Looking for long throw 8" passive radiators

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#24
I think the foam board (or whichever is used for the PR diaphragm) should be reasonably rigid, but this may be important mostly to minimize sound conduction through it at frequencies well above its box resonant point.

As far as rocking goes, a little more than with a double suspension PR seems to be probable, but I doubt anything dramatic or particularly detrimental to its sound along these lines would occur since it would essentially be responding to what looks to it like a fairly uniform pressure wave within the box at the frequencies at which it will actually be undergoing excursion. However, I can rig up a test for this once I receive the surrounds just to see how much might actually occur.
 
#27
Of course, WH Geiger makes a salient point - if rocking is a significant issue, it would likely be a result of asymmetry of the back pressure wave - the good news is that for the dual chambered design, the 8" woofer will be more or less back to back with one of the two PR's and the inter chamber port exhaust can probably be arranged to be away from & roughly centered behind the other PR without too much trouble.
 
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#28
Remember that if you are making your own PRs, there is no specific reason to make them circular. A rectangular one will work just as well and give you more area in a given space. Surrounds are easy to make with heavy cloth soaked with rubber cement. (You can buy rolls of suitable material from dressmaker's supply shops, it's used as stiffening in facings, cuffs, collars, hems etc.) The only tricky part is pleating the surround material in the corners. You can make a mold for this.
 
#29
Please

thoriated said:
I think the foam board (or whichever is used for the PR diaphragm) should be reasonably rigid, but this may be important mostly to minimize sound conduction through it at frequencies well above its box resonant point.

As far as rocking goes, a little more than with a double suspension PR seems to be probable, but I doubt anything dramatic or particularly detrimental to its sound along these lines would occur since it would essentially be responding to what looks to it like a fairly uniform pressure wave within the box at the frequencies at which it will actually be undergoing excursion. However, I can rig up a test for this once I receive the surrounds just to see how much might actually occur.
Click to expand...

I would be interested to know the results and findings of your tests and the specific geometry and elasticity of the compliances used.

Regards,

WHG
 
#30
Well, it looks like I scored a couple of woofers at a good price - supposed to be in 'like new' shape. They're Faital W8N8-200's, not B&C's. The Faitals looks pretty good spec wise with a rated sensitivity of 92dB, but their Fs at 74hz is a bit higher than my objective and I noticed their Sd of 177cm2 is actually on the low side for a 8" woofer. But they have a really good Xmax of ~8mm and supposedly a pretty smooth response. I might be able to work some of my spider magic on these like I did with the Aura NS3 knockoffs I scored from Parts Express a couple of years ago for my HT speakers where I was bringing the average Fs down from 80hz to 55hz. So far no problems with VC rubbing from any of the 72 in my HT system I did that to!

I also had my eye on a couple of Beyma 8LW30's but the sniffy distributor has not responded to my question about shipping so it looks like probably no Beymas for this project. Their Sd is significantly higher than the Faital's at about 220cm2 but their Xmax is about 7mm (rated the same way Faital rates theirs), so, overall about the same maximum swept air volume, but a little higher efficiency and a bit less excursion for the Beymas for the same output.

Btw, any opinions on these two woofers?
 
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#31
Well, I got the Faital W8N8-200's last night and had to check them out a little. I visually verified their initial free air resonance at 67hz apiece (which is somewhat below their 74hz rating). But then again, they were supposed to have been 'tested' before I got them, so were not absolutely brand new, so it seems reasonable there was some suspension break in before I bought them. This made me curious - is the free air resonance more accurately determined by measuring the impedance peak or by observing which frequency the maximum excursion occurs at? I assumed they were pretty much the same frequency in most cases, but could see where there might be some offset, presumably with the visible excursion maximizing at a bit lower frequency than the impedance peak.

IAC, I tried my spider and surround softening technique that I had previously used on the Parts Express near ND90's for my HT and can report a similar success in reducing Fs. In about 20 minutes, I was able to reduce the maximum excursion frequency of both drivers from 67 hz to 47 and 48 hz for the two which is almost exactly what my objective was, so I'm ready to move to the next step, now. I believe that this lowering of Fs is likely to work out better with a double chamber tuning with an objective of the tuning below 40hz at the lower resonance.

Btw, I noticed in some of my BR modeling with this driver that the importance of driver Vas seems to be less than for a closed box tuning at least as far as frequency response goes. Any comments on this?
 
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