hakanson@orstcs.UUCP (12/20/83)
#N:orstcs:2900006:000:1303
orstcs!hakanson Dec 19 09:20:00 1983
I am intrigued by the "Honeycomb Disc" speaker drivers that some manufacturers
are bragging about (apologies for not citing the name, it escapes me). Are
they right in saying speakers should not be cone-shaped, and that a flat driver
is more accurate and/or realistic than a cone?
Apparently the claim is that cones used to be the only way of getting a stiff
enough driver, but that improved technology has given the method of reproducing
sound the way it was "meant to be." So what's the verdict from you experts
and engineers out there? Are cones that way for a reason, or can they be
flat? Should they be flat? Does this arguement apply to woofers, midrange
drivers, tweeters, passive radiators, all of the above, or none of the above?
To show you where I'm coming from, my current speakers are the Infinity RSa
model, which are two-way's with a ten-inch plastic woofer (cone) and the
"famous" EMIT tweeter. I am not in the market for any new components (I'm
saving up my money for a CD player, and at this rate I should be able to afford
one by the time they get the bugs worked out), but am always on the lookout for
improvements. I'd like to hear technical opinions on the Infinity RSa's, too.
Marion Hakanson CSnet: hakanson@oregon-state
UUCP : {hp-pcd,teklabs}!orstcs!hakansonpmr@drufl.UUCP (Rastocny) (12/21/83)
Recently in one of the big three audio magazines there appeared a good article on the several different types of ways to transduce electrical energy into the air. Good arguments were stated at the time as to the attributes of each type. The driver you are referring to is still basically a dynamic radiator (linear motor connected to a radiating diaphragm). All dynamic radiators have a set of problems associated with this principle independent of the radiator type. The problem lies in the ability of the diaphragm to act as a piston at all frequencies without flexing or distorting in any way. While it is true that some diaphragms may operate more like a true piston (e.g., Celestion's tweeter), there is more to this transducer type than meets the eye. New materials (polypropylene, laminated graphite, et.al.) and new concepts (ferro-fluid filled air gaps, rolled-edge cone suspensions, et. al.) all reduce the magnitude of these unwanted nodes, but the cone is still the stiffest geometric shape available to mechanically couple the large diaphragm excursions encountered in low frequency reproduction. Planar radiators act as a true piston when the entire diaphragm is driven uniformly (e.g., the EMIT tweeter of your own loudspeaker). This class of drivers is known as "ribbon" and "leaf" drivers. If the entire diaphragm is not driven, the diaphragm may flex much worse than the cone it is was trying to replace. Another way around the flexing problem is to use more than one voice coil and magnet assembly (linear motor) and attatch them to different points on the diaphragm. This helps but each of the linear motors must operate identically. (You never get anything for nothing.) Think of how your car acts when one of the cylinders starts to miss. A similar problem occurs when the linear motors are not well matched. The slow one will drag down the faster ones. Historically, other manufacturers have attempted to keep the diaphragm from developing nodes of vibration, all unsuccessfully. (How many people remember styrofoam planar drivers?) In summary, it is not the shape of the diaphragm that is important but rather the ability of this diaphragm to act as a piston throughout the operating range. The best way to reproduce sound then would be to eliminate this diaphragm and the associated problems and move the air electrically. This type of driver is known as an ionophone and it has another set of associated problems. Since large radio frequency signals are needed to polarize the air to be moved, the driver interferes with radio and television reception in the area. (Some also create ozone that may be harmful to your health.) Another way to ionize the air is to use a flame. But then you have to buy "gas" for your stereo (AND your car). Welp, this is a lot longer than I thought it would be but I hope you can see some of the real world problems facing speaker designers. Hope it answered your question. Yours for higher fidelity, Phil Rastocny ..!drufl!pmr
burris@ihopa.UUCP (David Burris) (01/04/84)
JBL has somewhat solved some of these problem in their newest line of professional high-frequency drivers. The drivers use a diamond-shaped surround to house the diaphram. The diaphram is a titanium dome with aluminum voice coil( the material the wire is on, not the wire) with a flat, edge-wound coil. I'm not sure of the gap width or flux density but I believe they are 1 cm. and 25,000 nano-webers respectively. They are EFFICIENT at approx. 123 db. @ 1 watt. ( Approximate because I don't have the spec. sheet handy) thus requiring little power. I have used these drivers in professional situations and have heard them in the Cabaret(tm) series loudspeakers in my home, connected to my stereo, and they are quite impressive. -- Dave Burris ..!ihnp4!ihopa!burris AT&T Bell Labs, Naperville, Il.