Dual Sealed 12" Build with facing Drivers

[scottandmo]

I have 2 Meniscus 1284 Drivers, supposedly same as ACI SV12, 2 SA240 Amps with only a single 6 cu ft max area due to WAF. I thought about building the subwoofer I have attached which would be about 5 cu ft before amp and drivers if my calculations are correct, inspired by the beolab 11 Flower subwoofer that just came out. I plan to wire them in series (total of 8 ohm) out of phase and only use one amp.

My question is how wide should the middle gap be? I also don't know if this classifies as isobarik or push-pull or push-push or something else. It is a single sealed enclosure with two powered woofers. Is this a stupid build? My other option is build a more traditional isobarik/push pull or a single sealed/ported woofer and sell the leftover equipment, but I'd like to make the most of what I have. Thanks in advance for any help/suggestions.

[Dr.EM]

I think it'd work but you'd have to wire them in phase. You'd achieve what I think is termed push-push, but the advantage anyhow is minimal enclosure inertia (vibration which can travel to the enclosure panels and floor, etc) due to equal forces acting in each direction.

A smaller gap might lower the drivers effective fs. I am unsure how to simulate this, but you could run some experiments and measure the driver parameters in different gap sizes. Lowering the fs should result in lower effeciency but also a lower F3 point, a sealed enclosure is at least quite flexible about exact sizing.

For maximal vibration cancelling you must couple the drivers together tightly. I'd use threaded rod to join them both at their basket mounting points with a design like this, but joining at the magnets is better.

Another point you may consider is mounting one driver backwards, with the magnet in that gap. In this case you do wire them out of phase, but you gain the advantage of cancellation of motor non-linearity

[WithTarragon]

There is a variation on this known as a "slot loaded push pull". Do a search and see if it has merit in your situation.

[GM]

Hmm, looks like a hybrid 8th order BP to me, so drivers should be wired in acoustic phase and unless AkAbak can model it, finding the various chamber net Vbs, tunings will have to be found empirically. The main question now is how much time can you afford to spend either learning AkAbak and/or developing such a 'beast' through experimentation?

GM

[scottandmo]

I don't have the tools to measure the driver parameters, although I thought about getting a cheap spl meter, but I don't really have to the time to experiment outside winisd. Currently the drivers would be 3" apart. Is that something you would consider a smaller gap, Dr EM? "Lowering the fs should result in lower effeciency but also a lower F3" sounds good to me.

This will be my first build and probably only one. My only concern is that the driver orientation will cause major cancellations. I wasn't planning on porting since slot loading or 8th order BP seems like it would be hard to configure into a small box like this. Seems wiser to go with a single driver if I did a ported or slotted design. I figure if someone screams FAIL regarding my current design then i'd look at something like the MX-125 MKII.

[jerryo]

Looks similar to a "Ripole" loading but isn't quite.
As it is, the loading on the rear of each driver will be different so might cause issues.
A Ripole design might be worth a look at as an alternative especially as the loading for each driver is the same.

[Dr.EM]

What I'd do is turn one driver round, so in the gap you have one driver magnet and one cone. You'll need to wire one out of phase in this configuration. To accommodate this you'll need to increase the gap size and hence it should have minimal effect then. Couple the drivers together with threaded rods through the mounting points.

Doing this you reduce motor non-linearity distortion and minimise vibrations. Be sure your drivers have a quiet motor (no chuffing noise from any pole vents) by running them to excursion free air with test tones and listening. I'd keep the box sealed personally. Should be a nice clean sounding sub

[scottandmo]

Last question, what if I put both amps in there? It'd go from 85 watts RMS per driver @ 8 ohm to 240 watts RMS per driver @ 4 ohm, so almost triple the power, plus having independent controls for each driver. Any drawbacks besides weight and power consumption, such as being slightly out of phase or something?