Dusty Chalk Posted January 21, 2009 Report Share Posted January 21, 2009 I put this under a separate thread with the understanding that the audience for this thread might be a 100% exclusive union with the orthodynamic thread, because it's really a separate issue, and is not necessarily an issue indigenous to orthodynamics. blah blah blah future audience growth potential blah blah blah So without preface, let me start with my fundamental question: Why felt? I mean, there are other materials that are flexible and dense at the same time -- corduroy, for example, or perhaps certain dense weaves such as linens or velvet. And I ask not to question felt's supremacy, but rather as a learning exercise. What is it about felt that makes it superior? Is it its chaotic nature (no weave implies no consistent surfaces to reflect any one particular frequency)? Would I want felt with a backing or not? Alright, yes, I went to G Street Fabrics (for those not from this area, G Street is a high end fabric store -- they have, or can get, anything and everything) and looked around. Found some nice...uh, something, might be felt, might not, not sure, didn't ask. Price was less than $3 so I bought it. Worst case, I can fix any holes in my pea coat with it. But while I was there I (uh) "felt" a bunch of other materials that I couldn't imagine would be any worse. I mean, felt just seems so acoustically transparent compared to some of these things. What is the goal? 100% absorption, zero reflection would be the ideal towards which we strive, right? In a more realistic world: high, frequency-independent absorption, low -- yet still frequency-independent -- reflection would be the characteristics we seek, right? I mean, we want to reduce the backwave as much as possible (except in the rare cases of bass reflex), and the worst offenders are the bass frequencies, right? Or in the small enclosures of headphones, do priorities shift, do we suddenly become more interested in higher frequencies as well? So...enlighten me, I'm all ears. I do intend to start with the orthos, but there are other headphones that I'd be interested in doing interesting things with, perhaps putting some ribbons in some sealed enclosures... I still haven't gotten together with Justin to feel his uberfelt, but I didn't want to expose him unnecessarily. So I can't compare what I got with what he has, or even get his opinion on it. PS Should I wash it? It was in the scraps heap, so there are lots of loose threads and dust on it. Quote Link to comment Share on other sites More sharing options...
faust3d Posted January 21, 2009 Report Share Posted January 21, 2009 Well felt is not the only material to use, you can try efferent fabrics like chamois to reflect and deflect sound waves. Felt is very useful because of its varied density and ability to provide resistance to the escaping sound waves. With electrostatic headphones you have what is called air damping, basically only air provides resistance to the thin diaphragm. Because ortho diaphragms are thicker they need more resistance and air by itself is not enough, so here felt comes in to play as it traps the air and creates a compressed air cushion to dampen the drivers. With different thickness felt you can control that resistance. You can also use it in the back of the cup (as well as cotton, fiber-wool and foam) to minimize reflections and vibrations. This is what wualta wrote some time ago about felt and damping: My working hypothesis throughout this series of posts is that while the reflective earcup certainly isn't helping anything except possibly to shore up a sagging treble, Yamaha's diaphragm is simply too massive for its oscillations to be damped by the acoustic resistance supplied by the little foam pad-- imagine a heavy jumper on a trampoline "damped" by nothing but a big fluffy layer of meringue on the trampoline's underside. This is why in other threads I've advocated applying discs of dense felt to the back of the driver. As the diaphragm tries to push air through the felt, it meets resistance that damps out overzealous (ie, due to resonance) motion, just like a shock absorber in a car. This, it turns out, makes all the difference. When applied to the back of the driver in an Orthodynamic headphone, a damping pad's primary effect is to drastically flatten the response curve, depressing the broad lower-midrange resonance hump and effectively bringing up the formerly weak bottom and top ends. It also has the salutary effect of greatly tightening up the bass, making the HP-1s behave as they were presumably meant to 30+ years ago, maybe better. Bass becomes percussive, tactile, almost speakerlike. A damping pad also soaks up some of the treble backwave, keeping it from ricocheting around the cup. It also makes the 'phones even less efficient. You'll notice that most high-quality dynamic drivers also use either damping pads or tiny pinholes in their frames or baskets to perform the same shock-absorber function. For example, you can see the holes method used on the back of the Koss KTX and KSC drivers. You can easily see a white damping pad under the mesh grilles of Sennheiser's HD-600 and -650. A black strip of porous material is visible on the back of Grado's drivers. Quote Link to comment Share on other sites More sharing options...
Duggeh Posted January 21, 2009 Report Share Posted January 21, 2009 I use only electrical tape in my final Orthodome. No wool, no felt, no tissue. Quote Link to comment Share on other sites More sharing options...
mypasswordis Posted January 21, 2009 Report Share Posted January 21, 2009 Did you use the electrical tape as a reflex dot? Or did you just use it to hold the drivers in place or something? Dusty, come to my house anytime this week and I'll cut you off a big chunk of the superfelt. Hell, I might even just give you the whole thing. Quote Link to comment Share on other sites More sharing options...
Duggeh Posted January 21, 2009 Report Share Posted January 21, 2009 Reflex disc I guess. Only the centre hole is fully uncovered. Quote Link to comment Share on other sites More sharing options...
mypasswordis Posted January 21, 2009 Report Share Posted January 21, 2009 Yeah, the SFI drivers really don't have much bass to speak of on their own. I ended up taking everything off the backs of mine and putting a bunch of crap on the front, like felt and weatherstrip, and it still doesn't have enough deep bass. I need to get to work on my AT-702 SFI some more. The fact that you had to use a reflex disc is good since it probably mean you're getting enough bass. As Colin said, I think I'm going to have to use leather or something for pads to seal the bass in. Luckily I don't actually need to know how to make pads to do this on the AT donorphone, all I need to do is cut out donut shapes. Quote Link to comment Share on other sites More sharing options...
Dusty Chalk Posted January 21, 2009 Author Report Share Posted January 21, 2009 Dusty, come to my house anytime this week and I'll cut you off a big chunk of the superfelt. Hell, I might even just give you the whole thing.Thanks, I'll wait until all signs of whatever I have has passed before I do so, just to be on the safe side. Quote Link to comment Share on other sites More sharing options...
mypasswordis Posted January 21, 2009 Report Share Posted January 21, 2009 If you do come, don't forget to bring your T40RPMkII. I want to listen to it so bad... and it'll only take a few minutes. And a few more minutes for me to take pics if you want. And you can listen to my modded T50RP and whatever else I have. I'm close to getting it to sound really good. Micro micro meet, yeah! Quote Link to comment Share on other sites More sharing options...
wualta Posted January 21, 2009 Report Share Posted January 21, 2009 Felt's just a cheap, convenient way of getting a reasonably consistent amount of acoustic resistance-- ie, resistance to air flow-- to control the broad resonance hump of the typical Orthodynamic (and orthodynamic) driver, which comes without any damping of any kind, unlike even the cheapest dynamic driver. This resonance is centered in the upper bass but extends smoothly well into the midrange and give the headphone a warm, mellow, treble-lite sound. Since the diaphragm is moving most at this bass resonance, the felt can act as a shock absorber. It has little effect on frequencies where the diaphragm is barely moving. Absorption of mid and high frequencies is something else-- the mechanism is different and the materials are different. Fiberglass or rock wool are the preferred materials, though felt is much better than nothing. Low frequencies are difficult to absorb at all. If you've found something that's denser than a high-quality felt, try it in the Fostex T20v2 or maybe even the YH-100. Quote Link to comment Share on other sites More sharing options...
Smeggy Posted January 21, 2009 Report Share Posted January 21, 2009 I have been looking into other materials, one interesting one I recently acquired (from my wife) is a Japanese silk scarf. Very fine weave, very light and very wind resistant with the blow test. I'm going to try it with an SFI when I have time. Should provide good air damping and even reasonable reflex properties without any of the absorption properties of felt. Should be interesting to see what it does. I also bought some pressed cotton pads from Safeway, 50 little 2" discs in a packet like pringles in the first aid section Quote Link to comment Share on other sites More sharing options...
mypasswordis Posted January 21, 2009 Report Share Posted January 21, 2009 Ooh, silk scarf. Doesn't sound like something that should be cut up and used for headphone modding, but what do I know, I'm the opposite of married. Cotton discs sound very interesting. I hate working with cotton balls, but maybe the cotton balls I have are terrible. Quote Link to comment Share on other sites More sharing options...
Smeggy Posted January 21, 2009 Report Share Posted January 21, 2009 Very fine silk isn't too expensive, and she has lots more. This was one she was going to throw out so I rescued it. The cotton pads are standard makeup remover type things like these on the left. Quote Link to comment Share on other sites More sharing options...
mypasswordis Posted January 21, 2009 Report Share Posted January 21, 2009 Ah, very nice. Let us know how they work. Weatherstrip turns out to be extremely effective; thanks for recommending it. Brb cutting some foam to jam in the cups of my T50RP and then going to bed. Quote Link to comment Share on other sites More sharing options...
Dusty Chalk Posted January 21, 2009 Author Report Share Posted January 21, 2009 Alright, so to test my understanding: it's not to absorb acoustic backwave, but to act as sort of a broad "notch" filter? Except that wouldn't wind resistance continue to go up with lower frequencies (I.E. wouldn't it act as a broad sloped filter)? Quote Link to comment Share on other sites More sharing options...
Smeggy Posted January 21, 2009 Report Share Posted January 21, 2009 Yeah, it's a pain because it's combining properties which might not be totally desirable which is why I'm trying to separate them out with the silk in conjunction with either felt or cotton or rockwool or whatever. Trouble is that it can get complex. Sone of us have been using donut configurations where we make a ring of one type and a center piece of another so we get variable density damping. I guess that's one of the things that we tweakers enjoy, trying all sorts of wacky thing. Quote Link to comment Share on other sites More sharing options...
Torpedo Posted January 21, 2009 Report Share Posted January 21, 2009 I wonder how would work the high density urethane which Sony used for the rings around the drivers in the R10. Anyone tried anything like that? Quote Link to comment Share on other sites More sharing options...
mypasswordis Posted January 21, 2009 Report Share Posted January 21, 2009 Probably the same effect weatherstripping has, since they're both closed cell foam. This may explain its forward midrange (so I read). I find physical damping is extremely effective in getting rid of the resonance of the drivers. I put a square of foam in the back like I did with my other orthos and it nearly killed all the bass. I think I'll just try another layer of felt instead. The different materials put on the drivers do have multiple effects on sound, and of course you may or may not want back wave to be reflected by whatever you're damping with. Usually not. Quote Link to comment Share on other sites More sharing options...
Smeggy Posted January 21, 2009 Report Share Posted January 21, 2009 Yep, you name it, I've tried it. Everything from felt to leather to memory foam to urethane to gel. I rummage around in hardware stores constantly looking for cool things to try. My latest, along with the cotton pads was a pack of bunion pads. Small soft, dense rings of sticky back foamy stuff. You have no idea the crazy lengths some of us go to.... Quote Link to comment Share on other sites More sharing options...
swt61 Posted January 21, 2009 Report Share Posted January 21, 2009 I weave the underarm hair of polynesian fisherman. They must be between 24 and 37 years of age for the best effect. And I find that if they've used roll on deoderant as opposed to gel the highs are better. Quote Link to comment Share on other sites More sharing options...
mypasswordis Posted January 21, 2009 Report Share Posted January 21, 2009 Only one question: How much do you charge per square inch? I'll take a combo of the roll-on and gel deodorant, I can't have my highs being too good, it won't sound real. Quote Link to comment Share on other sites More sharing options...
faust3d Posted January 21, 2009 Report Share Posted January 21, 2009 swt61 lies, there are no polynesian fisherman, he just shaves his back to get the hair Quote Link to comment Share on other sites More sharing options...
mypasswordis Posted January 21, 2009 Report Share Posted January 21, 2009 As long as it isn't his pubes. And as long as it makes my orthos sound like real life. I'll take an order of ERS paper, too. Quote Link to comment Share on other sites More sharing options...
Salt Peanuts Posted January 21, 2009 Report Share Posted January 21, 2009 swt61 lies, there are no polynesian fisherman, he just shaves his back to get the hair That reminded me of the guy I knew at high school who was so hairy that a t-shirt didn't actually touch his chest or back. On topic - are there certain types or 'grades' of felt any of you found to work better than others for orthos? Quote Link to comment Share on other sites More sharing options...
Dusty Chalk Posted January 21, 2009 Author Report Share Posted January 21, 2009 I can delete you all. Quote Link to comment Share on other sites More sharing options...
faust3d Posted January 21, 2009 Report Share Posted January 21, 2009 That reminded me of the guy I knew at high school who was so hairy that a t-shirt didn't actually touch his chest or back. On topic - are there certain types or 'grades' of felt any of you found to work better than others for orthos? Well, various felt works differently with different headphones. T20v2 needs dense felt as they are bass heavy in stock form, so do YH-100 and HP-50/YH-3 it seems. YH-1 need something that is more transparent as they don't have as much bass to begin with and heavy felt can kill the bass that is there instead of tuning it. I discovered after playing with different felt and materials that the denser the felt the faster and snappier the headphones will be and the tighter the bass will be, but it will also reduce in quantity. Quote Link to comment Share on other sites More sharing options...
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