My open baffle dipole with Beyma TPL-150

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Originally Posted by StigErik

It makes me wonder if three 21" or four 18" per side is enough down to 20-25 Hz?

I doubt it.

I once tried 3 18" per side, severely EQ'ed, but the low 20's were not boosted effectively. The RTA readings barely changed when I made huge 20Hz boost on EQ. Some gain on 25Hz can be made. (I didn't use up the excusion of the woofers.)

Dipole bass is not good at pressurizing the room.

[StigErik]

Yes - dipole bass does not pressurize the room like sealed subwoofers. I think that's one of the reasons dipoles sounds so good, and why I would like dipole bass down as low as possible. If that means 25 Hz at best, I'm happy with that.

I do remember that the baffled 21" was much better at 30 Hz than without baffle. With a large enough H-baffle and enough drivers, I hope 25 Hz will be possible? (please? )

Guess I should build a really deep H-frame to check this out to begin with.

[jerome69]

I think you cannot make a deep H frame because you will catch quarter wave resonance. it depends on the crossover frequency ?
If you want the peak 2 octaves above 100Hz (400Hz), the total deep will be 0.42m (16.5")

[StigErik]

I wish to cross over the H-baffle subs around 50 Hz, so they could be rather deep without getting into resonance problems.

[jerome69]

Yes ! If you consider resonance two octave higher (200Hz ) because more easy to suppress the peak, no phase problem 340/(2xdeep) 0.84m (33") total deep.

[StigErik]

Dont think I can make them THAT deep, they have to fit in my room too, with enough free space behind them. Around 50 cm total depth is what I had in mind.

[mige0]

Originally Posted by StigErik

...
The main speaker will then become an array of 15"-8"-5"-AMT-5"-8"-15".
...

Alert by your findings, Cuibono and Stig Erik, I've (re)done some outdoor polar measurements of my 6" and 8" by myself.
Whoow freezing cold in the early dark....

I do have to repeat without the minimalistic baffle to gain confidence but there definitely *is* room for improvement – exactly like you said.
Interestingly (and as I remember) the 6" shows significant worse polar peaks than the 8". (OB being roughly 30cm wide)

I was ready to order these 4" Illuminator ScanSpeak's but the point is, excursion and thus intermodulation would go through the roof – or – bandwidth would be way less than even a single octave when I checked back

http://members.aon.at/kinotechnik/di...distortion.xls

All my design was started to keep IM at or below 1% at 120dB SPL.
No way to get this with such tiny 4" speakers nude.

So, for now I'm a little bit lost – either to skip my IM goal or to live with some polar wiggles in the upper OB department.


Anyway – thanks a lot Stig Erik and Cuibono for pointing this out in full clarity!


Michael

[StigErik]

Here's the design ideas I'm thinking of right now.
Four 18" in H-baffle
The rest hung from the ceiling, or a very tall frame.

[Paul W]

Here's another approach for your dipole woofers. (This is Monte Kay's system.) He uses 24x15" in two towers. Neat thing about this is the force cancellation achieved with opposing driver pairs.




Yet another would be a damped U-frame with heavy wool felt across the back of the U. ~6-12mm of F13 felt should substantially reduce the dipole peak.

[jerome69]

Ok it works for 50cm deep too
Nice design "StigErik" and very sportive to tune the five channels.