BM15CX-38 is a horse for a course
The BM15CX38 is a very fine driver indeed but it is far from being a "General Purpose Big Coax".
Its T/S parameters do not suit sealed or OB use very well and flattish reflex alignments result in F3's and F10's that are barely adequate for home listening. Maybe an EBS in a bigger box, back to the wall? Maybe a big sealed box with a heap of EQ? You could use them with a sub but then you wonder why you bought a great big 15" in the first place.
A compact reflex box, with an F3 of, say, 60Hz and a 2kHz 2nd or more order x-over will give a little weapon that will knock birds out of the sky in a PA application, and sound very nice doing it.
For home use, a TL or BLH looks feasible but ye gods the boxes are big.
As for a single capacitor crossover, I am not sure how this resolves the 9-10dB sensitivity difference between the cone and the horn. Perhaps tiny values are chosen to "cross over" at 20kHz and use the downward slope to match up to the cones natural rolloff. Can't see it working myself.
And where would you cross it over for HiFi anyway? The horn will happily cross over around 1kHz and handle any reasonable domestic power requirement. Sucks as a x-over frequency though, right in the voice range and as you move up further the radiation angle and breakup of the 15" cone get worse so it's hard to see 2.5-3kHz working either.
No, I don't think this is a driver for a first project.
I love it but it has been a beast to tame. Its strengths are enormous (Unlimited upward dynamic range, DDR to die for, that 'live and effortless' presentation and OMG imaging and soundstaging, spleen mashing kick) but it takes a bit of massaging to suppress its PA roots.
Hope this perspective helps.
Rgds
blakktothefuture
The BM15CX38 is a very fine driver indeed but it is far from being a "General Purpose Big Coax".
Its T/S parameters do not suit sealed or OB use very well and flattish reflex alignments result in F3's and F10's that are barely adequate for home listening. Maybe an EBS in a bigger box, back to the wall? Maybe a big sealed box with a heap of EQ? You could use them with a sub but then you wonder why you bought a great big 15" in the first place.
A compact reflex box, with an F3 of, say, 60Hz and a 2kHz 2nd or more order x-over will give a little weapon that will knock birds out of the sky in a PA application, and sound very nice doing it.
For home use, a TL or BLH looks feasible but ye gods the boxes are big.
As for a single capacitor crossover, I am not sure how this resolves the 9-10dB sensitivity difference between the cone and the horn. Perhaps tiny values are chosen to "cross over" at 20kHz and use the downward slope to match up to the cones natural rolloff. Can't see it working myself.
And where would you cross it over for HiFi anyway? The horn will happily cross over around 1kHz and handle any reasonable domestic power requirement. Sucks as a x-over frequency though, right in the voice range and as you move up further the radiation angle and breakup of the 15" cone get worse so it's hard to see 2.5-3kHz working either.
No, I don't think this is a driver for a first project.
I love it but it has been a beast to tame. Its strengths are enormous (Unlimited upward dynamic range, DDR to die for, that 'live and effortless' presentation and OMG imaging and soundstaging, spleen mashing kick) but it takes a bit of massaging to suppress its PA roots.
Hope this perspective helps.
Rgds
blakktothefuture
So what other drivers would you recommend? I would like to stay with open baffle.
I can't find many contenders.
Sterling silver iris, audio nirvana, phy-hp. I would prefer something over eight inches in diameter.
I can't find many contenders.
Sterling silver iris, audio nirvana, phy-hp. I would prefer something over eight inches in diameter.
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For OB, members usually start with a list of what they like more or something. Look for this one example in diyAudio. It's a good starting point for criticism and ideas, isn't?
http://www.diyaudio.com/forums/multi-way/233045-ae-speakers-dipole-15-lo15-need-advice.html
edit: ok, I see you already have a new thread...
That's the right thing to do, the title of this wasn't helping going that route. 🙂
http://www.diyaudio.com/forums/full-range/242340-open-baffle-help-design-driver-picks.html
http://www.diyaudio.com/forums/multi-way/233045-ae-speakers-dipole-15-lo15-need-advice.html
edit: ok, I see you already have a new thread...
That's the right thing to do, the title of this wasn't helping going that route. 🙂
http://www.diyaudio.com/forums/full-range/242340-open-baffle-help-design-driver-picks.html
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Time Travel blakkshepeaudio
No, I don't think this is a driver for a first project.
I love it but it has been a beast to tame. Its strengths are enormous (Unlimited upward dynamic range, DDR to die for, that 'live and effortless' presentation and OMG imaging and soundstaging, spleen mashing kick) but it takes a bit of massaging to suppress its PA roots.
blakktothefuture .....Was reading your coax chop-up....above....I think I have
some in storage....If a down to 800hz......horn drive was used on that P Audio
15" coax.....how would those numbers work...crunch it....dude...
No, I don't think this is a driver for a first project.
I love it but it has been a beast to tame. Its strengths are enormous (Unlimited upward dynamic range, DDR to die for, that 'live and effortless' presentation and OMG imaging and soundstaging, spleen mashing kick) but it takes a bit of massaging to suppress its PA roots.
blakktothefuture .....Was reading your coax chop-up....above....I think I have
some in storage....If a down to 800hz......horn drive was used on that P Audio
15" coax.....how would those numbers work...crunch it....dude...
Well, the T/S parameters speak for themselves. A (massive) horn loaded enclosure is their likely best home given the extremely low Qts. Sealed or OB enclosures give unacceptably high F3s. Even Reflex and MLTL enclosures are huge beyond most domestic acceptability. I maintain that you must either accept a massive (and I mean HUGE) MLTL or horn or make a nice reflex with an F3 of 60 or so Hz and EQ the hell out of it, a sealed alignment with even more EQ, or just bite the bullet with a sub, although it is a hard act to keep up with !
Given that you want the center of the coaxial driver to be about 75cm (30") above the floor, why not have a 15" sub below the coax driver? Keep the coax driver in a smallish sealed sub-enclosure and cross over at 100Hz or so. Given the inevitable differences in sensitivity between the coax and the sub (at least any sub that would go low) I would go for active crossover.
That would prob be a pretty good sys. in home ...Whats the smallest box the BM15CX38
could go in ...ported??? anyone...
thanks hweb......go down to the DIY Audio hotdog and chili stand ...its on me.....thanks
could go in ...ported??? anyone...
thanks hweb......go down to the DIY Audio hotdog and chili stand ...its on me.....thanks
A potential design solution
As a reference, I own a pair of the 18" version and have experimented with them quite a bit. Before you do anything, you need to verify the T/S parameters. Assuming your 15's are in or very close to spec, you are looking at a 5.0 cu. ft. net internal volume enclosure. Using Theile alignment, and tuning the box a couple of Hz below woofer resonance at 40 Hz, you can use a 6" port, (MUST be flared at both ends!) about 7.5" long. This will give you an approximate (half space calculated) F3 of 40 Hz. In room will be more like 36 Hz as that low there will be a bit of room gain. Plenty low for most music. Xmax 4.5 mm peak and SD 800 sq. mm can deliver around 105 db each in the mid 40's in half space in this configuration. J
As a reference, I own a pair of the 18" version and have experimented with them quite a bit. Before you do anything, you need to verify the T/S parameters. Assuming your 15's are in or very close to spec, you are looking at a 5.0 cu. ft. net internal volume enclosure. Using Theile alignment, and tuning the box a couple of Hz below woofer resonance at 40 Hz, you can use a 6" port, (MUST be flared at both ends!) about 7.5" long. This will give you an approximate (half space calculated) F3 of 40 Hz. In room will be more like 36 Hz as that low there will be a bit of room gain. Plenty low for most music. Xmax 4.5 mm peak and SD 800 sq. mm can deliver around 105 db each in the mid 40's in half space in this configuration. J
Need to define 'small' since this ~10 ft^3 MLTL required an 8" dia. vent , so as net Vb shrinks, vent length quickly turns into TL length: P-Audio BM15CX38 in MLTL cabinets
GM
GM
A bit more info
Part of the info I should have included is I am assuming a passive crossover that has a series resistance of 0.65 ohms. (RG value) This raises the effective QTS to about 0.35. Sorry I did not include that in my previous post. J
Part of the info I should have included is I am assuming a passive crossover that has a series resistance of 0.65 ohms. (RG value) This raises the effective QTS to about 0.35. Sorry I did not include that in my previous post. J
Gray - If you cross over the coaxial to the sub at >100Hz you could probably stuff the coaxial into a pretty small enclosure. You'd probably end up with a fairly high F3 and a small hump (maybe a db or two) at the low end, but who cares? It's being crossed over at a higher frequency anyways. I did this with a B&C 12" coax in the past and it worked great (I have the cabinets in my shed if you'd like them).
In any case, I think we should listen to John Busch's advice here as he has worked with a similar P Audio coax (unlike me ;-)
In any case, I think we should listen to John Busch's advice here as he has worked with a similar P Audio coax (unlike me ;-)
Thanks hweb.....How small of box, of course it cant be but so small being 15" also checked
the 15" coax it was a PAudio 15" CXA Coax which is close .
P.Audio Coaxial Speakers - P.Audio BM15CXA coaxial 15" speaker - P.Audio BM15CXA 350 watt 15" coaxial speaker for all full range applications. P.Audio BM15CXA 15" coaxial and other P.Audio coaxial speakers here.
Thank again ......hweb........gray
the 15" coax it was a PAudio 15" CXA Coax which is close .
P.Audio Coaxial Speakers - P.Audio BM15CXA coaxial 15" speaker - P.Audio BM15CXA 350 watt 15" coaxial speaker for all full range applications. P.Audio BM15CXA 15" coaxial and other P.Audio coaxial speakers here.
Thank again ......hweb........gray
And there you have it - a little over 1 foot^3. Probably about as small as you could practically make for a 15" driver. Given the amount of space that the driver itself takes up you'll probably end up with a Qtc of about 1. Add some stuffing (which you should do) and you'll bring that down a little. The F3 will end up around 180Hz, so cross over to the sub at 200Hz or so.
Given the natural roll-off of the coaxial driver you might even get away with a first order high pass (you'll probably need to go with a 2nd or 3rd order low pass for the sub though). I think that would work pretty sweet.
Given the natural roll-off of the coaxial driver you might even get away with a first order high pass (you'll probably need to go with a 2nd or 3rd order low pass for the sub though). I think that would work pretty sweet.
hweb....Im not sure if GM is posting not "fake news" but "fake box volume"....
in my process to "make my stereo grate again"......Im kidding GM....thank you
very much hweb and GM....dudes....
in my process to "make my stereo grate again"......Im kidding GM....thank you
very much hweb and GM....dudes....
Thanks GM....and you are right...thanks allot....gray
Loud is Beautiful if it's Clean!....
Except extremely loud is also Beautiful......
My personal poison....fusion jazz
https://www.youtube.com/watch?v=P49qX90S2Hc
https://www.youtube.com/watch?v=D6_fQIqLdls
https://www.youtube.com/watch?v=ntZuw4XbRDk
A couple comments from the peanut gallery Oh My!
The P-Audio CX 15 & 18 tend to have a bit higher QE than spec. The 15CX is usually around .33 to .34. So with a bit of RG you usually end up with a QTS' of .35 or so. Figure around 40 liter net internal volume heavy stuffed box with an F3 of around 85 Hz. This assumes you achieve a 0.707 QTC. Box resonance (FC) will also be close to 85 Hz. YMMV. J
The P-Audio CX 15 & 18 tend to have a bit higher QE than spec. The 15CX is usually around .33 to .34. So with a bit of RG you usually end up with a QTS' of .35 or so. Figure around 40 liter net internal volume heavy stuffed box with an F3 of around 85 Hz. This assumes you achieve a 0.707 QTC. Box resonance (FC) will also be close to 85 Hz. YMMV. J
Yeah, I assume as much for any driver with no measured specs and always add a 0.5 ohm for wiring, but folks tend to stuff sealed alignments, so it averages out close enough for human hearing IME. 😉
GM
GM
Thought I'd chime in here as I've just picked up a pair of these big blue buggers and feeling a bit unsure how to proceed. lol
Interestingly the p.audio published spec sheet parameters that I managed to track down are a bit different to that on the USSpeaker site. Namely the Fs of the woofer is higher at 42Hz and the QTS higher at 0.31 (as noted by John Busch above). Am I allowed to attach the full spec sheet here?
I'd not sure if I could possibly get away with cabinets the size of those big TLs so maybe my future involves subs too! 😆
Interestingly the p.audio published spec sheet parameters that I managed to track down are a bit different to that on the USSpeaker site. Namely the Fs of the woofer is higher at 42Hz and the QTS higher at 0.31 (as noted by John Busch above). Am I allowed to attach the full spec sheet here?
I'd not sure if I could possibly get away with cabinets the size of those big TLs so maybe my future involves subs too! 😆
Attachments
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