If I was to build a subwoofer like this, with the 2 drivers facing each other and wired in phase, what would be the effects? Would I be getting cancellation, or would I just be getting an increase in SPL due to the 2 drivers?
Yes, it would be big, but it's just a head exercise at the moment...
Yes, it would be big, but it's just a head exercise at the moment...
Attachments
2 X 18" Selenium
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Drivers are not push-pull, they are wired in Phase
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Active powered by 4kW Class-H Mosfet Amp
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Cloth Ears said:
That is all wrong. If you want to cancel the even order distortions due to DuMax non-linearity than you must reverse mount one of the woofers. You must also reverse the polarity on one woofer too. The only thing you are doing in a clamshell configuration is doubling Sd and halving excursion. See below graphic how to do push-pull correctly. I’ve done this with direct radiators and with horns. The difference between your example and what I do is very audible.
planet10 said:
Clever idea and design. I hope you won't patent it hehe !
You cancel even and odd distortion, single driver sized box... only problem is the maintenance... some concept of removable baffle would need to be done, the huge power requirement and quadruple drivers pricing.
This could be a good concept for a top-of-the-line subwoofer which need to meet a certain size limit, where price is a non-issue but WAF is.
Re: Re: Opposed drivers
Having talked to a number of driver designers, and done a number of experiments, the gain from push-pull drivers (even mounted push-push) is not as good as the tighter coupling you get by mounting magnets near one another. Having the woofer magnet hang out injects all sorts of noise into the outside world (especially if it has a vented pole-piece) and has low WAF. If one pays attention to the details it does work.
http://www.t-linespeakers.org/projects/steve/index.html
Also one has to consider the audibility of the distortion cancelled in light of Geddes ground breaking work on how little importance distortion in on loudspeaker sonic quality.
One would also question reducing 2nd order below 3rd order.
The push-pull-push-push quad of drivers in the torus sub deals with all the issues except spider noise.
dave
JLH said:
Having talked to a number of driver designers, and done a number of experiments, the gain from push-pull drivers (even mounted push-push) is not as good as the tighter coupling you get by mounting magnets near one another. Having the woofer magnet hang out injects all sorts of noise into the outside world (especially if it has a vented pole-piece) and has low WAF. If one pays attention to the details it does work.
http://www.t-linespeakers.org/projects/steve/index.html
Also one has to consider the audibility of the distortion cancelled in light of Geddes ground breaking work on how little importance distortion in on loudspeaker sonic quality.
One would also question reducing 2nd order below 3rd order.
The push-pull-push-push quad of drivers in the torus sub deals with all the issues except spider noise.
dave
simon5 said:
Access to the inside is critical, still a bit of a stumbling block in terms of churning one out.
Power requirements don't go up -- you get 3 dB more efficiency (@ 8 ohms) than a single driver.
(i'm sitting on a pile of 20-some suitable Foster 12" woofers, so using more woofers is actually a plus)
dave
planet10 said:
Well, if I calculate correctly... by going isobaric, with two drivers, you lose 3 dB efficiency. You have two pairs, so you gain 3 dB efficiency.
Impedance is a non-issue since you end up with the same impedance.
You just end at the same point, if I calculate correctly !
But then, you quadrupled power handling...
Show it to us if you build it !
Dave, Simon, JLH and Workhorse - thanks for your responses.
JLH - sorry if you misunderstood, but I was meaning cancellation from the 2 waves from the drivers hitting each other and cancelling out - not even order distortion cancellation. It's only a bottom octave subby which i don't even need in my current (small) room.
The reason for the torus shape, and the opposed drivers, is to protect the drivers, yet get a stable platform (like the Apex Jr box). I remember a small Mirage sub that you could put a glass of water on, and even at high volumes (for a 2x6" subby) there was very little ripple effect. As I'd want to use it as a TV stand, having the drivers mounted in a push-push, rather than a push-pull configuration is what I'm looking for.
I've only got 2 drivers left (from the original Lambda stock I bought) so I might settle for the design attached. It will save having to put any holes in the box for the wires, as it can all be done externally. But I don't think it's necessary to go the isobarik way - and it would require to work out how to be able to remove them. This way I'd just have to unscrew the bolts and slide each driver out. The only hassle with this way is supporting the magnet structure, which I like to do on all big drivers. If I went this way, rather than the magnets being internal, then I'd have to put the supports in after I'd mounted the drivers - a simple bolt-on structure, maybe.
Workhorse, nice! I've got 2x15" and an old EP2500 amp. I probably won't be getting the chest thump, though, as I'd be crossing lower than that (40-50Hz)...
A lotta responses while I was asleep, thanks everyone.
JLH - sorry if you misunderstood, but I was meaning cancellation from the 2 waves from the drivers hitting each other and cancelling out - not even order distortion cancellation. It's only a bottom octave subby which i don't even need in my current (small) room.
The reason for the torus shape, and the opposed drivers, is to protect the drivers, yet get a stable platform (like the Apex Jr box). I remember a small Mirage sub that you could put a glass of water on, and even at high volumes (for a 2x6" subby) there was very little ripple effect. As I'd want to use it as a TV stand, having the drivers mounted in a push-push, rather than a push-pull configuration is what I'm looking for.
I've only got 2 drivers left (from the original Lambda stock I bought) so I might settle for the design attached. It will save having to put any holes in the box for the wires, as it can all be done externally. But I don't think it's necessary to go the isobarik way - and it would require to work out how to be able to remove them. This way I'd just have to unscrew the bolts and slide each driver out. The only hassle with this way is supporting the magnet structure, which I like to do on all big drivers. If I went this way, rather than the magnets being internal, then I'd have to put the supports in after I'd mounted the drivers - a simple bolt-on structure, maybe.
Workhorse, nice! I've got 2x15" and an old EP2500 amp. I probably won't be getting the chest thump, though, as I'd be crossing lower than that (40-50Hz)...
A lotta responses while I was asleep, thanks everyone.
Attachments
You do indeed lose efficiency going isobaric, 3dB to be precise. Your sensitivity is what does not change (with 1 pair wired in parallel). With 2 pairs wired series-parallel, your efficiency and sensitivity will be the same as a single driver.
I was toying with the idea of something similar to post 18 but wedging a piece of PVC pipe drilled with holes (like Swiss cheese) between the magnets. The contact of the drivers would further help couple the opposing forces.
With the drivers mounted on the inside of the baffle the pipe would help push them firmly on the baffle.
With the drivers mounted on the inside of the baffle the pipe would help push them firmly on the baffle.
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