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» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » poll: how many subs and what power do you usally use in your cinemas ?

   
Author Topic: poll: how many subs and what power do you usally use in your cinemas ?
David Baum
Film Handler

Posts: 90
From: Brussels, Belgium
Registered: Aug 2000


 - posted 06-24-2002 04:08 PM      Profile for David Baum     Send New Private Message       Edit/Delete Post 
good afternoon ( usually that is )

I have recently seen a large 400seats cinema without (!) subwoofers ( I have 2 18" in my home theater ) , just 3 mains (KCS speakers).
But I wonder what you usually have for your theaters, say the 200, 400, and 600seats or so. (how many subs and what power you feed them AND if you high pass them and at which frequency usually, 30hz? 25hz? 20hz ?).


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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000


 - posted 06-24-2002 04:16 PM      Profile for Josh Jones   Author's Homepage   Email Josh Jones   Send New Private Message       Edit/Delete Post 
Our theatre has 4 woofer cabinets, each has 2 18" JBL drivers. 2 cabs are used for PA, 2 for film, never both at the same time(it would bring the roof down ).

The system is powered by two QSC amps running at 6KW for the combined power of both systems.

Josh

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David Baum
Film Handler

Posts: 90
From: Brussels, Belgium
Registered: Aug 2000


 - posted 06-24-2002 04:19 PM      Profile for David Baum     Send New Private Message       Edit/Delete Post 
Josh

hi

that's very nice !! you don't seem to have headroom problems.

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John Westlund
Expert Film Handler

Posts: 204
From: Burney, CA, USA
Registered: Jun 2001


 - posted 06-24-2002 04:28 PM      Profile for John Westlund   Email John Westlund   Send New Private Message       Edit/Delete Post 
The theatre I work in has 1 subwoofer cabinet with 2 JBL 18" drivers. They are powered by a QSC 1500 watt amplifier. This is in a 252 seat auditorium.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999


 - posted 06-24-2002 05:00 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
How many? The correct amount with the proper amount of power. One needs to be able to get up to 113dB in the middle of the auditorium (within the passband of the subwoofer).

Thus, I have used anywhere from a single 18" up to eight 18" subs.

Seat count isn't so much the issue as volume of air one needs to move. If the room is big, you need to move alot of air. As to the high-pass, yes I high pass my subs based on what they can play. Also, I'll high-pass a sub system to keep those frequencies from passing through a wall too much.

I think you are asking for rule-of-thumb questions that there are no rule-of-thumb answers. I will say that the vast majority of theatres I've seen often under-sub the the theatre. But, then again, they even more often fail on making good walls so it is probably just as well.

Steve

------------------
"Old projectionists never die, they just changeover!"

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David Baum
Film Handler

Posts: 90
From: Brussels, Belgium
Registered: Aug 2000


 - posted 06-24-2002 05:27 PM      Profile for David Baum     Send New Private Message       Edit/Delete Post 
hi Steve

not a rule of thumb, just a small poll among the pros here , to have an general idea, sort of, of what you use. if money was not an issue, we would see much more headroom ( subs, amp power ) indeed but the walls issue is also to be considered as you mention: one does not want to have U571 blasts go through the next theater showing Kate and Leopold

The nr of spectators present in a theater plays also an important role: human beings absorbs a lot of energy. 4 subs with 1000w each in a 400-seat theater do not sound the same when it's full or 1/3 full...

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Adam Fraser
Master Film Handler

Posts: 499
From: Houghton Lake, MI, USA
Registered: Dec 2001


 - posted 06-24-2002 10:26 PM      Profile for Adam Fraser   Author's Homepage   Email Adam Fraser   Send New Private Message       Edit/Delete Post 
We have 2 JBL 18" Subs powered by an Altec Lansing 9444 amplifier, not sure how much power that amp puts out. Surrounds also use another 9444 amp (12 surrounds, each with a 10" 8" and a 6") To power the screen channels we use 3 Alshy FTX-2000 amplifiers with the JBL speakers that have 2 15" or 18" drivers and a large horn. This is for a 450 seat auditorium, about 3000 watts.

------------------
Adam Fraser www.pinestheatre.com


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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 06-24-2002 10:32 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
David said"The nr of spectators present in a theater plays also an important role: human beings absorbs a lot of energy. 4 subs with 1000w each in a 400-seat theater do not sound the same when it's full or 1/3 full."
If the room has proper reverberation control the bodie count doesn't effect it as much as one would think
If the room is reverberant then it would but if it was reverberent a lot of sub will just confuse the intelegability even more

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