Acoustic treatment and room measurement

[Roust_m]

Hi,
I measured my cinema room before applying acoustic treatment and after using the approach described in this video:

I used this page for my room treatment calculation:

Home Cinema Systems

Select the Quality Level and Room Size below to see which Sonitus U.S.A. acoustical package you will need. Use the results to order those products at the Sonitus U.S.A. store via the link above "Shop All Products". Your ears, mixes, movies, friends, and family members will all thank you!

www.sonitususa.com

I've put "Quality Level" as Ultra and "Room size" as 300-400 sq. ft.
I measured my room before treatment for the two seats in the front row I use 99% of the time. After treatment I measured all 6 seats.
To my surprise my measurements showed that my acoustics did not get better. They actually got worse.
This is a OneDrive folder with the measurements and the screenshot of acoustic treatment selection:
_cinema
I also attached them to this post.

Wondering why this has happened?
Thanks.

 

[benito]

I downloaded your data, but it is difficult to analyze since we do not know what the data corresponds to. For example, what does "s4 L R" mean? Where is the microphone placed?

Room acoustics depend on a lot of parameters: room dimensions (length, width, and height), the building materials used, where the speakers are placed, as well as your seat.

From 'Before treatement.mdat' your room exhibts several couplings ; at 25 and 130 Hz:



form the S2 R R :

 

[Roust_m]

S1, S2, ..., S6 are the seats and I placed microphone where the ear position would be when someone takes the seat. For pre-treatment time I only measured seat 1 and seat 2 (the front row I use 99% of the time)

Next character is "L" or "R" meaning left or right ear.
Next character is "L" or "R" meaning left or right speaker.
So, S1 L R means seat 1, left ear right speaker.

I measured it according to the instructions of the video.

My question is why post treatment measurements are worse (left - before treatment, right - after) for same location:

 

[benito]

My question is why post treatment measurements are worse (left - before treatment, right - after) for same location:

To be honnest, I don't know. Room Acoustic is difficult subject.

What are your room dimensions (length, width, and height) ?

What do you mean by meaning left or right ear ?

How many speakers and seats ?

That is your set-up ?

 

[Roust_m]

To be honnest, I don't know. Room Acoustic is difficult subject.

What are your room dimensions (length, width, and height) ?

What do you mean by meaning left or right ear ?

How many speakers and seats ?

That is your set-up ?
View attachment 148211

It is about 7 by 4.2 meters, and 2.7 meters high. When you rest your head on the recliner your ears end up in certain position. I put the microphone in those locations where the left and right ear of a human would be. I have 7.2.4 system: 7 speakers 2 subs and 4 atmos speakers in the ceiling. I have 6 seats: 2 in the front row and 4 in the back. Yes, this is my setup.

 

[benito]

Your peak ar 25 Hz is a longitudinal mode (from REW Room simulation). You should cancel it up first.

I do not know anything in home cinema system, do not know if recepies for two speakers system apply in multi-channel system.

You should contact the store that sell you the system.

 

[ecwl]

Hi,
I measured my cinema room before applying acoustic treatment and after using the approach described in this video:

I used this page for my room treatment calculation:

Home Cinema Systems

Select the Quality Level and Room Size below to see which Sonitus U.S.A. acoustical package you will need. Use the results to order those products at the Sonitus U.S.A. store via the link above "Shop All Products". Your ears, mixes, movies, friends, and family members will all thank you!

www.sonitususa.com

I've put "Quality Level" as Ultra and "Room size" as 300-400 sq. ft.
I measured my room before treatment for the two seats in the front row I use 99% of the time. After treatment I measured all 6 seats.
To my surprise my measurements showed that my acoustics did not get better. They actually got worse.
This is a OneDrive folder with the measurements and the screenshot of acoustic treatment selection:
_cinema
I also attached them to this post.

Wondering why this has happened?
Thanks.

I just took a quick look at the first measurement position. Looks better to me

The long decay in low frequencies are measurement artifacts or errors. You can verify that because all your other seat measurements show totally random inconsistent decays from seat to seat and measurement to measurement. So it’s probably just noise coming from the HVAC turning on and off or kids stomping the ground upstairs during the after treatment measurement process.

The spectrogram decay time looks worse on the new measurement because the scale is different? You can see on the left that red is 84dB whereas on the right it’s 78dB so you’re not really comparing apples to apples.

The overall frequency response is slightly smoother after treatment.

Even with room treatment, you’re going to have to re-run your processor’s digital room correction anyway to hear the optimal sound

I usually recommend people to buy Lyngdorf processors if they can afford it because people like to tweak and DIY and I find Lyngdorf RoomPerfect to give the right balance to let tweakers tweak but still should get fairly optimal results, unlike Audyssey or Dirac where people can under or over correct more easily.

 

[Roust_m]

How do I cancel the 25Hz mode?

This is the setup I have BTW:
I currently have a dedicated cinema room with 7.2.4 Monitor Audio Silver range speakers and Yamaha A8A AVR and 5-channel Rotel 1585 power amp dedicated to front and side speaker:
2 x Monitor Audio Silver 500 (front)
1 x Monitor Audio Silver c250 (centre)
2 x RXW12 (sub)
2 x RXFX (side)
2 x RX1 (back)
4 x Monitor Audio CP-CT380 8" In Ceiling Speaker

 

[Roust_m]

And this is my room layout

 

[Roust_m]

I just took a quick look at the first measurement position. Looks better to me

The spectrogram decay time looks worse on the new measurement because the scale is different? You can see on the left that red is 84dB whereas on the right it’s 78dB so you’re not really comparing apples to apples.

The 84 and 78 is just how loud the sound is going. The reason it is lower after treatment is because the absorption panels absorbed some of the sound, so the sound got quitter. But the scale is the same, it goes from -200 to 950 on both pictures.

 

[Bruce B]

How do I cancel the 25Hz mode?

1. Use EQ settings on your sub to turn down 25Hz
2. Use Phase settings on your sub for cancellation
3. Move your Sub/Speakers
4. Move your listening/measuring position
5. I'm sure you meant "decrease" instead of "cancel". You might have to go outboard EQ

First.... I always point the microphone forward to the front of the room which provides the best polar pattern. I'm pretty sure with the pattern of the mic, the 25Hz freq. (or anything below 40Hz.) is going to be rolled off. This is the first time I've seen someone do this!!!

 

[Roust_m]

This is the first time I've seen someone do this!!!

Are you referring to my way of measurement? I used that video above. Or are you referring to the type of acoustic treatment I put?

 

[ecwl]

I agree EQ is probably best way to deal with 25Hz room mode. To truly remove the resonance, you would need extremely thick bass traps with enormous surface area or you want a digital bass trap like PSI AAVA C20 or C214. Since digital bass traps are still bass traps, you still have to place them optimally or else they’re going to do nothing for the 25Hz. Which is why EQ is probably best solution.

 

[Bruce B]

Are you referring to my way of measurement? I used that video above. Or are you referring to the type of acoustic treatment I put?

Positioning of the microphone (straight up) in the video. I always measure with the mic pointing to the source from my listening position. The polar patterns in mics vary differently from straight-on.

 

[Roust_m]

I agree EQ is probably best way to deal with 25Hz room mode. To truly remove the resonance, you would need extremely thick bass traps with enormous surface area or you want a digital bass trap like PSI AAVA C20 or C214. Since digital bass traps are still bass traps, you still have to place them optimally or else they’re going to do nothing for the 25Hz. Which is why EQ is probably best solution.

I tried adjusting EQ at around 25Hz, but the level of sound dropped dramatically compared to automatically calibrated settings. Red was the original measurement and green was after adjusting EQ around 25Hz.

 

[Roust_m]

Positioning of the microphone (straight up) in the video. I always measure with the mic pointing to the source from my listening position. The polar patterns in mics vary differently from straight-on.

I did both measurements (before and after treatment) with the microphone up like in the video. This way I can compare apples with apples.

 

[DonH50]

Most if not all HT measurements use a 90 degree (pointed to the ceiling) mic at the main listening position to enable measurement of all the speakers from one mic position, and to obviate changes in response from (small but inescapable) changes in mic position. The small capsules of most measurement mics provide a pretty good circular polar pattern in that orientation, but require frequency response compensation, usually a cal file provided with the mic (e.g. UMIK-1 for REW). For a stereo pair, I would position the mic at the listening position and likely point the mic straight ahead. For speaker measurements, close in (near field) and pointed directly at the speaker, natch.

 

[ecwl]

I tried adjusting EQ at around 25Hz, but the level of sound dropped dramatically compared to automatically calibrated settings. Red was the original measurement and green was after adjusting EQ around 25Hz.

Yes that’s how EQ would work. It reduces the volume to reduce resonances as the actual resonance would stay the same as percentage of the direct sound but since the direct sound volume is reduced so would the resonance.

To me, the issue you showed in the graph is that your EQ is not fine grained enough to just reduce around the 25Hz. As a result the surrounding frequencies are also reduced in volume which I presume is what you take issues with. You would only be able to improve that with a different processor using a different EQ algorithm. Alternatively, you can just stick with the auto EQ because presumably this is the optimal EQ your processor can do given its EQ capabilities. It is also possible that there are other measurements that would suggest you shouldn’t lower the 25Hz further that we can’t see on your measurements.