Sources for small PR's???

[netgeek]

I'm looking for small passive radiators to be used in a mini monitor design - and haven't found much. SEAS makes a 6.5" and Dayton makes an 8" model. Ideally, I'd like to find something smaller than 8". The SEAS looks good, but costs more than the active drivers I'm looking at (!!) - so I'd be better off to just buy two drivers and either run them both active or simply disconnect one and use it as a PR (which makes no sense). Any pointers?

Thanks in advance,

Bill

[454Casull]

You want to use PRs because ports won't fit?

[netgeek]

I'm trying to make some mini-monitors which are impossibly small in order to expect any decent bass output. PR's are something I'm looking into in order to wring every last drop from the bass output. Might work - might not. But the overall "package" size (i.e. less than .3 sq. ft. total) won't allow drivers larger than about 5" for the bass. So..... I'd like to experiment with using PR's in order to increase the output in a small enclosure. It may be a lost cause but I'm really doing this for "entertainment" purposes just to see what can be done.

I've played with the modeling programs ad naseum (e.g. WinISD) and the obvious conclusion is that you run out of excursion long before you reach reasonable output levels using small drivers in small enclosures.... What a surprise! In other words - the laws of physics cannot be cheated or ignored..

Various combinations of peaking 2nd-order filters and Linkwitz tranforms yield the same inevitable results - i.e. you can't get there... But, what the hell - I'm going to build them anyway and see what I can get. My goals are modest - basically flat response (including room gain) at something near 90 dB - and down to about 30 Hz. Perhaps something 6 dB lower than that is achievable... we'll see.....

The target application is small apartments/bedrooms, near-field use, and perhaps mobile monitoring (much like the old LS-3/5a applications). In other words - an improvement on either LS-3/5s's, NS-10's, small Genelecs and the like.

Hence the interest in passive radiators...........despite all reason or odds....

[joe carrow]

Have you considered a rectangular port? I assume that the main reason you can't just use a port is that the port has to be longer than any internal dimension of the box in order to keep the port mach within reasonable limits.

If you have a folded rectangular port (like some vented subs) and are willing to accept some port noise at high volume, it just might work out for you.

Good luck!

[netgeek]

Basically, the internal volume required by any reasonable port is too great. Added to that is the potential port noise created by using one that is obviously too small in order to minimize the volume (a major goal of this project). In other words, too much risk - and virtually guaranteed to creates too much noise. Ideally, the enclosure would be sealed - use of a PR is already seen as a compromise...

[joe carrow]

Yes... now that I think about it, 30 hz is very low for something that size. Did you say what drivers you plan on using? I played around with an Audax 5.5" driver in WinISD for about 5 minutes, and it looked ok to 65ish... but not 30!

[Zaph]

Have you considered making your own with a surround kit?

Basically, you cut a hole in your box, and you cut an appropriate size disk too. If the weights work out, this could be done in one step.

The best way to do this is with two surrounds, one on the inside and one on the outside. This is to promote linear movment and limit sagging. The inside surrond has to be vented to the inside of the enclosure to avoid suck-out under excursion.

If you're interested in that, I'll go into more detail and post a passive radtiator design spreadsheet to help you calculate the weights. I've got one that has the density of mdf built in so you can figure out the starting disk thickness.