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We've seen the tweaks you can do to minimize diffraction effects along the baffle around tweeters by way of felt, neoprene rings, etc. Damping these "diffractive-nasties" is supposed to focus the sound more, the treble, imaging. Treble is supposed to take on less hashy type qualities, sound sweeter.Why don't we see this more in speaker designs? I only see positives in doing this. One could argue the treble might sound too damped, the tonal character of the speaker could change, maybe the voice of speaker would change too much. It doesn't make much sense to me that voicing a speaker by way of factoring in characteristics of baffle diffraction makes much sense. Is it the time consuming task of applying felt to a design versus cost that turns designers off?
I have a pair of Paradox 1's, which I like very much. They are not nearly as hot in the treble as I was led to believe by some owners here at the Asylum. Actully a very accurate but musical tweeter with good equipment. However, due to my personal tastes and my room aberrations, I am going to experiment with applying some felt around the Focal tweeter on the Paradox 1's after having an enlightening experience yesterday. I had applied some thick egg crate acoustic foam around the tweeter, albeit way grossly overboard- but just a fun experiement, and found that the treble took on not only a more focused quality but a very smooth and musical quality as well. So I plan to try some felt for fun to see what happens.
Follow Ups:
I bought a used pair of Mirage SM-1's several months back. Felt rings were used around the tweeters to reduce "defraction" is what the literature said. Problem was only one tweeter had the felt and the other had fallen off and lost. To my ears the one speaker with the felt ring around the tweeter definitely sounded smoother and more focused. I tried findig a source for 1/4" thick felt to make another ring but was unsuccessful. Anybody know where to get some? The felt was similar to that of chalk board eraser but softer.
Check your nearest fabric store.
Checked all the fabric stores but none sold anything remotely close the kind of thick fabric used on the Mirage speakers. I was almost tempted to take a chalk board eraser apart and cut a ring using three or four pieces.
... who has done this? Their speakers sound like the natural candidate with a 14 inch front face.
Why not just put felt rings around your ears?
First time I ever heard of this it was in the owners manual to the Carver c-9 Sonic holography unit. At that time many speakers (even Advents) had a recessed front pannel. These days with flush from pannels and rounded edges, felt around the tweeters may be somewhat redundant.I've noticed, however, that M&K uses a variation -- a strip avove and below the driver to control vertical dispersion. It's not felt, though -- super secret unobtanium or something.
Ar introduced the AR-9 in late '77 featuring what they called the "sound blanket" which was a thick, soft felt like material. This surrounded the tweeter, upper and lower midrange drivers. They also used this feature on the smaller brother to the model 9 as well. Later, just about all the models in the AR line used this technique. There are other companies that used felt to combat edge and grill diffraction. AR was just one.
It is interesting that this subject has come up. I have recently bought a pair of Royd Doublets and they have not felt but a foam material aroung the tweeter mounting. I guess it is used for the reason everyone has stated in this thread. Interesting....
nt
Clickit!
I doubt Dunlavy or anybody could possibly patent the idea. As others have noted AR has been using the idea since the 70's as had the BBC on the dimunitive little monitor that is the fave of so many; the LS3/5a... Also down under in Australia, Mr Dunlavy's former brainchild "Duntech" still uses the technique as do two other speaker manufacturers founded by former employees/associates of his, called "VAF" and "Sonique". If one were to dig around a bit more into the past as well as the present, I am sure one could find many other examples. That being the case I would say that it is in the public domain, therefore it is common knowledge and hence unpatentable...
Cheers.
tomcat
I've been recommending this simple expedient for several years. It's definitely worth spending the time and effort (with the placement and amount of felt) to tune the treble just the way that you like it.Obstructions around the dome cause secondary reflections that "roughen" the frequency response of the tweeter. Using the formula for determining the frequency of quarter-wave boundary nulls (N=1130/D x .3) (boundary nulls are just one aspect of the phenomenon - there are peaks as well), its possible to determine that an obstruction within 1 inch of the tweeter will cause a null at 4 kHz (other frequencies might experience a power increase and the peaks that result) everywhere in the room. An obstruction within 1/2 an inch from the tweeter will cause a null at 8.137 kHz everywhere in the room. These boundary effects (created by obstructions 1 inch and 1/2 inch from the tweeter - such as the fixing screws that bind it to the baffle) occur in a part of the treble that we are very sensitive to. The colorations are very audible, as well as visible. When graphed, these treble oscillations resemble the rough edge of a saw. Using felting prevents the secondary reflections that create these boundary effects and greatly smoothes the response of the tweeter.
I agee with you that many speaker designers don't bother to take into account (fully) how the baffle will interact with the speaker's treble response. 90% of speakers have exposed fixing screws around the tweeter that will roughen the tweeters response. Designers seem unaware of the problems that this creates. Other designers mount the tweeter in a wave-guide (horn). The wave-guide is intended to prevent baffle-edge diffraction effects, but occasionally these oscillations are created by treble interactions with the horn itself (one famous example comes to mind - that of the KEF Uni-Q driver, which over the course of 10 years, dispayed a power response null in the high treble created by interactions between the dome and its surround/horn/woofer - this problem was only corrected in the most recent iterations of the Uni-Q driver).
Furthermore, it seems many designers voice the treble using the baffle. Specifically, the designers use the baffle itself as a wave-guide. It will tend to brighten the sound of the tweeter, by concentrating its power in a forward direction (the same principal as using reflective material behind a flashlight bulb to increase the brightness and directionality of the beam it produces). Consumers can re-voice the relative level (the brightness) of the tweeter by experimenting with felting, which absorbs rather than reflects treble output. The ultimate expression of this effort (which I have tried) is covering the entire tweeter baffle with felt, which greatly reduces the relative level (brightness) of the tweeter output.
To sum up, anything in the immediate vicinity (less than a few inches) of the tweeter will interact with the tweeter's frequency and power response. Speaker designers don't seem to have full understanding or control over these interactions. Felting (by smoothing treble response and controling the reflectivity of the baffle) allows consumers to re-voice speakers just the way they like them.
Thanks for the reply. I actually read a number of your posts on just this subject and a other really good information you have provided about room acoustics. I actually tried paging you through a post to email me a few days ago, I actually somewhat solved my problem and you hadn't replied so I deleted it. I had two room boundaries that were equal, distance from woofer to side wall and to the floor of one of my speakers that was slightly causing a small null in the mid bass. Moving it a touch fixed it. However, I am still dealing with a nasty 50Hz bass peak in my room, which both my Paradox speakers and subwoofer are suffering from. I think treatments is my only hope. Your extremely informative posts have been great, thanks.All your points duly taken. I might start by way of a large amount of coverage to see what happens. I was stunned at what the large pieces of foam did in my experiment yesterday. The effect made the treble seem so sweet, even more integrated in the whole sound (coherence) and more focused too. Given the wide dispersion of this tweeter, it's mounting plate relectivity and the 8 mounting bolts, it seems a good candidate to benefit from tweaks like this. I'll report back with some findings for curiosity sake. Thanks again.
My computer was taken down all yesterday by a very malicious virus, so that's probably why I missed your page (got some functions - like internet - working again today). That 50 Hz room mode is a tough one to tackle. I don't put too much stock in treatments for room modes. Have you tried listening from a different position? You will hear a different spectrum of modes in a different position. Perhaps the 50 Hz mode will disappear. Alternatively, curing bad room modes might be as simple as opening a door (or a window) unto your listening space, as the change in room dimension seems to "spread" room modes to different (hopefully less obnoxious) frequencies.
Felting (by smoothing treble response and controling the reflectivity of the baffle) allows consumers to re-voice speakers just the way they like them.Are there any explanations or diagrams on how to do this? My lower end B&W tweeters could really use something like this.
Jeff
Actually, its just trail and error, but I have found that a felt-ring around the tweeter is probably the best starting point. Start with a small ring. If the speaker is still too bright, try a larger ring, and so on, until you have covered the entire tweeter baffle (if necessary). Be careful not to touch the tweeter dome or drip adhesive on it (I apply rubber cement to the felt and I wait until its tacky - semi-dry - before I adhere the felt to the baffle).
I'm still lost. I have no idea where to put the felt. Maybe if you pretend I'm a six year old (not too far off) then I could understand where the felt goes.
Jeff
Have you not been following this discussion? We've been talking about placing felt around the tweeter. The tweeter is mounted on the baffle. The tweeter is a circular dome. In order to apply felt around the dome (without touching or covering the dome), you will need to get a pair of sharp scissors and cut a ring out of your felt squares (obtainable at fabric stores). Start with a small ring, and as I outlined above...progress to an upper-baffle sized piece of felt (with a hole cut out in it for the tweeter) if necessary. Apply the felt using an adhesive like rubber cement (ideal because it will not damage the speaker's veneer). Let me know if I can make it any plainer?
OK, I was thinking it went inside the speaker and around the tweeter to reduce vibration but it actually goes on the outside of the speaker (wasn't sure what the "baffle" was) and covers part of where the tweeter sound is going out. If I'm getting it now.My wife is a seamstress. She has a room full of fabric samples so I can try just about anything.
Jeff
You have the right idea now. Apply your felt rings to that board that holds the drivers (aka the baffle). Be careful to cut the right diameter circle (hole) in the felt, so that all the area around the tweeter is covered (by the ring), but the felt does not actually touch the tweeter.
quite a difference. Sometimes just a little thin ring (like 1/8", or less, wide is all that it takes. I found any ring @ all to be too drastic a change on a pair of Castle Isis speakers and instead ended up placing tiny dots of "wool" felt over the two woofer mounting screws which were adjacent to the tweeter (this cleared up a hard artifact that I was hearing @ louder volumes).It can also work with recessed tweeters as you are trying to dampen the edge surrounding/blocking the tweeter (such as I did with a pair of Minimus 7's). I used a 1/16" strip on the inner edge (formed into a circle) and a 1/2" flat ring on the front of the baffle.
Another easy tweak used by a guy (THOR) on his single driver speakers was to drape a piece of single ply tissue (TP) in front of the driver (which was a bit hot sounding).
My Twins have a 5/8" thin felt ring around the tweeters that I once covered with glossy paper. I kind of liked the brighter sound as our room is a little dead, but my wife did not care for it.
Anway, it's good cheap fun as squares of wool felt are available @ fabric stores for a buck or less. I also use this thin felt to adjust the VTA on my TT (slip in an extra disc of it for thinner LP's).
Thanks for the responses. The tweeter in the Paradox 1 speakers I have uses the Focal Tc90Tdx. Now, with this tweeter, the dome is flush mounted on the baffle but actually has an inverted diaphragm. Is this technically a recessed tweeter or could it still be considered a flush mount?Dekay- I saw your post the other day talking about using some felt around a tweeter and being a former Reynaud Twin owner I started thinking about the effects of felt around a tweeter. That prompted me to experiment a little with the acoustic foam. I liked the results. It's no secret the Focal tweeter in the Paradox speakers is very transparent, open and dynamic with very wide dispersion. Given it's very large and possibly reflective mounting plate, which actually does have a number (8) protruding mounting screws, I'd like to see what can be done with a little dampening. Interesting your experiement with the Twins, I wish I would have tried that. It might have been interesting because my gear was a bit too smooth at times and my room is pretty dead like yours which could sometimes make the Twins sound a bit too round.
This experimentation is only that, the way Danny at GR Research implemented the Focal tweeter in the Paradox is WELL done. This speaker never sounds bright or forward in my system. I just happen to like a little more of a sweeter sounding treble. I'll heed your advice and try different amounts. I'm glad you said that, my initial plan was to cover the entire Focal mounting plate, but that maye be WAY too much. I'm only looking to tweak. Maybe a decent sized ring at first, plus little dots to cover the outside screws? How about type of felt, would garden variety from a local fabric store work? You mentioned depth of the ring, are you talking stacked rings versus single layer? Thanks!
little Radio Shack speakers is flush with the front baffle (I consider this recessed). Idealy it should probably come out more, but I am too lazy to spend much time reworking a pair of $5 speakers. These are the speakers that I posted about and the felt made them sound a lot better (not as beamy).I have only used wool felt as I have read that wool is better (something about the fibers and their configuration that I do not quite understand). Our local fabric store sells precut 12" squares of wool felt for under $1 (probably cut from remnants/end of rolls that would otherwise be unsellable.
I would start with the little dots to see if any of the exposed screw heads are creating something wrong. I often see little self stick felt dots in drug/dime stores, but don't know what the felt is made of. I am certain, that as I, you will be amazed by what a difference just a single dot can make when it is placed close to the driver. With the Castle speakers the the tweeter screws were recessed (the way they should be), but the four screws holding the woofer were not. It took me a while to figure out that the two woofer screws, closest to the tweeter, were the culprits (causing a hard sound in the HF's @ higher volumes).
I have some very thick 1/8" wool felt but never tried this as the thin stuff made such a drastic change in the sound (it does however make a decent TT mat).
The best thing is that you don't have to mess anything up in order to experiment with this (it's completely reversable).
I have also noticed that natural fibre felts (wool or cotton) work best. They absorb sound better and don't reflect sound as much (or as badly) as synthetics. Ordinary polyester felt (made of tiny plastic fibers) does not sound as good. By extension, carpets made of natural fibers sound much better than acrylic carpets (which have a tendency not only to absorb and dry out the mid-range but also reflect a confused treble pattern).
Ironically, after felting, I have often found that I wanted to increase the level of the tweeter output by adjusting the crossover. Designers often voice the tweeter using the baffle. Felting will remove the wave-guide aspect of the baffle.Your Focal tweeter is flush mounted into its faceplace as the dome surround is contiguous with the surface of the mounting plate (even though the dome is concave). I do not recommend using really thick or raised material around the dome as these might prove REFLECTIVE and create the kind of problems that you are trying to solve.
It depends entirely on the design of the speaker and the implemenation of the tweeter. In some cases, felt is used to improve performance. In other cases, obviously, it's not.In terms of "factoring in characteristics of baffle diffraction..." many good designers do, indeed, look at the baffle and design the baffle to work *with* the drivers. Part of that may be the application of felt, other times not.
Are you the same Doug Schneider that use to have a publication in the 80's like Bound For Sound. Thanks Jeff
No.....but I am the Doug Schneider who has some current publications that are part of www.soundstagenetwork.com.Didn't know about the other one!
AFAIK the felt trick is used for a tweeter, when it is top mounted and not recessed.
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