Has anyone built and M&K Style subwoofer?

[DaveFred]

I was wondering if anyone has built an M&K style subwoofer or has any experience with this design,

[philthien]

I don’t remember seeing any posted.

Does something about the design appeal to you?

[DaveFred]

Does something about the design appeal to you?

It's different, I am different, I like different.

I would like a front and down firing sub, I thought this might be a neat way to do it.

(Why I want and front and down firing, again, not sure, just because...)

[kenrhodes]

This is just a form of isobaric subwoofer often referred to as a push pull. I would recommend building 2 subs if you have the space or stick to a normal isobaric like wogg's ISO el-Cheapo. Rooms ahve enough issues with bass without trying to push and pull simultaneously from the same location.

[cooper]

Not an iso. Lower driver fires out the bottom. Just two drivers in the same sealed enclosure, but one reversed, hence the “push pull”.

[billfitzmaurice]

Not an iso. Lower driver fires out the bottom. Just two drivers in the same sealed enclosure, but one reversed, hence the “push pull”.

On the surface that's how it appears. But if you envision the chamber housing the drivers as being much smaller and the chamber housing the port as much larger it's a different story. This is an isobaric bass reflex. It differs from the MK cab in the relative sizes of the chambers.

The bit about it lowering distortion is marketing nonsense. Even if you accept that a standard push-pull arrangement lowers THD, which is itself questionable, this configuration wouldn't, as the output of the lower chamber is acoustically low passed, so it can't cancel out the harmonic content of the forward firing driver.

[wogg]

That lower chamber is not what I would consider vented or acoustically low passing at all. It's just bottom firing. The opening toward the front of the box is large enough that loading effects from that chamber should be minimal. This is really a simple 2 driver sealed box, one driver just happens to be mounted backwards and flipped electrically to be in phase with the other.

The distortion cancelling is likely minimal, if at all, but Bill's got more experince with that than I do. Question... wouldn't some of the distortion cancellation come from the interaction of the two drivers in the common sealed airspace, not just from the acoustic cancellation in the room?

[billfitzmaurice]

It's not bottom firing if there's an actual chamber. Even if the opening was the same size as the cone it would still have an Fb. It would be bottom firing if it was on legs. FWIW at one time all ports were at least as large as the driver Sd, with no ducting, until someone realized that Bernouilli's Principle allowed ports to be smaller than Sd with no ill effect. For example, the Altec A7.
The theory with drivers firing in opposite directions reducing THD is similar to a balanced interconnect input reducing noise via CMRR. Even it was true, which is debatable, to realize that reduction the two drivers have to be on the same baffle, both firing the same direction, closely spaced.

[Chris Roemer]

If Wogg's view is the correct one (and I tend to share it with him), then a pair of UM-10s using a commom sealed/stuffed chamber of 2cf would yield a Qtc in the mid 0.70s w/an F3 in the upper 30s, before any room gain. No excursion issues w/1000w RMS rated power . . . (8 ohm load, though (or 2!)).
About 114dB or so.

[6thplanet]

I kinda did that on my 442 design. It's basically for mechanical driver noise cancellation and it looks cool 😀

[billfitzmaurice]

As with all isobarics the reason for it is size reduction. Two drivers isobaric gives half the Vas of one, with the attendant box size reduction. But as only the area of one cone is exposed to the air displacement limited maximum SPL is the same as with one driver. In short for a size reduction you pay the price for two drivers but only get the output of one. That's fine if space is at a greater premium than money, but not the other way around.

[DaveFred]

As with all isobarics the reason for it is size reduction. Two drivers isobaric gives half the Vas of one, with the attendant box size reduction. But as only the area of one cone is exposed to the air displacement limited maximum SPL is the same as with one driver. In short for a size reduction you pay the price for two drivers but only get the output of one. That's fine if space is at a greater premium than money, but not the other way around.

The M&K is not an isobaric. An isobaric has one speaker totally inside the sealed space to double the motor and half the VAS. The M&K is has one face of each driver outside the sealed space to be a dual driver system.

[billfitzmaurice]

It will not act as a dual driver system, to do that both sides of both cones would have to be in play. They're not. The only thing that makes the M&K appear to be a push-pull is the very large plenum, what they refer to as a sealed enclosure, that the rear waves of the two drivers fire into. If that plenum was of the usually seen small size and the vented chamber of the usually seen large size there'd be no debate, being so obvious what it is.

[wogg]

It will not act as a dual driver system, to do that both sides of both cones would have to be in play. They're not. The only thing that makes the M&K appear to be a push-pull is the very large plenum, what they refer to as a sealed enclosure, that the rear waves of the two drivers fire into. If that plenum was of the usually seen small size and the vented chamber of the usually seen large size there'd be no debate, being so obvious what it is.

I'm sure it behaves like a dual driver system, does this picture help?



I believe you're right about that size of the lower down-firing portion with it's limited front output "hole" would have some sort of effect on the output from that driver, but I don't think it would be in the sub pass band so much and this is effectively a dual driver system.

[billfitzmaurice]

Count the number of cone surfaces that fire through the baffle, and the number of cone surfaces that fire into the vented chamber. If it operated as a dual driver system each of those numbers would be two.