|
|
This topic comprises 3 pages: 1 2 3
|
|
Author
|
Topic: Amp for driving 2 QSC DCS-SB-5218s?
|
|
|
David Buckley
Jedi Master Film Handler
Posts: 525
From: Oxford, N. Canterbury, New Zealand
Registered: Aug 2004
|
posted 01-04-2016 10:20 PM
OK, a QSC DCS-SB-5218 is a 4 ohm speaker with a recommended amplifier power of 1600W RMS. You have two of them, so they are either being driven by one channel each of the amplifier, or paralleled to 2 ohms, and being driven by the amp in bridge mode.
The amp into 4 ohms can deliver 525 watts, rather than the 1600W recommended. Thus seriously underpowered. There is no 2 ohm bridged output quoted for the amp.
In bridge mode, the amp can deliver 1500W into 4 ohms, which is a good match for one of your subs. So an easy upgrade path would be another amp. This also gives a degree of redundancy, in that if you lose an amp or a speaker, you still have a surviving amp and speaker so the show can go on, albeit with reduced LFE, as long as you don't turn up the level to make up for the missing sub...
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
|
posted 01-05-2016 02:56 PM
Andrew, here is the no BS answer. Given your room dimensions, and those two subwoofers, you need (and are you ready for this?) 5,450 watts or thereabouts. You only have 2000-watts of power handling capacity in the subs so if you had the power, you'd blow em apart.
So lets presume it is one sub on each side of the amp, you have 1050 watts. Not quite 5450 is it?
So the next question is...was your room tuned to "spec"? That is, using a -20dB pink noise signal, are your subs, in the pass band 10dB hotter than your stage channels with the same level of pink noise? If the answer is YES...then the next question is ... where do you run your fader? Is it around 7 (or 0dB for those that think they are in a recording studio or something).
If the answer is YES to both questions...KABOOM! It is a system incapable of delivering the demands of any movie that chooses to use the full dynamic range of the DCinema system.
You could double your subs and go to an XLS 2500 and STILL not have enough for that sized room. However, if you use 4 subs and four XLS 1000s (one bridged into each sub), then you'd finally have enough sub and power to match the room, tuned to industry standard levels and the fader at "7"
Now if you run your fader lower (doesn't have to be much) and the power required change dramatically...just lowering to say "5.5" would drop the power requirements by 5dB. Doesn't sound like a lot but 5dB to your power requirements drop to a mere 1725-watts...within the power of your subs but still beyond your amp.
I think it is a dumb way to design a sound system but I guess one sells more mis-designed systems than to tell one what they really need and scare them to the guy that designs cheap ones.
Your best bet, really is to add two more subs and put in a pair of QSC DCA2422 amps (drive each sub off of one channel of each amplifier). It will last forever, never blow apart and be able to play whatever Hollywood can throw at it.
| IP: Logged
|
|
|
|
|
|
Andrew Thomas
Master Film Handler
Posts: 273
From: Pearland, TX, USA
Registered: Jun 2012
|
posted 01-05-2016 04:58 PM
Steve, very helpful info. The short and sweet answer is that when Christie came out and did the install (we re-opened a long closed 5 plex), neither the guy who originally did the site survey nor the guys who did the install actually knew a thing about audio.
Which is why I'm trying to learn more myself, trying to get the right equipment, and eventually having the right person come out and tune everything.
Amusingly, I don't think a single patron actually cares. But I want to do my best, even if it isn't readily apparent that there are deficiencies. Most of our customers are just happy it isn't the disgusting place it used to be, but I want more than that.
If you guys don't mind, can I tell you the rest of the system and maybe get your recommendations on what else I should look to add?
The way it is currently set up is this
L/C/R stage speakers: JBL-4722, each with a separate XLS1000
Subs: QSC SB5218, single XLS1500
L/R Surrounds: 16 JBL 8320s (8 left, 8 right) on a single XLS1000.
As I said, I want to replace all the Crown's with QSC amps, but should I also be looking to add more surround speakers? I have a USL JSD-60 processor, which I think can handle 7.1. There are actually speakers mounted on the back wall (2 each for left and right), so I think I should be able to get them on another amp and feed the additional signal in.
Thanks for taking the time to respond guys, I appreciate your valuable knowledge!
| IP: Logged
|
|
Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
|
posted 01-05-2016 06:15 PM
Andrew,
The problem with your system really is that it wasn't designed, it was cut and pasted using equipment that isn't necessarily junk but isn't necessarily adequate or proper for the room you describe. The JBL 4722 is a good BUDGET speaker but I wouldn't use it in an 86 foot long room.
The JBL 8320 isn't the worst surround speaker in the world but is vastly inferior to the 8340A and the 8350 (The 8350 response is easily the best of the three in that line and the 8320 is very much the worst).
The 5218 isn't a bad sub but 7218s should have been used, if using QSC double 18s. Why? Power handling and sensitivity. When you are talking about subwoofer where power demands start to get crazy and a mere 3dB of savings via sensitivity cuts your power requirements in HALF...you need to look at that sort of stuff.
I'm firmly in the QSC camp for amplifiers. The cost/feature/benefits are just all there. I'm partial to the DCA line too.
For your big rooms with that long throw...you really should consider something like the SC 423 (or SC424 if you don't mind more amp channels and more wiring...the SC424 is one of the most pleasing sounding cinema speakers out there. I'm using the 424 as the "base" model with 2 woofers, depending on the particulars the 434 or 444 may make more sense (the quantity of woofers can affect power handling or sensitivity).
In the small to medium rooms, the 4722 is just fine though again, not the best speaker in the world is FAR from the worst too. It has a real good bang for the buck.
When it comes to sound, you have three powers in play at all times
1) Subjectivity (what YOU think sounds best)
2) The physics of how sound works and what is required for it to work properly.
3) Budget. What you can afford versus what you may want.
If you do end up going with the QSC 4-way stage speakers, I DO recommend "quad-amping" them. The VHF diaphragm is much easier to tune/control if by a separate amp rather than EQ.
And if the 4-ways are not in the cards, the SC-423 is awesome too.
| IP: Logged
|
|
|
|
|
|
|
|
|
|
All times are Central (GMT -6:00)
|
This topic comprises 3 pages: 1 2 3
|
Powered by Infopop Corporation
UBB.classicTM
6.3.1.2
The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion
and agrees to release the authors from any and all liability.
|
Home
![[Razz]](tongue.gif)
Printer-friendly view of this topic