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post #3181 of 3194 Old 07-14-2015, 05:49 PM
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Quote:
Originally Posted by AustinJerry View Post
What about measuring output voltages with a DMM?
DMM = ?

And where would I measure them? 7702 or miniDSP or both?

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post #3182 of 3194 Old 07-14-2015, 06:21 PM
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Quote:
Originally Posted by audioguy View Post
DMM = ?

And where would I measure them? 7702 or miniDSP or both?
Digital Multi Meter. How to do it is in the 2x4 write-up linked in my sig. You would measure the 7702 output under load, and then the MiniDSP output to your power amps or subs. Check to see if readings exceed the rated input of the MiniDSP or the amps.

If you are inclined to try this, a DMM is relatively inexpensive at Home Depot or Lowes.
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post #3183 of 3194 Old 07-15-2015, 08:26 PM
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[Another] Input and Output Sensitivity Question

I have an Open DRC-AN. The input sensitivity can be either 2V or 8V. The max output is 2V. Theoretical question: If I change the input sensitivity to 8V, do zero processing in the miniDSP, what happens to the 8V when it shows up at the output channel that only outputs 2V. Is the 8V input scaled so that at the full 8V it will drive the 2 volt output, at 4V input it would drive 1 volt output, etc?

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post #3184 of 3194 Old 07-15-2015, 08:30 PM
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It's going to cut the voltage to 25% of the original voltage (ie: divide by 4).
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post #3185 of 3194 Old 07-15-2015, 08:33 PM
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Originally Posted by Stereodude View Post
It's going to cut the voltage to 25% of the original voltage (ie: divide by 4).

Not sure I understand. Will the 8V input get 2V output?

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post #3186 of 3194 Old 07-15-2015, 08:43 PM
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Originally Posted by audioguy View Post
Not sure I understand. Will the 8V input get 2V output?
Yes.
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post #3187 of 3194 Old 07-15-2015, 08:55 PM
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So will 1/2 of the input (4V) generate 1/2 of the output (1V)?

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post #3188 of 3194 Old 07-16-2015, 04:49 AM
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Quote:
Originally Posted by audioguy View Post
So will 1/2 of the input (4V) generate 1/2 of the output (1V)?
Yes, that's what I meant when I said you would get 25% of the input voltage on the output.
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post #3189 of 3194 Old 07-16-2015, 01:10 PM
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All is well. Raised the sub amps gain to maximum; removed the jumpers to allow an 8V input on the miniDSP; adjusted the 7702 trims and viola - it worked.

I can now reach Reference + 5 with the multiple shelf filters engaged and the sub about 5db hot!! (I can't ever recall but one time I played the system at that volume with real material.) After that, the response curve gets a bit weird.

Thanks for all of the recommendations. Love AVS!!!

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post #3190 of 3194 Old Yesterday, 03:26 PM
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Did my first dive into subwoofer room correction and nothing but good things to report. The setup guides for 2x4 provided by this site and MiniDSP.com along with REW have made a great improvement in my listening room.

I have a question about time alignment of the subs. I have old Definitive Technology BP2002's in front each with a powered 12. I have a third subwoofer that can be read more about here.

Transmission Line Isobaric Subwoofer for home.

I seem to notice that when I performed the time alignment step by measuring and adding an offset more and deeper nulls occurred in the REW sweeps.

What does this mean? Or rather how should I interpret this change? I rely on a setup disc with "pops" or "clicks" that helps to fine tune timing delays of surround channels vs fronts & centers. Is there a test tone or method to listen and tune low frequency delays? I have a disc from Sheffield labs that does 100Hz bursts but would like to here from the folks here about audible test methods that are used with consistent good results. I am going to drop a post over on HT Shack in the REW forum too I think.

Here some more details about the setup as it stands.

1 - I measure SPL at 6 postions along the main seating area. Lots of data from which to generate biquads so any huge nulls or peaks will be averaged out significantly (IMO).
2 - As the front Left/Right BP2002's have internal cross overs I have left MiniDSP settings as pass through.
3 - The BP2002's are physically closer to MLP so the sub output is delayed by 1.3ms. Also wondering is delaying these subs is okay as they are build in to the main L/R mid & high frequency drivers. I.e. MTM in bipolar setup.
4 - The third sub is a 30Hz transmission line. MiniDSP is used to invert the phase and filter. HPF 20Hz 48dB/oct BW & LPF 85Hz 48dB/oct BW
5 - The averaged results matched the REW predicted curve very well.
6 - No room treatments whatsoever.

Here is a capture is an in process comparison. All three subs active. GREEN is with no timing delay at all. RED has 1.3ms delay for BP2002's based on physical distance delta. I am wondering about the nulls at 60Hz, 70Hz and 85Hz. I did ABA testing so I don't believe it is measurement error. All measurements taken from center of sub woofer (side firing and down firing.) I had also thought about taking my measured and adding delay based on the distance to each subs port instead of speaker. But not time yet to fiddle.

PS - Thanks to several contribution members to the setup guides etc.... for MiniDSP and sub integration. My hats off to YOU!!!!
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post #3191 of 3194 Old Yesterday, 05:08 PM
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Do REW sweeps at different ms settings. Even try delaying the other sub. Pick the delay value that gives you the flattest response.
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post #3192 of 3194 Old Yesterday, 06:07 PM
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Quote:
Originally Posted by Stereodude View Post
Do REW sweeps at different ms settings. Even try delaying the other sub. Pick the delay value that gives you the flattest response.
Ha! I was afraid someone would suggest as much. Lots of sweeps ahead. Would 0.5ms increments be alright? I guess I could try 1ms and 0.5ms using one microphone position too get a feel for the process.

Last edited by Gaugster; Yesterday at 06:08 PM.
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post #3193 of 3194 Old Today, 04:50 AM
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Originally Posted by Gaugster View Post
Ha! I was afraid someone would suggest as much. Lots of sweeps ahead. Would 0.5ms increments be alright? I guess I could try 1ms and 0.5ms using one microphone position too get a feel for the process.
Put the mic at your MLP and try 1ms increments. You should find a few good candidate values. Once you've identified them check .5ms more or less and see if they're better or worse. Then, use the best values you found to check the other mic positions (seats).
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post #3194 of 3194 Unread Today, 06:16 PM
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Quote:
Originally Posted by Stereodude View Post
Put the mic at your MLP and try 1ms increments. You should find a few good candidate values. Once you've identified them check .5ms more or less and see if they're better or worse. Then, use the best values you found to check the other mic positions (seats).
Good point. Making the LF decent across the seat positions is kind of a secondary goal vs the MLP.

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