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.🙂
You have to have the last word on every topic don't you. I have substantial expertise in acoustic measurements and I'll stand by my claim. There - your turn!
soongsc said:
I know that you don't provide data on this because it would be OT.😉
There is an AES paper on a comparison of all measurement techniques and it was referenced in Farina's latest paper. Read that. It's pretty clear on what works best.
What works best depends on the purpose of measurement. There is nothing that is best for all situations. Especially when we talk about test wave forms.gedlee said:
As usual, I would disagree. There is a better way and a worse way to measure loudspeakers. Log-swept sines is the better way.
Don't know why you continue to provide opinions on a topic you don't want to clutter the read with. But if one understands how diffraction patterns differ with different acoustic signals, it is quite obvious why we see the differences in measurements.
I really would like to post more on wave guides, but these sims really take up lots of time. I wish I had 10 computers running.
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".
gedlee said:
Sorry for the OT but I had to mention that I buy MathCAD out of my own pocket even though Matlab is free to me for the simple reason that the interface is so intuitive.
scott wurcer said:
Agreed. Once you've used MathCAD its hard to use anything else.
I jusy wish that they had better graphics.
Truth is in the mind of the believer. Can't argue with that. Just like the truth is there is a God.gedlee said:
Even if I show data signifying diffraction effects, you will not provide data on the contrary. So no need for further discussion.
soongsc said:
Start another thread. This is simply too ridiculous to respond in this thread. I would ask the moderators to move this and any further posts on this topic to another thread should any arise.
Dave
Keeps getting better and better! Digging into the "God" thing is a new touch. Making this into a religious discussion is very appropriate.
tiki said:
I have looked at ARTA before, it is very capable, but the polar maps are too coarse for my needs. It is a good first step however and I'm glad to see that people are looking to polar maps as they are really the best way to look at this kind of data.
The Foam insert? can we DIY our own.
Im matching up waveguides with TD12 drivers from AE. Im thinking about using DDS 1-90 waveguide, no compression driver picked yet.
Im matching up waveguides with TD12 drivers from AE. Im thinking about using DDS 1-90 waveguide, no compression driver picked yet.
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.