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Multi-Way Conventional loudspeakers with crossovers

Is it possible to cover the whole spectrum, high spl, low distortion with a 2-way?
Is it possible to cover the whole spectrum, high spl, low distortion with a 2-way?
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Old 12th September 2019, 08:10 AM   #2971
Ro808 is online now Ro808  Netherlands
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The natural termination for conical horns is no termination at all, just oversize the horn considerably. A mouth of 1.50x1.50m would suffice for a 500Hz XO.

Last edited by Ro808; 12th September 2019 at 08:13 AM.
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Old 12th September 2019, 08:16 AM   #2972
AllenB is offline AllenB  Australia
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Not literally of course. I mean moving on with minimal disturbance. Maintaining its directivity moving out of the waveguide with minimal source creation. An example is the way that the LeCleach horn grants graceful independence to higher (gradually lower) frequencies, except that to do so it continues to increase its width.
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Old 12th September 2019, 08:17 AM   #2973
AllenB is offline AllenB  Australia
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Correct Ro, I took that as an axiom.
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Old 12th September 2019, 08:20 AM   #2974
mabat is offline mabat  Czech Republic
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To smoothly terminate a conical horn you need a curve with zero (or almost zero in a case of OSWG) curvature at the beginning. When I look at LeCleach profile I don't see this as suitable as the clothoid. I have no doubt it would still work well (it's only a very minor difference I guess), only that the resulting waveguide would have to be bigger in the end. Or not? Don't forget that I want to maintain the directivity constant as much as possible.

Last edited by mabat; 12th September 2019 at 08:31 AM.
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Old 12th September 2019, 08:35 AM   #2975
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by mabat View Post
you need a curve with zero
I'm not suggesting a simple radius termination, just that the wavefront not be allowed to "follow" the curve around.

There is going to be the same amount of diffraction on the whole. 'Minimising' could only mean 'spreading'. I think this is important.

Doing this, especially on a waveguide, may mean a smaller region within which to effect the diffraction. Then again, a radius in general does have a more diverse profile early on than an equivalent varying radius profile.

Is it better to have lower frequency axial resonances or room reflections?
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Old 12th September 2019, 08:36 AM   #2976
whgeiger is offline whgeiger  United States
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Default Mitigating Reflectance

Quote:
Originally Posted by AllenB View Post
You once suggested to me that LeCleach was a possible termination choice. I wonder whether your goals are focussed on diffraction minimisation, where another option would be to embrace and allow but control the inevitable diffraction in other ways?
Beneficial diffraction occurs gradually in the throat of an OS horn.
Here we have a boundary condition of declining curvature which ideally transforms a plane outbound wave front into a oblate spheroidal surface that is approaching that of a spherical cap. While this spreads the wave energy uniformly within the horn body, this orderly propagation will become significantly disturbed if mouth reflectance is not mitigated. This requires reversing the curvature decline in the horn profile as the mouth is approached. The best way to do this is with a fairness transition curve.
Le Cleach's method will yield a satisfactory curve in this regard, but their others as well.

For the purposes of clarity I am not addressing the host of other design issues, including compression driver wave front matching and other propagation modes present in a finite horn. WHG
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Old 12th September 2019, 08:52 AM   #2977
AllenB is offline AllenB  Australia
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Originally Posted by whgeiger View Post
this orderly propagation will become significantly disturbed if mouth reflectance is not mitigated.
I like to allow my lowest frequencies to pass thereabouts a mouth of a wavelength before attempting significant extra curvature (but after shedding the highs). I feel this is likely a significant mitigating factor in the need to do this.
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Old 12th September 2019, 08:55 AM   #2978
whgeiger is offline whgeiger  United States
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Default Curvature

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Originally Posted by mabat View Post
There is no point of inflection. If you mean at the join, yes, it should match (I guess). It will.

Thanks for the reading. I'm actually quite happy with how it's done now - this is the waveguide I will go for.
You are close enough. Design iteration might just be a little bit slower however.

1) I intended to recognize a point of curvature minimum where your "join" occurs. As the sign of curvature does not change, of course it is not a point of inflection.

2) A C-Bézier curve can follow the locus of a hyperbola and then depart from it to a fairness curve of increasing curvature proportional to its length. Euler's Spiral is just one member of the fairness curve family but requires a "join" to a hyperbolic throat segment. This tack to horn design is not new. [1]

3) Important to this approach (of terminating a hyperbolic throat in a fairness curve) is that it opens up an additional degree of freedom in throat design, otherwise fixed by specification of throat diameter (@ Slope = 0) and an asymptote (coverage) angle of a hyperbola.

WHG

[1] Post: 21st January 2013, 07:47 PM
Subject: A Contrary View
URL: Geddes on Waveguides

Excerpt: “This finding supports the conjecture that horns of infinite extent, that require mouth truncation to make them real, are a bad idea for loudspeaker applications. Alternatively, curves such as a segment from Euler’s spiral [1] might be a superior choice. Here boundary curvature gently increases with curve length to form a smooth transition to free space from the confines of throat aperture of a compression driver. One could argue that this approximation comes closer to meeting the mission of a loudspeaker horn where unlike that for a musical instrument, reflectance is to be avoided. We do not want to trap acoustical energy within the horn; we want all of it to leave!”

Last edited by whgeiger; 12th September 2019 at 08:59 AM.
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Old 12th September 2019, 09:20 AM   #2979
mabat is offline mabat  Czech Republic
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Quote:
Originally Posted by whgeiger View Post
1) I intended to recognize a point of curvature minimum where your "join" occurs. As the sign of curvature does not change, of course it is not a point of inflection.
If you intended just that, then I don't understand why you called it an inflection point.

Curvatures of both segments will match at this junction, i.e. it should be smooth enough. There's no need to go for splines as I have it already working as it is. Is it possible to do it a bit differently? Of course it is. Will it be any noticeably better? Please show me that.

- It was year 2013. So where are all the waveguides terminated by Euler spiral segment?
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Old 12th September 2019, 11:51 AM   #2980
gedlee is offline gedlee  United States
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Quote:
Originally Posted by AllenB View Post
Aren't you concerned that might help maintain the wavefront at the edges and allow it to widen, rather than dissipating it? (At the least a combination may serve)
What happens is a gradual reduction in the wavefronts amplitude at the edges. In my book I show how this has the net effect on the directivity of smoothing it, which is why it mitigates the midrange narrowing and the axial holes. They get "averaged out. The slower the mouth transition is the greater the averaging effect will be with the least amount of diffraction and reflections.

And let's all remember that whenever there is diffraction there must also be reflection. A new diffracted wave propagates out, but the counter to this wave must be reflected back down the device. So both are issues.

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Widening of the wavefront is not the purpose of an OSWG. I guess minimizing/elimination the narrowing, the on-axis null and interferences at the mouth were areas of concern.
Dr. Geddes has opted for an asymetrical mouth, whereas mabat optimized the throat to mouth transition.
Please, correct me if I am wrong.
My commercial waveguides are all symmetric. I have built several non symmetric ones and they are usually not an improvement.
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