I need some amp tuning guidance.

So I purchased an Alpine PDX-M12 amp to run two Shok Industries 12" subs in a 4 ohm load configuration. Last night, I put the DMM on the speaker leads, and turned up the gain. I got to maximum gain, and still didn't reach the suggested voltage of the formula that I'm told works to tune amps.

The formula I used is :
Square root of Watts x Ohms.
Now, I have a 1248w amp at 4 ohms, so that's 4800. Square root of that is 69.28. But the DMM on AC voltage only read to a maximum of 33 volts. The subs pound, doesn't sound like there's any distortion, and I had all the settings set to 0 on the deck so there's no bass boost or anything like that. I turned the gain down a little, to about 29v, and I'm getting great bass, but am I doing something wrong? I had the subs connected to the amp, and played a 0db 50Hz test tone on loop to tune.

The amp is set to input from .1-1v as I think my deck is dying, but it's supposed to put out 4v. Should I switch that to the 1-8v setting and try again? Also, I could only find an 80Amp fuse for the amp, even though it should be 100Amps. Could that be causing a problem as well?

 

What volume level do you have your HU set at? You're supposed to set it to the maximum unclipped volume. It's hard to determine what your max unclipped volume is without an o-scope, but you may find people out there who have taken measurements of your HU to determine maximum unclipped volume knob setting. In the absence of data, I'd recommend setting it to 75% of the maximum allowable setting, then take measurements.

I don't think the amp input setting should make a difference. If anything, a lower input should make it more sensitive to your voltage and give you more gain. Try changing to see if it makes a difference.

Also, the amp fuse shouldn't make a difference either. Since you're setting the gains with no load (speaker) attached, there's no current outputting from the amp. Now if you keep blowing fuses, then I'd recommend upping the size to match what alpine recommends.

 

Thanks ike. I'll try it again, this time disconnecting the subs from the amp. Last time, I had the subs connected. And maximum unclipped on this deck is 28. So I set it to 27, just to be safe. I guess, I'm breaking out the DMM again and trying one more time.

 

BINGO!!! Disconnected the speakers and put the DMM leads in place. Played my 50Hz 0db test tone, and put the parametric EQ on the deck to where I normally have it, and set the bass boost to 7. Put the volume on 27, and pressed play. I was able to turn the gain UP a little from where I had it, and nailed 69V. Getting maximum unclipped power out of the amp now. Thanks for all the input ike, I got it where I want it, and the bass is outstanding! More than I could have hoped for. Now to chase down all the rattles

 

H/U should be set to 3/4 of max volume then adjust gain on amp.

Gain on amp shouldn't pass 1/4 or its too much.

This is a decent tutorial. Without an o-scope its all a guessing game.

http://www.crutchfield.com/S-ftA5rGxZnzh/learn/car/subwoofers/tuning.html

 

get the smd-1 the best thing ever

 

glad you got it working. what you set is the maximum, unclipped output of the speaker system. this will enable you to provide the cleanest, maximum signal to the amp and speakers. your speakers may have some distortion at high output levels, but it's hard to discern that at such low frequencies.

i set my gains with HU sub level at 0db, then adjusted level down to my liking. that way i can give it all, and then some, if i'm in the mood.

 

Yeah, that's kind of what I did. I rarely go to 3 or 4 on the bass boost, so setting it to 7 gives me a bit of freedom. I'm happy with how it tuned. Now to get my 4-CH amp from Crutchfield.

 

Bassboost = Distortion. Stay away from it.

 

Yeah, I know. But there are those old AC/DC and Metallica songs that can use a little help. I normally have it zeroed out.

 

i'd bet those beefy shok industries speakers can handle some nasty (distorted) signals without problems. it may not sound great, but it won't hurt your subs.

the fact that you set your gains at the highest level of boost means you'll never drive the amplifier harder than it's capable of. max out the boost and have fun with it.

my amp can technically put out 750W at 4 ohms on the sub channel, but i set the gain to coincide with about 600W at max volume. i did something similar for the mid and tweet channels - i.e. set gains just below spec'd max output. power and crossover frequency settings are all within manufacturer recommendations. it's comforting to know i can play near the maximum volume without fear of breaking anything. the only frustration is that at such high volumes the sound stage is all over the place. everything is still clear without significantly noticeable distortion - just not "coherent" so to say.

i just ordered a new set of exodus anarchy mids that i'm anxious to try out. i'm also thinking about swapping out my single 10" for two 12" with more xmax and lower fs. i miss the "in the gut" feeling i got from my 12w6v2. just gotta figure out how to sell it to my wife.

 

OOOOHHH Exodus Anarchy's. Those are gonna sound great. I actually just bumped the gain down a little on the amp, not a lot, but a notch or two. So it's putting out a little less than max wattage, but I feel comfortable with where it is now. Goal was 69V, and now it's at 66.5V. Bass was a little much even at low volumes, and it should help with clarity a little. And I can play with the boost a little on those older tracks that can use it. But the overprocessed and maxed out tracks that come on most CD's nowadays, I have a little safety, that I'm not gonna beat anything up or clip the signal. I'm still waiting on my PDX-F4, that should be here tomorrow. I already have the wiring in place, and the signal cable came yesterday, so that's already run. It should sound great powering my JL C2-650's, and the Infinity rear-fill speakers I have. My new deck is coming for an anniversary gift in a couple weeks, so I have that to look forward to as well. An Alpine CDEHD149BT. Never had bluetooth on a deck before, and with the tuning capability of the Parametric EQ and my tablet, I should have hours of fun tweaking it for great sound.

Enjoy those Anarchy's, wish I was that lucky. And GL with putting it past the "boss".

 

this site is really good for basically any information pertaining to subs the link i posted tells you how to do just what your trying... i would use a 55-60hz fq but thats just me ive used 40 50 and 60 and always seems like 60ish sounds best. also make sure your using max rms of the lowest of the 2 if your amp is pushing 1248 watts rms and say your subs are pushing only 500watts each go with the 1000 watts of the subs totalled it will have less distortion if any and less chance of blowing subs

http://sparky3489.webs.com/settinggainampclass.htm

 

Thanks for the link. Maybe I'll break out the DMM again, and aim for 63.25V. Safety of equipment is what I'm shooting for after all.

 

talking to the guy who runs the site he said running between 1-5v higher isnt bad but gives the extra bump.. he said if there cheap pos subs dont exceed 1v higher but for good solid subs you can go up to 4-5 v higher. id set it see where it puts you tune up a couple v and see where that puts you. hook subs up and tune to where you want it in between the spots

 

Yea i'm really excited about these anarchys. I love the sound of my Legatia L6's, but they just don't have the bottom end and kick like i would expect. I've taken to research data myself and not let the "wow" factor of a product sway me. Those anarchys have much more throw and are a heck of a lot cheaper. I'm nervous about how they will perform in a door. Some reviews I've read said they sounded better when put into a smaller enclosure within the door. They're just not meant for infinite baffle like the car door presents. Fingers crossed

That Alpine unit looks great.

 

Yeah, I was thinking about it last night, and I'm gonna retune the system. Just to be safe. I know my subs can handle a lot more power, the guy who sold them to me is matching them to a 1800w amp. So power isn't the issue, it's the distortion. I'm trying to eliminate any distortion, and turning the gain down a little did help with clearing up the sound without losing any power, so, I'll probably use that chart, and retune. Thanks again.

That's what I heard about the Anarchys too. I'm not sure how they'll handle IB in the door. How good are you at fiberglass? You may be able to make an enclosure that fits the door, and still allows window function, but it'll be tough. GL with the tuning, and I hope they work out for you.

And thanks, I can't wait to get the new HU.

 

Okay, devanb, you'd be proud. The only way I can get some serious voltage out of the amp is with the sub level control on the deck. Otherwise, I max the gain and only get around 38V. So I turned the Sub level control up to 10 out of 15, and reset my gains on the sub amp. Nailed it between 63.2 and 63.3V. Figured that was close enough. Turned the sub level down, and tried out some bass specific music. Pounds loud and clear. And I know, even if I go a little crazy with the sub level control, I don't have to worry about clipping. Thanks for the website, it provided some clear insight.

 

not a problem i found this site probably 4-5 years ago and still reference it for anything i need to know regarding subs and stereo questions

 

I've seen several threads on other forums where guys were only able to get the spec'd HU voltage output by maxing out all gain controls, bass boost, EQ levels, volume compensators, etc. But it still seems odd that you would get so little voltage output from an Alpine HU.

On my Pioneer 80PRS, I set the volume to 60 out of 62, played test tones, and was able to get spec'd max amplifier output at about 80% of the amp gain knob. And that was with HU gains set at 0dB, EQ flat, and all sound level attenuation set to OFF. I never measured the 80PRS voltage, so I can't say how much it was putting out.