3 x woofer force cancellation

[Dave Zan]

It is classic to use 2 opposed woofers to cancel the reaction forces and reduce excitation of the cabinet.
It occurred to me that it could done with 3 woofers in a delta, which would fit pretty neatly in a corner, one woofer to the front, one to each side and loaded a bit like a corner horn, or a slot load.
Can't have complete cancellation of woofer asymmetries like with push-pull pair but it would be possible to reverse the two side woofers to partially achieve cancellation.
The best modern woofers are very symmetric anyway.

Anyone seen this or tried it?

David

 

[troystg]

Martin Logan Depth subwoofer.

 

[Patrick Bateman]

This might work nicely too.

Only one woofer is out of phase, but that will still reduce 2nd order distortion when wired out-of-phase.

 

[Dave Zan]

...Depth subwoofer.

Thanks, I expected someone else must have already had the idea.
They look pretty nice.

Only one woofer is out of phase, but that will still reduce 2nd order distortion when wired out-of-phase.

Hi John, it seemed the sort of off-beat idea that would appeal to you.

I had in mind to make the box essentially equilateral for optimum force cancellation.
A bonus is nice tapered slots between the box and the wall.
We can use this space for the back of the woofer if we invert these ones instead.
Then the front woofer is conventional- looks better flush, and out of harms way.
A little smoother for less diffraction for the mid frequency driver too.

Best wishes
David

 

[jamesblonde]

The arrangement which Patrick posted could work perfectly if the two perpendicular woofers were attenuated (-3dB should do it) to result in the force vectors adding up to 0.


Or, make life easier and go with an equilateral triangle design

 

[hifijim]

If it were an equilateral triangle, the forces would cancel.

Since it is a 45-45-90 triangle, the forces almost cancel, but not quite. It is still a big improvement versus putting all three on the same baffle.

 

[planet10]

I designed a Martin Logan inspired triple force cancelation box for 3 Peerless 8” i had.

From what i saw of the ML they relied on the external of the cabinet for driver coupling, i would not consider that sufficient.

dave

 

[Dave Zan]

So Martin L. is the only commercial user of the idea?
I expected a few more because it should work pretty well.
Not much demand for triplicated sub-woofers, I suppose.
But I am surprised it hasn't been used for an over-the-top system, say 3 x 18".

David

 

[planet10]

It does not work as well as an even number of drivers where the reactive forces are cancelled ore directly. But if you only have 3 (or 6) woofers, and you can get a decent impedance, then go for it.

I had 4 but 1 died.

dave

 

[Juhazi]

It does not work as well as an even number of drivers where the reactive forces are cancelled ore directly. But if you only have 3 (or 6) woofers, and you can get a decent impedance, then go for it.

I had 4 but 1 died.

dave

How does one connect 3 woofers to get decent impedance? I am seeing those quite often, eg. from Magico.

 

[xrk971]

Three 16ohm in parallel is 5.3ohm - could be reachable by some 8ohm amps but easily handled with 4ohm amp. Or 3 x 2ohm in series is 6ohms which are often used on 8ohm amps.

 

[planet10]

Alldrivers need to be connected iin series or parallel. You either have to have to have a high impedance driver (parallel) or low impedance (series).

16 ohm woofers would give 16/3 = just over 5Ω, 2 ohm woofers would give 3x2 = 6Ω.

With typical 8Ω woofers you will need a good 2Ω amp or 3 smaller amps to driver each speaker directly. I had a similar issue with the 2 4Ω woofers in my push-push subs. I use a 4 x100 into 4Ω amp to drive them.

If you are a big manufacturer like ML, you can just get the drivers you need made for you.

dave

Edit: X said pretty much the same thing.

 

[Juhazi]

So us diyers with hifi units better stay with 1,2 or 4 units!

 

[xrk971]

or 9, 16, 25 work well too if you want to keep same nominal impedance. A series-parallel 25 driver line array is very impressive with sensitivity.

 

[planet10]

For balanced load/reaction force cancelation purposes an even number of woofers is much preferred (and the boxes can be rectangular).

dave

 

[cowanaudio]

So Martin L. is the only commercial user of the idea?
I expected a few more because it should work pretty well.

David

How about the Paradigm SUB 1 and SUB 2 subwoofers?

Or the Persona?

Close enough to three drivers?

 

[planet10]

They are relying totally on the enclosure to provide coupling. Not sufficient AFAIC.

But yes, essentially 2 MLs stacked on top of each other. 2 x 3 would be better than 1 x 6.

dave

 

[Dave Zan]

For balanced load/reaction force cancel[l]ation purposes an even number of woofers is much preferred...

2 or 3 both cancel reaction completely so I see no reason to be stuck on an even number for that reason.
Even does allow for half to be reversed and some asymmetry cancellation but the effect is limited.
3 would fit my space much more neatly, it's just the cost...

How about the...SUB 1 and SUB 2 subwoofers?
...Or the Persona?

Yes, essentially what I had in mind.
So it's not just one manufacturer, thanks.
I was interested to note that these are their top of the line subwoofers.
Where are you in Canberra, if I may ask?

Best wishes
David

 

[planet10]

2 or 3 both cancel reaction completely\

But it is a lot easier to get the structural rigidity needed to make the theory work in the case of an odd number of woofers. It is a metter of practicality.

dave

 

[SpeakerBob]

I've heard the Martin Logan sub it is an excellent subwoofer. I've also heard a Paradigm servo15 sub which to my ears was equally good. I've got a feeling the servo circuitry is much more important than the force cancelling aspect.

However, the next subs I build will me push push just because it makes sense. (they'd be servo subs if I had the money)

Rob.