creating a list of features that you want in your car audio equipment, you
can significantly narrow down the eligible equipment list. This list
allows you to focus on the feature set that you really need, rather than
being unduly tempted by marketing brochures and flashing lights.
Our Requirements for the Project Car Audio Equipment Installation:
We want to be able to watch (passenger only) and listen to DVDs.
We want the head unit to play CD-Rs with MP3s.
Screen - Since this is being installed in a two seat roadster, there is no
back seat. So, the screen has to be able retract into the head unit.
The unit has to be able to output 5.1 (DTS and DD), or decode it
Pro Logic II (DPL-II) - The unit has to be DPL-II capable (External
Digital Out - We plan on running a digital signal to the external processor, bypassing all the possible noise issues RCA
connections can expose.
CD/DVD Changer Control - There is little room upfront for a multi-CD case,
so changer control is a must.
On long trips, satellite radio is a really neat feature, because you never
drive out of range of the transmitter. We may not use it
right away, but we need the capability.
Navigation - Being able to interface to a navigation unit is a hot feature.
We may use it, so we need a head unit capable of controlling a slave navigation
unit. Or at least have a dedicated Navigation input.
Quality - In general, we want the head unit to have an S/N of at least 105 dB
for CD, and a THD no more than 0.01% . Now this is where reputation comes
in, as some manufacturers inflate their numbers.
Sound - Listen to the unit in the
store, and if possible, partnered with the amplifiers you will be
Usability - In the car, usability is very important, as you don't want to take 45
seconds to navigate around to find your favorite track while driving.
Power - We want 100 rms watts - 200 rms watts of clean output, into 4 Ohms. We want to be able to push them,
because power leads to a
tight sound and great dynamics. Note that car audio amplifiers are usually
specified as power into 4 Ohms rather than 8 Ohms, because the speakers
are usually 4 Ohms due to the relatively limited voltage (12 v - 14v)
coming from the car battery. Often, there will even be 2 Ohm ratings,
which are used with 4 Ohm drivers wired in parallel. The lower impedance
results in more current, and thus more watts delivered with the 12v
supplied from the car battery.
Power Generation - Since an SQ car (term used in car audio contests) is judged with the
engine off, we need an
amplifier that will make its rated power at 12v. Many amplifiers make 50%
less power when the car isn't running, which results in a drastic change to how your music
sounds. Having an amplifier that makes the same power at 12v (engine off) vs 14v
(engine on) is a
Quality - We want an amp that's neutral, so the frequency response should
be within ±
0.5 dB throughout the audible range. Signal to Noise should be equal to or
better than the head unit (>105 dB). THD should also match or exceed
the head unit, with a maximum of 0.01% at rated output. These numbers in a
spec sheet mean nothing if the company has a shady history.
Sound - Listen in the store.
Crossovers and Inputs - Plan your installation, because you may find out you need an
amp with speaker level inputs, or built-in crossovers. Our 5.1 processor
will be doing all that for us, so it isn't a consideration for us.
Listen at the store. Good speakers are an investment, because good
speakers cost good money. Stay with
established names and listen before you buy.
Size - I recommend that you fit the largest speaker you can in the front
door. This brings the mid-bass closer, and gives better clarity.
Quantity - I highly recommend a 2-way (tweeter and mid-bass) or 3-way design
(tweeter, mid, and bass). This allows the
individual speaker driver to focus on what it can reproduce the best, rather then having to
play all the frequencies.
Placement - If you do a 2-way or 3-way system, keeping all three of the
speakers physically close to each other is key. The greater the distance, the greater
the chance for noding (places in the car where the sound is canceling), and staging problems.
Rear-Fill - For two-channel reproduction, you really don't want to hear the
back speakers. Spend all your money on a high quality front set, and
disconnect the back, or leave them connected directly to the head unit.
For surround sound, of course, this is a different issue.
Size - A single 10" or 12" driver will be more than enough for 90% of us.
12" drivers are a great compromise of size and extension. Often the space
you have to dedicate to a subwoofer is a very important factor in
selecting the correct one. Talk to a local shop, tell them what music you
listen to, and demo a few. Show them where you want it installed. They
will tell you what will fit in that spot.
Power - While you demo the sub, make sure you are listening at a
power level (wattage) that you will be using in your car. The more power, the higher the SPL, and tighter
Enclosure - With today's drivers, I always recommend a sealed enclosure
rather than a ported one. A sealed enclosure allows for better cone
control, and a more linear playback. The tradeoff is 3 dB - 6 dB less
output for the sealed
enclosure. I recommend staying away from drivers that are geared at
producing extreme loudness, as they usually give up some quality (more
Bass-reflex enclosures, also known as ported enclosures, are much more
prone to output variations due to tolerance difference between drivers,
actually common. Every enclosure has a tuning frequency called F3 (F3 is
the - 3 dB down point, and is one of the Thiel/Small parameters for
characterizing speaker design). When a subwoofer plays below that tuning
frequency, it's harder for the cone to maintain a linear motion. Due to
the damped nature of a sealed enclosure, the sealed design lends itself to
lower extension with more
cone control below that F3 point. Although the ported enclosure has a
benefit of generally being 3 dB louder at that same tuning frequency, the
design doesn't damp the cone very well bellow F3. This leads to leads to
lower output and less extension when compared to a sealed enclosure.
For a given -3 dB point, a reflex system can be designed with roughly half
the box space. However, if you took a given driver in a sealed enclosure,
you could not put it into an enclosure half the size by porting it. On the
contrary, you'd need a larger box. However, you'd end up with a much lower
F3 point. If the F3 point were fixed, you could also get more output
(above the tuned frequency) out of the ported system with the same cabinet
size, through not only the contribution of the reflex device, but greater
efficiency. That's not to say that you can do any of this simply by
changing one parameter. If you change the alignment, you must also change
the enclosure and/or driver to get a good response.
In terms of drivers that play loud, from what I've seen of good drivers,
the compromise tends to be more in terms of bandwidth. Playing very deep
requires excursion. More excursion requirements mean less output
capability. Generally speaking, for woofers, you want high thermal
capacity, a linear motor, and a large X-max, particularly with sealed
alignments. (X-max is the maximum length that a driver's voice coil can
move back and forth inside the magnetic field of the driver.)
now, see our own choices for our project car . . .
Click HERE to see the
products we chose.
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