[CAUT] Dampp Chaser with bottom & Edwards String Cover

[Andrew Anderson]

Fred,
Down here in Laredo, humidity is quite an issue.  In the larger 
institutions they use chilled water to condition the air coming into 
the buildings and during the air conditioning season (quite long 
here) I rarely measure humidity under 70%.  I occasionally measure 
humidity over 80%.

In residences with regular air conditioning the humidity will 
sometimes drop to 45%.  In winter we occasionally get drops into the 
mid thirties when a "cold" front passes down through.  Otherwise the 
humidity is usually in the fifties and higher in homes.

This has quite an impact on tuning stability as they call me at the 
least opportune times.  I tune in the fall when relative humidity is 
in the seventies and then in January when it is generally in the 
fourties.  Opposing pitch corrections each time...

I've been pushing humidity control and string-covers.  The community 
college went for humidity control and it has made a big difference on 
their S&S D and the rest of their piano stock.  Their tuning fees 
went down too.

Here in our studio we have several Sauter Grands and a refurbished 
Everett Concert Grand.  Sauters are quite stabile when compared to 
the Chinese pianos (weather yo-yos) in the studio but they do move 
with the weather.  I put a full DC system with undercover and Edwards 
string-cover on the Sauter Delta and tuned it up about a week 
afterwards.  Six months later I could barely detect any unison 
drift.  I've put a full system on the Everett with undercover and 
string-cover and I think I might be able to get a stabile action 
regulation in it now.  Tuning-wise, it was not entirely stabile with 
the DC system alone with undercover.  The addition of the 
string-cover has made quite a difference.

Adding a string-cover is not without sonic consequences.  Think of 
the sound you hear 15 to 20 feet away from the piano as compared to 
what you hear right up close to it.  That is how I would describe the 
difference.  If the piano tends to be a little too brilliant, the 
addition of a string-cover generally will satisfy the pianist.  If it 
is quite mellow, you might have to add some bite.  Generally from a 
distance the difference was not obvious.  Its the really high 
partials that seem to be damped.  Basically duplex noise and other 
trash that no-one notices in the audience but annoys the **l! out of 
the pianist.

I've been quite satisfied with the results.  My wife records and it 
has reduced the need for tunings to something a little more manageable.

I recommend string-covers first and the addition of a DC system 
second.  String covers do keep things clean and condensation off of 
the strings.  Wool ones buffer humidity.  A DC system with a 
string-cover is much more effective.  I've lived with DC system only 
in several pianos  including another Sauter and compared to the 
covered one it was not as stabile.

YMMV
Andrew Anderson,



At 03:52 PM 6/9/2007, you wrote:
>On 6/7/07 5:13 PM, "Ron Nossaman" <rnossaman at cox.net> wrote:
> >
> > That was Darrell, and his premise was based on strings not
> > rendering through the bridge. An interesting thought though.
>
>Yes, an interesting thought as a component of what happens. But as I worked
>through it in my mind, the friction would eventually give way, strings would
>render, and you'd end up with the original tension, and a longer speaking
>length to boot (so you might even expect lower pitch). One would predict
>that one could manipulate the wire (push on it in the speaking length) to
>equalize the tension, and so strings that had gone sharp could be fairly
>easily made to get the string back to pitch. Or do it by vigorous pounding.
>Tried that and that, didn't happen.
>     Also, part of Darrell's thesis was to "prove" that bridge rise (caused
>by soundboard expansion - increase crown) couldn't account for pitch rise,
>using calculations. He came up with a calculated bridge rise of .5 inch to
>account for observed pitch change. There were typos, and, I think,
>miscalculations. I think the calculations based on the distance between
>tuning pin and hitch pin (based on changes in deflection) are far more
>reliable and closer to real life. My own empirical experiments showed that
>0.1 inch rise in string deflection would yield a pitch rise of 15 - 30
>cents.
> >
> > Nothing is simple or isolated, and this isn't a discussion on
> > every potential detail of why and how pianos go out of tune,
> > is it? My initial intention was to illustrate that string
> > stretch wasn't the likely primary reason for long term pitch
> > drop. I don't have authoritative details on everything that
> > happens in soundboards with moisture changes, and most likely
> > never will. I've picked up what I think are a few clues, and
> > reported why I think so. That's the best I can do.
> >
>Yes, I understand that. And your thoughts about bridges, bridge pins,
>angles, and so forth are excellent and make a whole lot of sense. I'm just
>balking at your more "absolute" seeming statements, like
> >"Hasn't it already been determined fairly reasonably that 
> soundboard rise, or
> >fall, isn't a significant (there's that word again - not absolute or
> >exclusive, even if measurable) factor in pitch change?"
>I'm perfectly willing to go along with a statement that probably bridge
>changes are actually more important than soundboard rise or fall, but I'm
>not willing to discard rise or fall as not being "significant" until I have
>seen that proved in some fashion. All right, "significant" is an inexact
>word, but your own calculations show that a .6 degree change in downbearing
>(soundboard rise/fall, perhaps) is equivalent to your measured and
>documented .2 mm expansion in bridge. Now, you say you have never measured
>more than .5 degree, but wouldn't that .5 degree change be "significant,"
>nearly as significant as the .2 mm bridge expansion? Maybe it is clear that
>the bridge contributes more than the soundboard, but the soundboard may
>still contribute a good bit. Could be 60/40. Or 70/30. I'd call the 40 or 30
>significant.
>     My experience tells me the grands at UNM with dry humidistat and a 50
>plus a 25 watt rods change pitch about half or less as much as those
>without. Lids are almost always up. Air is in constant motion from the HVAC
>system. I'm real skeptical that enough moisture is pulled from the bridges
>into and through the soundboard to overcome what is being absorbed into them
>from the air. Or that the heat from the rod raises the temperature of the
>bridges through convection enough to do the same. Maybe it's true, but my
>common sense notion is that most of what I am affecting with my rods and
>humidistat is the board.
> > When it rains outside, the humidity level in my house
> > increases even though the doors and windows are closed.
> > Dampp-Chasers are least effective when the lid is always wide
> > open, with no bottom cover, and most effective with a top and
> > bottom cover.
>Very true, and I a pretty well convinced by your writings that the reason DC
>systems work less well than expected often is that the bridges are exposed.
>I haven't got around to fooling with top covers yet. I have, so far, found
>bottom covers less effective than I would have liked to expect. Effective,
>but somewhat marginally in many cases. I'm wondering if I can work out a way
>to manufacture string covers using material similar to bottom covers without
>overmuch time and hassle. One of these days . . .
> >
> > Ron N
> >
>Thanks for your thoughts.
>Fred