Rotar valve noise, Venturi and recording bells.

[2ba4t]

I am a shy new member. I have three questions:

1) Noisey Rotary valves:
I have tried overhauling a few rotary tubas and find the valves which are noisey impossible to really fix. Obviously I have replaced the bumpers with very soft material (softer that neoprene), oiled all linkages and greased with the heaviest copper motor grease all the mini-ball joints, and used a medium oil on the rest. The source seems the ball-joints within the linkage ball and sockets at the arm's tips. These rock and clank before actually operating as you first press the paddle. If you tighten them too much the valve sticks. Even, as above, heavy grease does not help. HEELP. I am a piston valve man.
2) The real importance of the 'Venturi' effect.
Venturi was a 17th dude who discovered that a narrowing pipe creates more pressure on the water passing through and therefore more speed. With us that means that the molecules in the column of air in the instrument, which the sound wave from our buzz is passing through, jolt into each other more rapidly. A sound wave is simply like a subway train - when someone jumps in at one end all the crowded standing passengers jolt forward and then backwards when the guy at the other end is slammed against the door and bounces back. Do very small differences in the inner bore REALLY make such a difference? Do instruments with a perfect inner consistent bore really sound better. After all almost every mouthpiece does not perfectly butt up against the inner receiver's edge. Also every inner, moving tuning slide cannot be the same bore as it's receiver. IS THIS ALL FAKE NEWS?
3) Do guys out there have any hard experience or evidence about the difference made by recording/sousa or 45 degree bells. Do they coarsen the sound? I cannot understand why every tuba is not built with one but then I am a noisey barbarian.

Thanks all.

2ba4t

[Lectron]

The venturi.....or a venturi, can help overcome the negative effects caused by the step-up after the MPC (increased volum->lower speed) and get a better airflow, but really. You tuoch on so many aspects that it is not easy to give an answer.

But yes. Differences in inner bore and % taper makes differences.

I have a small mod. with an AGR followed by a venturi on several of my tubas, and it has opened up the low register. Made it easier accesable. Less kick-back

[TheGoyWonder]

Recording bell will always sound different because it is directed toward a further wall, full of nice corners and angles and with plenty of sound diffracting and attenuating objects in the room too. Will always sound better than playing pointblank into the ceiling.

Rotary valve noise is all about freeplay - sounds like you found it already. Hopefully you can replace those sockets.

Leadpipe venturi would be a fascinating subject. The one place you routinely see a leadpipe venturi is on sousaphone bits, which taper the wrong way compared to the rest of the leadpipe. A practical leadpipe venturi would probably be much less dramatic than the sousaphone bit which tapers down to under .500" ID (why nobody made alternative sousaphone bits that don't do this is whole nother question)

[Donn]

I have a small mod. with an AGR followed by a venturi on several of my tubas, and it has opened up the low register.

What does that procedure involve, physically - do you constrict the leadpipe right after the receiver?

Some tuba receivers have no gap to speak of, and some slight Venturi as the narrowing receiver transitions to the expanding leadpipe, true? But normally too slight to be of much consequence?

One confounding factor with forward facing bells, is that they often have wider flare. I guess if forward facing bells have a coarser sound, the wider flare compensates for that.

[Tom]

Rotary Valves:

The parts you have your tuba may just be plain 'ol worn out.

There several moving parts in a rotary valve linkage system as well as several "wear items" to be aware of. The minibal links may just be worn out from lots of use and metal-on-metal contact. The screw holding the minibal to the stop arm could be loose or worn causing clicking. The minibals may not be tight on the rod arms. Your tuba may be the type with a "T" joint in it that can wear and make noise. Your tuba also might be the type that has nylon bushings in the linkage system - those could be worn or missing. Or, you could be hearing play in the rotors themselves moving vertically up and down in the casing, bumping into the top and bottom plates. In other words, there are many possible issues and we won't really know enough about your tuba to say more definitively what the noise issue is.

I would not, however, use heavy grease on the linkage parts nor would I use really soft bumpers but that isn't directly related to the noise. Grease is messy and can turn sticky or dry out - I would not want that on my linkage. Really soft bumpers allow for a lot of bounce and can also impact valve alignment. Try real neoprene, hard rubber (like vacuum belt or thick o-ring), or cork instead.

Venturi:

It matters, but pinpointing exactly what/where/when/why is virtually impossible to define. You touch on leadpipe, receiver, mouthpiece gap and even bore size. They all matter individually, but since they are impossible to individually isolate, the important part is how well to they all work together on a given design. There is no such thing as a "perfect inner consistent bore" on a tuba, unless you mean specifically valve bores. But again, you cannot isolate only the valve bore from the rest of the instrument, so the whole design has to work together to be a good instrument.

I have no applicable experience with recording bells aside from trying a few out for fun here and there. Certainly not enough experience or insight to make any comment even remotely worthwhile.

[pjv]

About the front bell;
Horn players have always played on an instrument with a bent bell. It works for them. In other words the concept of a bent bell has a champion in the horn world.

The front bell gives a lot of options to the player allowing them to choose the best place to direct their sound. It's not just front or nothing. I hold my tuba at about an 80 degree angle. By turning a front bell to the right it ends up facing the ceiling, also at about an 80 degree angle, giving it the upright bell type of projection.

I once did a recording and faced the bell backwards. This way I could see the other players and avoid bleeding into their mics. I also did this once in bass-boomy hall, pointing the bell into the drapes. Made a huge positive difference.

The succes of a front bell is dependent upon how well the instrument was manufactured in the first place, how well it was designed, and how well the bell seals.

[Erik_Sweden]

Venturi: when flowing through a pipe diameter reduction speed increase and pressure decrease (constant energy)

[roweenie]

After about 45 minutes (based on my chops) I realized that I was blowing my brains out. I was plenty loud, but (ref: recording bell) I couldn't hear much of what I was doing, and the sound was bouncing off the people (along the wall far) who were chatting their heads off while sampling/voting-on gumbos.

This is the (IMO) #1 issue (from a player's POV) with a recording bell - less feedback to the player than normally expected. For me, it's a matter of trusting that your sound is carrying to the audience (which it is!)....

Once you get the hang of it (mostly overcoming your own sonic expectations), it is actually a great labor-saver. I just wish I could use one for more than just trad jazz gigs....

roweenie "spreading the Gospel of recording bell tubas"

[Donn]

I just wish I could use one for more than just trad jazz gigs....

What other music would you like to play?

[roweenie]

I just wish I could use one for more than just trad jazz gigs....

What other music would you like to play?

I already play all different kinds of music I'd like to bring a recording bell horn to all of it (and not create a crisis)

[Donn]

So bring it.

[pjv]

I'm not sure about why some players feel like they are getting less reference from a front bell. We listen to music with our faces (and ears) pointing towards the sound source, not the top of heads (right?).

Maybe players have this because they are used to every bodies sound being around them but their own sound being above them. I've also always played trombone and the trombone bell is also fwd, so I've never noticed this.

But as others have already mentioned it's important to hear ones sound in the room; focus your ears on whats far away as well as close up.

I've never played trad jazz but have often used a front bell in; modern music, jazz bands, pop bands, brass quintet, recordings, etc. I'm not part of the orchestra scene but if I was I would probably try it there as well. You would always have control over where the sound is best, especially since some works might benefit from a bell adjustment. Just turning the bell only 1 inch can make a big difference. And as I mentioned, the bell can point up as well.

[Donn]

I'm not sure about why some players feel like they are getting less reference from a front bell. We listen to music with our faces (and ears) pointing towards the sound source, not the top of heads (right?).

Maybe players have this because they are used to every bodies sound being around them but their own sound being above them. I've also always played trombone and the trombone bell is also fwd, so I've never noticed this.

I've fooled around a little with a trombone - but never played one with an upright bell, so lack any basis for comparison. With the forward bell on a tuba, I don't just "feel like" I can't hear as well, I know that for a fact.

But I'm not sure I can account for the reason. It seems to me that, on my own tuba anyway, which is a big bell front Holton, the 24" bell flare is wider than a normal upright bell, and the bend brings it a little closer to my ears. But I could be wrong, maybe someone with both bells could make a more detailed comparison of the geometry. Confounding factors might include that this tuba has a relatively dark sound, and indoors I may get less reflection from surfaces in front of me than I would from the ceiling. I believe my sousaphone is also harder for me to hear well, than my helicons were. Naturally the sousaphone has a much wider bell flare, so I expect the sousaphone's sound is dispersed over a wider angle towards the front, but the acoustic "shadow" is deeper right in back.

[Lectron]

I have a small mod. with an AGR followed by a venturi on several of my tubas, and it has opened up the low register.

What does that procedure involve, physically - do you constrict the leadpipe right after the receiver?

The venturi would be straight after the mouthpiece, and the gap used (preferred) is pretty close to a minimum.
It would also just be a small constriction, just enough to increase the speed a little and then an even taper up to the leadpipe.
The start diameter is the same as the inner diameter of the backbore end.

This does, from experience (nothing I care to discuss very much), DECREASE the impedance and kickback,
especially in the lower register and gives a more overall even impedance.

So..it is not about gaps and venturi etc, but having the equivalent "interface" work more like an "ideal" system

[swillafew]

The recording bell was made for the same reason as the name: recording. One microphone used to record straight to the finished product for the whole ensemble. If you shop a new instrument today, pick your favorite three brands, look at their catalogues, and count how many of the best models have a recording bell. You could amuse yourself by going back through old catalogues and seeing how far back you need to go find one for sale.

If you want to sell new ones next year, I am guessing that the cost of it, and the cost of a usable case, will not be viable.

[2ba4t]

Thank you to all you wonderful tubapeople. I have learnt a lot. It is a pity the world is not populated only by tubists. Another question. I am amazed and puzzled how the lefreque acoustic plates work. Do they? Any solid scientific evidence beside the Valencia single piece of research?