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KM-U2
2-Way Book Shelf Design
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KM-U2 is 2-way design using Usher 8945P as woofer. On the tweeter side, three different tweeters are used: North Creek D25-06S, SEAS 27TDFC and Usher 9950-20, which actually yielded not one but very similar three designs. Same filter is used on the woofer in these three designs, and same high pass filter target is used for the tweeters. As a result the differences between these three are dictatedby the differences in the charecteristics of the tweeters.
Usher 8945P woofer has the same frame and spider as 8945W. The diffences is that 8945P has an aluminum phase plug instead of a dust cap, a different textured carbon-paper cone, and it uses a T-shaped pole piece with a copper short-circuit ring sleeve that covers almost all of the pole piece, which results in a very low inductance. Even though the T/S parameters of 8945-P is different than 8945-W, the resultantbox alignment turns out to be same for these woofers. As a result I used the same box with the same volume and box tuningas I had used for Dennis Murphy's Usher 2-way design. You can find the details on box volume and alignment here. In short, I used Parts Express 0.75cbft box with inner net volume reduced to 19lt and a box tuning of 39Hz. A 2" diameter port with 4.875" length does the job. Feel free to experiment with the port length though, and the amount of filling you use inside the box to your liking.
Front baffle dimensions and driver placement can be found at the below picture. (Note that it's not exactly same as Dennis Murphy's 2-way. |
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I found all these three versions easy to listen to and detailed sounding speakers. On the bass department 8945P is very similar to 8945W, solid bass from a bookshelf speaker. They image very well also, I think mostlydue to the lower crossover point of 1.9Khz. Overall I am very pleased with the result. If you ask me to compare each tweeter version, to me Usher 9950 version is definitely the best one. With that tweeter, the sound is more effortless, less fatiguing.27TDFC sounds very detailed, the vocals and instruments appear to be more in your room, but after some listening it was causing fatique to me. I found D25-06S version to be warmer than 27TDFC, but not as clean as 9950. For my taste, I would definitely chose 9950 version over 27TDFC and D25-06S. Between 27TDFC and D25-06S, I think it comes down to personal choices. It you give moreimportance to detail I think you will like 27TDFC more. But if you prefer a warmer easier sound more than detail, you may like D25-06S more.
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Woofer crossover:
This is a 3rd order LP electrical filter, which results in an 4th orderish LR acoustic filter at 1900Hz. The RLC shunt elements are used to equalize the 1Khz peak in the woofers response. Other than this peak, the upper cone break-ups at 2.8Khz and 4Khz of 8945P are better behaved than 8945W
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North D25-06S tweeter crossover and resultant system response:
Following is the HP filter to be used if North D25-06S is chosen.
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System SPL 2.83V@1m with North D25-06S tweeter. Below 325Hz is nearfield measured and spliced:
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System, reverse-null, tweeter and woofer responses with North D25-06S. The crossover frequency is at 1.9Khz
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SEAS 27TDFC tweeter crossover and resultant system response:
The HP filter to be used if SEAS 27TDFC is chosen:
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System SPL 2.83V@1m with SEAS 27TDFC tweeter. Below 325Hz is nearfield measured and spliced:
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System, reverse-null, tweeter and woofer responses with SEAS 27TDFC.
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Usher 9950-20 tweeter crossover and resultant system response:
The HP filter to be used if Usher 9950-20 is chosen:
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System SPL 2.83V@1m with Usher 9950-20 tweeter. Below 325Hz is nearfield measured and spliced:
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System, reverse-null, tweeter and woofer responses with Usher 9950-20.
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A. Feyz Pirimoglu
5/25/2004
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