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Beyma 8XC20 What kind of box would do?
Beyma 8XC20 What kind of box would do?
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Old 14th July 2008, 04:48 PM   #1
Nicodimdom is offline Nicodimdom  France
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Default Beyma 8XC20 What kind of box would do?

Hi everybody,

I'm a french guy retired in the wonderful "Lot" region in south-west of France. and this is my first post.

Well,
I have These Beyma coaxial drivers and would like to build a pair of loudspeakers for the son of good friends.
I could find the specs for these drivers: http://www.prescomaudio.com/pagini/beyma/coaxial.html (PDF file)

...but could find nothing about an enclosure which could match. I don't want a big extension in the bass (I know these drivers can't go down too much) but If using them in, say a Bass reflex or TQWT box, they can win a little bit down (50hz or so) it will be perfect!

Somebody told me the BR box we can find on the Fostex site for the 206E should work well with the Beyma:
http://www.fostexinternational.com/d...ec_enc_1.shtml (see at the right bottom of the page in PDF)

What do you think? Has anybody already built something with these speakers? Any design to suggest? any idea?

Please, note that I have got the crossovers specially made by Beyma for these drivers:
http://www.usspeaker.com/beyma%20FD2XC1-1.htm

Thanks for your kind advices.
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Old 14th July 2008, 07:18 PM   #2
BHTX is offline BHTX  United States
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A simple vented enclosure as small as 15-16 liters tuned to Fs (75 Hz) will give you a QB3 alignment, -3dB at about 75 Hz. Just to get an idea.. if using a non-flared port tube, a 6.3 cm port or smaller would need to be used if pushing the 1st port resonance anywhere above the crossover point (2.2 KHz) was desired. With a port tube with two free ends 6.3 cm wide by 7.33 cm long (15 liters @ 75 Hz), 1st port resonance would be around 2344 Hz. In this alignment, the Xmax of 5mm would be reached at 40 Hz with just 20w input if no highpass crossover is used. Up to 10w of input without a highpass crossover should keep excursion below Xmax all the way down to like 5 Hz. With 10 watts to the above system, air velocity within the port should reach a peak of just over 12 meters/sec at 65 Hz. With 20 watts, a peak of about 17.5 meters/sec at 65 Hz. With 20 watts, expect up to around 107-108 dB at 1 meter. With 10 watts, expect about 104-105 dB at 1 meter. This can all be changed by using different port sizes/tunings/slightly larger cabinet volume. Regardless, don't expect much usable output below Fs (75 Hz).

In a horn or TL, I would expect a slightly lower cutoff, and perhaps a bit more power handling. However, I'm not so sure that usable output down to 50 Hz with reasonable power handling is possible.
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Old 15th July 2008, 04:47 AM   #3
GM is offline GM  United States
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Greets!

Here's an MLTL I did several years ago, but AFAIK he never got back to me, so I assume he didn't build it:

L = ~56.16"
w x d = ~68.38"^2
zdriver = ~19.26" down from the top
rp = 2" (4" diameter)
Lp = 5"

All dims inside and approximate and due to the ~high Qts and technically a too small Vb/short a pipe for the desired ~32 Hz Fb (to get the driver down to around seated ear height) you will probably need quite a wad of stuffing at the very top of it, with the usual minimal amount to cover one wall and back down to below the driver.

GM
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File Type: gif beyma 8bx 32 hz ml-tl.gif (6.8 KB, 467 views)
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Old 15th July 2008, 05:04 AM   #4
GM is offline GM  United States
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Here's an ML-horn I did at the same time, but again, no one built it AFAIK:

L = ~73.32"
w x d top = ~34.1"^2
w x d bottom = ~136.4"^2
zdriver = ~36.66" down from the top
rp = 2" (4" diameter)
Lp = 3"

GM
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File Type: jpg beyma 8bx 32 hz ml- horn.jpg (27.1 KB, 458 views)
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Old 26th July 2008, 01:21 PM   #5
Nicodimdom is offline Nicodimdom  France
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BHTX & GM, I thank you very much for your replies. I am sorry but I had no computer at hand to post for the last weeks.

As I can see, you'r real professionnels!
Well, since I'm not, I'm not sure I could understand everything but at least, I understand that
- a small ported enclosure (16-18 liters) would be the best .
- It's not reasonable to expect more than around 62hz down (at -3 or -6 db) depending the port(s).

- I must forget the Fostex BR design I mentionned.

Am I right?

Once again, thanks a lot.
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Old 26th July 2008, 07:57 PM   #6
Nicodimdom is offline Nicodimdom  France
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GM,
a horn design would be too big for my friend's room.

About the Transmission line you mentionned (your own design), could you explain more simply what you said:

"Here's an MLTL I did several years ago, but AFAIK he never got back to me, so I assume he didn't build it:

L = ~56.16"
w x d = ~68.38"^2
zdriver = ~19.26" down from the top
rp = 2" (4" diameter)
Lp = 5""

what is rp, lp and what is this mesure: 68.38"^2 ?

Could you tell your dimensions in metric system?
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Old 28th July 2008, 10:15 PM   #7
Nicodimdom is offline Nicodimdom  France
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Well GM, I read again your message and it looks clearer by now. I think I understand all your rp and Lp...

Only the ^ is still a bit strange ;-)

Dom
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Old 29th July 2008, 12:48 AM   #8
GM is offline GM  United States
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Greets!

rp = port inside radius

Lp = port length

~ = approximate, so use the nearest fraction or cm or mm

^ = raised to a power, so ~68.38"^2 = approximately 68.38 square inches and divide your desired width into it to get the depth.

Here's a great little conversion program I use: http://joshmadison.com/article/convert-for-windows/

GM
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Old 29th July 2008, 09:05 AM   #9
Nicodimdom is offline Nicodimdom  France
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OK. Everything's clear.

Dom
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Old 24th March 2017, 03:53 PM   #10
arcgotic is offline arcgotic  Romania
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Reviving an old thread..

Anybody built recommended enclosures by GM?
I would like to experiment with this coaxial.

Or if anyone can share his experience with it, please.
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