
X = distance of the center of the left speaker from your left ear.
Y = distance of the center of the right speaker from your right ear.
Z = pathlength difference.
Applying this formula, assume that the distance of the left speaker from your left ear is
140cm, and the distance of the right speaker from your right ear is 100cm, the pathlength
difference is 40cm.
Good stereo imaging is completely dependent on arrival times of the fundamental vocal
frequencies. Differences as little as 10 microseconds can be detected by the brain. A PLD of
30 centimeters equates to the sound from the nearest channel arriving about 0.9 milliseconds
earlier than the furthest channel. It is Hybrid Audio’s opinion that the end-user should try to
keep PLD’s to less than 30 centimeters in a vehicle which is intended to have good imaging
and staging character from both seated positions.
The best way to go about evaluating certain locations in your vehicle is, in general, to look for
the potential locations as far forward and away from you as possible, but still with a general
“line of sight” to the speakers (particularly the speaker on the far side of the vehicle). An easy
way to test various potential locations is to hold a tape measure or other measurement device
from the potential speaker mounting locations, and measure those locations with respect to
your ears.
Reference Figure 2, below. In this scenario, three potential locations for the mounting of the
I5 midbass driver are shown:
Figure 1: Potential Locations for Mounting the Imagine Midbass Speakers
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In scenario “a”, we show the installation of the I5 in the dashboard, high in a door panel, or apillars. As you can see from the diagram, the PLD’s between the left and right speakers are
large, due to the proximity of the listener to the near-side speaker. While the mounting of
primary drivers in the dashboard or a-pillars has become increasingly popular, this
configuration will undoubtedly require both time and intensity domain equalization in most
vehicles to ensure a good, focused center image, properly located in the center of the vehicle
for one seated position. There are, however, some rare exceptions, and you may actually
find that the dashboard locations provide the best equalized PLD of the available mounting
locations; this is very rare though – in our experience, less than one percent of vehicles on the
market today have optimized dashboard speaker locations for the midbass drivers.
In scenario “b”, a typical door installation location is shown, and in many vehicles represents a
good improvement in PLD’s from the dashboard, high in the door panel, and a-pillar location
identified in scenario “a.” The door speaker installation scenario is the one detailed in the
basic installation section at the beginning of this manual, and in most vehicles represents a
satisfactory location to mount speakers; not ideal but satisfactory. The door speaker
installation scenario will likely also require some amount of time and intensity equalization to
ensure a centered image in most vehicles; this can be as simple as adjusting the balance
control on your source unit, to more advanced ways of digital time and intensity manipulation.
The third and final potential mounting location as shown in this diagram (scenario “c”)
represents a kick panel installation, where the midbass are placed far forward in the A-frame
cavity of the kick panels, present in most vehicles. The kick panels are the small panel next to
the throttle and brake pedals, down by your feet. While it is not immediately obvious looking
at a two-dimensional drawing, in many cases the kick panel location affords the best
equalization of pathlength differences for most vehicles. And the reason why this is a good
choice for most vehicles is defined in the second full paragraph of Lesson Three, below.
The lesson to be learned here is that by taking a few moments to evaluate the potential
mounting locations in your vehicle, in a very short period of time, you will be able to find the
best location for your I5 midbass by determining the location with the smallest PLD.
Lesson Three: The Effect of HRTF, ITD, and IID
Head-related transfer function (HRTF), interaural intensity differences (IID), and interaural
time delay (ITD) all play a key role in the optimum placement location for the Imagine
component speakers. A sound wave approaching the eardrum from your chosen speaker
location is shaped by interactions with the size and shape of your head, torso, and outer ear,
resulting in the HRTF. More specifically, the HRTF is the ratio between the sound pressures of
the wave at the eardrum, as compared to the sound pressure that would exist at the center of
the head if the head were removed. In general, the sound arriving at the ear further from the
source is attenuated and delayed relative to the sound arriving at the ear closer to the source.
This generates an interaural intensity difference (IID) and an interaural time delay (ITD). As a
sound approaches the head, the ratio of distances from the speaker location to the near and
far ears increases, and the effects of head-shadowing are amplified, causing the IID to
increase. The spectral shaping caused by the head and the shape of the outer ear may also
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change. The ITD, which results from the absolute difference in path length from the source to
the ears, remains approximately constant as distance decreases. From this we learn:
ITD is the dominant factor for frequencies below about 500 Hz;
A combination of ITD and IID are dominant for frequencies between approximately 500 Hz
and 2,000 Hz; and
IID, in concert with HRTF, are dominant above about 2,000 Hz.
These are generalizations, and are subject to the size and shape of one’s head and torso, and
size and shape of the outer ear (the folds and ridges of the ear), but in general, the above is a
good guideline for establishing ITD, IID and HRTF thresholds for the human auditory system.
Because the I5 midbass’ ability to play into the sub-200 Hz range, an effect clearly dominated
by ITD, up to and including frequencies exceeding 6,000 Hz, an effect clearly dominated by
IID and HRTF, placement of this driver is extremely important. The driver should be placed as
far forward as possible in the vehicle to optimize ITD. Lateral (forward to back) placement is
much more important than horizontal placement (up and down). This is because of the brain’s
ability to process sounds such as spectral envelope cues, and use a phenomenon known as
the “precedence effect”; the brain can be easily “fooled” into thinking a sound stage is high
with kick panel or floor-mounted speakers (a word to the wise: the best place to put a set of
speakers is not always “up high”, as most vehicles do not offer an amicable location in the
dashboard or a-pillars for good image placement for both seated passengers, especially in the
critical frequencies sub-500 Hz). In addition to the time equalized placement of the drivers,
the end-user must also consider that above approximately 2,000 Hz, intensity plays a key role
in good sound staging and imaging. Therefore, the Imagine midbass’ should be placed in an
area where intensity differences can be equalized, either mechanically or electronically, to
ensure good imaging and sound staging.
The lesson to be learned is that, like Lesson Two, the Imagine midbass should be placed as far
forward from your listening position as possible, and every effort should be made to optimize
time and intensity domain characteristics of the installation.
Lesson Four: Point-Sourcing
The term “point-sourcing” is often used to describe the technique of having a single pair of
speakers in an installation cover the majority of the critical middle band frequencies. In many
installation scenarios, the Imagine midbass could be considered a point-source speaker driver,
because it has the ability to reproduce six octaves of tones. Point-sourcing, if done correctly,
can lend itself to a variety of valuable attributes, including precise image definition and stable
sound staging character. By applying Lessons 1-3 above, the Imagine I5 can be used as a
point-source midbass driver to achieve excellent staging and imaging results.
The lesson to be learned here is that the I5, given its wide-bandwidth design, can faithfully
reproduce as much as six octaves of tones, and would make a valuable addition to any sound
system as a point-source driver for the spectrum comprising vocal imaging cues.
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Lesson Five: Reference
One of the most important things to do before completing your Imagine installation is to get a
reference for your future listening tests. To really know what a snare drum sounds like, you
must go and listen to one, in person, live and un-amplified. There is no substitute for the
visceral impact and emotion of live music. Nothing else in life can touch your soul the way
music does. Whether it’s a 200-member orchestra, or a four-piece fusion band, nothing
compares to the phenomenon of live music.
Take this as Hybrid Audio’s official request: become a student of music and your mobile audio
sound system will be better for it. We want nothing more than to know there are great
sounding audio systems around the world using our products, and you’d make us all very
proud if you became a student of music and learned its beauty and passion.
Advanced Installation of the Imagine Component Systems
Mounting Baffle Considerations
Now that we have revealed five of our most important “Lessons Learned”, we can now apply
these lessons to the Imagine installation. The first important matter is the physical installation
of your Imagine midbass, and more specifically with respect to improving the Imagine
midbass’ mounting baffles. Most vehicles’ factory mounting locations for speakers are less
than ideal. In most cases, the OEM speaker mounting flanges are likely nothing more than
flimsy extruded plastic, and provide no sonic benefit to your Imagine installation. The Imagine
drivers are long-throw midbass, and the plastic mounting baffles that come from the factory in
virtually every vehicle will lead to buzzes, rattles, vibrations, and resonances, all of which
negatively effect the Imagine installation. In other vehicles, you may have attached the
Imagine midbass’ directly to the door metal (hopefully with a layer or two of self-adhesive
sound damping in between), but this is still not entirely ideal. In whatever scenario you have
installed your Imagine midbass, there are certain “tricks” and techniques that may be applied
to get the most out of your Imagine component set, specifically the midbass installation, as
Mounting the baffle, sound damping, and “decoupling”: the mounting baffle or
mounting location should either be secured extremely well to the vehicle’s body, or
completely isolated from the vehicle’s chassis. The reasoning is that the speaker baffle
panel will vibrate and will radiate sound. Even small vibrations can result in the baffle
itself radiating more sound than the actual speaker at certain frequencies. The
mounting baffle or mounting location should be damped with a layer of typical sound
damping to reduce the Q of the baffle and lower its vibration resonance frequency
below the range of the driver’s frequency response. In many cases, using thicker baffle
panel in concert with self-adhesive sound damping can also be advantageous, provided
the rearward wave of the speaker has no obstructions created by the baffle itself.
Finally, if possible, the speaker should be mechanically decoupled from the baffle. This
can be something as simple as a layer of self-adhesive foam tape, to more exotic
examples of decoupling, including rubberized rings or multiple-layer septum shielding.
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Building solid mounting baffles: in many cases, it is advisable to mount your
Imagine midbass’ in high-stiffness wood or high-density fiberglass (or wood treated
with fiberglass resin). Hybrid Audio Technologies recommends the use of a solid
hardwood, such as birch or oak, namely because these woods are stiff and help to
dissipate resonance, and screws can be inserted and removed multiple times without
stripping. Avoid Medium Density Fiberboard (MDF), particularly in wet environments
like the door, as the MDF will act like a sponge with humidity and moisture, and not
only that, the MDF is a dense, but not stiff type of wood, and the results may not be
particularly noticeable if you use MDF. Once your baffle is built, it must be covered in
one or two layers of a good-quality, brand name self-adhesive damping product; a solid
wood mounting baffle with sound damping treatment will augment the Imagine
installation by eliminating resonances.
Mounting baffle dimensions: While building baffles is important, it is notable that
mounting baffle size is equally important. All mounting baffles should be kept as small
as possible with respect to the size of the speaker. The purpose of using a small baffle
is to avoid the potential for low amplitude diffracted sound waves becoming summed
with the incidental waves. A narrower baffle also becomes increasingly important as
frequencies range into the Imagine midbass’ upper bandwidth, where the power
response is more uniform and incident and reflected waves are indistinguishable. In
practical terms, keep baffle dimensions small with respect to the size of the Imagine
midbass, chamfer or round sharp edges (including, in particular, the mounting hole’s
rear inner edge), flush-mount the speaker whenever possible, and use shallow, surfacemounted hardware. Also, remove all unnecessary protrusions from the baffle surface.
Acoustic Treatment
A considerable benefit can be made to any mobile audio system with the select placement of
acoustic treatments. The purpose of using acoustic treatments is to reduce the amount of
reflected energy in the hostile automotive environment, and hear more of the direct sound
being emanated from the speaker. It is akin to the signal to noise (S/N) ratio in a piece of
electronics, where the signal could be considered the direct energy coming from the speaker,
and the noise could be considered the reflected waves off of nearby surfaces, such as
windows, hard center consoles and door panels, windscreens, and etc. A word of warning
though: there is a fine line between too little and too much acoustic treatment; just as some
vehicles can benefit from some selectively applied treatments, there is a point where the
vehicle can begin to approach “semi-anechoic” conditions, and lose its liveliness, which is not
ideal. Reflections are all around us, and are a part of our day-to-day lives. It is our opinion
that some lateral reflection is a good thing; it helps to establish stage boundaries, and gives
the recoded playback and more visceral and “believable” sound.
The first principle to understand is that below 200
virtually useless. It is Hybrid Audio’s assertion that
benefit from the use of treatments, given that a 200
meters is less than or equal to most vehicle widths.
Hz, acoustic treatments are rendered
only those frequencies above 200 Hz
Hz waveform is about 1.7 m long; 1.7
This is also the frequency where we
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believe pure tones in the vehicle are going to be difficult, if not impossible to localize. Finally,
most vehicles exhibit a Schroeder Frequency (Fs) between 50 at 125 Hz; the Fs (or cabin-gain
frequency) is vehicle dependent, and is the frequency at which resonances become so tightly
packed in frequency and space that the acoustical properties of the vehicle behave quite
Acoustic treatment can be very effective above 200 Hz, depending mostly on the polar
radiation pattern of the speaker. In the case of the Imagine midbass, the polar radiation
pattern is quite large at lower frequencies, with a narrowing of the radiation pattern
(“beaming”) at frequencies into the treble bandwidth.
Should the Imagine midbass be placed in the kick panel locations, one may find that a notable
improvement can be made by adding acoustical treatments, such as open-cell foam, into the
underside of the dashboard. Likewise, should the midbass, or in fact the I1 tweeter be placed
up high on a-pillars, or in the dashboard, where comb filtering (reflective summation and
cancellation off of a hard surface, such as a windscreen) may become an issue, a dashboard
“mat” or other soft furnishing may be a noticeable improvement. It will require trial and error
to get it right, but the learning is in the experimentation!
Advanced Installation Conclusions
Sadly, there are no rules in mobile audio, only several hypothesis and theorems that seem to
work for most vehicles. Your vehicle may be different, and defy everything we know, and
everything written in this manual. You may find that getting that rich, detailed sound that you
crave may require some experimentation and a lot of work to make it right. Or you might be
fortunate to have a vehicle that sounds excellent with minimal work. Have patience and work
through the issues; the result will be a rewarding musical experience in your vehicle! Just
remember, it is critical to get a reference, as detailed in Lesson 5. Go out and become a
student of music and audio, learn, and improve your audio system one step at a time. The
journey is exciting and rewarding!
What we have included above is only a very brief primer to the world of high-end mobile audio
systems. We invite you to read more by going to our Downloads web page.
As an aside, one significant benefit of car audio sound systems is that frequencies below the lowest room resonance increase at a theoretical
12 dB/octave…it’s no wonder car audio systems have such great bass!
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Hybrid Audio Technologies extends a limited one year warranty to the original purchaser,
certifying that this product will be free from defects in materials and workmanship under
normal and proper use for one year from the date of purchase.
Hybrid Audio Technologies’ responsibility under this warranty is limited to replacing or
repairing, at Hybrid Audio Technologies’ option, products or parts determined by Hybrid Audio
Technologies to be defective either in materials, or workmanship. To attain warranty service,
the customer must deliver the product or the defective part(s), appropriately packed with
proof of purchase date, to an authorized Hybrid Audio Technologies dealer. In the event that
a direct return from a consumer is required, the consumer must obtain from Hybrid Audio
Technologies a return authorization number, and ship the defective product directly to Hybrid
Audio Technologies. All shipping expenses are the customer’s responsibility. If the product
has been updated or superseded, a replacement will be made with a current model of the
same quality and function. Warranty of the replacement parts is limited to 90 days or the
unexpired portion of the warranty period of the product on which the parts are being used,
whichever is longer.
This warranty does not cover any defects or costs caused by: (1) modification, alteration,
repair or service of this product by any persons or company other than Hybrid Audio
Technologies; (2) physical abuse to, overload of, or misuse of, the product or operation
thereof in a manner inconsistent with the use indicated in the instructions; (3) any use of the
product other than that for which it was intended; or (4) shipment of the product to Hybrid
Audio Technologies for service. This warranty does not cover labor costs.
Hybrid Audio Technologies is not liable for any special incidental or consequential damages,
including, but not limited to, personal injury, property damage, damage to or loss of
equipment, lost of profits or revenue, costs of renting or buying replacements and/or any
other additional expenses, even if Hybrid Audio Technologies has been informed of the
prospect of such damages. Any express warranty not provided herein, and any remedy which
other than the warranty contained herein might arise by inference or operation of law, is
hereby excluded and disclaimed including the implied warranties of merchantability and of the
fitness for a particular purpose.
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Thank You!
Hybrid Audio Technologies is delighted that you have chosen an Imagine component system
for your high-end mobile audio sound system. We are convinced that a great product
offering, backed up with unsurpassed customer service and technical support will advance the
Hybrid Audio Technologies namesake in the coming years. We are pleased that you have
joined us in our “new generation of in-car audio.”
If there is anything we can do to help you get the most out of your Imagine installation,
please do not hesitate to contact us at [email protected], or by visiting us on line at
© Hybrid Audio Technologies, 2010
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