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Multi-Way Conventional loudspeakers with crossovers

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Old 30th June 2020, 07:34 AM   #2491
Snickers-is is offline Snickers-is  Norway
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Quote:
Originally Posted by Ro808 View Post
Click the image to open in full size.

The figure above illustrates the interpretation of the intermodulation distortion measurement using a fixed low frequency tone f1 and a high frequency tone f2 which is varied over the audio band (“voice tone sweep”). While the stiffness nonlinearity can not produce significant intermodulation, the other nonlinearities generate wide-band distortion which can not be detected by a harmonic distortion measurement.


Click the image to open in full size.

The figure above shows the intermodulation of a high frequency tone f2 by a low frequency tone f1 caused by a nonlinear force factor Bl(x) characteristic. If the voice coil is at the rest position x=0 the instantaneous value of Bl(x=0) is maximal and generates the peak in the envelope of the sound pressure signal. For a negative and positive peak excursion, the Bl-value becomes minimal generating the bottom values of the envelope. The temporal variation of the envelope of the high-frequency generates a fluctuation and roughness in the perceived sound.
There are two factors (at least) making the transition between THD and IMD difficult.

Some mechanisms produce THD and IMD in a certain relationship, for example BL(x), while others (for example Kms(x) produce THD and IMD in a very different relationship. It is easy to lower THD in a driver by having BL(x) and Kms(x) work against each other, but that would only increase IMD.

At the same time, if we look at how THD is interpreted, we do not get factors like power compression as part of this equation at all. A more immediate factor than heat is flux modulation. Playing a transient will produce one result, but playing the same transient twice within a very short amount of time will produce two different results. Such artifacts hardly filters as harmonic distortion, but it sure is a very audible form of intermodulation distortion.

And then we have not even discussed AM vs FM. I mean, FM is arguably less audible than AM, but factors causing FM are commonly not filtered as harmonic distortion.
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Old 30th June 2020, 07:40 AM   #2492
TNT is offline TNT  Sweden
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Sigh... which driver type has the least of these problems... electrostats?

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Old 30th June 2020, 08:27 AM   #2493
mabat is offline mabat  Czech Republic
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Quote:
Originally Posted by kessito View Post
... a waveguide with a custom phase plug ( maybe as a replacement in an excisting compression driver) which has a great constant directivity behaviour for at least 4 octaves without using diffraction mechanisms where the bias is much more put on sound quality instead of maximum output compared with excisiting solutions ( phase plug much more focussesd on great wavefront coherence than high compression/ cheap to manufacture) ...
What size of a compression driver had you in mind (if any)? What lower frequency limit?

I think we are already not that far from your 4 octaves actually.
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Old 30th June 2020, 08:47 AM   #2494
mabat is offline mabat  Czech Republic
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Right now there is this waveguide being made (422 x 364 mm; 1,4" throat for 18Sound ND3T) -

Click the image to open in full size.

I'm really eager to see how it turns out, it's probably my best so far. Two different loudspeakers will be made with it, the second one with BMS 4554. Hopefully, we'll see the measured data soon.
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Old 30th June 2020, 08:58 AM   #2495
Boden is offline Boden  Netherlands
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How is the waveguide in 2494 made? 3D print or 3D-CNC?
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Old 30th June 2020, 09:11 AM   #2496
bmc0 is offline bmc0  United States
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Quote:
Originally Posted by kessito View Post
...which has a great constant directivity behaviour for at least 4 octaves without using diffraction mechanisms...

I think the speaker that I built recently comes close. The DI is almost perfectly flat from 1kHz to 16kHz.
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Old 30th June 2020, 09:31 AM   #2497
mabat is offline mabat  Czech Republic
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Quote:
Originally Posted by Boden View Post
How is the waveguide in 2494 made? 3D print or 3D-CNC?
On CNC router from a solid block of MDF. As this worked so well for me in the past, no reason to change it. I'd maybe prefer a different material myself but actually these are not for me.

Quote:
Originally Posted by bmc0 View Post
I think the speaker that I built recently comes close. The DI is almost perfectly flat from 1kHz to 16kHz.
Yeah, I think we should extend the goal at least by an octave
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Old 30th June 2020, 11:03 AM   #2498
mabat is offline mabat  Czech Republic
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Trying to divide the interior of the horn into several subdomains. If I understand it correctly, this should speed up the calculation considerably, hopefully even make it more stable.

BTW, these surfaces can also be used for the "field" feature, i.e. to show a pressure distribution across of it. These can be placed anywhere you want along the length, can be flat or not (I gathered from ABEC manual that it is better to avoid narrow spaces, i.e. not to join walls at sharp angles).
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Old 30th June 2020, 02:56 PM   #2499
Boden is offline Boden  Netherlands
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Mabat, it's a bluddy work of art.

I want a pair....
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Old 30th June 2020, 02:56 PM   #2500
Ro808 is offline Ro808  Netherlands
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Quote:
Originally Posted by mabat View Post
Right now there is this waveguide being made (422 x 364 mm; 1,4" throat for 18Sound ND3T) -

Click the image to open in full size.

I'm really eager to see how it turns out, it's probably my best so far. Two different loudspeakers will be made with it, the second one with BMS 4554. Hopefully, we'll see the measured data soon.
Same entrance angle for both drivers?
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