• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

New Room, New Measurements & What helped

MetalDaze

Member
Joined
Aug 13, 2020
Messages
94
Likes
63
Hello again!

After a move and stepping into a finished basement space, there was a lot of work to be done, and continues to be! Thankfully there has been some good progress made after a fair amount of messing about.

I can't stress enough how much research, making extensive use of REW's Room Simulator feature, measurements and multi sub really helped me get much closer to where I wanted to be with my room response. I already had a good amount of room treatment which I transferred from my previous listening space. Pic here:

This is what I wound up with in REW Room Simulator, and after doing the sub crawl. I first had one sub in each front and rear opposite corner. But that just didn't do it. This arrangement was the trick:
Screen5.jpg

The software doesn't have unlimited capability, but got pretty close for me. I sort of guesstimated with my input of surface absorptions. Since my measured response came in similarly, I feel for now it's close enough.

Here is the raw response with the towers at full range. The speakers have built in passive 'subwoofers' which operate from 32-100Hz. The Rythmik L12's are set to 24dB slope @ ~80Hz, no EQ:
Screen4.jpg

I set my target SPL for ~70 dB, disregarding the intentional elevated shelving of bass below 200Hz (At 20Hz the level needs to be around 60dB for the human ear to even hear it! :oops:) . I followed Anthony Grimani's advice from his discussions at Audioholics for an acceptable deviation of +/-5dB from the targeted level. Luckily, and with a little clean up from 1/6 octave smoothing, the measured response is pretty much there.

For those who like a more visually appealing graph:
Screen6.jpg



The time domain really benefited from implementing a bit of EQ. There was (still is some) significant ringing around 50-70Hz which is modal for the room dimension. I wanted to stomp down that ringing as best I could. What worked well was actually leaving the left sub as is, and activating the PEQ on the right sub, at the problem peak. I then set a -3dB filter in the RME DAC which I can turn on and off via the remote as needed. With the RME the resonances are a non issue. And with only the PEQ on one sub engaged, the resonance is still lowered to an acceptable level:
Screen3.jpg


That leaves the spectrogram to contend with:
Screen2.jpg


That 'knee' in the peak energy time is right around where I cross the subs over. Does someone have input on if this appears to be something I can/should smooth out with a delay adjustment? I thought the alignment was good but I'm not totally sure what this suggests. I have moved and measured the L12's cross over previously to match the speakers at 100Hz, but that caused other undesirables in the frequency response. This configuration resulted (so far) in the smoothest FR graph.

As time goes on and the aesthetics of the room continue to come together, I'd like to add a few more well placed panels/traps. Especially at 1/4 length wave intervals from the back wall. This should allow a 2" absorber to function as a much deeper one, further smoothing out the modal issues in the 50 - 70 Hz range. There is minimal treatment there currently.

Hopefully some find this helpful! And as always any input is appreciated.

Cheers!
 

ernestcarl

Major Contributor
Joined
Sep 4, 2019
Messages
2,245
Likes
1,620
Location
Canada
Hello again!

After a move and stepping into a finished basement space, there was a lot of work to be done, and continues to be! Thankfully there has been some good progress made after a fair amount of messing about.

I can't stress enough how much research, making extensive use of REW's Room Simulator feature, measurements and multi sub really helped me get much closer to where I wanted to be with my room response. I already had a good amount of room treatment which I transferred from my previous listening space. Pic here:

This is what I wound up with in REW Room Simulator, and after doing the sub crawl. I first had one sub in each front and rear opposite corner. But that just didn't do it. This arrangement was the trick:
View attachment 190786
The software doesn't have unlimited capability, but got pretty close for me. I sort of guesstimated with my input of surface absorptions. Since my measured response came in similarly, I feel for now it's close enough.

Here is the raw response with the towers at full range. The speakers have built in passive 'subwoofers' which operate from 32-100Hz. The Rythmik L12's are set to 24dB slope @ ~80Hz, no EQ:
View attachment 190789
I set my target SPL for ~70 dB, disregarding the intentional elevated shelving of bass below 200Hz (At 20Hz the level needs to be around 60dB for the human ear to even hear it! :oops:) . I followed Anthony Grimani's advice from his discussions at Audioholics for an acceptable deviation of +/-5dB from the targeted level. Luckily, and with a little clean up from 1/6 octave smoothing, the measured response is pretty much there.

For those who like a more visually appealing graph:
View attachment 190799


The time domain really benefited from implementing a bit of EQ. There was (still is some) significant ringing around 50-70Hz which is modal for the room dimension. I wanted to stomp down that ringing as best I could. What worked well was actually leaving the left sub as is, and activating the PEQ on the right sub, at the problem peak. I then set a -3dB filter in the RME DAC which I can turn on and off via the remote as needed. With the RME the resonances are a non issue. And with only the PEQ on one sub engaged, the resonance is still lowered to an acceptable level:
View attachment 190791

That leaves the spectrogram to contend with:
View attachment 190792

That 'knee' in the peak energy time is right around where I cross the subs over. Does someone have input on if this appears to be something I can/should smooth out with a delay adjustment? I thought the alignment was good but I'm not totally sure what this suggests. I have moved and measured the L12's cross over previously to match the speakers at 100Hz, but that caused other undesirables in the frequency response. This configuration resulted (so far) in the smoothest FR graph.

As time goes on and the aesthetics of the room continue to come together, I'd like to add a few more well placed panels/traps. Especially at 1/4 length wave intervals from the back wall. This should allow a 2" absorber to function as a much deeper one, further smoothing out the modal issues in the 50 - 70 Hz range. There is minimal treatment there currently.

Hopefully some find this helpful! And as always any input is appreciated.

Cheers!

The overall decay looks already very good. I would look at an overlay of the phase response of the speakers and accompanying subs (with appropriate time reference) if you want to make sure if further improvements in the alignment as measured at your listening position can be had... here's one example: https://www.audiosciencereview.com/...ase-control-on-a-subwoofer.20889/post-1108162

*Since you have two subs (stereo pair or mono?), I would do a L+R sweep with the mains muted and without a timing reference. Then mute one of the mains with the sub still on and use the right channel as your time reference. Perhaps do the same for the opposite pair and create a new vector average of the subwoofer response from both results. You could also just re-route the sub channels together into one and use one of the mains as its reference. I know this might sound a bit confusing... perhaps somebody can explain this better than me. :facepalm:
 
Last edited:
OP
MetalDaze

MetalDaze

Member
Joined
Aug 13, 2020
Messages
94
Likes
63
Thanks! I'm picking up what your putting down. Massaging the last bit of smoothness from the response comes with some finesse.

I had measured them separately in my previous room, but haven't made that measurement yet here. I'll have to do that. I have banana jacks for the mains so its easy to unplug them and just let the subwoofers do the sweep. Then turn off the subs and run the same sweep on the mains and see where they cross once super imposed. I can also do L vs R and see how they interact. I think I did something similar to what you suggest here for the timing reference, so I'll be sure to do that again. I remember trying it once without it, and the result was malarkey.

I have 2 Rythmik L12's, in what I would call dual mono? Since my AVR only has a distance adjustment for one subwoofer, but 2 outputs. Ditto my P5 preamp but its analog and only gain is adjustable at the front of the unit. So I put the L12's behind the towers, as equidistant as I could from each other and my main seating position.

I see now that my screens didn't grab the phase, so here is that measurement with the right sub PEQ engaged:
Screen7.jpg


For the phase to be as close to aligned as possible, would we be looking for no abnormalities in the diagonal lines between the vertical dashed lines? I extrapolated these correlate to the dips and peaks in the frequency response. But that's about where I stopped for a beer o_O
 

ernestcarl

Major Contributor
Joined
Sep 4, 2019
Messages
2,245
Likes
1,620
Location
Canada
Thanks! I'm picking up what your putting down. Massaging the last bit of smoothness from the response comes with some finesse.

I had measured them separately in my previous room, but haven't made that measurement yet here. I'll have to do that. I have banana jacks for the mains so its easy to unplug them and just let the subwoofers do the sweep. Then turn off the subs and run the same sweep on the mains and see where they cross once super imposed. I can also do L vs R and see how they interact. I think I did something similar to what you suggest here for the timing reference, so I'll be sure to do that again. I remember trying it once without it, and the result was malarkey.

I have 2 Rythmik L12's, in what I would call dual mono? Since my AVR only has a distance adjustment for one subwoofer, but 2 outputs. Ditto my P5 preamp but its analog and only gain is adjustable at the front of the unit. So I put the L12's behind the towers, as equidistant as I could from each other and my main seating position.

I see now that my screens didn't grab the phase, so here is that measurement with the right sub PEQ engaged:
View attachment 191045

For the phase to be as close to aligned as possible, would we be looking for no abnormalities in the diagonal lines between the vertical dashed lines? I extrapolated these correlate to the dips and peaks in the frequency response. But that's about where I stopped for a beer o_O

One needs to see the separate phase traces of the mains and subwoofers e.g. L+R mains and mono subs. See: this illustration: https://www.audiosciencereview.com/...ase-control-on-a-subwoofer.20889/post-1107737

Some of the abrupt phase rotation may be caused by the room and not inherent of the loudspeakers native response. You might want to use at least some frequency dependent windowing to clear up your phase response a bit.

Alternatively, ditching the detailed phase comparison part altogether... you could just use the RTA window and play random full-range periodic PN in REW's generator. Adjust the ms time offset and xo settings (including polarity) of the mains and/or sub manually (don't forget to save your baseline and press 'reset' with every change) until you get the best summation. That last trial and error method is way easier to perform if the time delay difference is minimal.
 
OP
MetalDaze

MetalDaze

Member
Joined
Aug 13, 2020
Messages
94
Likes
63
Okay! I will chew on this for a while and post measurements (hopefully with improvements) when I have the time. Thanks again for all your input! Yourself and the forum in general on this and previous threads has been very helpful in furthering my room acoustics understanding and measured response. :)
 

ernestcarl

Major Contributor
Joined
Sep 4, 2019
Messages
2,245
Likes
1,620
Location
Canada
Okay! I will chew on this for a while and post measurements (hopefully with improvements) when I have the time. Thanks again for all your input! Yourself and the forum in general on this and previous threads has been very helpful in furthering my room acoustics understanding and measured response. :)

BTW, you can roughly, but quickly figure out manually the individual time and phase polarity alignment offset (between mains and subs) when you do not have the proper acoustic time reference by doing a quick sweep of the mono subs and LR monitors at your MLP.

Just bring up the "overlays" window and check the step responses (summed and individual speakers) on top of one another.


Visual example:

1647894786557.png



1647894795190.png



Without the proper acoustic time reference, perhaps you might see something like the ff:

1647894856359.png

*I inverted the phase and used "estimate IR delay" function to help illustrate why we need to have the correct acoustic time offset from the start


Given the incongruity above, adjust the sub's correct position in time and change the polarity so that it fits our expected sub+mains "Summed Response" (green trace) step:

1647895225329.png



Once we get that "close enough", the overlayed step responses should look like the ff:

1647895271860.png


Alternatively, if L+R are swept together and precisely centered (or simply vector averaged)

1647895280077.png



We're doing all of this so that in REW's alignment tool, we can now more easily observe how good really is the overall fit between both the magnitude and phase:

1647895363482.png




WAVELET SPECTROGRAM
1647896082816.png


In an ideal world, GD or the peak energy time of the subwoofer(s) should be under 10 to 20 ms. Hmmmn... but in an imaginary "perfect world", everything should be closer to 0 ms -- not that it audibly matters much in the lowest bass frequencies, of course!



---------

*BTW, I'm applying windowing in here to make the phase response easier to read:

1647896861717.png


Feel free to change the cycle value setting as desired.
 
Last edited:
Top Bottom