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Author Topic: Cinema Sub Limiter?  (Read 869 times)

David Buckley

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Re: Cinema Sub Limiter?
« Reply #10 on: April 15, 2018, 10:47:09 pm »

You say "burned up the driver in his subwoofer".  "The" driver, not "a" driver.  It would have to be a small cinema to have a single sub with "a" driver.  So I'm in the "not enough sub for the gig" camp.

For digital cinema, the subs are supposed to be able to deliver 113dB to a seat two thirds of the way back from the screen.  This is achieved with the fader on 7, and a movie that goes to movie full loudness, which is -20dBFS. 

Here is a handy calculator.  Enter the distance as whatever is 2/3rds back from the screen, enter the SPL required as 113dB, enter the appropriate sensitivity of the speaker you've chosen, and that's how much power needs to be delivered. 

Fortunately, most cinemas play movies quieter than 7, and most movies don't hit "full". 


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Craig Hauber

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Re: Cinema Sub Limiter?
« Reply #11 on: April 16, 2018, 12:50:15 am »

You say "burned up the driver in his subwoofer".  "The" driver, not "a" driver.  It would have to be a small cinema to have a single sub with "a" driver.  So I'm in the "not enough sub for the gig" camp.


Yes, this.
So check the other three sub boxes to see if the employees stole the woofers out of them to bump-up their car stereos ;)
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John L Nobile

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Re: Cinema Sub Limiter?
« Reply #12 on: April 16, 2018, 11:34:31 am »

Yes, this.
So check the other three sub boxes to see if the employees stole the woofers out of them to bump-up their car stereos ;)

Employee theft is real. I inherited 2 JBL 2x 15" "subs" from a former AV company install. When I finally got around to using them, there was no bass. I opened them up and found that someone had taken just 1 woofer out of each box. I wound up putting both speakers in one box but that was a waste of time. I imagine that the speakers were damaged flopping around with that big hole in the box.
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Peter Kowalczyk

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Re: Cinema Sub Limiter?
« Reply #13 on: April 16, 2018, 05:46:54 pm »

Thanks all,

The theater is a small one, <200 seats, and yes this is (was) the only sub in the room (he got a bose 2x10 or something that's been handling the LFE channel since this EV box died, quite a while ago.)  The owner tells me it was calibrated to dolby standard.  If so, it's not surprising that single 18" driver gave up trying to push 113dB two-thirds of the way back. 

Regarding calibration, I'm curious why 'Full Movie Loudness' would be -20dBFS - that must be a long-term average, not a peak figure, right?  That'd be a lot of digital headroom to waste...
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Jean-Pierre Coetzee

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Re: Cinema Sub Limiter?
« Reply #14 on: April 17, 2018, 04:50:10 am »

Thanks all,

The theater is a small one, <200 seats, and yes this is (was) the only sub in the room (he got a bose 2x10 or something that's been handling the LFE channel since this EV box died, quite a while ago.)  The owner tells me it was calibrated to dolby standard.  If so, it's not surprising that single 18" driver gave up trying to push 113dB two-thirds of the way back. 

Regarding calibration, I'm curious why 'Full Movie Loudness' would be -20dBFS - that must be a long-term average, not a peak figure, right?  That'd be a lot of digital headroom to waste...

Cinema crest factor is recommended at 20dB so it makes sense for the meter(which is usually averaged) to be -20dBFS.

Re: the LUFS statement, LUFS is only applicable at 85dBSPL. LUFS is pretty much a K-Weighting scale with an average constant to hit, it's good science but not difficult to implement, if the movie was consistently above 85dB(probably something close to A-weighting) then the cinema was cranking it to give you a "larger than life" experience.

The explosions and such can be much louder(up to 20dB as I said) but the average should be tolerable.

The measurement is averaged over the entire length of the film, has to hit -24LKFS(america) or -23LUFS(everywhere else) which is supposed to be calibrated to 85dBsplA
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Joe Pieternella

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Re: Cinema Sub Limiter?
« Reply #15 on: April 17, 2018, 05:07:45 am »



Thanks all,

The theater is a small one, <200 seats, and yes this is (was) the only sub in the room (he got a bose 2x10 or something that's been handling the LFE channel since this EV box died, quite a while ago.)  The owner tells me it was calibrated to dolby standard.  If so, it's not surprising that single 18" driver gave up trying to push 113dB two-thirds of the way back. 

Regarding calibration, I'm curious why 'Full Movie Loudness' would be -20dBFS - that must be a long-term average, not a peak figure, right?  That'd be a lot of digital headroom to waste...

I'm pretty sure the reference level is specified differently.
As far as I know it says that when applying pink noise at -20dBFS to a single channel that channel should produce 85dB. Movie dialogues seem to be around these levels mostly. This gives 20dB of headroom for explosions and car crashes etc.
The LFE channel should produce 95dB at - 20dBFS.

A single 18inch driver pushing 120+ dB at (and sometimes below) 20Hz... Can't really think of an EV box suited to this application especially without a (steep) HPF. the double ten is probably close to failing too.

Ps. I assume the spl levels in the specification are a-weighted RMS values.

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