Stax Sigma wood mesh housing? - Page 2

You may want to check the polarity of the driver of the Sigma vs the Lambda.  If I remember correctly, the Sigma is reversed vs the Lambda apparently in an effort to account for the fact that there is no direct sound from the Sigma driver.  I seem to recall a discussion between John Buchanan and Spritzer  on this issue.

The drivers are mounted with the dust cover facing outwards, not into the cavity. There is a phase reversal when reflected off the internal mineral wool, so the Sigmas were wired to compensate for this. That is, compared with a Lambda earspeaker, BOTH sides + and - were reversed. Both sides have their absolute phase wired backwards.

The Sigma Pro used a Lambda Signature driver, not a Lambda Pro driver, so you will be hearing yet another different type of Sigma. The housing looks rather tasty so far.

Leave it my friend - the only thing that you have there is a phone that MAY not be absolute phase correct. That may also vary according to your preamp, your amp, and recordings, which may or may not be absolute phase correct, and that may change between tracks on an album.

I have a phase inverter (some say this should be called  a polarity inverter) on an old Denon CD player and the effect on sound doesn't exactly stand out like dogs' balls (to use an old Australian expression)  .   So I wouldn't worry about it too much either.

 

I am still curious about phase shift of a reflected sound , which we discussed some time back. I worked for several years with sonar engineers who never even mentioned it, and you would think if anyone would care about this  it would be people who were making their living off reflected sound. 

 

Trying to research this on the Interenet I came across a number of references which lead me to think that the phenomena is not a simple one.  It seems to be affected by the angle of incidence as well as the rigidity of the reflecting surface and ties in with Newton's Third Law,  impedance matching and the like.

 

http://www.avsforum.com/avs-vb/archive/index.php/t-1073322.html indicates no  phase shift with a rigid wall.

 

http://paws.kettering.edu/~drussell/Demos/reflect/reflect.html  Deals with string demonstrations in which there is phase shift with a clamped string but not when the end is free.

 

To which I add one thing I did learn from my sonaring colleagues, that you don't even get a reflection unless the the size of the reflecting object is greater than the wavelength (or was it some fraction of the wavelength)  of the sound, so there are frequency issues  affecting reflections  as well.

 

 

As regards the Sigma, it seems to me that one of the profound differences between it and other phones is that because the drivers are located, ahead of the ear, no direct sound is getting to the eardrum from the driver.    I would guess that the first sound to get to the eardrum would be that which is reflected off the pinna, with  reflection from the the mineral wool coming later. How much and what frequencies come off the mineral wool are unclear to me because some energy may be absorbed.

 

Now to the extend that the Sigma gives you pinna reflections that is fine since that means that it is giving you something comparable to what your ear would get from a sound source in front of you.  Normal headphones fire straight down the ear canal and that would only correspond to sound sources right beside you.  This I suspect is one of the reasons why most phones don't sound quite right and furthermore are somewhat harsh sounding . Regualr phones have a pronounced direct signal from the headphone driver which you would not generally experience at a concert where what you hear are sounds that have been bouncing   off  and and around the parts of the ear.

 

But when you just run Lambda drivers in the open air, located where the Sigma drivers are, you don't get any bass.  The mineral wool of the enclosure is necessary because it  probably blocks some of the back wave and also creates a resonating chamber.  But which aspect is more important i.e blocking the back wave or cretaing a resonance chamber I don't know.   

 

I think the resonating chamber aspect is not good because it creates some artifactual sound.  In this regard the AKG K1000 has an advantage in that it doesn't use a chamber.  How it gets its bass up at all I don't know but I suspect some equalizing process must be at work.  Still one major complaint about them is weak bass.

 

I wonder if it woud be possible to create a Lambda-type K1000 by using a second set of drivers in front of the main drivers, running  like one of those active noise reduction phones, to cancel the back wave?

 

 

 

 

 

 

 

 

 

 

 

And it is also frequency dependent.  In this set of measurements the mineral wool worked best at absorbing the middle and upper frequencies

and is  also dependent on the thickness of the layer of mineral wool. 

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http://www.iig-llc.com/pdfs/IIG408.pdf

 

 

Looks great. Fantastic project.  Maybe you will shame Stax into reintroducing the Sigma line.

I am surprised that you would get boominess with these phones before you added the mineral wool, or that you would get much bass. When I pulled my Lambda 404's off their arc assembly and held them in position, more or less where Sigma drivers are I got virtually no bass. I wouldn't have thought that the wire mesh would have acted as any kind of enclosure to make your phones sound any different than the opened Lambdas.

I am not sure that I would want to alter the mineral wool.  Stax just leaves it uncoated.  However with the thin mesh you use I would guess that you would feel the mineral wool  when you pick up the earcups.  You don't feel the mw with a Stax Sigma because the plastic case has thicker pieces so the mw doesn't protrude through.  If you end up sealing the mw on the outside of the earcups. you may end up altering the sound.  When I used tape to seal the earcups, the sound got very echoey and boomy.  Possibly you could add a plastic grate over the mesh to protect the hand from the mw.

 

 

I think they meant if you use the diffuse field equalizers they are kind of semi panoramic.

 

Regards Georg