Compression drivers; how do they work?
I have read many threads on the compression drivers like the recent "4344MKII and 275ND problem" and ones on how you should not test there ploarity with a battery etc. I really don't get how these things work and no way am I game enough to pull mine apart to have a peek.
I understand they have a diaphram; like a mini speaker cone right??? and that makes the sound ??? but what is the 'plug' I read about and how does it fit into the picture? Why is there not a correlation of polarity to forward movement of the diaphram (like mentioned in normal speaker datasheets)?
Any exploded views of a driver around or someone post a pic of the innards???
Finally the 2405H seems to be a 'normal' speaker as they mention in the datasheet that positive to black gives forward montion. So why is this, which works at even higher frequencies, seem to revert to 'normal' speaker technologies that I do understand.
thanks, Jarrod
starting to get it now.....
so (7) presses against (5) the plug and makes it compress. the spikey bits of the plug move up and make a sound wave out the horn. is this plug made of a sponge type material or something harder?
this is fascinating. i wonder why this strange arrangement makes better highs sound that a small diameter cone 'tweeter' or is it just that it makes a lot MORE VOLUME highs sound than you could get out of a tweeter??? which of course suits us... no substitute for LOUD... hahaha.. well not true!
jarrod
btw Rob, those snaps of insides look great. wow that 2405 with the 'crystal' tongue looks hot. better than black.
Re: starting to get it now.....
Quote:
Originally posted by jarrods
so (7) presses against (5) the plug and makes it compress. the spikey bits of the plug move up and make a sound wave out the horn. is this plug made of a sponge type material or something harder?
I hope you are joking. (7) should NEVER touch (5) the phase plug. The diaphragm vibrates air just like an exposed dome tweeter. The difference is that the area of vibrating air is compressed into the area of the slits (the dark areas between the spiky bits which need to be very rigid due to the pressures that build in this area) so the final vibrating column of air is smaller than that originally vibrated by the dome itself. The throat and horn work together to make an acoustic transformer that couples the diaphragm to the listening room.
Is a horn superior to a direct radiator? It is certainly electrically more efficient, but significantly more expensive to produce. Is the very best compression driver better than the very best direct radiator? That is a question to be debated.
Widget
Re: starting to get it now.....
Quote:
Originally posted by jarrods
so (7) presses against (5) the plug and makes it compress. the spikey bits of the plug move up and make a sound wave out the horn. is this plug made of a sponge type material or something harder?
No no no - the diaphragm/voice coil is the only moving part. 'See that thin air space between (7) and (5)? As the diaphragm moves in and out it compresses the air in this thin space, which is then pushed through those thin, expanding slots in the plug. It then exits via the horn throat. The plug is a hard, immovable material.
Edit: I see Widget beat me to it.
My question is on the ring radiator series - I've never had one open, but from pics I've seen of the diaphragm it looks like there's a hole in the center, hence "ring" radiator? Could someone explain the details behind these?
John
Re: Re: starting to get it now.....
Quote:
Originally posted by johnaec
My question is on the ring radiator series - I've never had one open, but from pics I've seen of the diaphragm it looks like there's a hole in the center, hence "ring" radiator? Could someone explain the details behind these?
It has been discussed on some thread or other. I also believe I've read about it in a JBL Tech bulletin, but I may be making that up. It has to do with cone (dome) break up modes. The ring has an inherently higher mass break point than a complete dome which allows it to run out to a higher frequency. I have no idea why. Perhaps due to less mass? Only guessing here.
The actual vibrating diaphragm is a very thin, very narrow annular band of aluminum.
Widget
Re: Re: starting to get it now.....
Widget mused: "Is the very best compression driver better than the very best direct radiator? That is a question to be debated.
surely, much like the comment of the phase plug. There is really no debate. For horns it's volume ueber alles - caveat emptor re the ultimate sound quality of horns vis a vis a direct radiator. Nevertheless, one wonderful attribute of a horn is it's 'realistic' dynamics - that's what sold me.
guenter
outstanding discussion!!!!!
outstanding discussion!!!!!, I had some of the pieces of how a compression driver worked, but now it is crystal clear, awesome!!! As the question of which is better, cone or horn?; I think it could and has been debated ad nausium but just look at Project May and the mission statement and the driver choice. Also look at just about most every desirable JBL model and you will find a compression driver of some sort in the mid and/or high positions, that is no accident.