# Sub-measurement - rolls off prior to c/o freq



## Mikkel (Jan 4, 2009)

Hello everyone,

I hope you can help me. It would be much appreciated!
Here is the problem: when measuring my subwoofer-response the REW graph starts to roll drastically at around 80 hz, even though the cross-over on the sub is set to max and the bass management software of my soundcard is set to 150hz. It seems as if a 24db filter is applied at 80 hz.

The odd thing is, if I use e.g. NCH tone generator and make manual measurements, the level at 80 hz is e.g. 70 db(c) and at 150 hz it is 66-68 db(c).

That tells me two things (I believe):
1) Nothing's wrong with the soundcard
2) Nothing's wrong with the subwoofer

What is left is REW.
I have followed the guide, so everything is connected as it should, calibrated (both soundcard and mic) and no house curve is applied.

Here is the setup:
ASUS Xonar HDAV1.3 Deluxe analog output --> AV Reciever multichannel inputs
Sub is connected to the pre-out
Experimentally I tried connecting the sub directly to the output of the soundcard. Made no difference, though.

Do you have a clue of what is going on? If you need additional info I'll collect it.


Best regards,
Mikkel


----------



## Mikkel (Jan 4, 2009)

Perhaps I should add I'm using the old analog radioshack to measure the response. I'm using the calibration file from this forum.
Furthermore I have difficulties achieving adequate leves when "checking levels".


----------



## SAC (Dec 3, 2009)

A few questions worth verifying...

You say the sub is connected to the "pre-out"... 

In what configuration guide have you seen a recommendation to attach the sub to a pre-out and not to a "sub-out"?

How are you assured that the signal being passed is full range?

Knowing nothing about the receiver...

But if this receiver has internal bass management, an LFE out and a crossover providing a low pass filter for the sub, you may be sending the high passed signal intended for the Satellites to the sub - especially as a corner frequency of ~80 Hz is awfully coincidental ... 

"It seems as if a 24db filter is applied at 80 hz" ....and this sounds exactly like what is happening...


----------



## Mikkel (Jan 4, 2009)

Thx for your reply 

Mind you I'm no expert, so perhaps the pre-out-term is incorrect. It is the sub-output of my H/K 23? reciever, anyway.

So I connected the sub to both the sub-output of my receiver and as an alternative directly to the sub-out of my soundcard. 

There is no management when using the analog connections on my receiver.
When using the soundcard it controls the bassmanagement.

The signal isn't full-range but limited to 15-200hz - I suppose it wouldn't make a difference to the current problem, though...?


----------



## SAC (Dec 3, 2009)

I must now admit to being utterly confused by your descriptions. :dontknow: 

And the soundcard does bass management? What? (Not in the context of interfacing with REW it doesn't!)

With REW the sound card does NOT do bass management - it is there essentially only for routing.source control and gain. Other than that it is (or should be) basically passive except as a pre-amp.

May I suggest you create a detailed wiring diagram complete with component model numbers and specific ports/interconnections labeled.
We need the detail and not simply an general description of the interconnections and an abstract symptomatic description of the problem.

And with regards to REW, do NOT band limit sweeps - allow them to run as full range sweeps.

There is something wrong with the software configurations or how things are connected, as this behavior is not a fundamental limitation of REW. 


Help us help you!


----------



## JohnM (Apr 11, 2006)

Hi Mikkel,

Can you post a screenshot of the result you get? Click the camera icon at the top left of the graph to capture the image. Also try using the REW signal generator to check how the results compared to using the NCH generator.


----------



## Mikkel (Jan 4, 2009)

Hi John and SAC,

I'll provide you with both a graph and a connection diagram as soon as I get time (today or tomorrow). Thx for your help.


Best regards,
Mikkel


----------



## Mikkel (Jan 4, 2009)

Hello again,

Follow images have been attached:
1. Showing the connections based on the diagram from the REW-help file
2. Showing my specific setup
3. Showing a measurement from 15hz - 20.000hz

Ad2. The only difference between the ideal-setup and my setup is I do not use stereo-out. Reason is a) my soundcard will not send any bass to the subwoofer if I do, and b) in 8ch multichannel analogue mode the receiver only works as an amplifier bypassing any soundprocessing unit of the reciever. Thus, I have to use 8ch output, with soundcard bass-management turn on, applying a cross-over at 200hz.

Ad3. As you can see, past 52db there is no soundpressure in the graph. However, I can assure you there is. The sweep played as it should from 15 to 20.000hz.

About the difference in measurement between REW signal generator and NCH: There is no difference. A test tone at 120hz measures e.g. 64db(c) in both programs.

As for soundcard drivers I have tried a few different drivers, including some 3rd-party drivers that works quite a lot better than those provided by ASUS.

I hope this is enough info for you, if not let me know 


Best regards,
Mikkel


----------



## JohnM (Apr 11, 2006)

Try making a measurement with the soundcard output you are using looped back to the line input to see what is actually coming out of that connection and eliminate the receiver.


----------



## Mikkel (Jan 4, 2009)

JohnM said:


> Try making a measurement with the soundcard output you are using looped back to the line input to see what is actually coming out of that connection and eliminate the receiver.


Hi John,

Thx for your feedback.

Unfortunately I've already tried. It performs excellent, with a perfectly flat curve from 20-20.000hz, so the output from the soundcard is fine. 

When just playing a single tone, e.g. 5.000 the soundpressure is approximately the same as at 100hz.

So I suspect neither soundcard nor receiver is the problem.

I don't know if a radioschack-meter a little low on battery could be the problem...? I suspect finding another battery could answer that question...


Best regards,
Mikkel


----------



## JohnM (Apr 11, 2006)

Which soundcard output are you using, and which receiver input channel is it connected to? Difficult to understand how you would hear all of a 20Hz to 20kHz sweep, or a tone at 5kHz, if you are driving the sub input channel.


----------



## Mikkel (Jan 4, 2009)

JohnM said:


> Which soundcard output are you using, and which receiver input channel is it connected to? Difficult to understand how you would hear all of a 20Hz to 20kHz sweep, or a tone at 5kHz, if you are driving the sub input channel.


Soundcard sub-out --> reciever sub-in
Soundcard L/R out--> reciever L/R in
Soundcard LB, RB, LS, RS out --> reciever LB, RB, LS, RS in

Soundcard bass-management set to cross-over at 200hz.

I suspect you would tell me it is wrong to measure in any mode but stereo. As mentioned that is not possible due to a design-flaw in the soundcard software.

If you think it makes a difference, I could run the soundcard in stereo-mode, connecting soundcard left-out to reciever sub-in.


Best regards,
Mikkel


----------



## JohnM (Apr 11, 2006)

Mikkel said:


> If you think it makes a difference, I could run the soundcard in stereo-mode, connecting soundcard left-out to reciever sub-in.


That would be worth doing, to measure other channels simply move the soundcard output to other channels of the receiver's analog inputs.


----------



## Mikkel (Jan 4, 2009)

JohnM said:


> That would be worth doing, to measure other channels simply move the soundcard output to other channels of the receiver's analog inputs.


Sorry for the absence. I did as promised and no change in measurement. I also tried new batteries in the radioshack sound pressure meter. Didn't work.

As a test I downloaded Audiolense and did a complete measurement of all speakers. And it did record the full range frequency response as opposed to the pictures you can see above.

Best regards,
Mikkel


----------



## JohnM (Apr 11, 2006)

Not sure what to suggest then. Mikkel. You said in an earlier post that you got a perfectly flat measurement with a loopback connected, so it is difficult to see how REW could be the issue: REW doesn't know whether you have connected a loopback or are making a room measurement, it behaves in exactly the same way for both.


----------



## Mikkel (Jan 4, 2009)

JohnM said:


> Not sure what to suggest then. Mikkel. You said in an earlier post that you got a perfectly flat measurement with a loopback connected, so it is difficult to see how REW could be the issue: REW doesn't know whether you have connected a loopback or are making a room measurement, it behaves in exactly the same way for both.


Indeed. I'll double check again for driver issues, since that is about the only reason I can come up with.


----------



## Mikkel (Jan 4, 2009)

Just a heads-up:
Installed the most recent beta-verison (the one with ASIO-support) and now everything works!
Thx for your help, anyway, though.


----------

