Push push subwoofer design

[Trdat]

My current subwoofers are a dual subs with the RSS315HO driver in an elongated cabinet around 60 litres, unfortunately it's not braced but it has double thickness for the side walls and front and back. I am considering adding a second subwoofer to the other side of the cabinet and if I am not mistaken it is called a push push subwoofer design. I have DSP so I am not too fussed about the actual internal volume as I can manipulate the extension.

Two questions that come to mind is
1. Is there any chance I can ruin the accuracy and perfect thump I already get from my current subwoofers placed on the front side walls?

2. Does any one have any experience or at least on theory if this is a good idea or a bad one? Do I need to take anything in consideration?

Of course I am not expecting miracles but adding another two 12 inch subwoofers has to increase that thump right?

Below is a picture I found that shows what the upgrade will look like, just to confirm the concept as I am not sure if it is called a push push or dual opposing subwoofer.

 

[ppataki]

I have designed/built several DOS subwoofers
(you can search for my username in the DIY section to see all of them)

I totally love this idea, it kills all the resonances, provides a bigger cone surface area, etc.
I can definitely recommend the approach

 

[Trdat]

Great to hear from someone who has given it a shot. I have generally seen positive commments with in the DIY audio forum and I will also check out your posts in the DIY section of this forum. The only downside is that my amp can only handle 3.2 ohms so I will need a new amp after wiring each cabinet in parallel which will probably bring the impedance closer to 2.5ohms at around 80-90hz.

By the way, I had planned to make it to the Bonus festival in Budapest this year and obviously sight see the city but unfortunately with two kids it was only a dream and didn't eventuate although I had bought the tickets for the event.

 

[ppataki]

Great to hear from someone who has given it a shot. I have generally seen positive commments with in the DIY audio forum and I will also check out your posts in the DIY section of this forum. The only downside is that my amp can only handle 3.2 ohms so I will need a new amp after wiring each cabinet in parallel which will probably bring the impedance closer to 2.5ohms at around 80-90hz.

By the way, I had planned to make it to the Bonus festival in Budapest this year and obviously sight see the city but unfortunately with two kids it was only a dream and didn't eventuate although I had bought the tickets for the event.

Let me know next year

 

[DanielT]

Try this. Costs basically nothing. Cast tube in cardboard. Plop in two drivers at each end. The tube do not need to be braced. Use them as they are.

Make sure to have a steep cut off LP filter of at least 24dB. Any resonances that are pushed up in frequency are then effectively cut off.

Edit:
In the attached picture at the top right corner you see my cardboard tube subwoofer. It consists of two JBL 12 inch bass drivers mounted in a saucer shape at the bottom of the subwoofer, directed downwards. No problems with resonances, from what I can hear.
(messy with various hifi stuff in that picture, but you can see the subwoofer)

 

[bigjacko]

With two drivers on each side we can have two configurations.

First kind is both diaphragm goes out at the same time called dual opposed. Benefit is vibration from driver can be canceled out.

Second kind is one diaphragm in and the other one out called push pull. Benefit is distortion gets lowered because suspension asymmetry is evened out.

 

[Trdat]

With two drivers on each side we can have two configurations.

First kind is both diaphragm goes out at the same time called dual opposed. Benefit is vibration from driver can be canceled out.

Second kind is one diaphragm in and the other one out called push pull. Benefit is distortion gets lowered because suspension asymmetry is evened out.

I think I will opt for the dual opposed.

 

[DVDdoug]

Check your proposed modifications with speaker design software. I've used WinISD (FREE).

With two drivers, each driver gets half the box volume. The "tuning" and cut-off frequency will go-up (it's going to sound like a smaller box) and a ported box could get really fouled up! With a sealed box you can EQ it to work better than a single driver. Without EQ it will probably have less bass... certainly less deep-bass.

 

[Trdat]

Check your proposed modifications with speaker design software. I've used WinISD (FREE).

With two drivers, each driver gets half the box volume. The "tuning" and cut-off frequency will go-up (it's going to sound like a smaller box) and a ported box could get really fouled up! With a sealed box you can EQ it to work better than a single driver. Without EQ it will probably have less bass... certainly less deep-bass.

I have Eq so not a problem.

I will be using DSP to manipulate the tuning frequency. My understanding thanks to this forum is that DSP essentially changes the effect the cabinet has on Fs which is not rocket science i know and have designed the cabinet volume double the size anyway so it should be fine. I just hope I don't loose any transients from the smaller cabinet but again it seems that once I DSP the extension flat to 30hz then my transients will be connected to that specific roll off from the DSP rather than the roll off from the cabinet size produces. Perhaps the cabinet might have some effect but mild. This is my interpretation after many threads.

And yes it is tightly sealed.

 

[gnarly]

Dual opposed works .... Cabinent vibration decreases greatly, and ime requires less internal bracing.
It's interesting and telling imo, that both Genelec's latest and greatest, and the Danley Hyperion use dual opposed.

I've tried both push-push (clamshell), and push-pull, that supposedly reduces distortion. I found there was no significant difference in distortion, using 18n862's.
I think maybe push-pull helped older drivers with issues, but modern ones probably don't benefit much if any.

 

[Wolf]

Clamshell is a mounting method equated with face to face driver arrangements, is usually used in isobaric arrangements, and is not likely what has been done here. Drivers on opposed sides with magnets exposed and cones inside is- inverted dual opposed.

I find "push push" to not be descriptive enough of an arrangement, as it also describes adjacent drivers on a baffle forward firing. It just does not portray the image of the arrangement properly by the description alone. Magnets inside, cones firing out, one on each end is like that of an engine- dual opposed.

Don't confuse the orientation of the drivers without respect to the box volume. Push-pull is cone out 'pushing from' for one driver, and magnet out 'pulling from' for the other. They do not have to be opposed.

I think the OP's idea is a great idea since he has EQ. 4x RSS315 will do very well to excite every room resonance he has.

 

[gnarly]

Good points Wolf. There's a ton of confusion with opposed driver terminology. Best to be as completely descriptive as possible.

I should have said my "push-push" or "push-pull" subwoofer is slot loaded design,
with both cones moving towards each other, towards the center of the slot, whether the cones are facing each other (push-push), or with one cone facing the other driver's motor (push-pull).

 

[DVDdoug]

My understanding thanks to this forum is that DSP essentially changes the effect the cabinet has on Fs which is not rocket science

DSP/EQ should work fine with a closed/sealed box. You might not be able to "repair" a ported box with EQ. And of course it takes more amplifier power to re-boost those lower frequencies. Or with boosted-power you could burn-out the woofer(s). Like everything else, there are trade-offs.

I don't loose any transients from the smaller...

Transients aren't usually a problem in a woofer/subwoofer. Transients are "fast" (higher-frequency). Maybe it's a problem with a poorly-tuned one-note "boomy" speaker.