EON615 JBL woofer directivity control waveguide

[Cahudson42]

Directivity Control Waveguide - interesting reads on subject. Plus a great tutorial on understanding Spinoramas:

https://www.sausalitoaudio.com/intro/

 

[A800]

From my understanding distortion will be increased.

 

[astrawso]

These are from the BBC LS5/5 white paper (attached).

Very interesting. The slit must be creating some interference @ ~1300 and augments an existing null @ ~3000. Maybe the shape the JBL unit uses is able to mitigate this. I notice that its curved in towards the driver, maybe it pushes any interfering signal higher in the passband by reducing the chamber volume and/or the driver/"waveguide" distance...

 

[Patrick Bateman]

The JBL EON615 from their pro line uses a very interesting "waveguide" over the woofer, presumably to handle the on-axis beaming at higher frequencies for such a large driver. Directivity charts aren't included, but they list the coverage at 110 degrees. Looking at directivity charts for other 2-way 15" pro sound applications on the JBL site, there's the predictable narrowing before the woofer hands over to the hf driver.
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Anyone have experience with this unit or something similar? Would it result in resonances that are unacceptable in a hi-fi situation but are fine for pro-audio and inaudible at those higher spl levels?

I've written a few articles that explain how it works:

3) https://www.diymobileaudio.com/threads/improve-your-midbass.322554/

2) https://www.diyaudio.com/forums/multi-way/247050-jbl-m2-poors-73.html

1) https://www.diyaudio.com/forums/multi-way/274647-diy-woofer-wave-guides.html

 

[Patrick Bateman]

a 15" woofer will start to beam above 8-900hz regardless of what you put in front of it.

A 15" woofer will generally have a diaphragm that's about 13" in diameter and will start to beam around 1038Hz. (speed of sound / diameter.)

This assumes the diaphragm is perfectly rigid.

A lot of paper cone woofers and soft dome tweeters are designed so that the center 'decouples' and they behave as if they're smaller than they actually are. One way you can see this happening is if they have a rising response at high frequency.

The reason that the response raises at high frequency is because the motor force remains constant, while the loudspeaker cone behaves as if it's mass is lower, because the center of the cone has 'decoupled' from the rest of the cone. This causes a high frequency rise.

 

[AnalogSteph]

The reason that the response raises at high frequency is because the motor force remains constant, while the loudspeaker cone behaves as if it's mass is lower, because the center of the cone has 'decoupled' from the rest of the cone. This causes a high frequency rise.

While that sounds plausible enough, what about the effect of narrowing dispersion? So far I had assumed that this would be the dominant mechanism causing this high-frequency rise on axis.

The sort of behavior tends to crop up relatively often in wideband speakers, where it would offset the effect of narrowing dispersion. It is quite obvious e.g. in the Visaton SL87ND, while e.g. their FRS8 is much flatter.

I suppose you would have to take polar plots to say for sure - do they line up with pistonic movement or do things widen substantially less than you'd expect. That could mean bad news for loudspeaker simulation implying the former.

 

[tuga]

While that sounds plausible enough, what about the effect of narrowing dispersion? So far I had assumed that this would be the dominant mechanism causing this high-frequency rise on axis.

The sort of behavior tends to crop up relatively often in wideband speakers, where it would offset the effect of narrowing dispersion. It is quite obvious e.g. in the Visaton SL87ND, while e.g. their FRS8 is much flatter.

I suppose you would have to take polar plots to say for sure - do they line up with pistonic movement or do things widen substantially less than you'd expect. That could mean bad news for loudspeaker simulation implying the former.

This is from Tannoy if I'm not mistaken.

 

[astrawso]

A 15" woofer will generally have a diaphragm that's about 13" in diameter and will start to beam around 1038Hz. (speed of sound / diameter.)

This assumes the diaphragm is perfectly rigid.

A lot of paper cone woofers and soft dome tweeters are designed so that the center 'decouples' and they behave as if they're smaller than they actually are. One way you can see this happening is if they have a rising response at high frequency.

The reason that the response raises at high frequency is because the motor force remains constant, while the loudspeaker cone behaves as if it's mass is lower, because the center of the cone has 'decoupled' from the rest of the cone. This causes a high frequency rise.

Does the decoupling involve phase or distortion errors? Seems like it acts as somewhat of a physical crossover.

 

[Patrick Bateman]

Does the decoupling involve phase or distortion errors? Seems like it acts as somewhat of a physical crossover.

I'm 90% certain that the answer is "no" but someone else may know better. As I understand it, most loudspeaker distortion comes from the suspension and from the motor. This is why high performance motors have shorting rings.

 

[jamescarter1982]

Sure the driver will beam, but that's due to the wide cross section of the driver surface area at those frequencies. Playing around in Hornresp, it seems that a panel in front of the driver that's narrower than the driver causes the wavefront to diffract around the smaller opening, creating a smaller apparent driver with higher spl. There seems to be a limit though when a too small area deforms the wave.

please are there any videos explaining hoe to simulate thing like this in hornresp ? I would like to make such a waveguide for my fane 15300tc . I have tried to find this waveguide as a spare part but am unable to so far