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Thought I would sign up here to see if someone would be able to offer me some direction. Would anyone be able to suggest a manufacturer of equipment that is capable of producing sound waves of the infrasonic type (below 20hz) as well as ultrasonic (above 20k)?
I know this is an off the wall question but I didn't really have any idea of where to start. If not, a suggestion as to where else I might look for this kind of information would be helpful.
This would be in relation to materials testing.
Thanks
Follow Ups:
Try the Cuban Embassy in Washington.
what? can't hear you!?
all the best,
mrh
GE, PCE, Olympus, Sonotec, NDT... lots of companies produce ultrasonic inspection equipment. Ameteksi, ACS, MTS and a few others provide low frequency analysis equipment.
nt
Maybe you should check with the Cuban Embassy :).
I married the perfect woman. The downside is everything that goes wrong is my fault.
Heeeee yeah those guys seem to have it down!
"Would anyone be able to suggest a manufacturer of equipment that is capable of producing sound waves of the infrasonic type (below 20hz) as well as ultrasonic (above 20k)?"
You need to clarify exactly what you mean by this statement. If you just want to generate these waveforms, then any signal generator will do. If you wan to amplify these waveforms then any decent solid state amp of the appropriate wattage will do with the signal generator as the input.
about using the venerable Radio Shack (Fostex) 40-1310 add-on 'super-tweeter' as an ultrasonic transducer for some similar (and similarly nefarious) purpose :-)
Perhaps he'll see this, or perhaps a 'ping' is in order.
As to infrasonics, I seem to recall that Dr. Bruce Edgar did some stuff, too. He and/or Mr. Danley would be excellent folks to ping on the topic.
Dont' excite any resonances and destroy your laboratory building, though!
;-)
all the best,
mrh
Thanks for the references hardy. And yeah my little endeavor will be conducted out in the barn, literally. Can't be letting these sound waves out loose around everywhere!
see below :-)EDIT: Also:
More from Mr. J on the 40-1310
all the best,
mrh
Edits: 10/11/17
Danley Labs has built high-power infrasonic sources for military weaponry usage. 105dB at 250 meters. Probably $50,000 or $100,000. See link below:
Lord I'll have to start saving up the dough! Have to leave that stuff to the military guys. I'd like to achieve that kind of sound pressure but not at that distance. Hopefully I'll be able to find a less expensive route to get my project going.
Beals Brothers in New York were asked to create 7hz at enough amplitude to make people on the ground lose control of their sphincter muscle by a "government agency". This is back in the early 90's. Danley is the real deal for LF.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
Shoot, I'd like to keep my bowels just where they are but I'll take Danley as a reference. Is this a person here on the a asylum board or possibly a manufacturer?
Going past 20kHz is possible, but more difficult. Currently the easiest thing to do is to purchase a 1" beryllium dome tweeter from Scan-Speak. This will give flat frequency response to about 30kHz and then start to rise as the diaphragm "breaks up" at its first "oil can" resonant mode, with a 10dB - 15dB peak at around 40kHz. Diamond is stiffer, but also heavier and won't go much higher. The max SPL at 1 meter will be around 96dB or so. More than that and you will likely blow the voice coil.
If you need higher SPLs, then try to purchase the 1" Be dome horn tweeter used in the JBL K2-S9800. It's discontinued now, but the horn loading will give another 10 dB output over roughly the same frequency range.
To go beyond that, you will either have to have something custom-made or else use what they use for ultrasonic transducers - piezoelectric crystals. These operate in a resonant mode and are only good for creating one single frequency. This is OK for a signaling system but horrible for music.
There were also some Be ribbons made by Pioneer/TAD that would go to 40kHz, but they were super expensive ($1000 each) and discontinued 5 years ago. They had a built-in horn, but the rectangular shape of the diaphragm made the off-axis dispersion different in the two axes.
Hope this helps.
I once built an adjustable frequency utrasonic pest repeller using a piezo horn tweeter driven by a NE555 oscillator. I'm not sure if it worked on pests but I was surprised to learn that even if I could not hear ultrasonic sound, I felt it's presence. It created an annoying pressure around my head when the device was turned ON. ;-)I used a speaker similar to this one and an NE555:
Edits: 10/12/17
"I once built an adjustable frequency utrasonic pest repeller using a piezo horn tweeter driven by a NE555 oscillator. I'm not sure if it worked on pests but I was surprised to learn that even if I could not hear ultrasonic sound, I felt it's presence. It created an annoying pressure around my head when the device was turned ON. ;-)"
I contend that the switching in active digital audio devices and PCs has this very effect...... I feel as if my brain wants to escape from its cranium........
Back in college, a physics friend had one of these setups for his projects. I believe only 1-watt RMS sine waves. You HAD to have ear protection. Like plugs and cans over your head. The tone was that painful.
"The tone was that painful. "
It's useful to reiterate that it was a JBL 075.
Which, IIRC, wasn't quite as painful as the 077 slot.
;)
HI Abe,Good call. I'm not sure how flat or extended the frequency response of those once-ubiquitous tweeters was, but they were everywhere for about a decade. The first speaker I saw that used them waas the Dahlquist DQ-10. It was generally agreed that the best thing one could do to improve the sound was to simply disconnect that tweeter.
Radio Shack used to sell them for $4.99 and they were used a LOT in cheap "pro" gear. They didn't require any crossover - just wire them in parallel with the speaker input. They were super nasty sounding, presumably because of horrible resonances in the piezo element itself that cuased them to ring like a bell. I suspect that the frequency response was a series of resonant peaks that extended fairly far into the ultrasonic range.
As usual, the problem is actually measuring them accurately. About the only way is with a lab-grade 1/8" condenser capsule microphone. Not a common device to have hanging around, but something the OP will likely need. Otherwise he will nave no idea what is actually happening during his "materials testing".
Edits: 10/12/17
I slept in a room with one of those. I slept on my right side so my right ear was buried in the pillow. I woke up and had ringing only in my left (exposed) ear so I'm with you on this.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
Infinity Emit-K is flat to 45khz.
I find it funny when I hear the Emit-K tweeter is fragile, or prone to failure. My pair are 26yrs old and still sounding as sweet as the day I bought them.
Edits: 10/11/17 10/11/17
> > Infinity Emit-K is flat to 45khz. < <
Possibly, but I doubt it. The only way to measure this properly would be with an 1/8" Bruel & Kjaer measurement microphone. While there *may* be some output at 45kHz, I would be shocked if it were "flat". That floppy diaphragm will have all kinds of resonances above a few kHz and so will the plate with the slots. One could spend months trying to juggle the resonances to approximate a "flat" response, but my guess is that one would be lucky to achieve ±6dB between 10kHz and 45kHz.
Almost all loudspeaker manufacturers use 1/2" measurement microphones that barely make it flat to 15kHz and then are 1dB or 2dB off by 20kHz. After that they are pretty much dead by 30kHz.
The Modulus speaker measured +/- 1.5db 180hz-30khz, when reviewed back in 1990 so I guess it's at least flat within these parameters.The entire system was rated by the manufacturer to be +/- 2db 22hz-45khz, but to achieve this wasn't cheap at $3300 back 1990, but I read they lost money on them even at that price.
Edits: 10/11/17 10/11/17 10/11/17
Hello Kingshead,
Those tweeters were originally made by the OEM company Bohlender-Graebener, in Reno, Nevada. Soon Infinity had copies made in Taiwan, and later (when trade relations were "normalized") China. B-G has gone on to produce products aimed at cinema applications, and also marketed to the audiophile market under the trade name "Wisdom". All of these are planar-magnetic ribbons, meaning that the electrical conductor is printed onto a plastic (typically Mylar) substrate. In contrast a true ribbon has the conductive element (typically aluminum) pressed into a foil and used as the radiator itself.
Not many reviews publish measurements of the speakers tested, Stereophile being the main exception. Linked below is the "Measurements" page of the Stereophile review of the Modulus + subwoofer package. The frequency response on-axis is rising smoothly toward the 30kHz measurement limit. However JA uses a Bruel & Kjaer (the semi-pro model JA uses was from a division spun off as DPA) electret condenser microphone with a 16mm diaphragm. The response of a capsule this large gets squirrely above ~15kHz. At some point in the 1990s he realized this and entered a correction curve for that particular microphone into the MLSSA measurement system he uses and he reprinted the measurements of many previously-measured speakers. I believe the response at 20kHz was about 2dB off due to the microphone error.
Going beyond 20kHz with any accuracy, whether generating sound waves or attempting to measure them is rather difficult. As 20kHz is generally considered the upper limit of human hearing, almost all equipment is focused on that range. The most accurate measurement microphones are condenser microphones. The larger the diaphragm, the more sensitive it is and the better the S/N ratio. The largest measurement microphones use a 1" capsule, but the frequency response begins to vary above 5kHz or so. Virtually all loudspeaker measurements are made with a 1/2" capsule, which starts to vary above 10kHz or so. They can measure up to around 30kHz with reasonable accuracy but require an understanding of both the correction curve and the angle of incidence between the sound source and the plane of the microphone diaphragm.
You can see this more clearly with specialized very small diameter capsules. The original B&K is still making measurement-grade 1/4" and 1/8" capsules for specialized high-frequency measurements. But take a look at the datasheet for the 1/8" capsule here:
https://www.bksv.com/-/media/literature/Product-Data/bp2030.ashx
Figure 1 on page 2 shows the correction curves that must be applied, depending on the angle of incidence. Even with this very tiny measurement element, its physical external dimensions are large enough to disturb the sound field of very high frequency (short wavelength) sounds.
If measured directly on-axis (mic pointed at the sound source), the frequency response will be boosted by +11dB at 100kHz. For most measurements the microphone should be oriented at 90º to the sound source (so that the sound waves graze across the diaphragm). When used like this the response is within ±1dB all the way out to 100kHz.
The OP did not specify how high in frequency he wanted to go, nor how loud the sound source must be. Since he said that he was attempting to perform materials testing, I would imagine that he is looking for very high SPLs that would deform or stress the material. The EMIT planar ribbon tweeters are not very efficient, nor do they have very high power handling, so they likely would not generate the SPLs that he is trying to achieve. But just getting accurate measurements above even above 10kHz is much more difficult than expected.
Hope this helps.
Julian Hirsch
Thanks for the image! I've not seen a Stereo Review for a long time... :-)
I don't remember what equipment Stereo Review used to use to measure loudspeakers, as I stopped reading it in the 1970s. Measuring speakers is really far, far more difficult than measuring electronics. There are two problems that are related:
1) The audio band varies by a ratio of 1000:1. (Compare this to the visual spectrum, which is less than 3:1 in wavelength.)
2) When you measure the loudspeaker in a room, you are actually measuring the combination of the loudspeaker *plus* the room. The only way around this is to use an anechoic chamber, where all 6 surfaces are designed to absorb sound. Essentially there is "no" room. Since it is impossible to make any wall be *completely* non-reflective, even in an anechoic chamber one wants to put the sound source as far away from any of the walls as possible. This means that the "floor" of the room is actually made from a grid of steel ropes under high tension, and the loudspeaker, technicians, microphones, et cetera are all placed on this (essentially) acoustically transparent "floor" that is midway between the actual floor and ceiling.
Even then very low frequencies are difficult to absorb, so an anechoic chamber has a rated "cutoff" frequency (lower limit) of usually between 50Hz and 100Hz. They are massive, expensive, and very rare - with only a handful around the world.
Since very few have access to one, it has become common to use one of two techniques to make "quasi-anechoic" measurements. The first to be developed was by Richard Heyser of CalTech, called TDS for "Time Delay Spectrometry". Several years later Doug Rife developed a digital tool that could perform many of the same functions and he called this MLSSA (pronounced "melissa") for Maximum Length Sequence System Analyzer. Both tools have the same limitation, in that they are only accurate up to the point that the first reflected wave hits the microphone.
Using really rough numbers, sound travels through air at about 1 foot per millisecond and one meter is roughly 3 feet. If the microphone is 3 feet from the sound source and the sound source is 3 feet off the floor, the initial arrival time will be 3 milliseconds after the signal starts and the first reflection will be 3.7 milliseconds later. This only allows measurements down to around 300 Hz with any degree of accuracy. There is an excellent article by Keith Howard on the Stereophile website that explains some of the limitations of this method. (See link below.)
And that is just the tip of the iceberg. Stereo Review simply *describes* the results of Julian's measurements, whereas Stereophile actually prints them. You can see these at:
https://www.stereophile.com/content/infinity-modulus-loudspeaker-modulus-subwoofer-measurements
While measuring relatively flat, JA's measurements were not close to JH's ±1.5dB. Furthermore in looking at both the frequency response of the tweeter and its waterfall plat in Stereophile's measurements, it is easy to see that the ribbon tweeter has a cluster of moderately severe resonances centered around 10kHz. It seems to clean up above that frequency, but again all sorts of things come into play. From 12kHz or so the tweeter's response rises fairly steeply, reaching +7dB or +8dB by 30kHz.
Without the use of a special high-frequency measurement microphone (1/4" or smaller), it is difficult to say what is happening here. It looks to be a resonance of some sort, perhaps the cavity resonance created by the metal front plate.
Again, without knowing more of the actual frequencies and SPLs that the OP is trying to reach, recommending a 27 year old, long discontinued planar-magnetic ("quasi-ribbon") tweeter of likely limited power handling might not be all that helpful for what he is attempting. But you are correct that it has a more extended treble response than typical 1" soft-dome tweeters.
Was a subscriber to most stereo rags for many decades, including Stereophile, would trust just about anything JH said over the ad biased reviews regularly printed in Stereophile. That was always my biggest problem with that rag, don't spend advertising dollars to support the rag and you get shit on. Case in point, Bob Carver, and I just love the fact he made them eat crow.
About the only reviewer at that rag that has anything to say that I want to read is MF, or the late great JGH.
> > would trust just about anything JH said over the ad biased reviews regularly printed in Stereophile < <
I would disagree with you on that point. The problem with Julian Hirsch (and I met the man in person) was that he truly believed that everything about audio could be measured with the test equipment of the day. Since everything except loudspeakers measured essentially perfectly, he came to the unwarranted conclusion that the only thing that mattered any more were loudspeakers.
There he is, listening to his perfect source, through his perfect electronics, only to have the sound be damaged by the imperfect loudspeakers. The irony is that he ended up using the tools developed by one of the all-time true audio geniuses ever - Richard C. Heyser, professor at CalTech who invented Time Domain Spectroscopy and the ability to create a "waterfall" plot of a loudspeaker.
Heyser was about 10,000x smarter than Julian Hirsch and he was trying to figure out ways to measure things that clearly sounded different, even though conventional measurements showed them to be identical. Heyser was successful in creating an instrument that could measure previously unmeasurable differences in speakers, but to date nobody has been successful at measuring the difference between different sounding amplifiers or wires or many other things that trained listeners can hear.
If you have not trained your listening skills to hear the difference, then you should be happy, as you will save yourself a lot of money. It is not cheap nor easy to build electronic equipment that truly lets music's full emotional power connect to the listener.
Stereophile's reviews may be biased, but they are not biased by advertisers. That is not true for the other major print magazine that covers high-performance audio equipment, as they routinely only review equipment provided by advertisers, with the exception of one or two of their reviewers who are either independently wealthy and buy things to review or are away from the center of corruption and review things about which they have preconceptions and review specific products to confirm their own biases.
http://www.eminent-tech.com/main.html
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