I will try to find out what is 0 dB means in Adobe Audition. I don't change any settings in Audition so I will assume it is the default value.
Hi Jim, Sorry I'm still confused. What was the excitation for this plot? was it a sweep and did you capture the entire sweep or a single tone.
I got my stethoscope today and had a listen.
I used a music record. The sound is the loudest at position 1. This is what I expected. The loudness is almost the same at positions 2, 3, and 5. The sound at position 5 is somewhat louder than at other positions. But I can't say for sure. All the sounds are almost inaudible at positions 2, 3, and 5. The sound is completely inaudible at position 4. I can't judge the loudness by just listening to it. So, I may try to hook a mic with the stethoscope later on.
I used a music record. The sound is the loudest at position 1. This is what I expected. The loudness is almost the same at positions 2, 3, and 5. The sound at position 5 is somewhat louder than at other positions. But I can't say for sure. All the sounds are almost inaudible at positions 2, 3, and 5. The sound is completely inaudible at position 4. I can't judge the loudness by just listening to it. So, I may try to hook a mic with the stethoscope later on.
There will most likely be a few dB options because different dB scales have different references like dBm is referenced to 1mwatt and dBv to 0.7746v but none of these will have any meaning to measuring the level of a signal below another this is dBc where the reference must be set to an input.
If you look at the image below I have set the marker to the 300Hz peak and then set this as the reference (square box) then set the marker to one of the sidebands (triangle) which is -47.7905dBc below the 300Hz. If I used 0dB of the analyzer that would add another 20dB so the triangle marker would be -67.7905dB below the 0dB of the analyzer not the signal.
I run a sweep from 30 Hz to 30 kHz from Cardas Frequency Sweep and Burn-in Record. This is the result. The contact mic was attached to the end of the air bearing shaft, i.e., position 1 in my photo. You can see a small peak at 3.5 kHz.
The contract microphones look like the type used for pick-ups on acoustic musical instruments. If they are they may not be suitable for this application. The amplitude they are designed to work with will be very high compared to what we are trying to measure, they are probably just not sensitive enough. That you can hear energy transmission with a stethoscope but the microphones don't pick up anything would seem to confirm this.
I connected a small microphone to the stethoscope, but the microphone couldn't pick up anything from the stethoscope. Then, I listened again by using the stethoscope alone. Again, the sound levels at positions 2, 3, and 5 were so low that I doubt any microphone can pick them up. The sound level at position 1 is almost two times the sound level at other positions.
Carlo, Niffy,
When I saw warrjon and Mike used stethoscopes to listen, I presumed the stethoscope is a medical one. I am going to get one for mechanics. Thanks for the tip!
Anyway, the sound level I heard from my medical stethoscope is very low. The level is close to or even lower than the environmental noise of New York City. I used to live in New York City. It is probably unmeasurable. I guess I may have to give up the idea to measure the level of the sound transmitted from the cartridge.
Jim
When I saw warrjon and Mike used stethoscopes to listen, I presumed the stethoscope is a medical one. I am going to get one for mechanics. Thanks for the tip!
Anyway, the sound level I heard from my medical stethoscope is very low. The level is close to or even lower than the environmental noise of New York City. I used to live in New York City. It is probably unmeasurable. I guess I may have to give up the idea to measure the level of the sound transmitted from the cartridge.
Jim
I use a medical stethoscope, I never thought to use a mechanics. I will buy one and try it out.
I mainly use the stethoscope to listen to the plinth and arm bearing housing. The platter on my SP10 is made from Gunmetal and POM and sounds pretty inert when tapped, but put the stethoscope on it and tap it and it sounds completely different. I suspect the sound in the stethoscope is what the cartridge will hear.
Just remember if you can hear it in a stethoscope the cartridge will also hear it and turn it into signal. I live in a rural area with no traffic and only 4 houses in an area of 1km and when I placed my TT on a Minus K there was a huge improvement in clarity, so the cartridge was hearing the house vibrate, which I can't hear with the stethoscope. I can measure it by placing the stylus on a stationary LP and measuring the output of the phono pre, the noise floor is lower.
In fact thinking about measuring your air arm Jim you could use this method with air on and off. Use an oscilloscope and spectrum analyser on output of the phono-pre and measure with air on and off. If you can measure the arm before and after making changes it will give you a good idea of what and why the change works or not. @Mike56 started measuring his LTA and made huge advances.
I mainly use the stethoscope to listen to the plinth and arm bearing housing. The platter on my SP10 is made from Gunmetal and POM and sounds pretty inert when tapped, but put the stethoscope on it and tap it and it sounds completely different. I suspect the sound in the stethoscope is what the cartridge will hear.
Just remember if you can hear it in a stethoscope the cartridge will also hear it and turn it into signal. I live in a rural area with no traffic and only 4 houses in an area of 1km and when I placed my TT on a Minus K there was a huge improvement in clarity, so the cartridge was hearing the house vibrate, which I can't hear with the stethoscope. I can measure it by placing the stylus on a stationary LP and measuring the output of the phono pre, the noise floor is lower.
In fact thinking about measuring your air arm Jim you could use this method with air on and off. Use an oscilloscope and spectrum analyser on output of the phono-pre and measure with air on and off. If you can measure the arm before and after making changes it will give you a good idea of what and why the change works or not. @Mike56 started measuring his LTA and made huge advances.
Warrjon,
I put the air-bearing arm on a stationary LP and measured the output from the phono with and without air. Here are the results. It seems to me that there is nothing going on except the noise level of the phono and there are no differences between with air and without air.
Without air.
With air
I put the air-bearing arm on a stationary LP and measured the output from the phono with and without air. Here are the results. It seems to me that there is nothing going on except the noise level of the phono and there are no differences between with air and without air.
Without air.
With air
Looks pretty good Jim.
The 3.5kHz is only just above the noise floor. The peaks not circled look to be a product of the test setup mains hum and harmonics so I'd disregard them. If you wanted to explore them further you could run the same test playing a 300Hz laterally modulated tone, this will give you a reference.
The 3.5kHz is only just above the noise floor. The peaks not circled look to be a product of the test setup mains hum and harmonics so I'd disregard them. If you wanted to explore them further you could run the same test playing a 300Hz laterally modulated tone, this will give you a reference.
One of the factors I found so interesting about this discussion was all about coupling, its benefits and measurement of it.
As I understand it a lot of folk feel coupling is essential if one is to approach high end performance, but not all.
I imagine this to be because it is beneficial that the record modulation and cartridge are on the same motionless base if best extraction of the signal is to be achieved, any relative motion of modulated groove to stylus introduced by the lack of rigid coupling or anything else will change the final signal.
So, what would that do to the sound and what would one see in measurements to confirm that. I imagine, attack, timing and clarity in the sound would all be a little blurred, but to what degree, and what compromises does coupling introduce in comparison to decoupling? - which is the best compromise?
M
Hi Jim - yes the level is very low, living in a city I make these listening at night. But it is a good sign, if the level is high there is to worry.
A mechanical stetho with its rigid probe has the advantage of making the instrument as one with the part being measured. On rigid objects I fear that the medical one acts on one point only, losing the surface effect of the listening on human body is made for.
The other gadget I recommend to everyone is a macroscope on a tripod: a tonearm is just a mechanical device, not a musical instrument (if it becomes, you have to worry).
....lot of folk feel coupling is essential if one is to approach high end performance,
let's say it's a great conversation piece, as plinth materials
imho of course - carlo
A mechanical stetho with its rigid probe has the advantage of making the instrument as one with the part being measured. On rigid objects I fear that the medical one acts on one point only, losing the surface effect of the listening on human body is made for.
The other gadget I recommend to everyone is a macroscope on a tripod: a tonearm is just a mechanical device, not a musical instrument (if it becomes, you have to worry).
....lot of folk feel coupling is essential if one is to approach high end performance,
let's say it's a great conversation piece, as plinth materials
imho of course - carlo
warrjon,
Here is a 300 Hz sweep. The track is from HiFi News Test LP, Side 2, Band 1 300 Hz L+R at +15 dB. I am not sure if the track is a lateral or vertical modulation. From the sweep, I can clearly see the arm/cartridge resonant frequency is about 9 Hz. The cartridge is Ortofon A90, a medium compliance MC cartridge. The arm is my 1" air-bearing arm. It is a heavy arm. I usually don't like to fit a medium compliance cartridge on a heavy tonearm.
Jim
Here is a 300 Hz sweep. The track is from HiFi News Test LP, Side 2, Band 1 300 Hz L+R at +15 dB. I am not sure if the track is a lateral or vertical modulation. From the sweep, I can clearly see the arm/cartridge resonant frequency is about 9 Hz. The cartridge is Ortofon A90, a medium compliance MC cartridge. The arm is my 1" air-bearing arm. It is a heavy arm. I usually don't like to fit a medium compliance cartridge on a heavy tonearm.
Jim
A really complex subject.
Some TT manufacturers like Continuum with the Caliburn use decoupling, the tonearm board is suspended on string held with magnets others like Techdas use rigidly coupled tonearm mounts. I'm in the rigid coupling between pivot and spindle.
One thing the TT needs to be decoupled from the environment. A TT has similar resolution to an Atomic Force Microscope so this gives you an idea of just how sensitive the TT is and Carlo hit the nail on the head with his comment of the tonearm is a mechanical device, I would go a step further and say the TT system is a precision measuring instrument.
Measuring this is not overly difficult. If the stylus is being modulated by external vibration it will produce sidebands on the note. If you look at the plots I posed in #4836 you can see the reduction in sidebands with a more rigidly attached counterweight.
https://www.diyaudio.com/community/threads/diy-linear-tonearm.238027/page-242#post-7157315
The plots I posted also used the same test track I believe it's horizontal modulation. It's a very good test track to give the arm/cart a workout and help improve things.
Do you see what I was talking about with the dB reference. You 300Hz signal is about -20dB so the -70dB 3.5kHz is actually -50dB from the signal. This is still a good result when compared to some expensive commercial arms, I have a plot from the Linn Ekos and the first sideband is -40dB. Kuzma et-al don't publish any measurement data in fact no highend tonearm manufacurer does I sispect because they don't measure well.
The harmonic fall off looks excellent in that it's almost a linear decrease.
If you zoom in on the 300Hz fundamental there are a couple of sidebands visible at about -50dB if you want to improve the arm further find out what is causing these and you will hear an improvement in clarity. If you look at the plots in my post #4836 you can see the sidebands at 8.5Hz -47dB. These were caused by the OEM CW and its dynamic damping, basically decoupled CW. I made a new CW and stub that rigidly locked and the sidebands just about disappeared.
I understand it. However, it may be very difficult to find what causes these side bands.
I also used my oscilloscope to see the waveforms of this 300 Hz track. In my air-bearing arm thread, I tested the trackability of my air-bearing arms by using different test LP and different waveforms. They looked pretty good though. But for this 300 Hz waveform, it doesn't look too good. Maybe it is time to roll up the sleeves again. But at this moment, I don't have a clue where to start with.