How Passive Radiators work

[pmakres1]

Keep it going guys...I'm really liking this thread, though I confess I get a bit lost in the enclosure alignment discussions. I'll be re-reading the thread a few times I'm sure. The discussions about first, second, third and so on alignments brings me to a question I've wondered about for some time. The brochure I have on the B460 states the following: "The B460 uses the JBL model 2245H 18-inch (460mm) driver in a vented enclosure of 8 cubic feet (226 liters). The combination is a third-order quasi-Butterworth alignment. The enclosure is tuned to 26Hz." Could some of you fellows who are more up on this than I explain what this means? I was never an expert in this area, and I need at the very least a basic refresher on 1st, 2nd, 3rd and so on order alignments and what it all means. Keep it simple, or, if you like just point me to some relevant reading. Pardon my ignorance, I'm trying to learn a bit here.....

I can tell you first hand that the B460 combined with the L220 is a great combo!

Peter

[4313B]

I must be on your ignore list...

http://audioheritage.org/vbulletin/s...4&postcount=22

http://audioheritage.org/vbulletin/s...ead.php?t=4557

The B380 and B460 enclosure volumes and tuning frequencies are such that the 2235H and 2245H exhibit responses equivalent to a quasi-third order filter. Tune the stock B380 volume up a bit to ~ 29 Hz and you get Keele's maximally flat response for the 2235H which is closer to a classic fourth order Butterworth response (still QB3 due to the low Q's of the transducers). Think of enclosure/transducer systems as passive filters. Add a BX-63 to a B380 or B460, with it's second order bump filter, and you end up with a 5th order system -similar rolloff to a classic PR system. One JBL transducer that fits almost perfectly into a classic 4th order Butterworth vented box alignment without forcing any "compliance shifting" would be the LE10 with it's Qts close to 0.38

[pmakres1]

I must be on your ignore list...

http://audioheritage.org/vbulletin/s...4&postcount=22

Sorry Giskard,

I did read that post, and I was going from memory of the B460 brochure, which I thought had said quasi fifth-order. When I pulled the brochure again it said quasi third-order. I should have re-read your post before I asked the question. (no you are not on my ignore list). What about the term "Butterworth" alignment?
I apologize again for my ignorance..I'd still like to see some basic reading on the driver alignments.

Peter

[4313B]

Butterworth - they're people's names. Invent a new filter and we'll name it after you. Linkwitz-Riley, Zobel (which should probably be called Boucherot?), etc.

I'd still like to see some basic reading on the driver alignments.

There has to some good stuff out there on the net. Some of the AES stuff is too deep without a Mathematics Degree from M.I.T.

This might be a place to look - http://www.diysubwoofers.org/

This might have some stuff - http://www.mhsoft.nl/default1.asp

[Steve Gonzales]

Wonderful discussion!. I will say that in my limited (so far), non LHS reaserch, as in the case of my original link, it is hard to tell who's the real deal (right), as far as the bottom line. I would love to be able to see a read-only article in the reference section on this site. It could be used as a learning tool for budding builders. I want to thank every participant for their input. I'm definately much more aware of what is going on and what to expect, when using a PR. I would like to make one observation. I have owned 3 pairs of (sorry)-ESS AMT1A,B,D's in the past and these speakers use a VERY crude and simple PR. Their bass output is nothing short of AMAZING!. As I see all the pitfalls one will have to overcome to eventually come out with a good sounding product when using a PR, it is even more amazing. Thanks again, Steve G

[pmakres1]

Butterworth - they're people's names. Invent a new filter and we'll name it after you. Linkwitz-Riley, Zobel (which should probably be called Boucherot?), etc.

I'd still like to see some basic reading on the driver alignments.

There has to some good stuff out there on the net. Some of the AES stuff is too deep without a Mathematics Degree from M.I.T.

This might be a place to look - http://www.diysubwoofers.org/

This might have some stuff - http://www.mhsoft.nl/default1.asp

Thanks Giskard!

Very helpful.

Best regards,

Peter

[4313B]

Hopefully others can add in some links. I've noticed that some of my old links are now broken. Books are still worth owning.

[Chas]

Okay here's what Villchur, AES Sept.1956, had to say regarding Baffled direct-radiators which I interpret to be what I used call to infinite baffles and assuming these would have the same charecteristics as acoustic suspension boxes:

"Below resonance, however, the speaker mechanical system is no longer mass-controlled. If it were resistance-controlled, velocity would remain constant, and output would be attenuated at a rate of 6db/octave due to the continuing drop in air-load resistance. In fact, it is compliance-controlled-the predominant impedance is that of the elastic restoring force of the system-and bass output is therefore attenuated at a rate of 12 db/octave."

This must have been what I was thinking about earlier.

I also found an old article in the AES book where Olsen describes a "drone cone" i.e. a passive radiator. He thinks that effeciency goes up with a PR due to the fact that losses are less with a PR versus a vent. He wrote that in 1947.

[4313B]

Ah!

Thanks Chas

This might be interesting - http://www.audioasylum.com/forums/pi/messages/2062.html

[Chas]

Holy crap! I think you are introducing too many variables just to be argumentative!

Ever check out a range of delta T of ambient air or maybe even altitude versus change in FB in a vented system?

Very interesting graphs based on even more variables, though.....
Just proves to me once again, build, listen, change, listen, etc....science. art and ears all combined. That's what makes this so much fun.

[4313B]

Holy crap! I think you are introducing too many variables just to be argumentative!

Nope, just wanted a quick and easy way to show how the tuning/volume can affect the knee of the curve with a transducer/box system just like doing something like adding DCR to a parallel inductor in a filter does, hence the link. My intent should be clear. If it isn't, then I suck at explaining things... whatever...

Ever check out a range of delta T of ambient air or maybe even altitude versus change in FB in a vented system?

Perhaps this will help -

Sensitivity of Thiele's Vented Loudspeaker Enclosure Alignments to Parameter Variations
Volume 21 Number 4 pp. 246-255; May 1973
Additional information on the use and application of Thiele's alignments for the vented loudspeaker cabinet is presented. A rewritten alignment table which has all the frequency terms normalized to the speaker resonance frequency is included. Computer-run frequency responses for all the alignments are displayed along with a new fourth-order Chebyshev alignment beyond no. 9. Variations and sensitivity functions for the vented cabinet output with respect to various system parameters (both Thiele system parameters and driver physical parameters) are derived and plotted.
Author: Keele, Jr., D.B.

[Chas]

Quote: "My intent should be clear." It is, I was kidding. I should also have added "measure" to my diatribe too.

[4313B]

Just proves to me once again, build, listen, change, listen, etc....science. art and ears all combined. That's what makes this so much fun.

Understood.

I'm going to generalize something I heard recently -

Some guys are indispensable when it comes to theory and mathematics but their implementations kind of suck, other guys aren't so good with theory and mathematics but their designs wouldn't reflect it.

[tomt]

I'm going to generalize something I heard recently -

Some guys are indispensable when it comes to theory and mathematics but their implementations kind of suck, other guys aren't so good with theory and mathematics but their designs wouldn't reflect it.

here is a man who has a degree from mit and has 'invented', 'filters',

as such,named after himself(post 34) and has even as this site says

get this,Repaired Transistors! What a Talent!

http://web.mit.edu/invent/iow/bose.html

Repaired Transitors? How?

must have put them in piles of two.
then did it again

[4313B]

Are you posting an example of the former as opposed to the later?