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[robotmay]

Having some time off from work at the moment, I finally decided to spend half an hour widening the air hole on an old A/D Maugein box. That was a reasonable success (though I might now need to repad the air paddle if it doesn't bed back in properly), but in doing so I got to see the bass mechanism in this box for the first time. I suspect it's nothing special to those on here who tune melodeons, but I hadn't seen one like this before and I dunno if there's a proper name for how this works, so I'm not sure if it has been posted before.

Commence the images!

The mechanism


Pressing a bass button lifts a bass pallet and another pallet shared with the chord:


Pressing a chord button lifts both chord pallets:


The rather agricultural blocks (with terrible tiny airhole pre-enlarging):




Anyway, something interesting came out of a rather mundane task I'd been putting off for a while

[Lester]

V similar to the bass mech in my old Castagnari Tommy

[robotmay]

Ooh, that's interesting. I did wonder if this mechanism was the reason for this box being disproportionally large for a 2-voice 2-row, but clearly that's just exuberance on the part of Maugein if the same system fits into such a tiny box

[Theo]

It's a system you are more likely to see on compact boxes because it is the way that the tonic reed or reeds are shared between bass and chord.  Preciosa has something similar.

[robotmay]

I think I came across a mention of it in relation to the Tommy or Lilly in the past but I hadn't actually seen it. From what I can see this Maugein has 4 reeds for both bass and chords due to this system, which might explain why they're so meaty (and where the air goes).

[Lester]

I think I came across a mention of it in relation to the Tommy or Lilly in the past but I hadn't actually seen it. From what I can see this Maugein has 4 reeds for both bass and chords due to this system, which might explain why they're so meaty (and where the air goes).

The current Lilly shares a reed between the bass and the chord but not by clever linkages but by having two separate holes o=in the soundboard for one reed, one opened by the bass pallet and one by the chord pallet but both sounding the same reed.

[Theo]

The current Lilly shares a reed between the bass and the chord but not by clever linkages but by having two separate holes o=in the soundboard for one reed, one opened by the bass pallet and one by the chord pallet but both sounding the same reed.

It is clever, but has a side effect that is not universally admired: it is not possible to get the shared reed perfectly in tune in both bass and chord. 

[Steve_freereeder]

It is clever, but has a side effect that is not universally admired: it is not possible to get the shared reed perfectly in tune in both bass and chord.

Why not?

The shared reed serves as both the root (tonic) of the chord and the upper octave of the associated bass note.

E.g. for a left-hand push G bass/chord of a Tommy/Lily, the bass fundamental is G2 and the upper bass note G4. The latter is the shared reed with the G chord. Both these reeds can be tuned in perfect 2-octave unison (0 cents offset from ET).*

The remaining reeds are for the chord only: D4 (the fifth) and B3 (the third). These are on separate reed plates and can be tuned independently of each other, hence the D4 can be tuned slightly sharp if desired, to give a beatless perfect fifth and the B3 can be tuned flat if desired, to give a sweeter major third or can even be taped off altogether to remove the third entirely.

The same situation holds for all the other push/pull reeds on the LH side.

* In practice I've tuned the low bass fundamental slightly sharp (+1 to +2 cents)  to compensate for the flatness of the transient start-up of the big reeds. So the set-up of the bass mechanism allows me to do that too.

[Theo]

The problem is that the pitch of the shared reed is different depending on which pallet opens.  I'm not sure why - I think it's because the two "tunnels are considerable different in size and shape.

[benammiswift]

My dads l'imaginiere has bass action almost identical to that but the same idea with shared pallets

[Steve_freereeder]

The problem is that the pitch of the shared reed is different depending on which pallet opens.  I'm not sure why - I think it's because the two "tunnels are considerable different in size and shape.

But on a modern Tommy/Lily at least, the shared reed block chamber ('tunnel') is a constant shape/volume for each reed plate. There are two pallet vent openings at the end of the chamber, one for half of the bass pallet, the other (a similar size) for the portion of the 'L'-shaped chord pallet. So the three possible open combinations are:

- bass pallet vent open, chord pallet vent closed
- chord pallet vent open, bass pallet vent closed
- both pallet vents open

I can see why there might be a very small difference in pitch due to 'end correction' effects*, depending on which combination of pallets are open or closed, but to be honest, I've never found it makes a noticeable difference to the perceived pitch during normal playing. Perhaps this is due to the overall acoustic coupling effect of the adjacent low bass fundamental reed 'pulling' the shared reed into line, and hence minimising any possible end correction anomalies.

I think corroboration of this is demonstrated by taping off the thirds in the chords to make the tuning easier to hear. So long as the tonic, fifth and bass fundamental reeds are properly tuned, to my ears the LH end sounds perfectly fine regardless of whether one is playing chords only, bass only, or bass and chords together. At least - this is my experience based on the few Tommys and a Lily I've worked on. You've now got me wondering. I don't have one to hand to try out at the moment, but I will have one coming in in a couple of weeks, so I will tune and check, and report back.


* 'End correction' strictly speaking refers to the position of the anti-nodes of a standing wave in an air column in an open tube such as a wind instrument or an organ pipe. The last anti-node is located just outside the end of the pipe and the pitch of the note produced can be affected by partially introducing an obstacle close to the end of the pipe. This is why a wah-wah trumpet mute is able to vary the pitch according to the position of the player's hand.

In a free reed instrument, the pitch is not dependant on standing waves set up in the reed block chamber, although it can be modified by the size/shape of the chamber to a certain extent. But we know empirically that the pitch can be affected (flattened) by a pallet or valve not opening fully. So perhaps we should more correctly refer to this flattening effect as a pallet/valve 'proximity effect'?   

[Theo]

Thanks for the mini lecture Steve!


My point was completely non-theoretical.  I have always found that on the basses in question I have to make a compromise in the pitch of the shared tonic reed because it sounds a slightly different pitch when played through the bass pallet compared with the chord pallet.

[Steve_freereeder]

Thanks for the mini lecture Steve!

Sorry - I do tend to get carried away sometimes! However, perhaps other people find my musings useful. 

...I have to make a compromise in the pitch of the shared tonic reed because it sounds a slightly different pitch when played through the bass pallet compared with the chord pallet.

That's what I wanted to know! Have you got any numbers to hand of what sort of differences you've found? Also, is there the same sort of difference depending whether it is a push reed or a pull reed?

Just to reiterate my own experience: I've not noticed this difference, but perhaps I'm not listening properly. I'll try again in a couple of weeks.

[robotmay]

Speaking of tuning, I really need to get this box tuned at some point; it actually has a really nice tone. I was going to wait until I've tried tuning a few practice boxes first then give it a go myself, but I don't want to ruin the nice old reeds in this thing, so I suspect it'll be a job for someone else when I have some spare cash

On the plus-side the air hole improvement has made it much easier to play! It was like sucking air through a straw, before.

[Kimric Smythe]

I have seen something like this, perhaps on a old Miller I worked on. As Theo mentioned it would be possible to get some tone shift when sounding through different hols due to internal resonance and turbulence.

 As far as opening air holes , you can get a impressive increase in flow by just chamfering the hole on either side. This cuts way down on turbulence which causes quite a bit of resistance on high speed flow.