Amp tuning with a DMM

[stryfe]

Got all my gear installed "professionally" but I'm convinced the guy didn't tune my amp correctly....when I got in, the "bass boost" control was cranked all the way up...and it sounded like ****.......but if I turn the "bass boost" down all the way....my sub cuts out completely....not how I understood it to work.

I would like to be able to tune it myself using my multimeter....but I'm not certain what values to shoot for.

Front channels Speaker RMS 60W Amp RMS 70W
Rear channels Speaker RMS 50W Amp RMS 70W
Sub channel Woofer RMS 300W Amp RMS 210W

Can anyone point me to a guide so I can do this myself....thanks.


Also....is there anyway to have my SVC 4 ohm sub present a 2 ohm load to my amp.....without having to add another 4 ohm sub

 

[rhauf]

Got all my gear installed "professionally" but I'm convinced the guy didn't tune my amp correctly....when I got in, the "bass boost" control was cranked all the way up...and it sounded like ****.......but if I turn the "bass boost" down all the way....my sub cuts out completely....not how I understood it to work.

I would like to be able to tune it myself using my multimeter....but I'm not certain what values to shoot for.

Front channels Speaker RMS 60W Amp RMS 70W
Rear channels Speaker RMS 50W Amp RMS 70W
Sub channel Woofer RMS 300W Amp RMS 210W

Can anyone point me to a guide so I can do this myself....thanks.


Also....is there anyway to have my SVC 4 ohm sub present a 2 ohm load to my amp.....without having to add another 4 ohm sub

"professional" car audio guys are (not always but most often) just car audio enthusiasts who are in the business. they usually are not audio or technical experts. the wattage ratings are the max watage the amp is capable of delivering, does not have to do with setting the levels. a multi-meter is not used for setting the levels. the way most people set the level of the sub is simply by adjusting the level to what sounds right and fits your taste.

you would tune you're subwoofer to match the levels of the other speakers. there are usually 3 adjustments on the sub's amp, 1: the level adjustment, 2: the low pass filter, 3: bass boost.

start by turning bass boost (if it has it) all the way down, turn you're low pass filter to somewhere around 80 hz (most car speakers work down to about 80 hz, so this is a good place for you're sub to take over) then adjust the level control until it sounds right to you. you can adjust it while the music is playing to make it easier. after setting this, you may want to turn up the bass boost slightly, as it boosts the low-bass more (usually around 40 hz) this may give it a little more depth.

now if you really want to get technical, (and i don't recommend it for a car stereo) the correct calibration equipment for setting you're subwoofer level would be a spectrum analyzer, this would graph out the frequency response of you're system and would help you tune it "correctly" .....this is what you'd have to do if you owned a theater and wanted to be thx certified (i think you would also have to boost the bass about 10 db at 30 hz or something)

to answer you're question about changing the impedance of the sub, no you cant. unless it is dual voice coil then you can wire it in a variety of ways to change impedance. another 4 ohm sub wired in parallel would change it to two ohm.

 

[BigBoom]

here's a chart i made for power ratings at given impedances

imo it's better than setting it by ear and just turning knobs, but still cant tell if a signal is clipping or not. best way for that is to use an o-scope.

i agree with rhauf and the filter settings, but i wouldnt use bass boost. that's an easy way to start clipping. i solely use the gain.

 

[stryfe]

Thanks for the info....guess I'll just grab an oscilloscope from work and give it a shot.

 

[rhauf]

what are you going to do with the oscilloscope? set it so that with continuous pink noise the sub and the main speakers clip at the same volume level? i cant see anything else you would use it for. and that wont guarantee that they are "matched" output level wise, but i suppose it would guarantee you the highest potential playback level w/o clipping.

 

[stryfe]

That's what I was thinking.....just a measure to avoid clipping the signal from the HU and the amp. Isn't that the point? to maximize output while avoiding clipping

It's funny....I've read a lot of articles on amp tuning.....most people say by ear is the best.....some folks say DMM is the best.....and still others say a scope is the best.

I've got access to a spec an....but wouldn't know where to begin

 

[BigBoom]

ummm...that's exactly what an o scope is for. allows you to see a clipped signal so you can avoid it and properly set the gains. going by ear you can *sometimes* hear when a signal starts to clip, but not in all scenarios. you cant tell when an amp is clipping with a DMM either. using a scope is the best way. watch these videos:

http://www.youtube.com/watch?v=AgJShBpesI0#movie_player
http://www.youtube.com/watch?v=tQDEkxD8ed8&feature=player_embedded
http://www.youtube.com/watch?v=xSUuBBJQ4Wk&feature=player_embedded

 

[rhauf]

i realize a scope is the way to test amp clipping, i have worked in the hifi business and done repairs, tested every amp for distortion with a scope, 8 ohm resistor load, and distortion analyzer after it's finished, and logged the results for the customer (high end tube amps)

and i agree that if you simply want to max you're sub out it's the best way of setting that max level (with respect to the input and the other speakers) but my sub for instance, if it's any where close to "maxed" in this manner, there is way too much bass for the other speakers.

 

[stryfe]

i realize a scope is the way to test amp clipping, i have worked in the hifi business and done repairs, tested every amp for distortion with a scope, 8 ohm resistor load, and distortion analyzer after it's finished, and logged the results for the customer (high end tube amps)

and i agree that if you simply want to max you're sub out it's the best way of setting that max level (with respect to the input and the other speakers) but my sub for instance, if it's any where close to "maxed" in this manner, there is way too much bass for the other speakers.

I get what your saying. And may combine methods. Use scope for the 4 door speakers to get the most out of them....and tune sub by ear so it doesn't overpower. I'm not looking for boomy bass.....would like it to hit hard....but none of that exaggerated stuff for me.


I think I see the advantages of "ear tuning" and "DMM tuning".....you can take the speakers limitations into account.

I'm assuming if I tuned with an o scope....my four front channels would all be close or the same. But my front speakers and rear speakers have different RMS ratings....so the lower rated speakers would break up first.?.?


Is that a valid concern.....or am I off?

 

[stryfe]

ummm...that's exactly what an o scope is for. allows you to see a clipped signal so you can avoid it and properly set the gains. going by ear you can *sometimes* hear when a signal starts to clip, but not in all scenarios. you cant tell when an amp is clipping with a DMM either. using a scope is the best way. watch these videos:

http://www.youtube.com/watch?v=AgJShBpesI0#movie_player
http://www.youtube.com/watch?v=tQDEkxD8ed8&feature=player_embedded
http://www.youtube.com/watch?v=xSUuBBJQ4Wk&feature=player_embedded

Great vids...thank you

 

[BigBoom]

but my sub for instance, if it's any where close to "maxed" in this manner, there is way too much bass for the other speakers.

ahh as in drowning them out? i see what you mean. bass knobs can help this a bit. or just more speakers up front