I have a JVC head unit with 2.5V preouts. I have a Sound Storm Labs amp rated at 50W rms. My multimeter reveals that even at max volume on the HU and max sensitivity on the amp, the amp is only generating 11.5V (should be 14.1). This means the amp is putting out 30W rms, not 50. Correct me if I'm wrong, but this sounds like 2 different issues:

1) The amp is way overrated. That would be a severe quality control issue.

2) The HU is unable to drive the amp to power. This is the part that really bugs me. I know a 2.5V preout is on the low end, but at max sensitivity the amp should be able to accommodate that, right?

I called the Sound Storm Labs and they were unable to give me any numbers relative to the gain spectrum, so I have no clue what the range is. Any opinions?

 

a few thoughts:

• did you measure the voltage with a true 4-ohm load (resistor) or with the speaker?
  - speaker impedance is not static and varies with the input signal
• have you resolved your previous ground issues?
  - if you have a bad ground the amp cannot get all the current it needs
• does the amp manufacturer rate the amp using a standard methodology (eg. CEA 2006)?
  - if not, the rating is meaningless

 

Are you using the proper test tones?

 

I used a speaker load but isn't this taken into account in the power rating? I measured the ground at 1 ohm and I'm not sure about the methodology used to rate the amp.

I used a 1K hz test tone. I was able to get the amp to full power with the car running, but that's still at max volume & sensitivity.

What also confuses me is that the speakers are supposed to be rated at 60W but they start distorting at 7W (5.5v) according to the multimeter. It certainly sounds like 60W though (very loud, great midbass). This makes me think my measurements are wrong...

 

Is your test tone at 0db?
I download my files from My link
Do you have an iPhone? The JL Audio App has all the tools and instructions for you to tune your system and its free.

 

I'm actually not sure if it's 0db. I'll try with your tone. Thanks for the link.

 

Is this with the car running or just in ACC? If it's in ACC, it won't read much more than 12V. You should be able to get 14.1 if you crank the car up.

 

Yeah this was in ACC. I was able to get the amp to 14.1 when the car was running but that was at max volume and sensitivity. I think it should be able to achieve this with less gain.

I'm going to try to get my ground down to .5 ohms or less. This may be contributing to the problem and I'm getting a bit of noise at higher gain levels.

 

If you are going to benchmark your amp, you need to know exactly what your test conditions are.
If the amp is specified to produce 50 watts @ 4 ohms, that means exactly 4 ohms, not something
that is around 4 ohms, but goes up or down depending on the signal sent to it.
Similarly, you need to know the actual input voltage. An amp with an unregulated power supply
(which is most of them) that produces 50 watts with 14.5v will only produce 41 watts with 12v.
Without more information about how the manufacturer has rated the amp, you don't know what the
rating means. Many cheap amps are rated using unrealistic conditions - an input voltage higher than
likely to be seen in the real world, measured over a narrow frequency range, with an unacceptable
amount of distortion, and not producible continuously.

 

Yes test and tune your gains with your car running!