AVS Forum banner

1 - 4 of 4 Posts

·
Premium Member
Joined
·
336 Posts
Discussion Starter #1 (Edited)
Hi guys,

This is the setup:

AVR Denon X4400H (LFE enabled, speakers to small) --> subwoofer 1 out
MiniDSP 2x4HD, with LinkWitz transform and PEQ on the two output channels -->
Crest Audio Pro-LITE 7.5 amplifier-->
Two sealed subwoofers.


  • AVR LFE pre-out voltage RMS: unknown
  • MiniDSP 2x4HD max input and output: 2V RMS
  • Power amp input sensitivity: 2.25 V ± 3% for 1 kHz 4 Ω rated power
This means no matter what, I'll never be able to ask the full power of the amp. I'd need something high a slightly higher voltage than the MiniDSP. However, this is fine.

I would like to understand how I properly set the input and output levels all across the system to ensure the highest SNR (a correct gain structure).

1) I connected the laptop to the AVR over HDMI. Disabled all the processing in the AVR. Using ASIO output in REW, I played pink noise at -3dB on the LFE channel only. With the AVR at +0dB, I checked the MiniDSP input level and it was slightly over -3dB, so I lowered it a bit. REW output and MiniDSP input now looked similar in terms of dB numbers, when the AVR is set at 0dB.

2) Since I use PEQ etc on the MiniDSP, I needed to verify that the output matched the input (as there might be PEQ which is boosting frequencies). So, I lowered the output channels on the MiniDSP a bit. Now, the AVR, MiniDSP input and output show similar dB levels.
Again, this is playing pink noise through the LFE channel only.

3) Now with the AVR again at 0dB, it appears I've an output signal from the MiniDSP which is not clipped. This is fed to the power amp. However, I've no idea how to set the gain on the power amp. It's currently at 12 o clock (-6dB) - I assume there's no way to set this other than with a multimeter - which would be playing from AVR at 0dB, a 60Hz sine wave, disconnecting speaker output from power amp, raising the gain on the power amp until I see distorsion?



Questions:

Wouldn't that mean I'll _never_ see distorsion as the MiniDSP can only give 2V RMS which is less than the input sensitivity of the amp? ... so I can set the gains on the amp to +0dB / max?

Should this be done with the LFE channel - or playing stereo left/right with the crossovers active and LFE out trim on the AVR set to 0? (outputting to L, R and sub, with a stereo input from REW)

Is subwoofer pink noise the correct signal to play, or something else?

(a multimeter has been ordered... not here yet. No access to an oscope)

Thanks
 

·
Premium Member
Joined
·
4,585 Posts
Don't forget that the LFE channel from REW (HDMI4) will be +10db "hot" coming out of the AVR. If you're adjusting the level to some reference, you'll lose 10db on the subwoofer when running sub+mains. I usuallu either subtract 10db from REW's generator level if I'm driving the HDMI4 (LFE) input, or, I'll just drive one of the mains and turn off the mains' amplifier so only the sub runs (and it won't be 10db "hot".)
 

·
Premium Member
Joined
·
336 Posts
Discussion Starter #3 (Edited)
Don't forget that the LFE channel from REW (HDMI4) will be +10db "hot" coming out of the AVR. If you're adjusting the level to some reference, you'll lose 10db on the subwoofer when running sub+mains. I usuallu either subtract 10db from REW's generator level if I'm driving the HDMI4 (LFE) input, or, I'll just drive one of the mains and turn off the mains' amplifier so only the sub runs (and it won't be 10db "hot".)
So, if I understand correctly, playing pink noise to front L/R out from REW, at -3dB, would be better?

(just unplug the front LR speakers and go from there)

edit: Tried that. Pink noise is definitely not as loud as a sine wave, at the same REW output (duty cycle?). With a sine wave loop, 10Hz-60Hz, I have to set the MiniDSP input to -3dB when the AVR is at 0, to match the REW's -3dB max output.

So that should be correct?
 

·
Registered
Joined
·
11,534 Posts
In an ideal universe, all of the equipment would clip at the same time.
In reality though, it is good-enough if the amplifier clips just slightly before the rest of the equipment does, say 0.1db or whatnot.
That maximizes the SNR and SPL for any given master-volume position.

You may want to try a squarewave as a worst-case scenario.

Testing the max RMS voltage is easy, a REW sinewave and any decent multi-meter.
Determining the clipping point requires an O-Scope, or REW\Audacity soundcard input with a voltage-divider.
 
1 - 4 of 4 Posts
Top