Gain Structure for Home Theater Discussion Thread

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hi Wayne,

I have read many of your articles on REW and just recently started playing around with implementing a hard knee house curve as a result of your suggestions on the topic. Thank you for another great article!

I am using my AVR to power my speakers but am using a pro amp on my subwoofer. My setup is as follows;
-Denon 4311ci AVR: spec'd at 1.2Vrms output (I have not measured)
-MiniDSP balanced with selectable .7V or 2V input sensitivity and 2Vrms output
-Peavey Ipr2 5000 amplifier on my subwoofers- 1.95V input sensitivity.

The Peavey owner’s manual recommends keeping the gain dial turned all the way clockwise for “maximum headroom” and this is how I have always ran it. I have noticed that at lower volumes the subwoofer doesn’t seem to do much, I have felt the volume the speakers turned down and the volume the subwoofer turned down wasn’t parallel to each other and there was a certain point the subwoofer finally would kick in or drop off. For example at -35db on the Denon the subwoofer had very little output in comparison to the speakers. But with the volume at -25 or -20db then the subwoofer would be at an appropriate level to match the speakers.

I am under the impression, and hope, that the MiniDSP outputs a signal equal to what it is receiving so is there a need for me to optimize the gain structure on the MiniDSP? And if so how would I perform this? One idea I had was to adjust the gain from the receiver to the amplifier just to the point of the clip light flickering. Then adding the minidsp in between the two and getting it to the same point where the clip light on the amp starts to flicker. Would this work well enough?

One more question. If, for example, I end up finding that having the subwoofer gain in the AVR at +6 and the gain on the amplifier at say -12 is the optimal level to have their gain matched what should I do when I run audessey and it turns the subwoofer down to -3 or -1 or whatever it may be. Should I turn the gain on the amplifier up the level that the receiver was turned down?
Thanks again for all your knowledge and sharing it with all of us!

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System


Thanks for the kind words, Devon. :T

DevonD said:

The Peavey owner’s manual recommends keeping the gain dial turned all the way clockwise for “maximum headroom” and this is how I have always ran it. I have noticed that at lower volumes the subwoofer doesn’t seem to do much, I have felt the volume the speakers turned down and the volume the subwoofer turned down wasn’t parallel to each other and there was a certain point the subwoofer finally would kick in or drop off.

Click to expand...

The information from the Peavey manual doesn’t make much sense. Any amp naturally gets its highest noise floor with the gains all the way up, so you actually get more dynamic range (defined as the “distance” between the noise floor and highest clean input signal) with the gain reduced. Of course, this assumes that the incoming signal is hot enough to begin with to accomodate lower gain settings.

As far as the inconsistent levels with various volume controls, I have no explanation for that. It sounds like some kind of signal gate is in play. If you don’t know what that is, it’s an effect commonly used in pro audio to shut the output signal down when the input signal falls below a certain threshold. For things like drum mics, for instance, to keep cymbals from bleeding into the snare drum mic when it’s not being hit. Check the miniDSP to see if has some kind of feature like this, and if so disable it.

In case you haven’t already, I’d set the Peavey’s back-panel filters for full range and let the AVR or miniDSP provide the low pass filtering.

I am under the impression, and hope, that the MiniDSP outputs a signal equal to what it is receiving so is there a need for me to optimize the gain structure on the MiniDSP? And if so how would I perform this? One idea I had was to adjust the gain from the receiver to the amplifier just to the point of the clip light flickering. Then adding the minidsp in between the two and getting it to the same point where the clip light on the amp starts to flicker. Would this work well enough?

Click to expand...

Like any other outboard equalizer, the miniDSP should not need any level settings to optimize gain structure. It should pass the signal straight through (along with whatever is added with any equalization, of course). So what you’d want to do is re-adjust the Peavey’s gain settings after the miniDSP is added to the signal chain, to accommodate any changes to gain the equalization brings.

My only concern is that the miniDSP, with only 2 Vrms capability, it might not have enough headroom to pass the signal level the Denon as actually capable of generating, and will clip. As noted in Part 7, the receiver I used while researching the article put out way more voltage than the manufacture claimed, so I wouldn’t put much stock in Denon’s spec.

One more question. If, for example, I end up finding that having the subwoofer gain in the AVR at +6 and the gain on the amplifier at say -12 is the optimal level to have their gain matched what should I do when I run audessey and it turns the subwoofer down to -3 or -1 or whatever it may be. Should I turn the gain on the amplifier up the level that the receiver was turned down?

Click to expand...

If you’re not happy with the sub level Audyssey generates, then I’d over-ride it and set it where you think it should be. If Audyssey won’t let you do that from the receiver specifically for the sub output, then it’s easy enough to change it on the back end – i.e., the amplifier gain controls.

Hope this helps!

Regards,
Wayne

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Thanks for these articles. For years I had used a Behringer DCX2496 to drive my power amplifiers. The 0dbfs corresponds to about 10V RMS, way too much for any power amplifiers I have (though one requires 5v RMS for actual clipping). Over at DIYAudio there is a thread on the DCX2496 and there are endless variations of modifications to get 0dbfs more "appropriate" to consumer hifi. One thing to do, for example, might be to attenuate the existing outputs by 6 or 10dB. I long ago determined this was not a good idea. The rated distortion of 0.002% only applies at 2V output. Before you get to 10V output, distortion has risen to 0.3% (not spec'd, this is my measurement). So you really want to keep output level from existing circuitry below 5v if not 2V anyway. Since I only use digital input to the DCX, I've never thought much about input levels. I didn't worry much about the S/N in digital domain given that I still have >16bits at -30dB, which seems to be like your argument.

But now I do something different in my main system, where I don't cut corners. Instead of using DCX as crossover for the midrange, I use a Behringer DEQ 2496. I create the required high pass filter using a pair of PEQ's that produce a perfect LR24. The DEQ gives me digital output which I run to a repurposed Onkyo RDV-1 as DAC. I like RDV-1 because it's well made piece with true PCM 1704 ladder DAC's.

This has completely changed the gain structure. Now, at 0dBfs I get barely above 2V output. That means I can't drive that amplifier to full voltage output…but it's still plenty loud enough. I had to dial down the remaining sub and super tweeter outputs from the DCX to match (subwoofer is dialed to maximum -15dB cut).

Incoming digital now plays at -10dB attenuation or less, often as little as -2dB (before it was -20dB). I watch the midrange and it never runs out of headroom, but much closer than before.

I like this a lot better, and I think it sounds a lot better. I play a lot of 24bit digital recordings, and I think this gain structure preserves the information much better than before.

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hi Mr. Pflughaupt and all,

Let me start off by telling you that French is my first language so if i am unclear just let me know


I was reading your post on using an avr with pro power amps and I have a few questions regarding how to do it with my setup.

Fisrt of all, I am using a Integra DTC 9.8 connected via XLR outputs to 3 Crown CTS600 amps. My speakers are 5 Martin Audio Effect 5 speakers that have an sensitivity of 95dB 1 Watt/1 metre. All that stuff in a 13x22 room.

If I am right, the way to calibrate a THX certified pre-pro to reference level is to get -30dB relative to full scale (0dB) that creates 75dB as measured with a C weighted SPL meter at the listening position.

So, I set my front left speaker SP Level to 0dB, I start the internal pink noise signal and play with the gain of the Crown Amplifier until reading on the SPL meter is 75dB. After that, I set all the Crown amps inputs on the same page and calibrate the other channels using the SP Levels until each channel read 75dB. To acheive that, I am reducing the input level on the Crowns to +- 3/4.

But I guess, I am missing something as the reading on the amps are not near to lit the clipping light. I mearly got the -20dB light flashing...


As for the Crowns, the sensivity is 1.4V, the Voltage Gain is 31dB and it puts out 300W in 8 ohm.

The amp is putting out 48.99 volts of output at full power (300=Voltage^2/8).

I Used "Voltage Gain (Av) = 20 * Log (Vout/Vin)" to found the voltage gain.

So to deliver full power, the pre-amp needs to put out 11.4V right?

Do my Integra is putting enough voltage to drive the Crowns?

If so, should I put up the gain on the amps and listen with the pre-amp to -XXdb?

Thanks.