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Topic: Best way to connect 3X JBL 3635 subs to one amp?

Steve Guttag
We forgot the crackers Gromit!!!

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

posted 03-18-2013 08:57 AM

I had actually saw this thread growing all week. I only had time to offer my opinion when I did. And seeing the advice offered...particularly the series/parallel stuff did/does tick me off because people are offering up their ignorance, not help. Intent is not sufficient. When one posts advice on corrective measures, they should have something behind that advice...not just good intentions. Or they should qualify their advice in some manner to allow the receiver of that advice to be able to qualify the validity of said advice. Heck, it should be common courtesy!

quote: Mark Strube
I'm working with what's available. This wasn't an audio design decision.

Somebody designed it because somebody had to decide..."let's use 3 subwoofers on this auditorium." JBL didn't just randomly ship three or, if acquired used, someone decided to put three in this theatre. It is understood that you have three to work with.

With this statement:

quote: Mark Strube
If there was a complete lack of understanding I wouldn't even be asking this question. The speakers will live for now, at the level we're running, it clips probably once or twice during the entire run of trailers. Not great, but I've seen systems (that I didn't design) clipping for years at levels more severe than this without damaging anything.

This statement becomes evident:

quote: Mark Strube
I'm asking for advice, implying that the people I'm asking (all of you) have more knowledge than myself.

quote: Mark Strube
Do you recommend not performing an EQ to flat response with these subs? Should I ensure a rolloff starting at 38Hz going down? What about the affects of 3 or 4 of them coupling, doesn't that allow for a bit lower response without adversely affecting the drivers?

When looking at the response, keep in the back of your mind what the natural response of the system is...that is, it is going to roll off sharply below 38Hz. Will you get some boost below from the coupling, yes. That said, ensure that you apply no boost in your tuning below that point and let it roll off. It may even be advisable to apply a high-pass at 35Hz so you don't waste amplifier power (and speaker excursion) with frequencies that the speakers can't faithfully reproduce. This will allow more power for the passband that they can handle.

quote: Mark Strube
Since it's the safest solution for our system, I will be on the hunt for a 4th sub, but it may be some time before I have the ability to purchase it. I'll just run the LFE at a lower gain until then.

Smart move. It allows you to live for today and gives you a plan for tomorrow.

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Sean McKinnon
Phenomenal Film Handler

Posts: 1712
From: Peabody Massachusetts
Registered: Sep 2000

posted 03-18-2013 12:03 PM

I will say that the title of the thread was "best way to connect 3x jbl 3635 subs to one amp?" not "how to make my sound system correct" and when I looked up the specs and saw the frequency response I considered it more like a low frequency stage or surround speaker than a subwoofer. I would have thought it better to get close to a resistance that the amp likes to see than run these three "subs" on one 2 channel amp and cause clipping and damage. I did not consider the other effects for reasons i address below. I guess i was trying to save the guy some money which should not be the goal and is outside my usual priorities. I guess I felt like he was not going to buy another amp or sub either way because that was not the question he asked and that trying to improve his situation was the best compromise but I can see that is not cinema done right and for someone who has advocated such is embarrassing.

I would prefer a lapse in judgement to incompetent but it is what it is. You guys are absolutely right and I was completely wrong. I have been out of this industry for quite a while now and was out of the service end when digital cinema was still mostly an experiment on a few screens in the larger cities. I suppose it's time to be realistic and realize that I have not kept up with the industry or kept my skills sharp so rather than give someone bad advice again in the future or cause someone to do something damaging I will choose to bow out and simply be a "lurker" on the technical parts of the forum.

The last thing on this is there seems to be a lot of mis information out there as if you google the subject there are a lot of sites advocating wiring subs in series not specific to pro cinema but a lot on the home theatre car stereo world I would trust Steve and Tony's word over car stereo or home theatre guys any day.

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Richard Hamilton
Phenomenal Film Handler

Posts: 1341
From: Evansville, Indiana
Registered: Jan 2000

posted 03-18-2013 12:51 PM

Mark,
Here is an article that might give you a little more insight. Speaker Wiring/Loading Examples

It explains why not to use a resistor in place of a speaker and different wiring configurations. Towards the end it has some 3 speaker wiring configurations along with warnings.

At the end:

quote:
NOTE: We do not work on Home or Car Audio. We work only with Pro-Audio applications. We cannot help you with Home or Car Audio questions.

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Marco Giustini
Film God

Posts: 2713
From: Reading, UK
Registered: Nov 2007

posted 03-18-2013 04:44 PM

Thanks Richard,

Very educational.

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 03-18-2013 09:09 PM

There are two factors in play when dealing with a series/parallel system.

Putting the load at a compatible impedance to the amplifier. Minimizing series impedance that will reduce damping.

Lets take six (6) surround speakers (on one channel) as an example since it will make the situation more clear. Presuming an 8-Ohm speaker, if all six are paralleled, you present the amplifier with 1-1/3 Ohms. Below what most amplifiers can deal with on one channel.

You can make three groups of two or two groups of three. However, there is really only one good method of satisfying both conditions (usable load, minimal series impedance). The best method is to create two groups of three. But beyond that, each group should be paralleled. So if you parallel three speakers to make a group you have 2-2/3 Ohms in the group. You then series the two groups to present the amp with 5-1/3 Ohms. Something most amps can handle just fine.

But a key to this wiring method is EACH surround speaker only has 2-2/3 Ohms in series with it (the other group)...which is the minimal amount you are going to get with this quantity.

If you, instead series three speakers to make a group. You get 24-Ohm group and when paralleled with the other group present 12-Ohms to the amp (workable but inefficient with a solid-state amp). However, you also have each speaker have 16-Ohms of series impedance with it...bad.

You can work the problem using groups of two but again you are going to have a greater series resistance than the paralleled group of three.

The goal is always to minimize (eliminate, if possible) series connections when it comes to audio...particularly on "bass" components where the effects of damping are more important.

Note, QSC, with the DCA1222 purposely designed it (and has done a VERY poor job advertising, publishing the fact) to allow for driving into 1.6-Ohms. The DCA1222 will take five 8-Ohm speakers in parallel without issue. It makes it particularly suited for surround applications.

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Sean McKinnon
Phenomenal Film Handler

Posts: 1712
From: Peabody Massachusetts
Registered: Sep 2000

posted 03-19-2013 09:01 AM

How come some cabinets (not necessarily speaking professional cinema but non pro applications) are wired internally with drivers in series? Specifically my buddies bass guitar amp head and cabinet contains 4 4 ohm drivers with 2 drivers each in series and both sets of two in parallel? (I am honestly interested in learning not trying to defend my error)

I was trained that if you have one speaker in a surround array that is blown you can use a resistor as a replacement to protect both the amp and not cause a noticeable volume difference between sides until a replacement or repair can be obtained, I guess what I am trying to understand is the damping effect mentioned above and why the resistance of the speaker itself has such a different effect than than adding resistance through a resistor?

I have also seen double voice coil speakers (again, not in a pro cinema application) that are specifically intended to be connected in series? I apologize for my confusion it is just very unsettling to find out that the what you were taught was the right way (ie; series/parallel configuration when installing a surround array vs. connecting them all in parallel) was wrong. Even though I have moved on to owning and operating my own business and have no plan to ever re-enter this industry I still have an interest in it and I still want to know and understand what is the right way. Any help you guys can give in helping to understand this issue is greatly appreciated.

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 03-19-2013 12:34 PM

Sean:

The bass guitar amp has a very ragged and "inaccurate" response as it is intended to deliberately color the sound of the guitar. (That is also why two musicians rarely agree on using the same amp for the same instrument, they all sound different.) There is not a single "instrument" amp/cabinet combo that will have a flat and smooth response curve because they are designed on purpose to "enhance" (a questionable statement at best) the sound of the instrument it is designed for.

The temporary use of a resistor to bypass a blown surround speaker is not really that bad of a thing, but using one permanently (like UC Irvine's HIB100 does) is not acceptable. Like I said in my last post, I am not fond of the idea of series connecting surrounds, but the audible artifacts are minimal in that application. But also like I said, if I ever get to build my ultimate room, each speaker will have it's own amp channel. [Big Grin]

And in surrounds, where deep bass is not needed, the loss of damping caused by the series connections is not really an issue.

As for dual voice coils, in general they still are NOT intended to be connected in series! For example, in car subs, the dual coils are used to drive a single speaker element from the 2 stereo channels. A really dumb idea in any event, in those (rare) cases where the bass frequencies/levels/phase are NOT identical will result in some very odd cone movement and excessive heating of the coil(s).

And in regards to your earlier post where you suggested you just become a lurker...don't. You are certainly welcome to voice your opinion or suggestions, but just be ready to hear about it if you're wrong. [Smile]

In the case of technical subjects, if you are not really sure, just preface your suggestions with "could you try..." or "would this work?....." that way it doesn't sound like an "expert" opinion. [Big Grin]

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Sean McKinnon
Phenomenal Film Handler

Posts: 1712
From: Peabody Massachusetts
Registered: Sep 2000

posted 03-20-2013 11:09 AM

Thank you tony between your post and Steve's post above it makes a lot more sense now. I appreciate you guys taking the time to educate.

I think your right about properly qualifying ones posts such as "I have this idea that I have never tried in practice so make sure you validate it before trying it" or some such is a very good idea. I was just upset at myself for giving bad advice and for making myself look stupid in front of people that I respect.

I also have been bothered at the fact that a lot of skills I had learned are becoming obsolete and even though I have moved on to different things and had great success so far I hate feeling like all my prior experience has become wasted and worthless. My training and skills are obsolete. I know I am not the only person who must feel this way and I don't know why I even care but I think I took it a little harder than normal because I was already feeling that way when my ignorance was called out.

However, I don't have the time to Check up here much anyways because I spend most of my time running my business or with my family but if am here and think I can add something useful I will. I will just make sure to qualify my posts appropriately in the future.

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