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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » Amplifiers for Screening Room? (Page 1)

 
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Author Topic: Amplifiers for Screening Room?
Joshua Waaland
Jedi Master Film Handler

Posts: 800
From: Cleveland, Ohio
Registered: Dec 1999


 - posted 02-22-2005 08:05 PM      Profile for Joshua Waaland   Email Joshua Waaland   Send New Private Message       Edit/Delete Post 
I need some help in choosing some amps for my home theater. I know zilch about these so any help you can give me would be great. I have a room that measures 12' x 22' for a total of 264 square feet. I want to be able to run 5.1 sound with DTS and need to know the following:

1. How many amps do I need? I see that some of the QSC amps are 2-channel. Am I correct in thinking I would need 3 2-channel amps? Should I have one dedicated to the sub?

2. How many watts do I need? Any recommendations on speakers here?

3. Would the QSC 1400 model be too much? 200W@8-ohms, 300W@4-ohms. Most of the theaters I have worked for have used QSC and they seem to be pretty good. I would like to stick with these. Any recommendations on model to get? Preferably something used that may be an older model. I cannot afford new ones.

Again I am clueless when it comes to this stuff so you may need to spell it out for me. When in doubt, figure I am clueless. That means I probably won't understand any industry jargon. The most I have dealt with amps was installing one in my car once. It didn't sound too good so I know I didn't pick the right one.

Thanks.

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Jonathan M. Crist
Jedi Master Film Handler

Posts: 524
From: Hershey, PA, USA
Registered: Apr 2000


 - posted 02-22-2005 08:34 PM      Profile for Jonathan M. Crist   Email Jonathan M. Crist   Send New Private Message       Edit/Delete Post 
Do not use a QSC, Ashly or any other MOSFET amplifier for the subwoofer channel. MOSFET's are not made for low frequency reproduction and as a result sound "blurry" when used for subbase. (Although like most things on this board I am sure some one will disagree with me on this.) MOSFETs are best for standard range music, vocal and dialogue.

The QSC 1400 is a MOSFET amp and IMHO is one of best amps ever made. It will work well for the main channel, left channel, right channel. It is always better to have more power than you need so that you do not have to drive the amps too hard. I would get an even bigger wattage amp than the QSC 1400 for the surrounds.

If you want to do it right,I would bi-amp the front three channels. Bi-amping means that you split the signal from the processor into its high and low components before you put it into the amp and then out to the speakers. This is done with a crossover. You would then need a total of five amplifiers. One QSC 1400 amplifier each for the left, right and center highs and lows.

One bigger amplifier for the surrounds - one side of the surround amp would run the right surrounds and one half would run the left surrounds (you will need to do this if you run DTS digital which has the split surrounds). You should always "balance' the number of surrounds in even numbers (e.g. 4 on left side & 4 on the right side). This is so the amplifier 'sees' an even load as the surrounds are in series.

The last amp would be for the subwoffers which is typically run in 'mono bridge' mode for double the power. Bridging means one channel of the amp is run into the drive channel and then out to the speaker. Subwoffer is a mono channel. The bigger the subwoffer amp the better since the subwoffer amp does the biggest workload and it takes a lot of power to reproduce low frequencies correctly.

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David Stambaugh
Film God

Posts: 4017
From: Eugene, Oregon
Registered: Jan 2002


 - posted 02-22-2005 08:50 PM      Profile for David Stambaugh   Author's Homepage   Email David Stambaugh   Send New Private Message       Edit/Delete Post 
The title of this thread says "Screening Room", which implies film (it does to me anyway). But the post itself refers to "home theater" and "DTS 5.1", which to me is some kind of audio/video setup for DVD, HDTV, and whatever else, such as might be purchased at Circuit City.

So, my really dumb (but not intentionally smart-ass!) question is: Are you talking about film projection in a home screening room? Or do you mean "home theater" in the Circuit City sense?

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Joshua Waaland
Jedi Master Film Handler

Posts: 800
From: Cleveland, Ohio
Registered: Dec 1999


 - posted 02-22-2005 09:11 PM      Profile for Joshua Waaland   Email Joshua Waaland   Send New Private Message       Edit/Delete Post 
I mean film. Karen Hultgren from DTS referred to it as 5.1 when we corresponded by e-mail so I feel confident in using that term. She must know what she is talking about. I believe that most people don't refer to film DTS as 5.1 though.

Thanks for the help. I have a THX 3417 monitor with crossover cards that I could use to bi-amp.

So let me get this straight. I have one QSC 1400 for the left channel, one for the center, and one for the right? Then I feed the highs into one channel of the amp and the lows into the other channel of the same amp? Then there is one amp for the left and right surrounds and another for subs correct? What model would you recommend for the surrounds and the sub?

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16272
From: Bountiful, Utah
Registered: Jun 99


 - posted 02-22-2005 09:31 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
quote: Jonathan M. Crist
The QSC 1400 is a MOSFET amp and IMHO is one of best amps ever made.
Jon, Actually its not a MOSFET amp! Very Bi-Polor all the way through...... with a very unusual output stage. Its a very old design that has been kept somewhat up to date by QSC which always does a good job at this aspect of things. Unfortunately many 1400's and other related models are getting VERY old now and we are seeing many come in for repairs... but considering the age they have given good service. The way QSC handles the repairs/rebuilds assures them another 20 plus years of useful life.

BTW: Mosfet amps generally sound more pleasing because they tend to exhibit lower odd order harmonic distortion whilst Bi-Polar circuits tend to exhibit more odd order harmonic dostortion. The ear dislikes odd order and is less sensitive to the even order harmonics. Also the higher you bias a MOSFET the more it will lean towards producing just even order harmonics. There are fully class A MOSFET power amps that only produce even order and no odd order. They measure piss poor but sound terrific [thumbsup] .

Mark @ CLACO

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Gordon McLeod
Film God

Posts: 9470
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 02-22-2005 09:40 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
I have yet to have an issue with mosfet amps even on a subwoofer
The 1400 is an excellent service amp and relatively easy to repair ususally the failure is in the powersupply so it is often an easy fix

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16272
From: Bountiful, Utah
Registered: Jun 99


 - posted 02-22-2005 09:50 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
The age that some are approaching it is time to completely rebuild them. QSC offers complete overhaul kits for theor amps with updated semiconductors and capacitors for reasonable prices.

Mark

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Scott Norwood
Film God

Posts: 8002
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99


 - posted 02-22-2005 10:17 PM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
What type of speakers will you be using?

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12298
From: Annapolis, MD
Registered: Dec 1999


 - posted 02-23-2005 06:29 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
I must admit...I'm no big Mosfet amp fan. I've yet to hear one that I thought was a good sounding amp. I have heard many that I thought sounded quite harsh. Some claim that the MOSFET amps give you that "tube" sound....I just haven't heard that at all yet.

And the QSC 1400 is indeed a BJT amp, not MOSFET. It is certainly a decent amp.

Steve

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Joshua Waaland
Jedi Master Film Handler

Posts: 800
From: Cleveland, Ohio
Registered: Dec 1999


 - posted 02-23-2005 07:46 AM      Profile for Joshua Waaland   Email Joshua Waaland   Send New Private Message       Edit/Delete Post 
I am not sure what speakers to get. It's not at all a big room so I won't need theater size speakers I'm sure. So do you guys think I can use all QSC 1400 amps for the screening room?

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16272
From: Bountiful, Utah
Registered: Jun 99


 - posted 02-23-2005 07:58 AM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
quote: Steve Guttag
I must admit...I'm no big Mosfet amp fan. I've yet to hear one that I thought was a good sounding amp. I have heard many that I thought sounded quite harsh. Some claim that the MOSFET amps give you that "tube" sound....I just haven't heard that at all yet.

Then you haven't been around, thats for sure! There's a company that builds single ended class A all mosfet amps that are phenominal. Not necessarily practical for cinemas..... but they could be used if one wanted to..... BTW: They don't sound like tubez or solid state and they only show even harmonics as a distortion by-product. As a result they are actually better sounding than the best of both worlds.

Mark

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Dave Macaulay
Film God

Posts: 2168
From: Toronto, Canada
Registered: Apr 2001


 - posted 02-23-2005 09:35 AM      Profile for Dave Macaulay   Email Dave Macaulay   Send New Private Message       Edit/Delete Post 
Joshua: Reading between the lines a bit, I think you have a source for QSC1400 amps and want to know if they are OK. This is a good basic power amp. At 200W/ch they will handle your size room if you have reasonably efficient speakers. Speakers are the big question though. "Professional" cinema speakers tend to make adequate fidelity sound but lots of it and are designed to cover a fairly large area... they don't necessarily work well in a small room. Basically you can't just take any cinema speaker and get good results in a small screening room, but some models would be fine. Home stereo speakers can give very good fidelity sound but most are quite low efficiency. They also have a very wide M+HF dispersion pattern - this requires more attention to room accoustics to maintain good intelligibility and separation (theatre speaker patterns should avoid firing sound at the side walls). You'll probably find cinema surround speakers a bit large for your room and they should be fairly far from the "good" seats to give the right effect. Smaller dipole speakers are my suggestion; they give good coverage with less localization of the sound.
Since you seem to be going with digital (DTS) sound, you need decent accoustic headroom. This is where efficiency comes in. A theatre speaker will have efficiency at around 98dB spl/W @1metre; this gives you about 120dB spl at 200W ... but the amp will have the ability to provide peaks of higher power. Home thatre speakers vary widely but most I've looked into are around 89dB/W and about 111dB spl with 200W. This is a big difference. If you set the reference level correctly then the digital source will be asking for 110dB and more on the loud stuff... explosions etcetera. With inefficient speakers the amplifier will be perilously close to clipping, with efficient speakers it won't. Bi-amping helps, but 90%+ of the speaker power goes to the LF driver in normal use. Bi-amping isolates the HF driver from any clipping on the LF channel; minor clipping causes massive HF distortion effects while not really destroying the LF sound quality. Home theatre speakers may or may not be amenable to bi-amping.

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Pete Lawrence
Expert Film Handler

Posts: 192
From: Middleburg, PA
Registered: Aug 1999


 - posted 02-23-2005 10:25 AM      Profile for Pete Lawrence   Email Pete Lawrence   Send New Private Message       Edit/Delete Post 
Once you have chosen your amp and speakers don't forget to include the "proper" AC line cord for optimum performance! An example is the one below from Runnng Springs Audio.

 -

A bargin at $499.95! No kidding! (Dedicated Audio)

I'm not picking on those guys, they just happened to be the first good example with a picture that I came across. It's just one example of the [bs] that runs rampent through the audio market.

The truth is most any good quality commericial amp(s) will work just fine. I happen to have Crown Com-Tech amps in my home screening room only because I was able to get them surplus at a very good price. QSC amps are pretty much the industry standard and very good. I probably would have bought QSC's if I hadn't found the Crowns. I'm sure there will be some nasty comments as to why the Crown amps were so inexpensive. [evil]

Remember that the folks here will pick amplifiers based on several criteria. Profit margin, repair frequency, overall quality and manufacturer support, and oh yes, how they "sound". Some may question the order of these items but that's the real world. Most good quality amps will "sound" essentialy the same, unless of course they are defective in some way. It's way to subjective to make any absolute statement that "Xyz amp is the best sounding ever made".

As Dave suggests, your choice of speakers is going to be the biggest factor, but don't neglect room equalization and and any necessary acoustic treatments. That can make or break your room. With a little care in those areas you can get a lot of improvement in performance.

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Joshua Waaland
Jedi Master Film Handler

Posts: 800
From: Cleveland, Ohio
Registered: Dec 1999


 - posted 02-23-2005 12:08 PM      Profile for Joshua Waaland   Email Joshua Waaland   Send New Private Message       Edit/Delete Post 
Thanks for the help guys. Any suggestions on a good intro book to help explain some of this stuff? i.e. harmonic distortion, dipole, clipping. I am not into my M.E. classes yet so a lot of this is greek to me and I doubt we will even cover anything like this. Maybe in Physics next semster though? [Eek!]

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Pete Lawrence
Expert Film Handler

Posts: 192
From: Middleburg, PA
Registered: Aug 1999


 - posted 02-23-2005 12:25 PM      Profile for Pete Lawrence   Email Pete Lawrence   Send New Private Message       Edit/Delete Post 
Take a look at the technical librarys at JBL and Rane Audio. They are good starting points and free. Lots of good stuff in there.

In particular check out the JBL Professional Sound System Design Manual and Cinema Sound System Manual: Setting up a cinema sound system. Both available in PDF on the JBL website.

[ 02-23-2005, 02:06 PM: Message edited by: Pete Lawrence ]

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