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Old 10th May 2005, 01:50 AM   #1
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Default New WR125ST TL design

I've been contemplating what to do with "Rosa" for a few months now and finally decided to go ahead and share the design with everyone. My thanks to David Dlugos for creating a very professional drawing of the design. I'm hoping a few people will take the plunge and build this little beauty. It runs at about 88db efficiency and has very friendly impedance so it works well with both tube and solid state amps. Here's the link to the design. I hope you like it.
http://www.timn8er.com/alegria_audio_rosa_tl.htm
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Old 10th May 2005, 04:35 AM   #2
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Wow, that's a nice looking speaker and your decision to share the full design is very generous. That slim cabinet profile and use of shielded drivers should make this an appealing project for a wide variety of DIYers with varying goals.
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Old 10th May 2005, 12:55 PM   #3
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I like the looks of this tower with the narrow front and small overall footprint. But while the performance of this design is likely quite pleasing, it can be even better. With a change or two, the overall performance can be improved.

Notice that the frequency response graph tails down about 3 dB below 5-600 Hz. This can be improved with baffle step compensation. BSC would flatten the overall performance.

Furthermore, the roughness in the upper part of the response is caused by interaction between the two woofers (at frequencies beyond one wavelength center to center spacing between these drivers). This can be fixed if the woofers were attenuated by an inductor and the crossover network adjusted to bring the tweeter in a little sooner.

Jim
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Old 10th May 2005, 02:35 PM   #4
konut is offline konut  United States
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Jim-- could you elaborate a bit about the size and value of the inductor you would start with? At what frequency would the crossover have to be to avoid this problem completely or no matter what the crossover point an inductor would be needed?
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Old 10th May 2005, 02:55 PM   #5
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Quote:
Originally posted by Jim Griffin
I like the looks of this tower with the narrow front and small overall footprint. But while the performance of this design is likely quite pleasing, it can be even better. With a change or two, the overall performance can be improved.

Notice that the frequency response graph tails down about 3 dB below 5-600 Hz. This can be improved with baffle step compensation. BSC would flatten the overall performance.

Furthermore, the roughness in the upper part of the response is caused by interaction between the two woofers (at frequencies beyond one wavelength center to center spacing between these drivers). This can be fixed if the woofers were attenuated by an inductor and the crossover network adjusted to bring the tweeter in a little sooner.

Jim
Thanks for your input Jim. I should point out that while I said "in room response" it's actually a quasi-anechoic measurement taken at about 2 meters, therefore, there isn't any room enforcement of the bass response taking place. BSC may or may not improve things depending on placement. As for the crossover, there is certainly room for experimentation. I was going for the "full-range driver" concept with a helper tweeter. The FT207D is no help below 5k but it may be worth trying a 2nd order just above that point to take care of the peaking from the woofers. For those that would like to experiment it may be worth trying a different tweeter. The selection of shielded super-tweeters is very limited, however, there are many un-shielded models to choose from. One that I've been eye-balling is the Hi-Vi radial planer.
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Old 10th May 2005, 03:34 PM   #6
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Tim, I realize that room placement can impact BSC. The rear port would encourage placement away from the back wall. The measurement shown is indicative of the performance at that specific location in the room and I'm pointing out that you could flatten out the overall response via BSC.

Someone asked about specific crossover values. Now any good overall crossover design would start with good measurements on these drivers in this enclosure. Hence, the crossover values would be derived based on the crossover point and the response flatness achievable. A capable crossover design program that uses these measurements would be what I would suggest to derive the values vs. the target performance response.

Jim
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Old 10th May 2005, 04:10 PM   #7
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Quote:
Originally posted by Jim Griffin
Tim, I realize that room placement can impact BSC. The rear port would encourage placement away from the back wall. The measurement shown is indicative of the performance at that specific location in the room and I'm pointing out that you could flatten out the overall response via BSC.

Someone asked about specific crossover values. Now any good overall crossover design would start with good measurements on these drivers in this enclosure. Hence, the crossover values would be derived based on the crossover point and the response flatness achievable. A capable crossover design program that uses these measurements would be what I would suggest to derive the values vs. the target performance response.

Jim
Agreed. Thanks again for your comments. This could be a very good starting point for someone willing to do some tweaking. I may get back to it sometime but it would be interesting to see others give it a shot. We should be seeing a bipole variation soon (I hope).
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Old 10th May 2005, 05:28 PM   #8
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The reason I asked about the crossover frequency that would be required to avoid problems by the interaction of these woofers in close proximity would be to help determine the optimal tweeter to be used. Many are using the WR125 without, or in Tim's case with, a helper tweeter. I would rather use a tweeter where it's dispersion starts to narrow between 4-5khz. I was just wondering weather I will avoid the proximity problem of the woofers and also be able to avoid using the inductor when crossed over in this range.
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Old 13th May 2005, 09:05 AM   #9
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Here is a bi-pole version that i drew up -- Scott is still building the prototype...

dave
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File Type: gif bipole-wr125-v02-plans1000.gif (56.1 KB, 2448 views)
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Old 13th May 2005, 09:25 AM   #10
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Just a comment on the WR125 designs i have heard... in each and every case the more larer the role of the tweeter the less engaging the speaker sounded... the sample was limited to some early designs at the last RAW-fest, but i would be very cautious when doing a design that puts anything between the amps & the WR125. You may end up with a speaker that measures flatter, but it may not sound as good... FR is only one facet of making an engaging speaker ... in many a case pursuing flat FR as an end in itself leads to a sterile speaker.

dave
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