suspending a small tweeter in front of woofer for "coaxial" effect? - diyAudio
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Old 2nd January 2006, 06:47 AM   #1
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Default suspending a small tweeter in front of woofer for "coaxial" effect?

long story short, i'm building a set of 15" Karlsons for myself. my non audiophile brother wants a set of speakers - if my Karlsons work out nicely i'll build him a 12" set.

for my own, i was going to take a 3-way approach.

for a smaller set, though, i thought it would be interesting to use a coaxial speaker. unfortunatley the Eminence Beta12CX has too high of a Qts to be ideally used in a Karlson so i had for a while scrapped the idea because any other coaxial i came across was way expensive. then earlier today i was thinking about a possible solution when i remembered seeing pictures of vintage coaxial speakers in which a tweeter was suspended centrally over the woofer cone as part of the frame. this got me thinking...

in most Karlsons the speaker is mounted to the back of the baffle. if i were to attach a minimal crossbar from the front side of the baffle, with a disc in the middle to attach a 3/4" or 1" tweeter(like a Morel MDT12 or Peerless 811435) to, i could come up with what would seem to be a reasonable approximation of a coaxial of that style. this would allow me to maintain a reasonably point-sourced setup and grillecloth it like an old skool Karlson so that neophytes would be none the wiser

has anyone tried this sort of thing before? is it doomed to failure? Karlson or no Karlson.
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Old 2nd January 2006, 09:07 AM   #2
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Diffraction - coaxial tweeter?

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Old 2nd January 2006, 10:01 AM   #3
Aghead is offline Aghead  Canada
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ONe of the worst speakers I've ever heard was a coaxial KEF selling for C$1500 about 15 years ago. WIth any complicated signal it just fell apart. Hard to describe, but psychotic would be a good descriptor.

The salesmen had just given a big spiel on how great this coaxial point source thing was.
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Old 2nd January 2006, 02:04 PM   #4
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bikehorn, Audio Physic is using suspended tweeter in front of the midrange driver in their top-of-the-line Kronos and Caldera speakers. They know what they're doing so go ahead and try it.
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Old 4th February 2015, 06:11 PM   #5
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Default Reviving this

I'm considering this arrangement for an upcoming build and was curious as to what may affect quality of the final arrangement.
Obviously anything on axis will create diffusion issues but I imagine particular shapes and treatments may alleviate some of the issues. Secondly, considering crossover network order, distance from woofer to tweeter (wave originating points) should accommodate phase alignment shifts. Likewise phase alignment should be considered in general. I imagine the frequency at which to tune to would be the crossover frequency. Also as mentioned earlier the size of this suspended tweeter should not exceed wavelength of any frequency reproduced by the woofer behind it? Assuming limits to that are crossover frequency. I'm thinking curves are better than flat surfaces? Sound absorbing surface materials on rear surfaces?

I'm wondering if this would not behave like a phase plug?

I also imagine a previous posters experience with "psychotic" performance was most likely do to phase alignment and crossover point issues as I asked about earlier.

Anything else I may be missing?
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Old 4th February 2015, 06:59 PM   #6
S4m is offline S4m  Germany
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I listened to a type of selfbuild coax. Had been a small fullrangedriver in Front of a woofer. Was really nice sounding. The best coax I know are build by Geithain. They are really awesome. Probably they give you some inspiration?
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Old 4th February 2015, 07:09 PM   #7
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Thanks I'll check them out.
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Old 4th February 2015, 08:24 PM   #8
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Why are the majority of coaxials so bad, apart from Tad?
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Old 5th February 2015, 03:18 PM   #9
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In the 60s EMI made a 13"x8" driver with one, or even 2 tweeters in front of the dust cap. From memory the single tweeter model was the "350".
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Old 5th February 2015, 09:34 PM   #10
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This worked really well. The waveguide made it such that the tweeter didn't see the woofer behind (increased directivity). Conversely, the tweeter and waveguide had almost no effect on the woofer response.

Better than any post mounted tweeter I have ever seen, by far. Plus smoother overall response than Uni-Q, which tends to have reflection problems with the neck blend and cone surround.

David S.
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