https://www.youtube.com/watch?v=683FoCDilOE
in the end the design engineer speaks about the extra chamber are in phase with the driver so how is the length of the extra chamber is calculated?
consider we have a driver with 40Hz resonant frequency so the speed of sound / frequency so (1120/40)/4 for the quarter wavelength so its 7feet is the transmission line length so how is the extra chamber length calculated? with what formula?
in the end the design engineer speaks about the extra chamber are in phase with the driver so how is the length of the extra chamber is calculated?
consider we have a driver with 40Hz resonant frequency so the speed of sound / frequency so (1120/40)/4 for the quarter wavelength so its 7feet is the transmission line length so how is the extra chamber length calculated? with what formula?
My crappy AT&T DSL won't let me watch youtube anymore at any sort quality to hear what all they're saying, but any time there's an impedance mismatch between ducts, the new duct extension is a half WL resonator [AKA vent, port], so use a TL and/or horn program to design the TL, vent [AKA MLTL].
GM
GM
Calculating a TL is straightforward. You choose the Ftl about 1/2 octave lower than the Fres of the bass-unit. From this Ftl you calculate the wavelength. Your TL ought to be 1/4 wavelength.
BUT: you have to include the speed of sound in the TL. Damping materials cause that speed to drop beneath the 342 m/s sound travels at 20 degrees and 1013mbar.
In the movie you can see the TL is filled with some kind of foam. The foam does the trick of slowing down the sound speed in the TL, and thus shortening the length required.
I take it then that by 'mbam' you're referring to Malwarebytes? If so, I use it and it has no impact on my problems with youtube, which I assume is due to the fact that when I check the quality of my DSL connection using pingtest.net, it returns a 'F' rating.
Regardless, as a very general rule-of-thumb you choose the frequency ~ a 1/2 octave above Fs to find the acoustic path-length to get a ~ Fs tuned TL, but taper, terminus end correction and pipe net volume [Vb] plays a role, so not the simple computation many seem to think it is if one wants to do it as accurately and with the best overall performance as practical.
GM
Regardless, as a very general rule-of-thumb you choose the frequency ~ a 1/2 octave above Fs to find the acoustic path-length to get a ~ Fs tuned TL, but taper, terminus end correction and pipe net volume [Vb] plays a role, so not the simple computation many seem to think it is if one wants to do it as accurately and with the best overall performance as practical.
GM
Hi GM, obvious question perhaps but have they done the remote diagnostics from their end? They can confirm (once you get escalated to the right department). If nothing else has worked, they "should" be willing (last I checked) to come out and check the copper line for noise (to the home exterior).
If none of that works, there may be (a) a locally based DSL provider (using the same copper but with better service), or perhaps (b) reasonable 4G cellular data which isn't perfect but (from the sound of it) can't be worse.
What 'extra chamber'? I've not seen any chambers in PMC designs, extra or otherwise. I've seen offset driver & / or offset terminus line typologies, but that's it. PMC lines are fairly straightforward; there's nothing particularly novel about them, other than what the marketing boys come up with. They work well enough for what they are. I suppose I'll now have to listen to the Youtube video to find out what form the waffle is taking...
Three minutes and thirty three seconds of my life that I will never, ever get back. Three minutes and thirty three seconds in which the gentleman talked, and said nothing other than marketing for a magazine copy. Three minutes and thirty three seconds in which I still didn't see any chambers, or hear anything whatsoever that was new.
It's a straightforward TL / labyrinth. End of.
It's a straightforward TL / labyrinth. End of.
Nah, it's just this. http://www.audio.de/testbericht/im-test-pmc-db1-i-1145211.html DB1 standmount. Pretty straightforward 3-4 fold (depending on how you like to term it) offset driver line. Excuse the link, my PC for some reason has decided to stop letting me attach pictures. 
PMC look like they've got about half a dozen or so different line configurations. Nothing unusual about any as far as I've seen though.
PMC look like they've got about half a dozen or so different line configurations. Nothing unusual about any as far as I've seen though.
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None in the one in the youtube video (same as the one in the link I gave) AFAIK, unless I suppose arguably the part after the XO, which appears to severely restrict the CSA at that point. They do sometimes have a foam-stuffed / grilled termination though -whether it's larger than the final line stage CSA for the build-material thickness or not I'm not sure.
+1, albeit probably not the most effective I've ever seen judging from the picture & the CSAs involved...
They look so large I suspect it's acting as much like an extension of the line with a terminus offset as it is a Helmholtz. Ha! I hadn't seen that paper before. Cheers Greg.
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