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Offline Martin Colloms  
#1 Posted : 06 June 2010 18:14:37(UTC)
Martin Colloms


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we are thinking of giving away a custom design for a low group delay sealed box stand mount , at wall boundary , speaker

something like the performance profile of the old Linn Sara but with a top notch power response

but with the linear phase flat profile , balanced mode radiator unit for mid treble, plus a modern high power long throw 7inch for the bass

also on the cards is partial baffle step correction . It should time well...............!

A straw poll might help decide whether we embark on it..................


MartinC
Offline ashleym  
#2 Posted : 06 June 2010 19:58:09(UTC)
ashleym


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Hand. Bite. Off.

I would find it helpful if you could work with someone like Wilsmlow to provide a flat pack cabinet. I mention them because I know they already do and that making an accurate sized and cut out cabinet is beyond what I can achieve. (note to self, get router compass and improve woodworking skills). I would also like the potential to supersize- get some real bass out of it.

However what you describe sounds like the perfect step up from my ES14s. Try an 8', go on, jut a bit more bass........!!!
Offline darkmatter  
#3 Posted : 06 June 2010 21:18:56(UTC)
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Martin Colloms wrote:
we are thinking of giving away a custom design for a low group delay sealed box stand mount , at wall boundary , speaker

something like the performance profile of the old Linn Sara but with a top notch power response

but with the linear phase flat profile , balanced mode radiator unit for mid treble, plus a modern high power long throw 7inch for the bass

also on the cards is partial baffle step correction . It should time well...............!

A straw poll might help decide whether we embark on it..................


MartinC


I for one would be prepared to build either /both design(s); have need to get building again as I always think too big with any ideas that I come up with BigGrin

Drool Drool

Edited by user 06 June 2010 21:19:50(UTC)  | Reason: Not specified

Offline mat  
#4 Posted : 07 June 2010 09:56:59(UTC)
mat


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Is the BMR readily available for people wishing to build the design?

With the 7 (or ashley's 8") in the bass, stuffed against a wall, off the shelf woofer in a (small?) sealed box, the alignment may be tricky. Can't ask people to tweak the BL, so you may have to add mass to drag the boundary boosted level down at 150-250Hz. Even a big series inductor won't touch it and might make it worse, other option is large passive notch filter, but it will drag power out of the upper bass.

Getting the bass-mid alignment right will make or break the speaker before BMR kicks in, it's the difference between a big realistic sound and a congested boxy mess.

Sounds like a fun project!
Offline ashleym  
#5 Posted : 07 June 2010 10:59:04(UTC)
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Thanks for the compliment but 8" is what I want rather than what I've got............

(sorry all)
Offline ashleym  
#6 Posted : 07 June 2010 13:37:13(UTC)
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Mat- if you are using the BMR to cover mid and treble you will gain freedom in the type of bass driver, surely there would be some room for the correct BL etc if the driver only has to cover bass? AudioTechnology do a range where you can spec the magnet and coil length, could there be a group buy?
Offline mat  
#7 Posted : 07 June 2010 15:37:15(UTC)
mat


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ashleym wrote:
Mat- if you are using the BMR to cover mid and treble you will gain freedom in the type of bass driver, surely there would be some room for the correct BL etc if the driver only has to cover bass? AudioTechnology do a range where you can spec the magnet and coil length, could there be a group buy?


A custom spec would be perfect!

The bass-mid alignment for a given room position is based on box size and the T-S parameters for the woofer, and can be influenced but not fixed by the lead inductor.

If you have too much BL then the balance between low bass and low mid will be wrong, too much 100-300Hz which mask the 50-100Hz and so the speaker won't play a bass line. This is usually the case when a woofer is too big for the box. One of the difficulties with near wall speakers is that anything below about 600Hz gets a great big boost, anything below 200Hz will get even more of a boost depending on room acoustics, in free space you can move the speaker to correct minor imbalances, against a wall your options are limited and unless you get that in-box peak right then you can't rescue it.

With BMR run from say 300Hz you can adjust the midrange to balance with the 100-300Hz level but it will be too loud for the bass and you won't hear the deep notes. On the other hand if you balance your BMR to the bass level, then the extra 100-300Hz will make the speaker sound boxy.

Using a notch filter to crush the in box resonance allows you to precisely tune the alignment but it is heavy handed and will chuck away around 2dB of useful upper bass output.

Now if your box is large than about 30L then your bang in the territory for decent sensitivity and easy, natural alignment. If you are making a compact, then its a lot harder and you need to be prepared to fake it!

Mass loading the bass driver is an answer, but you need to make sure it won't fly off or break the woofer.

lots to consider.....................
Offline ashleym  
#8 Posted : 09 June 2010 13:05:36(UTC)
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Looking quiet.

Whatever the outcome I feel there could be mileage in documenting the design process to give "amateur" designers an insight into the detail of thought required. I am sure we have plenty of ideas but because of the woodwork and cost of drivers these remain ideas.

I will be interested to see which BMR driver is proposed. I mulled over using the small electrostatic panels from Final in Holland as the mid/top for a speaker. That got as far as most do and now it looks like the company has closed down.

Mat, once again thanks. Is a solution to roll both drivers, say a gentle HPF at 800Hz and a LPF at 150Hz, to tame any misbalance or is this more of a boom/resonance that takes more to be controlled? A good case for some Philips MFB's
Offline mat  
#9 Posted : 09 June 2010 15:49:06(UTC)
mat


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Hi Ashley,

Yes sometimes with a little bit of tweaking, and a big piece of luck you can find a solution to any problem! A soft rolling of the two drivers may be an option.

Either way I agree that Martin's description of the design process should be both fascinating and instructive.

mat.
Offline ashleym  
#10 Posted : 09 June 2010 16:18:21(UTC)
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Here are the MFB controls

http://www.mfbfreaks.nl/images/mfb/545/545_2.jpg

Here's a photo of the whole speaker for those who dont remember

http://www.mfbfreaks.nl/images/mfb/545/545_8.jpg
Offline markus sauer  
#11 Posted : 24 June 2010 18:24:30(UTC)
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Martin Colloms wrote:


A straw poll might help decide whether we embark on it..................


MartinC


Yes please.
Offline darkmatter  
#12 Posted : 25 June 2010 11:16:51(UTC)
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Go for it Smile
Offline Shuggie  
#13 Posted : 27 June 2010 09:42:05(UTC)
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What a great idea - please go for it. I do like the idea of a speaker that is properly designed to be used where most people are forced to place them (at least in little UK living rooms).
Offline ashleym  
#14 Posted : 06 July 2010 21:44:46(UTC)
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Another custom/OEM company for "our" speakers.....

http://www.a-t-e.de/
Offline mat  
#15 Posted : 07 July 2010 09:14:34(UTC)
mat


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Not a bad frequency response. I can't recall ever seeing a better one. I actually prefer the 6" to the 4", because there's is no 400Hz edge mode.
Offline ReneZ  
#16 Posted : 10 July 2010 09:33:45(UTC)
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Martin, which kidney do you want; left or right?? Eh, YES PLEASE!!

Cheers, Rene

PS Maybe Matt and Asleym can open a separate post Cool
Offline Martin Colloms  
#17 Posted : 21 July 2010 10:39:22(UTC)
Martin Colloms


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Slow start but we are making progress on permissions for the exclusive BMR mid treble, and a commercial supplier of kits.

We need to get closer to a retail 2 off price for the BMR which will then set the budget for an optimal bass driver.

We are now thinking for this wall location, a fairly compact tower or pillar floor stander so we can control the height and floor coupling, and avoid variations due to different stands.

It will be close to linear phase with low group delay using a critically tuned sealed box alignment.

The BMR is not very sensitive so we can trade bass efficiency for low frequency extension.

We think wall coupled 85 to 86dB/W 6 ohms , smooth electrical loading , -6dB at 37Hz 45 to 20kHz +,- 3dB 120W program power capacity

probably 90 cm tall on floor couplers, and guessing now, 25cm wide, 15cm deep.

Prototyping is still several months away.................

MartinC
Offline mat  
#18 Posted : 22 July 2010 16:32:33(UTC)
mat


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How will you deal with near wall placement flattening the soundstage and robbing spaciousness?

Offline Martin Colloms  
#19 Posted : 23 July 2010 08:49:36(UTC)
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Good question, it is all a matter of perception..........

It takes a little while but if the speaker is any good , and has transparency, the ear/brain learns the boundary acoustics, and magically depth and spaciousness return to one's perception.

No it is not quite the same as free space speaker location but very good, consistent and predictable results are obtainable.

MartinC

Offline ashleym  
#20 Posted : 23 July 2010 08:58:15(UTC)
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Or with the BMR dispersion pattern do we end up with the aspeakers set wider than usual and toed in a few degrees?
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