B20 on Open Baffle

[2litre]

Thanks InclinedPlane.

MJK, thanks for that information. I was wondering why that response graph lacked the distinctive hump one normally associates to a driver with a Qts of 1.26.

Godzilla, so the amp (APA150?) must be the smaller black box at the top of the electronics rack.
Now it makes more sense.

R/
Jim

[Godzilla]

>>> Godzilla, so the amp (APA150?) must be the smaller black box at the top of the electronics rack. Now it makes more sense.

Yes, the amp is key to making this all work properly. Efficiency of the drivers does not matter because i can raise and lower the volume of the woofers. The crossover control allows you to blend the woofers into the main driver. Everything works beautifully and the speakers produce effortless bass, get loud (the drivers don't even seem to move at low volumes and barely move when pushed) and sound excellent. This setup works with the Betsy full range driver too and i am ordering a pair of TB W8-1808s this week because that driver has gotten my attention over the last couple months. My sims indicate it will be a great choice for this setup. I'm sure the Fostex 207e or 208z would work great too but i have a few Fostex already and want to try different drivers.

Godzilla

[Godzilla]

Here is my simulation of the Alpha 15 on an open baffle the size of the Boomer kit. The baffle is 20" x 48". The rising response of the Alpha (green line) causes much overlap with the main driver but the 18db slope of the amps variable crossover, i believe, produces something like what i added represented by the red lines. In effect, you have control over the crossover frequency. This is just an estimate of what i hear and why i believe this combination of components works well together. I have not taken measurements but feel the performance is very customizable to different tastes and rooms. You can turn the bass completely off to hear how the main driver sounds without bass support or turn it way up and overload your room. Somewhere in between is where you will find the right setting.

Godzilla

[norman bates]

nice project godzilla.

I'd trim some of that b20 whizzer off and ghost in that tweeter a little lower.

The open baflle is a fun branch to play with in our hobby.
And in the back of your mind, you always know the mids would have been cleaner if you had then open baffle

I'm back to my open baffle focused array again.


The low volume clairity is awesome.

Think I'll start the 16 x b3s focused array.......

Norman

[InclinedPlane]

What does whizzer trimming accomplish? If there is a thread on this, could I get a link?

[c2cthomas]

Originally Posted by norman bates

nice project godzilla.

I'm back to my open baffle focused array again.


Norman

As long as the pussy cat is happy all is good!

[norman bates]

no link to whizzer trimming.

I cut about 1/4 to 1/3 of the whizzer off of a b20 (and had cotton ball between whizzer and cone).

It removed a good bit of honk but then I had to change 10 band eq from around +3 at 8khz and +6 at 16khz to +3 at 4khz, +8 at 8khz and +12db at 16khz.

So, trim a bit of whizzer off, add a planet 10 phase plug and that should be ideal.

Norman