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Old 2nd July 2009, 07:31 PM   #1
taotao is online now taotao  Germany
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Default bigger backchamber for bms 4550...?

Hello,

wonder what happens, if you open a bms 4550 and provide a larger backchamber.
Will it enable a lower x-over point than stock.
I even don't know, if it's posssible to open the backside (judging by view, I suppose it is).

I'll receive mine the next days, I'll use it with a fostex fe168esigma (in d37 enclosure).
I ordered also a tractix horn, with hornmouth diametre of 29 cm.
Producer claims its lower frequency as 400 Hz.
I would like to crossover it as low as possible, that's reason I ask 'bout the backchamber of the bms driver.

So just for curiosity: Somebody tried open it and eventually measured the open driver?

Bye
Olaf
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Old 3rd July 2009, 12:46 AM   #2
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Hi, I'm curious, where did you buy your 4550 from? I'm in the market for some
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Old 3rd July 2009, 12:53 AM   #3
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I don't think you can increase the back chamber of the BMS drivers. They don't really have one. They use a ring radiator that fires backwards and wraps around 180 degrees to the exit.
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Old 3rd July 2009, 02:13 AM   #4
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Quote:
Originally posted by fb
Hi, I'm curious, where did you buy your 4550 from? I'm in the market for some
Try US Speaker. They do the 4550 and have always been helpful and efficient when I've dealt with them. Much easier than getting anything out of Jack at (lack of) Assistance Audio.

4550 at US SPeaker
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Old 3rd July 2009, 03:57 AM   #5
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Thanks Brett


Jack at Assistance Audio was initially very helpful, but now that I'm ready to get quotes/buy he's nowhere to be found


www.soundworks-pa-shop.de also have them, awaiting a quote minus VAT


I'll contact US speaker
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Old 3rd July 2009, 04:04 AM   #6
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Quote:
Originally posted by fb
Thanks Brett


Jack at Assistance Audio was initially very helpful, but now that I'm ready to get quotes/buy he's nowhere to be found
After several unanswered emails, I rang one night wanting to buy 6 BMS18" drivers. I was ready then to give CC details, but he never got back to me with a shipping price.


Quote:
Originally posted by fb
www.soundworks-pa-shop.de also have them, awaiting a quote minus VAT


I'll contact US speaker
I'll be interested to see what they come back with as I'm also interested in some BMS 8CN252 drivers.

I've bought from them before. Good service but more expensive than I can usually get from the US, but they have lines many of the US stores don't. Probably being in the EU they can just get them sent on demand.

I'd love a reliable, affordable source of BMS drivers who will ship via Post to save me some money.
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Old 3rd July 2009, 04:50 AM   #7
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Default Re: bigger backchamber for bms 4550...?

Quote:
Originally posted by taotao
Hello,

wonder what happens, if you open a bms 4550 and provide a larger backchamber.
Will it enable a lower x-over point than stock.
I even don't know, if it's posssible to open the backside (judging by view, I suppose it is).

I'll receive mine the next days, I'll use it with a fostex fe168esigma (in d37 enclosure).
I ordered also a tractix horn, with hornmouth diametre of 29 cm.
Producer claims its lower frequency as 400 Hz.
I would like to crossover it as low as possible, that's reason I ask 'bout the backchamber of the bms driver.

So just for curiosity: Somebody tried open it and eventually measured the open driver?

Bye
Olaf

The SPL of any speaker is dictated by the surface area and the xmax. So you could take a speaker with an efficiency of 80db and an xmax of 1mm, and a speaker with an efficiency of 110db and an xmax of 1mm, and their maximum SPL is identical.

So once you realize that, you realize why compression drivers have such tiny chambers. They're severely limited by their suspension.

For the past few weeks I've been working on a unity horn, and I was pleasantly surprised by how effortless the midrange is. I believe this is due to the huge surface diameter of four midranges, versus a compression driver.

Just food for thought.

http://www.diymobileaudio.com/forum/...oundstage.html

So removing the back chamber will have the opposite result - it's actually going to raise your F3, because it will increase your excursion.
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Old 3rd July 2009, 08:50 AM   #8
taotao is online now taotao  Germany
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Hi,

I ordered the drivers here: http://www.musik-service.de/bms-4550...753766de.aspx. It's the cheapest supplier I found in Germany.
Don't know about shipping costs or import taxes.

@Patrick:
Yes, sounds reasonable to me; xmax (and therefore lower frequency) is limited by the suspension, not the backvolume.

In my case, distortions won't be something I'm concerned about.
The drivers will be tamed down in volume a lot (up to 17 dB)
Anyway the fostex will be the limiting factor.
Btw, in my room, fostex plus d37 go down to 40 Hz. Not bad.
I could use them fullrange, but my speakers unfortunately measure completely different. It's some kind of production fault, I guess.
The range starting at 3 kHz up to the top measures like two different speakers. I don't know why, maybe suspension is somehow not equal between both of them, or diferent amount of glue, or......
By using the tractix horn, the fostexes go only up to 800 Hz (24 dB linkwitz), so no problem here (except I loose the "oneness" of a fullrange system :-().
But anyway resolution of mid- and high frequencies will be a lot better.

Bye
Olaf
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Old 3rd July 2009, 09:05 AM   #9
fb is offline fb  Australia
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Join Date: Apr 2005
Location: Brisbane, Aus
Quote:
Originally posted by Brett
I'll be interested to see what they come back with as I'm also interested in some BMS 8CN252 drivers.

I've bought from them before. Good service but more expensive than I can usually get from the US, but they have lines many of the US stores don't. Probably being in the EU they can just get them sent on demand.

I'd love a reliable, affordable source of BMS drivers who will ship via Post to save me some money.

Prompt reply from soundworks, 285 euro for 2x 4550 shipped to my house on the Sunshine Coast. US speaker's shipping estimator quoted $141 US for shipping via USPS, making the total about $30 more expensive. I've sent them an email to question this, as I think it's a bit excessive.


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Old 3rd July 2009, 09:06 AM   #10
fb is offline fb  Australia
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Quote:
Originally posted by taotao
Hi,

I ordered the drivers here: http://www.musik-service.de/bms-4550...753766de.aspx. It's the cheapest supplier I found in Germany.
Don't know about shipping costs or import taxes.


Thanks, I'll check them out too
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