HELP! Sub placement - strange REW graphs?

[AlexRossFan]

Today I have learned how to use REW, moved my sub around (1 svs pb-1000 pro) and generated the REW file for 12 possible sub placements in my room. Please check the files attached for the REW graphs and my room layout/sub positions.

Since I don't own a UMIK-1 mic or any calibrated mic, what I did was connect the Audyssey mic (that comes with my Denon X3700H) to my soundblasterx usb sound card. My desktop pc is connected to the denon via hdmi.

Before starting the measurement for each position, I disabled MultEQ XT32, set the sub's distance and level back to 0, and changed the crossover to 250Hz for all speakers. I also level-matched the front left speaker (using master volume) and the sub (using sub gain in the svs app) so the REW spl meter displayed 75db for both. Finally, I ran the sweep from 10hz to 250hz from the front left speaker.

Seems like other people already tested and confirmed that the uncalibrated Audyssey mic is accurate for measuring sub with REW so I hope what I did here was correct. The strange thing is when I look at all the graphs, there seems to be down-sloping response for the low bass from 60Hz and below. Could someone take a look at the files and help out a novice REW users? Thanks.

 

[FargateOne]

Just general information here, others are more qualified than me. I would suggest to retake your measurements (...sorry) with a timing reference (check aid menu in REW and you will find the settings) I suppose that you used Asio4All so selecty one speaker (front left or center for instance) as reference.
For my untrained eye your sub response seems odd to me. did you forget by chance a highpass filter somewhere? Others will know better hopefully

 

[sm52]

The fact that the pressure drops below 100 Hz indicates some kind of improver. All improvers must be disabled when measuring. You may not need a time reference, but without it, it will not work to coordinate the sub and main speakers.

 

[AlexRossFan]

Just general information here, others are more qualified than me. I would suggest to retake your measurements (...sorry) with a timing reference (check aid menu in REW and you will find the settings) I suppose that you used Asio4All so selecty one speaker (front left or center for instance) as reference.
For my untrained eye your sub response seems odd to me. did you forget by chance a highpass filter somewhere? Others will know better hopefully

I use java. Somehow Asio4All does not detect the mic.

Sorry what do you mean by highpass filter? Where is the option for that?

 

[AlexRossFan]

The fact that the pressure drops below 100 Hz indicates some kind of improver. All improvers must be disabled when measuring. You may not need a time reference, but without it, it will not work to coordinate the sub and main speakers.

Sorry what do you mean by improver? Where can I find the settings for that?

I checked tutorials on this and they didn't mention anything about the time reference... should I set the distance of my front left speaker back to 0, just like with the sub?

 

[John Mulcahy]

That roll-off may be due to noise cancellation processing, which Windows tends to apply be default to any mic input that provides stereo data (assuming that one channel is signal and the other is background noise). Make sure enhancements are not enabled on the Windows audio input properties Advanced tab (System - Sound - Related Settings on right hand side - Sound Control Panel - Recording - select the mic, click Properties button) or Enhancements tab. Some PCs may have a separate application with similar features, e,g, Waves MaXXAudio, HP Audio Center, myASUS.

 

[sm52]

That roll-off may be due to noise cancellation processing, which Windows tends to apply be default

and you(Duc Vu) should also check the Sound Blaster control panel. There may also be something included that is good for listening, but not good for measuring.

 

[AlexRossFan]

That roll-off may be due to noise cancellation processing, which Windows tends to apply be default to any mic input that provides stereo data (assuming that one channel is signal and the other is background noise). Make sure enhancements are not enabled on the Windows audio input properties Advanced tab (System - Sound - Related Settings on right hand side - Sound Control Panel - Recording - select the mic, click Properties button) or Enhancements tab. Some PCs may have a separate application with similar features, e,g, Waves MaXXAudio, HP Audio Center, myASUS.

I already disabled all the processing/enhancement I could find, under both Windows and soundcard settings:

 

[AlexRossFan]

and you(Duc Vu) should also check the Sound Blaster control panel. There may also be something included that is good for listening, but not good for measuring.

Yes I did. Please see the post above.

Edit: Probably this sound card is no good for measuring. I found out that if I enable Direct mode on the sound card (which is supposed to bypass the processor entirely), then the mic port does not work. Maybe the mic path of this sound card is routed through the processor.

 

[sm52]

Probably this sound card is no good for measuring.

This is the right line of thought. If you have the ability to connect another external sound card with two inputs and two outputs, then you will get the correct results faster.

 

[AlexRossFan]

This is the right line of thought. If you have the ability to connect another external sound card with two inputs and two outputs, then you will get the correct results faster.

Unfortunately I don't have any sound card like that.

I read people having success by just plugging the mic directly into the mic port on their laptop. Mine is a win 11 desktop pc but when I plug the mic into the mic port on the front panel and use headphone to listen to the mic, sound only comes out of the left ear.

 

[sm52]

when I plug the mic into the mic port on the front panel and use headphone to listen to the mic, sound only comes out of the left ear.

Maybe that's a plus to measure. You can specify this channel as an input in REW.

 

[AlexRossFan]

Maybe that's a plus to measure. You can specify this channel as an input in REW.

When I open the spl meter in REW, it shows the level fluctuates, meaning the program detects the mic. However when I, for example, clap near the mic, the meter does not jump up. Same if I play the test tone to check level. No sound seems to be picked up by the mic. So weird. At least with the sound card the meter responds well to the noise around.

 

[jtalden]

Before starting the measurement for each position, I disabled MultEQ XT32, set the sub's distance and level back to 0, and changed the crossover to 250Hz for all speakers.

Your measurements were taken with the signal sent to the left channel of the AVR. With the XO set to 250 Hz the left channel signal is rolled of below 250 Hz. Your measurements reflect that.
Instead, you can either:

• Output the signal to the sub channel
• Disable the XO in the AVR so that the left channel is not rolled off.

 

[sm52]

Did you do it?

 

[AlexRossFan]

Your measurements were taken with the signal sent to the left channel of the AVR. With the XO set to 250 Hz the left channel signal is rolled of below 250 Hz. Your measurements reflect that.
Instead, you can either:

• Output the signal to the sub channel
• Disable the XO in the AVR so that the left channel is not rolled off.

I thought when I set the crossover in the AVR to 250hz, it meant all the frequencies below 250hz would be sent to the sub instead of the front left, meaning I was effectively measuring the sub? I can felt the rumble from the sub when the measurement sweep was running.

 

[AlexRossFan]

Did you do it?

This screenshot was taken when the mic was still plugged into the soundblaster. That's why I only enabled the mic input on the soundblaster and disabled the rest. If I plug the mic into the front panel mic port of the pc instead then yes Realtek input will be enabled.

 

[FargateOne]

I thought when I set the crossover in the AVR to 250hz, it meant all the frequencies below 250hz would be sent to the sub instead of the front left, meaning I was effectively measuring the sub? I can felt the rumble from the sub when the measurement sweep was running.

Yes but you measured the left front reponse as @jtalden findout. Disconnect the left speaker and send the signal to it and you will get the sub only or, measure the sub channel by itself.

 

[AlexRossFan]

Yes but you measured the left front reponse as @jtalden findout. Disconnect the left speaker and send the signal to it and you will get the sub only or, measure the sub channel by itself.

I don't understand why I still have to disconnect the left speaker... Since the crossover is set to 250hz, and the sweep plays from 10hz to 250hz, only the sub will emit sound, no?

 

[FargateOne]

I've learned a lot about bass management searching on Internet and doing so could help you too. Long story short, crossover means a highpass filter for high FR going to the left speaker and a lowpass filter for 250Hz and below going to the sub. Also the 250 Hz limit is not a brick in wall but like a downward curve beginning one octave before (125Hz ) going one octave after ( 500Hz)

 

[jtalden]

I thought when I set the crossover in the AVR to 250hz, it meant all the frequencies below 250hz would be sent to the sub instead of the front left, meaning I was effectively measuring the sub? I can felt the rumble from the sub when the measurement sweep was running.

Yes, you are correct.

 

[AlexRossFan]

@FargateOne
@sm52
@John Mulcahy

Hey guys. Some good news.

This morning I tried plugging the Audyssey mic into the Mic Input on the back panel of my pc and Voila!

Calibrated the SPL meter inside REW using the Decibel X app on the iphone. Adjust the avr master volume/sub gain so the SPL meter shows 75db for main speakers and 75-76db for sub. Check Level comes out perfect. Attached is the new measurement file for all 12 positions. No more downslopping. The peaks/nulls are still roughly at the frequencies expected.

This is Position 1 vs Position 12:

A new candidate is Position 5. Looks like the best of both world. But that puts the sub right in front of where I sit, blocking the avr, so not very ideal.

I notice a strange thing at Position 5: if I rotate the sub by 90 degree, the frequency response changes:

I ran Audyssey at Position 1 and Position 12 before so below are what MultEQ/DEQ do to the frequency response:

Any advice on what to do next is welcomed.

 

[sm52]

I notice a strange thing at Position 5: if I rotate the sub by 90 degree, the frequency response changes:

any change in the position of the subwoofer or its orientation will change the sound picture.
When I tried to find the position of the sub to get the most even response, I settled on the position down. That is, the driver looks at the floor at a distance of 7-8 cm from the floor. The sub cannot hang in the air, so I made a rack for this position.
Further, there may be smoothing the characteristics with the help of EQ or docking the sub with the main speakers.

 

[AlexRossFan]

any change in the position of the subwoofer or its orientation will change the sound picture.
When I tried to find the position of the sub to get the most even response, I settled on the position down. That is, the driver looks at the floor at a distance of 7-8 cm from the floor. The sub cannot hang in the air, so I made a rack for this position.
Further, there may be smoothing the characteristics with the help of EQ or docking the sub with the main speakers.

Today I also notice my sub makes this kind of rattling noise when it's driven loud. Do you think this is normal? Please wear headphones and increase the volume to hear it better (beside the woofer noise there's a faint rattling noise)

sub rattling

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