subwoofer pre-out response doesn't seem right

**absolootbs** · **07-23-09, 09:02 PM**

from what i've read on here, and from other people's graphs i've seen, if you take a measurement of your sub preout, response should match up exactly with a flat target thats configured with the same crossover and slope, right?

below are some graphs of my preout measurements, which as you can see, most certainly do not match up. the first and second are my onkyo 603 thats in my theater. the first is with an 80hz crossover set on the avr, the second is with a 100hz crossover set on the avr. both with matching target curves. as you can see, not only are the slopes not right, but there was a dip both times centered on 80hz, and response falls off like crazy where it should flatten out. the third graph is the onkyo 503 thats in my living room. after the 603 responded so unexpectedly, i decided to measure the 503 too, to get a "second opinion". it's a little better in that the slopes at least match up exactly, but just like the 603, it falls off where (as far as i know) it should flatten out. is this something onkyos do that i've somehow never heard/read about? or is it something inherent to a lot of "budget conscious" avrs? or is it option c: my gear has issues?

NOTE: measurements were taken with sound card calibration loaded, c weighted box unchecked, and mic calibration cleared.

**brucek** · **07-23-09, 11:10 PM**

When you measure a loopback cable only, is the response flat down to 5Hz?

Yeah, I would have expected the crossover to track a bit better than that. The dip at 80Hz seems a bit unusual too.

All electronics rolls off at low frequencies, although I'm surprised the low frequency rolloff is that poor. You can simply look at the owners manual to see what the -3dB down point is for your receiver. Looks like you're measuring that at about 20Hz.

brucek

**absolootbs** · **07-25-09, 02:07 PM**

a measurement of the soundcard via loopback shows it starts to drop off ever so slightly at about 30hz. doesn't hit -3db until 7hz though. but shouldn't the sound cards response not factor in, as long as i have it measured properly and the calibration file loaded? i was under the impression that was the whole reason for calibrating the sound card - so that its response is compensated for in other measurements.

in the 603's owners manual the only fr listed is for the amplifier (none listed specifically for the preout) and it says 10hz - 100khz @ -3db in direct mode. i would have to expect the preout should be (supposed to be) about the same, if not better than the amp spec though.

anyone else out there willing to measure their preout and post the results?

**brucek** · **07-25-09, 02:50 PM**

Quote:

but shouldn't the sound cards response not factor in, as long as i have it measured properly and the calibration file loaded?

Yes, the response of a loopback cable shouldn't be falling off at 30Hz. It should be flat almost down to 2Hz and may have a few small squiggles at that point, but that's all. Did you get a good soundcard calibration? Lets see your graph of the soundcard cal file..

Quote:

anyone else out there willing to measure their preout and post the results?

I've measured my processors sub out response and it tracks the target fairly well - mind you, it's a $5K processor, so that's expected. I don't know what can be expected of a standard retail receiver. Maybe others have tested theirs. Either way, I think you should be sure you have a flat response of a loopback cable before you attempt to measure anything.

Name: bryston sp2 processor sub response 60hz crossover.jpg
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Name: bryston sp2 processor sub response 60hz crossover.jpg
Views: 120
Size: 50.0 KB

brucek

**absolootbs** · **07-26-09, 03:27 PM**

wait, did you mean to take a loopback measurement with the soundcard cal file loaded, or without? when i said it was starting to drop off slightly at 30hz, i was taking it without the file loaded (cal cleared)... basically showing what the measurement looked like for the cal file. it just occured to me you were probably wanting to know what a loopback measurement looked like with the cal file loaded, to see if the sound card was being compensated for properly. am i right about that?

**brucek** · **07-26-09, 03:53 PM**

Quote:

it just occurred to me you were probably wanting to know what a loopback measurement looked like with the cal file loaded, to see if the sound card was being compensated for properly. am i right about that?

Yes, the only way to determine if the soundcard cal file is correct or not is to have it loaded when you measure a cable. Since we know before-hand that a cable is flat, then if it measures flat, we know our test equipment will not color the test results. Also be sure to have the SPL meter cal file cleared (since we're not using a meter).

Hopefully you measured your receiver with the cal file loaded?

Let's see your loopback cable measurement from 0-200Hz......

brucek

**absolootbs** · **07-26-09, 04:18 PM**

my bad... brain must have been at half throttle when i interpreted what you wanted the first time. loopback with cal loaded is +/- 0.2 db, just as it should be (see attached). and yea, as noted in the op, preout measurements were taken with cal file loaded. so that pretty much just leaves that my avr's stink, and are going to hurt my low end extension now matter how good my sub and placement are, right?

**brucek** · **07-26-09, 04:24 PM**

Quote:

so that pretty much just leaves that my avr's stink, and are going to hurt my low end extension now matter how good my sub and placement are, right?

Yeah, that sums it up for sure. I'm surprised that the low end electronics roll-off is poor with your receiver, although it isn't a show stopper really. It looks about -3dB at 20Hz and maybe -10dB at 10Hz....

brucek

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