...and ANother Question...Gains

[anger 10+ year member]

So i bought a new amp and trying to set the gain yesterday with test tones. this worked great with my last amp but it was a little underpowered. With this one I'm having trouble finding any distortion.

I haven't turned the gain past half way out of fear of damaging the subs (never seen 'em move like that)

From what I understand, distortion is caused by a clipped signal from the amp. So my Question is, if the amp can exceed the maximum power the subs can handle, is it possible to damage the subs before I hear distortion? Here's what I'm running

RF T1000bd-CP

Mono amplifier delivers 700W x 1 @ 4-Ohms, 1000W x 1 @ 2-Ohms, 1000W x 1 @ 1-Ohm (RMS)

Class-bd amplifier with MOSFET output stage and power supply

Variable low-pass filter with range of 35-250 Hz (24 dB/octave slope)

Variable bass boost (0dB to +18dB @ 45Hz) and infrasonic filter (-3dB @ 28Hz 12dB/Octave)

Audiophile grade speaker connections and RCA pass-thru

-and-

4 RF Punch HEs (wired in parallel - 2 ohm load)

FIBERLock woofer cone

large roll foam surround

CONsealer gasket hides mounting screws and provides an airtight seal

frequency response 28-200 Hz

power range 50-200 watts RMS

peak power handling 400 watts

sensitivity 87.6 dB SPL

8-ohm impedance

top-mount depth 5-3/4"

sealed box volume 0.9-1.75 cubic feet (1.25 cu. ft. recommended)

ported box volume 1.5-2.75 cubic feet (2.0 cu. ft. recommended)

Thanks again to the CA.com community!

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[bbeljefe]

Distortion technically comes from a clipped signal being fed to the amplifier. Amps are fairly dumb in that all they try to do is replicate the signal they get exactly, except at a higher amplitude. So if you have a really clean signal running to a good speaker(s) that are underpowered for the amp, you'll eventually burn the voice coils out an likely will never know it until they stop playing. If the amp is a lot more powerful than the speakers, it will cause them to reach Mech max and you will hear the voice coil hit the back of the motor.

I'm wondering... are you using a scope, a DD-1 or a DMM to set your gains and also, have you checked the line out signal from the head unit for its distortion point and if so, are you setting gains at the highest undistorted volume level on the head unit?

Also, are you setting the gains with the woofers connected to the amplifier? Lastly, what tones are you using... frequency and recording level?

 

[anger 10+ year member]

Thanks for the reply. I'm not using a scope or multimeter. I did set the head unit first to the highest, undistorted volume level. I did have the subs connected, as I am only using my ears to listen for distortion. I used 120hz for my mains (which i had no problem finding the distortion point) and 50hz for the subs, both 0db. I do have a DMM if you could explain the process or point me in the right direction. I have watched some videos of ppl setting gains with a DMM, but they lack explanation and seem to be far from experts. Would you have a reputable source with steps and possibly the equation or charts needed. Thanks again for your time.

 

[maylar 10+ year member]

Yes you can damage the sub if you don't limit the power. If the amp is clean then by the time you hear distortion the sub is being stressed badly. Get yourself a DMM.

 

[bbeljefe]

So what about a DD-1? Not using that either? I will presume no, since you said you're doing this by ear.

With respect to you ears... that isn't a reliable way to set gains. I suppose it's better than just cranking them all the way up but still, not reliable even for those of us with "golden" ears.

The DMM method is easy and if you have a smart phone, there's an app called Audio Toolkit that has a calculator in it that tells you the voltage to look for when setting with a DMM. I'll give an example that will be based on setting your Fosgate amp to deliver 500 watts to your 400w rms woofer pair wired to 2Ω...

For that wiring and desired output, you're looking for 31.6 volts coming from the amp's speaker outputs. So, you'd set your head unit's volume at max undistorted volume (75% if you haven't checked it with a scope or DD-1), set subwoofer level at max and with the speakers disconnected, set the DMM to AC volts and probe positive & negative amp outputs. Raise the gain (you should start with it all the way down) until you read 31.6 volts on the DMM.

At that setting, you will be sending ~500 watts to that pair of woofers. And just an FYI... for 1000 watts of output, you'd be looking for 44.7 volts.

The only drawback to this method is that there is no way to know if the source signal is clipped. However, with your setup, you aren't likely to have a problem since you're not looking for max amplifier output. Just be conservative with the volume level on the head unit or, get it checked by someone with a scope or DD-1 to be sure. Also, if you share the make & model of the HU, someone else may have already tested it and could give you that info. If it's an alpine Imprint capable head unit with no processor attached, it's 28 of 35 and if it's the same with a processor attached, it's 35. You could also Google that question.

Lastly, I always use 40hz and 1000hz for sub and mid/high amps, respectively. And if you're looking for more SPL and a little less SQ, you can use -5dB tones. This can also help to compensate for media that's not recorded at full volume.

 

[anger 10+ year member]

No DD-1. My head unit is a Pioneer Premier DEH-P700BT. My subs are rated for 50-200W rms/400 max. I have 4. Should i shoot for 800 watts or slightly more? Also when using the DMM, should I leave the subs connected? Will it see the correct load if i disconnect them.

Have to dip for a quick minute. Will be back in about an hour. Again, Thanks so much for your time & knowledge!

 

[bbeljefe]

I'm sorry, for some reason I had it in my mind that there were two subs. Personally, I'd send them 1000 watts, as overpowering slightly is not a problem and can help when you have media with poor bass volume. But for 800 watts, look for 40 volts. If you send them 1000 watts, just remember that and don't run them full tilt on bass heavy music for long periods. One or two songs for demo, etc, is no problem at all. And no, don't leave the subs connected. Speakers present wildly fluctuating impedances to the amplifier and you're looking for as pure and clean a reading as you can get when setting gains.

Also, I googled "Pioneer DEH-P700BT clipping level" but didn't find anything pertinent. That said, I also didn't spend much time reading. I suggest that you google that term and do some digging. Either that or try to find someone in your area who has a DD-1 or a scope. Some shops will do the testing for you for a minimum charge and if you plan to run that setup for a while, it might be worth the money. I'd be happy to do it but, I'm about 1600 miles away.

 

[anger 10+ year member]

Set it for 44 volts, should give me close to 1000 watts. Sounds great. Thanks for the help bbeljefe.