Using wool felt for baffles?

[Jason]

I was wondering if wool felt for baffles would be a good choice to mellow the sound of a concertina? It would look pretty too. Would it be breathable enough or would it need a standoff like leather? Thoughts? 

Edited March 2, 2023 by Jason

[d.elliott]

sounds like a lot of free fibres and a potential choke on airflow to me. 

[ttonon]

Hi Jason,

 

What do you mean by "mellow" the sound?  My guess is that you mean less harsh, which often translates to a reduction in higher overtones.  If that's the case, I don't think it would do that because felt would likely attenuate most all the overtones, resulting in only a reduction in volume.  

 

In some full size accordions, makers invented what they call a "cassotto," which is a 5-sided box, or slot, or chamber, in which the pallets are mounted.  This acoustic feature is fairly effective at mellowing the tone for much of the pitch range of the instrument.  It's most effective on the lower notes, because of their frequency relation to the dimensions of the chamber, and I don't think such a device can be effective the entire pitch range.  It's used by most jazz players in the States, who describe the sound as "ballsy." 

 

I suppose it's possible to build such a thing for a concertina.  Good luck!

 

Regards,

Tom

www.bluesbox.biz

[March Hare]

Hello Jason,

 

I think the felt is worth trying.  I have glued a layer of thin felt (ordinary craft felt, probably polyester rather than wool) to the inside of the fretwork on lots of concertinas.  It works for me, reducing the high overtones and taking the edge off the sound.  I just brush a few small smears of weak pva on the inside, no stand-offs, to cover the holes.  In my experience it doesn’t shed fibres or choke the airflow, and it pulls off easily leaving negligible residue.

 

When I sing with concertina accompaniment the felt helps my words to come across, and I feel that the instrument is supporting my voice not getting in the way.

 

I think that this is the result of a lucky coincidence: thin felt absorbs sound noticeably above about 1000Hz but not much below that frequency.  Human hearing is much more sensitive in the range from roughly 1000Hz to around 3000Hz which is (naturally) the range needed to hear the consonants in our speech, particularly T, S, K, D etc which enable us to understand what is said.  So the felt baffle helps to prevent the high frequencies from the reeds from covering up the words of the song.  As the listeners’ hearing is sensitive in that range the accompaniment sounds less intrusive (although the loudness measured by a meter would probably not show much difference, as the thin felt has little effect on the fundamental notes of the music).

 

This is my rough and ready theory - the only way to find out if it works for you and your instrument is to try it.

 

Some years back on the forum there was a post from Wim Wakker, saying that Edeophones had mahogany innards which reduced the high overtones to mellow the sound.  My favourite concertina to sing with is an Edeophone and I have never wanted to add any sort of baffle.  Also a New Model tenor with mahogany structure - same applies.

 

Hope this helps.

 

[ttonon]

March, I agree with what you say.  My own response didn't consider the frequency response of absorption, and you got it better.  In fact, I attach a figure showing how the sound absorption of felt increases with increasing frequency.  The three curves shown are for different thicknesses (4, 8, 10 mm) and densities (76, 116, 148 kg/m^3).  Here's the source:

https://www.researchgate.net/publication/321858922_Improvement_of_the_sound_absorption_performance_of_jute_felt-based_sound_absorbers_using_micro-perforated_panels/figures?lo=1

 

Best regards,

Tom

[David Lay]

I have designed theaters and auditoriums (auditoria?).  The acoustitians always had us apply dense but soft material to walls from which undesirable reflections could bounce.  The soft material (usually fiberglass board) cut reflections both at the surface and by attenuating any pass-through reflections that made it to the back-up wall.  Lower frequencies always caused problems for adjacent spaces rather than for an audience.  A heavy separating wall (mass) was the only way to mitigate that.  Soft materials will definitely change the sound of a concertina wherever they are placed inside.  Wood choices will also change the sound with their different densities.  That mahogany might have resulted in a different sound in-part because mahogany typically has open pores.  The pores possibly provide small chambers into which higher frequency waves enter and die rather than reflect.  I suspect that the effect is subtle, however.  (Based upon this principle, concrete masonry blocks are available with openings and internal chambers to be used for sound attenuation.)

[ttonon]

2 hours ago, David Lay said:

Wood choices will also change the sound with their different densities.  That mahogany might have resulted in a different sound in-part because mahogany typically has open pores.  The pores possibly provide small chambers into which higher frequency waves enter and die rather than reflect.  I suspect that the effect is subtle, however.  (Based upon this principle, concrete masonry blocks are available with openings and internal chambers to be used for sound attenuation.)

Hi David, the effect I believe would be too subtle to notice.  For sound attenuation within pores or cavities, the sound must cause air vibrations so that frictional (viscous) work is done in the boundary layers, and for that to happen, the dimensions of the cavity must be not too far different from the wavelength of the sound.  So with wood, the depth of the pores is so small only extremely high frequencies would be affected.  The table below shows that wood offers very little attenuation at the higher frequencies. 

 

I also have doubts that the effect of wood density would have much effect on impinging sound waves.  It could have an effect on the vibration of the tongue, but not much effect on impinging sound waves for the reasons I explain above.  If the wood structure vibrates from the pressure oscillations in the sound, that could cause some attenuation, because that vibration will cause viscous dissipation (friction) that absorbs the sound energy, though this is likely to occur only for the lowest frequencies that couple with a resonant frequency of the wood structure as a whole. And there, wood density could have an effect, but only to help determine the particular low frequencies the structure vibrates at.

 

The table below shows this effect, wherein the absorption coefficient for wood is much higher at the lowest frequencies, presumably because a region of the wood is set to vibrate. 

[Devils' Dream]

IMO experience felt cotton and such fibers with lint are a BAD idea. It will end up in your reeds and valves. Maybe maybe a very hard felt.  Better and what is most often used to mellow melodeon tone is fairly dense linen. Or some synthetics. 

[ttonon]

Hi Devil, if that's the case, maybe a fibrous plastic that doesn't shed would be useful, such as the one side of Velcro strips, which seems like a dense cluster of fibers that offer much surface area on which viscous forces can act, as with felt.

 

Best regards,

Tom

[David Lay]

20 hours ago, ttonon said:

Hi David, the effect I believe would be too subtle to notice.  For sound attenuation within pores or cavities, the sound must cause air vibrations so that frictional (viscous) work is done in the boundary layers, and for that to happen, the dimensions of the cavity must be not too far different from the wavelength of the sound.  So with wood, the depth of the pores is so small only extremely high frequencies would be affected.  The table below shows that wood offers very little attenuation at the higher frequencies. 

 

I also have doubts that the effect of wood density would have much effect on impinging sound waves.  It could have an effect on the vibration of the tongue, but not much effect on impinging sound waves for the reasons I explain above.  If the wood structure vibrates from the pressure oscillations in the sound, that could cause some attenuation, because that vibration will cause viscous dissipation (friction) that absorbs the sound energy, though this is likely to occur only for the lowest frequencies that couple with a resonant frequency of the wood structure as a whole. And there, wood density could have an effect, but only to help determine the particular low frequencies the structure vibrates at.

 

The table below shows this effect, wherein the absorption coefficient for wood is much higher at the lowest frequencies, presumably because a region of the wood is set to vibrate. 

I agree that the pores are too small.  This chart shows that even a B6 has a wavelength of about 6".

[ttonon]

4 hours ago, David Lay said:

I agree that the pores are too small.  This chart shows that even a B6 has a wavelength of about 6".

 

Well, how big is a pore?  If around 0.1 mm, that would give a frequency of the order of a couple million Hertz!  I don't think even dogs can hear those.

Tom

[4to5to6]

I sometimes love practicing late at night so tried to subdue my metal ended TT by gluing in some felt to inside of one end as an experiment. 

 

It didn't work.  I could barley tell any difference from the baffled end and the open end.  Very, very minor change in tone but no reduction in volume.

 

I would love to find an easy solution.  I've attached a photo of the experiment.

 

This was using about 1.5mm thick and dense felt.

 

Please help!

 

Edited August 11, 2023 by 4to5to6

[Cornishman]

In an ideal world - that could even be possible in this world of accessible 3d printing - you would create a thin ducting 'plate' to attach to the endplate. This donut of ducting would fold over itself a number of times (thereby lengthening the sound travel) with the inner duct padded with absorptive foam. You would need to leave a channel for proper airflow, and the sound reduction would still occur. If a thin hexagon (or whatever shape your end plate is) with a section in the middle for buttons, was placed over the end plate openings on either side, this would presumably do the job quite well. I doubt there would be room to do this internally.

 

A 'Concertenuator' perhaps....!

 

 

[ttonon]

Cornishman, you seem to have great powers of imagination. Have you done any calculations on the required length for such a passage?  My guess is that it would be far longer than your outstretched arms. Can you imagine that?

 

And that would do nothing for the sound that escapes through the walls of the bellows.

 

It would be far easier to put yourself in a closet and close the door. Preferably a closet that's stuffed with clothing on hangers.  But of course, in this heat wave, you'd better bring in an air conditioner that exhaust hot air to the larger room.  And then the sound of the running air conditioner would cause you to hear the concertina less. Oh I see, you want others not to hear the concertina.  O well, just one more brilliant idea shot down. 😄

 

Best regards,

Tom

www.bluesbox.biz 

[4to5to6]

In the very first concertinas they used wood and leather baffles as most know.  I’m no expert but constantly studying and learning…. I understand that these baffles were not there to keep the volume low but to omit certain harmonic overtones or inharmonicitys.  Unlike wood and string instruments where the harmonics / overtones are perfect pleasant intervals to the fundamental, free reeds generate certain inharmonic overtones that are out of tune and clash with the fundamental sounding terrible.  The baffles mute these overtones making the fundamental fuller, richer and stronger, one of the many interesting design feature unique to free reeds.  When tuning the reed, certain techniques are used to eliminate these overtones but they mostly eliminated by the design of the instrument.

 

I am personally searching for a way to reduce sound volume.  I am thinking of building new ends similar to the original 6-sided Aeolas with “dot and comma” openings.

 

Edited August 11, 2023 by 4to5to6

[ttonon]

2 hours ago, 4to5to6 said:

free reeds generate inharmonic overtones that are out of tune and clash with the fundamental sounding terrible.

This is not correct. The tone of a free reed contains exact harmonics (exact multiples of two), like that from any other instrument that plays sustained tones, such as the violin, woodwinds, and brasses.  Different are the instruments that play tones generated by transients, such as the piano, guitar, xylophone, bells, etc., and their tones contain overtones that are not harmonics. That's what makes the musical tones of these latter instruments interesting, particularly when multiple tones speak.

 

The fact that the tone is sustained over multiple cycles of vibration requires that the harmonic series occurs, otherwise periodicity would not exist. You cannot have a sustained tone without exact periodicity of all its components. That would be a contradiction.

 

Woodwinds and brasses interestingly differ from the free reed in that their vibrating air columns have the ability to generate overtones that are not pure harmonics, but the frequencies at which those overtones (their peaks) occur in the sustained musical tone, which involves other overtones, differ from the frequencies at which the peaks occur. You can generate a tone by exciting only one of these overtones by some artificial means (not by a player's mouth), in which case, the peak of the overtone frequency will appear. But when that overtone is in concert with others in a regime of oscillation (single tone) from the instrument, those overtones often vibrate away from their peaks, at the frequency that corresponds to the harmonic series. In fact, with some instruments such as the trumpet, some overtones contribute only a fraction of their peak amplitude to the musical tone, depending on the note being played.

 

With minor exception, only the fundamental transverse vibrational mode of the free reed tongue generates the musical tone. The overtones of the tongue vibration can be sometimes measured by sensitive instruments. It's not clear however how much they can be heard. Even the first torsional mode of tongue vibration can sometimes be measured in the musical tone during the start transient. But it quickly disappears during the steady state (periodic) tone.

 

The overwhelming steady state tone from a free reed is the result of the ear/brain system's ability to break a periodic sound into its Fourier components. Or at least, that's how we understand it. This ability is remarkable and mysterious, and it's connected to the magical way mathematics can provide an accurate description of physical phenomenon.

 

Even if such inharmonicity would occur in a concertina, it would be neigh impossible to filter it out by means of passive filters.

 

Best regards,

Tom

[Paul_Hardy]

8 hours ago, 4to5to6 said:

I am personally searching for a way to reduce sound volume.

 

Someone previously suggested using a pair of thick trousers - put your arms up the leg holes and the concertina in the groin area, and cinch the belt tight!

[4to5to6]

Here’s an interesting topic I was involved in about 7 years ago:

 

 

Without getting over complicated, I am just trying to simply answer the OP:

 

On 3/2/2023 at 6:57 AM, Jason said:

I was wondering if wool felt for baffles would be a good choice to mellow the sound of a concertina? It would look pretty too. Would it be breathable enough or would it need a standoff like leather? Thoughts? 

Two days ago I tried to install felt in my metal ended tenor treble Aeola as a quick fun experiment to reduce its volume and found there was really very little difference from the side with felt and the side without except a tiny mellowing of some harmonics but no discernible change in volume.  Breathing through the felt was no problem even though it was glued directly to the metal with no holes.
 

I have two very early treble Wheatstones, 

1856 - leather baffles

1852 - wood baffles, possibly Sitka spruce

 

Both have the baffles mounted on stand offs. The wood one can easily be removed while the leather one is permanent.  The one with the wood baffles is still in old pitch and looks wonderful but doesn’t really sound that great to me even though I’ve done a lot of work to it (labour of love ting) It’s more of a collector piece with it’s beautiful amboyna ends.
 

On the other hand, the 1856 with leather baffles is one of the best concertinas I have ever played and is a keeper for life.  it was my main player for years at home over many top period Aeolas until I started needing the extra low notes of a BT / TT.

 

The felt baffles brought back memories of my research years ago when first getting into reed tuning and then later reed design, reed scaling, slot drafts and tongue profiles, etc.etc. which I still struggle with.

 

I do strongly feel that the best concertinas as defined by their playability, tone, dynamics, etc. and mist of all musical expression, are the ones with a strong fundamental and pure fifth overtone and the entire instrument design takes into account eliminating inharmonicity overtones and balance between high and low notes.
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