This sounds really good! It's a Pioneer B20 on an open baffle. The woofers are Alpha 15 and the tweeter is an Eminence using the small Dayton waveguide. The woofers are crossed at approx 75Hz and the tweeter is at about 11kHz.
I will be selling this as a kit at a reduced price than buying everything separately but have not figured the price yet. Once the plans are drawn out i will offer them free so you can purchase the components from anywhere you want, build and modify.
Without sounding like all i want to do is sell the kit i must say this is a very nice sounding speaker. I have been enjoying these for weeks and feel they are a great way to implement the Pioneer B20. If you like this driver you will love it with the added tweeter and woofers. From top to bottom it's very enjoyable. Open baffle removes any boxy coloration, the soundstage is wide with instruments and vocals floating in space rather than emanating from a box. Pink Floyd the Wall will creep you out (and your kids) and large scale orchestral music really sounds like a large orchestra. I will provide more details later.
Godzilla
I will be selling this as a kit at a reduced price than buying everything separately but have not figured the price yet. Once the plans are drawn out i will offer them free so you can purchase the components from anywhere you want, build and modify.
Without sounding like all i want to do is sell the kit i must say this is a very nice sounding speaker. I have been enjoying these for weeks and feel they are a great way to implement the Pioneer B20. If you like this driver you will love it with the added tweeter and woofers. From top to bottom it's very enjoyable. Open baffle removes any boxy coloration, the soundstage is wide with instruments and vocals floating in space rather than emanating from a box. Pink Floyd the Wall will creep you out (and your kids) and large scale orchestral music really sounds like a large orchestra. I will provide more details later.
Godzilla
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Good to see someone has finally tried this 🙂
Given that the B20's list at 90db and the Alpha at 97db (an MJK OB friendly set of numbers there), what made you cross so low?
R/
Jim
Given that the B20's list at 90db and the Alpha at 97db (an MJK OB friendly set of numbers there), what made you cross so low?
R/
Jim
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Well keep in mind the Alpha is, according to Eminence's infinite-baffle loaded plot, 90 db at 75hz. The OB that Zilla is using would reduce that even more, but probably not much more. My concern would be that since the B20 is comparatively inefficient, the 100-200hz area might suffer a little considering that cancellation still does occur that high. BUT, this could probably be filled with room reinforcement, preventing the kind of midbass vocals-destroying bloat that I loathe.
InclinedPlane,
Looking at the response graph here:
http://www.eminence-speaker.com/pdf/alpha-15a.pdf
I see what you mean about SPL @75Hz.
But what do you mean about "cancellation still does occur that high"?
R/
Jim
Looking at the response graph here:
http://www.eminence-speaker.com/pdf/alpha-15a.pdf
I see what you mean about SPL @75Hz.
But what do you mean about "cancellation still does occur that high"?
R/
Jim
Baffle losses, where the front wave is meeting the backwave and partially 'canceling each other out'.
I measured the T/S parameters for the Alpha 15A and found it to be 92.4 dB/W/m. Due to the Qts of over 1.0, the driver should be flat down to fs on an infinite baffle. The geometry of an OB will start to eat away at this SPL value as a function of size.
The 97dB/W/m quoted on the spec sheet is probably a peak value. The SPL curve shown must be for the driver in a box of some kind, it is totally inconsistent with a driver that has an fs of ~40 Hz and a Qts of ~1.2.
Be careful with manufacturer's spec sheets.
It sounds funny to say the crossover is at 75hz and incorrect actually. Remember, i have an amp connected to the woofers. The woofers have a rising response so when adjusting the variable crossover the setting is at approx 75hz on the dial but the actual crossover is probably closer to 200hz. Tomorrow i will post a pic of the woofers simmed response and it may make more sense why the settings are what they are. Everything sounds great without any holes... probably more overlap between drivers than gaps. Also, the amp raises and lowers the overall volume of the woofers. So once the crossover is set to blend the woofers into the B20 then you can raise and lower the volume to adjust further. It's really just like setting up a powered subwoofer but in this case you have two 15" woofers.
Godzilla
Godzilla
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
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, 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
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
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
Godzilla
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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
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
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! 😀
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
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
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