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Author Topic: 7.1 surround speaker placement
Tom Wienholt
Master Film Handler

Posts: 371
From: Towson, MD, USA
Registered: Dec 2002


 - posted 09-16-2016 05:30 PM      Profile for Tom Wienholt   Email Tom Wienholt   Send New Private Message       Edit/Delete Post 
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?

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Jarod Reddig
Jedi Master Film Handler

Posts: 513
From: Hays, Ks
Registered: Jun 2011


 - posted 09-17-2016 02:29 AM      Profile for Jarod Reddig   Email Jarod Reddig   Send New Private Message       Edit/Delete Post 
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.

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Marco Giustini
Film God

Posts: 2713
From: Reading, UK
Registered: Nov 2007


 - posted 09-17-2016 04:52 AM      Profile for Marco Giustini   Email Marco Giustini   Send New Private Message       Edit/Delete Post 
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.

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Jarod Reddig
Jedi Master Film Handler

Posts: 513
From: Hays, Ks
Registered: Jun 2011


 - posted 09-17-2016 06:37 AM      Profile for Jarod Reddig   Email Jarod Reddig   Send New Private Message       Edit/Delete Post 
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.

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Tom Wienholt
Master Film Handler

Posts: 371
From: Towson, MD, USA
Registered: Dec 2002


 - posted 09-17-2016 07:19 AM      Profile for Tom Wienholt   Email Tom Wienholt   Send New Private Message       Edit/Delete Post 
The room is 40' wide and 60' deep.

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Tom Wienholt
Master Film Handler

Posts: 371
From: Towson, MD, USA
Registered: Dec 2002


 - posted 09-17-2016 11:00 AM      Profile for Tom Wienholt   Email Tom Wienholt   Send New Private Message       Edit/Delete Post 
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.

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Harold Hallikainen
Jedi Master Film Handler

Posts: 906
From: Denver, CO, USA
Registered: Aug 2009


 - posted 09-17-2016 11:28 AM      Profile for Harold Hallikainen   Author's Homepage   Email Harold Hallikainen   Send New Private Message       Edit/Delete Post 
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

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Stephan Shelley
Jedi Master Film Handler

Posts: 854
From: castro valley, CA, usa
Registered: Nov 2014


 - posted 09-17-2016 01:14 PM      Profile for Stephan Shelley   Email Stephan Shelley   Send New Private Message       Edit/Delete Post 
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.

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Marco Giustini
Film God

Posts: 2713
From: Reading, UK
Registered: Nov 2007


 - posted 09-17-2016 05:55 PM      Profile for Marco Giustini   Email Marco Giustini   Send New Private Message       Edit/Delete Post 
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.

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Harold Hallikainen
Jedi Master Film Handler

Posts: 906
From: Denver, CO, USA
Registered: Aug 2009


 - posted 09-17-2016 11:28 PM      Profile for Harold Hallikainen   Author's Homepage   Email Harold Hallikainen   Send New Private Message       Edit/Delete Post 
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

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Marco Giustini
Film God

Posts: 2713
From: Reading, UK
Registered: Nov 2007


 - posted 09-18-2016 05:22 AM      Profile for Marco Giustini   Email Marco Giustini   Send New Private Message       Edit/Delete Post 
Thanks Harold! [Smile]

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Tom Wienholt
Master Film Handler

Posts: 371
From: Towson, MD, USA
Registered: Dec 2002


 - posted 09-18-2016 05:28 PM      Profile for Tom Wienholt   Email Tom Wienholt   Send New Private Message       Edit/Delete Post 
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.

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