Different voltage readings

[tee 10+ year member]

Why is it when I measure my left speakers, I get a different reading then from my right speakers. One is 15.5 and the other one is 16.1 when I'm testing it with a -3 dB 1kHz tone.

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[Gary S 10+ year member]

Because the speakers do not match perfectly... most don't. Do a search for matched pairs on the web for more info.

 

[tee 10+ year member]

So would I use the lower reading or the higher reading.

Also, I have a 70Wx4 amp running (2) 60W speakers. To get 60W out of the 70W amp, shouldn't the gain be at least 80% for ch. 1+2? Then the last two channel is 200W because it is bridged. Shouldn't the gain be around 3/4 of the way if I have a 150W sub? I know it's kind of hard to understand what I just said but just... I don't know.. read it again if you don't lol.

 

[tcguy85 10+ year member]

the gain control does not work like that.

 

[tee 10+ year member]

the gain control does not work like that.

Thanks. WTF am I doing wrong now, I get crazy readings when testing the rear channels (bridged). I am using a -3dB 45Hz tone because it's for my small sub. I turn the gain ALL the way down and I'm getting around 28V. Any ideas?

 

[squeak9798 5,000+ posts]

28^2/4 = 200w

So it's not all that unreasonable. Does something not sound right with the sub connected ? Or are you just freaking out about the voltage reading ? Do you have bass boost or anything turn on ? Equalizer settings on the headunit ? Where is the lowpass crossover set ?

Keep in mind that the gain isn't a "wattage controller".....it is possible to obtain full power from an amplifier with the gain set to minimum....in fact the amplifier was intentionally designed to do such.

 

[tee 10+ year member]

28^2/4 = 200w
So it's not all that unreasonable. Does something not sound right with the sub connected ? Or are you just freaking out about the voltage reading ? Do you have bass boost or anything turn on ? Equalizer settings on the headunit ? Where is the lowpass crossover set ?

Keep in mind that the gain isn't a "wattage controller".....it is possible to obtain full power from an amplifier with the gain set to minimum....in fact the amplifier was intentionally designed to do such.

The reason why I think it's unreasonable is that the gain is ALL the way down and it's reading 28v. This is out of an amp that does 200x2. I think something is wrong there.

I have "Bass EQ" on the amp on. The equalizer settings are on in the HU also. The LP is set at around 80.

 

[helotaxi 5,000+ posts]

The "Bass EQ" is part of the problem. Like squeak said, amps were intended to be able to reach max power with the gain set to min all depending on the signal voltage. What HU do you have?

The Bass boost double the amount of power the amp is trying to make for every 3dB of boost applied. If the amp has a fixed 12dB boost (sadly not that uncommon) it is trying to make 16x the amount of power that it should for the same gain settings and signal voltage with the boost turned off. The amp simply cannot do this, will clip and many times either go into protection, blow the speakers or blow itself.

The purpose of the gain is to match the input signal voltage from the source to the voltage that the amp needs to make full power. Since every source unit is different (there is no industry standard for pre-out voltage) an amp needs a range of adjustment to be compatible with as many different sources as possible.

 

[J31Rob 5,000+ posts]

Also, IIRC, between the left & right RCA, they don't give the exact same voltage..

This can be helped by Maxxlink or a line driver..

 

[helotaxi 5,000+ posts]

Or using the balance control...

 

[thch 10+ year member]

so its all a question of which has better matching, the dual mdac on the HU, or the potentiometer on the amplifier.

I'd suspect there is a small difference between the channels due to the potentiometers on the amplifier. This is why some amplifiers have dual gain knobs. As mentioned, use of the "balance" control can help to balance the difference.

(also, filter mismatch can cause small differences in output. The HU, using DSP based filters, will have no issues with matching.)

 

[tcguy85 10+ year member]

yea, on my ZX550.2 i get a little more voltage out of the left side channel. it doesn't seem like enough to make a huge difference. i have the balance on my head unit just a hair to the right side.

 

[tee 10+ year member]

The "Bass EQ" is part of the problem. Like squeak said, amps were intended to be able to reach max power with the gain set to min all depending on the signal voltage. What HU do you have?
The Bass boost double the amount of power the amp is trying to make for every 3dB of boost applied. If the amp has a fixed 12dB boost (sadly not that uncommon) it is trying to make 16x the amount of power that it should for the same gain settings and signal voltage with the boost turned off. The amp simply cannot do this, will clip and many times either go into protection, blow the speakers or blow itself.

The purpose of the gain is to match the input signal voltage from the source to the voltage that the amp needs to make full power. Since every source unit is different (there is no industry standard for pre-out voltage) an amp needs a range of adjustment to be compatible with as many different sources as possible.

So it is better to turn off the "Bass EQ" even though it's running a sub?

 

[helotaxi 5,000+ posts]

It doesn't matter what it's running. A boost circuit is asking the amp to double its output for every 3dB of boost. At the same time, the amount of power that the amp can actually make has not increased. What you end up with is either a spot in the response where the boost peaks and the amp makes full power (and it makes less power at all other freqs) assuming that you used a tone the same as the boost center freq when you set the gains or a range of freq where the amp is trying to do more than it is capable of and clips like a mother (test tone different than the boost center freq or boost applied after gain is set). Neither is good. If you want loud, why would you want loud at one freq at the cost of the others? Why wouldn't you want a level amount of power across the freqs played by that amp? You don't get more power from the amp by using the bass boost, so why use it instead of just setting the gain correctly with the boost off and getting full power all the way across the board?

 

[tee 10+ year member]

What kind of tone do you suggest I use? I have Pioneer Rev in the front, and a Kicker TC10 (which is basically a Kicker C10 in their box). My amp is an Alpine MRP-F450; HU is Alpine 9881. Can you tell me the Hz and which dB to use to test them? Also, I will have my EQ on before I test them, with the "Bass EQ" turned off.