Constant Beamwidth Transducer (CBT) Speakers

[jaffar34]

How do you treat numerous speakers in CBT design while using dsp software like Dirac Live? DL measures data of a single speaker and creates filters based on this measurement. Here we have plenty spaced from each other

The measurements above show you that an array behaves like a single speaker . No problem for DIRAC !

 

[Slick Minkus]

Now measurements

first , mid array , 1 meter height at variant distances

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Than same 1.5 meter height

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now tweeter array , different heights and distances

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You can clearly see the quarter wave effect

now the same without the deep ( with foam )

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Than measurement averages

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You can see why the tweeter line is interesting : the spl curve is much smoother

I still have some work to do to fine tune the filtering and EQs but they already sound great to my ears .

Nice!
The improved aliasing/breakup after 5k make the little tweeters look very worthwhile...
How low is your current crossover, 2600 hz?

 

[jaffar34]

For now LR24 at 2500 Hz . I want to try a FIR . Xover between sub and mid is butt48 at 160 Hz ; I want to try butt18 at 140 Hz . Still a lot of work ...

 

[Newman]

the entire reason that coaxials are popular is so that you don't have to keep your head in a vise to enjoy good sound.

A large number of coaxial loudspeakers have beaming problems. They are more likely to be the reason you would need to keep your head in a vice than the reason you wouldn’t.

 

[berjine]

A large number of coaxial loudspeakers have beaming problems. They are more likely to be the reason you would need to keep your head in a vice than the reason you wouldn’t.

They can have diffraction problems on axis but off axis you are good usually

 

[Bjorn]

There are coxials that will will get narrower at part of the frequency range.

We see some narrowing here:

And here we see narrowing above 2.2 kHz:

And it's quite common to have narrowing above 10 kHz like here:

These are indoor measurements with no gating for your information.

Overall there isn't much beaming with coax' and the argument of "keeping your head in a vice" is generally more related to certain horn speakers.

A more common problem with coax drivers are the interaction with the two drivers that leads to deviations in the frequency response and which can't be effectively equalized. If it leads to a peak, the sound will often have some harshness and listening fatigue creeps in earlier. Genelec has solved this with a dampening woofer and KEF with a disperion lens.

 

[gberchin]

I created a system identification algorithm that I named "Frequency Domain Least Squares" (FDLS). This algorithm determines the transfer function associated with an arbitrary (within reason) magnitude/phase frequency response. And of greater relevance, in 2018 I created a variant of FDLS that determines the allpass transfer function associated with an arbitrary (within reason) phase response. I call that variant "FDLS_allpass".

The above quote from post #258.

FDLS_allpass.m in now available at http://www.sonicillusions2.co.uk/gberchin/ in the FDLS subdirectory. There are some other documents there that might also be of interest.

 

[jaffar34]

Hi everyone . Feedback today .

When i decided to build these speakers i was inspired by Jim Griffin's creation . In his thread he explains that he set the Fc between sub and array to 140 Hz .

SB acoustics SB65 are not known to provide much bass response under 160 Hz . Until recently i didn't try to cut these speakers under 140 Hz . And according to the bass response in used butt48 filters .

Today , after extensive simulations , i set up a LR24 filter at 100 Hz , without bass boost ( just a few ) of the wide banders .

The result is just amazing . My conclusion today is that CBT arrays need to play at least until 100 Hz to reach their real potential .

Bjorn could have told us about this .