Hello Jack,
There is a continuum between the catenoidal horn, the hypex, the exponential , conical and waveguides (sensus lato).
The first ones (catenoidal, hypex, exponential) are efficiently loading acoustically (with a resistive acoustic impedance dominance) the driver above a given frequency and there is a huge difference in efficiency between the "loaded" interval of frequency and the "unloaded"interval of frequency. The frequency who separates those 2 intervals may be called "cut-off frequency".
When it comes to waveguides (sensus lato) and conicals, there is very few difference in loading between the classical baffled loudspeaker and the waveguide/conical...
(an open baffle may be also considered as a 180° conical horn)
As in the case of waveguides/conical the power response (in a first glance) replicates the power response of the driver as measured on a plane waves tube, the cut-off is not marked by a neat variation in efficiency.
IMHO there is another method to determine the cut-off: we can call acoustical cut-off the frequency below which the resistive part of the acoustic impedance becomes smaller than the reactive part of the acoustic impedance.
See attached file with comparison betwwen the such defined cut-off for a Le Cléac'h horn (Fc = 160Hz) and an OSwaveguide of the same dimension. (Resistive part of the acoustic impedance = black. Reactive part of the acoustic impedance = red)
This is a very important indication for us as this is the lower frequency for which phase distortion (and GD variation) will be negligeible. (but this will obviously lead to flamed replies)
Best regards from Paris, France
Jean-Michel Le Cléac'h
There is a continuum between the catenoidal horn, the hypex, the exponential , conical and waveguides (sensus lato).
The first ones (catenoidal, hypex, exponential) are efficiently loading acoustically (with a resistive acoustic impedance dominance) the driver above a given frequency and there is a huge difference in efficiency between the "loaded" interval of frequency and the "unloaded"interval of frequency. The frequency who separates those 2 intervals may be called "cut-off frequency".
When it comes to waveguides (sensus lato) and conicals, there is very few difference in loading between the classical baffled loudspeaker and the waveguide/conical...
(an open baffle may be also considered as a 180° conical horn)
As in the case of waveguides/conical the power response (in a first glance) replicates the power response of the driver as measured on a plane waves tube, the cut-off is not marked by a neat variation in efficiency.
IMHO there is another method to determine the cut-off: we can call acoustical cut-off the frequency below which the resistive part of the acoustic impedance becomes smaller than the reactive part of the acoustic impedance.
See attached file with comparison betwwen the such defined cut-off for a Le Cléac'h horn (Fc = 160Hz) and an OSwaveguide of the same dimension. (Resistive part of the acoustic impedance = black. Reactive part of the acoustic impedance = red)
This is a very important indication for us as this is the lower frequency for which phase distortion (and GD variation) will be negligeible. (but this will obviously lead to flamed replies)
Best regards from Paris, France
Jean-Michel Le Cléac'h
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Jack,
Both Earl and Jean-Michel have much more experience than I have, and I understand, both their views.
Like Earl, I don't think we should generalize on how cutoff frequencies are determined. As Jean-Michel has also metioned, there is not such a clean line between the various configurations. As I go through various simulations, I try to get a feeling as to how various characteristics vary with shape, and it seems that there is no perfect solution, at least not as perfect as I originally thought when I started out on horns/guides.
I think the smaller sized devices have more cosmetic effect than a performance goal. For example, if one wanted to time align the drivers physically, the dome type drivers would have to be moved back to line up with cone devices, and the most appealing look would be to use waveguides which would also be a selling point even if only small changes to the performance is achieved. Thiel speaker just incline the whole baffle to align the drivers because it is more cost effective for them. As you can see, not all application make the same design trade-offs.
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I don't think the WG on those were aimed towards a serious directivity goal. They probably help beam the lower frequencies. The best way to find out is only to look at data measuring each driver as driven independently.
What are the XO points on these?
I think if a simple sim looking at the directivity of the difference sized drivers and the XO points were conducted, we could probably get a good feeling what's going on.
What are the XO points on these?
I think if a simple sim looking at the directivity of the difference sized drivers and the XO points were conducted, we could probably get a good feeling what's going on.
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In the light of my "diffraction alignment" concept your "oblate spheroide wave guide" concept looks possibly as limited, outdated, and obsolet as the Webster concept looks from your point of view...
In the same fashion you claim Webster's cut off does not happen. it easily could be said that your "throat-only" concept isn't any more useful nor applying in reality.
If I recall correctly, all that math you invested is brick wall limited with respect to included angle the physical length of the horn and also in frequency – so what ?
On the other hand, though all previous concepts (yours, Webster's that is in this case) look as to be outdated by its sheer limitations if we step forward - they nevertheless have their application and validity within their limits and for specific goals ...
Michael
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Except that its wrong. I don't know wjy he contnues to say such bogus things.
Earl, Is this because you believe what he is saying is based on 1-d horn theory?
Hi John
This
Is simply not true.
And his OS waveguide figure is deliberately staged and not a fair compaison. I've argued this with him so many time before i'ts not worth repeating, but, an OS can have any cutoff that is desired, just like any other horn or waveguide. His comparison is bogus.
Its really beneith a professional to do such things.
In what respect is it "simply not true"?
What would be a fair comparison? Why?
If it's been repeated before, please provide a link with post numbers.
Anything less isn't a discussion, it's bluster - and most certainly is beneath a technical professional to do such things.
Having done simulations on various configurations, although what Jean-Michel shows might not be comparible in size, but the general shape is pretty similar to what my sims are in terms of loading. The curvature from the throat thru the first 10cm or so pretty much shapes the loading although the outer part has some effect as well.
Hello,
I would really like to see an example of such an OS waveguide having a cut-off Fc as I define (the frequency above which acoustic resistance becomes larger than acoustic reactance) lower than 1000Hz.
Here is attached simulations performed using Hornresp for four different OS waveguides having the same length (126cm which is the length for the chosen 1 inch driver of my Le Cléac'h 160Hz horn , T = 0.8). The mouth area of the OSwaveguide are respectively 2000cm², 4000cm², 8000cm² and 16000cm².
The lowest cut off obtained with those four OS waveguides is around 1000Hz which is very far above the Fc = 200Hz obtained with the Le Cléac'h horn having the same length
May be I am doing something wrong but I would know what!
Best regards from Paris, France
Jean-Michel Le Cléac'h
I would really like to see an example of such an OS waveguide having a cut-off Fc as I define (the frequency above which acoustic resistance becomes larger than acoustic reactance) lower than 1000Hz.
Here is attached simulations performed using Hornresp for four different OS waveguides having the same length (126cm which is the length for the chosen 1 inch driver of my Le Cléac'h 160Hz horn , T = 0.8). The mouth area of the OSwaveguide are respectively 2000cm², 4000cm², 8000cm² and 16000cm².
The lowest cut off obtained with those four OS waveguides is around 1000Hz which is very far above the Fc = 200Hz obtained with the Le Cléac'h horn having the same length
May be I am doing something wrong but I would know what!
Best regards from Paris, France
Jean-Michel Le Cléac'h
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Jean-Michel
You are doing something wrong, but I have neither the time nor the patience to argue the point with you.
I thought that we agreed that comparing a waveguide whose design is based on directivity control with a horn whose design is based on loading, made little sense. Its like comparing a Porsche 911 to a Mercedes 500 over interior noise level, or top speed - they are simply not comparable.
Your designs load well, but don't control directivity and mine control directivity, but don't load well. I don't care about loading and you claim to not care about directivity. What is the point of arguing about it any further?
..actually they *both* control directivity, as you well know. They may not control directivity in the manner you deem most beneficial, but the basic operation is the same.
Nor do I remember Jean-Michel NOT caring about directivity. In fact I distinctly remember that he prefers a more directive upper freq. response to enhance clarity by reducing room reflections. Something you *both* claim, though to varying degrees (..yeah, bad pun).
All of this is "old ground", and you keep raising this issue anytime he makes a comparison - and now have gone on to accuse him of "setting up" something *purposefully* misleading. I've not *once* seen him display that sort of behavior.
Form-factor (or size), as you well know, *is* important to others - so the comparison of size *is* valid and as a result is eminently fair. That they achieve somewhat different goals is NOT contested.
This issue recently discussed is the *concept* of "cut-off" and added group delay of the waveguide (due to the waveguide's "mouth"). *This* is the current topic under discussion.
IF his sims are wrong, or his conclusion is wrong with regard to them, then please - *politely* correct them.
Hello Scott,
You are right and I confirm that not only I find some progressive increase in directivity benefitial but I would add that smoothness of the non axial response curves (without interleaving) and of the polar map is something that I find very important.
About loading, there is 2 main subjects that can be disussed separately:
1) loading in order to increase efficiency and reduce diaphragm displacement and distortion,
2) loading in order to obtain lower phase distortion and more constant group delay inside the used bandwith.
Until now the 2nd point was not discussed (or very faintly).
To avoid phase distortion and to obtain a constant group delay with a horn/waveguide the basic solution is to use a HP filter having a F-3dB at a frequency for which the resistive part of the impedance becomes far larger than the reactive part.
Without DSP phase (+ amplitude) equalization this signifies that a waveguide should be used with an HP filter having f-3dB above 2 to 6 kHz...
Best regards from Paris, France
Jean-Michel Le Cléac'h
You are right and I confirm that not only I find some progressive increase in directivity benefitial but I would add that smoothness of the non axial response curves (without interleaving) and of the polar map is something that I find very important.
About loading, there is 2 main subjects that can be disussed separately:
1) loading in order to increase efficiency and reduce diaphragm displacement and distortion,
2) loading in order to obtain lower phase distortion and more constant group delay inside the used bandwith.
Until now the 2nd point was not discussed (or very faintly).
To avoid phase distortion and to obtain a constant group delay with a horn/waveguide the basic solution is to use a HP filter having a F-3dB at a frequency for which the resistive part of the impedance becomes far larger than the reactive part.
Without DSP phase (+ amplitude) equalization this signifies that a waveguide should be used with an HP filter having f-3dB above 2 to 6 kHz...
Best regards from Paris, France
Jean-Michel Le Cléac'h
But they both have four wheels a motor and a stirring wheel - don't they?
Come on !
Whats the point comparing eggs the same size, the same weight, same color and being of same origin ??
I too find this loading topic very interesting – though I'd rather see it from intermodulation point of view, which is the lever to shift behaviour in the cut off region right into the pass band and thus contributes to perception of horn honk IMO.
So, for me the question is more how do horn contours compare with respect to displacement at throat needed for a given SPL at bottom end of band width ?
Michael
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The problem I have with it is that Impedance isn't showing linear decay. It may be a "tail-tell" sign of problems with linear decay, but in what respect and magnitude? Are there other factors in the intended *overall* design mitigating them? (..perhaps the overlay from the high-pass filter "swamps" the effects of the waveguide?)
Conceptually when I look at Jean-Michel's designs and Earls I get this impression:
Jmmlc: Lower freq. resonance, longer time resonance, lower magnitude (spl) resonance (when compared to the average).
Earl: Higher freq. resonance, shorter time resonance, higher magnitude (spl) resonance (when compared to the average).
With an appropriate low-pass filter Jmmlc's design should extend "cleaner" lower in freq..
On the other hand with Earl's design his low-pass filter may "swamp" any deviation in decay from the waveguide itself - and perhaps be subjectively benign. (..and in fact that seems to be the opinion from most posters who have heard it - i.e. no horn "coloration".)
But again, that's all a guess - what we really need is actual measured data displayed in a short-time period CSD plot. (..and thankfully Jean-Michel has supplied this, but I don't think Earl ever has - even though he has written papers on linear decay.) Perhaps oddly then, I *think* I remember commenting on such a plot on Earl's design (though not supplied by him), but d@mned if I know where it is on this forum.
Conceptually when I look at Jean-Michel's designs and Earls I get this impression:
Jmmlc: Lower freq. resonance, longer time resonance, lower magnitude (spl) resonance (when compared to the average).
Earl: Higher freq. resonance, shorter time resonance, higher magnitude (spl) resonance (when compared to the average).
With an appropriate low-pass filter Jmmlc's design should extend "cleaner" lower in freq..
On the other hand with Earl's design his low-pass filter may "swamp" any deviation in decay from the waveguide itself - and perhaps be subjectively benign. (..and in fact that seems to be the opinion from most posters who have heard it - i.e. no horn "coloration".)
But again, that's all a guess - what we really need is actual measured data displayed in a short-time period CSD plot. (..and thankfully Jean-Michel has supplied this, but I don't think Earl ever has - even though he has written papers on linear decay.) Perhaps oddly then, I *think* I remember commenting on such a plot on Earl's design (though not supplied by him), but d@mned if I know where it is on this forum.
Augerpro did measurements of the 10" geddes waveguides
Frequency Response w/ B&C DE250 (drivervault)
Frequency Response w/ B&C DE250 (drivervault)