soongsc said:
Of course they can - you can always represent yourself in court. More like 95% of all infringment cases are settled out of court.
Re: a question for JMLC
Hello,
You surely know that before Siegfried Klein patent the Ionosphere which one radiated omnidirectionally, he invented and patented the Ionophone which one was also built in USA by Dukane (under Klein's patent) and commercialized as Ionovac.
If you look at the patent 4306120 in the site USPTO:
http://patft.uspto.gov/netahtml/PTO/srchnum.htm
you can see the shape of the horn looking like a long tractrix with a very small throat. This means that Klein wanted to improved the efficiency of the Ionophone loading the plasma flame by this horn which insures a resistive load within a large interval of frequency.
If you use T> 1 you effectively tend to obtain progressiveley a conical shape or a kind of waveguide shape. You loose the on axis linearity brought by the loading due to the horn, you'll have to equalize but in the same tilme you'll improve off axis reponse linearity (within an interval of frequency...).
In fact we don't have really experience on Le Cléac'h horns using T>1 . Only John Hasquin reprted very good results using a T value of 1,3125 (value from memory).
Best regards from Paris, France
Jean-Michel Le Cléac'h
Hello,
You surely know that before Siegfried Klein patent the Ionosphere which one radiated omnidirectionally, he invented and patented the Ionophone which one was also built in USA by Dukane (under Klein's patent) and commercialized as Ionovac.
If you look at the patent 4306120 in the site USPTO:
http://patft.uspto.gov/netahtml/PTO/srchnum.htm
you can see the shape of the horn looking like a long tractrix with a very small throat. This means that Klein wanted to improved the efficiency of the Ionophone loading the plasma flame by this horn which insures a resistive load within a large interval of frequency.
If you use T> 1 you effectively tend to obtain progressiveley a conical shape or a kind of waveguide shape. You loose the on axis linearity brought by the loading due to the horn, you'll have to equalize but in the same tilme you'll improve off axis reponse linearity (within an interval of frequency...).
In fact we don't have really experience on Le Cléac'h horns using T>1 . Only John Hasquin reprted very good results using a T value of 1,3125 (value from memory).
Best regards from Paris, France
Jean-Michel Le Cléac'h
CV said:
gedlee said:
Right, although it's quite a complex field. OTOH, there are plenty of lawyers around now AFAIK, who will work on a no-win-no-fee basis, and if you know your case is strong - irrefutable, and it's a big wealthy company in opposition, they'll be delighted to take it on, as they know they'll recoup their costs from their opponent.
Hello Jean-Michel,
Many thanks for your thoughts; that all makes sense. I thought the very high T factors would need EQ, as they, superficially at least, resemble conicals for the initial flare. I do have a pair of ionovacs but would like to see what a lower x/o and "JMMLC" horn can do.
I do recall the T=1.3ish post from another site, though I can't say I agreed with the derivation and other assertions therein.
So perhaps I shall give the T=0.8 a go; whilst tempted by the conical + EQ, that would make for a rather large horn and be a lot more costly. I will keep you posted...
Best,
cv
Btw, I commissioned the 160Hz Azuras from Martin - have you seen the on-axis response he gets with the Yamaha driver?
http://www.azurahorn.com/6681_on_160.pdf
Many thanks for your thoughts; that all makes sense. I thought the very high T factors would need EQ, as they, superficially at least, resemble conicals for the initial flare. I do have a pair of ionovacs but would like to see what a lower x/o and "JMMLC" horn can do.
I do recall the T=1.3ish post from another site, though I can't say I agreed with the derivation and other assertions therein.
So perhaps I shall give the T=0.8 a go; whilst tempted by the conical + EQ, that would make for a rather large horn and be a lot more costly. I will keep you posted...
Best,
cv
Btw, I commissioned the 160Hz Azuras from Martin - have you seen the on-axis response he gets with the Yamaha driver?
http://www.azurahorn.com/6681_on_160.pdf
CV said:
A little too good to be true IMO (un-EQd of course), unfortunately the off axis response seems to be a secret.
Hello,
Here is the unequalized response of the TAD TD4001 compression driver on Marco Henry's J322 horn (Fc = 320Hz).
(I am not the author of that measurement. All the curves I publish are presented with a less than 30dB scale)
I can provide my own mesurements for TD2001 on a "Le Cléac'h" flare horn Fc = 320Hz obtained by Angelo Farina's logsweep + deconvolution method in order to recover the "quasi anechoic" pulse response. For that kind of horn the mesure done at very few distance from the mouth (5 to 10cm) are similar to the ones obtained at 1meter (but less noized). I can provide off axis measurements at 1meter too...
Best regards from Paris, France
Jean-Michel Le Cléac'h
Here is the unequalized response of the TAD TD4001 compression driver on Marco Henry's J322 horn (Fc = 320Hz).
(I am not the author of that measurement. All the curves I publish are presented with a less than 30dB scale)
I can provide my own mesurements for TD2001 on a "Le Cléac'h" flare horn Fc = 320Hz obtained by Angelo Farina's logsweep + deconvolution method in order to recover the "quasi anechoic" pulse response. For that kind of horn the mesure done at very few distance from the mouth (5 to 10cm) are similar to the ones obtained at 1meter (but less noized). I can provide off axis measurements at 1meter too...
Best regards from Paris, France
Jean-Michel Le Cléac'h
gedlee said:
Attachments
(forum just lost my reply and JM beat me to it!)
Hi Earl,
I hear you - I'd like to see off-axis and at a further distance away, *but* Martin isn't applying trickery; see his measurements of Lowthers in the 160 horn elsewhere!
http://www.azurahorn.com/lowther_on_160.pdf
and other compression drivers at
http://www.azurahorn.com/azurahorn_horns.html
What is clear is that the Yamaha is a rather special driver: the surround is terminated by angled beryllium copper fingers which I suspect will help prevent resonances:
http://www.azurahorn.com/pages/Yam 6681B diaph_jpg.htm
FWIW, Bear has posted similarly impressive measurements of these drivers on Altec sectoral horns.
The other thing is that the 160 is probably a good match to the internal flare of the JA6681B driver.
Martin has told me that these drivers come alive on the 160Hz horns in a way he hasn't heard before, even by comparison with his 204Hz horns (and a 400Hz x/o point) , which would underscore the importance of a good throat match - nothing controversial here!
Best regards,
Chris
Hi Earl,
I hear you - I'd like to see off-axis and at a further distance away, *but* Martin isn't applying trickery; see his measurements of Lowthers in the 160 horn elsewhere!
http://www.azurahorn.com/lowther_on_160.pdf
and other compression drivers at
http://www.azurahorn.com/azurahorn_horns.html
What is clear is that the Yamaha is a rather special driver: the surround is terminated by angled beryllium copper fingers which I suspect will help prevent resonances:
http://www.azurahorn.com/pages/Yam 6681B diaph_jpg.htm
FWIW, Bear has posted similarly impressive measurements of these drivers on Altec sectoral horns.
The other thing is that the 160 is probably a good match to the internal flare of the JA6681B driver.
Martin has told me that these drivers come alive on the 160Hz horns in a way he hasn't heard before, even by comparison with his 204Hz horns (and a 400Hz x/o point) , which would underscore the importance of a good throat match - nothing controversial here!
Best regards,
Chris
The technique of measuring in the mouth is totally invalid IMO. I'm tempted to do that with mine to compare, but since its bogus I don't like the idea of posting measurements that I know have no validity.
Hello,
I agree for a large part to Earl's statement: when the microphone is placed IN the mouth a more or large bump in the response curve appears near the frequency cut-off.
When the microphone is moved progressivley from the mouth to some distance, that bump will decrease and disappear.
So someone with bad intentions could eventually ameliorate the response curve of a driver+horn a bit anemic at LF placing the microphone in the mouth.
I am sure that this it is not the case with Martin Seddon's measurement (performed AT mouth not IN the mouth) but I can understand the demand for more indiscutable measurements.
Best regards from Paris, France
Jean-Michel Le Cléac'h
I agree for a large part to Earl's statement: when the microphone is placed IN the mouth a more or large bump in the response curve appears near the frequency cut-off.
When the microphone is moved progressivley from the mouth to some distance, that bump will decrease and disappear.
So someone with bad intentions could eventually ameliorate the response curve of a driver+horn a bit anemic at LF placing the microphone in the mouth.
I am sure that this it is not the case with Martin Seddon's measurement (performed AT mouth not IN the mouth) but I can understand the demand for more indiscutable measurements.
Best regards from Paris, France
Jean-Michel Le Cléac'h
gedlee said:
Jmmlc said:
Horns and waveguides need to be measured at the distance more in line with where they are used. Otherwise you are not looking at the radiated sound field, but the near field, and the two can be quite different. And, of course, looking at only one axis is a very limited look at performance.
I keep being told that the measurements don't contain EQ. Why then do they not fall off at 6 dB/oct as any constant directivity device must? Of course they may not be constant directvity. Only a full polar response can tell someone if what they are looking at has value or not.
Whats the difference between "at" the mouth and "in" the mouth?
gedlee said:
They surely aren't 'constant directivity' There is no such thing unless your idea of radiation is like 20 degrees.
I agree, the TAD is EQ'd to bring down the mid in that horn. Been there done that.
I like to measure at 3 feet, 6 feet, and 10 feet. In all cases with round tractrix horns there is a drop in low frequency response as you move out.., In this case the horn has a different flare but I feel it's safe to say at ten feet it would be rolling off sharply around 600-800 cycles. More then likely it beams badly too - In mouth or at mouth measurements are GREAT if you want to post them on the internet.
Hi,
Some of my thoughts on measurement, for what they are worth:
There is no standard on measurement of a horn / driver combination (afaik) - as long as one states how one did it, it is valid on its own terms. It may not be Useful – but that’s different. There is no intention to gain an unfair advantage.
Possibly one should add a health warning to the effect ‘ pls note that with the mic at the listening position this response looks like total ****, and you can only thank your brain that it sounds like music at all.’ But of course this applies to all transducers.
To get a useful measurement with the the mic placed away from the horn mouth one needs to take the horn outside and face it upwards- as Tom Danley recommends. Otherwise one is just recording room stuff. I should try this.
The ‘mic at the mouth’ is a quick way to isolate what one is interested in. How are Compression drivers measured? Isn’t it with a mic at the end of a plain tube? Perhaps a horn / driver comparable standard of measurement would be similar - with the mic at the horn mouth?
Would this method not reveal the acoustic effect of non-linearities imposed by the horn on the driver? Is it this we are interested in?
In simple laymans terms (my level) I reasoned that the nearfield wave creates the far field, so one wants to know if that is right first. The horn mouth is the last point at which the horn has control. I am sure there is a lot more to it, but perhaps a simple clean method that can be easily applied to all horn / drivers really does have its use?
Best rgds to all,
Martin
(Chief Perpetrator, Azurahorn)
Some of my thoughts on measurement, for what they are worth:
There is no standard on measurement of a horn / driver combination (afaik) - as long as one states how one did it, it is valid on its own terms. It may not be Useful – but that’s different. There is no intention to gain an unfair advantage.
Possibly one should add a health warning to the effect ‘ pls note that with the mic at the listening position this response looks like total ****, and you can only thank your brain that it sounds like music at all.’ But of course this applies to all transducers.
To get a useful measurement with the the mic placed away from the horn mouth one needs to take the horn outside and face it upwards- as Tom Danley recommends. Otherwise one is just recording room stuff. I should try this.
The ‘mic at the mouth’ is a quick way to isolate what one is interested in. How are Compression drivers measured? Isn’t it with a mic at the end of a plain tube? Perhaps a horn / driver comparable standard of measurement would be similar - with the mic at the horn mouth?
Would this method not reveal the acoustic effect of non-linearities imposed by the horn on the driver? Is it this we are interested in?
In simple laymans terms (my level) I reasoned that the nearfield wave creates the far field, so one wants to know if that is right first. The horn mouth is the last point at which the horn has control. I am sure there is a lot more to it, but perhaps a simple clean method that can be easily applied to all horn / drivers really does have its use?
Best rgds to all,
Martin
(Chief Perpetrator, Azurahorn)
My understanding is that measurements in near field ie less than 1 metre of a mouth or less than 2x the cut off wave length will not be representative of the actual output.
Any form of baffle in the vacinity of the mouth will also effect the measurements. For a measurement of down to 300 hz this of course must be a prime consideration.
Any form of baffle in the vacinity of the mouth will also effect the measurements. For a measurement of down to 300 hz this of course must be a prime consideration.
Truetone said:
macka said:
It's easy to see how measuring at the mouth can go very wrong. Say there are resonances in the horn (caused by standing waves along or across the horn) which lead to peaks and dips in the frequency response.
A microphone at the mouth could either be at a peak or dip in the sound level (or anywhere in between), depending whether there is a resonant node or an antinode at the horn mouth and/or mic position.
So the mic could show a peak where none exists in the far field response (e.g. non-uniform SPL across mouth which integrates to flat far-field response), or miss a peak in the far field because it isn't at the peak SPL point of a standing wave.
This isn't saying that measurements at the mouth don't tell you something useful -- especially if you make them with the mic over a grid of positions across the mouth area -- but they certainly can't be relied on to tell the truth about response peaks and dips.
Ian
It is a theorem in acoustics that the sound fields in any sequential set of "planes" (although they could also be spheres) must be related to one another and a measurement in one plane completely determines the measurements in the other. Thus measureing across the mouth has to contain enough information to predict the far field. This is of course true, but this relationship is not simply one-to-one, it is very complex. But it is doable. In the far field the central axial points can be shown to be the average of the wave motions across the mouth. So clearly, unless there is no variation in the wavefront across the mouth, which of course there has to be, the far field axis and the central point of the mouth will not be related in any meaningful way.
You can measure that point, heck you can measure the point behind the driver, but if it can't be related to siomething useful to understanding how the device will sound then what good is it?
I do all my measurements in doors, free field, and I don't have any problems with reflections above about 200 Hz. Its not hard to do with gating and anybody not doing this is either lazy or uninterested in taking good measurements.
You can measure that point, heck you can measure the point behind the driver, but if it can't be related to siomething useful to understanding how the device will sound then what good is it?
I do all my measurements in doors, free field, and I don't have any problems with reflections above about 200 Hz. Its not hard to do with gating and anybody not doing this is either lazy or uninterested in taking good measurements.
Truetone said:
Unfair advantage or not, I know of no one else who does this. I haven't read every standard but there are recommended practices and this is not one of them. Its easy to see that it does not show what one is interested in.
Compression drivers should be measured on plane wave tubes as this is know and understood and the acoustic effect is easily quantified. With a mic in the mouth of a horn the acoustic effect is unknow and indeed very difficult to quantify. No the mic is not at the end of the tube, its in the side of a very long damped tube such that there is no reflection.
gedlee said:
You're correct that if you know the amplitude *and phase* response at all points across the mouth you can calculate the far-field response anywhere both on and off axis. But it takes an awful lot of measurements (spacing should be a fraction of a wavelength to get reliable results, which means a grid smaller than 1cm at 20kHz) and a massive amount of number-crunching to do this, and most people don't have the skill, the software or the time to do this properly.
Gated measurements work fine so long as there are no relatively high-Q resonances, so the impulse response falls within the pre-reflection gating time. This isn't always the case either...
My vote goes for outdoors, facing upward, with the mic above the mouth by at least 4x the largest dimension of the mouth. The noise isn't enough to annoy the neighbours (unless you're doing maximum SPL tests rather than frequency response) and the results are very reliable and much less prone to gating setup errors.
Ian
iand said:
The mouth measurement procedure is not as complex as you say, but its not trivial either, and the real point is its not necessary.
I can gate about 6 ms in my living room. We are talking about horns and waveguide here and none of them is going to ring past that gating time. They'd be total trash if they did. Outdoors is simply not necessary for horns and waveguides. Fine if you can do it. But pointed up isn't ideal either, unless you have a pit. But then things are becoming a bit unreasonable. A rotating stand is the best approach, in as large a space as you can find. Then just live with the gate time because it most likely won't be a problem.
gedlee said:
Actually, gating at 6 msec can cause a *lot* of problems. There is a very good study of measurement techniques that was published in Stereophile and is posted on their website in two parts:
http://stereophile.com/features/105kh/
http://stereophile.com/reference/405time/
Take a look at Figure 3 in part one (gated at 6 msec) and look at all the measurement artifacts introduced relative to Figure 1 (gated at 217 msec). Well worth your time to read the full article.
Charles Hansen said:
None of that is applicable to what I was saying because we were talking about horns and such which work above 500 Hz and don't have very high-Q resonances. The whole weakness of that article is the fact that it is simulated and the resonances that were added had very high Q and very low damping. A good loudspeaker won't have these problems making the points mute. Its not that it couldn't happen, but a resonance that rings out for 20 ms would be highly audible and as such one would hope that something was done about it.
That said, I don't like horns that are cast plastic or fiberglass unless something is done to dampen them out. The JBL that I measured was very resonant and its ringing was gone in 6 ms.
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