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Exciting new line of fullrange drivers from Feastrex

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When I auditioned the drivers I listened carefully to the drivers alone and ignored a lot of other aspects of the sound that were contributed by the horns. Even mounted in the horns there was hardly any bass to speak of, although the installation was not ideal. But when I put my head 1 foot in front of the driver I could hear what I wanted to hear. Perfect tone and speed from ~120Hz on up to and including the most perfect jazz ride cymbal I have ever heard out of any speaker. I knew I could fix the bass with a bass driver.

Phil, if you are considering the D5nf, be aware that there is a promotional offer running on the D5nf through Nov 1, selling at the wholesale price of $2400/pair. On Nov 1 the price will jump back to full retail, $4000/pair. Contact Joe Cohen at http://www.lotusgroupusa.com/ to find your local dealer, or you can order from him for this deal. I have no horse in this race, except that I want more people to enjoy them, and I want Feastrex to stay in business at least long enough until I can afford to buy D9e drivers. hehehe

The Feastrex D9e speakers will be shown in the Lotus Group's room this weekend at RMAF. I can't wait to hear them.

I built up Scottmoose's speakers today, from solid pine. I should be able to get them playing music by tomorrow. They look cool.
Rich
 
Thanks for the Heads up...

Yes, I know about the price jump on Nov 1 and have placed my order yesterday with Joe.
Please let us know about the new M.King box via ScottMoose. I plan to build one next week. It kinda looks like a bass reflex box with a horn tagged to the bottom.

I have a paper from D. Olsher somewhere that used the 5dnf and a n Augie from Hawthorne but I was some what put off by all the high valve caps etc .
Joe thought they like to simple see an amp and thats about it. Amp.. wire... Feastrex.

Phil
Santa Fe
 
Here is what I have for the D9nf:
Revc = 15.0239 ohms
Fs = 63.7892 Hz
Zmax = 242.4445 ohms
Qes = 0.4280
Qms = 6.4784
Qts = 0.4015
Le = 0.8499 mH (at 1 kHz)
Diam = 180.0000 mm ( 7.0866 in )
ConeArea =25446.9030 mm2( 39.4428 in2)
Vas = 22.8764 L ( 0.8079 ft3)
BL = 18.6603 N/A
Mms = 24.7485 g
Cms = 251.5342 uM/N
Kms = 3975.6030 N/M
Rms = 1.5311 R mechanica

What method did you use for determining Vas? Added mass or closed box?

Based on the quoted specs I calculated the efficiency to be 1.3% using the equations in Joe D'Appolito's 'Testing Loudspeakers'. Given the massive motors this strikes me as being rather low.
 
Gerrit, you are correct. In all honesty, I don't know what to make of some of the the parameters that the Woofer Tester Two calculates for me. The added mass method was used, and it gives me results concerning the efficiency of the drivers that seem to me to be on the low side. I'll come back to that in a moment.

First, as an aside, the motors of the D9nf are not as massive as they might at first seem. I'm writing from memory but I think the magnets in the drivers are 650g, versus 2.6kg magnets in the D9, However, the gap tolerances are tight (1mm if I recall correctly), the materials used in the motor are all of high quality (alnico 5-7, etc.) and the moving parts are quite light. (Again, I'm quoting from memory but I think the cone assembly of the D9nf weighs something like 4g.) The gap flux density is about 1.6T on the D9nf.

Mr. Teramoto bought the much more sophisticated Woofer Tester Pro from the same company but he has not been able to figure out how to use it. (He's not very good at working with Engish manuals.) He will be receiving instruction during RMAF (Lord willing) and after that he should be able to take much better measurements of the drivers.

Only once did Feastrex get their drivers professionally tested. That was back in late 2005, when the first prototype of the D5nf had been created, and they also had 6.5-inch drivers at that time (which were later dropped and all the motors and voice coils used to make 9-inch drivers instead -- the larger drivers are much better balanced). Anyway, the company that tested their drivers back then had a rather odd way of testing the drivers, but their equipment was quite sophisiticated and other makers were using them too, so I assume they knew what they were doing. But the efficiency numbers that they came up with were much higher than what I get with the Woofer Tester Two. And if anything the current drivers should be of higher efficiency than the original prototypes, so I'm left scratching my head. And then recently a Hedlund Horn owner put the D5nf drivers in his Hedlund Horns using an adapter and reported to me that he's confident the D5nf is a 95dB driver -- which actually conforms to what the professional tester had reported, but it is way lower than what I get with WT2.

So anyway, that was a long-winded way of answering your question, but you are right, the numbers in that department don't make sense and I expect the reality is actually a good deal higher. If you have any insights as to why I might be getting numbers on the low side, I'd be grateful for your feedback. Thanks!

-- Chris Witmer
 
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Joined 2002
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cdwitmer said:
So anyway, that was a long-winded way of answering your question, but you are right, the numbers in that department don't make sense and I expect the reality is actually a good deal higher. If you have any insights as to why I might be getting numbers on the low side, I'd be grateful for your feedback. Thanks!

-- Chris Witmer


What are your reference points for measuring the overall diameter of the cone you input in WT2?

And also, how much added mass you used to determine the parameters?
 
Yeah, there must been a dumb mistake in the input of the numbers. Actually, I don't think it will make much difference to the designs that have been calculated here, but in any case after Mr. Teramoto comes back from RMAF one of the top priorities will be reposting proper measurments. Thanks for drawing it to my attention.

-- Chris
 
Salas,

The measurements were taken with my WT2 unit but they were done by Mr. Teramoto. I have been looking at the WT2 application software trying to figure out what he might have done wrong, and I suspect he may have been mislead by the WT2 software's recommendation for a typical 8-inch woofer, which involves placing several nickels (US 5 cent coins) on the cone. That could account for the excess weight.

The reference point for cone measurement would likely have been the outer edge of the paper cone, rather than the center of the edge.

-- Chris
 
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Joined 2002
Paid Member
You are welcome. To make it clear to him, give him an example. If his moving cone mass is 7grams, he must add 5.6grams for instance. He can weight on a precision scale some silly putty or Blu Tack, then make ring out of it and put it around the neck of the cone. It must not bounce, it should be pressed. I prefer Blu Tack because it isn't oily, sticks well, and goes off without moisturizing or peeling the expensive cone. For high mass normal drivers I use evenly distributed tire balance weights but thats another story.
 
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