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a novel way to set gains?

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Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
Printed Date: August 18, 2022 at 5:38 AM

Topic: a novel way to set gains?

Posted By: aaron9999a
Subject: a novel way to set gains?
Date Posted: September 01, 2008 at 1:50 PM

I am thinking about getting a Bazooka Bass Tube DVC 12 (600 watts RMS)for my '98 RAV4. I don't have room to put anything massive in it and am on a pretty tight budget. I have an old school Rockford BD1000 that I want to use to power it. It's birth certificate says it will put out 1265 watts. I really don't want to fry the sub by over excurting (sp?)it, and was thinking of a way to set the gain without buying an oscilloscope.

What I want to do is get a 60 Hz sine wave mp3, play it through the headunit (Pioneer DEH-P680MP from 2005 w/ 6 volt pre-amps) with it at full volume/ as loud as I will use it, sub-out set to 0. With the subwoofer hooked up to the amp along with an AC voltmeter on the +/- terminals of the Rockford, slowly adjusting the gain up to approx. 34.6 volts Volts = (sqrt(600 watts*2 Ohms)). Will this work? Will the voltmeter be able to read it?

This is all just stuff floating through my head right now nad I don't know if it will work...

Side note: has anyone used Bazookas before? Are they long-lasting? Are they good quality?

Side side note: I have Infinity Reference 6.5" 4 ohm components up front and 6.5" 2 ohm coaxials in the rear, powered by an Infinity Kappa 50 X 4 @ 4 ohms, 75 x 4 @ 2 ohms amplifier. Can I use the same method to set the gain on those? Will they fry? For that matter, should I disconnect that amp when setting the gain on the subwoofer?

Sorry about the long post, and thanks in advance for any replies!


Posted By: aaron9999a
Date Posted: September 01, 2008 at 1:54 PM
The rear coax speakers are actually 2.65 ohms. And I am thinking about replacing the front components with 2.65 ohm References also.

Posted By: DYohn
Date Posted: September 01, 2008 at 2:03 PM
Please read the "How to set your gains" sticky post.  Thanks.


Posted By: aaron9999a
Date Posted: September 01, 2008 at 2:44 PM
I read the sticky post and have more questions now. :) What makes a DMM so difficult to use? I don't want to use the max output of the Rockford; rather, I want to match the power of the amplifier to the rated power of the bass tube. I just want information on the why, not to argue. Does the resistance change in the VC when under power? Is it the resistance in the wires? To accurately calculate the power, would I need to read both the amperage AND the voltage? (which I would have no way of doing) Is that why it wouldn't work? Or is there something else I'm not seeing?

Posted By: DYohn
Date Posted: September 01, 2008 at 5:52 PM
Who said using a DMM was difficult?  If you know how to use one, you can certainly set an amplifier using that method, however the downside is you cannot measure clipping with a volt meter so using tones and your ears (or an oscilloscope) is generally also required to make sure your set voltage output level is not clipping.


Posted By: megaman
Date Posted: September 02, 2008 at 9:17 AM

One issue with using only a DMM to set the gains, is that the impedance of the subwoofer will vary with frequency and will vary completely different from the impedance that the DMM presents to the amp while testing.  When you connect the DMM to the amplifier, it has a purely resistive load on the amplifer and you will end up getting a different output to the subwoofer.  The DMM has a very, very high resistance which presents a different load on the amplifier.  So you can set the output voltage of your amplifier using the DMM, but the subwoofer will get a completely different output from the amplifier.

The best way is to use your ears.  If your subs start to make that "different sound" you're in the bad zone.  If you subwoofer is a low power handling one, then you'll notice it very early while turning up your gain.

*impedance load*  sorry sorry haemphyst

Posted By: stevdart
Date Posted: September 02, 2008 at 9:02 PM

What I want to do is get a 60 Hz sine wave mp3, play it through the headunit (Pioneer DEH-P680MP from 2005 w/ 6 volt pre-amps) with it at full volume/ as loud as I will use it

It's important, as well, to find the clipping level of the deck.  You could very well find that it may be below the highest volume level you intend to allow it to go.  Here again is where listening to the clipping sound in the pure sine wave tone is important.  Once this deck level is found, you make a note of that level and use it to find gain level of the amp.  And because, as megaman said, impedance varies by frequency, you should have a few tones available (all recorded at 0db) in the target driver's range.

A voltage reading using a meter cannot be accurate in finding the highest clean deck output.

As DYohn said, it is not enough in itself to use the DMM to find proper gain level.   I understand that you are concerned that by setting gain by ear you may not be able to properly match amp output to deck output without giving the sub too much power.  But as you are actually listening to the output (wear protection) when using the hearing method,  you are also able to watch as well as listen to the sub.  If there is too much discrepency (mismatch) between amp and sub you will likely not find a suitable gain level...but you would notice violent behavior from the sub, if that is the case, while gain is at lowest level.  In a case such as yours, use a gentler music source first before switching to the sine wave tones. 

That is to say, test with a music source while amp gain is at lowest setting just to see if you should proceed with trying to match the gear you want to use.

The tones are hard on a driver, so keep the tests short in duration and allow some cooling time if this becomes a difficult setup.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

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