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Multi-Way Conventional loudspeakers with crossovers

The umpteenth large format coaxial driver thread
The umpteenth large format coaxial driver thread
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Old 15th November 2017, 10:42 PM   #191
Adolf Corkscrew is offline Adolf Corkscrew  Finland
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A 15-inch two-way coaxial speaker - the ingredients and the crossover

Okay. So, back when I started this thread, my goal was a two-way speaker that could hit the mark of producing the lowest notes of a bass guitar with aplomb. And I'm quite happy to report that this mark was met, and even exceeded, though slightly depending on your room.

And of course I wanted this goal to be met with a coaxial driver. Not an easy task, mind you. With these goals and driver sizes we've nothing to utilize but PA-drivers, and most of these are unusable for Hi-Fi use. Most, but not all of them, mind you.

I think it was "ScottG" here at diyaudio.com, who pointed me to take a look at B&C's quite recent 15FCX76 drivers. And this was luckily no dead end. They do however need some space to thrive, when it comes to the enclosure. A hundred liters isn't enough, but 170-180 liters is nearer the optimum. Now, these speakers do rely on some room enforcement in the lowest octaves, but that seems to be normal with most high efficiency designs. What you end up with is something like 95dB/W/m efficiency and a response that goes straight down to 20-40Hz depending on your room. Not that bad for a two-way design? It took me quite a while to finalize the crossover, though. These large PA-coaxials are just that much harder to work with. Not because of their response, but more because of their directivity. They're not pointy, as some panels are, but they nonetheless have a very different directivity pattern to most "normal" loudspeakers (read: 6,5" 'bass' and a dome tweet...). This means you have to voice them very differently. A completely straight response isn't what you're aiming for, lest you want to feel the listening fatigue...

So, thus far we have the first two prime ingredients, the driver and the crossover. The crossover is in the file attached, though feel free to ask me for more info if you feel like it.

Though the crossover seems to be electrically of the second order, it's actually closer to third order acoustically. Considering components, use the best quality polypropylene caps you can afford. The first coil on the bass hand of the X-O should be one with a low resistance. The coil on the tweet side can be an air cored one with higher resistance, doesn't matter that much here. Considering resistors, I've tried some more 'high end' ones, and for me they've been no revelation. They should nonetheless be of 10 watt variants, and use the best quality you can afford. The quality of the resistors - at least for me - makes not much of a difference. I use Jantzen wirewounds here, since they're not ridiculously expensive.

I'll try to post the specifics of the cabinetry as soon as I can. As stated, I'm currently piled up with fun (=projects), so this may take some time.
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File Type: jpg Contrapunctum Xover.jpg (110.4 KB, 428 views)
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Old 27th November 2017, 03:06 PM   #192
AudioGeek is offline AudioGeek  United States
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any BSC on these speakers? Do you have a final response curve for them? Great project!!
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Old 11th February 2018, 04:20 AM   #193
ScottG is offline ScottG  United States
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Quote:
Originally Posted by Pano View Post
The thing I find tough about Coaxial drivers is - where to set the crossover point?
The woofer cone rarely seems to make a horn quite big enough for the tweeter to cross at a point low enough to be inside the good response of the woofer cone. The smaller the cone, the higher you can cross it, but then the smaller the resulting horn! The two chase each other.

I suppose with DSP and very steep slopes it could be done neatly.

I've had some luck with passive crossovers on 18" and 15" coax. Not so good on smaller.


I thought this would be interesting addition:

Taipuu Speakers

Taipuu Speakers DSP active speakers - Taipuu Speakers

-maybe?:

B&C Speakers

or (the coaxial used in this thread),

B&C Speakers


(..too "hot" for my liking, but very pretty measured result non-the-less.)
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Last edited by ScottG; 11th February 2018 at 04:24 AM.
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Old 11th February 2018, 04:29 AM   #194
ScottG is offline ScottG  United States
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Measured Comparisons (..and you can see that near 1kHz is a good point for matching directivity with a steep filter - like the one used on the Taipuu.)
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File Type: png Taipuu_2-way_SPL.png (24.9 KB, 244 views)
File Type: png Taipuu_2-way_Dir-polarmap.png (145.5 KB, 228 views)
File Type: png file.png (489.4 KB, 221 views)
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Old 11th February 2018, 04:33 AM   #195
ScottG is offline ScottG  United States
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..and:
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Old 11th February 2018, 04:35 AM   #196
ScottG is offline ScottG  United States
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..and: (note the reason for the multiple posts is that the .png link from B&C is seen as the same address apparently.)
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Old 11th February 2018, 04:36 AM   #197
ScottG is offline ScottG  United States
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..finally:
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Old 11th February 2018, 09:35 PM   #198
Soldermizer is offline Soldermizer  United States
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Thank you for continuing your tweaking. Adolf, I must ask: from your user name, does this mean that you are a conoseiur of German wines vintage 1930s to 1945?
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Old 13th February 2018, 11:32 PM   #199
Qts is offline Qts
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Quote:
Originally Posted by ScottG View Post
I thought this would be interesting addition:

Taipuu Speakers

Taipuu Speakers DSP active speakers - Taipuu Speakers

-maybe?:

B&C Speakers

or (the coaxial used in this thread),

B&C Speakers
It is BMS 15C262.
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