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Can a felt damage the frequency response of a driver ?

post #1 of 8
Thread Starter 

Hello to Everyone !

I have a very basic question

Can a felt be too thick to cause a dip in the frequency response of an headphone like the one present here just above the 10kHz ?

Or the effect of a felt is measurable only in fraction of dB of attenuation ?

 

http://www.google.it/imgres?imgurl=http://cdn.head-fi.org/3/3e/1000x500px-LL-3e3629a2_graphCompare.php&imgrefurl=http://www.head-fi.org/forum/thread/553497/hd598-review-jack-of-all-trades/15&usg=__iqkvXLqCI99SfkUkGHGpqPkYb1Q=&h=340&w=425&sz=51&hl=it&start=0&zoom=1&tbnid=ouLUlibCLiF_lM:&tbnh=120&tbnw=150&ei=D0vZTaneCcqEswb_vuT3Ag&prev=/search%3Fq%3DSennheiser%2BHD%2B558%2Bgraph%26um%3D1%26hl%3Dit%26client%3Dfirefox-a%26sa%3DN%26rls%3Dorg.mozilla:it:official%26biw%3D1138%26bih%3D533%26tbm%3Disch&um=1&itbs=1&iact=hc&vpx=122&vpy=75&dur=137&hovh=201&hovw=251&tx=136&ty=98&sqi=2&page=1&ndsp=18&ved=1t:429,r:0,s:0

 

Could the FR without the felt be flatter in the range 10 to 20 kHz ?

Personally I am worried by felts blink.gif after hearing sensible improvements in sound every time I have removed them.

Thanks and kind regards,

gino

 

P.S. just some readings

 

http://metricfelt.com/felt-sound-vibration.htm

 

Since the effectiveness of vibration/sound absorption increases with frequency, it can be assumed that, as felt is effective at very low frequencies, it is even more effective at higher frequencies.

 

Any time I remove it I heard a better sound. Any.

 

 

 


Edited by ginetto61 - 5/22/11 at 12:15pm
post #2 of 8
Thread Starter 

Excuse me for retake the issue

I address the question to people who know well these two sennheiser models, 600 and 558

 

http://assets.head-fi.org/d/d6/1000x500px-LL-d6cb6f4f_hd558hd600.PNG

 

the dip in 558's curve just above 10 kHz can be caused by the felt placed over the driver ?

Is there a felt separating the driver and the ear in the 600 as well or it is missing ?

Thanks a lot and kind regards,

gino

 


Edited by ginetto61 - 6/12/11 at 8:48am
post #3 of 8
i did that once removing felt from my akg 240 studios improved them. i removed the felt off the ear cup vents and used a thinner foam padding to put in front of driver and used pair of akg 240 sextett earpads cause they felt lot better and was thinner. the pleather pads on the studios felt too stiff and artifical. noticed midrange came in lot cleaner/clearer,bass tighten and sound stage widen and gotten deeper as well.

that's my experience. never touched my other headphones. i read the article. interesting. didn't know wool was a great absorber as well but makes sense. i'm guessing it can impact the response of the drivers in the headphones same way how wool,carpet,ect. can effect room acoustics. i think the wool felt is used for headphone driver due how close they are to your ears to help dampen some higher frequency resonance that affect your ear drums. i find felt only useful on the driver itself unless it was closed headphone. i find with open/semi-open it can help removing the felt if any around the ear cups to get rid of bass resonance cause allowing frequencies/air to escape more freely.
post #4 of 8

Well, my HD558 sound about the same with or without the filters (they are removable). It's not felt, it's a really, really thin fabric they're made of, which seems to have no effect on the sound.

post #5 of 8

The past Lambda series Stax phones (202, 303, 404) used to have a thin sheet of (very) open cell foam between the ear and the driver. A couple of years ago or so Stax replaced the old pads with a new model, featuring a detachable piece of thin cloth instead of that foam. I have extensively compared the same pads with foam and with cloth, respectively, as well as with a lot of other materials. Big difference to my ears! The foam was definitely better: more transparent and better tonal balance.

So yeah, everything between the ear and the driver affects the sound, in many respects, and often some are for good and others are for bad. But overall, the thinner is usually the better (or at least the more transparent), provided one can compensate for the different tonal balance resulted. Exception: none at all is not necessarily better, I suppose it has something to do with suppressing some reflections or so.

post #6 of 8
Thread Starter 

 

Thank you very much for all your valuable advice

I would prefer a grid with large meshes place over the driver just to protect it against bumps (a solution similar to the one adopted by Grado)

I think that a good driver should be intrinsically  flat and with wide bandwidth and not to rely on felt/foam to tame its irregularities

In the end I strongly think that the secret of performance is basically in the driver

Thank you very much again

Kind regards,

gino

post #7 of 8

You're welcome!

That driver you are talking about is an ideal that might just be harder to attain than we consumers think sometimes. And then there is the problem of the reflections from head to the housing or driver and back, and there might be some more. I'm not a specialist, I can just tell you things are not so easy. Each of the AKG K1000 drivers (not a cheap or underengineered headphone by any means) are put in a cage made of a sort of plastic wire mesh and free floating close to the ear, without any pad around the ear or anything, and they needed to insert a small PCB with a circuitry into each headphone just to filter a certain frequency that would otherwise get much elevated because of these reflections, I think around 2kHz or so iirc.

post #8 of 8
Thread Starter 

 

Thank you very much again for your kind and valuable advice

I understand the complexity of the task.  A little variation in the ear cup can cause a sensible variation in the FR for instance

It seems as a sort of fine tuning is needed with headphones to extract the best performance from a driver

Thanks and regards,

gino

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