JBL Air coupler subwoofer enclosure (Off Topic)
by leifchristensen 
, Saturday, March 17, 2007, 01:23 (6244 days ago)
Hello folks
Thought I´d share the thoughts about my plans for a REAL subwoofer.Picture was posted under the PASS EL-PIPO.
Had some correspondance with Bert on the execution of the concept and a tube was mentioned as the ideal form for such an enclosure.The narrower the tube,the faster the bass.So basically for my JBL2245 18 incher I need a tube of about 500mm inner diameter.The length will be determined by my centerfrequency preference: in my context,however excellent the custom BD 15 towers,I wish some more impact in the 40-15 hZ region,and it´s got to be able to follow the rest of the system ALL the way up to the 115+dB levels.For a center freq. of 30 Hz the tube length will be 343/30x,25 = 2,85 meters.
My assy thought was to mount the central dividing wall to one of the end "lids" and then when the driver is mounted on this assy,it can be "threadded" into the tube,Then the whole thing has to be sealed.
The opening in front of the driver has to be "adjustable" by a slideable lid over the port to adjust the bandwith and hence the output level capacity.
The whole thing could be driven by a Hypex 700watt dig amp module.
Any thought anyone.
Drawing under the PAS EL-PIPO link.
Best
Leif
Oslo
JBL Air coupler subwoofer enclosure
by MikeH , Saturday, March 17, 2007, 08:54 (6243 days ago) @ leifchristensen
Have a look at this, a small sealed enclosure deliberately driven below resonance with an active filter before the amplifier with gain from unity at resonance increaasing as you go down in frequency. I haven't finished mine yet so I can't tell you how it sounds. Will save a lot of space for you but you need a very tough cabinet and driver
JBL Air coupler subwoofer enclosure
by Bert , Saturday, March 17, 2007, 10:23 (6243 days ago) @ MikeH
Hi Mike,
That will go deep too but as you said, it takes much power and the driver has to work hard (distortion). With a resonating column the driver is not doing much (hardly moving at all!) and very efficient too giving much less distortion and if you power that like the enclosed system then the SPL will will much higher... 
Ciao,
Bert
--
BD-Design - Only the Best!
JBL Air coupler subwoofer enclosure
by MikeH , Sunday, March 18, 2007, 04:06 (6243 days ago) @ Bert
That will go deep too but as you said, it takes much power and the driver
has to work hard (distortion). With a resonating column the driver is not
doing much (hardly moving at all!) and very efficient too giving much less
distortion and if you power that like the enclosed system then the SPL will
will much higher...
I agree Bert, it is a sledge hammer solution to a problem that can be solved with a feather. It is the opposite end of the spectrum to the BD design philosophy. Good quality bass without taking up too much space in a small room is a difficult thing to do. I suppose it comes down to the person choosing which compromise they are most comfortable with at the time. The more I learn about high efficiency speakers the more doubts I have about the path I have chosen.
JBL Air coupler subwoofer enclosure
by Bert , Saturday, March 17, 2007, 09:34 (6243 days ago) @ leifchristensen
Hi Leif,
tube was mentioned as the ideal form for such an enclosure.The narrower
the tube,the faster the bass.
Correction: the more narrow, the faster the air in the tube making it seem a bit longer acoustically. It does not change the bass in fast as in quality...
I put the image below here, saves people clicking back and forth... :wink:
Enjoy building the thing and let me know how it works out!
![[image]](images/uploaded/image232.jpg)
--
BD-Design - Only the Best!
JBL Air coupler subwoofer enclosure
by leifchristensen , Sunday, March 18, 2007, 20:23 (6242 days ago) @ Bert
Here´s an alternative supplier of tubes
http://www.halfen-frimeda.no/doc/tubbox02-kat.PDF
Best
Leif
Some additional thoughts...
by Bert , Saturday, March 17, 2007, 10:52 (6243 days ago) @ leifchristensen
Hi Leif,
If I would make a cloumn like that for my listening room then I would tune it to 25Hz. My room has a stronger 35-40Hz range (room modes) and less below so if the column gives its most energy at 25Hz and one octave below and above then that would give me an even response from 20Hz up to 65Hz if tuned properly.
Pity that my ceiling is only 2.9m high.... too short. Then I could use the corner wall and a rigid angled panel so that you do not see it similar to my bass horns which are not visible (if you do not know that these are present...) 
Ciao,
Bert
--
BD-Design - Only the Best!
Some additional thoughts...
by leifchristensen , Tuesday, March 20, 2007, 13:05 (6240 days ago) @ Bert
Hello B
Why can´t you just lie it down along the side walls?mouth in the corner behind main speakers.
another thing that puzzles me:
according to my understanding of the aircoupler drawing the length of the box is calculated 343/freq.x0,25 e.g 30hz equals 343/30x0,25=2,85m
on the link from Frode the entire 30hz trapped horn box is no more than 1.85 and it´s also supposed to be a quarterwave design.
how come?
is it the horn lenght in the aircoupler that should be 2.85 for 30 hZ
if so the difference is HUGE.
is the aircoupler a halfwave horn?
what is correct?
best
Leif
Some additional thoughts...
by jeno , Tuesday, March 20, 2007, 22:09 (6240 days ago) @ leifchristensen
edited by unknown, Tuesday, March 20, 2007, 22:14
Just a shot in the dark...
Maybe it has something to do with that the 30 Hz of the JBL Air coupler is the center frequency from where you can reach up to one octave lower (15 Hz), while the 30 Hz of the tapped horn is the actual lowest useable frequency?
I may be completely wrong though, cause I dont't know much about the theory of these matters.
I look forward to learn about your experience though if you are going to put this thing to life. (I bet you are )
Jan Egil
Some additional thoughts...
by leifchristensen , Tuesday, March 20, 2007, 22:29 (6240 days ago) @ jeno
good point,but I guess a comment from the great B. would clarify a few things!
best
Leif