ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hi everyone,
Article #3 is now public at
http://www.tonmeister.ca/wordpress/
Have a nice weekend!
Cheers
-geoff
Thanks Geoff.
As informative as ever. I am just warming to the Beolab 3.
Graham
Thank you again for all of your insights on this forum and these articles. It is truly wonderful that you are so willing to share your knowledge.
Beolab 28s Beolab 9s Beolab 12-3s Beolab 1s Beolab 6000s 2 pairs Beolab 4000s Beovision 7-55 Beovision 10-40 Beoplay V1 32 inch Beovision Avant 32 inch Beosound 1 (CD player) Beosound 3000 Beosound 5 Core Essence MKII Beoplay M5
Thanks again to Geoff
MM
There is a tv - and there is a BV
I would just love to know how much free volume there is in the BL3 for the driver to work with? Vb has to be incredibly tiny. Interesting use of PRs too, usually the rule of thumb I learned was diameter equal to the driver and then mass load until you get the alignment right, but with two I'm unsure, I guess same thing,MOUT them in and choose a mass for them that gives you the alignment you want.
Jeff
I'm afraid I'm recovering from the BeoVirus.
Must confess to thinking the same - one always imagines a nice smooth air passage between driver and radiator. Having rebodied my BL2, it came as quite a surprise that the electronics are all just sitting there. I suppose I imagined there would be a smooth cover protecting them, which would reduce volume futher I suppose!
Peter
Jeff: I would just love to know how much free volume there is in the BL3 for the driver to work with? Vb has to be incredibly tiny. Interesting use of PRs too, usually the rule of thumb I learned was diameter equal to the driver and then mass load until you get the alignment right, but with two I'm unsure, I guess same thing,MOUT them in and choose a mass for them that gives you the alignment you want.
Hi Jeff,
Sorry - I have no idea what the total volume is in the BL3...
As for the passive radiators... To simplify slightly (mainly because I don't understand the details...) the total surface area and the excursion determine their sound pressure level. The compliance and mass determine the resonant frequency. Since the two passive radiators on the BL3 are matched in all four of those parameters, they move in opposite directions at all times. And, if it were a perfect world, when the passive radiators are moving with maximum excursion, the woofer is not moving at all.
From the outside world, having two radiators is basically the same has having one with 1.4 times the diameter (and therefore the same total surface area) assuming that the other parameters are tuned to result in the same resonant frequency. However, the vibration in the total system will be balanced and therefore reduced. How they time-align with the woofer above the resonant frequency is largely dependent on the relative distance between them and the listening position in a free field.
cheers
Peter: Must confess to thinking the same - one always imagines a nice smooth air passage between driver and radiator. Having rebodied my BL2, it came as quite a surprise that the electronics are all just sitting there. I suppose I imagined there would be a smooth cover protecting them, which would reduce volume futher I suppose!
Hi,
It may be reassuring to remember that air does not really flow directly from the woofer to the passive radiators as it would through a pipe except at VERY low frequencies - far below the resonant frequency of the passive radiators - where you have almost no total output from the system anyway.
At the resonant frequency of the passive radiators, they are moving equally in opposite directions and the woofer is not moving at all. This means (in a perfect world) that the air molecules inside the BL3 at the midpoint between the two drivers are not moving, since they are being pushed an pulled from both sides equally all the time.
Going below the resonant frequency of the passive radiators, the lower you go, the more they cancel the woofer output, so you're moving outside the frequency range of the total system.
If you go far enough above the resonant frequency of the passive radiators, then they don't move and all the movement is in the woofer. So you have to consider the volume inside the BL3 as being a compression chamber. This means that, at the "back wall" of the BL3 the air molecules are also not moving.
Of course, if the loudspeaker had a port instead of passive radiators, then the story would be different - however you would only worry about a smooth air flow around the ends of the port.