Shared Reed chamber

[Theo]

2 hours ago, Isel said:

Interesting Stephen,Thank you!

(A propos... I have noticed the Harmonika's Tipo A Mano II Class reeds are tuned with 5 cents  accuracy ...An interesting matter to discuss in topic apart could be the "subjective" percepction of tuning?)

Yes but they expect that the person who installs the reeds will complete the tuning process. 

[Clive Thorne]

I'm obviusly teaching grandmother to suck eggs for most people here, so apologies to them, but, as I understand it:

 

If you have two closely coupled resonant systems, that are only slightly apart then then will tend to both resonant at a common frequency, half way between the two, and in sync with each other (i.e. no tremelo). It becomes a forced resonance system where they both resonate slightly off their 'free' resonant frequency

Systems less closely coupled will each go at their own frequency, to generate a tone the numerical mid frequency of the two with a beat at the numeric difference of the two.

 

Two reeds in the same chamber will be closely couple via the air in the chamber and so "phase lock" as Geoff correctly describes it. Two reeds in separate chambers would , I imagine, be less closely coupled so allowing a finer tremelo affect, if that's what you wanted.

 

In Stephen's example of the chord blocks the reeds would tend synchonise at the natural harmonic resonances, so I guess that they would tend to produce a sweeter chord, without the harshness of some equal temperament chords.

 

Please feel free to disagree.

 

Edited August 30, 2020 by Clive Thorne

[Isel]

This question does result fascinating to me. Thank you very much!!☺️

 

How don't get fascinated when terms as "celestial " do take part??. @Takayuki YAGITakayuki, I am intrigued by the rationale for applying this term specifically to that setup, when I think concertinas already sound celestially overall.?

[Isel]

1 hour ago, Theo said:

but they expect that the person who installs the reeds will complete the tuning process. 

Ah..thanks Theo....that makes sense?

[Stephen Chambers]

9 hours ago, Takayuki YAGI said:

 Celestial means double reed tremolo tuning according to the Dan Warroll's article here.

 

Here's an old post of mine, from March 2005, about double-reeded concertinas, including "celestial" and "organ-toned" ones...

 

 

[alex_holden]

29 minutes ago, Stephen Chambers said:

Here's an old post of mine, from March 2005, about double-reeded concertinas, including "celestial" and "organ-toned" ones...

 

Wow, on the second page of that topic there are photos of a fascinating Wheatstone English from 1920 with double-tongue reed frames.

[Stephen Chambers]

50 minutes ago, alex_holden said:

Wow, on the second page of that topic there are photos of a fascinating Wheatstone English from 1920 with double-tongue reed frames.

 

I was going to post a link to that when I got a chance: Wheatstone #28438

[Isel]

???

[Richard Mellish]

On 8/30/2020 at 4:57 PM, Clive Thorne said:

I'm obviusly teaching grandmother to suck eggs for most people here, so apologies to them, but, as I understand it:

 

If you have two closely coupled resonant systems, that are only slightly apart then then will tend to both resonant at a common frequency, half way between the two, and in sync with each other (i.e. no tremelo). It becomes a forced resonance system where they both resonate slightly off their 'free' resonant frequency

Systems less closely coupled will each go at their own frequency, to generate a tone the numerical mid frequency of the two with a beat at the numeric difference of the two.

 

Two reeds in the same chamber will be closely couple via the air in the chamber and so "phase lock" as Geoff correctly describes it. Two reeds in separate chambers would , I imagine, be less closely coupled so allowing a finer tremelo affect, if that's what you wanted.

 

In Stephen's example of the chord blocks the reeds would tend synchonise at the natural harmonic resonances, so I guess that they would tend to produce a sweeter chord, without the harshness of some equal temperament chords.

 

Please feel free to disagree.

 

I think I do disagree! If two oscillators tuned to exactly the same frequency are coupled, they have two eigenmodes, one slightly higher in frequency than the original and one slightly lower, according to whether they are oscillating in phase or in antiphase. (Off hand I can't think which frequency goes with which, but anyway that may depend on the nature of the coupling.) So the effect is to separate the possible frequencies rather than to pull them together. This used to be used in radios to provide a bandpass characteristic, but in that case the excitation is from the incoming radio signal. With two things, such as two free reeds, that are excited to oscillate at whatever their natural frequency may be, but coupled, I'm not at all sure what happens. I feel a simulation coming on.

[Theo]

2 hours ago, Richard Mellish said:

I think I do disagree! If two oscillators tuned to exactly the same frequency are coupled, they have two eigenmodes, one slightly higher in frequency than the original and one slightly lower, according to whether they are oscillating in phase or in antiphase. (Off hand I can't think which frequency goes with which, but anyway that may depend on the nature of the coupling.) So the effect is to separate the possible frequencies rather than to pull them together. This used to be used in radios to provide a bandpass characteristic, but in that case the excitation is from the incoming radio signal. With two things, such as two free reeds, that are excited to oscillate at whatever their natural frequency may be, but coupled, I'm not at all sure what happens. I feel a simulation coming on.

 

That's interesting.  I mainly tune accordions where there are usually two reeds at the same nominal pitch.  I know from experience that phase locking can occur when the difference between the pitch of the two reeds is small.   It is something to be avoided because it generally sounds rather unpleasant.  I had always assumed that the unpleasantness was simply a result of the slow beat disappearing and coming back as playing pressure varies,  but if their is also a pitch shift when phase lock happens then that would be another reason that the sound is unpleasant.

[Isel]

Uff!!. What interesting!.

Forgive me, as I am an absolute prophane at this Matter. However I had some considerations to do.

- Surprised by Richard's affirmation. I intuitively thought same frequencies triggered at same time would be on phase ??

- In uilleann pipes, I have listen to the phase lock does benefict drone sound in both stability and harmonic blending.

- I wonder if the real advantage of phase lock could be that the phase difference remain stable (and small if the i.e.,Two sounds, do have same frequency -or integer multiple-).

- Could the unpleasant sound referred by Theo have to do with unequal frequencies of the reeds involved, causing unstable phase differences?

Edited September 2, 2020 by Isel
Clarity

[Richard Mellish]

I think I need to clarify my own thinking as well as my post above, though I haven't yet got around to the simulation.

 

The effect of coupling two oscillators is, as I said, to create two possible frequencies, according to whether they (in this case two reeds) are in phase or in antiphase. But whichever of those modes they settle into, they are both at the same frequency; it's just slightly different from the frequency that one would have on its own. I can't work out whether in phase or antiphase is more likely. I'm also not sure of how much the coupling changes the frequency (up or down) from the frequency of one reed alone, but I suspect it's considerable, as there is coupling both by transmission of vibration through the reed pan and by the flow of air.

[Clive Thorne]

On 9/2/2020 at 9:02 AM, Richard Mellish said:

I think I do disagree! If two oscillators tuned to exactly the same frequency are coupled, they have two eigenmodes, one slightly higher in frequency than the original and one slightly lower, according to whether they are oscillating in phase or in antiphase. (Off hand I can't think which frequency goes with which, but anyway that may depend on the nature of the coupling.) So the effect is to separate the possible frequencies rather than to pull them together. This used to be used in radios to provide a bandpass characteristic, but in that case the excitation is from the incoming radio signal. With two things, such as two free reeds, that are excited to oscillate at whatever their natural frequency may be, but coupled, I'm not at all sure what happens. I feel a simulation coming on.

 

Having refreshed myself on the net, as far as I can see, when they are in phase then the Eigen mode corresponds to resononance frequency of the two independent systems. If they are in antiphase then the eigen mode is at a higher frequency determined by the stiffness of the 'coupling' mechanics relative to the stiffness of the two indivudual oscillators. I.e. the higher the stiffness of the coupling then the higher the anti-phase frequency (which makes intuitive sense as well as mathematical).

 

On the other hand the stiffer the coupling between the two is then the more likely the two will go in phase rather than out of phase. E.g. imagine a solid coupling between the two - the two reeds can (for practical purposes) only move in phase. and the higher frequency eigen frequency will be at an very high frequency but at a very low amplitude.

 

However whatever the combination of Eigen modes that establishes, both reeds will be doing the same thing.

 

Unfortunately I have no idea how rigid the coupling between two reeds in a single chamber is relative to the spring of the reeds themselves (but I'd imagine quite weak). All this before we even start to take the chamber resonace into account.

 

Please feel free to disagree/discuss further, my physics degree was over 40 years ago and I've not used it since!

 

 

 

Edited September 3, 2020 by Clive Thorne

[alex_holden]

8 hours ago, Clive Thorne said:

Unfortunately I have no idea how rigid the coupling between two reeds in a single chamber is relative to the spring of the reeds themselves (but I'd imagine quite weak).

 

More so if they are clamped to the same metal plate, as with some of the earlier examples in this topic.

[Richard Mellish]

9 hours ago, Clive Thorne said:

 

Having refreshed myself on the net, as far as I can see, when they are in phase then the Eigen mode corresponds to resononance frequency of the two independent systems.

 

 

Can you point me to where you found that? It seems to me that each one experiences the same restoring force that it would when on its own, plus a force from the other one via the coupling. According to the phase of the additional force (which might depend on the nature of the coupling as well as the phase of the other oscillator), that surely makes the frequency either higher or lower.

 

9 hours ago, Clive Thorne said:

Please feel free to disagree/discuss further, my physics degree was over 40 years ago and I've not used it since!

 

Mine (two of them) were also that long ago. I have made some use of them but not much.

 

However we are indulging in significant thread drift here.

[Clive Thorne]

14 hours ago, Richard Mellish said:

 

Can you point me to where you found that? It seems to me that each one experiences the same restoring force that it would when on its own, plus a force from the other one via the coupling. According to the phase of the additional force (which might depend on the nature of the coupling as well as the phase of the other oscillator), that surely makes the frequency either higher or lower.

 

 

Mine (two of them) were also that long ago. I have made some use of them but not much.

 

However we are indulging in significant thread drift here.

 

I would have thought that if the two reeds are in phase then the affect of any coupling would be cancelled out, any spring coupling between the two would effectively not be compressed. Yes you have twice the restoring force, but also twice the mass, effectively behaving like one large reed. However this is intuition, which can be very misleading (unless it's a woman's of course).

 

Obviously this assumes that the two have the same identical natural frequency in the first place. If the two frequencies are different enough for a phase lock not to occur (which I guess depends on the strength of the coupling),  then the whole thing becomes more complicated and beyond my understanding (and to be honest, beyond my level of interest!!).