STAX SR007 Resonance Problems?

[edstrelow]

I don't recall seeing this issue raised before about the 007A.  The other day as I was listening to my 007A (Serial # SZ2-1286) I noticed that if I tapped the metal bands in the arc assembly (as Stax calls it) I could hear a low frequency  ringing for a bit over a second. Now I have always thought that resonances were the enemies of good sound, especially in speakers and headphones because they can be excited by similar sounds being played and artificially enhance those particular frequencies. In other words they cause coloration.   Generally you expect that if you tap a good quality speaker you will just get a dry thwack.
 
So it seemed that if I could hear a ringing from a tap on the assembly, while wearing the headphones, this could indicate a resonance issue when the phones are being played.
 
I have always thought the 007A had a muddy bass.  There was considerable discussion about this problem shortly after this model came out as there also was for the original 007 which was criticized as being "dark" sounding.  I adopted the "Spritzer mod" of flattening the spring that pushes the earpads out.  And that does seem to help this problem a bit.
 
Interestingly when I put my finger across the 2 metal bands  the resonance seemed to stop.  Today I experimented putting  a crude linkage across  the 2 bands with 2 parts of a cut-up old credit card held together by a nut and bolt and it seems to dampen the resonance.
 
I am still listening to this set-up but my initial observations are that it does reduce the bass and make it drier and give a better attack to some sounds.   The photo shows the mod
.

 
 
I assume that Stax has used this same metal assembly on all the 007's, i.e. the original, the 007A aka mk2, and the more recent model which some people call the mk2.5.  I think mine is the original A or mk2 design and I recall buying it within a year of the release of the 007A.
 
I notice that the 009 has a similar looking double metal band except that the two strips appear to be held together (by plastic?) Since I have not actually seen one in person, I can't say for sure. Possibly this is not just a cosmetic change but that Stax realized there was a problem to be addressed?

 

[jaycalgary]

Interesting and wouldn't be too hard to make a single wider metal headband. The 009's are totally different "plastic 1 piece a lot like the 507's" but somebody modified theirs to a 007 style headband.
 
Wouldn't having a a metal strap going from 1 driver all the way to the other resonate and cause some crosstalk let alone 2 metal straps?

 

[wuwhere]

With speakers, designers (like Wilson Audio) try to push down in frequency the resonance frequency of the cabinet so that they don't get excited. Easier said than done. But with headphones could it be an issue? I would like to know myself.

 

[spritzer]

Never had this issue though I always adjust my arcs so that the headband touches them lightly when the set is on my head. 

 

[edstrelow]

Quote:

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Wouldn't having a a metal strap going from 1 driver all the way to the other resonate and cause some crosstalk let alone 2 metal straps?

 
I would think so, more than say plastic.

 

[duncan1]

Other than mechanical problems[and I agree with spritzer]  that would cause vibration is distortion of the signal causing a peak at a set   frequency/frequencies.   that I have witnessed first hand.Curing the distortion cured the "buzz".

 

[n3rdling]

Don't you wear the pads incorrectly?  That would explain your bass issues. 
 
Binding the two arcs together won't eliminate resonance, but rather shift the resonance.

 

[edstrelow]

Quote:

Don't you wear the pads incorrectly?  That would explain your bass issues. 
 
Binding the two arcs together won't eliminate resonance, but rather shift the resonance.

I have tried every orientation possible and have settled on having the seam about at eye level.  This puts the thickest part of the pads to the rear and below the ears, keeps the phones flat ( as opposed to tilted) and gives a good seal for me.
 
I take your point about the binding only shifting resonance. Most recently I  placed thin strips of sorbethane, a material fairly widely used for audio damping, between the  plastic bindings and the 2 metal bands (well actually metal covered with (p)leather.  Now the phones are sounding quite different, the bass boom is much reduced and the tonal balance is warmer i.e. shifted towards the treble.  But it's not as if the bass is gone, it shows up strongly when it should be there.  When I used just the straight plastic binding, the sound changed, and the boom seemed reduced but I can't say I liked the sound a whole lot.  Using sorbethane gives a more pleasurable sound.
 
I am going to try to use 2 of these damper attachments to see how far the sound changes.. 
 
I find it very odd that fiddling with the headbands could have  any effect on the sound but I am starting to think along the lines of jaycalgary that having the two ear cups linked by metal bands is a poor design  because these bands can both resonate and transmit sound to the opposite cup. i.e there may be a crosstalk issue here as well.
 
The damping I am doing is only a half-way solution.  The best solution would seem to be an acoustically dead headband.  Apparently the 009 uses plastic here. Is there no metal in the 009 band?

 

[carbonfet]

The 009s headband is identical to the 507s headband, which is all plastic.

 

[edstrelow]

Quote:

The 009s headband is identical to the 507s headband, which is all plastic.

 That is interesting.  It may be that Stax realized it had made a mistake with the 007.

 

[edstrelow]

Quote:

Never had this issue though I always adjust my arcs so that the headband touches them lightly when the set is on my head. 

An example of how  2 different people can hear different sound through the same phones.  I  expect that there are other factors like, for example, differences in the shape and size of each persons outer ear, giving different acoustical effects with different people particularly with sealed headphones.

 

[edstrelow]

This is my latest effort to put a damper on the metal bands of the 007A arc assembly.   Now I am using pieces of rigid plastic holding 8 pieces of sorbethane onto the bands. Curiously you seem to be able to tune the phones a bit like a guitar or violin. When I replaced my first single  sorbethane effort with this dual effort it seemed that the system was somewhat bass heavy.  So I loosened the screws to ease the tightness of the sorbethane and
things sounded a bit more treblish.  I assume this is because the exact amount of pressure on the sorbethane determines which frequencies get dampened and by how much.  Anyway it's darn clever of Stax to make headphones you can tune this way.
 
 

 
I'll play with this to see what sounds best to me.  These do seem to have got rid of most of  the boom though and I don't see  myself going back to the stock set-up.  Obviously the better solution would be to replace the arc assembly with one more like that on the 009.

 

[deadlylover]

I recall you had experimented with the port mod, are you still using it?

 

[edstrelow]

Quote:

I recall you had experimented with the port mod, are you still using it?

  I used it very briefly.  It added a ton of bass, way more than I wanted.    I have stayed with the spring mod however.

 

[edstrelow]

I find I am now enjoying the 007A more than ever have and am listening to them more than I have in years. Most of the vices of this model are gone or considerably tamed. There is still a hint of bass boominess, but probably only by comparison with the SRXIII PRO which has about the least of any phone I have heard.

The spatial image seems wider now as well. I think Jaycalgary was right that there is crossfeed between the cups. This would essentially act as a mix/blend between the channels, reducing the stereo effect.

I may try some more adjustments of the dampers although the best solution, other than installing an 009 arc assembly, might be to cut the steel bands and hold them together with some more accoustically dead material material like wood or plastic.

This makes me wonder about the 009. Stax made a big deal about the redesigned drivers of this model improving the sound. However the more prosaic redsign of the arc assembly may be a big reason for its sonic improvement over the 007.