Back surround speakers SPL matching

[WiSl]

Hi all,

Last year I have built my home theater and I have still a little issue that bothers me and I hope
you can help me with that.

Problem:
I have currently the problem that my back surrounds speakers in my 7.1.2 Dolby Atmos setup do not sound as loud as the front speakers.
This is after calibration and checking the frequency responses and SPL using REW. Based on the measurements everything looks reasonable. However,
I have to boost the back surrounds by at least 3-4 dB in order to perceive these speakers as loud as the LCR.
This issue came apparent by running the Dolby Atmos Amaze demo. For example, the bird flying around did not sound the same compared to the LCR and SRs when passing the back surrounds. I have checked this also using the pink noise generator (400 Hz – 4kHz). Again, with no additional boost LCR and SRs sound significantly louder. Also, the pink noise did sound different compared to LCR/SRs.

Setup:
Pre-amp: Stormaudio MK3
LCR and SR = Neumann KH 420
Back surrounds = Neumann KH 310
TOP surrounds = Neumann KH 120

Troubleshooting:
Here is a comparison of the frequency response of the front left and back surround speaker.
In order the perceive both speaker equally loud I have to boost the Back-SRs by 4 dB.

In a first step I have put the left back surround speaker beside the front left speaker in order to make sure that it is not an issue of the speaker. In this case both speaker sound very much the same using pink noise and did sound equally loud. Hence, if both speaker have the distance to the main listening position, they both sound the same.
In my 7.1.2 setup the front left are 3.8 m and the back surrounds 0.9 m away from the main listening area.
In a second step I did a cross check. I put the main listening / measurement point 1 m in front of the front left speaker. Now, the back surround speaker was much further away. In this case it was the other way around. The back surround did sound louder and I had to boost the front left speaker. In addition the pink noise of the front-left-speaker@1 m did sound very much as the same as the back-sr-speaker @ 0.9m

Questions:
Is it reasonable to think that this different perception of SPL and spectral balance (pink noise) is caused by a different mix of direct and reflective sound? In this case 3.8 / 0.9 m is a quite a huge ratio. And if so, is a general boost the right way to compensate for it? Shouldn’t it be frequency dependent – hence, a different type of targe curve must be applied? Would it be possible to derive such a target curve based on the spinorama data?

 

[DVDdoug]

The rear speakers are typically mixed lower, but I don't know anything about the bird demo. If the measurements are good, I have to assume it's the mix/production.

It's OK if you want to boost the rear volume. It's your setup for your enjoyment!

 

[Guddu]

What do you use as sources?
For app or internet based content, I have always found it a bit dissatisfying. However lossless format like DTS-HD etc. are always louder than others.
Try with demo file and see if it is same as other content, that should give you some idea.
BTW, I know many who always keep center spl slightly elevated and surround even more specifically if surrounds don’t have good directivity. Some work best when pointed to sitting location while others slightly out.

 

[WiSl]

Thanks for the quick replies. It is independent of the source or mixing of the content. Simply by using the internal pink noise generator in the Stormaudio it is reproducable.

 

[Guddu]

Thanks for the quick replies. It is independent of the source or mixing of the content. Simply by using the internal pink noise generator in the Stormaudio it is reproducable.

In that case you can adjust the gain and leave it there.