“Throat distortion is continuous, and increases with output, and inversely as the size of the throat area.”
To get a better handle on how this may or may not be a factor, additional details are required.
This effect is caused by the shocking up effect of air at reasonably high intensities. The pressure side of the wave is slightly warmer than he rarefied side and so after traveling some distance, the positive side moves forward in phase, distorting the waveshape and can eventually produce a saw tooth wave if intense enough as with an acoustic levitator.
In a horn, the effect is primarily 2nd harmonic and is greatest at the highest frequencies while at the low end of a horn drivers response it is the driver non-linearity which strongly dominates.
The shocking up effect is reduced the more rapid the horn area expands, thus a multi way horn system (high mid and low horns) all things being equal will suffer less than a single broad band horn where the expansion rate is limited by the lowest F requirement.
Another way to solve the rubic’s cube is a Synergy horn.
This design evolved from a comment about conical horns Don Davis made at a Synaudcon in the 90’s.
In that approach a conical horn is used which has a very rapid initial expansion rate which slows as you move away from the apex.
By coupling suitable mid drivers and lower drivers into the horn body where the rate of expansion is suitable for horn coupling for that frequency, at a dimension where they add coherently into one source, one can drive a single horn over a very wide bandwidth with no driver to driver interference.
By passing the sound from the mid and low frequencies through an acoustic low pass filter before entering the horn, one can remove some of the distortion that is always present and always above the intended band and minimize any perturbation to the horn for other frequencies.
In this approach one can produce a much greater SPL for a given harmonic distortion than direct radiators and with the proper crossovers, measure acoustically as if they only had one driver and can reproduce a square wave over some bandwidth.
Best,
Tom Danley
Danley Sound Labs
Here is a large version of it if you have headphones handy. It’s a single horn, one lobe, no pattern of lobes and nulls (with a sub on the ground).
It’s a 4 way horn, 4 hf drivers, 4 mid high drivers, 8 cone mid horn drivers, 6, 15inch horn loaded woofers.
It has a 60 by 40 pattern and very high directivity as you can tell when the camera guy walks under the speaker.
This was a demo for some sports stadium sound people, at about 2:30 the camera guy pans out to the field where the people are standing on a ridge at 450 feet.
Danley Sound Labs - YouTube
It’s nice when even the players notice the difference;
Rodgers Likes New Danley Sound Labs System. "Nice to be back at Lambeau" - YouTube
To get a better handle on how this may or may not be a factor, additional details are required.
This effect is caused by the shocking up effect of air at reasonably high intensities. The pressure side of the wave is slightly warmer than he rarefied side and so after traveling some distance, the positive side moves forward in phase, distorting the waveshape and can eventually produce a saw tooth wave if intense enough as with an acoustic levitator.
In a horn, the effect is primarily 2nd harmonic and is greatest at the highest frequencies while at the low end of a horn drivers response it is the driver non-linearity which strongly dominates.
The shocking up effect is reduced the more rapid the horn area expands, thus a multi way horn system (high mid and low horns) all things being equal will suffer less than a single broad band horn where the expansion rate is limited by the lowest F requirement.
Another way to solve the rubic’s cube is a Synergy horn.
This design evolved from a comment about conical horns Don Davis made at a Synaudcon in the 90’s.
In that approach a conical horn is used which has a very rapid initial expansion rate which slows as you move away from the apex.
By coupling suitable mid drivers and lower drivers into the horn body where the rate of expansion is suitable for horn coupling for that frequency, at a dimension where they add coherently into one source, one can drive a single horn over a very wide bandwidth with no driver to driver interference.
By passing the sound from the mid and low frequencies through an acoustic low pass filter before entering the horn, one can remove some of the distortion that is always present and always above the intended band and minimize any perturbation to the horn for other frequencies.
In this approach one can produce a much greater SPL for a given harmonic distortion than direct radiators and with the proper crossovers, measure acoustically as if they only had one driver and can reproduce a square wave over some bandwidth.
Best,
Tom Danley
Danley Sound Labs
Here is a large version of it if you have headphones handy. It’s a single horn, one lobe, no pattern of lobes and nulls (with a sub on the ground).
It’s a 4 way horn, 4 hf drivers, 4 mid high drivers, 8 cone mid horn drivers, 6, 15inch horn loaded woofers.
It has a 60 by 40 pattern and very high directivity as you can tell when the camera guy walks under the speaker.
This was a demo for some sports stadium sound people, at about 2:30 the camera guy pans out to the field where the people are standing on a ridge at 450 feet.
Danley Sound Labs - YouTube
It’s nice when even the players notice the difference;
Rodgers Likes New Danley Sound Labs System. "Nice to be back at Lambeau" - YouTube
Hi John
I don’t have a K horn to measure, while I used to have a collection of old style horns, that wasn’t one of them.
My comments were more general, where the distortion comes from, when it is an issue and when it isn’t, transducer design / acoustic issues.
Many people would guess that a subwoofer or bass horn would suffer from this as well but that is not the case at all, it is very nearly entirely driver non-linearity that is the cause here.
Best,
Tom
I don’t have a K horn to measure, while I used to have a collection of old style horns, that wasn’t one of them.
My comments were more general, where the distortion comes from, when it is an issue and when it isn’t, transducer design / acoustic issues.
Many people would guess that a subwoofer or bass horn would suffer from this as well but that is not the case at all, it is very nearly entirely driver non-linearity that is the cause here.
Best,
Tom
Makes me wonder what they would have thought if they could have used active crossovers, EQ and time delay on this. These three new technologies have really changed what can be done with all speaker systems.
Yeah, using my DCX, on my K Horn Klones I can cinch up the delay with music having a good bass line until it "clicks." More than 2 feet.
When my dad and I built those things about fifty years ago and fired them up for the first time I couldn't stand the sound. Too horny, too loud. After he died I gave it active x overs and stuffed the mids with Geddes's foam. They sound OK now, but there's no way that sort of system can sound as good as a modern 2 way like Geddes's with OS waveguides and subs, or Danley's Unity or Synergy horns. Their design is better.
I think the reason those old movie sound system sounded so nice to us was due to the good dynamic response and the big size of the rooms which gave lots of decorrelated sound, a HF roll off which in that sort of space is "natural," a lack of room mode problems which so afflict home listeners, and
, they didn't run them too loud. The horny nature of the sound was still apparent but didn't bother us because of these other compensating factors plus the distraction of the movie itself.
Tom, your yootoobe videos are very impressive indeed!
If it sounds like I expect it would in person, I'd be quick to use ur stuff if I was looking for PA/SR speakers!
I am wondering, since I have you here how the "acoustic low pass filter" or other means keeps the mid drivers from modulating the HF diaphragm?
so what % 2nd harmonic are we looking at with an SPL that is down at home levels?
Assume a good quality horn, maybe an tractrix expansion or even an old WE or Altec multicell?
how does that level compare to a traditional high quality dome at the same SPL?
What the heck shape is "This design evolved from a comment about conical horns Don Davis made at a Synaudcon in the 90’s.
In that approach a conical horn is used which has a very rapid initial expansion rate which slows as you move away from the apex. " ??
Sounds like a description of the modern "waveguide" ?
_-_-bear
If it sounds like I expect it would in person, I'd be quick to use ur stuff if I was looking for PA/SR speakers!
I am wondering, since I have you here how the "acoustic low pass filter" or other means keeps the mid drivers from modulating the HF diaphragm?
so what % 2nd harmonic are we looking at with an SPL that is down at home levels?
Assume a good quality horn, maybe an tractrix expansion or even an old WE or Altec multicell?
how does that level compare to a traditional high quality dome at the same SPL?
What the heck shape is "This design evolved from a comment about conical horns Don Davis made at a Synaudcon in the 90’s.
In that approach a conical horn is used which has a very rapid initial expansion rate which slows as you move away from the apex. " ??
Sounds like a description of the modern "waveguide" ?
_-_-bear
Hi bear
Thanks, I saw one of the attendees of the demo walking around with a small camcorder but I was impressed when I saw / heard his video.
The idea came about around 12 years ago when I was faced with starting over after the space hardware contractor I had worked for closed due to NASA cutbacks.
I had started a small speaker division selling servomotor drive n subwoofer for commercial sound but the motors had gotten extraordinarily expensive so that was out. I wanted to design a full range speaker for commercial sound and remembered a Synaudcon seminar from at least 10 years earlier.
I had little interest in full range speakers then, I was a subwoofer guy so I was surprised it popped into my head. Don explained that the conical horn had the strength in that it had nearly constant directivity, a good thing if you have an audience, every one hears the same thing.
He said the down side was it had much poorer acoustic loading at the low end, something you can see if you look at a chart of the resistance vs horn profile.
The ‘light went on” when I realized the reason was at the apex, the expansion is very rapid only suitable for a high frequency driver while further away, the expansion had slowed to more like a mid horn and later a low frequency horn. I realized one could access all of those expansion rates IF one entered the horn at the right place.
I knew that if individual sources were about a quarter wavelength or less apart, they combined coherently in to one new source so those were the initial guidelines that lead to the first version, the Unity horn. About 6 years later I had learned more about making them work and applied for the Synergy horn patent where it was finally possible to eliminate most /all of the phase shift that conventional crossovers impose making them truly act / measure like one single driver.
So far as the low pass filter, it is made of the air volume trapped between he baffle and the mass effect of the port that connects to the horn passageway. These form a 2nd order low pass filter (two reactance’s, the air mass and air spring) and by sizing them so that the low pass corner is somewhat above the electrical crossover, it progressively attenuates any sound the driver does make above that.
Some Diy’rs are fiddling with them and having some luck. I can’t tell them what to do, but it’s kind of fun to watch. Part way down here is a drawing showing the speakers on the exterior of a 3 way synergy horn.
http://www.diyaudio.com/forums/multi-way/156988-gedlee-summa-vs-lambda-unity-horn.html
Part way down this page is a front view of a somewhat different / smaller Synergy horn. Here one can see the ports which communicate the driver pressure, the most forward ports are the lf , the next set inward are lf drivers which cover up to about 300Hz, just barely visible are the midrange ports and not visible is the hf driver. While the first case had separate hf and mid drivers, the second uses an adapted coax driver to accomplish the same thing. Here the horn extends and connects to the hf exit while the cone’s radiation enters through the small holes. The low pass filter is the same trapped air and port mass.
http://www.diyaudio.com/forums/mult...midrange-cone-bandpass-mid-unity-horn-52.html
Some square waves from a dusty speaker (I had a pair of old prototypes).
http://www.diyaudio.com/forums/multi-way/71824-making-square-waves.html#post817215
Hope that helps fill in some blanks.
Best,
Tom Danley
Thanks, I saw one of the attendees of the demo walking around with a small camcorder but I was impressed when I saw / heard his video.
The idea came about around 12 years ago when I was faced with starting over after the space hardware contractor I had worked for closed due to NASA cutbacks.
I had started a small speaker division selling servomotor drive n subwoofer for commercial sound but the motors had gotten extraordinarily expensive so that was out. I wanted to design a full range speaker for commercial sound and remembered a Synaudcon seminar from at least 10 years earlier.
I had little interest in full range speakers then, I was a subwoofer guy so I was surprised it popped into my head. Don explained that the conical horn had the strength in that it had nearly constant directivity, a good thing if you have an audience, every one hears the same thing.
He said the down side was it had much poorer acoustic loading at the low end, something you can see if you look at a chart of the resistance vs horn profile.
The ‘light went on” when I realized the reason was at the apex, the expansion is very rapid only suitable for a high frequency driver while further away, the expansion had slowed to more like a mid horn and later a low frequency horn. I realized one could access all of those expansion rates IF one entered the horn at the right place.
I knew that if individual sources were about a quarter wavelength or less apart, they combined coherently in to one new source so those were the initial guidelines that lead to the first version, the Unity horn. About 6 years later I had learned more about making them work and applied for the Synergy horn patent where it was finally possible to eliminate most /all of the phase shift that conventional crossovers impose making them truly act / measure like one single driver.
So far as the low pass filter, it is made of the air volume trapped between he baffle and the mass effect of the port that connects to the horn passageway. These form a 2nd order low pass filter (two reactance’s, the air mass and air spring) and by sizing them so that the low pass corner is somewhat above the electrical crossover, it progressively attenuates any sound the driver does make above that.
Some Diy’rs are fiddling with them and having some luck. I can’t tell them what to do, but it’s kind of fun to watch. Part way down here is a drawing showing the speakers on the exterior of a 3 way synergy horn.
http://www.diyaudio.com/forums/multi-way/156988-gedlee-summa-vs-lambda-unity-horn.html
Part way down this page is a front view of a somewhat different / smaller Synergy horn. Here one can see the ports which communicate the driver pressure, the most forward ports are the lf , the next set inward are lf drivers which cover up to about 300Hz, just barely visible are the midrange ports and not visible is the hf driver. While the first case had separate hf and mid drivers, the second uses an adapted coax driver to accomplish the same thing. Here the horn extends and connects to the hf exit while the cone’s radiation enters through the small holes. The low pass filter is the same trapped air and port mass.
http://www.diyaudio.com/forums/mult...midrange-cone-bandpass-mid-unity-horn-52.html
Some square waves from a dusty speaker (I had a pair of old prototypes).
http://www.diyaudio.com/forums/multi-way/71824-making-square-waves.html#post817215
Hope that helps fill in some blanks.
Best,
Tom Danley
I thought I'd elaborate on why the top sixties HiFi was better than most junk you buy today. But this is not for discussion. I will simply state 6 good reasons, and you can stuff them in your pipe and smoke them.
1) Engineers were older, had lived through WW2 and had a much broader background in Radio and antennas and high frequencies and would even make their own components like coils and oiled paper capacitors. They had far better mental arithmetic ability than most of you, and could use a Smith chart for matching impedance and a slide rule for calculation much faster than you can with computers:
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An externally hosted image should be here but it was not working when we last tested it.
2) I have no particular axe to grind on transistors versus valves, and in fact classic performers like the Radford STA25 had a single rail transistor preamplifier driving a valve output stage with a defined source impedance. But they were Class A designs with all the lovely cancellation of common-mode that makes them sound so good. The power supply for instance had only to drive a constant current and all electrolytic capacitors had the proper bias which keeps them linear.
3) Record pickups were wide bandwidth and low source inductance moving coil designs. These avoided trying to jump out of the groove due to LC resonances which plagued later moving magnet designs and LP crackle and pop was less obtrusive.
4) Bass speakers would often be 10" paper cones in huge solid closed boxes mounted literally as bookshelves against a wall. Tweeters would often be simple 3" paper cones with a single capacitor crossover. It didn't much matter how good the speaker surround was, because acoustic suspension essentially kept the speaker linear. Frequency response was probably not the last word, but rolled off gently. In fact the reputable WLM La Scala speakers rather recreate these babies.
5) Components like transistors were doubtless not as fast, but then feedback was kept much lower too, so gross distortions like slewing tended to be avoided in favour of gentle rolloff of frequency response.
6) Recording engineers really knew their equipment like the backs of their hands. They set up levels to avoid overload and at their peak would record straight to the record-cutting lathe via a mere couple of microphones with no recording console worth mentioning. The result was breathtakingly direct recordings like Count Basie with Frank Sinatra, which if you've never heard them on Vinyl with it's 70dB signal to noise ratio, well you haven't lived, my friends!
An externally hosted image should be here but it was not working when we last tested it.
Onwards and upwards!
Puts that on my vinyl 'to-get' list.
Also, don't forget the SR-71 Blackbird, one of the greatest aeronautical achievements of all time, designed long before the age of computers or electronic calculators!
Thanks Steve. By the way, I've repaired my calculator ready for the other thread, not that I need it
Re. a 50% maximum, I may be guilty of spreading obsolete theory here.
I went looking for the origin of this. The early Olson (RCA) articles don't support it and he shows some theoretical plots with motional resistance as the numerator term and the ability to approach 100% if Rm is much greater than Rd ("damped resistance of voice coil"). His practical example, which appears to be the "8" full range horn unit" that Shearer and Hilliard rejected, hovers around 30%.
Beranek assumes a higher Rg (amp source resistance) and factors that into efficiency. He gives and example with 24 ohms drivng it (!) and, with an optimized throat size he achieves 22.1% efficiency. He recalculates the same system with a 1 ohm driving source and sees the efficiency drop to 2.4%. He concludes that "for maximum efficiency the amplifier impedance should approximately equal the loudspeaker impedance."
If it is as simple as that, then this would get us to the usual generator/load relationship where maximum power transfer is when the load resistance equals the generator resistance. If the load is higher, then it will get more of the open circuit voltage but less current will flow. If it is less, then more current will flow but the loads voltage will drop. Maximum power transfers when the load equals the source and both share half the power, i.e. 50% efficiency.
Keele initially repeats the 50% maximum and calls it "power available efficiency", still assuming that the maximum power transfer will come from matching of source and load.
http://www.xlrtechs.com/dbkeele.com/PDF/Keele (1976-05 AES Preprint) - Efficiency, Horns vs DR.pdf
Leach does a good analysis too, for those into horn theory.
http://users.ece.gatech.edu/~mleach/papers/HornPaper/HornPaper.pdf
Keele finally gets past the notion with this analysis:
http://www.xlrtechs.com/dbkeele.com...Maximum Efficiency of Compression Drivers.pdf
Here he splits the notion into "Nominal power transfer efficiency" which has a 50% maximum due to a presumed doubling of Dcr by optimum horn loading, and "true power transfer efficiency" which can approach 100%. I now think this is the more proper way to look at this.
I'd note as a practical matter that I haven't seen documented evidence of real efficiencies much above 30%, and the Western Electric claim sounds like a bit of marketing speak as in "approaching the theoretical maximum (50%)".
David S
I went looking for the origin of this. The early Olson (RCA) articles don't support it and he shows some theoretical plots with motional resistance as the numerator term and the ability to approach 100% if Rm is much greater than Rd ("damped resistance of voice coil"). His practical example, which appears to be the "8" full range horn unit" that Shearer and Hilliard rejected, hovers around 30%.
Beranek assumes a higher Rg (amp source resistance) and factors that into efficiency. He gives and example with 24 ohms drivng it (!) and, with an optimized throat size he achieves 22.1% efficiency. He recalculates the same system with a 1 ohm driving source and sees the efficiency drop to 2.4%. He concludes that "for maximum efficiency the amplifier impedance should approximately equal the loudspeaker impedance."
If it is as simple as that, then this would get us to the usual generator/load relationship where maximum power transfer is when the load resistance equals the generator resistance. If the load is higher, then it will get more of the open circuit voltage but less current will flow. If it is less, then more current will flow but the loads voltage will drop. Maximum power transfers when the load equals the source and both share half the power, i.e. 50% efficiency.
Keele initially repeats the 50% maximum and calls it "power available efficiency", still assuming that the maximum power transfer will come from matching of source and load.
http://www.xlrtechs.com/dbkeele.com/PDF/Keele (1976-05 AES Preprint) - Efficiency, Horns vs DR.pdf
Leach does a good analysis too, for those into horn theory.
http://users.ece.gatech.edu/~mleach/papers/HornPaper/HornPaper.pdf
Keele finally gets past the notion with this analysis:
http://www.xlrtechs.com/dbkeele.com...Maximum Efficiency of Compression Drivers.pdf
Here he splits the notion into "Nominal power transfer efficiency" which has a 50% maximum due to a presumed doubling of Dcr by optimum horn loading, and "true power transfer efficiency" which can approach 100%. I now think this is the more proper way to look at this.
I'd note as a practical matter that I haven't seen documented evidence of real efficiencies much above 30%, and the Western Electric claim sounds like a bit of marketing speak as in "approaching the theoretical maximum (50%)".
David S
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Thanks for the links, David.
I never had a chance to measure any of this stuff, the 115dB/1M/1W figures and the 50% came from those who owned them. Considering that I've seen them used as part of a 4 way system padded way down to match the other parts, they must have been pretty efficient. Don't know the real numbers, tho.
I suppose it could be measured, if anyone was interested. Not likely to happen any time soon, tho.
I never had a chance to measure any of this stuff, the 115dB/1M/1W figures and the 50% came from those who owned them. Considering that I've seen them used as part of a 4 way system padded way down to match the other parts, they must have been pretty efficient. Don't know the real numbers, tho.
I suppose it could be measured, if anyone was interested. Not likely to happen any time soon, tho.
True efficiency is actually pretty hard to measure. You have to start with total radiated power, which either means reverberent room measurements, or lots of free field polars and their integration to get the power curve.
Then you have to decide if your calculated electrical input power should be with respect to the actual impedance vs. frequency (properly, its real part) or vs. a nominal rated impedance.
In the end most people just give a fudged number based on mid band sensitivity and directivity index.
David S.
Then you have to decide if your calculated electrical input power should be with respect to the actual impedance vs. frequency (properly, its real part) or vs. a nominal rated impedance.
In the end most people just give a fudged number based on mid band sensitivity and directivity index.
David S.
Yep. I was sitting here thinking about how to do that with something as large as a W.E. 15A.
Not an easy task.Could fudge it and figure backwards, I suppose. As you say, midband sensitivity then figure the basic H&V angles.
I don't claim to be a WE expert by any means, but I have had the pleasure of listening to a few totally stock WE speakers including the 757 in the Silbatone room at last year's RMAF. I have also heard several systems that used stock WE drivers and horns but with new crossovers and/or new cabinets for the woofer. These include variations on the 753 2-way and a 3-way setup using 22A horns. In my own system, I use a variation of the 753 that uses the same woofer and HF horn as the 753 but with an Altec compression driver, my own bass cabinet design and my own crossover.
From my own experience, I have to agree that there is something really special about the old WE speakers that is simply not equalled by anything I have heard that was built in more recent times. Voices sound more like real people. I have no idea what is responsible for the sound quality. Good engineering certainly, but it seems like there should be more to it than that. Has anyone tried reverse-engineering one of the WE gems like the 755 or the 713 compression drivers?
From my own experience, I have to agree that there is something really special about the old WE speakers that is simply not equalled by anything I have heard that was built in more recent times. Voices sound more like real people. I have no idea what is responsible for the sound quality. Good engineering certainly, but it seems like there should be more to it than that. Has anyone tried reverse-engineering one of the WE gems like the 755 or the 713 compression drivers?
We were just talking about the measurement of efficiency. Efficiency is watts out over watts in, that is acoustic watts radiated by a speaker for every electrical watt applied. Acoustic watts are always defined as the total "energy" radiated in all directions, so some means of measuring all directions, or measuring level in a reverb room (where radiation direction doesn't matter) would be needed.
A speaker with wide dispersion and 105 dB output might be more efficient than a narrow dispersion unit giving 110dB on axis.
I agree that frequency response under anechoic conditions is more revealing than reverb measurements. You just can't use it to compare efficiency.
David S.
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