Hi Tom,
What's the coverage angle of that horn? Is it smaller than you've had in that room before?
I wonder if most its goodness is from minimized room reflections.
I've been reading about using waveguides with standard dome tweeters, and I'm sold on the benefits.
Not to hijack the thread, but is it correct to say that a waveguide is a horn with low compression ratio?
Is it just the way the expansion formula works out that waveguides are mostly concave, while horns are convex?
Thanks
What's the coverage angle of that horn? Is it smaller than you've had in that room before?
I wonder if most its goodness is from minimized room reflections.
I've been reading about using waveguides with standard dome tweeters, and I'm sold on the benefits.
Not to hijack the thread, but is it correct to say that a waveguide is a horn with low compression ratio?
Is it just the way the expansion formula works out that waveguides are mostly concave, while horns are convex?
Thanks
Hi Noah
The horn is a 50 by 50 degree wall angle, the mouth is 28 inches square.
Actually I have never tried this on a big speaker indoors before, all the smaller ones were from much closer. I have a tower for measuring speakers in full space (and so no reflections) but it’s not warm enough to do it outside now.
I would say in audio, horn and waveguide are sort of interchangeable terms. If anything there may be a carryover from the RF world where a waveguide is more for controlling radiation patterns, even sacrificing gain.
A small dome in a waveguide does feel the radiation load from the horn loading, until the dome becomes about 1 wl in circumference. The waveguide also defines the directivity, starting at some lower frequency governed by the horn wall angle and physical size.
A conical horn (round or square like the one in the photo) has a constant radiation angle vs frequency, a curved wall horn has a collapsing directivity pattern with increasing frequency.
The conical horn has a frequency response equal to the acoustic power of the driver (vs frequency).
The curved wall horn has more output at the high end due to the concentration of the radiation angle.
As compression drivers have an acoustic power that falls off starting at about 2500Hz, this must be EQ’d in the conical horn and if everything is perfect, the curved wall horn needs no compensation.
The reverberant sound spectrum in your room is related to the acoustic power and room absorption.
A curved wall horn usually will have a dark murky sound outside the direct pattern, which reflects the true acoustic power.
A constant directivity speaker with a flat power response sounds the same spectrally everywhere, just quieter and no stereo image when your out of the direct pattern.
A soft dome may or may not be loaded by a horn however, it is not a piston radiator over much of its band.
Yes, the 100Hz square wave is suspicious although they may have been able to find a position where it made one.
The 250 Hz square I posted already shows a tilt due to the speaker’s 50Hz low cutoff and phase response.
Cheers,
Tom
The horn is a 50 by 50 degree wall angle, the mouth is 28 inches square.
Actually I have never tried this on a big speaker indoors before, all the smaller ones were from much closer. I have a tower for measuring speakers in full space (and so no reflections) but it’s not warm enough to do it outside now.
I would say in audio, horn and waveguide are sort of interchangeable terms. If anything there may be a carryover from the RF world where a waveguide is more for controlling radiation patterns, even sacrificing gain.
A small dome in a waveguide does feel the radiation load from the horn loading, until the dome becomes about 1 wl in circumference. The waveguide also defines the directivity, starting at some lower frequency governed by the horn wall angle and physical size.
A conical horn (round or square like the one in the photo) has a constant radiation angle vs frequency, a curved wall horn has a collapsing directivity pattern with increasing frequency.
The conical horn has a frequency response equal to the acoustic power of the driver (vs frequency).
The curved wall horn has more output at the high end due to the concentration of the radiation angle.
As compression drivers have an acoustic power that falls off starting at about 2500Hz, this must be EQ’d in the conical horn and if everything is perfect, the curved wall horn needs no compensation.
The reverberant sound spectrum in your room is related to the acoustic power and room absorption.
A curved wall horn usually will have a dark murky sound outside the direct pattern, which reflects the true acoustic power.
A constant directivity speaker with a flat power response sounds the same spectrally everywhere, just quieter and no stereo image when your out of the direct pattern.
A soft dome may or may not be loaded by a horn however, it is not a piston radiator over much of its band.
Yes, the 100Hz square wave is suspicious although they may have been able to find a position where it made one.
The 250 Hz square I posted already shows a tilt due to the speaker’s 50Hz low cutoff and phase response.
Cheers,
Tom
Of course a speaker cannot produce real acoustical square waves because a speaker cannot maintain sound pressure when the cone is in a stationary position defined by the DC top and bottom of the input square wave. Try a 0.1 Hz square wave and you'll see what I mean.
The Jordan JX92S in a TL housing (Konus Essence clone) performs very nice square wave lookalikes. After performing a number of tests on a couple of single drivers I saw that the square wave response is just a repetitive step response which may look like a square wave.
Once the step response is known (with high enough accuracy/resolution), the square waveform response can be predicted for almost any audible frequency. If the ringing of the driver caused by the slope transiënt fits nice you get a nice square wave lookalike.
That way I chose a couple of frequencies where the Jordan performs nice. If I would have chosen 80 Hz instead of 100 Hz, there would not be much of a square wave left.
Placing the microphone is critical. With the microphone placed on-axis a Jordan driver does not produce square wave lookalikes.
Problem may be to produce a good low frequency input square wave. My sound cards are not very good at producing low frequency square waves. I use an opamp which switches from rail to rail driven by a sine wave.
The Jordan JX92S in a TL housing (Konus Essence clone) performs very nice square wave lookalikes. After performing a number of tests on a couple of single drivers I saw that the square wave response is just a repetitive step response which may look like a square wave.
Once the step response is known (with high enough accuracy/resolution), the square waveform response can be predicted for almost any audible frequency. If the ringing of the driver caused by the slope transiënt fits nice you get a nice square wave lookalike.
That way I chose a couple of frequencies where the Jordan performs nice. If I would have chosen 80 Hz instead of 100 Hz, there would not be much of a square wave left.
Placing the microphone is critical. With the microphone placed on-axis a Jordan driver does not produce square wave lookalikes.
Problem may be to produce a good low frequency input square wave. My sound cards are not very good at producing low frequency square waves. I use an opamp which switches from rail to rail driven by a sine wave.
"A small dome in a waveguide does feel the radiation load from the horn loading, until the dome becomes about 1 wl in circumference."
That comes to 3.8 kHz for a 28 mm dome; so it's loaded up until that freq, right? That would agree with what Zaph got with his waveguide.
Can you explain why what are called waveguides have such a shallow concave shape?
Thanks
"Of course a speaker cannot produce real acoustical square waves because a speaker cannot maintain sound pressure when the cone is in a stationary position "
DC would have the cone moving at constant velocity (or maybe it's acceleration).
That comes to 3.8 kHz for a 28 mm dome; so it's loaded up until that freq, right? That would agree with what Zaph got with his waveguide.
Can you explain why what are called waveguides have such a shallow concave shape?
Thanks
"Of course a speaker cannot produce real acoustical square waves because a speaker cannot maintain sound pressure when the cone is in a stationary position "
DC would have the cone moving at constant velocity (or maybe it's acceleration).
"Have you ever put a small DC on a driver to observe the cone movement?"
Yep.
If your point is that the cone is stationary so that corresponds to DC, that doesn't follow, since there is no acoustical output at DC.
Well, I guess there is very briefly, until the excursion limitsa are reached, but I don't think that counts.
Yep.
If your point is that the cone is stationary so that corresponds to DC, that doesn't follow, since there is no acoustical output at DC.
Well, I guess there is very briefly, until the excursion limitsa are reached, but I don't think that counts.
DC results in a stationary cone which does not produce sound.
Switching between + and - DC at a very low (0,1 Hz) frequency corresponds to a cone which switches from excursion limit to excursion limit because the time between switching is long enough for the cone to stop moving (ringing).
At higher frequencies switching occurs before the cone has stopped ringing.
And since cones only produce sound when they move it is critical to keep it moving if you want to see an acoustical square wave lookalike.
Switching between + and - DC at a very low (0,1 Hz) frequency corresponds to a cone which switches from excursion limit to excursion limit because the time between switching is long enough for the cone to stop moving (ringing).
At higher frequencies switching occurs before the cone has stopped ringing.
And since cones only produce sound when they move it is critical to keep it moving if you want to see an acoustical square wave lookalike.
PB2 said:
For those interested, I have that paper scanned. Nothing fancy-no pdf. Each page is in GIF, as if it had come from a copy machine. Anyone who wants it sent to to them just Email me.
Here are some oscilloscipe traces for on axis response. As you can see, they are very good.
The article also gives the method to make a third order crossover with the same qualities.
Here is the second order square wave response. This wave form is for a second order crossover at the crossover frequency.
Attachments
Here is a pretty good square wave
http://www.diyaudio.com/forums/full-range/162827-mpl-14.html#post2240194
dave
http://www.diyaudio.com/forums/full-range/162827-mpl-14.html#post2240194
dave
I posted about "A Novel Approach to Linear Phase Loudspeakers Using Passive Crossover Networks" Erik Baekgaard
Back in 2006.
Just stumbled onto this article that mentions the Kido-Yamanaka, or “Filler Driver” crossover from Panasonic in 1967:
A Unique Loudspeaker Crossover Design with Waveform Fidelity
From the above link:
The unique and little-known cross over presented here is alternately known as a Kido-Yamanaka, or “Filler Driver” crossover. It exhibits both flat frequency and phase response giving the speaker system the potential for real waveform fidelity limited only by the characteristics of the individual loudspeaker drivers used in the system. It is a three-way net work that uses 2nd-order slopes for the woofer and the tweeter plus first-order slopes for the midrange. The outputs of the Yamanaka crossover’s low, mid, and high frequency bands can recombine electrically to form a perfect replica of the input signal and can pass perfect square waves (Fig. 1).
The Kido-Yamanaka crossover was first described by Bunkichi Yamanaka of Matsushita Corp. (Panasonic) in 1967. The following references give a full mathematical treatment of the Yamanaka crossover network and design method. (Note that this crossover is patented and its commercial use is restricted.) The first reference is by far the most thorough and informative.
1. Audio Engineering Society Preprint No. 1059 “Design of Linear Phase Multi-Way Loudspeaker System” by Ishii and Takahashi
2. US Patent No. 4,015,089, Ishii et al. “Design Method for a Linear Phase Multi-way Loudspeaker System,” US Patent and Trademark Office website United States Patent and Trademark Office. (The US Patent Office website is a fantastic free resource on anything that’s ever been patented and is probably the best free knowledge-base available anywhere.)
3. Engineering Brief, Eric Baekgaard, “A Novel Approach to Linear Phase Loudspeakers,” May 1977 issue of the AES Journal.
Bunkichi Yamanaka realized that subtractive crossovers could theoretically produce all manner of perfect crossover functions, but they require active implementation and multi-amplifier systems that were considered too expensive to have the mass-market appeal desired by a corporate giant like Matsushita- Panasonic. As mentioned before, a conventional 2nd-order crossover with the high- and low-pass sections summed in phase results in a response with a deep notch, or null, at the crossover frequency. Yamanaka used the subtractive crossover method to restore the response lost to this cancellation.
Yamanaka’s associates, Ishii and Takahashi, replaced the active subtractor with a simple passive circuit and added it to a conventional 2nd_order crossover, eliminating the requirement for multiple amplifiers (Fig. 2). The complex math in Fig. 3 shows the bandpass function that is required to restore flat response after the low-pass and high-pass functions are subtracted from the input signal (Vin).
Simply stated, a Yamanaka dividing network is a conventional two-way 2 order crossover network connected with both drivers in electrical and acoustic phase, which causes a cancellation in the overlapping range of the woofer and tweeter outputs. To this is added a mid range driver, also connected in phase, fed by a bandpass filter centered on the same frequency, which fills in the void (Fig. 4). When the combined acoustic outputs of all three drivers are positioned so that they are time adjusted and each of their signals blend together arriving at the listener’s ear at exactly the same time, the resulting acoustic waveform will be flat in frequency and phase response, limited only by the imperfections of the individual drivers.
Eric Baekgaard of Bang and Olufsen Co. published an Engineering Brief in the May 1977 issue of the AES Journal showing an identical circuit, with the only difference being a scaling of the filter Q from .5 in the Yamanaka design to .707. Because the level at the crossover point is given by the formula 20Log(Q). in the Yamanaka version the electrical crossover between the woofer and tweeter is at 20Log(.5) = -6.02dB, and -3.01dB in the Q= .707 Baekgaard version.
Baekgaard coined the very appropriate term “Filler Driver” for the midrange speaker used with this type of crossover network. He also showed that an alternate version was possible using 3rd_order filters for the low and high passbands. However, Baekgaard’s 3rd_order version requires the midrange level to be +6dB greater than the woofer and tweeter levels in order to achieve flat response. The circuit and formulas for Baekgaard’s 3 order filler driver crossover are included at the end of this article.
Interesting to see the frustration in making square waves reach your ear as square waves (that is, all the phases lined up in a row). Kind of suggests the heart-felt pleas all over this forum for phase exactitude is ardent but a waste of effort. Because: great speakers for generations have made great sound but atrocious square waves.
BTW, a friend with Quad electrostatic speakers says he makes good square waves. With enough exploration with your mic and tone generator, good looking spots can be found (and moving your mic an inch leads to awful square waves). But again, I think it is of no importance to hearing since it doesn't influence hearing.
If somebody could post some evidence on this matter, we'd all be glad to be the wiser for seeing it.
BTW, a friend with Quad electrostatic speakers says he makes good square waves. With enough exploration with your mic and tone generator, good looking spots can be found (and moving your mic an inch leads to awful square waves). But again, I think it is of no importance to hearing since it doesn't influence hearing.
If somebody could post some evidence on this matter, we'd all be glad to be the wiser for seeing it.
My plea would be to look at the evidence. Take a drum sample (as artists often do) and reverse it in time: The audible difference is stark. Ohm's Acoustical Law applies to steady state signals and phase is clearly audible beyond the audible limits established by group delay measurement thresholds.
Does any sound in nature come close to a square wave? I don't think so, but I could be wrong.
Imagine you record a violin, or a trumpet, or a snare drum at several different positions and angles, and look at the wave form on an oscilloscope. You will see very different waveform shapes from each of the different positions/angles. But to your ear/brain, it all sounds like a violin, or a trumpet, or a snare drum. I don't think we understand enough about the sound/ear/brain process to conclude that wave form fidelity means a lot... or perhaps it is important in ways we do not yet understand and can not yet measure.
Imagine you record a violin, or a trumpet, or a snare drum at several different positions and angles, and look at the wave form on an oscilloscope. You will see very different waveform shapes from each of the different positions/angles. But to your ear/brain, it all sounds like a violin, or a trumpet, or a snare drum. I don't think we understand enough about the sound/ear/brain process to conclude that wave form fidelity means a lot... or perhaps it is important in ways we do not yet understand and can not yet measure.
It is not about producing square waves, it is about not distorting the relative phases of various spectral components.
Time reversed drums are perfect examples that show the phase response matters - and without violating Ohm's Acoustical Law.
That is closer to the truth and an answer might be found in the bispectrum. Notably this was discussed many decades ago for modelling our auditory perception, but seemingly ignored thereafter.
hifijim, in relating his evidence to oscilloscope traces is talking about the relative phases and how they are totally discombobulated as you walk around the violinist and you are missing the evidence that phase relationship seems not to matter.
B.
Is that some kind of bad joke? Of course a recording of a drum strike played backwards would sound much unlike the original. Or do I misunderstand what "time reversed" means to you?
B.
It would matter if you walked around the room and the phase information did not change. Possibly you underestimate the processing that our brain's are doing? We also need take account of how the various spectral components come and go, and the expression the violinist can endow in his/her playing as a result.
Have you considered taking an opportunity to update your knowledge of psychology?
B.