BK20 modification to mass loaded?

[Rob7]

I have a set of BK 20s folded BLH from madisound I built some time ago gathering dust. The bass response is not horrible but not good.

I have been toying with the idea of closing off the horn mouth with a piece of plywood and leaving a slot port to make a mass loaded transmission line of sorts out of them.

Is this feasible or just crazy? I know absolutely nothing about speaker design nor do I have the knowledge or means to model or test such.

If it all feasible, any suggestion to port size and placement appreciated. Even just a rough starting point

Seems like an easy experiment and a bit of fun—curious what others think.

 

[Ivo]

No, it's not crazy. It is a tool that allows you to adjust performance of the design, which is very useful. However, you need to be able to see what it does in a graph to fine-tune it to be an actual improvement. So I would definitely get some sort of measurement equipment (basically a dedicated USB microphone is enough, combined with freely downloadable software).

 

[nandappe]

Please close the mouse and attach the adjustable duct.
If sound-absorbing materials are used, remove them as much as possible.
No measuring device is needed, just adjust the duct area to your preferred sound.

 

[nandappe]

First, try the L-shaped board to see if it works.

 

[Rob7]

Please close the mouse and attach the adjustable duct.

excellent suggestion! Quick fun project with nothing to lose! Maybe get some use out of these cabinets yet. What drivers are you using?

 

[DRONE7]

First, try the L-shaped board to see if it works.

View attachment 1353740

I like your setup and L-adjustments !

Do I see a seat,? bottom right? or table.
Near-field listening ? ...those shoji screens how do they affect/control the sound-stage ? is there a larger space outside of those ?
Best.
Bob

 

[nandappe]

The photo in the previous post was taken when my friend was adjusting the ducts, he have a separate listening room and usually listen 4m away from each other.
The box used is similar in construction to the BK20 and the drivers are TangBand W8-1808.

 

[DrBoar]

What you get is something not far from a Voigt pipe. With a Voigt pipe you can reduce the pipe opening cross section to lower the fundamental resonance while maintaining output. That is to a area that is about half that of the surface area of the cone.

 

[Ivo]

That's a good comparison, a mass loaded Voigt pipe.

I have simmed that in hornresp and I think the area can be smaller as well. It solves some of the cancellations between driver and horn mouth as well. Hmmm I should give it another look really.

 

[nandappe]

The opening area of my Voigt Pipe is set about the same as the diaphragm area.
It would be great if I could actually build it and get the sound I like instead of using a simulator.