[edstrelow]

 
 
As for dynamics, I have a BeyerDynamic DT990 Premium....that has some boomy/treblish signature that works ok for electrical music but certainly not for any acoustics. I have added small pieces of sorb around the driver and onto the back of the driver - not much, because the space is very limited - but the result is about the same. It still have the signature but the sound is definately more clear and dynamic in comparison

That's very interesting. Tends to confirm my thoughts that the damping issue is a general one in headphones and not just stats. It's been so long since I owned any dynamics that I was in no position to tell. I hope to get a chance to  try some sorb on others at the upcoming Canjam where I will be setting up most of my sorbed phones.

 

[soren_brix]

Did some 'investigations' of mine 007s.
Putting them on my head, and then start tapping various places on the house, the mesh, and right onto the tab where the arc is fixed to.
As far as I can hear there are several clear  resonanses going on.
The arc has a few dominant ones and the mesh contribute with some as well.
Tabbing the mesh with my fingernail returns some ringing as well as a more distant deeper one that is clearly reduced when holding onto the arc.
I disassembled the arc from the housings and investigated the houses alone.
Sounds like there are some not so prominent resonanses when tapping the mesh.

I have not damped the black metal plate onto where the pads are fixed. Tabbing those did provoke any ringing as far as I could hear.
The arc resonances are really the most significant and also hardest to get rid of in my experience.
The approach described by Edstrelow seems to work the best.
Tried to strip the arc from the leather stockings and add sorbothane ... didn't work out.
I guess Edstrelow has a point when he suggest that the 007 arc is a mistake.
The Omega arc/Lambda type of arc seems to be a better choice.
AFAIK Spritzer had (or has) an Omega with 007mki replacement drivers + some other Birgir specials, that he has described as the best Stax ever. Maybe it boils down to the being the arc? The 009 arc seems to be more similar than different from the Omega arc.
 
I have done almost the same mod as Edstrelow to one of my 007's, and added to that:
two pieces of sorbothane approx 1" x ½", which is placed on the tab where the arc is fixed (on top of the STAX logo that is), and another piece across the housing/mesh rim.
Yellow areas on the pic. On the red areas I've laced clamps like Edstrelow.
I can confirm the same findings as Edstrelow as to the improvement in sound quality.
 

 

[soren_brix]

Attached a FG to one channel and swept through the lower fq's <200Hz.
Sounds like the arcs resonance is close to 150Hz. not actually measured - but found by hearing with help from a FG, like tuning a guitar)
What I noticed the most is that somewhere between 150-200Hz and below there is a clear resonance present in the opposite channel.
Putting the clamps on, or even just damping the arcs with a hand is enough to remove the resonance.

 

[edstrelow]

  Attached a FG to one channel and swept through the lower fq's <200Hz.
Sounds like the arcs resonance is close to 150Hz.
What I noticed the most is that somewhere between 150-200Hz and below there is a clear resonance present in the opposite channel.
Putting the clamps on, or even just damping the arcs with a hand is enough to remove the resonance.

That looks like an excellent way to study this problem.  A 150 Hz resonance would be quite audible and deletetious to sound. (I assume that FG means frequency generator?)
 
I don't fault Stax for missing the need to dampen the earcups with sorbothane or whatever other means one can find because I think this problem has been largely or entirely missed by other headphone designers.  However, I do think they should have spotted that their arc assembly was a bad design. I suspect that they did and that is why the 009 has a different assembly. It is probably too much to expect them to say "we goofed."

 

[soren_brix]

no japanees say we "goofed" ... would be kamiaze ;o)

 

[edstrelow]

Post deleted

 

[edstrelow]

"Damping" and "resonance" mean several different things as applied to headphones and speakers. "Damping" in my use refers to the reduction of  vibrations in headphones  by materials (in this situation, sorbothane.)  What  vibrations? In this context we are referring to the vibrations passed to the earcups and other parts of the headphone by the movement of the driver. Newton tells us that there is an "equal and opposite" reaction to the driver's motion. That seems to indicate that the energy getting into the earcup is equal to what is making all the sound we listen to and thus there is considerable potential for distortion of headphone sound by these vibrations. 
 
Here is a definition from Wikipedia: 
 
"Damping is an influence within or upon an oscillatory system that has the effect of reducing, restricting or preventing its oscillations. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation"
 
How does sorb dampen vibrations?  According to the company by converting the vibrational energy to heat.  Again according to  Newton, energy cannot be created or destroyed but it can be turned into some other form of energy.   I would assume that the vibrational energy getting into the cups normally dissipates, probably as heat, but probably a bit slowly.  What I think the sorb does when added to the cups, is get rid of the vibrations faster so they have less impact on what we hear.
 
 Damping also is used to refer to the use of foam and other materials behind the drivers which is used to tailor the sound.  Thus my SRXIII's have a wad of fiber material behind the drivers. The 007's don't. Presumably these materials behind the drivers dampen specific frequencies.
 
I have also used the term "resonance," sometimes when I probably meant vibrations. Resonance refers to the tendency of physical objects and airchambers to vibrate at specific frequencies. Thus  a headphone has a specific frequency which it will tend to maximally vibrate at.  soren-brix, above, also notes that individual parts may have their own resonant frequencies and that for the 007 arc assembly that seems to be about 150Hz.
 
A definition from Wikipedia:
"In physics, resonance is the tendency of a system to oscillate with greater amplitude at some frequencies than at others."
 
In these experiments the sorbothane appears to be dampening vibrations, including resonant frequencies although exactly how much of what frequencies I don't know.
 
I am uncomfortable in these discussions because I have no background in physics other than some high school and college classes, nor am I a mechanical engineer. My doctorate is in experimental psychology in perception, including the study of vision and hearing. I also spent 5 years doing post-doctoral work in a Department of Electrical Engineering but I have been a lawyer for the last 25 years. But none of this background  really prepares me for this specific topic. However I have observed the various odd things about sorbothane and headphones described above and am trying to make some sense of it all. Anyone else is free to have a go, preferably after having tried some sorb mods themselves.
 
soren_brix "no japanees say we "goofed" ... would be kamiaze ;o)
 
Hopefully no-one at Stax will fee the need to commit ritual suicide because we criticize their design of  the 007.

 

[soren_brix]

  "Damping" and "resonance" mean several different things as applied to headphones and speakers. "Damping" in my use refers to the reduction of  vibrations in headphones  by materials (in this situation, sorbothane.)  What  vibrations? In this context we are referring to the vibrations passed to the earcups and other parts of the headphone by the movement of the driver. Newton tells us that there is an "equal and opposite" reaction to the driver's motion. That seems to indicate that the energy getting into the earcup is equal to what is making all the sound we listen to and thus there is considerable potential for distortion of headphone sound by these vibrations. 
 
Here is a definition from Wikipedia: 
 
"Damping is an influence within or upon an oscillatory system that has the effect of reducing, restricting or preventing its oscillations. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation"
 
How does sorb dampen vibrations?  According to the company by converting the vibrational energy to heat.  Again according to  Newton, energy cannot be created or destroyed but it can be turned into some other form of energy.   I would assume that the vibrational energy getting into the cups normally dissipates, probably as heat, but probably a bit slowly.  What I think the sorb does when added to the cups, is get rid of the vibrations faster so they has less impact on what we hear.
 
 Damping also is used to refer to the use of foam and other materials behind the drivers which is used to tailor the sound.  Thus my SRXIII's have a wad of fiber material behind the drivers. The 007's don't. Presumably these materials behind the drivers dampen specific frequencies.
 
I have also used the term "resonance," sometimes when I probably meant vibrations. Resonance refers to the tendency of physical objects and airchambers to vibrate at specific frequencies. Thus  a headphone has a specific frequency which it will tend to maximally vibrate at.  soren-brix, above, also notes that individual parts may have their own resonant frequencies and that for the 007 arc assembly that seems to be about 150Hz.
 
A definition from Wikipedia:
"In physics, resonance is the tendency of a system to oscillate with greater amplitude at some frequencies than at others."
 
In these experiments the sorbothane appears to be dampening vibrations, including resonant frequencies although exactly how much of what frequencies I don't know.
 
I am uncomfortable in these discussions because I have no background in physics other than some high school and college classes, nor am I a mechanical engineer. My doctorate is in experimental psychology in perception, including the study of vision and hearing. I also spent 5 years doing post-doctoral work in a Department of Electrical Engineering but I have been a lawyer for the last 25 years. But none of this background  really prepares me for this specific topic. However I have observed the various odd things about sorbothane and headphones described above and am trying to make some sense of it all. Anyone else is free to have a go, preferably after having tried some sorb mods themselves.
 
soren_brix "no japanees say we "goofed" ... would be kamiaze ;o)
 
Hopefully no-one at Stax will fee the need to commit ritual suicide because we criticize their design of  the 007.

 
Talking about Newton's Third, you'll have factor the mass'es in question into account, so the moving diaphragm weighs significant less than the housing.
Just had a quick glance at the mylar density, (is the mylar density really roughly the same as air?? looks like it) and some quick calcs ends up in the area of 20mg (using 5cm radius, and 2my as thickness).... I guess the housing itself would be in the neigbourhood of 200g ... so the relation would 1:10.000 .... it shouldn't be audiable at all ...
 
In rgrds to a mecahnical system there are often several resonances present and usually one dominate one where the system will 'burn' the energy that came from the system being excited; like hitting a door bell - hiting the bell and you hear the ringing (resonance(s)) in return.
If you disassemble the 007 and hold the housing on the tip of a screwdriver and hit it gently ...theres a ringing going on ... putting in the driver and that ringing is gone (or damped significantly).
if you tap in the mesh with your fingernail, theres a short ringing from the mesh ... putting a gentle fingertip on the mesh ... that ringing is gone.
Taking the big O-ring (that holds the housing) and is attached to the arc's, and hold the O-ring on a screwdriver and hit it, you have the doorbell.
 
Now, the two big O-rings are attached to each other by the two arc's forming a close-loop (the arc's seems to be made of a material that pretty much resembel the steel used for making springs. Bad choice IMO.
If one the arc's are being hold fix at one end and the other end is free, there is a resonance (not surprisingly) that resembels the sound that can be heard when wearing the phone and tapping on the housing.
 
I noticed a small difference between the two 007s I have.

 
Sorry for the fuzzy pic.
The 70xxx I have has the arc's fixed directly to the big O-ring(holding the actual house), and on the other side there are those small washers inbetween the arc and the big O-ring.
The Sz1-xxx I have has no such washers.
The O-ring resonance is damped when the Arc is mounted in either way (with or without washers).
But the arc resonance is of course more damped if the washer is not used. Having washers one side only or both sides one one arc doesn't change things much. I prefere to not use the washers.
I find it a bit peculiar to use washers like that, I mean washer are intended to be right under the head of the screw.
If the headphones are adjusted to the arc's is touching the headband the coloration is also damped.
 
I suspect that the culprit is a combi of the construction (having two arc's) and the arc matrial.
 
Finally, as said in the begining of this post, it shouldn't possible for the driver to excite the resonans to an extent that it flows back as an audiable coloration, but it actually does ...I am puzzeld by this.
 
 
 
 
 
"

 

[edstrelow]

 
Finally, as said in the begining of this post, it shouldn't possible for the driver to excite the resonans to an extent that it flows back as an audiable coloration, but it actually does ...I am puzzeld by this.
 
 
 
 
 
"

So is the distortion we hear in the undamped phones feeding back to the drivers or are we hearing it from the vibrating earcups?

 

[edstrelow]

"More is not better. A large lightly loaded sheet will have a high spring rate and will not deflect enough to provide good isolation. Over compression will lead to short service life. The proper compression range is 3 to 20 per cent depending on the "Shape Factor." Shape factor is the ratio of contact surface (one side) divided by perimeter area. Use many small discs rather than a few large rectangles for best vibration isolation performance. Thickness matters. The thicker the sheet the lower the natural frequency. You need a sheet at least one-inch thick to get your natural frequency down to 10 Hertz. (10 Hertz is your target natural frequency for a 900 RPM motor.) 3M 200MP pressure sensitive adhesive backing easily bonds the Sorbothane sheet to metal, plastic and other surfaces. This sheet is perfect for cutting to meet the needs of special applications or can be used whole. Can be but using a sharp utility knife or scissor. Apply sheet as a whole or use to coat the inside of speakers or equipment housings to provide sound insulation. 1 cm of Sorbothane can isolate up to 40 dB of sound"
 
I found this on an Amazon add for 1/8 in sorbothane.   I have no idea how accurate it is but it gives some suggestions.

 

[soren_brix]

  So is the distortion we hear in the undamped phones feeding back to the drivers or are we hearing it from the vibrating earcups?

I do not believe so much in the action/reaction theory on this, the mass realtion is simply too small.
What I came to think of is some music instruments.
For instance the spanish guitar (Torres), has been altered for seven, eight and sometimes even more strings. If you play one of those, you'll instant notice, that the bass become fuller and get more sustain. That is also true if you play it as a regular six string (not using the seventh or eights string), but those string will add to the sound anyway since they will vibrate sympathetically.
That is also used in various ways in grand pianos.
Blüthner uses an extra string to create this, called aliquot (meaning something 'extra', also known from number theory in Math).
Steinway also uses a similar method called duplex, which is actually a short tail to the string itself.
Fazioli uses a more refined version of the Steinway duplex, as those can be individual adjusted. Steinway has their duplex fixed to the frame and cannot be adjusted.
What happens is that the system (string, or arc) has a resonance, and when this resonance, or octaves of it, are hit by sound (air vibrating), those 'free' systems (the aliquot, duplex, or the arc) will kick in.
In the case of the 007, my experince is that it is the arc itself that has this resonance, and it is transfered to the house by the connection to the big O-ring.
 
The most effective way of 'finding' this resonance, is to wear the phone, and tap on the outside of the one house with the finger tip, at 1-2 o'clock ...then it is clearly audiable.
Also doing the same, while placing a light finger tip on only one arc, an inch or two distant to the connection point, you can almost dampe it away. Not entirely, but almost.
When playing music, the arc adds some reverb and sustain to the lower end, and also a bit of smear. As far as I have experienced.

 

[soren_brix]

 
"More is not better. A large lightly loaded sheet will have a high spring rate and will not deflect enough to provide good isolation. Over compression will lead to short service life. The proper compression range is 3 to 20 per cent depending on the "Shape Factor." Shape factor is the ratio of contact surface (one side) divided by perimeter area. Use many small discs rather than a few large rectangles for best vibration isolation performance. Thickness matters. The thicker the sheet the lower the natural frequency. You need a sheet at least one-inch thick to get your natural frequency down to 10 Hertz. (10 Hertz is your target natural frequency for a 900 RPM motor.) 3M 200MP pressure sensitive adhesive backing easily bonds the Sorbothane sheet to metal, plastic and other surfaces. This sheet is perfect for cutting to meet the needs of special applications or can be used whole. Can be but using a sharp utility knife or scissor. Apply sheet as a whole or use to coat the inside of speakers or equipment housings to provide sound insulation. 1 cm of Sorbothane can isolate up to 40 dB of sound"
 
I found this on an Amazon add for 1/8 in sorbothane.   I have no idea how accurate it is but it gives some suggestions.

if you hold up the baffle from a lambda (404 and older) and hit it, you'll have a clear door bell.
Placing two 1/5" x 1/5" sorbothane in each corner, and this is gone.
The thing that puzzels me is the fact that the baffle with mounted driver and mount in the house sounds rather dead, and still the sound is clearly improved by add damping.
I recall back in the days that I modified a Thorens 166.
All in all a nice turntable but with hugh potential.
The platter itself was ringing as hell and even a rubber mat that took away almost everything left 'something' behind. I damped the platter using some car damping from Volvo (very light, much lighter than sorbothane) and the improvement was significant.
A friend of mine which had the Thorens 160 (a bigger model, that had a heavier platter, and an innerplatter that in combination sounded like they cancelled each other out - the outer platter, and inner platter were both ringing, but together, no ringing). He did the same damping of his platter, and had the same experience.
Since then I have got an Oracle Delphi that has this MVSS system. The MVSS (Micro Vibration Stabilisation System) is mount just nearby the springs and according to Jaques damps micro vibration that travers through the springs.
The Delphi is mechanical so well built (the electric part is kind of having the 'french' charm, so to speak that it is kind of surprising that something like MVSS should improve anything at all - but it actually does.
Basically the MVSS is crying simpel - just a stick in a small tub filled with silicone. Taking the stifness and masses of the floating plate, the platter etc into account, it shouldn't have any effect.

 

[edstrelow]

  I do not believe so much in the action/reaction theory on this, the mass realtion is simply too small.

I think I see the point you are making here, that because the electrostatic drivers are virtually massless  their mass is not contributing much to the vibrations of the driver housing that are presumably the source of the vibrations getting into the earcups.  However the electrostatic drivers are still pushing air around which has a resistance and the housing and earcups are still going to have energy pumped into them because of  that action, Newton's "equal and opposite" energy  principle. Presumably with heavier drivers such as magnetic planars and dynamics,  there is even more energy transmitted into the earcups to be damped because now the mass of the driver is a significant factor.
 
I agree that ringing exists, especially in the 007's arcs.  .   Every object is going to have a resonance, the earcup, one, and individual parts may have their own giving a complex set of resonant peaks when stimulated by sound.  You can thus clean up headphone sound by damping generally, especially when by placing sorbothane close to the driver, or target specific problem areas such as the 007's arc assembly.
 
I am more familiar with pianos, having 2 in my house. Pianists use damping to adjust the sound by depressing the pedals.  The right pedal allows "sympathetic resonance" in which other strings, even if they have not been struck by the keys can be induced to vibrate and contribute to the richness of sound.
 
Here is a description from Wikipedia
"The sustaining pedal, the right pedal on the modern piano, has been called "the soul of the piano".^[1] This pedal raises all the dampers off the strings so that they keep vibrating after a key on the keyboard has been released. It adds much expressivity, allowing notes to resonate, and certain harmonies and notes to be connected together."
 
There is also on some pianos a middle pedal which leaves damping in place except for the notes being struck:
 
Again Wikipedia:
 
"The last pedal to be added to the modern grand was the middle pedal, the sostenuto, which was inspired by the French. By using this pedal, a pianist can sustain selected notes, while other notes remain unaffected"
 
However, what may be good in a piano is not good in a headphone. There is no way we want "sympathetic resonance" in headphone cups. That would always be distortion in my estimation although I am sure many designers have played with it deliberately or inadvertently to give a  headphone its particular "euphonic" sound.  With substances like sorbothane you don't have to play the euphonic game so much.

 

[edstrelow]

 
"More is not better. ..Use many small discs rather than a few large rectangles for best vibration isolation performance."

Getting my damped 007A ready for Canjam. I felt that it lacked the additional bounce and dynamics that I have been getting with my other damped phones.  My last damping of the 7 involved putting a solid ring of 1/4 inch sorb on the metal plate in front of the drivers.  Following the suggestion of the Amazon retailer noted above I decided to cut the ring at the top and the bottom so the ring was now 2 semi circles with a gap of about 1/8 inch between them. That made a big difference.  Now its dynamics are similar to other phones and the bassiness is reduced.    I will probably show this one at Canjam.  I don't want to be fiddling with phones up to the last minute.

 

[edstrelow]

Damn! Cable coming out of the 007 left earcup just broke.  I am going to have to patch something up before next weekend but  I will be away this whole weekend.