There's life beyond 20K
There's life above 20 kilohertz! A survey of musical instrument spectra to 102.4 kHz
There's life above 20 kilohertz! A survey of musical instrument spectra to 102.4 kHz
How do I substantiate that I can hear to 17.5Khz, is that what you're asking ? How exactly am I supposed to prove that on an Internet forum ? C'mon.
I've always been able to easily hear the 15.625Khz (PAL) line frequency from the line output transformer in a CRT TV - not just barely, but to the point that it is irritatingly loud and bothers me anywhere in the same room. Thankfully CRT TV's are almost a thing of the past.
I don't have to turn the volume up to hear 17.5Khz - I can do a sine sweep at a moderate listening level and it goes up to 17.5Khz and then completely disappears. It still sounds like a tone to me as well, up until the point where it disappears.
I can hear 17.4khz easily, I can't hear 17.6khz even if I turn the volume up another 10dB or more. Its not a gradual rolloff like a normal low pass filter, its more like a brick wall filter. I don't think being able to hear up to 17.5Khz is particularly unusual either, so I see no particular reason for you to disbelieve me.
My point is that a resonance at 15Khz is audible to me as its well within the limits of my hearing, and my tweeters do have a small resonance at 15Khz which I have also notched to audible benefit.
I'm the first to admit that I find a resonance at 15 kHz far less noticeable than one at 8khz, it is rather subtle but it is still noticeable and its absence is noticeable on particular material when it has been removed. Imaging is also noticeably affected by its presence or absence on some material. On other material notching it out or not makes no difference.
Take what you will from my comments, I offer them as is.
Hello, I can hear 15.734khz easily.
I can also hear the 3rd harmonic of 15.0khz.
I have tested this using sine/square wave, and a microphone and FFT analyzer to prove there was no content added below 40khz.
I have always protected my hearing.
For instance, using hearing protectors when I run the vacuum.
All it takes is a trauma such as a firecracker on the 4th of July being closer to one ear than another.
Don't forget to include the statistical "bell curve" each of us has different abilities
It also depends on the loudness of the sounds that you are exposed to before the test.Hello Kindhornman
Here's what the audiogram looks like when you get tested. Not sure if it follows the curve so to speak as it is done over a smaller bandwidth. I was tested last week. It was interesting to say the least.
Rob
If you wear hearing protectors before the test you adjust your ears your test will be different than if you drive to the test in a car with no muffler or play your radio loudly.
Many of my late 70 early 80's amps were in the DC to 150k range. I've always figured it was around 100k transiently eg slew rate, not necessarily frequency bandwidth. Which is akin to fast bass and slow low flub sub sound.102K is what we need to get the whole envelope
Generally the lower frequency limit is more of a problem.102K is what we need to get the whole envelope
Late comment on frequency response v distance
The pressure wave in a horn and exiting a horn is not a plane wave but a spherical cap. It can be approximated at low frequencies by a spherical cap with a solid angle corresponding to the average angle between the horn walls. The 0" distance is therefor a measurement inside the horn and not a nearfield measurement outside the horn.
The lowest frequencies are attenuated due to the radiation impedance when the pressure wave leaves the horn (fairly similar to the radiation impedance of a flat disc of the same radius), even if the horn mouth is not a sharp transition but is gradual. The difference between 0" and 12" measuring distance is as theoretically expected.
Late comment:OK, I should not be allowed to play unsupervised in the lab after a long day at work... The measurement fixture was set for impedance measurements when the distance series was taken so there was a 35 ohm resistor in series with the driver causing the lumpier than expected results.
I re-did the measurements this morning with the fixture set correctly for frequency measurements. Not going to make guarantees though... Bumbling around in the lab at 5:00am before coffee has it's risks also.
John, if you want to play around with the measurements I can send you the ARTA .pir files via email. They add up to 1.9M zipped. PM me if you want them.
Tom, yes, there is a impedance wiggle at 8K so a mechanical resonance is likely.
New distance series-
And the impedance curve-
The pressure wave in a horn and exiting a horn is not a plane wave but a spherical cap. It can be approximated at low frequencies by a spherical cap with a solid angle corresponding to the average angle between the horn walls. The 0" distance is therefor a measurement inside the horn and not a nearfield measurement outside the horn.
The lowest frequencies are attenuated due to the radiation impedance when the pressure wave leaves the horn (fairly similar to the radiation impedance of a flat disc of the same radius), even if the horn mouth is not a sharp transition but is gradual. The difference between 0" and 12" measuring distance is as theoretically expected.
Yep, the measurements between 0" and 1' are only useful to support the discussion on close mike measurements on horns that was earlier in the thread.
This series of measurements was made to support both the close mike and FR with distance discussions. Seems to support both quite well. The close mike shows low frequency emphasis, and the the 2' to 10' series shows that the FR stays the same with distance once you get into the far field. Now if you did measurements at a much greater distance I would expect to see the top roll off due to the HF loss caused by the sound traveling through the air. Not going to happen in my basement though...
Your welcome!
I wonder if near field or far field should be defined as a number of wavelengths rather than feet?
In regard to full range frequency measurements, Pat Brown (a master of measurement) wrote :
"A working “rule-of-thumb” for determining the boundary between near-field and far-field is to make the minimum measurement distance the longest dimension of the loudspeaker multiplied by 3."
He then writes:
"It is often thought that a remote measurement position is necessary for low frequencies since their wavelengths are long. Actually the opposite is true. It is more difficult to get into the far-field of a device at high frequencies, since the shorter wavelengths make the criteria in Item 4 more difficult to satisfy."
Item 4:
"4. The distance from the source where the path length difference for wave arrivals from points on the device on the surface plane perpendicular to the point of observation are within one-quarter wavelength at the highest frequency of interest."
This is an important distinction between high frequency and low frequency measurement, criteria #4 can be satisfied at 95 Hz for a subwoofer of one square meter measured at one meter, but to satisfy the same criterion for a one meter mid/high horn to 20 kHz would require a very long distance.
That said, the "rule of thumb" for a HF horn the size of the La Cleac'h used in Gary's tests can be satisfied at a few meters.
Art
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Hi Lynn,
I have had my ultimate 2 way on ice for several years and now I have my garage cleared I am looking at it again.
Some thoughts.
I reading Gary's posts regards the AE 15M and the GPA 416 and comments on AVR forum regards the AE15M I am wondering if the notion of power response in terms of the "system" tilt is effecting the way the AE15M sounds.
A ruler flat response on axis is not always a good listen.
On the AVR and diy sound groups they have been messing with SEOS wave guides and initially got mixed feelings about the AE15M until measurement averaging of direct and power response suggested optimising for a non flat but slightly tapered response above 300 hertz extending slightly down across the bandwidth of the system.
This bought back the subjective impression of tonal density.
The notion being that with the AE15M very low 2nd and 3r THD, while being articulate it was sounding thin and lacked tonal color compared to otherwise similar drivers in the bass and mid band which subjectively had more warmth (much like single ended amps).
Given the AE15M has better power response above 800 hertz then most 15 inch woofers I think this could be a contributing factor.
None of this is particularly easy to measure but I plan to build a turntable and do some measurements soon in an open space with LMS, Leap5 and Sound Easy and see what I come up with. I have a AE15M and plan to use an Azura 425 with my Tad 4003 and the Tad UHF.
Hope this makes some sense from down under.
I have had my ultimate 2 way on ice for several years and now I have my garage cleared I am looking at it again.
Some thoughts.
I reading Gary's posts regards the AE 15M and the GPA 416 and comments on AVR forum regards the AE15M I am wondering if the notion of power response in terms of the "system" tilt is effecting the way the AE15M sounds.
A ruler flat response on axis is not always a good listen.
On the AVR and diy sound groups they have been messing with SEOS wave guides and initially got mixed feelings about the AE15M until measurement averaging of direct and power response suggested optimising for a non flat but slightly tapered response above 300 hertz extending slightly down across the bandwidth of the system.
This bought back the subjective impression of tonal density.
The notion being that with the AE15M very low 2nd and 3r THD, while being articulate it was sounding thin and lacked tonal color compared to otherwise similar drivers in the bass and mid band which subjectively had more warmth (much like single ended amps).
Given the AE15M has better power response above 800 hertz then most 15 inch woofers I think this could be a contributing factor.
None of this is particularly easy to measure but I plan to build a turntable and do some measurements soon in an open space with LMS, Leap5 and Sound Easy and see what I come up with. I have a AE15M and plan to use an Azura 425 with my Tad 4003 and the Tad UHF.
Hope this makes some sense from down under.
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Do you have a link to that handy? That really sounds like a misinterpretation from the way you describe it, I think. Because...
- you need a bit of a slant down at some point relative to the baffle size, depending on placement, and that's always tricky to get right.
- As long as you measure from a healthy distance, the on-axis response does start rising at a lower frequency than you often see DIY indoor measurements reaching, so you've got "baffle step", modal range, and the natural rising response all getting into the mix around the same low frequency range. A real conundrum for indoor measurements.
- resonant behavior comes in around 900Hz, so when crossing higher you need to pull down 2-3dB more above that, if not using DSP to address it more precisely.
I attached an early version of my TD15M filter below. It eventually got more complex, but the basic shape is still like this (it's the only image I had handy).
- you need a bit of a slant down at some point relative to the baffle size, depending on placement, and that's always tricky to get right.
- As long as you measure from a healthy distance, the on-axis response does start rising at a lower frequency than you often see DIY indoor measurements reaching, so you've got "baffle step", modal range, and the natural rising response all getting into the mix around the same low frequency range. A real conundrum for indoor measurements.
- resonant behavior comes in around 900Hz, so when crossing higher you need to pull down 2-3dB more above that, if not using DSP to address it more precisely.
I attached an early version of my TD15M filter below. It eventually got more complex, but the basic shape is still like this (it's the only image I had handy).
Attachments
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The polar response and power directivity of a 15" midbass change quickly above 500Hz. Typical 18" - 21" cabinet widths (13550/21" = 645Hz) also jiggle the response in the 1.4" compression driver 600-700Hz crossover region.
I wonder if using the larger JMLC 350 horn with a digital time aligned 4th order xover would better dovetail match the TD15M.
I wonder if using the larger JMLC 350 horn with a digital time aligned 4th order xover would better dovetail match the TD15M.
