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| rdrysdale wrote:|
|Our bass driver has a 12v field coil motor, it developes just over 20 kilogauss flux density using a low carbon steel pole piece. The exit diameter is 4 inches at the moment. The diaphragm is 6 inches in diameter and made of a single layer of carbon fiber with a 2 inch diameter voice coil using copper clad aluminum wire. The design of the driver is very different from most, the diaphragm is cone shaped and clamped rigidly to the center of the phasing plug, and the perimeter of the diaphragm is made of felt, and clamped with a mounting ring to hold it in place. The combination of rigid center mount and felt surround give a very well damped and precisely located diaphragm. Because the diaphragm is fastened to the phasing plug, it wouldn't be possible not to have the plug, however it would be possible to machine it in such a way that it would act as an exit throat and blend right into the horn. We haven't taken many measurements yet, and the final design is still being optimised. We are trying to find the best compression ratio by machining different exit configurations, and found some errors in calculations in our first design, which was very constricted. We redesigned the voice coil and the phasing plug and have made great improvements over the first drivers. We plan on the operating range to be from 40-50 hz up to 250-300hz. This driver is rather large, the phasing plug is 9 inches diameter, and the driver weighs about 40 lbs.|
lately there was here and there some unhappy voices of the pissed audio-subscribers about the fact that some idiots-reviewers lately got tendency to writhe their reviews based upon the release notes of manufactures and without actually auditioning the components. I mean: a manufacture announces a new model, the reviewer read the specifications and 20 words description of this new product and then…. the “reviewer” go over the pages and pages of audio publications spreading his fantasies how wonderful his Patricia Barber’s double bass sounded in his listening room and how much he felt the Patricia’s attendance on his laps, I am not kidding: it is what they do lately.
Well, I would like to do the very much the same and to share some my own concerns that I got after I read your description. Feel free to disregard them and an imagination of my madness.
1) With the targeting upper frequency of 250-300hz you have no need to make any phase plug at all. The phase plug is useful to optimize the delays at the throat arriving in the situations when the wavelength is comparable to the geometry of the pathways. In case of 300hz the phase plug is juts a waste of time/money that you spent to make it available. If you need some kind of surface to “bounce pressure off” with intention to damp the cone then there are many other, less painful ways to do so, not to mention that your cone should not be damped but rather viagranized…. (it will be more about it below)
2) The highpass of 250-300hz make me to question it. There is not good compression drivers that would confidently and with reasonable quality to do down to 250-300hz. So, are you planning to use your driver only in context of 6-chanle installations?
3) The bandwidth narrowness of your driver concerns me and makes me wonder if the midbass that your driver does is the correct one. Let me to explain. As far as I can see it, one of the greatest problems with any bass driver is the bass-driver’s ability to introduce the HF harmonic overtones within their bass. For instance many bass driver has different type of “bad” rubber suspension. Their paper cones do OK but the rubber 9mostly very wrong rubber used) suck the HF is and then kills all high frequency’s overtones. As the result, the driver sound completely artificial. The introduction of a complimentary HF channel matching with this rubber-death bass driver do not assist the situation but juts mask it out.. The very similar is taking place in those curved horns. Let forget that in the bent horns each section acts as a individually-tuned resonant chamber and let to look only at the overtones killing. When sound travels across a curve of horn then higher frequencies attenuated more in the curve then LF (reflections). So, the LF harmonics and the fundamentals go through but the HF get killed in the horn’s curves. That is one of the reasons why all curved horns, with conditional exception of the “J-horns”, sound like a dehydrated camel who juts cross Sahara and who is covered with a think layer of shampoo (but without water) on his skin. Looking at all of this I usually feel that a properly sounding midbass driver must be able to handle at least one octave above it’s lowpass cut off.
4) Something suggests me that the carbon fiber cone is NOT something that you will use in this driver eventually and that that the carbon fiber is primary responsible party for the paragraph #3 and #2. I am sure that the VC is trembling in the gap like crazy trying to do wider range but the carbon fiber cone holds it up saying: “Oh, shut up, you shaky little bitch. I’m the carbon fiber - the material that used to suck vibrations out of tonearms, airplanes, and sports motors. I was designed with the specific objectives to increase the harmonic dampening characteristics and you, the miserable voice-coil, should not anticipate me to have any compile with your hysterical movements, even if you’re driven by the reference signal.” Rich, I feel that by using the carbon fiber cone you severally compromise your driver and I think you eventually will look at the different direction. Perhaps it should be a different type of fiber/cellulose, perhaps it will be metal or some kind of plastic, or perhaps you should explore the opportunity to pre-marinade the cellulose cone (some people I know report promising results with chitin). However, when everything will be working properly I would anticipate that your driver would able to care in a straight horn up to 3K without plug or 4K with phase plug.
Now, I’m as well, feel the Patricia Barber right behind me….
Romy the Cat
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche