Signal / Head Units
Receivers ("deck", "source", "radio", "tape deck", "CD Tuner", or
whatever you want to call them), are simply the component that generates
the signal that you are trying to hear. The "format" is always changing,
and although the Compact Disc is currently dominant, in the future we
may (soon) be playing decompressed digital audio files (such as the MP3
format) in our vehicles that we have downloaded from the Internet, or
using some digital broadcasting system.
Of all the components in your sound system, the signal source component
you choose has the least amount of affect on the acoustic performance of
your sound system. You can build a fantastic sounding system around an
entry-level CD deck. Of course it will sound a little bit better with a
high dollar head unit, but, if, for example, you have an extra $100 to
add to the budget for your system, and you want to have it help with the
sound more than say, looks or ease of use, add it to your speakers or
amplifier(s).
Factory Head Units
Many vehicles now feature CD players from the factory. These decks can
be used as a source if a line level converter (about $25) is added since
they only have speaker output leads and not "pre-amp outputs". The
performance can be satisfactory but never superb because the signal is
still traveling through the IC chip amp inside the deck, which adds
distortion and muddys-up the over all signal a little.
Amplifiers
"Factory" or "stock" sound systems that come with vehicles today sound a
little better than they used to. Many people, after buying a car, can be
heard saying that they sound "not too bad". That's great that they don't
sound too bad, but shouldn't the goal be to get it to sound GOOD? Your
listening to music in your car MUCH more than at home, not that you're
in your car more, but when your home there's TV, phone, conversation,
sleeping, etc. and we just don't get around to really listening all that
carefully even if the stereo is on. Your car is the place to listen to
what you want when you want, as loud as you want, singing along if you
want, and it can actually be a great "room" to listen in. Although the
road noise can detract somewhat from appreciating the quiet parts of the
music, the small dimensions of the room and the fixed listening position
are actually ideal for creating a superb acoustic demo chamber. So,
ironically, at home we have a quiet noise floor (10 to 20 db) and 100
watts per channel and in our vehicles we have a loud noise floor ( 50 to
80 db) and yet people try to get away with listening to just 12 watts
per channel !? The 12 watts refers to the little amp built in to your
deck. All radios now a days have the same little amp in them (no matter
what they claim to have for power - "40 x 4" is just a marketing trick -
read lie) There are really just two types of amp designs found in 12
volt environments.
The first type of amp is found inside radios and is commonly referred to
as a "chip amp," or "IC amplifier." These are extremely low cost "amps"
that use the 12 volts DC that is present in the car to produce a maximum
of about 12 watts of usable power. This is the most they can make due to
the Laws of Physics: power (watts) = current (amps) X voltage (volts).
Some additional drawbacks to this type of amp design are: high
distortion (typically 1% THD-"Total Harmonic Distortion"), low signal to
noise ratio (slight hiss always in your speakers), and crummy stereo
separation. The advantage is that it is a small integrated circuit chip
and does not give off much heat and so they are included "free" inside
all radios. The confusing part is that the manufacturers, who are not
regulated regarding this, put numbers like "30 or even 45 watts per
channel" on these units, which sounds as if it might have enough power.
They do produce micro-second long spikes up to 40 watts, (if turned way
up), but it is then accompanied by about 20% distortion--and when you
turn it down until it sounds okay, it is then at about 12 watts again.
Remember that number - 12 watts at 1% distortion.
Amplifiers that use the second type of design are called "transformered"
or "discreet" since they have separate power transistors and true power
supplies. These amps take the 12 volts DC and convert it to AC. Only
after you have AC, can you make higher voltage. This lets you produce
more than 12 watts, and at much less distortion (typically .1%
distortion [a tenth of one percent]- that's ten times cleaner than IC
chip amps, and a lot more power). The disadvantages to these amps is
that they are expensive (starting at $100 for a 50 w. / chan.), big and
heavy (need to be mounted under seat), and they need a big, fat, wire
hooked up to the battery to run them. However, it is all well worth it
once you hear the difference!
Most speakers will handle more power than you think. What they can't
handle is distortion. Distortion is what an amplifier puts out when it
isn't big enough to play as loud as you would like it to. It's that
extra, fuzzy sound over the top of your music when you reach the limit.
All amplifiers distort when you turn them up past their maximum output
limit. Your amp tries to amplify the small signal from your deck without
altering its smooth shape. Your amp has a "voltage rail" limit of how
big it can do that before it chops off the top and bottom of the sine
wave, causing distortion-which will damage your speakers.
To summarize, if your stereo is not loud enough, or if you've blown a
speaker from distortion (which isn't covered under any warranty) and had
to get another one, buy a bigger amp. Almost every time a speaker
"blows" it is due to distortion. It is very rare indeed that a
manufacturing defect doesn't show up in the first few hours or minutes
of play. For best performance use an amplifier that puts out as much
power as the rating of the speaker. The only other way a speaker can
blow (even with clean power) is from over-excursion. However, you need
to play it at over-excursion levels for a while in order to break it,
and it sounds so terrible and obvious, that anyone would turn it down
long before that would happen.
Bigger the Better? Yes. That is, the more power an amp can produce, the
better the sound quality will be, all other things being equal. The
physical size of an amp, however, will not tell you much about how much
usable power it can produce. In fact it is quite common for cheaper,
lower quality amps to feature a huge, over-sized heatsink to try to look
big and powerful.
Power ratings. Since there are no regulations to ensure truthful,
comparable power ratings of car amps, the best way to determine the
output of a particular model is to look in the owners manual, and under
specifications, read what is usually the SECOND line (the first is just
Maximum power with any amount of distortion) that should state the "RMS"
(average) continuous power at a certain distortion rate (.1% or less),
per channel, at 4 ohms, while playing a full-frequency signal
(20-20khz). Only then can you know how much "usable" power is available,
and even then there are other aspects of a amps' design that can make
one sound better than another with the same power specs.
Speakers
Factory vs Aftermarket
A discussion of speakers must always refer to the amplifier that will
drive the speaker. This is very important to understanding speakers, so
be sure you've read the discussion on "Amplifiers". "Stock" or "factory"
speakers that come with your car are often good enough to be part of a
great sounding system IF you power them with a clean, discreet amp. As
an additional measure of building a really great sound system, you could
upgrade the door speakers and lastly the rear speakers.
Do I really need "midbass" drivers? "Midbass" drivers in a car audio
system are ones that only play a narrow band of frequencies typically
between 70 and 2or300hz. They usually are in the form of a pair of
6"drivers shoe-horned into the front doors. There needs to be a midrange
speaker to play above 300 hz. and advanced crossovers and/or a dedicated
amp for the midbass drivers as well. In other words, midbass drivers are
usually only found in very elaborate systems and provide only minor
enhancement to a sound system when compared with other options available
with that much time, energy, and money (like a trunk e.q., for example).
Subwoofers
In order to make the right decision on which type, size, and model of
subwoofer you may need, you should ask yourself a few key questions:
"What type of vehicle do I have" (if sedan, see "Cars with Trunks")
"What level of sound performance do I need?" "How much space am I
willing to give up?" "What other items do I sometimes need to have in my
car?" (recreational gear, etc.) "What is the approximate budget for the
system or components being added at this time?"(sub, amp, etc.)
Placement
In optimizing placement of subwoofers in vehicles, one must be aware of
the "transfer function" of the interior space of the vehicle, commonly
referred to as "corner loading". Bass is resonating air, and it's easier
to do that in the semi-trapped air of a corner. Therefore, the best
place to locate your sub for maximum output is in and toward a corner.
Unfortunately, this is not always where you would like it for aesthetics
or ease of use, however, it will be loudest there and may allow you to
have a smaller box and/or amp. Also, if you use a "bandpass box" (which
is the best type for use in vehicles, which need small size and high
output over a narrow band), it will also minimize the slight port noise
inherent in all ported boxes. In home stereos, this corner loading is
undesirable, producing an unnatural peak of sound energy at a low
frequency, however in a car, or especially a truck, it is very welcome
to do battle with the road rumble trying to mask your music's rhythm.
Sedans (cars with trunks)
Bass is the resonating of air. In order to hear (or feel) bass, you need
to resonate the air near you. If you put a subwoofer inside a closed
trunk only a small portion of the bass can be heard or felt in the cab
of the vehicle. However, in sedans, there is no other place for a sub,
and so one theory (not a very good one), is to put in a huge sub and
huge amp and hope it can be heard up front. This idea of wasting ¾ of
the bass is not only very expensive, it leads to many blown subs since
you can't hear the amplifier's distortion limit or the driver's
excursion limit. Some cars have seats that fold down but the opening is
smaller than the trunk causing a destructive "loading" effect. In
addition, there is the inevitability that you will close the seats up
one day, causing the problems previously mentioned.
A simple and very effective solution for sedans is to use a
"band-pass" type of subwoofer enclosure since all of the energy is
focused into a small tube that can be "ported" into the cab through the
rear deck of the car. This way the box can still be in the trunk, but
the bass can be in the cab. Two SubSolution models are made specifically
for installation in these vehicles. The Thru Deck Port Kit adapts The
Sports Car SubSolution with the use of a 3" port tube. And for
audiophiles, The Low Bass Trunk Solution provides twice as much bass
energy through its 4" port (the four driver model can be modified for
trunks as well). It's simply a matter of feeding the energy into the
passenger area-where you want the sound!
What is a "Driver"?
"Driver" is the term used to describe the actual woofer that is in the
box. The "basket", (the stamped or cast metal frame), the "motor",
(magnet and voice coil part), the "cone", (the big curved paper-like
part), and the "surround", (the foam or rubber edge that attaches the
cone to the basket), are all parts of the driver.
A "Speaker" is made up of two main parts - the driver and the enclosure.
These two must be made with each other in mind in order to perform well.
Size - is bigger always better?
No. In fact most all people agree that smaller drivers sound better
since they can react to the changes in the music faster. Larger cones
have significantly more mass and it is very hard to get them to stop
moving at one speed and start moving at another speed, which is what
they need to do. This aspect is measured and referred to as "transient
response".
"Efficiency" or "Sensitivity" refers to how loud a speaker will play
with a specified amount of power on it. The standard for measuring it is
to play 1 watt of power into it, and measure the sound pressure level
(SPL) at 1 meter away, measured in decibels. For example, 89 db, @1
watt, @1 meter. In general, drivers with larger cones will be more
efficient than smaller cones, all else being equal.
Frequency Response
One of the most important things to understand in car audio is the
phenomenon of road noise and how it can cover up the bass energy that
your stereo is trying to play. Human hearing goes down to 20 hertz and
that is how low you want your home stereo to play, however, in a car it
is much wiser not to play frequencies below 40 hertz in order to help
the amp and woofer play the frequencies you do need (40 and above), much
louder and with less distortion.
How low a woofer can play at full volume before "rolling off", or
starting to be less loud, is a critical design criteria and is called
the "F3" or "3 db down". It is important to understand that although
ultra-low frequencies sound (or feel) interesting while parked, you
cannot hear them while driving and they demand massive amounts of power
from your amplifier -- power that could better serve you by providing
distortion-free sound at the frequencies you do need to hear. A sub that
plays linear down to 27 hz isn't all that smart, unless you have 1000
watts and like to listen in your driveway most of the time. In designing
subwoofers, the laws of physics require us to sacrifice efficiency for
low frequency. In other words, to make it play lower, it can't play as
loud.
Crossover Settings
In vehicles, we only need subwoofers to play from 40hz to 90 hertz, but
we need them to be very loud in order to hear the rhythm part of the
music over the vehicle's road rumble. A separate amp for just the
subwoofer is a must for a high performance audio system. It also must
have an electronic crossover, either built-in or external, to block both
the higher frequencies from going to the woofer (low pass) and the lower
frequencies from going to the mids and highs (high pass). Set the "low
pass" at about 90 hz -- or slightly lower (80 or 70 hz) if you have a
larger amp. The setting for the "high pass" output to the amp that runs
the mids and highs should be as low as your door speakers can handle
without breaking up at high volumes. Many two-way crossovers have only
one adjustment which determines a "center frequency" point; the sub amp
must play from that point and below, and the high-pass from that
frequency and above. If so, set it at 90 hz.
"Midbass" drivers in a car audio system are ones that only play a narrow band of frequencies typically between 70 and 2or300hz. They usually are in the form of a pair of 6"drivers shoe-horned into the front doors. There needs to be a midrange speaker to play above 300 hz. and advanced crossovers and/or a dedicated amp for the midbass drivers as well. In other words, midbass drivers are usually only found in very elaborate systems and provide only minor enhancement to a sound system when compared with other options available with that much time, energy, and money (like a trunk e.q., for example).
No. In fact most all people agree that smaller drivers sound better
since they can react to the changes in the music faster. Larger cones
have significantly more mass and it is very hard to get them to stop
moving at one speed and start moving at another speed, which is what
they need to do. This aspect is measured and referred to as "transient
response".
"Efficiency" or "Sensitivity" refers to how loud a speaker will play
with a specified amount of power on it. The standard for measuring it is
to play 1 watt of power into it, and measure the sound pressure level
(SPL) at 1 meter away, measured in decibels. For example, 89 db, @1
watt, @1 meter. In general, drivers with larger cones will be more
efficient than smaller cones, all else being equal.
That is, the more power an amp can produce, the
better the sound quality will be, all other things being equal. The
physical size of an amp, however, will not tell you much about how much
usable power it can produce. In fact it is quite common for cheaper,
lower quality amps to feature a huge, over-sized heatsink to try to look
big and powerful.
Power ratings. Since there are no regulations to ensure truthful,
comparable power ratings of car amps, the best way to determine the
output of a particular model is to look in the owners manual, and under
specifications, read what is usually the SECOND line (the first is just
Maximum power with any amount of distortion) that should state the "RMS"
(average) continuous power at a certain distortion rate (.1% or less),
per channel, at 4 ohms, while playing a full-frequency signal
(20-20khz). Only then can you know how much "usable" power is available,
and even then there are other aspects of a amps' design that can make
one sound better than another with the same power specs.