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Straight 8 - the original Bottlehead speaker kit

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Doc B.:
Possibly a cousin, but I'm afraid the DNA of the drivers is enough different that it would need it's own crossover design. The Straight 8 crossover addresses some warts that are peculiar to the drivers we used, and thus an optimized crossover for the ART array would need a crossover that addresses it's drivers' peculiar warts. Might be close, but not optimal.

Paul Joppa:

--- Quote from: booangler on October 16, 2009, 02:10:38 AM ---...I was surprised to see how similar the Climax and the ART seems to be. ...

--- End quote ---
(Of course you mean the Straight 8, not the Climax.)

Towards the end of the development chain of both designs, I wound up targeting the same acoustic crossover for both Straight 8 and Climax - fourth order Linkwitz-Riley at 3150Hz. In all cases (tweeters and woofers, Straight 8 and Climax) the individual drivers have responses that are not flat so the crossover electrical response plus the driver response works out to the target acoustic response. Therefor none of these crossovers are suitable for different drivers.

Here's a rundown on the various drivers:

Straight 8 midwoofers - the original drivers had a curvilinear cone; they were replaced without warning by the supplier with straight-sided cones at some point. This made a difference in the treble response. Various thin coatings were used on the woofer cones to damp the very high frequency ringing (an octave or two above crossover); the best of the coatings was discontinued - again without warning - by the manufacturer. The most recent published crossover is the best we have come up with.

Climax midwoofers - again, the original Eminence driver was discontinued. It had great promise, though the small excursion meant it needed a subwoofer like the SEXy Speaker design. The published crossover was quite good, matching the L-R amplitude and phase remarkably well to more than an octave past the crossover point. These were tough drivers and needed extensive break-in to perform at their best.

Straight-8 dome tweeter - this titanium dome has some problems with limited excursion (making it more fragile than the very sturdy woofer array) and a 20kHz resonance, but was otherwise very clean. The most recent published crossover included a 6dB trap to kill the resonance. The limited excursion makes it a little rough when pushed too hard, but at normal levels it works quite well. (Normal levels means Mahler is OK but Nine Inch Nails is not.)

Climax horn tweeter - This little Selenium is very tough, but it needed a lot of help. The response is far from flat, and the horn mouth reflections and cabinet scattering are quite severe. The crossover is fairly complex, and very different from a classical theoretical crossover. And the horn modifications described in the published design are essential to use in conjunction with the crossover; neither one alone is suitable. But combined, the amplitude and phase response is remarkably close to the design target.

Aurum Cantus ribbon - we tried many times to make this work, mostly in the Straight 8 but with the intention of using it with the Climax as another option. The difficulty was a huge resonance around 1700Hz (if I recall correctly) which is quite audible because it is right in the middle of the midrange where the ear is most sensitive. The last crossover design I made for it had a big notch to correct teh resonance, but it did not work as intended and did not alleviate the sonic problem. In addition, the ribbon was very easily damaged by testing (we blew out a number of them) and a half hour of Nine Inch Nails through a Paramount was enough to make the ribbon sag visibly. So I gave up on it, there is no crossover I can recommend. A very airy tweeter, I would not hesitate to use them as a supertweeter crossed at 8kHz or higher, second order or steeper.

Doc B.:
I think the resonance of the Aurum Cantus G2si (is that right?) was higher than 1700. I want to say it was more like 2200. Or maybe that was just what we accidentally designed for and why the notch filter didn't seem to work too well... Anyway when it comes to ribbon tweeters, even at 5 times the price I would say the RAAL ribbon is worth the difference.

Doc B.:
Thanks to Michael for digging up this nugget on Straight 8 kit cabinet assembly

http://www.bottlehead.com/straight%208/cabinetassembly/straight8cabinetkit.htm

glynnw:
I still have the original plans and will try to shrink them from 11x17 to 8 1/2 x 11 so I can scan and email them.  I won't know if they will be legible at this smaller size until I try it.  FYI, the woofers, MCM # 55-1870, are on sale at MCM for 8.95 each for the next week or so.  I have been in the process of comparing 3 speakers;  Straight 8 w/Selenium tweeter, Basszilla and Klipschorns.  Have already decided the Klipschorns come in last place, but still trying to figure out the other 2.  The Basszillas are by far the bass champs of the 3, not because they are overpowering, but because the bass notes are very distinct and accurate. You can really dissect drum recordings because you hear the skin as well as the boom.  But the vocals are another story.  I listen to the basszillas for a couple of days and then swithch to the Straight 8s and just relax more while listening.  Perhaps it is simply that I am more familiar with the sound, but I really think the Straight 8s just do something that is musically right that has nothing to do with detail retrieval or tone quality.  I should also point out that by now the crossover parts in the Straight 8 are almost all higher quality than those I used in the Basszilla.

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