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"To DUAL or NOT to DUAL, THAT is the question."

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FUBARD303 View Drop Down
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    Posted: 21 May 2009 at 3:50am
Yes I searched and nothing....

What are the advantages and disadvantages regarding diferent set-ups of ported subs? Seems like there's no real consistancy in the big leagues. JBL seems to like the dual cab with a single slotted port yet EAW likes to pair-up singles (dual box with isolated chambers per driver) with multiple round ports while 18-SOUND's design is a single with a slotted port. WHAT GIVES!? Do these diferences give a box difering responces? What do they do?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jethrocker Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 6:17am
Really not a lot in it. It's all about the same really, volume per driver and port volume/dimensions per driver is what makes the response.  Positioning of ports in relation to cabinet walls, corners etc can affect the tuning and therefore response. Many people build a box with the simmed values then tweak the port length or volume a little to fine tune by ear.
The decisions made by the big manafacturers will be made in about the same way, but if you're in any doubt and want to be sure of things there are plenty of plans for reflex cabs, doubles and singles with recommended drivers, the g-sub here for example, or B&C designs.

As for advantages/disadvantages between singles and doubles..all depends, if you're ahire company doing big gigs with big transport then doubles might be easier to load and transport, if you're a one man sound then singles will be easier to deal with and two singles=one double sound wise.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote levyte357 Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 10:51am
Originally posted by jethrocker jethrocker wrote:

Really not a lot in it. It's all about the same really, volume per driver and port volume/dimensions per driver is what makes the response.  Positioning of ports in relation to cabinet walls, corners etc can affect the tuning and therefore response.


+1

Originally posted by jethrocker jethrocker wrote:


if you're a one man sound then singles will be easier to deal with and two singles=one double sound wise.


Exactly what I had. But I don' t think anyone would build 2x BCsub18 as a single though. I also think 2x Bcsub18 would handle a Gsub, as less bracing, means more chamber, and its more chamber per driver anyway.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 12:43pm
There's one downside for having 2 or 3 speakers in one chamber. If one speaker fails, the tuning shifts and with that the behaviour of the remaining speaker(s) in that cab. Worst case the remaining good speaker(s) fail too. Not a real problem in low power use, but definately an issue when running full throttle.
 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 12:50pm

Good point if one speaker fails in a reflex enclosure then the tuning will drop way down, and dramatically (depending on how far the tuning drops) increase excursion at the previous tuning frequency.

 

 

edit:typo



Edited by Jake_Fielder - 21 May 2009 at 12:51pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitzo Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 4:36pm
but...if one speaker fail, this work like a passive radiator?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jethrocker Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 7:01pm
Might do to an extent, but the tuning of the box would still have changed dramatically. TBH the most likely result would be the other driver dying shortly after.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 7:03pm
Originally posted by bitzo bitzo wrote:

but...if one speaker fail, this work like a passive radiator?

You're assuming the bad speaker has just an open coil, no rubbing... Yes, that would make it some kind of passive radiator, but even than the remaining speaker(s) get to "see" a very different situation on a mechanical level. A passive radiator is not just the same speaker without magnet and coil. Passive radiators have very different parameters than the speakers they are paired with in a cab. The way to simulate and calculate a cab with a passive radiator is as different as doing that for reflex cabs versus bandpass cabs and so on. The chance that the remaining good speaker(s) find themselves in a somewhat favorable situation if another speaker fails, is soooo rare that you better not count on your speakers to survive if things are going full power.
Of course things are not so bad that it's absolutely not-done to put two or more speakers in one chamber cabinet, half the world is doing it that way and get away with it too. It's one of those so called "calculated risks" in speaker building.
 



Edited by Peter Jan - 21 May 2009 at 7:16pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steak'n'ale Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 7:17pm
Thought the double buisness was all about getting an extra 3dB from doubling Sd. Don't you lose that once you give them their own little compartment within the cab?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FUBARD303 Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 10:20pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deadbeat Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 10:38pm
Originally posted by Steak'n'ale Steak'n'ale wrote:

Thought the double buisness was all about getting an extra 3dB from doubling Sd. Don't you lose that once you give them their own little compartment within the cab?

Nah, it's all about the coupling.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2009 at 10:41pm
Originally posted by Steak'n'ale Steak'n'ale wrote:

Thought the double buisness was all about getting an extra 3dB from doubling Sd. Don't you lose that once you give them their own little compartment within the cab?

It makes no difference for each speaker on it's own if it sits in a seperate compartment with a certain tuned port or with two speakers in a shared ( double net volume of a single cab ) compartment and ports of double surface and the same length as for a single cab. If you feed two speakers, let's say in a 200 liter cabinet, than that gives you a 3dB gain over that same power fed to a single speaker in a 100 liter cabinet, all things equal, net volume/ port surface and port lenght tuned for that speaker.  In case of the two speakers fed with double power, you get 6dB gain in total. 3 dB from doubling speaker/cabinet (that's the coupling part) and 3 dB from double power (pretty obvious).
You might say :" oh... just give each speaker more cabinet volume and I get so much dB for free".
Well... that's not how porting works... You can get more low extention with more volume for each speaker, but that means also changing the tuning (lower) to get that low extention, read : longer port for the same port surface compared to a smaller cabinet. Benefit : more low extention. Downside : less power capability due to Xmax reached sooner. No free meal here... Xmax is proportional to frequency. Lower frequency equals more speaker excursion to get the same SPL.
Now a longer port for same port surface is just the opposite from doubling cab volume/port surface for one speaker and having the same port length... just what happens if one speaker fails in a double speaker/shared chamber cabinet. The tuning shifts roughly half an octave up (not down as someone mentioned before) and the speaker's power capacity goes down, because the port no longer "helps" the speaker to make SPL in the lower region. The port does however boost things higher up, where it's not wanted, so the normal more or less flat respons gets seriously messed up on top of everything else. Any change in one of the parameters involved with porting , cab volume or port length/port surface, changes the respons of the whole system, not just SPL. On a side note : using another speaker is again another set of close-related parameters to consider in simulations and calculations.



Edited by Peter Jan - 21 May 2009 at 11:17pm
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