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Old 09-12-2007, 10:11 AM   #1
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Default I don't quite understand car audio

Let me start off by saying that I would rate myself at around 6.5 in regards to car audio.


In my younger years I grew up with the understanding that home audio came three ways:
1. Receiver
2. Integrated Amp, Tuner
3. Pre Amp, Power Amp, Tuner
With car audio they only came 2 ways:
1. Receiver
2 Integrated Amp, Tuner

When I installed a Tuner (no amp) which I believe is now called a head unit it wouldn't play without an amp hooked up to it. If you had a receiver (head unit) and you wanted to boost the power output, you would add a power booster, not an amplifier. The problem with adding a separate booster is that it would only be as clean as the built in amp. We didn't have subs in those days, the separate amp or receiver had 4 separate sets of speaker wires (for front and rear) with a fader control on the receiver. I have a car that has a separate Pioneer GM 120 (120 amp) amplifier

This is what I don't understand about today'* car audio:

1. Why do you need a separate amp to run subs? Is it because it'* a cleaner sound?

2. When you are installing an amplifier to a head unit, will the head unit play without it? In other words, is the head unit a receiver or a tuner?

3. I have a Pioneer GM120 (120 watt) that sounds louder and cleaner than amps today that is rated for 500 watts. What happened to the ratings of amplifiers or is it my imagination.

4. Is you have separate amps for a sub, is there a separate control to adjust the volume of bass from the head unit.

5. Do the amplifiers need to be accessible?

I have more questions, but I'll ask them later.
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Old 09-12-2007, 10:22 AM   #2
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1. Yes. You need more power to reproduce bass cleanly. You also need speakers that can handle that type of frequency range properly. Which is why people run speakers at home with 10-15" woofers, or separate, amp'ed, subwoofers.

2. Head units are generally: AM/FM receiver, CD Player (usually with MP3/AAC/WMA capabilities [which is just compressed audio files burned on a data CD]), Aux-Input (could be USB, or just regular line-level input). Most have amplified outputs, with standard color-coded speaker wires, and they generally have line-level output. The output voltage of the line-level is anywhere between 1V and 5V, the higher the better. Ya know, the whole signal to noise ratio thing. If you install an amp attached to the line-out of the head unit, the amp must be on in order to hear anything.

3. You need to look at the CEA power ratings (http://www.ce.org/standards/Standard...*.aspx?Id=1455) to get some accurate numbers. My Kenwood amps are all rated by this method. Of course, signal to noise ratio and THD% are important, too.

4. Depends on the head unit. My Kenwood KRC-X790 has 3 sets of line level outputs. Front/Rear/Sub. The front/rear are controlled with the balance/fader controls, and have a high-pass crossover built in. The sub outputs are controlled with a separate "subwoofer" level, and have a low-pass crossover built in. So, I have 6 separate RCA lines (3 pairs) going to the two amps under my back seat. (One 4-channel for the door/dash speakers, One 1-channel Class-D for the two 15" subs.)

5. Only if you want to be able to adjust any controls on them. Mine fit nicely under the rear seat, and still have enough air gaps to breathe fairly well. I lift up the seats if I plan on stressing them past normal listening volumes.
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Old 09-12-2007, 10:40 AM   #3
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Default Re: I don't quite understand car audio

Quote:
Originally Posted by Maymybonnieliveforevr
This is what I don't understand about today'* car audio:

1. Why do you need a separate amp to run subs? Is it because it'* a cleaner sound?
Technically you dont. They make 5 channel amps that you could power everything from. But it is normally more efficient and easier to mount 2 amps then one large 5 channel amp. Also as Dopple said, bass frequencies take more power to reproduce and if you are running subs that require a lot of power you have no choice but to run a seperate amp
2. When you are installing an amplifier to a head unit, will the head unit play without it? In other words, is the head unit a receiver or a tuner?Technically both. Headunits now days have built in amplifiers that allow you to play front and rear speakers. They dont have to be externally amped as the headunit will do this for you. People who are serious about the speakers amp them seperately because 1 usually external amps distort less than the amplifier in a HU 2 if you upgrade your speakers and they have an RMS of 100 watts, it makes more sense to power them at/around their RMS. This would allow the speakers to play louder before they begin to distort

3. I have a Pioneer GM120 (120 watt) that sounds louder and cleaner than amps today that is rated for 500 watts. What happened to the ratings of amplifiers or is it my imagination. Yes that is an issue these days. MOST amps you see in stores and online have very bullshit ratings. There is no system that requires them to tell exact power, its based on honestly now days....so you know how that will go. This is until you get into the more expensive amps or amps made by smaller underground companies, the ratings begin to be honest and commonly are underrated.

4. Is you have separate amps for a sub, is there a separate control to adjust the volume of bass from the head unit. Normally yes. Depends on your headunit though. I know on mine I can turn the signal output on and off plus adjust -6 to +6 of how much extra bass there is. You are also able to put a switch on the remote turn on lead for the amplifier. This will allow you to physically turn of the subwoofer amp if you desire no bass

5. Do the amplifiers need to be accessible? No. Usually once you set(or tune) the amplifier you never need to touch it again. Just remember that they need some space for cooling especially if you chose for it to cool passive (vs active with a fan or similar)

I have more questions, but I'll ask them later.
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Old 09-14-2007, 01:22 AM   #4
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1) You need a seperate amp to run Subs for a couple of reasons.
The first being that a hard hitting bass note requires more power than what the built in amp on the HU can provide. Most only provide 25 watts RMS and a max of 50 watts peak.
The second reason is that you would overload the amp on the HU and burn it up.
Most HU'* can only handle 4 - 8 Ohm load not less or more.

2) The modern day HU is a reciever cause it has a built in amp 25 watts RMS per channel. Most people add an amplifer or 2, to power a sub or to increase the power on their midrange.

3) There are lots of different classes of amplifers these days. The most common for midrange and highs are class A/B which are your typical 2 & 4 channel amps.
There are more expensive amps that are class A but they are very expensive and not as effecient at delivering power (they are wasteful in the form of energy to heat). A good example of this would be a Macintosh amp. This is why most amps are class A/B more cost effective & more effecient (less waste of power).

4) Some HU'* have built in "Sub Control" which allows you to reduce the voltage from the RCA output on the back of the HU from a simple setting on the HU.

5) Amps don't necessary need to be accessible, unless something goes wrong. But they do need air circulation to disipate the heat which is a by product of the energy conversion to power.

Regards,
Dutch
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