Film-Tech Forum ARCHIVE: 7.1 surround speaker placement

This is topic 7.1 surround speaker placement in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Tom Wienholt (Member # 1510) on 09-16-2016, 05:30 PM:

I have a situation where the auditorium in question has 12 surround speakers. 4 on the left and right, and 4 on the rear wall. When wiring for 7.1, is it ok to have just 2 surrounds each for the rear channels and 4 each for the side channels?

Posted by Jarod Reddig (Member # 6363) on 09-17-2016, 02:29 AM:

Yes you will be ok. What is your theaters dimension btw and are you first run or ? Just curious.

After the room is properly EQ'd run some 7.1 material like the Dolby Surround 7.1 snippet and let us know.

Posted by Marco Giustini (Member # 4544) on 09-17-2016, 04:52 AM:

it is as long as the two back speakers are up to the job. Remember that as it is now you have 6 speakers per channel, that is, 6 speakers to produce 102dB peak at the listening position.

When you re-wire, you will end up with 4 side surrounds having to reach the same SPL and with only TWO back surrounds having to reach 102dB SPL at the listening position.

Check the speaker model and do some math if you don't want to damage them. If they are not up to the job 2 surrounds are still ok - if the coverage is ok - and you just need to replace them.

Also take into account what volume the customer is running their movies: for example if they never go over 5.0, then the max SPL would be about 96dB.

Posted by Jarod Reddig (Member # 6363) on 09-17-2016, 06:37 AM:

Ya good point about if surround is capable in the first place. As said level match to side surrounds. More info needed about theaters dimensions will help. Was the previous wire scheme setup for Dolby EX 6.1 with 4 per wall or just a future proofed 5.1 setup that was matrixed? Or are you already wired up for 7.1? It use to be 7.1 mixes were few and far between and those around had very little content in back channels. These days there's many more releases in 7.1 and with Atmos mixes originating from a 7.1 bed there's much beefier surround content at times. So like Marco said, for best performance the rears should preferably be same model as the sides. But realistically all things considered having two per back level matched and EQd should suffice.

Posted by Tom Wienholt (Member # 1510) on 09-17-2016, 07:19 AM:

The room is 40' wide and 60' deep.

Posted by Tom Wienholt (Member # 1510) on 09-17-2016, 11:00 AM:

Also, what is the proper way to set levels? 82dB for each of the 4 surround channels?

And how should power requirements be calculated for each surround channel? I am not familiar with setting up 7.1.

Posted by Harold Hallikainen (Member # 5405) on 09-17-2016, 11:28 AM:

Each of the surround channels (Lss, Rss, Lrs, and Rrs) should produce 82 dB(C) at the reference position (see SMPTE RP200) when SMPTE pink noise (about -20 dBFS) is played. Another method (SMPTE ST0202 Appendix A.9) is to set each 1/3 octave between 500Hz and 2kHz to 70 dB for screen channels and 3dB less for surrounds. It appears that the mathematically accurate 1/3 octave levels are 71.5dB (500 Hz to 2 kHz) for screen channels, 68.5 dB (500 Hz to 2 kHz) for surround channels, and 81.5 dB (25 Hz to 100Hz).

One thing to keep in mind is that when you play 5.1 content in a 7.1 room, you will typically use Ls to drive Lss and Lrs, and Rs to drive Rss and Rrs. The gains need to be reduced by 3dB since the level will be up about 2dB when you combine a side and rear surround. For example, the USL JSD-60 does input routing using a mixer. When playing 7.1 content, the mixer coefficients are set to 100%. When playing 5.1 content, the mixer coefficients for the surrounds are set to 71% (-3 dB).

Good luck!

Harold

Posted by Stephan Shelley (Member # 8587) on 09-17-2016, 01:14 PM:

What audio processor are you using? You will need two more channels of amplification connected to the left rear surround and right rear surround outputs along with moving the rear speaker to the appropriate amp output.

You will also need to program the processor, EQ and balance all surround channels.

Posted by Marco Giustini (Member # 4544) on 09-17-2016, 05:55 PM:

quote: Harold Hallikainen
It appears that the mathematically accurate 1/3 octave levels are 71.5dB (500 Hz to 2 kHz) for screen channels, 68.5 dB (500 Hz to 2 kHz) for surround channels, and 81.5 dB (25 Hz to 100Hz).

Harold,
Is there anything missing at the end of the sentence? What is 81.5? I'm curious, that's very interesting.

The -3dB offset is done automatically in Dolby Processors.

Posted by Harold Hallikainen (Member # 5405) on 09-17-2016, 11:28 PM:

Well, there SHOULD have been something at the end of the sentence about 81.5 dB! That's the 1/3 octave SPL for LFE. Sorry about that! I guess I was thinking faster than I was typing...

Harold

Posted by Marco Giustini (Member # 4544) on 09-18-2016, 05:22 AM:

Thanks Harold! [Smile]

Posted by Tom Wienholt (Member # 1510) on 09-18-2016, 05:28 PM:

Thanks for all of the info. As far as surround spacing is concerned, would spacing of 11 feet on the side walls be ok? I have seen spacing ranging from 8-12 feet between surrounds.