[fdandrews]

I apologize in advance for this long and somewhat rambling post. I had too much coffee this morning. I have been using the same test boxes in various OB configurations for several years. They have all had Fostex 166EN full range drivers mounted on top for mids/highs.  First, I had a pair of MCM 21" woofers in U-frames with a 24"x24" face and 18" depth. On the advice of MJK, I shortened the depth to 7" and they did indeed work much better. But the woofers needed boost at the low end and the x-max was so small that one of the woofers bottomed out regularly.Then I tried Alpha 15s in the boxes, with a filler baffle to cover the hole for the 21" woofers. Good, didn't need bass boost. Then I tried a baffle with a 6" diameter round hole over the 21" woofers to give them something to work against and maybe not bottom out as easily. This did not improve the lack of x-max. Then I tried the Alphas in 24" frames directly behind the MCMs in 24" frames, kinda like the Celestion woofers that went with the SL600. I did read S. Linkwitz' comments about this configuation, but tried it for giggles. I don't have the room for them side by side. I did like the way it sounded, but the great is the enemy of the good. I had four Selenium WPU 1509-SLF woofers in storage for about 15 years, and decided to try them, despite the small x-max and low Qts. (Qts .35, fs 36hz, x-max 3.75 mm)

I loaded the four into the four 24" frames and mounted them vertically. Unfortunately, one of the woofers makes noises similar to a sink garbage disposal being cycled by flipping the switch on and off. The other three work fine. So I took out a pair of the bass bins and am using one 1509 and one 166EN per side. My question is, is there anything I can do to fix the misbehaving woofer? I have not taken it out of the U-frame yet. Could this be a result of storing them horizontally for so long?
An an observation: I expected that the Selenium woofers would need significant bass boost, because of their low Qts. (low for open baffle use) I also expected them to bottom out easily, which is why I wanted to use four. But they have plenty of deep bass without boost, and they sound "better" than the Alpha 15s in the same baffles. And they play plenty loud for me.

I thought high Qts was desirable for OB woofs? What am I missing? (And how do I rotate photos that I am trying to post?

[AJinFLA]

I loaded the four into the four 24" frames and mounted them vertically. Unfortunately, one of the woofers makes noises similar to a sink garbage disposal being cycled by flipping the switch on and off.

Sounds like you might have some coil rub from an offset voice coil. Any woofer repair center should be able to fix. Maybe some Pro audio shops too. If you're feeling brave you could gently unglue/remove the dust cap and shim the coil. Otherwise, an example locally: https://reconingspeakers.com/

I think PE still carries Selenium, they are a possibility for repairs also, although your whereabouts are unknown...

cheers,

AJ

[srb]

(And how do I rotate photos that I am trying to post?

1.  Gallery > Manage my albums
2.  Click on Album
3.  Click on Photo
4.  Use Rotate Left & Rotate Right buttons at bottom right

[JohnR]

I thought high Qts was desirable for OB woofs?

It's a rule of thumb helpful for a particular design approach (passive, no EQ). What you're hearing could be due to other factors, measurements would be helpful.

[WGH]

Is the spider sagging compared to the other speakers? If so try this:
How to fix spider sag
https://www.youtube.com/watch?v=lgbPan_0Pq0

[fdandrews]

Thanks for the replies and suggestions. There have been new developments. I watched the video about spider sagging and was about to try some heat when I decided to try the woofer out of the baffle with a test CD. I put on the "bass decade" from a Stereophile test CD and played it at low volume. With the woofer sitting on a workbench facing up there were no nasty noises. I tried it louder and still no problems. I don't believe that it fixed itself, but I am at a loss to explain the original problem. If the amp was not working properly, I should still be hearing bad sounds. If it was because the amp didn't like driving two 8 ohm woofers in parallel, both woofers on that channel should have sounded bad. The other channel sounded fine. I suppose the next step is to put it back in the baffle and try again. If I learn anything useful to others, I will report it.