Bradford Perfect Baffle

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freddi

freddi

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Joined 2005
Merle Haggard - Swingin' Doors (with lyrics) - YouTube

- -"According to my invention, I provide in at least one wall of a totally enclosed cabinet, or bafiie, what might be termed a pressure relief valve one example of which is the formation of an opening or passage in said cabinet communicating with air therein, and supporting within this opening with suitable clearance between its perimeter and the edges of the opening, a freely swingable door. This door should be very light so as to have a minimum of inertia and it is preferably suspended within said opening with non-metallic means."
 
tca

tca

Member
Joined 2011
diale.org
freddi said:
Merle Haggard - Swingin' Doors (with lyrics) - YouTube

- -"According to my invention, I provide in at least one wall of a totally enclosed cabinet, or bafiie, what might be termed a pressure relief valve one example of which is the formation of an opening or passage in said cabinet communicating with air therein, and supporting within this opening with suitable clearance between its perimeter and the edges of the opening, a freely swingable door. This door should be very light so as to have a minimum of inertia and it is preferably suspended within said opening with non-metallic means."
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Yes, I know... did anyone try to build one?
 
DrBoar

DrBoar

Member
Joined 2003
If the leaking around the flapping part is small the thing is a bass reflex with a passive radiator with a far higher tuning frequency than normal. Otherwise is some kind of amplitude modulated resistive vent.

DIY
go to a fleamarket and buy the cheapest pair of closed boxed you can get.
Cut a large hole on one box
Cut a piece of cardboard slightly smaller than the hole
Suspend the cardboard in the hole.
Play some music and se the cardboard flap around....
 
freddi

freddi

Member
Joined 2005
fwiw - for cabinets of that era, I like the R-J

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An externally hosted image should be here but it was not working when we last tested it.

EV SP15 in the 15" RJ
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Lafayette's "Eliptoflex"
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one of my 4 old 18" RJ vent path woofers
An externally hosted image should be here but it was not working when we last tested it.
 
DrBoar

DrBoar

Member
Joined 2003
There was a swedish company that made similar bass reflex boxes. That is a subbaffle that creates a roughly conical cross section of the vent. Perhaps was the idea that a cicular vent close to the cone would confer some symetric loading? Jamo in Denmark had two concentric tubes outside with the driver in the center. The gap between the tubes formed a vent with a straight cross section around the driver.
 
xrk971

xrk971

Founder of XSA-Labs
Joined 2012
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You know, the topology of the RJ is a little more complicated than a plain BR now. Having the vent in the direct vicinity of the cone radiator provides feedback and what you have now is a bandpass alignment - kind of like a Karlson - but without the multi chambers - although the aperture shape of RJ has curves kind of like a Karlson. Might be neat to sim in Akabak.
 
Greebster

Greebster

Member
Joined 2010
xrk971 said:
You know, the topology of the RJ is a little more complicated than a plain BR now. Having the vent in the direct vicinity of the cone radiator provides feedback and what you have now is a bandpass alignment - kind of like a Karlson - but without the multi chambers - although the aperture shape of RJ has curves kind of like a Karlson. Might be neat to sim in Akabak.
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Placement of the port doesn't per se make a bandpass alignment. If this were true all ported speakers would be considered bandpass due to the extreme wavelength involved. How it loads the driver and room changes. For example the test MLTL sub I built contains a single 6.5" driver on the end of a 45" long tube that is divided in half lengthwise. The port is 40.5" away from the driver. To load a room best with this contraption is difficult, to say the least. In testing found that if you applied multisub rules (which is why I built it in this manner) the device works best when placed off the floor equidistant from the floor ceiling juncture. In this example that was ~23" for best placement. Which also made this 8.25" diameter tube sub stand 5'8" tall. Uggg

Now another experiment, if this tube sub is placed inside another tube, this time a 12" dia 48" long where the energy from the port is released into the room from the same point as the woofer. Because the outer tube is so much larger (>2x internal of the smaller's external dimensions ) it does not change tuning. What it does do is place the pressure wavefront of the port at the driver and result is a completely different room loading eg from a single point instead of two distinct points.
 
Greebster

Greebster

Member
Joined 2010
DrBoar said:
There was a swedish company that made similar bass reflex boxes. That is a subbaffle that creates a roughly conical cross section of the vent. Perhaps was the idea that a cicular vent close to the cone would confer some symetric loading? Jamo in Denmark had two concentric tubes outside with the driver in the center. The gap between the tubes formed a vent with a straight cross section around the driver.
Click to expand...

I copied a few Jamo designs back in the '80's and still like the porting they did. Problem is how critically difficult it is to get right ;)
 
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