Gain Structure for Home Theater Discussion Thread - Page 6 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #51 of 85 Old 07-31-14, 02:03 PM
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Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Great! That makes perfect sense. Thanks for explaining it. I have a lot of new things to try out and keep me busy this weekend. A Linkwitz transform, hard knee house curve and now optimizing the gain structure.

Thanks again, Wayne!
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post #52 of 85 Old 08-19-14, 07:07 PM
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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.

Last edited by charlesp210; 08-19-14 at 07:10 PM. Reason: correction--use PEQ's for high pass filter above 80Hz
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post #53 of 85 Old 12-09-14, 08:20 AM
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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.

Last edited by Stratfordguy; 12-09-14 at 08:50 AM.
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post #54 of 85 Old 12-09-14, 10:17 AM Thread Starter
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Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Quote:
Stratfordguy wrote: View Post
Do my Integra is putting enough voltage to drive the Crowns?

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

So to deliver full power, the pre-amp needs to put out 11.4V right?
No, the pre-amp only needs to put out 1.4V to drive the amp to maximum. Iím confident that the Onkyo can deliver that much.


Quote:
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...
No, you arenít missing anything. The situation is that your speakers are extremely efficient, and could be driven to ear-bleeding levels with less than 100 watts, yet your amp puts out 300 watts per channel. So you will never see high meter readings on the amp. If you drive that amp to maximum output with those speakers, youíll probably be breaking windows and getting visits from the police.

Bottom line, you donít have a problem with your amps or pre-amp. Everything is working fine.

Regards,
Wayne



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post #55 of 85 Old 12-09-14, 10:49 AM
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Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Is that what we call headroom to spare?
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post #56 of 85 Old 12-09-14, 11:57 AM
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Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

By the way, thank you Wayne for that quick and straight to the point answer
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post #57 of 85 Old 12-09-14, 03:13 PM Thread Starter
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Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Thanks for the kind words, and yes that’s definitely headroom to spare – kilometers of it!

Regards,
Wayne



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post #58 of 85 Old 02-27-15, 04:03 PM
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Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Great Guide, Thanks!!

Results Report

AVR Denon X4000

Max Preamp Output 7.14
Max Clean Output 4.2 (41% lower)

Right channel measured only
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post #59 of 85 Old 07-16-15, 12:22 AM
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Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hi, Wayne:

Thanks for the guide. My test results with EMOTIVA UMC-200:
https://drive.google.com/open?id=0B7...mpXdEEycDVtTnc

When measuring AVR subwoofer output voltage, you use 0 dBFS signal. Do we need to +10db for concerning about playing DOLBY/DTS LFE channel? Just like REW channel 4 add 10db output?

Last edited by guofong; 07-16-15 at 03:29 AM.
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post #60 of 85 Old 07-16-15, 07:21 PM Thread Starter
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Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hi Guo,

Glad you liked the article. I’m afraid I don’t understand your question, and I certainly have no idea what REW has to do with adjusting gain structure.

Regards,
Wayne



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