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Multi-Way Conventional loudspeakers with crossovers

Increasing loading of midbass in synergy horn
Increasing loading of midbass in synergy horn
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Old 9th September 2019, 08:48 PM   #11
mark100 is offline mark100  United States
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Quote:
Originally Posted by Patrick Bateman View Post
What I describe could be used to horn load the midranges, the woofers, or both.

The "trick" is that you're putting the midranges or woofers into a horn, and then using DSP to line up the wavefronts as they enter the Unity horn.

Similar to what was described in the first post:

Click the image to open in full size.
Thx.
And sure, makes sense. That's what we are seeing in Jerichos like the J7, isn't it?
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Old 9th September 2019, 08:51 PM   #12
mark100 is offline mark100  United States
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Originally Posted by fers View Post
Hmm... What about the J6-42 that seems to have those MLTL loaded woofer ports? Especially the delay settings for the woofer and the mids.
Sorry Fers, forgot ...just checked presets now.
There are no presets in the processor for any of the Jericho's...
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Old 11th September 2019, 04:53 AM   #13
fers is offline fers  Canada
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Originally Posted by mark100 View Post
Having smooth phase alignment through the entire crossover region requires time alignment.
I think you'll loose a lot of point source behavior without full alignment.
Check out page 117 https://www.rationalacoustics.com/do...User-Guide.pdf
I understand the concern. One would ideally have time and phase alignement throughout the entire crossover. However, what lead me to consider having the waveform at the midrange taps in phase but with a path delay equal to 360 degree of phase at the crossover frequency is that a similar concern should arise in the synergy horn as per the patent.

Indeed, in the typical synergy horn, one has the midrange taps at 1/4 the wavelength at the crossover frequency from the apex of the horn where the tweeter is located. This corresponds to a phase shift of 90 degree at the crossover. When used with a first order crossover, that path based 90 degree shift brings the two drivers in phase at the crossover. We know that in such a first order crossover, the signals are 90 degree apart at all frequencies, but the shift caused by the path difference will only equal that difference at the crossover point. So, one could have the two signal in phase and in time at the crossover, but not exactly so below and, specifically, above. This would be similar to the first image in figure 102, p. 117 of the document you attached. However, the end result seems to work out fine.

Now, imagine that there is a first order crossover on the tweeter, but a third order crossover on the midrange. At crossover, there is now a phase shift of 180 degrees, of which, 90 degrees is corrected for by the path delay between the apex and the taps. That leaves 90 degrees of path delay to be used for "pre horn-loading". Admittedly, the situation is worse than previously described as the signals will not be in time at the crossover, but I'm curious as to what part of the synergy behavior is retained.

A better option, regarding time alignment, would be to all-pass the tweeter so that the two signals are back in time at the crossover. This would be very close to the situation described above. However, passive all-pass filters seem like a bad choice. Of course a DSP resolves all the above with delays.

Thank you for that link. That user guide is useful. Also, thank you for checking the settings files.
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Old 11th September 2019, 05:07 AM   #14
fers is offline fers  Canada
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Originally Posted by Patrick Bateman View Post
If you are prepared to use DSP in your Unity horn project, I think it is VERY possible to use *extremely* long midrange taps. Possibly as long as a foot, maybe even two feet!
Yes, a DSP would solve part of my conundrum. However, I'd prefer not to HAVE to have one. It's not that I don't like DSPs, and I will definitely have one to be used with the system. However, I'd like to retain the option of operating the system completely passively and limit the number of amplifiers in some situations. If I can figure out a way of operating such a system acceptably without DSP, albeit with some features lacking, then that would fit!

Quote:
To make this work with a very long midrange tap, you'll want to mass load the tap.
[...]
In this scenario, we'd use mass loading because it allows you to make the exits of the midrange tap much smaller.
So, in this case, "mass-loading" really refers to inserting a constriction in the middle of the horn, with the constriction such that it do not affect the horn response too much. I see how that can be possible, provided the constriction is much less than a wavelength of the highest frequency desired in length.

One concern I would have would be reflections of that constrictions leading to standing waves in the first horn segment with accompanying peaky response. Stuffing might be sufficient to tame this, but the associated loss of efficiency worries me. From a video of your Metlako project, I saw you used stuffing in the mid taps expansion. Was it precisely for this reason? Did it worked enough without loosing too much efficiency?
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Old 11th September 2019, 05:17 AM   #15
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

In this project, the impact of the stuffing was fairly big, like 3dB IIRC

Click the image to open in full size.

But in Metlako it almost unmeasurable. About 1dB, and only at a small set of frequencies.

I think what's going on, is that the midrange taps are so far from the tweeter, the tweeter doesn't "see" them.

For instance, the midrange taps are spaced about 10cm apart. So the tweeter doesn't "see" the taps until 3.4khz. (3.4khz is 10cm long.)

The taps are 1.25cm across, which is a small fraction of 3.4khz.

So, that's my theory on why the polyfill has a noticeable impact on the older waveguide, but not much difference on the new one.

I'll still leave it there, because it lowers distortion, but it's not required.
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Old 11th September 2019, 05:53 AM   #16
fers is offline fers  Canada
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Quote:
Originally Posted by Patrick Bateman View Post
In this project, the impact of the stuffing was fairly big, like 3dB IIRC

But in Metlako it almost unmeasurable. About 1dB, and only at a small set of frequencies.
Ah, you're talking about the standing waves in the main horn. Indeed, that should not be a problem with the Metlako. My concern was with standing waves inside the flared ports themselves (especially if they are a foot long!), much the same as the peaky response from a truncated horn as it would be the same phenomenon (reflections of the mouth because of impedance discontinuity).

Indeed, stuffing in the older project might have helped more as the cavity formed by the ports would be better coupled to the tweeter output. I would think not because of the distance from the tweeter, but rather because of their orientation with respect to the horn axis.
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Old 11th September 2019, 06:09 AM   #17
Patrick Bateman is offline Patrick Bateman  United States
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To be honest, I don't think standing waves will be a problem. As long as the horn is expanding, the reflection from the transition from the midrange tap to the horn bell should be fairly benign.

In horns that load the front AND the back of the driver you get out-of-band peaks and dips. But that's not caused by standing waves, that's caused by geometry. Basically there are frequencies where the front and back are out-of-phase.

That's why tapped horns and back loaded horns have limited bandwidth.

Of course, the easiest way to find out would be to make an Akabak model. If I wasn't working so much this week I would
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Old 11th September 2019, 06:25 AM   #18
picowallspeaker is offline picowallspeaker  Italy
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Standing waves don't happen or exist in such a small box. Period
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Old 11th September 2019, 06:26 AM   #19
Patrick Bateman is offline Patrick Bateman  United States
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Good point, you're right.
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Old 11th September 2019, 07:27 AM   #20
fers is offline fers  Canada
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Originally Posted by picowallspeaker View Post
Standing waves don't happen or exist in such a small box. Period
Why would that be? The concern was not about standing waves in a box, but rather standing waves in a port. It might not be a problem in this case, but a port may certainly display resonances. A simple tube 4.3 cm long with one end closed has a quarter wave resonance at 2 kHz.
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