I have understood quite a bit about fabric. But I am curious about fabric made from animal hair in particular from goat hair. The fabric is quite hard but it is threaded and the air does go through. I know that the mid and lower frequencies will probably be okay I just am curious about high frequencies.
I will be using this for the RFZ zone so I really want it to absorb the highs.
Does anyone know if animal hair fabric that is a little hard(not soft like cotton) going to be a problem?
Yeah, rigging up a test sounds like a good idea but how? So we want to see what "bounces" back, if anything from a surface. We have to isolate the speaker and the mic, I guess we need a gobo between the mic and speaker so we get the reflective sound and not the direct sound of the speaker. Maybe this could be done or enhanced electronically somehow by filtering out the instantaneous part of the signal so we are left with only the reflections? I guess this is where it gets tricky.
Since we don't have an anechoic chamber, we'll just have to find the deadest room we can find and get away from walls and bare ceilings etc. Maybe under a cloud in the middle of a treated room? For an anechoic room substitute, F. Alton Everest suggested outside (on the side of a hill that drops away in front of you) on a quiet night could work... depending on where you live.
I suppose you would run at least 3 sweeps. One in the "Open field" with no or minimal reflections. The second with a know highly reflective panel, maybe smooth hard plywood or masonite, placed in front of the test mic. The third could be a bare uncovered RFZ panel of fiberglass or mineral wool. That should be enough for "Known" or control materials. The subsequent sweeps would be to test various materials.
This is all off the top of my head so if anyone has a better or simpler way to do this test, please chime in.
I was wondering this too. Maybe you can make a small isolation box by propping up a cuboid similar to a cardboard fort, stick a speaker and mic in there and test with and without the goat hair. You could put the fabric on a makeshift wire frame that doesn't block the panel. If there's a difference, however small, the decay of the higher frequencies should show it. An impulse response could also be taken and you could look for reflections.
Maybe you could also put the goat hair in front of the speaker similar to how Ethan did his 'tissue' test on the NS-10 monitors. From what I remember, there was a big enough difference to see in the results. You could also fold the fabric over on itself to see what two layers would do and compare that to something like muslin.
I have been trying to digest this over the weekend.
And I think I got the jist of it. But the best I can do is Rocks idea of performing the test in the middle of a treated room, perhaps put the speaker right infornt of the mic and the panel behind the mic(is that correct?).
I will try with a reflective surface, then some rockwool then a few different panels.
I will post the results so we can see how it worked out and if it did. Also, I am still struggling to read an impulse response and baffled how that will tell us about reflection at high frequencies, so Ill post that too.
But again thanks for the replies, this is great stuff!
I meant create an isolation cube with panels and do the test in that. If the reflectiveness is there at all then it should change the impulse response. Either way, I think a simple SPL measurement with the fabric just draped over the mic or speaker should be fine too.
But lets just say I can't design a makeshift box and we go with Rock's idea for now. He mentions that a gobo needs o go in between the mic and the speaker? So where do we put the panel with the goat hair?
And Hexpa with your idea your saying just drape the mic with the material and take a normal measurement perhaps in the middle of the room?
I like Hexspa's idea of draping the fabric over the mic. First make a sweep like you normally would do. Make another sweep with the fabric over the mic. When you compare your two SPL graphs, you'll see if there's and HF attenuation with your goat hair fabric. If you do this, while you're all set up, test a few other fabrics and materials. Try some really thick non transparent materials and see how much difference there is.
But now that I think about it. Hexspa's draping method tests for transparency, which is good to know but your initial question was regarding reflectivity of HF.
My idea was to place the speaker and mic pointing in the same direction (into the room) separated by a gobo. The panel or D.U.T (device under test) is placed about 3 feet in front of the speaker and the mic so the DUT can reflect the sound from the speaker back to the mic (a gobo behind the mic and speaker might help isolate sounds from the rear as well)...Wait! Now that I think about it, maybe a directional mic would be better for this test. Sure, a directional mic is not great for typical acoustic testing but in this case, we are interested in the sound bouncing off a relatively small area.
Anyway, the first measurement would be taken without anything in front of the mic and speaker. This would be your control. Next you could try a hard panel in front of the mic and speaker to see if there is any difference caused by the panel reflecting the sound more directly back to the mic. My guess is you'll get more mid and HF. When you test your goat hair fabric, you can compare them to both the open room and the hard panel. You can test other materials too. I'd be very interested to see your results!
Thanks for the laymen explanation. I will try both methods and see what results I get. Interpreting the results is another matter but I will get started.
I know we have diverged into materials but I can source cheap fabric where I am but unfortunately, its hard to get ones that look good, are transparent, and soft to also absorb HF. I need to make a few panels for restaurants which what I learnt from Hexpa needs HF absorbtion so I need to get it right.
Hexpa I am curious in this case which the panel is for conversation like we chatted about in the other post would loosing that last octave of absorbtion gonna cause problems? I mean even for the RFZ for mixing would it be problematic? Is it absolutely essential to absorb all the way to 20 000? You get my drift...
This may be a subject for another thread but in general Human high frequency hearing falls off with age. So I my guess is you really don't need to worry too much above 10K to 15K and above. Since the rolloff varies for each individual, you'll have to find an average.