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

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

Thanks for the compliment but 8" is what I want rather than what I've got............

(sorry all)

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.....................

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.

Yes please.

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).

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.

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

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