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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 11th September 2019, 07:34 AM   #21
picowallspeaker is offline picowallspeaker  Italy
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I'm no expert, but the term standing waves refers to the room and are part of the room modes ( of vibrating).
To exist, those need to find the energy and the space and the frequency at which they occur. Otherwise is a matter of reflection and refraction with the peaks and dips etc.
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Old 11th September 2019, 06:08 PM   #22
fers is offline fers  Canada
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Quote:
Originally Posted by picowallspeaker View Post
I'm no expert, but the term standing waves refers to the room and are part of the room modes ( of vibrating).
To exist, those need to find the energy and the space and the frequency at which they occur. Otherwise is a matter of reflection and refraction with the peaks and dips etc.
No, standing waves are the superposition of a forward and backward travelling wave that does not propagate. It can happen in a room, as anywhere else, as the reflections lead to such forward and backward travelling waves. Sharp (compared to the wavelength) impedance changes cause diffraction and reflection that can lead to standing waves if not properly damped. Those standing waves are what causes the peaks and dips in the response as the transfer function of the system is perturbed close to a resonant mode (a standing wave).

Refraction is the bending/reflection of a wave passing from one medium to a different one. Often seen in audio as the sound passes through a mass of air with a temperature gradient or when one introduces stuffing in a pipe. In the extreme, the difference between refraction and diffraction is a bit blurry, but it is not the term I would have used here.

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Geoffroy
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Old 12th September 2019, 07:19 AM   #23
fers is offline fers  Canada
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Originally Posted by Patrick Bateman View Post
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
So I ran a little simulation of the concept. The picture is the 2.00 V (1W on 4 ohm nominal load) power response in 4 pi at 1 meter on axis (same as default in hornresp) with the setup as described below. The results of my code matched up to hornresp in other situations, but as I understand, it can't handle this situation.

top2.png

The result is really encouraging, however, I remain a bit sceptical as efficiency seems way too high. I model the ports as lumped mass elements as their length is like 1/16 of the highest frequency of concern. Also, the mass loading is modelled as simply using the port input impedance as the mouth impedance. It should work in principle.

If those results can be trusted, then the initial idea seems very worthwhile! The standing waves do not seem to cause problem indeed! 4.3 cm is 1/4 wavelength at 2kHz and thus a delay of only 90 degree: the tweeter can even be "delayed" around the crossover with a simple passive all-pass when no dsp is used.

Here is a detailed description of the simulation. Two 6" drivers (Dayton's PA165 in parallel) are each fitted with a 2 liters back chamber and a front chamber of 70mL and a 1/2" long slot port of area 12 x 2.54 cm (4.7" x 1"), followed by a short 4.3 cm conical horn segment flaring to a final area of 24 x 8 cm (9.4" x 3.1"). In turn, these short horns are each mass loaded by 1/2" long slot port of area 12 x 2.54 cm tapping in the main astigmatic conical horn at area 0.011 m^2 that flares over 21.5 cm to a mouth area of 0.21 m^2.
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Old 12th September 2019, 02:47 PM   #24
mark100 is offline mark100  United States
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Looking very promising. Please continue !!!
I'm slugging out trying to add bass-reflex ports to my synergy attempt..would be nice not to have to go that route


re crossovers

my take on the patent has been that the goal is acoustic first order.
That the 1/4 wave spacing, and acoustic port location design accommodates that goal
So, no additional first order electrical crossover needed, just whatever additional filter it takes to achieve acoustic 1st order.
Maybe I'be been misunderstanding...
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Old 12th September 2019, 04:15 PM   #25
Patrick Bateman is offline Patrick Bateman  United States
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first order xovers don't really work on a Unity horn

In order for them to work, the pathlengths would have to be equidistant

Check out "Crossovers, a Step Further" by LeCleach
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Old 12th September 2019, 06:24 PM   #26
mark100 is offline mark100  United States
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Quote:
Originally Posted by Patrick Bateman View Post
first order xovers don't really work on a Unity horn

In order for them to work, the pathlengths would have to be equidistant

Check out "Crossovers, a Step Further" by LeCleach
Yep, all I was trying to say is that it appears something close to a net first order acoustical crossover between sections is the final design. Not electrical first order at all..

Looking at a SH-50, which is the speaker I use for a synergy reference, it looks like roughly 90 deg phase lag per crossover (assuming say 300Hz and 1000Hz cross points).

Thx for the link. I've read that excellent paper before.
I just wish it, or rather an updated version of it, had current studies of phase audibility.
Better experiments are easier to do today, i think.
And same thing with the crossover recommendations...too complicated...too dated imho.
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Old 19th September 2019, 06:44 PM   #27
fers is offline fers  Canada
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It turns out something was wrong with my simulations. I was putting the "pre-horn" throat impedance in series with the main horn impedance... When I properly put the horn itself in series (that is, connect the bandpass port impedance to the throat impedance of the pre-horn and its mouth impedance to the main horn throat impedance), I still get the same increase in loading at lower frequencies. However, the mass loading causes major resonances that vary according to the length of this first horn. The more I increase the mass loading, the worst it gets. Without substantial mass-loading, I get mild peaks such as the following (pre-horn length is 1/2 wavelength at 2 kHz)

top2.png

If this length is sufficiently short, those can be made to occur outside the pass band, but HF extension is sacrificed. In the following the pre-horn is 1/4 wavelength at 2 kHz:

top3.png

It seems that the main conical horn throat does not resistively load the port sufficiently to avoid reflections. Simply using the bandpass chambers, everything seems alright, except I loose all the gain advantage:

top4.png

Moreover, the horn above cannot really be physically built... I can recover some driver loading by increasing the mass loading of the port at the cost of a somewhat peaky response. This is the direction I'm considering with some EQ to reign in the peaks. In the following, the port is twice as long:

top5.png

In conclusion, the suggested approach seems to work if one restricts the bandwidth of the driver. I am sceptical of its usability in a two-way synergy where the driver has to get in the 2 kHz range...

Another option would be to ditch the synergy concept, although an efficiency above 100dB/W @ 1m as the last simulations suggest seems enough. How much should I value constant directivity / the synergy approach versus efficiency in a portable battery powered PA context?

Last edited by fers; 19th September 2019 at 06:47 PM.
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