How Passive Radiators work

[Steve Gonzales]

I found this short article an interesting read.

http://www.humanspeakers.com/whatis/PR.htm

[pmakres1]

Good reading Steve...thanks for posting it.

Peter

[4313B]

"They are mathematically identical"

False.

"An acoustic suspension system also tapers off in its response at only 6 dB per octave. The vented, or passive radiator, system rolls off at 18 dB per octave"

False.

Zilch posted in another thread that he is currently reading the AES Anthologies. Hopefully he can explain why the above two statements are false.

Zilch? Pop Quiz!

[Steve Gonzales]

I was hoping to get some minds working on the subject. There seems to be little dicussion of PR's, at least in depth. I know very little about the fine details of how they function and want to learn more about them.

[4313B]

Hopefully Zilch will accept his pop quiz.

[Zilch]

An "open book" quiz?

Oh boy, oh boy!

[Three papers to absorb here, first....]

[4313B]

Absolutely! Open book. Open notes.

Sorry if I put you on the spot Zilch.
You've got some really cool reading material there wouldn't you agree?

[Zilch]

You've got some really cool reading material there wouldn't you agree?

Yup, it's fun to read it chronologically and watch the concepts develop.

[Did we REALLY usta look like that?]

[4313B]

[Did we REALLY usta look like that?]

'fraid so...

[boputnam]

"...vented systems in general are a poor choice for small speakers that roll off much above 40 Hz - there is too much signal present, in the range they respond to poorly, for them to work well."

Gadzooks. Guess I should sell those 4313B's afterall...

"A larger speaker will work better with this sort of set up because at the frequencies that might be troublesome, there is rarely any musical signal present."

Complete . The inference is, I suppose, that a "vented" system is OK for large cabinets simply because at the LF's "there is rarely any musical signal present".

[4313B]

Take it for what it is Bo. Just an opinion based upon the author's personal perception of the universe and everything in it. I'm sure there's some grain in there, I just don't have the desire to take the time to separate it from the chaff.

[4313B]

*****

Here's something else to read -

http://www.adireaudio.com/Files/Tech...GroupDelay.pdf

I found it Googling for Passive Radiators (I was actually looking for schematics so I wouldn't have to bother drawing them up myself! ).
Pay special attention to the very last paragraph on page 4.


*****

Here's another one and it's The Real Story - I don't feel like reading it right now but here's the link anyway.

http://www.greenhydrant.com/~drees/ht/pr-vs-port.php


*****

GordonW should be able to add to this thread based on his experience with the newer, non-JBL passive radiators and their implemenation.


*****

[Chas]

"An acoustic suspension system also tapers off in its response at only 6 dB per octave. The vented, or passive radiator, system rolls off at 18 dB per octave"


I think the first "fact" is correct, but I have other ideas about the second, but then I don't want to spoil the fun for Zilch . I have spent a bit of time with the AES reprints too, they're great fun, there's stuff there you'll never forget.

I remember building my first woofers some 25 years ago from the AES T/S papers with four Altec 414z's, there were no T/S parameters published ever by Altec that I have ever found. The whole thing had to be learned and measured from scratch.

Going through all this coupled with the JBL learning curve I am having from you guys here has given this analog circuit level guy a real appreciation as to what is involved in high quality transducer (JBL pro stuff shouldn't be called "speakers" IMHO) system design.

[pelly3s]

i've talked to the guy from human speakers and he is a little odd... i tried to sell him some parts before

[4313B]

I think the first "fact" is correct

I suppose the opperative word is "mathematical". Since he doesn't elaborate we can only speculate how he arrived at that.

I have spent a bit of time with the AES reprints too

Ok, comparing the acoustical analogous circuits of a vented-box loudspeaker system and a passive radiator loudspeaker system we see that the passive radiator loudspeaker system has the additional element denoted by CAP - the acoustic compliance of the passive radiator's suspension (usually drawn between MAP and RAP in the schematic below).

If I read correctly, the vented-box system and the passive radiator system are only mathematically identical if the compliance of the passive radiator is infinite.

acoustical analogous circuit of a vented-box loudspeaker system for reference
MAP = acoustic mass of passive-radiator diaphragm including air load = acoustic mass of port or vent including air load
CAP = acoustic compliance of passive-radiator suspension = no equivalent for vented box system
RAP = acoustic resistance of passive-radiator suspension losses = acoustic resistance of port or vent losses