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Crazy PA Coaxials for Hifi

Clavius

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For the sake of completeness, here are the results of the passive filter:
 

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voodooless

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Much less directivity issues it seems
 

nc535

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that is a lot of money to pay for a 15" pro audio coaxial driver in a box. Usually it takes a DSP crossover to tame the high end of one of those. For coaxial done correctly with measurements, look here:
Taipuu Speakers
 

Vacceo

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Since this thread is about coaxials, perhaps this is the best thead to ask technical stuff about them.

In the spinoramas, I have realized that the array in Perlisten speakers offers a very similar and symmetric response pattern (controlled directivity in the horizontal and vertical axis) to a coaxial. How is that so? Are both systems practically interchangeable in terms of final results? Any differences?
 

nc535

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There are various ways to get mids close to tweeters to reduce lobing and control directivity: Synergy horn, coax, small mids flanking tweeter in a waveguide, as in Perlisten. They differ in detail and in execution, but they are all trying to skin the same cat. One of the major differences is with regard to horizontal beamwidth. Some like it wide, others narrower for small rooms. I would think the Perlisten approach tends to produce a wider beam; synergy approach tends to be narrower and by intention. with coax's, directivity depends on the shape of the woofer's cone.
 

Plcamp

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that is a lot of money to pay for a 15" pro audio coaxial driver in a box. Usually it takes a DSP crossover to tame the high end of one of those. For coaxial done correctly with measurements, look here:
Taipuu Speakers
Interesting that on the 3 way they use a 15” cone all the way up to 1100 hz, and that they cut off that driver below 200 hz (prob to avoid IM distortion).

I wish they provided distortion measurements.
 

Vacceo

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There are various ways to get mids close to tweeters to reduce lobing and control directivity: Synergy horn, coax, small mids flanking tweeter in a waveguide, as in Perlisten. They differ in detail and in execution, but they are all trying to skin the same cat. One of the major differences is with regard to horizontal beamwidth. Some like it wide, others narrower for small rooms. I would think the Perlisten approach tends to produce a wider beam; synergy approach tends to be narrower and by intention. with coax's, directivity depends on the shape of the woofer's cone.
First of all, thanks for the response! I have seen several criticism towards coaxials as lacking in dynamic range and not the best option for content that is not strictly, music (cinema, games...). This criticism feels strange as coaxials like KEF´s have been marketed as all-terrains and even adapted to home theatres for decades.

Does that have to do with the particular implementation of a coaxial or does it come by nature of the arrangement?
 

nc535

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The dynamic range of a coax has a lot to do with how much excursion is required of its midwoofer. That can be dealt with in the system design. For good dynamic range with a small coax, you need to cross over to a separate woofer at a fairly high frequency. e.g. the Kef R3 crosses at 450 Hz. The excursion of the midwoofer cone can frequency modulate the HF using it as a waveguide. Limit that excursion and there is no problem.

The Kef R3's single 6.5" woofer needs help below about 130 Hz, where the THD starts to rise. You definitely want subs using a small coax in your home theater.
 

tmuikku

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^ also the woofer makes environment of changing pressure for the tweeter, and the tweeter works as microphone modulating the electronic parameters for the sound its bandwidth perhaps causing some distortion. Not sure what the magnitude of such "issue" is though. Minimized with high pass filter.
 
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voodooless

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^ also the woofer makes environment of changing pressure for the tweeter, and the tweeter works as microphone modulating the electronic parameters for the sound its bandwidth perhaps causing some distortion. Not sure what the magnitude of such "issue" is though. Minimized with high pass filter.
In a 3-way this should be mostly a non-issue since the crossover will be in the hundreds of Hz, even for a smaller coax you can limit the excursion to within 1 mm or so for a high enough SPL.

In a 2-way, you'll really need a massive Coaxial, 12" or bigger to keep the excursion down. And even then, it makes sense to use reflex tuning and optimize it to lower excursion further for the bandwidth in which you need it working as I explained in the first post.
 

Plcamp

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Question. If I have two coax drivers and one has half the woofer cone area of the other, will the IM distortion of the larger one be lower or the same at the same Spl? If the product of cone area times excursion is equal, does that make IM equal?
 
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voodooless

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Question. If I have two coax drivers and one has half the woofer cone area of the other, will the IM distortion of the larger one be lower or the same at the same Spl? If the product of cone area times excursion is equal, does that make IM equal?
The modulation has mostly to do with the excursion, and far less with the surface area. And since you need 4x the excursion for the same SPL for half the diameter, this adds up fast.
 

Plcamp

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4x? I said half the cone area, not half the cone radius.

I thought IM would track displacement and not simply excursion. But thinking more about it, the peak cone velocity will be increased with the smaller cone, so the delta frequency of the Doppler might be 2x higher with the smaller cone?
 
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