An engineer's explanation of AGR and Weighted Valve Caps
Hi everyone,
I've been seeing a lot about the AGR and how different valve caps can affect the response of an instrument.
I'm going to try an explain from an engineer's perspective, what is going on when these devices are being used.
As you read through the following explanation, please keep in mind the following two points:
1. These devices absolutely make a difference to the sound and feel of the instrument - there are no doubts about that (I will explain why)
2. Whether these changes are positive/negative, or noticeable/negligible to the player or audience is SUBJECTIVE and depends on the player and the audience (very important to remember at the end).
I'll start by describing a guitar amp:
1. A "pick up" on the guitar converts the pluck of a guitar string into a small electrical signal.
2. This small electrical signal is passed through a "filter" - a configuration of resistors, inductors and capacitors which does "SOMETHING" to the signal, to produce an output signal.
3. This output electrical signal is passed to a speaker to convert the electric signal into sound.
On many amps there are knobs that lets you manipulate the characteristics (timbre) of the output ("EQ" knobs).
These knobs changes the amount of resistance, inductance and capacitance at various points of the filter circuit.
You can boost or kill the bass, or the treble or the higher frequency stuff.
Electrical energy passing through wires in a circuit is similar to kinetic energy passing through air in the euphonium.
Both cases we have energy waves travelling through a medium.
Electrical Resistance, inductance and capacitance all have acoustic equivalents:
Air resistance, air mass, compliance/stiffness are the acoustic counterparts (mechanical counterparts too).
The AGR changes the amount of air mass right after the input of the filter (i.e. a variable inductor knob).
Different weights changes the characteristics of the wall that surrounds the air by changing the amount of energy that is lost at various points of the circuit. (i.e. EQ knobs).
So just like an electric amplifier, you can't fiddle around with the EQ knobs (i.e. gadgets on our euphonium) and not expect a change to the characteristics of the output (i.e. they all do SOMETHING).
We're now onto the subjective part of my piece:
1. The air column actually extends into our mouths, so we can override some of the hardware changes to create our signature sound. This may lead some people to think that they are working harder to get the same result (i.e. "this does nothing").
2. These gadgets may not deliver an outcome that is desirable. Too much weight makes the instrument sound dull, and difficult to play. Too little weight and you can't centre a note so it's hard to play in tune.
3. In acoustic filters, you always have to make compromises - every desirable outcome will introduce something negative for you to put up with.
If your euphonium comes with knobs, you have to use them. Even the default setting is a setting.
If your euphonium doesn't come with knobs, and you would like to buy one:
1. The knob may not work in the way you want it to.
2. The knob may deliver what you want, but you pay for it in other ways so ultimate you may choose it's not worth it.
3. You get exactly what you want out of a knob.
You do need a level of vision and knowledge to take a set of valve caps, and work out which configuration suits you the best, and what trade offs you're willing to put up with. When you buy a set, and realises that you prefer the factory defaults, you haven't wasted money. You've bought the knowledge that they're not for you. You also have the option to use them, should you ever change your mind.
Here's the thing:
How you set up your euphonium (valve caps, AGR) is just the start, what about mouthpieces?
A "free" mouthpiece like the 4AL can help you play a stiff horn with all the heavy caps on.
A "stiff" mouthpiece like a 5G megatone might help you tame a free horn like a 967 with no heavy caps.
There are so many variables available, we really need to know what we want to feel and hear when trying out these gadgets, and then it's a lot of trial and error.
For many people, the best option would be to let the instrument designers make those choices.
Regards,
Ted
Ted
Besson Prestige BE2052-8G-0 Euphonium
Besson Sovereign 956 Baritone