Some questions about how drivers for open headphones work
May 15, 2015 at 4:09 AM Thread Starter Post #1 of 22

ginetto61

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Hi !
i am interested in drivers used in open back HPs
This is a exploded view of the AKG K812 i have found in the web
 
http://www.techpowerup.com/img/13-10-09/AKG_K812_headphones_exploded_view.jpg
 
As a very expert Forumer here has told me i see between the magnet and the diaphragm a load chamber
My question is so basic to sound trivial
But all the other parts on left of the " Tesla magnet " are just there to support the driver itself or they contribute to the actual sound of the HPs ?
I do not know if my question is clear enough  
rolleyes.gif

This is very important for me to understand
Thanks a lot,  gino
 
May 15, 2015 at 8:20 AM Post #2 of 22

cdsa35000

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Ofcource the design of cup, chamber, earpads, frame, contents have acoustic influence to the driver FR design etc.
hp cup/driver are shaped like a horn to direct/focus sound to the front like megaphone etc.


http://en.wikipedia.org/wiki/Megaphone
 
May 15, 2015 at 8:24 AM Post #3 of 22

ginetto61

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Hi thanks for the reply
i said left of the magnet ... behind the plane of the magnet
Leaving everything else on the right equal
I knew that i was not clear
And i am talking about completely open back headphone of course
with closed one the cups have an effect because the cups work as additional acoustic chamber for the driver
But drivers supposed to work in open HP should come already ready let's say
Of course a support is needed but can have no impact on sound
Instead everything esisting from the diaphragm plane and forward (i.e. ear pads, protective felts, and so on) will have of course a big impact on sound.
To explaing better look at this picture of a Grado HP open
 
http://cdn.head-fi.org/9/94/946f317f_20-inside.jpg
 
if i keep the part on the right, put the ear pad on, and listen ... will the sound will be much different from the one of the original cap ?
I do not think so ... what kind of impact can have a short cilinder applied to the driver ?  no one ...
Because the driver comes already optimized
Instead the shape of the ear pads impacts a lot because, for instance, changes the distance from the ear, the dispersion of the driver ...
Thanks, gino
 
May 15, 2015 at 8:44 AM Post #7 of 22

ginetto61

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Read the description: Air-flow dome for controlled membrane movement ...
Again the bigger the cup chamber just like big loudspeaker case, the more better bass there will be! 

 
Hi ok .... but as you have explained me very clearly headphone drivers supposed to be employed in a fully open headphone like the Grado comes already ready let's say
with their own load chamber calculated in order to give them an adequate bass response
Maybe yes if you put cups beyond the same drivers the bass will increase.
But this means to me that the drivers had a limited bass response ...
Just to simplify
How much do you think that the earcups influence the sound in the Grado HPs ?
for me almost nothing
Maybe i am wrong.
Not the earpads ... the earcups, what is behind the driver
Regards, gino
 
May 15, 2015 at 8:53 AM Post #8 of 22

ginetto61

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Read the description: Air-flow dome for controlled membrane movement ... 

 Ok ! Agreed !  let's consider that air-flow dome part of the driver
rolleyes.gif

 
but all the other structure behind that is there just to support the driver assembly
The horn comparison is not applicable because that is clear.  W
hat lies in front of the driver is clearly impacting the final response and in the case of the horn greatly.
But also the earcushions i agree completely (sorry i made confusion ... i mean these ones here)
 
http://www.elusivedisc.com/images/gradoearg.jpg
 
these ones can have a huge impact on sound ... but they are in front of the driver ... not behind
And i am talking only of drivers for open back headphones of course
I have the sr200 and i put some Senheiser earcushion in place ... the sound went completely
And i went back to the original earcushion immediately
Thanks, gino
 
May 15, 2015 at 8:54 AM Post #9 of 22

Music818

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Hi what is that ?   i dont know it
Please explain
Thanks a lot,  gino


Well, put it simple. Movement of diaphragm need to have air flow from the back side. The "air-flow dome" with a damper attached and then acts as a value control to control the amount of air-flow. In most cases, the air-flow amount affect the bass level. More the air flow, the higher the bass amount.
 
May 15, 2015 at 8:59 AM Post #10 of 22

ginetto61

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Well, put it simple. Movement of diaphragm need to have air flow from the back side. The "air-flow dome" with a damper attached and then acts as a value control to control the amount of air-flow.
In most cases, the air-flow amount affect the bass level.  More the air flow, the higher the bass amount.

 
Hi and thanks for the explanation 
Thinking a little more about the influence of the cup will be zero only if the driver back is completely sealed
Like it seem in the case of the Grado HPs for instance
 

 
I do not see any hole/vent in the back of the driver
So the ear cups are not necessary
Just a disc of the right shape and size to support the drivers is needed
Thanks again,  gino  
 
May 15, 2015 at 11:33 AM Post #11 of 22

cdsa35000

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If the back was completely closed, the diaphragm/excursion won't move, because of the small volumed vacuum inside.
Thats why there's always some air holes and a big ring of felt to let air-stream small or big volume in and out.
Even closed hp have always some felt/holes around/in the cups.

 
May 15, 2015 at 12:00 PM Post #12 of 22

ginetto61

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Hi and thanks a lot 
I did not know this.  I thought they were completely  sealed 
redface.gif
  like in acoustic suspension speakers let's say
Do you think that the drivers above with the ear cushions in place would have a much different sound that the HP ?
I would be curious to try out.  After all the Grado cups are just cylinder with a grill on the bottom
I see more design in the ear cups and i know from personal experience that they influence a lot the response.
What do you think ?  sound with only the ear cushions in place and with the ear cups removed.
would it be much different from the sound of the complete HPs ?
Thanks again,  gino  
 
May 15, 2015 at 12:22 PM Post #13 of 22

cdsa35000

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The design of the cups have the most sound FR influence, whether closed/open design, there's ALWAYS a CUP with TRAPPED AIR VOLUME to create/amplify the push/pull air vibration to form loud sound.
Otherwise if cupless hp ever worked, they everybody would make them by now! No cup= no loud volume possible.
Why would they make open/closed types if its have minor influence?

bushmills-grado-headphones-xl.jpg


521.jpg
 
May 15, 2015 at 1:16 PM Post #14 of 22

ginetto61

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The design of the cups have the most sound FR influence, whether closed/open design, there's ALWAYS a CUP with TRAPPED AIR VOLUME to create/amplify the push/pull air vibration to form loud sound.
Otherwise if cupless hp ever worked, they everybody would make them by now! No cup= no loud volume possible.
Why would they make open/closed types if its have minor influence?  

 
Sorry but what trapped volume there is in the Grado HPs ?  if i look at the cup i see just a cylinder of different material (i.e. plastic, wood or aluminum) closed on one end by the driver and on the other by just a a grille with a logo in the center
I understand that driver side the cylinder is close but on the other side there is only a grille ... do you mean maybe  that the grille acts like trapping some volume inside the cup ?
The removing the grille will alter the FR ?  i am just asking.  It appears strange to me that the air inside the Grado cups is really trapped.
do you mean that the cup actually loads the drivers even if it is open ?
 
 

 
 
 
I do not understand what you mean saying that no loud volume is possible without cup.
The driver put under pressure the air "trapped" between the driver and the ear. It can create and enormous level of pressure if powerful enough of course
But 100dB/1mW is easily achievable.
I have to slap myself because now i have disconnected the driver in the hi2050 i have opened.  But i will reconnect them for sure and try them only with the ear cushions.
I am sure they will make loud sound ... maybe i will loose the bass if i do not put on the cups again.  
But from the midrange up there will be everything like the original with cups. No difference in FR neither.
I understand clearly that a same driver used in a closed back design will have much more bass than when used in a open back design
Thanks again, gino   
 
May 15, 2015 at 1:44 PM Post #15 of 22

cdsa35000

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The cup volume surrounding, grill and middle disc still covers 80% from outside air.
Otherwise they can make the whole cup 100% grill, they dont because it sound crap and no some isolation.

Test it out your experiment and report the conclusion, then we know.
 

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