Sorry if this was OT, but I just thought it worthwhile to make people aware that smooth data using one method may not be so smooth with another. Some people might make claims that the method they use is more revealing. The Angelo Farina's method seems to claim better noise rejection, but whether there is any other difference would be very controversal and yield hand waving statements. After reading the documents from the links provided by Jean-Michel, I am not convinced it's the best method for all purposes. The "state-of-art" blanket description for this method could be misleading.
Now that I have voiced this, I'd be glad to get back on topic.
Now that I have voiced this, I'd be glad to get back on topic.
soongsc said:
I do that because it amazes me how you will keep saying things that are more and more ridiculous just to be the last word. Like the last sentence above, completely ridiculous. You claim something that is not even true ( "diffraction patterns differ with different acoustic signals ..." - truth: diffraction is independent of the acoustic signal) is "obvious".
Hello,
For what its worth, here a paper on acoustic impedance of open cell foam with a comparison to glass fiber.
http://www.akustikforschung.de/pdf/huebelt_impedance_measurement_ICSV2005.pdf
Additionally here is a link to 2 papers on the subject of FEM acoustic analysis of open cell foam.
"Finite element frequency-domain acoustic analysis of open-cell plastic foams"
http://portal.acm.org/citation.cfm?id=1138976
"Three-dimensional finite element frequency domain acoustic analysis of open cell plastics foams"
http://cat.inist.fr/?aModele=afficheN&cpsidt=18264561
Best regards rfom Paris, France
Jean-Michel Le Cléac'h
For what its worth, here a paper on acoustic impedance of open cell foam with a comparison to glass fiber.
http://www.akustikforschung.de/pdf/huebelt_impedance_measurement_ICSV2005.pdf
Additionally here is a link to 2 papers on the subject of FEM acoustic analysis of open cell foam.
"Finite element frequency-domain acoustic analysis of open-cell plastic foams"
http://portal.acm.org/citation.cfm?id=1138976
"Three-dimensional finite element frequency domain acoustic analysis of open cell plastics foams"
http://cat.inist.fr/?aModele=afficheN&cpsidt=18264561
Best regards rfom Paris, France
Jean-Michel Le Cléac'h
doug20 said:
The type of foam Dr. Geddes uses has been discussed before in this long set of posts, as well as ways to buy it. However, it would be my suggestion that you simply consider buying Dr. Geddes raw wave guide with foam plug, as it will be easier. There is really good measured data on Dr. Geddes waveguide showing just how good it really is. I've not seen comparable data for the DDS model, nor, due to it's size, can it be used as low in frequency. The foam is stupidly expensive, unfortunately, and not so easy to cut to the profile of the waveguide. If it was me, I would simply buy it all pre-done, as it's quite a bit easier, and you will have a better end product.
The foam used by Dr. Geddes is open cell reticulated polypropylene foam with I believe 30 ppi, or maybe 60, I don't recall an exact number. If I can be so crude it describing it, it looks and feels identical to filter foam used in foam auto filter, air filters, fish tank filters, etc. The biggest problem is sourcing it is that you basically need a block in which an ice cream cone shape equal to the size of the waveguide can fit within. This means foam that is something like 12" square in the case of the DDS, and bigger for Dr. Geddes larger wave guides. When I tried pricing it, I was given prices in the many 100's of dollars through manufacturers, as they all had minimums.