|
|
This topic comprises 2 pages: 1 2
|
|
Author
|
Topic: Best way to connect 3X JBL 3635 subs to one amp?
|
|
|
|
|
|
|
Marco Giustini
Film God
Posts: 2713
From: Reading, UK
Registered: Nov 2007
|
posted 03-16-2013 10:34 AM
This may be a very stupid question, but when doing series/parallel with an odd number of speaker, does it end up with one speaker receiving more power?
In this scenario, you would end up with two paralleled subs (4 ohms) wired in series with a third one (8 ohm) giving you a final value of 12Ohms (a bit too much for LF I'd say, but this is another story).
Now, electronically speaking, you'd end up with the same Voltage drop between all speakers, but the one wired in series would get the full current, while the two in parallel would split it 50%.
If P= V x I, does it mean that the sub wired in series is getting twice as much power as the other ones? I may be saying rubbish here!
Back to the subject, did you make sure that the two channels are set to provide the same power to the three speakers? Because one channel has a load of 4Ohm and one of 8Ohm, you may need to adjust the gain of the two channels so the subs get the same amount of power.
How to do that... Not sure, either measuring the SPL out of each speaker, or measuring the voltage - maybe applying a sinewave signal.
But another amp would definitely be better!
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
|
posted 03-17-2013 12:23 PM
Alright...you all are starting to tick me off ![[Roll Eyes]](rolleyes.gif)
Let's look at the problem.
Somebody "decided" on 3 subwoofers but only one amplifier...mistake #1.
Someone is using a subwoofer who's design is based on size and NOT having real deep bass but is looking for deep bass...mistake #2. Seriously, this is a subwoofer that has a frequency response down to 38Hz (barely wider than a stage speaker) and only handles 300-watts of continuous pink noise. It does have a sensitivity of 100dB 1w/1m. Compared to other single 18" SW...that is pretty darn sensitive...almost as sensitive as a double 18" sub from any brand. It is only 14.5" deep (368mm to our metric friends)...it is shallow so it will FIT into places.
Anyone that recommends wiring subwoofers in "series/parallel" is incompetent and should be discarded as such...as Harold properly stated...you can wire in parallel but NEVER series...when it comes to subwoofers. The series resistance kills the damping of the system and will cause an exaggerated bass response and will lead to driver failure (due to lack of damping at high levels).
The phrase quote: Mark Strube
The channel with 2 subs is clipping a bit, more than I'd like it to (but things do sound great).
displays a complete lack of understanding too. There is NO level of clipping that is acceptable. Clipping means the amplifier has run out of available power to supply to the speaker...the output will be "clipped" This means that the driver is being asked to, instantly, STOP, then sent in the opposite direction and then stop again. Why not just destroy the system now and get it over with?
When looking at the power rating, with respect to subwoofers...it is continuous pink noise that is the relevant number as that best simulates a typical subwoofer signal. Subwoofers are not dialog channels nor do they just play music...they often carry effects that may be sustained, at high level. Ratings like "program" power are nothing more than a doubling of pink noise power. It is under the presumption that the signal is only momentarily at the high level. Pink Noise often has a 2 or 6 hour rating for it to be continuous. Note too, the continuous rating does not take into account that as the VC heats up, the drivers output will decrease with the same level of input to it is wise to not drive a driver continuously to its limits.
To improve the system's design...the best suggestion was to add another subwoofer. With three 3635 subs tightly spaced (take advantage of mutual coupling), the system has 104.8 dB of sensitivity. If the theatre were say 60-feet deep, this would mean that the system would need 982-watts...which exceeds the rating on the drivers (and the amp).
If another 3635 is added...the sensitivity increases to 106dB. In the same example 60-foot deep room, the requirement of the system drops to 745-watts. You then have enough drivers to handle the requirements (1200-watts of capacity). The MX-1500a has 500-watts per channel into 4-Ohms or can deliver 1000-watts total to the system (two subwoofers on each channel). In this example the system now will meet spec, if set up properly. This also means that the subwoofer response is taken into consideration...and no exaggerated boost is applied to the bottom end to try and extend its bass beyond its design.
| IP: Logged
|
|
|
|
Tony Bandiera Jr
Film God
Posts: 3067
From: Moreland Idaho
Registered: Apr 2004
|
posted 03-17-2013 07:30 PM
quote: Mark Strube
Someone woke up on the wrong side of the booth.... (And)...but let's calm down.
Here we go again.....
Steve was actually far more diplomatic that I would have been, and he addressed all of the things wrong with what has been said in this thread so far. I'm gonna leave it at that so Brad doesn't send me to my room.
Mark, your situation as outlined is not possible to correct without doing EXACTLY as Steve said. You are trying to do the physically (acoustically) impossible with what you have.
You solution is easy and cheap: ADD another sub of the same model!! With all the conversions and theatre shutdowns going on you can locate a used sub under $400 with minimal effort. Wire two subs each in parallel and drive each pair with one channel of your existing amp. Done.
quote: Mark Strube
Not great, but I've seen systems (that I didn't design) clipping for years at levels more severe than this without damaging anything.
Well good for you. But I call BS as clipping, especially with subs, ALWAYS results in blown drivers sooner or later.
quote: Mark Strube
....however a 4th subwoofer is not an option right now, again, as previously stated.
Oh really? Not what you said before at all:
quote: Mark Strube
I'm running a QSC MX1500A amplifier to three JBL 3635 subwoofers. At this point, an additional amp isn't really an option.
Again, even a used amp can be had for well under $400 if you can't physically fit another sub into the room...BUT as Steve pointed out the REAL issue is you do NOT have enough subs for the space!!
Now to pick on someone else: ![[Big Grin]](biggrin.gif)
Sean, your resistor idea will NOT work or help in this situation at all for the reasons Harold and Steve both stated. Never, EVER series connect subwoofers!! I honestly am not fond of series connecting surrounds either in the purest sense, but despite the logical and electrical reasons it is bad, for surrounds the side effects are minimal compared to the substantial added costs of amplification for each speaker. (Now if I had my way and for an ultimate setup, you bet I would line up a set of QSC DCA1644's and drive each speaker individually. )
| IP: Logged
|
|
|
|
|
|
All times are Central (GMT -6:00)
|
This topic comprises 2 pages: 1 2
|
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
![[Smile]](smile.gif)
![[Wink]](wink.gif)
Printer-friendly view of this topic