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GBOGH 20th August 2019 06:19 AM

Multiple stacked dipole bass
 
1 Attachment(s)
Hi all , just wondering if anyone has knowledge on this. A stacked set of dipole woofers facing the listener without the front or back blank so that the woofer cones are visible. Closest pic i can find is linked ( I hope.)
Kind of like legacy audio but with 4 or 6 woofers per side.
I have seen them in vertical towers like the sureal sound 5th row speaker, page 85 of the ultime open baffle gallery, but never horizontal.

mattstat 20th August 2019 04:51 PM

You sure it's not an incomplete variation of the same thing you are describing in the vertical array examples? Vertical or horizontal doesn't really matter if it's a subwoofer.

You normally see alternating plates at the front and back between woofers, and a solid top plate matching the bottom plate of your image.

A couple examples of typical stacked arrays:

Alternate drivers 3

Gainphile: Dipole Bass Array

If you're referring to the Legacy Whisper, that one is open to the front, back, and sides. They say they are are trying to control dispersion with that layout.

Project Whisper | An Engineers Perspective | Legacy Audio - Building the World's Finest Audio Systems
"The low frequency drivers operate in phase with each other and combine acoustically as a pair of figure- of-eights, one behind the other. The result: a compound null formed at the sides of the enclosure, which minimizes resonances and room reflections."

GBOGH 20th August 2019 10:44 PM

Thanks for answering mattstat,
The image was from a PE build thread and as you suspected incomplete. The end product was vertical. The image was the only thing i could find similar to i was thinking of building.
I have a massive gap in my knowledge compared to others on this site and was wondering if there was any advantage to this idea of stacking drivers behind each other for lower mid bass reproduction in IB or dipole configuration.
I have 4 18s i was going to clamshell out of phase for lowest frquencys and position where best in room separate to main towers.
This will be my first build and i am planning active 4 way IB but willing to hybrid any part for best result.
My room is quit large 85m2 so im not shy about size of speakers.
Another question is if stacking 10s or 12s in an equal number is beneficial, would different types of drivers behind each other be bad? Eg ae drivers first followed by cheeper mcm.

Different sizes behind each other same or different brand be bad eg 10,12,12,10.?

Would rear firing the last driver in the stack be beneficial?

Please anyone who knows answers to any or all questions feel free to school me.

Davey 21st August 2019 12:30 AM

1 Attachment(s)
Completed version of the unit in question.

Dave.

mattstat 21st August 2019 02:11 AM

For midbass, you'll need to watch cavity resonances, depending on how far up in frequency you are going and how your baffle is designed. Some info here:

http://www.linkwitzlab.com/frontiers.htm#L

The "spl_max1" spreadsheet on this page is worth messing around with also. It gives you some idea of the volume displacement required to make X output at Y frequency. These are just basic numbers though, not baffle modeling. It's an easy way to see rough numbers.

http://www.linkwitzlab.com/publications.htm

If you don't need extra drivers and a complex baffle to give the SPL you want, I wouldn't use them, especially at higher frequencies. A flat baffle is easiest to implement, but typically gets large for low bass frequencies and the number of drivers required.

In addition to allowing for a compact array, drivers are stacked and driven out of phase to decrease distortion inherent in the driver. If you stack different sizes or different models, you'll lose that benefit.

Juhazi 21st August 2019 07:04 PM

I wonder what was the objective of that construction - enormous spl capacity? Even 2x12" dipole can give good bass at home, because we are not very sensititve to distortion in bass freq.

adason 21st August 2019 08:42 PM

How to squeeze as many woofers in the smallest enclosure possible...

SoundRight 23rd August 2019 08:21 AM

Stacked dipole bass
 
Yes, why not.

At low frequencies, no problem, but the 1/2 & 1/4 wavelength lobing rules stay the same depending on driver vertical spacing.

There is a solution to lobing at higher frequencies and this is to triple stack...not double stack. Attenuate the top and bottom cabinet by 3-6dB each and apply a delay between around .2ms to .6ms to the middle cabinet. 15" drivers with 1.5ft vertical centres (1.5ft baffles) may be used up to a max of around 600Hz with this method.

You have created a constant beamwidth design!

The smaller delay will provide narrower vertical dispersion...so now by adjusting the delay you can control the vertical pattern. Brilliant!!

GBOGH 23rd August 2019 11:57 PM

Thanks soundright,
Now we are getting some where, would i therefore need separate dsp control over every woofer in horizontal stack to give the appropriate time delay as you suggested?
I was looking at various ohm resistors for shading drivers elsewhere and presume they would work to knock 3 or 6 db in the stack of subs, but is there a passive way to tjme delay?
Also any thoughts on mixing bass driver in the stacked array?

SoundRight 24th August 2019 12:59 AM

There are two ways to achieve this. One is dsp, but use it on all channels because you need to keep the latency the same so the small delay to the middle cabinet is relative to the others.

The other method is to offset the middle cabinet drivers so they are physically displaced behind the others. Around 6" will provide an equivalent delay but not adjustable of course. L pad resistors may be used to reduce the output of the other cabinets to provide the -3 to 6dB attenuation...

This would enable you to use an analogue active crossover instead of a digital solution? Make sure of course the amps are seeing a sensible impedance! Top and bottom cabinets could be series/parallel connected to match the sensitivity of the middle cabinet before they are attenuated?

Hope that all makes sense!!


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