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Jensen BLH

172.56.33.100
Posted on December 6, 2014 at 23:54:30
zenegillette
Audiophile

Posts: 32
Location: Washington
Joined: March 2, 2013






Hi ... I'm going to build these back loaded horns. Original drivers were the G-610 Triaxial (not in my price range this century).
Can anyone suggest drivers that might work?
I have JBL D130's, PWK K33's and P.Audio P 150's (JBL 2226 clone) to try, but have no idea how they might sound.
Thanks, Zene

 

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RE: Jensen BLH, posted on December 7, 2014 at 06:25:00
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 Hi Zene, nice drawing.

With any luck you should be able to find a pair of Altec Duplex around there, or even consider new GPA drivers.
They go for a fraction of what some of those Jensens sell for.

I don't know how Altecs will work in your cabinets, you may be able to optimize them to the driver.

Also consider raising the speaker higher if possible.

Looks like fun.
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RE: Jensen BLH, posted on December 7, 2014 at 06:49:53
zenegillette
Audiophile

Posts: 32
Location: Washington
Joined: March 2, 2013
 GargOyle ... Can't take credit for drawing (web). I'll see if I can find specs on the tri and duplexes and see if a GPA driver will come close.
I certainly would have put the woofer near bottom (old habit for bass extension), forgetting about the proximity to mid, thx. Zene

 

RE: Jensen BLH, posted on December 7, 2014 at 09:25:15
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 NP

If you want I can make you up some drawings like the one you posted when you are ready to go.

Actually it is a 3D file which is nice because you can take the measurements from wherever you want on the drawing and don't have to clutter it up with dimensional text. Changes on the fly can be made easily.

The "Sketchup" program is free for educational use.
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RE: Jensen BLH, posted on December 7, 2014 at 12:24:53
Paul Eizik
Audiophile

Posts: 2120
Joined: September 15, 2001
 Zene

There are several options for tuning this BLH to optimize it for a particular driver. The volume of the triangular chamber at the back of the driver seems a bit on the large size. The volume of this chamber (Fhc) will determine a point where the high frequencies (typically in the 200 Hz region) exiting the back horn will begin rolling off:

Fhc=(2Qts)Fs(Vas/Vfc)

This is where: Fhc is the beginning of the roll off trend in Hz; and Vfc is the volume of the chamber in liters.

The size of this chamber was apparently optimized for the original tri-ax driver and can probably be tuned with a smaller volume to match one of the drivers you choose which will apparently not be tri-ax's. Actually the chamber as pictured is a rectangular prism (cuboid), see link.

Also, this chamber plus the driver's output exhaust through 2 very tall narrow slots on the sides which define the beginning of the 2 throats of the bifurcated folded bass horn. In a back loaded horn it's necessary to make this total area considerably smaller than what would be used for a front loaded horn which would have a throat optimized more towards optimum efficiency. The reason for this is to keep the output from the bass horn in a BLH from overpowering the output from the front of the driver which is a direct radiator in the higher frequencies. I would make these slots adjustable, perhaps with a sliding section to allow a possibility for adjusting the slot wider than pictured, for tuning to the driver. Making the slots wider will effectively make the volume of the chamber smaller, as well as alter the volume and geometry of the section of the horn before the first fold. Don't forget to add some fiberglas sound absorbent material to the triangular sides of the chamber to minimize sound bouncing off the walls and coming back through the driver cone.

Good luck, and let us know how it goes!

Paul

 

RE: Jensen BLH, posted on December 7, 2014 at 17:39:08
zenegillette
Audiophile

Posts: 32
Location: Washington
Joined: March 2, 2013
 GargOyle ... Thanks for Sketchup offer. I still use the old school method. Been drawing for 56 years (old habits are ...). I use sign board (paper one side) plywood which has the dual purpose of being the alignment jigs for assy. I've used this technique for any upright type horn, such as LaScalas and Bells and you can use over and over for duplicates.
Quick note if someone wants to try: make two identical, even outside plate dimensions and you can place against a vertical flat/square surface (wall) and that will keep it from skewing while glue sets (I stress 12 hrs min; no exceptions).

Paul ... Thank you for your engineering approach to re-designing (rare in forums). I will definitely heed all your suggestions. I always like my speakers to be fairly universal to allow for changes such as interchangeable woofer plates.

Zene

 

Tri-Plex, posted on December 10, 2014 at 15:19:26
lokie
Audiophile

Posts: 1989
Location: Georgia, USA
Joined: January 28, 2003



.

 

RE: Tri-Plex, posted on December 11, 2014 at 06:25:06
zenegillette
Audiophile

Posts: 32
Location: Washington
Joined: March 2, 2013
 Thanks, Lokie. That's the kind of pics I like (look under the hood, not the paint job). Zene

 

RE: Jensen BLH, posted on December 11, 2014 at 16:53:26
Zedguy
Audiophile

Posts: 142
Joined: September 14, 2007



I have a single that housed a Tannoy 15 for awhile.

 

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