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MaVo 19th July 2008 03:20 PM

BMS 4552ND exit angle for os waveguide?
Hi, i need to know the exit angle of the BMS 4552ND to construct an OS waveguide. I asked BMS, but got no answer. I hope that someone here has this information. If not, is there a way to measure it? If that also doesnt work, would you just guess an angle like 5 degree in the hope that it comes close or build a horn with zero degree?


Tom Danley 19th July 2008 05:53 PM

Not having a blown one lying around, Via bright flashlight, that one appears to be about a 15 or 20 degree conical taper down to maybe 5/8 inch diameter, past which is the radial summation.
A small but very powerful driver to be sure.
Tom Danley

MaVo 19th July 2008 06:28 PM

Thanks Tom :)

That angle surprises me, since i heard that most other drivers are around 5-6 degree.

MaVo 19th July 2008 07:20 PM

Can i screw it open and measure diameters with a ruler or will it be damaged by this?

Tom Danley 19th July 2008 09:58 PM

You can remove the drive assembly with the 6 screws at the rear, just be slow and careful.
This is not a normal style driver however as you will see when its apart.
It's construction, lacking multiple path lengths in a phase plug and starting with a smallish diameter on exit , allow it to produce a diverging wavefront at the final one inch exit which makes it consistent with conical horns like i use or or other horns which have a fast initial expansion.
This is not a good driver for a long exponential horn for example.
Eye balling it again, it looks to be a conical section about 3 /4 inch long which (peering through the screen) begins at about 1/2 inch dia and ends at 1 inch dia.
If you take off the drive assembly, you will be able to measure that inner diameter.
Tom Danley

MaVo 19th July 2008 11:35 PM

Your comment makes me wonder if a OS waveguide will work well with this driver. Well, best thing to do is see for myself.

Thanks for helping me out Tom!

MaVo 20th May 2009 04:19 PM

I recently opened one of my drivers and measured the inner geometry of its exit tube. Ill just post the results in case someone is also interested in building an OS waveguide for the BMS 4552ND.

The tube is preceded by a short segment that seems to be of constant area. I cant measure this one without risking to damage the driver. The flared part of the exit tube is 12mm long. Its starting diameter is 20mm and ending diameter is 25mm. This should equate a wall angle of 11,8 degrees.

As a sidenote, the change from the constant diameter part to the flared part of the tube is abrupt, so this should allready be a source of HOM, if i am not mistaken. I am curious if other compression drivers have similar abrupt changes in exit flare, so please tell me if you know.

fb 20th May 2009 11:00 PM

Thanks for the info MaVo, I'm also investigating building a waveguide for this driver. :) :smash:

JoMoCo 28th November 2010 07:34 PM

BMS Adapter Screw Thread 1 3/8 " for 1" Driver
Has anyone tried this BMS adapter on the 4552nd driver? I am wondering if BMS's design might be more acoustically transparent...especially because of the drivers design ....or just more of the same 1" generic adapter blues:cannotbe:

BMS Adapter screw thread to 1 3/8" for 1" driver flange - eBay (item 200290174840 end time Dec-09-10 10:25:36 PST)

Flaesh 28th November 2010 08:29 PM


Originally Posted by MaVo (
I am curious if other compression drivers have similar abrupt changes in exit flare, so please tell me if you know.

Radian 950 PB

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