Do analog Peterson strobe tuners compensate for temp?

Hi guys,
I figured I'd ask here because I haven't found an answer yet. I use an old Peterson 420 strobe tuner for tuning marimba bars. I love my old baby. I try and tune bars at 72 degrees farenheit, but I don't always get that opportunity.

A couple weeks ago it was 50 degrees and I had to tune a bunch of bars. I got real clever with complex math and speed-of-sound as it relates to frequency. I thought I came up with the proper math, and adjusted my Peterson to -32 cents and tuned the keys.

Well I got a call today that the marimbas are flat. I'm not up there to check for a couple weeks, so it begs the question-was I just wrong with my math, or do petersons account for ambient temperature?

If I have to tune a bar to middle C in 50 degrees on a Peterson, do I need to compensate for temp?

Minus THIRTY_TWO cents???

Without even doing any math, my instincts scream that's got to be wrong.

I cannot conceive of a temperature in which humans could SURVIVE which could make marimba bars shrink to the amount where it's such a significant chunk of a semitone off.

So yes... I'm betting that they're flat.

Hi Keith,
It's not a question of mbira bars shrinking-in fact as the bars themselves get cold, they negligibly go up in pitch. As temperature goes down, air gets denser and so the speed of sound is affected and pitch goes down-yes it is noticeable. That's why instruments are made to be in tune at 72, and resonators on the bottom of tubes are often adjustable-to compensate. Cold days, there can be as much as 1/4 step difference.
http://theconcertband.com/resources/music-a-physics/pitch-and-temperature.html

Im not shure if I got you right, you want to tune an instrument in a room temperature of 50 degrees Farenheit and then use the instrument at the same temp?
Just tune as always, 440Hz is 440 Hz. (or whatewer)

Or does the frequency of the bar differ much from the combination bar/tube?
Then maybe an acoustic tuner is the best solution.

No-my shop was 50, and I need to tune the bar to be a=440 at 72 degrees, so what do I tune to at 50 degrees? What I've read is pitch goes down around 3.5 cents per degree celcious, so around 32 cents flatter at 50...
The resonator rube isn't in the picture here-just the key.

I think youre compare apples with pears, if you try to tune the key (bar ?) itself, you shouldnt have to mess with air resistance.
You mentioned in your second post that the change of the bars is negligable. Anyway, it should depend on the properties of the  material (wood) and not the air around it.

I dont think its a good idea at all to tune an instrument in a much lower temperature than normal. Cant you do it in a room where you could adjust the temp to 72 deg.?

How do you tune a marimba bar actually, filing away material or adding some (chewing gum)?  

Mbira said:

Hi Keith,
It's not a question of mbira bars shrinking-in fact as the bars themselves get cold, they negligibly go up in pitch. As temperature goes down, air gets denser and so the speed of sound is affected and pitch goes down-yes it is noticeable. That's why instruments are made to be in tune at 72, and resonators on the bottom of tubes are often adjustable-to compensate. Cold days, there can be as much as 1/4 step difference.
http://theconcertband.com/resources/music-a-physics/pitch-and-temperature.html

Click to expand...

OK, the link you posted is talking about a wind instrument, so indeed the air temp and speed of sound "in air" will shift the pitch sharp or flat inside the resonant chamber of a wind instrument. For the marimba you are dealing with the speed of sound inside the marimba bars which will be much faster and change much less than air for a given temp change (since the bars will shrink or expand much less than air).

32 cents which is almost 1/3 of a full note, seems like it would be way off...  I suspect the marimba could change some, just not that much.

AFAIK tuners do not attempt to compensate for instrument/air temperature, and if anything would work to maintain their own internal accuracy over temperature.

JR

I am totally open to being wrong, AND I don't think you guys are understanding my question.

When I strike the marimba bar, the sound travels through air.  It goes through the air and hits the internal mic on the Peterson strobe tuner.

Sooo....At different temperatures,wouldn't a note's wavelength be different and need to be compensated for?

Edit: OK I just got off the phone with Peterson, and the guy there said that I wouldn't need to compensate for the difference in the air-it's only the differences in the key itself that would matter.

So it is what you guys are saying, BUT I still don't understand WHY the difference in the air wouldn't make a difference?

Perhaps you are not understanding our answers. 

In the case of your marimba the air is just the medium that the sound created by the marimba bars vibrating, travels through (like signals in wire). The speed of sound in that air only affects how long it takes for the sound to reach you.

In the case of a wind instrument, the speed of sound through the air along the length the internal resonant chamber path, where the note is developed, will affect the pitch of that resonance (pitch= 1/wavelength,  or 1/time to travel the resonant path).

Getting back to warmer or cooler air in your listening space, the temperature of that air will affect the pitch of any standing wave room modes, but they will generally be at relatively LF (based on room dimensions) and changes are probably not going to be very noticeable unless you are using a lot of sound reinforcement and instruments that excite those lower frequencies. 

JR

Mbira said:

No-my shop was 50, and I need to tune the bar to be a=440 at 72 degrees, so what do I tune to at 50 degrees? What I've read is pitch goes down around 3.5 cents per degree celcious, so around 32 cents flatter at 50...

Click to expand...

I can't imagine that this would be a linear scale.

What you want is a walk in closet with a thermostat...

I remember from my high school orchestra days that wind instruments changed pitch the opposite direction that stringed instruments.

http://www.bandbrilliance.com/The_PHYSICS_of_Tuning_for_all_Wind_Instruments.pdf

This document says:

Cold-makes all aerophones flat (opposite for piano and string instruments and metal percussion)

Click to expand...

I would say to try and tune one true @ 50 deg and then bring it inside to see what happens. 

Hi guys,
Thank you for your replies, and for helping me try to understand this dilema.  I understand that I'm incorrect, and I'm still trying to wrap my head around what is wrong with my thinking, so please bare with me and point out where I am going astray:

So I understand that the pitch is formed inside the key when struck.  It vibrates at the frequency that it is tuned to...

What is throwing me off is when You tune a resonator tube to be in tune with a pitch, you make the tube to be 1/4 the wavelength of the pitch.  The key is struck, and the frequency wave goes down the resonator and bounces off the bottom and when it reaches the top of the tube, the wavelength is at its widest point, so creates the resonance.

OK, that is all understood.  Now when it gets cold outside, that resonator tube goes flat-meaning that I would have to play a lower pitch in order to achieve that resonance.  If I want it to resonate at the normal pitch, I need to shorten the tube.  So therefore, in cold weather, the frequency that is leaving the marimba key is a shorter wavelength than it is when it is hotter, right?

So I am extending that to assume that the Peterson is "listening" to the wavelengths and so a shorter wavelength would appear to be a higher pitch, and a lower wavelength would appear to be a lower pitch...

Where am I going wrong?

Mbira said:

Sooo....At different temperatures,wouldn't a note's wavelength be different and need to be compensated for?

...So it is what you guys are saying, BUT I still don't understand WHY the difference in the air wouldn't make a difference?

Click to expand...

As I've always understood it, the wavelength changes proportionately to the change in speed, resulting in a constant frequency when passing through air. When depending on air volume for resonance (e.g.: room modes, wind instruments, & resonator tubes) the resonances are determined by the relationship of the internal dimensions to the wavelength, so in these cases the resultant frequency is affected by temperature. So basically, temperature changes will (minimally) affect your keys according to their expansion/contraction coefficients and your resonator tubes will be affected by the changes in air temperature & the resultant wavelengths.

Does that clear it up?

Mbira said:

At different temperatures,wouldn't a note's wavelength be different ... ?

Click to expand...

yes. But speed of sound as well. Lets say you strike a string of guitar. When string starts to move after initial disposition it creates ripple - wavefront in sorounding air. After ceratin amount of time string will be (almost) back to initial position after strike, that time would be first full period of wave. Depending on air temeperature, initial wavefront would have traveled certain distance from string , that would be wavelenght in air. That wavelenght would depend on sound velocity, and thus air temeperature, but time between same positions on waveform would be the same, and thus frequency of wave, since timing is governed by initial oscilating body. What would be an issue is if air temperature would shift during wave travel to listener. That would cause tiny random vibrato, and that is real issue, but effect is so small (because it depends on derivate of air temp) that only practical effect is that impulse response reverbs dont sound like real rooms because of large distance traveled during all that bouncing around the walls (btw, this effect is real, and rooms do "breathe" - I've done some dereverberation algos, and it's big issue in such cases). So, pitch is not afected by air temp.

And another way to look at it. Take fretless guitar. Start tuning E string up and down. You will allways find fretting postion on fretboard where plucked string produces lets say C note, but that postion would shift up and down the fretboard depending on string tension. Since wavelenght on string is exactly the same as lenght of freely vibrating part of string, that would mean that for different tensions of vibrating object, wavelenghts for C would differ, but C will still be C.

Mbira said:

So I am extending that to assume that the Peterson is "listening" to the wavelengths

Click to expand...

No. Peterson is "listening" to changes in air pressure at microphone membrane. Period between two peaks of pressure would be period of wave. Wavelenght is an issue when you study how sound travels trough air or room. But peterson doesn't give a damn how long wave looked like, it only cares on how fast wave cause pressure oscilation at membrane.

Are you tuning the bars or the tubes?

The tube resonance will shift with the speed of sound in AIR. You found that formula.

However the tube is user-adjustable, at home and touch-up on stage. As I understand your business, that's not your job.

The bar resonance will shift with the speed of sound in WOOD. Not the same.

And the bar resonance is _NOT_ easily user adjustable. It comes down to a chainsaw (not the good plan) or a FedEx sticker and 2-week wait.

I don't have a clue what the tempco of wood is; considering the nature of wood, I bet it is not the same piece to piece, even from the same log.

The bar's resonance is NOT (significantly) affected by air. Put it in a vacuum, tap. It will resonate fine. You won't hear it, but you can sense the vibration and frequency many ways. The frequency may be slightly different in air, hardly enuff to notice. Coupled to a resonator it may tend to shift toward pipe-resonance but this is small (you tune the pipe TO the bar for best output, you don;t tune the bar to the pipe to reach pitch).

Third snarl: I would not trust the Peterson away from room temp. It may have first-order compensation for small temp change, but 50-72 is a large temp change. Can't you get a Sharp or BOSS chip-tuner? Yes, I know the Peterson has advantages, but the Japanese make very fine crystal oscillators are are liable to pick a cut with low tempco either side of nominal room temp.

At least take the Sharp and a bar and a thermometer to a nice warm pub, check it AT 72, before you ship it away.

I really think you want a temperature controlled room. Even a closet. I keep a 3'x3'x7' space 10 or 15 deg F above ambient with a $30 room heater and a "baseboard thermostat". The 1,500 Watt heater runs in short spurts; I calculate 130W average heat loss. (Somewhat more than the old vacuum-tube Peterson dissipated...)

PRR said:

Can't you get a Sharp or BOSS chip-tuner?

Click to expand...

Apparently, this:
http://www.turbo-tuner.com/st122-index.htm
is mother of all tuners (or at leats, buzz on ze internetz claim so). A bit more expensive than Boss, but cheap compared to top of the line Petersons (and claimed to be as good as them or better)

No, the mother of all tuners is this:

http://www.tunelab-world.com/

Neither of those tuners lets you check the tuning of your overtones simultaneously while checking the fundamental which is essential in marimba bar tuning.  The Peterson has them both beat :-D

I've been crazy busy with family, etc, etc.  I'm still trying to wrap my head around the difference between air temp being a factor is instruments using air volume, and instruments not using air volume, but I'm getting there.

One very nice thing about this is that getting the resonator tubes in tune is a one-time deal of making the proper measurements (at the right temp Haha), and then that work is easily repeatable.  Marimba keys on the other hand have to be tuned individually every time because of differences in the wood.  It's nice that temp is less of a factor there.

Thanks for your patience.

This one is easy. Tune one A bar to 440Hz  @ 72 degrees and then move it to a 50 degrees temp... hIt it and read the result in Peterson... Now you know the pitch diference.
Sometimes less maths and more hands at work means fasters and confirmed results...
Cheers