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mcjasonb t1_j9i0f0u wrote

I’ve always wondered if you could seal an open back, but do it with a cup so large that it still acts as an open back.

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rhalf t1_j9iss47 wrote

On the upper end you just move the back chamber modes lower into the midrange.
On the lower end you get more bass extension.

With the space gained you can fit more resonators and damping material, so there ais more room for improvement.

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NoScoprNinja t1_j9j7d8c wrote

Could you explain this to me as im a stupid person

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rhalf t1_j9jmif6 wrote

Every chamber has a number of modes. Modes are resonances of an enclosed empty space. A small chamber like the back of a headphone has these modes above 5kHz. A medium one, like a loudspeaker box will have them lower, around 500Hz. A big one like your room will have modes around 50Hz.

These resonances at the back of an earcup will stop the diaphragm from moving at certain frequencies and boost it at other, creating the zigzagging response that you see in measurements.

IF you want to get rid of them, you can damp them with some sound absorbent material or with tuned resonant chambers. At least this is the way loudspeakers are made. Headphone earcups are usually too small for absorption so the only way we deal with this problem is by venting them. That's why we have open headphones.

Bass in headphones and loudspeakers is created by diaphragm excursion. The diaphragm rests on an air spring created by the closed chamber behind it. In headphones there is also a front chamber and the eardrum, but let's ignore it. The air spring opposes high excursion of a diaphragm. In practice it reduces bass extension, but amplifies the frequencies just above that. This is why you rarely get deep bass with closed headphones. They often have a bump around 100Hz and then roll off like it's nobody's business.

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