Another Sensitive OB Woofer Design

[fwater]

Originally Posted by Andrew Eckhardt

As an aside, I recently made a set a of dipole PC speakers using the square basket PE 10's, and they work great with some EQ. I know EQ isn't what the flea power crowd wants to hear, and these square drivers haven't been in fashion since the early 80's, but they spec. out great if you come to appreciate a more highly damped sound at the usual frequency / transient response tradeoff midpoint of natural Q=.7. They have bigger magnets, longer coils, and higher excursion compared to the Goldwoods at about the same money. The Fs is nice and low. They are really good drivers for moderate power and low crossover points considering the cost. I will say I had to add glue to large sections of the surround right out of the box, other than that build quality is slightly better than the GW215s I bought years ago, where the surround was glued well enough but quite a bit out of round. Now if only we could get someone to make drivers of similar design with shorting rings added, a finishing touch that only the OB crowd would want in such "wimpy" speakers.

Excursion is higher on the no names by mere 0.75mm, the magnets are bigger by maybe 10%, and the Qts is lower resulting in less of a bump at Fs. The lower Fs combined with the lower Qts will probably result in a FR nearly identical to the Goldwoods. I suppose the hands-on experience of having to repair a brand new driver gives them the edge? Buying in quantities over four make the no names more expensive, too. One thing is for sure, though...there's no replacement for that vintage square frame and white cone.

[Andrew Eckhardt]

I understand how people get attached to brands, but if you're looking for improved transient response then the funny square drivers are significantly better. For all I know they're made by Goldwood anyway.

You can get the black cone ones if you like or you can pretend they're actually made from bananna peels like Fostex and get the white.

[fwater]

I'm not shure if a person could exactly get attached to Goldwood...

Why, would you say, the transient response is better in the no names? I'm always looking for something a little better in the ultra-cheap catagory, and if these are a better value, I'll bite on a pair or two.

[cuibono]

A discussion a few months back indicated that the way the above woofer is arranged may not be making the best use of the drivers output - ie, I could get the same output using two drivers in a single frame of the same depth. It took me while to realize, but alas its true. There is a redeeming quality of this design though - much lower nonlinear distortion. Particularly below 50Hz, the distortion is much lower (about 15dB). None the less, I decided to redesign the woofer. I also wanted something that looked better. Alas, that was not to be.




It actually works pretty well - it has good voltage sensitivity, good polar response, much greater low frequency output and a great nonlinear distortion profile. The only trade off is on the upper end - there is a serious cavity absorption at 700Hz - really steep and narrow. I cross them about 330Hz, so I don't think it is too big an issue.

But they are seriously ugly. I want to go with something more organic, but it just didn't come off. So I'm going to redo them again, and probably make them a 4 way...


The design aspect worked well, and someone might want to implement it. Basically, there are four drivers stacked (per side) into sections of sonotube. I then cut openings into opposite, alternate sides of the tubing. Hopefully a picture makes it easier to understand. It is quick/cheap, and maybe a little flimsy. But considering the direction of the forces involved, probably is just fine.

[CLS]

Well done! Congratulations. And it looks pretty good to my eyes

Isn't that the construction of LAT sub? IIRC.

For the cavity resonance, did you try absorbing material on the inner wall, the opposite side of the opening? Or different shape of opening (eg. oval?)?