Down Firing Passive Radiator

[JRT]

I had been under the impression that because of typically high moving mass, a down firing passive radiator would sag excessively, making it a generally bad idea, unless the dangling static mass was countered/supported in some way that would not excessively damp dynamic motion.

Today I received a weekly clearance specials email from a longtime hifi gear mailorder house. I won't say who. The listing included a discounted demo unit of the REL Acoustics T9i 10_inch 300_Watt powered subwoofer. I have zero interest in buying that, but noticed that the seller describes it as having a down firing 10_inch PR and front firing 10_inch woofer.

To me that seems like a bad idea, but what do I know.

Just thought some might find that unusual variation provocatively interesting.

[billfitzmaurice]

It's probably not as much a concern as with a driver, since there's no voice coil to be adversely offset.

[fpitas]

I would guess you can design a PR to be down firing by pre-loading the cone upwards.

[Chris Roemer]

Even though there's no v.c. to wander off-center, it seems obvious (to me) that any PR could be loaded w/too much mass so that it would begin to lose Xmax/Xmech from the effects of gravity. PE has a calculator to help determine whether a woofer would work well (enough) mounted vertically, one for (loaded) PRs would also be welcome.

AAMOF, I'd really like to see a DATS procedure for determining T/S parms for PRs - it SEEMs like there should be some way to determine them.

[tomzarbo]

Even though there's no v.c. to wander off-center, it seems obvious (to me) that any PR could be loaded w/too much mass so that it would begin to lose Xmax/Xmech from the effects of gravity. PE has a calculator to help determine whether a woofer would work well (enough) mounted vertically, one for (loaded) PRs would also be welcome.

AAMOF, I'd really like to see a DATS procedure for determining T/S parms for PRs - it SEEMs like there should be some way to determine them.

I've thought this myself more than once, they have to be 'testable' somehow or else how does PE come up with the specs for them? The nice Reference Series PR's have in depth specs that are set up for X amount of added washers.

Something like a bass shaker with rigid arms that would press firmly against a driver frame and an extendable center portion that could be adjusted to press onto a PR cone with a blob of insta-tac. Then run a sweep on DATS with different software to model the PR params. I've always wanted to try making my own PR's out of hardware store stuff but knew It wouldn't work very well.

TomZ

[PEB]

It is a bad idea in general to mount any low-F drivers horizontally. Any sag obviously causes a DC offset to the VC rest position, which implies distortion.
The same is true for a PR, because now there is an offset to the rest position of the suspension. Picture a tighter spring in the upward direction and a looser spring in the downward direction. It is worse for PR's simply because of their low resonance. Klippel graphs clearly show these effects.

Mainstream brands have marketed these subs for a long time. They will spin the design as superior from getting the woofer closer to the floor. Buyers may aesthetically like them because of a plainer appearance.