All the proof I need is available on my website. I see no need to post anything more.
And frankly, I am tired of your rudeness. I'm not going to change your mind, that is obvious. You certainly aren't going to change my mind, so I'll not be continuing in this argument.
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It all depends on what you find enjoyable from a speaker system.
If flat on axis response and near constant directivity is your thing, this is pretty easy to accomplish with an SEOS and a woofer and DSP.
There are MANY speakers that won't come close to those parameters that would be subjectively preferred in listening tests in an average listening space.
........but it seems since the thread topic is waveguides, the paramount criteria is constant directivity. Maybe that's the problem.
Yep....I've been through the early days of the "Hey guys" thread on AVS many times. I'm just trying to figure out exactly what that "secret" is to improve my wg designs and further my knowledge, and the knowledge of the group of course.
Dr. Geddes,
regarding the discussed "hole-on-axis", if I understand correctly, the problem is caused by (1) a coherent waveform, (2) equidistant diffraction on the mouth edge, and (3) possibly a resonance in the pass-band across the mouth aperture.
Since (1) is desirable and rotationally axi-symmetric device may be preferable, to mitigate the diffraction and (3), the solution would appear to be an increase of the radius at the mouth. This would, in turn, require a larger device.
Is this the reason why you went to the 18 inch device? If so and it is not prying into "secret sauce" is there a method to determine the mouth radius based on the device's pass-band?
Kindest regards,
M
regarding the discussed "hole-on-axis", if I understand correctly, the problem is caused by (1) a coherent waveform, (2) equidistant diffraction on the mouth edge, and (3) possibly a resonance in the pass-band across the mouth aperture.
Since (1) is desirable and rotationally axi-symmetric device may be preferable, to mitigate the diffraction and (3), the solution would appear to be an increase of the radius at the mouth. This would, in turn, require a larger device.
Is this the reason why you went to the 18 inch device? If so and it is not prying into "secret sauce" is there a method to determine the mouth radius based on the device's pass-band?
Kindest regards,
M
Hi, I missed your post earlier.
I've had some plasticine in place for over ten years at room temperatures and as far as I can tell it doesn't seem to have changed its characteristics at all.
I've got some extra around from that time, I'll stick a bit in fridge attached to something rigid, see what happens..
Never used Mortite
Hi M - you have that almost exactly correct. The 18" device also has a larger mouth radius which helps to reduce the edge diffraction. But in all honesty, I didn't completely understand the axial hole initially, i.e. when I built the first waveguides. It took me many years and several devices to put together exactly what was happening. I also developed a technique which allowed me to reconstruct the waveform at the waveguides mouth and this let me visualize what was happening. I had suspected the mouth edge diffraction, but not the standing wave across the mouth, this came as a "Oh yea! of course" moment. One could probably work out the "secret formula" for the mouth radius, but in all honesty it is likely to be just make the mouth as large as possible with as large a radius as possible.
The NA-12 does not have a circular mouth and it does not have an axial hole (or a minimal one when compared to the older Abbey.)
How come is the JBL M2 so constant low in frequency? It doesn't seem to start widening much before 400 Hz. I thought the horn worked till around 800 Hz. So how have they achieved this?
While I think the "smaller" waveguides work really well, I also find the sudden widening from midrange/woofer (at 1KHz or higher) a weakness. My conclusion and so far is that I prefer a speaker with wide but constant response.
If the speaker are going to have a high Q, I'm of the opinion that it needs that fairly low in frequency. The lower the better but it probably also becomes less critical the lower you go. Difficult to say where the minimal limit should be, but for me it's definitely lower than 1KHz.
While I think the "smaller" waveguides work really well, I also find the sudden widening from midrange/woofer (at 1KHz or higher) a weakness. My conclusion and so far is that I prefer a speaker with wide but constant response.
If the speaker are going to have a high Q, I'm of the opinion that it needs that fairly low in frequency. The lower the better but it probably also becomes less critical the lower you go. Difficult to say where the minimal limit should be, but for me it's definitely lower than 1KHz.
My thought on this Omholt; it's an anomaly produced by the way of measuring and the normalizing. Measuring directivity below 800hz in a normal/small room is difficult.
JBL's own plots look much different and much more realistic in this regard.
I also think you are to some degree right about high Q speakers that looses pattern control to early. The transition should happen lower and as smooth as possible, but its always a compromise. 1m wide speakers are just not gonna sell in any quantity. Not for home, not for studio.
I actually think this is one of the "tricks" in the M2. It's not as high Q in the 800-8kHz region (120 deg horizontal). So the transition is smoother. Many people has said it doesn't sound like a typical horn. And a part of that could be that it radiates wider than most other horns.
JBL's own plots look much different and much more realistic in this regard.
I also think you are to some degree right about high Q speakers that looses pattern control to early. The transition should happen lower and as smooth as possible, but its always a compromise. 1m wide speakers are just not gonna sell in any quantity. Not for home, not for studio.
I actually think this is one of the "tricks" in the M2. It's not as high Q in the 800-8kHz region (120 deg horizontal). So the transition is smoother. Many people has said it doesn't sound like a typical horn. And a part of that could be that it radiates wider than most other horns.
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The directivity of the woofer is a function of its size and the enclosure dimensions (baffle size). This is typical for such a large box.
I don't know how the NS-15 was measured. Maybe the floor was not absorptive.
If you simulate such a large speaker like M2 under free-air condition you'll get a similar directivity pattern.
Thank you!
Thanks FredrikC for the clarification.
The wider coverage (120 degrees) to get a smoother transition is a great choice IMO.
The very best in small rooms, and unless one specifically desires lateral contribution, is probably a horn with controlled directivity and high Q very low in frequency. But it becomes huge and isn't exactly wife friendly.
The wider coverage (120 degrees) to get a smoother transition is a great choice IMO.
The very best in small rooms, and unless one specifically desires lateral contribution, is probably a horn with controlled directivity and high Q very low in frequency. But it becomes huge and isn't exactly wife friendly.
Earl, to be honest I've never really understood why Oblate Speroids like the ones you designed for your speakers have the on-axis hole in their response. I've considered a lot of possible causes, but I just don't get it. You mention a standing wave across the mouth. I have trouble forming a mental image of what that is. What kind of standing wave is that and what causes it?
Cheers,
Martijn
This is my opinion as well. Not an easy product to market, but clearly the best way to do things.
Hi Martijn
First, it should not be too hard to envision the wave front reaching the mouth of a sharp termination generating a diffracted wave from this edge. The acoustic impedance suddenly changes because of the change in boundary conditions and this change generates a diffraction wave that propagates - in all directions - along with the major waveguide wave. (lets ignore the standing wave for a minute.)
In the far field there will be a frequency at which the major wave and the diffraction wave are out of phase. At this frequency the two waves will cancel leaving a response dip. But slightly off of the normal axis there will never be a frequency at which the entire circumference of the mouth is in phase. Hence the hole will be right on-axis and very sharp. Smooth the edges and the hole gets shallower and broader.
Now lets get back to that diffracted wave. It also crosses the mouth and hits the other side. If it is a circle then all of the mouth ring will all be in phase across the mouth. At some frequency all of these phases will be in phase. This will create a standing wave across the mouth that is exactly synonymous with waves on a drum (on the drum there is a fixed edge, but here we have a free edge - there is still a resonance.)
If this later resonance happens to coincide in the same frequency range as the far field axial hole then this hole can get worse as a result or better, depending on the phases. This is why the Abbey had a greater hole than a Nathan even though its mouth was larger. The Abbey had a measureable standing wave across the mouth in precisely the same frequency range as the axial hole.
It is
3D printed device:
Simulation:
Measurement:
Note: the simulation is on an infinite baffle. The measurement was taken without a baffle.
It seems rather simple math to convert these plots to a power response curve and show that. Can you pls do so as well?
THx-RNMarsh