Why is there a hole in my first REW measurement for Left and Right?

Scion

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Hi

After adding bass traps and a new receiver/amp, I'm trying to measure the performance of my cinema room but the results look strange. There is a large dip between 100-150 Hz for both the Left and Right front speakers (no subs or centre). I did use REW previously and there was no big dip in 100-150Hz. I did however recently update to the latest version (5.19 Beta 11) to get it to work on my Windows 10 laptop. And while it does work now I can't work out if I have the wrong settings in REW or in the Denon/Audyssey.

I set REW to output to the headphone jack rather than speakers since my Surface Pro 4 doesn't have an HDMI soundcard. And after running Audyssey, I manually set the crossovers to 90Hz for the fronts and LPF for LFE at 120. I'm will use DTS Neural X for measuring the Centre (in lieu of Dolby PLII), although measuring with Stereo made no real difference to the dip.

I must be missing something obvious because I'm also measuring sound below 90Hz, which is where there is a crossover for the fronts to the subs. Does the REW measurement bypass the Audyssey (e..g. crossover) settings?

Thanks
Ion

Front R vs L.jpg
 

Almoped

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You can try toggling Pure Direct on the AVR while you play sine waves at 125hz/do measurements to help figure out if Audyssey/ADC is causing undesired effects.
 

Scion

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Good idea; I played sine waves at 125Hz and toggled Audyssey using the remote. The SPL meter showed no drop in volume so it seems unlikely that Audyssey is the culprit. I wonder if it might be a room mode after all...

Separately, can anyone explain why the REW graph shows bass being measured on the fronts when the crossovers were manually set to 90Hz (after letting Audyssey run its EQ). I assumed that the crossovers would be sending ALL the bass to the sub. Does REW override that setting or is there another explanation for the bass being played?

Ion
 

Matthew J Poes

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The holes you see are cancelation effects. Certainly need to rule out other sources like eq, but unlikely eq would have that Q. The two most likely culprits are room modes or SBIR effects (or a combination of the two).

I would suggest taking more measurements in more locations. Run the speakers full range and with no sub. Move the speakers farther or closer to the wall. That will help identify the problem.
 

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Forward to your "Separate" question... Audyssey may determine that you have a "large" speaker capable of sending low frequencies to...
 

Scion

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Forward to your "Separate" question... Audyssey may determine that you have a "large" speaker capable of sending low frequencies to...

Yes, Audyssey measured the fronts as 'Large' during the initial EQ (according to the 'Results' section in Setup). But then I manually changed the speakers to 'Small' and raised the crossovers to 90Hz. My understanding is that those manual settings would prevent any bass under 90Hz from playing thru the fronts. Is it possible that REW somehow overrides/ignores the Manual settings in Audyssey? Or is there another reason why I would be measuring that sort of bass from my fronts?

Ion
 

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Scion said "I set REW to output to the headphone jack rather than speakers since my Surface Pro 4 doesn't have an HDMI soundcard."

If I understand what you are saying above, there is only a physical analogue connection (headphone jack) capable of a mono or stereo signal to your AVR... What your AVR is capable of doing to that signal (read signal processing effects) would have nothing to do with REW...

I would follow Matts suggested advise in post #4 above...
 

Scion

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I think Matt's advice is spot on. After more measurements, the dip from 100-150Hz does indeed seem to come from room modes.

Unfortunately that doesn't resolve the other/separate question of why REW is measuring bass below the crossover setting. This is probably an Audyssey issue rather than an REW issue. As you said, this is an analogue signal fed from the headphone jack to the AVR using a Y cable. Although I have tried every Audyssey setting, I can't stop the fronts from playing bass below the crossover. This means the bass management in the 4400 is not working properly. And if the crossovers are not effective, then I don't see how to integrate the subs with the fronts.

Ion
 

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I do not have a definitive answer for you Scion... I was only stating that REW would have no control over your AVR's crossover for your speakers...

What did Audyssey originally set the crossover at before you changed it to 90Hz? And have you thought about running thru the Audyssey setup again if you moved your speakers?
 

Scion

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Audyssey originally set the fronts at full range with no crossover. I haven't moved the speakers but have moved the mic to confirm Matts room modes suggestion.

I just used REW to compare the front left speaker's output when set to Large and then to Small. Since the Small graph is essentially identical to the Large I can only guess that it is the Denon bass management system that isn't doing it's job.

Ion
 

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Hi Scion, I would imagine that there is some setting in Audyssey that is overriding your manual crossover setting like LFE+Main for instance... I am not an Audyssey expert and the Denon Owners Manual is pretty terse...

Maybe an Audyssey expert will join in to help...

100Hz and below are not very directional... Are your subs off when making this measurement?
 
Last edited:

Matthew J Poes

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Audyssey originally set the fronts at full range with no crossover. I haven't moved the speakers but have moved the mic to confirm Matts room modes suggestion.

I just used REW to compare the front left speaker's output when set to Large and then to Small. Since the Small graph is essentially identical to the Large I can only guess that it is the Denon bass management system that isn't doing it's job.

Ion

Hi Scion, You really need tot ake measurements of the speakers with and without the highpass filter in place to help diagnose this. However, what I see in the above measurements does look like a high pass filter is in place. Keep in mind that a high pass filter does not remove all bass like a brick wall. It applies a 2nd order (12dB per octave) filter. If it is set for 80hz, then the sound will fall at a rate of 12dB per octave below the cut frequency (but since these are not ideal filters, it will be about 3dB down at the cut frequency already.

Here is an example of a measurement of a main speaker in a theater with no highpass filter and what it looks like after I apply a 2nd order high pass filter in REW.
Response with Highpass.PNG

Notice that while clearly, the full range response has more output below 100hz, the filtered speaker is still producing output. This is based on a speaker that had a mostly flat in room response, imagine what it might look like if the speaker had a boosted bass response. Then the speaker might look like it has no high pass when it does, but the boosted bass response is making it harder to see. In any case, here you see that 1 octave below 80hz, 40hz the response goes from 75dB to 63dB, or 12dB's less. Since it is 12dB per octave, that is exactly what we expect.

Hopefully this is helpful.
 
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ddude003

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As an aside, why crossover at 90Hz when the mains will go down to 28Hz???
 

Scion

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The graph below shows a comparison of the Front Left speaker; first set to Large and then to Small. I did the measurements with REW, using the headphone jack and a Y cable connected to AUX1 on Denon X4000 front panel, input set to Stereo.

To make certain speaker the was set to Small for the second measurement I made these 4 changes to in Setup menu:
1. Audio/Audyssey/MultEQ XT32/Reference
2. Speakers/Manual Setup/Speaker Configuration/Front=Small
3. Speakers/Manual Setup/Crossovers/Front=80Hz
4. 2Channel/Playback/Front=Small

The graphs are identical apart from the slightly different smoothings to separate the lines.

It seems to me that the Denon is still sending bass below the crossover to the front speaker, regardless of settings. I still wonder if I'm missing something obvious or if indeed the Bass Management system is faulty.

Re. the question of why 80/90Hz inititally; the fronts use the Denon pre-outs and are driven by a separate 2 channel Marantz MM7025 amp. The speakers are 4 ohms but the amp is only rated down to 6 ohms. By relieving the fronts of the low bass I hoped to protect the Marantz amp. I believe the bass management is in the pre-amp section of the Denon, so I assume that using a Marantz amp won't create this issue.

Thanks
Ion

Comparing Front Left 'Large v Small'.jpg
 

Jeff Ames

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Thank You for this post, I took My first measurement tonight with a similar dip around 140hz.
You all have given Me ideas on My next plan of action before adding any equalization
initial measurement.jpg
.
 
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