I'm new to installing audio equipment so please excuse the nube questions.

I just installed the equipment from my former ride into a 2004 Honda Accord as follows:

Replaced rear speakers with JL Audio TR690TXI
Added a Rockford Fosgate Punch 200M Amp and a Kenwood KFCXW1025DB 10" Subwoofer which I fed through the speaker level inputs on the Amp.

Question #1 - Do I need to be concerned about amplifer Clipping? I've been reading about it and I'm not sure I understand it. Maximum power for the amp is 400 Watts, Dynamic Power Rating - Mono into a 4 Ohm load = 100 Watts, Mono into a 2 Ohm load = 200 Watts. The subwoofer has a nominal impedance of 4 Ohm + 4 Ohm, Peak input power = 1,000 Watts and rated input power = 250 Watts.

Question #2 - What is the propper way to set up the amp's gain and variable crossover? The manual for the amp states that it has a built in 12dB/octave Butterworth filter with a crossover point variable from 50Hz to 210Hz. The crossover can be set to LP (low pass) or it can be bypassed by setting it to AP (all pass). This amp also has a Punch Bass control. The control is a narrow band adjustment at 45Hz switchable from 0dB to 6dB to 12dB.

Any advice would be appreciated

 

What a wonderful question. I have a lot of information for you, that will also benefit anyone else reading this...

here goes.

How to set your amplifier gain with a DMM:

There are a lot of tutorials on the internet talking about setting your amplifier gain using a DMM (Digital Multi-Meter). Here I will clean up the process as simply (but accurate) as possible.

Necessary Tools/Skills

1. A volt-meter or DMM with standard test leads.
2. Ability to do 6th grade math.
3. Screwdrivers and/or Allen Wrenches (to make amplifier connections).
4. A CD with test tones - 50Hz for subs, 1000Hz for speakers.


Start by making a quick list of your equipment and their output voltage (head unit, Line Output Converter,(LOC), processor, crossover, eq, etc.) and input sensitivity of each amplifier.

Next, list your power output ratings (actual RMS power) You prefer something with a CEA rating. Without a CEA rating, you then need to look at amplifier fusing to get an idea of the likelyhood the rated power is attainable. There are a lot of tricks when rating amplifiers - both RMS power and Total Harmonic Distortion (THD) are of concern. You want to see a power rating at a specific impedance and at a specific THD. If the two numbers are listed separately, then you may not know the THD at their power rating. 100W @ 4 ohms and 0.5% THD sounds a lot better than 100W @ 4 ohms and 5.0% THD.

Then, list your speaker/subwoofer impedance(s).

You need to know how your speakers/subs are wired - what the final impedance is going to be at the speaker terminals. If you can't figure out these numbers, then you shouldn't be installing amplifiers. Pay someone who does and save yourself the damaged equipment. That isn't meant to discourage anyone who doesn't know, it just means you need the information before you proceed. You can look up the speaker impedance (ohms) in the owner's manual or mfr website, you can usually just read it on the magnet, and you can always use your DMM to measure resistance, then you get in the ballpark of impedance (the DC resistance is slightly below the AC impedance). There are a couple websites that offer subwoofer wiring diagrams - the Rockford Fosgate Woofer Wiring Wizard, and the12volt.com both have diagrams.

The speaker/sub impedance is VERY important to get right, as it is needed for the calculations below:




We are going to use the equation solving for Voltage using Power and Resistance.

Voltage = SQRT(Power x Resistance)



Example:

I have a single subwoofer with 4 ohm DVC coils. I'll wire the coils in parallel for a 2 ohm load. The sub is rated for 500W RMS.
I have a single amplifier rated 500W x1 at 2 ohms. I want all of that power available (knowing that power will only happen for small durations).

Volts = SQRT (500W x 2 ohms)
Volts = SQRT (1000)
Volts = 31.6VAC

-----------------------------------------------------------

Determine the maximum head unit voltage you want to use as follows:

1. if you have a factory head unit and factory speakers and are using a LOC for your sub amp, use the highest volume level you do for music (without distortion to the speakers).

2. if you have an aftermarket head unit powering factory or aftermarket speakers and are using the HU preouts for your sub amp, use the highest volume level you do for music (without distortion to the speakers).

3. if you have a factory or aftermarket head unit feeding a signal to amplifiers for speakers and subs, you need to verify the maximum unclipped, non-distorted output - or just use a 75% volume setting if you are unsure if your headunit is capable of 100% unclipped volume. You can verify this with an oscilloscope.

When setting a subwoofer amp - if your head unit is powering speakers, you really want to disconnect them or use a high pass crossover on them. however, this may not be realistic for you. if not, then your max volume setting may not be possible without distorting your speakers. don't distort your speakers for this exercise. use whatever volume you can that doesn't distort your speakers. This is not the ideal situation, to do it right you should put high-pass crossovers on speakers when you have a sub.

----------------------------------------------------------

Once you have the head unit max volume determined, and the test tone CD playing on repeat. Set the EQ to flat, turn off processing. Make sure the fader is centered, balance is centered, sub level controls are maximum (sub level is just attenuation anyway).

You can go back to your amplifier.

Disconnect any speakers/subs not associated with the channels being adjusted. Set the gain to minimum. Turn off any bass boost. With the DMM set to VAC (Volts AC), touch the DMM positive leads on the speaker outputs. Slowly increase the gain until the DMM reads the voltage determined above.

While you're increasing the gain - LISTEN TO YOUR SPEAKERS/SUBS!!! Listen for any distortion - popping, scratching, noises that go away when you turn the volume back down.

You can use resistors to load the amplifier so you get a more accurate reading (like in the eD video), but the resistor load bank must have a power rating greater than the output power expected. Most of you reading this won't have a load bank on hand, especially for loads over 500W. Don't worry. You should be able to leave the speakers/subs connected - you're listening for clipping and distortion anyway.

Once you have set the gain on all of the channels separately, all of the amps separately. Hook up everything as it should be - all speakers and subs.

Now listen to your system with music. Listen for balance between all of the speakers and subs. If you desire a more balanced sound (i.e. subs overpower speakers) you TURN DOWN GAIN on the loudest speaker/sub. DO NOT INCREASE GAIN past your set points determined above. Most head units have sub level controls, fader, etc. that allow you to attenuate the signal from your HU.

Now you can start introducing EQ, boosts, etc. Note that any bass boost more than 6dB can result in clipping or damage. You've already set the amp gain as high as it should be. Once you get your EQ and boosts set, you should check your gain setting once again. Excessive bass boost settings will cause clipping.

If you get noises then reduce the gain at the point where there are no noises or popping as it may be an indication of amplifier clipping, or speaker/sub distortion.

If it's not loud enough - buy more or larger speakers/subs, more or larger amps, and start over. Don't force your equipment to be louder than it can, or you'll destroy it.

 

Clipping is when your amplifier is given too strong of a signal, and when the amplifier tries to reproduce that signal, it exceeds it's internal voltage rails.

http://en.wikipedia.org/wiki/Clipping_%28audio%29

It sound bad, you can hear it when it happens. It's easier to hear with tones, since you can clearly identify when the tone changes (not just volume, but it takes on a different sound when the amp is clipping). With a 50Hz tone, you can hear the point where the sub starts to distort or clip.



The following images were taken by myself using my scope, a head unit, and a power amplifier.



When you're within the voltage rails, the output looks like this (amplifier bridged output):



when you have clipping, the output looks like this (head unit speaker outputs at max volume):



The power supply in a car amp can increase the voltage at the supply rails to +/- 50 VDC or more - all from +12VDC. To do this the supply converts the battery/alt voltage from DC to AC then uses a toroidal coil or AC transformer to step up the voltage, then rectifies that AC back to +/- DC for the amplifier. Instead of typing it here, reference the following link to see what i'm talking about. http://www.caraudiomag.com/specialfe...wer_amplifier/
notice how the supply rails are equally positive and negative to allow for the signal to swing in both directions.

 

Now, all of that may be information overload. But i'm going to use this post as a platform for this information. Now to your specific questions:

You should wire the dual 4 ohm voice coils in parallel for a 2 ohm mono load. The amplifier wired to these speakers can provide 200W RMS. You will be under-powering your sub, so clipping is of great concern.

Since you have a factory head unit and you are tapping the speaker outputs, you won't be able to get the test tone volume high enough, without distorting the speakers. if you took the time to disconnect all four speakers, you could properly set your gains using the calculations above using a DMM with an output voltage of

Volts = SQRT (200W x 2 ohms)
Volts = SQRT (400)
Volts = 20VAC



You will set the crossover to Low Pass, and dial in around 80Hz. You can adjust the Hz to your liking.

The 45Hz boost should not be set to 12dB. If you like the sound/output better at 6dB, then go for it - it's user preference. I would recommend using this bass boost at +6dB and keeping the bass control on the head unit at 0.

If you find that this is not loud enough for you, then you need a larger amp first, and a larger or second sub second.



One often referenced method of setting gain is to play the 50Hz tone on your CD player, set the head unit volume until your cabin speakers start to distort, then adjust the amp gain until the sub distorts, then back the gain back down a bit. This can work, if you know what clipping sounds like. Setting the amp gain as outlined above (and disconnecting the cabin speakers by just unplugging the wire harness at each) would be your best bet.

 

Thanks for all the really great and technical info. Now I've got a lot to digest.

 

if you have any questions on any of that, just ask (and quote what you want to know more about). if you have a list of questions, number them like you did before.