Just listened to some Fostex T50RPs today... WOW!

I'm paralyzed. I'm waiting for mrspeakers final mods... ;/

I just noticed that I have had these headphones on for nearly 5 hours....they remain ubber-comfy.
 
Seriously guys...try that suspension headband mod....it's awesome.

Quote:

bluemonkeyflyer said:

^ arnaud, 
 
Thanks for the information and graphs.  Very interesting.  Good stuff on the HD800 mod, too.  I found melamine sponges on Amazon.
 
So, it appears melamine sponge is better at absorbing higher frequencies and can be tailored to target various frequency range absorption by using different thicknesses.  Is this correct?  Do you know of a material to add to the internal volume of the cups to attenuate the quantity (not the quality) of frequencies from 20hz to 250 hz?  
 
I happen to like the bass quantity/quality of my current T50RP mods but my wife wants a set with less bass quantity, thus the search for a fix.  I think one possibility is to use standard mods of plasticine in the baffles and Paxmate or Silverstone in the cups, leave the denser white felt on the back of the drivers, and try with/without a reflex dot - OR standard mods but remove the white felt and apply more than one layer of Organdi.  It make sense to try leaving the white felt intact, first.
 
Could you explain why/how loose, non-compressed fiber in the cups increases the effective volume vs. why/how densely packed fiber reduces the effective cup volume?

Click to expand...

Hi there,
 
- In regards to the effectiveness of the material scaling with the thickness, you are absolutely correct. Here's an example with mineral wool:

- In regards to a sound absorber for low frequencies, I am afraid it is not available for headphone due to the small size. On the other hand, you can (and have I believe) play with the earcup volume to change its compliance (since there are no acoustic resonances at those frequencies, the driver "sees" the stiffness of the air volume). Obviously, opening or closing the vents has a major impact on the compliance as well...
 
- As for explaining why/how loose, non-compressed fiber in the cups increases the effective volume:
1. Intuitively, my take is that replacing the air volume with a fibrous medium make it effectively look bigger because sound waves can no longer travel straight through but have to go around a maze of small intertwined fibers.
2. Physically, I can't write it down here but it's like wave propagation in air vs. water, it's a different acoustic medium with a different sound speed so resonances (and thus apparent dimensions) are shifted.
3. On the other hand, when you stuff fibrous material to the point that there is no longer air trapped between the fibers, you're basically reducing the effective air volume of the cavity, which also shifts the resonances (in the opposite direction though)
4. Best illustration is in image so here it goes:
 
First the SPL comparison between 3 earcups models: the green curve is a "bare" earcup (cylinder of 3cm radius, 1cm depth) without wool (but with some average surface absorption of 10%). Its first acoustic resonance occurs at 3.4kHz. The red curve correspond to a same size earcup filled with (uncompressed) mineral wool. Its 1st acoustic resonance is drastically shifted down to 1.6kHz (so it looks like 2x bigger than the bare cavity!). Note that although it's simulated as filled volume, the effective absorption is also 10% to allow comparison with the other models (in reality is much higher toward high frequencies, see curve above). The blue curve is a smaller size earcup (see animations below) due to heavy stuffing of material. The 1st resonance is pushed up to 4.2kHz (so it goes the opposite way to the cavity filling with uncompressed wool).

Next is an animation of the pressure response at the 3 frequencies mentioned above so that you get a feel for the acoustic behavior. The stuffed cavity is on the left, the "bare" earcup in the middle and the one filled with mineral wool is on the right. As you can see, the response is more complex in the right cavity by the time the 1st resonance is reached for the other 2 (the wavelength is smaller, the sound speed is higher):
1.6kHz:
3.4kHZ:
4.2kHz:

Interesting post Arnaud. I'm not sure I completely understood it, but since we seem to be on the topic of different sound damping materials I was wondering if anyone had considered sound dampening paint, I've seen a couple of different kinds used for dampening sound in boats, Noxudol 3101 and Silent Running. Both products seem to work on the principle that sound energy and vibrations are converted into heat. So I'm curious if anyone else has used the stuff or think it's a viable dampening material to try in the T50? 

Having nearly infinite liquid to disperse heat generated from the hull of a boat is a different scenario than a very small closed volume with delicate electronics in it. Although this is an interesting concept and I need to look further into these paints.
 
I really need to learn to better read headphone measurements such as those posted by Arnaud or Tyll. My biggest obstacle is that I have read enough complicated plots in my schooling and day jobs that I am not sure my brain is open to learning a totally different set of acoustic reading skills. Does anyone have any good advice for figuring the measurements out?

Quote:

sharkz said:

Having nearly infinite liquid to disperse heat generated from the hull of a boat is a different scenario than a very small closed volume with delicate electronics in it. Although this is an interesting concept and I need to look further into these paints.

Click to expand...

 
The heat generated is minute. If you click on that silent running link they have an explanation of how their product works. What makes me curious though is the way it dampens sound and vibration (plasticky resonance). There is also a video on that link that is really interesting. My thinking is if it can dampen the noise coming from that machine the way it does it could certainly dampen the resonances in the T50. The flip side is why reinvent the wheel. I'm pretty happy with the paxmate. Although it's been about a month since I've listened to them. I loaned them to Questhate who has since bought a pair of his own and he forwarded them to Tyll to measure, Like you my coniferating skills reading FR graphs and charts are next to Nil, hopefully I can glean something. My SR60's with the African Blackwood cups and the African Mahogany driver housings are also being measured. So hopefully I'll have something interesting to add to both threads soon.

Quote:

arnaud said:

Hi there,
 
- In regards to the effectiveness of the material scaling with the thickness, you are absolutely correct. Here's an example with mineral wool:

- In regards to a sound absorber for low frequencies, I am afraid it is not available for headphone due to the small size. On the other hand, you can (and have I believe) play with the earcup volume to change its compliance (since there are no acoustic resonances at those frequencies, the driver "sees" the stiffness of the air volume). Obviously, opening or closing the vents has a major impact on the compliance as well...
 

Click to expand...

Hey there, arnaud!
 
I was wondering if you could plot simulations like ^ that for more popular materials like wool felt or cotton or even paxmate?
Or do you ANYBODY?! know where one can find a sort of online database with such kind of information for different materials?
 
It would be information of great value for a lot of us modders...
I don't think there's such kind of information on Head-fi...
 
Thanks!
 

arnaud,
 
Thank you for taking the time to answer my question with such detail and rich data - Brilliant!  I understood the second part of my question but could not get my head around how loose fill material increases effective cup volume  Very interesting and practical information.
 
Quote:

arnaud said:

Hi there,
 
- In regards to the effectiveness of the material scaling with the thickness, you are absolutely correct. Here's an example with mineral wool:

- In regards to a sound absorber for low frequencies, I am afraid it is not available for headphone due to the small size. On the other hand, you can (and have I believe) play with the earcup volume to change its compliance (since there are no acoustic resonances at those frequencies, the driver "sees" the stiffness of the air volume). Obviously, opening or closing the vents has a major impact on the compliance as well...
 
- As for explaining why/how loose, non-compressed fiber in the cups increases the effective volume:
1. Intuitively, my take is that replacing the air volume with a fibrous medium make it effectively look bigger because sound waves can no longer travel straight through but have to go around a maze of small intertwined fibers.
2. Physically, I can't write it down here but it's like wave propagation in air vs. water, it's a different acoustic medium with a different sound speed so resonances (and thus apparent dimensions) are shifted.
3. On the other hand, when you stuff fibrous material to the point that there is no longer air trapped between the fibers, you're basically reducing the effective air volume of the cavity, which also shifts the resonances (in the opposite direction though)
4. Best illustration is in image so here it goes:
 
First the SPL comparison between 3 earcups models: the green curve is a "bare" earcup (cylinder of 3cm radius, 1cm depth) without wool (but with some average surface absorption of 10%). Its first acoustic resonance occurs at 3.4kHz. The red curve correspond to a same size earcup filled with (uncompressed) mineral wool. Its 1st acoustic resonance is drastically shifted down to 1.6kHz (so it looks like 2x bigger than the bare cavity!). Note that although it's simulated as filled volume, the effective absorption is also 10% to allow comparison with the other models (in reality is much higher toward high frequencies, see curve above). The blue curve is a smaller size earcup (see animations below) due to heavy stuffing of material. The 1st resonance is pushed up to 4.2kHz (so it goes the opposite way to the cavity filling with uncompressed wool).

Next is an animation of the pressure response at the 3 frequencies mentioned above so that you get a feel for the acoustic behavior. The stuffed cavity is on the left, the "bare" earcup in the middle and the one filled with mineral wool is on the right. As you can see, the response is more complex in the right cavity by the time the 1st resonance is reached for the other 2 (the wavelength is smaller, the sound speed is higher):
1.6kHz:

3.4kHZ:

4.2kHz:

Click to expand...

 

Here is a picture of my suspension mod that I mentioned back in post 2607. 
 
Some people have posted along the lines of "Why bother, the stock band is OK for me?"  Well, you only THINK  it's comfortable, the way people who have only heard entry level cans THINK they have good SQ. 
     The stock band "sort of fits" the "sort of average" head.    With the structural steel separated from the headband, the fabric PERFECTLY conforms to YOUR head. 
 
 
 
 

Drat, my Stax puppies are complaining they are not being attended to anymore.

Quote:

sardonyx said:

Here is a picture of my suspension mod that I mentioned back in post 2607. 
 
Some people have posted along the lines of "Why bother, the stock band is OK for me?"  Well, you only THINK  it's comfortable, the way people who have only heard entry level cans THINK they have good SQ. 
     The stock band "sort of fits" the "sort of average" head. 

  With the structural steel separated from the headband, the fabric PERFECTLY conforms to YOUR head. 

 
 
 
 

Click to expand...

 
Missed that post of yours.
 
Here I was thinking I was the second person to do a proper suspension mod.
 
 


Quote:

dogears said:

Drat, my Stax puppies are complaining they are not being attended to anymore.

Click to expand...

Time to sell them to fund another T50RP....
 

^Will keep 'em - just when I want that kind of sound (sounds great on certain albums) PLUS its getting rare y'know Would be a great headphones for my kids someday
Who's the first then (suspension mod)?
Hope to start the open ortho project next month.

Patiently awaiting mrspeakers mods...

What did not work:
 
I thought I had a brainstorm but it turned out to be a little squall.
 
I stopped by the drug store and looked for 3M Micropore and Transpore tape.  They didn't have any so I bought some paper tape made for bandages.  It looked a little bit thinner than the stock white driver felt.  I applied one layer on the driver backs, glued it down to the grid, and let it dry.  Result?  Sounded like a tin can or a cheap transistor radio.
 
I pulled it off and scratched my head.  O.K., put the white driver felt back on.  I'm glad I saved it.

And I'm also glad you saved it