French Horn/Valve Vacuum
Hi Alan, it's me again. I've noticed that in comparison to newer horns, the pop sound older horns make when valves are pulled out to check the interior vacuum is much softer. As long as they make a noticeable pop sound, does it matter how loud it is? Does a softer popping noise mean the horn should be avoided?
Thanks again for your time!
This is what you often see referred to as "valve compression". Basically how airtight the valves are, they do wear with age and also with neglect. It does depend on to some extent on whether there's oil in there - one way to test blow an old and leaky-seeming horn, to see how it blows if the valves were restored, is to take the valves out and coat them with thick oil, then replace. This can have magical effects! Of course you can't exactly use the valves that way though. But it tells you whether it's the valves that are the problem or whether there's a leaky joint somewhere.
I did see one US secondhand horn website where they had a way of measuring compression, and gave a figure to all their horns. Can't remember what site that was though... I suppose a simple comparison would be to pull out, say, the second F slide to its end, then push it in all the way and listen in the bell, see how many seconds the hissing sound lasts for.
Anyway, good valve compression is definitely a plus, but some older horns seem to blow ok although it the valves are not very tight. Some horns (notably Holtons) have tapered valves which bed down as they wear, so the compression stays good forever. My H104 still ahs very tight compression although I've played it non-stop for 20 years.
So I guess the answer is, blow the horn, if the compression is affecting it, it will feel a bit stuffier and less clear to blow. Particularly with more valves pressed. I suppose the test with the thick oil would be a good one to compare but I can't see many sellers allowing you to take the valves out ;-)