Dear forum members,
I need your helpful advice and information, namely from an experienced person on Kawai RX line.
I've been around with a problem on my Kawai Rx-3 (that i love) on the A1. I have a high frequency (twang) sound. This note is a double string and copper wound one. I tried different mitigation actions, by myself and with my tuner, and none provide the desired outcome.
However, now I'm pretty sure about what the problem itself is: It is a disruptive longitudinal harmonic mode. It is hard to support it and strongly constraints the playing.
For those that could be interested on the topic, you can find here (http://www.speech.kth.se/music/5_lectures/conklin/longitudinal.html) many examples of notes having this "issue". The modulation of this effect hardly depends on the string mass/string length.
I can find this effect in some other close notes but none is audible/bad as this one.
Having a detail look on the strings, I could conclude that this effect is shown in the notes that don't exactly have the same copper spinning length. On this particular note (A1) there is a gap of 3mm in the lengths of the copper spinning. Having a detailed look on the notes I consider as very good ones, both strings have exactly the same copper wond length. On the notes that have a slight disruptive l-mode (but acceptable), the copper wond length has a slight difference.
So I have the following questions:
1- If I could change the copper spinning length to the right one, should I expect the correction of this effect?
2- What is the correct copper spinning length for the Kawai RX-3 note A1?
3-From where can I get the Kawai RX-3 scale design?
4-If there is an excess of copper spinning in the A1, is there any known good technique do unwind and cut it?
5- I'm prepared to pay for the right sized strings. Which is the manufacturer for the Kawai and from where should I get them?
Now just to present my self, I'm a piano aficionado - player and mechanics -, I do my own tunings both on ETD and aural, and I have Msc on math and electronics, though I'm a strong believer of the technology in the piano (that's also why I have a Kawai), and .....in the tuning. I also believe that I should improve my English skills :-)
Best regards, ZeH

ZeH,

I don’t have answers, unfortunately, but I have a small Young Chang (Weber) and I could (actually wanted to) have posted exactly the same topic as yours (except that there are two notes with LM on my piano, F# and G). I also tought about changing the weight of the wrapping wire in relation to the weight of the core wire. Not sure it’s a good idea, however...

JMG

Where is the piano situated in the room? If it is close to the walls, as in a corner, this can occur. Move the piano(straight side) out from the wall a few inches. You may need to experiment a bit. This is the exact problem I had on my piano. A strange howl on A1. Moving it out from the wall 8 inches rectified this occurence.

Where is the piano situated in the room? If it is close to the walls, as in a corner, this can occur. Move the piano(straight side) out from the wall a few inches. You may need to experiment a bit. This is the exact problem I had on my piano. A strange howl on A1. Moving it out from the wall 8 inches rectified this occurence.

Hi Curry, the straight side is directly facing the wall and is 10-20in away from it - It is not paralel
tks, zeh

Pull it out more. Then you can at least rule out acoustics.

If you can see a 3 mm difference in the wound length of two strings on the same note you have a problem. Knowing which string is the offender (if not both) might be harder to determine. Check to make sure the strings are firmly seated and terminated at the bridge pins first.
Will your ETD analyze the string spectrally? This might help. Good string makers could make you a pair of strings(yes have a pair made)if you give them all the information they need from the strings of the two notes on either side. You will need a micrometer to measure the core and winding diameter, and a good measuring tape to get all the lengths needed. Your tech should be able to do this for you and there are string makers on the internet that could better tell you what info they need like wound length, free lengths, termination point lengths, back string ect. Do check the acoustics as suggested by previous posters but paired strings should be matched better than 3 mm on winding length. Best regards.

If you are going to replace those bass strings I'd stick to OEM. Order them from Kawai. It would be so much easier.

I have the same problem on my August Forster 215
(7'2") with the Bb2. The notes close above and below have it slightly but it is most noticable on the Bb. I have gotten used to it and it doesn't bother me any more. There was a technician from the factory in Germany who came in to address another problem and I pointed out this problem to him... he fooled with the tuning a bit and managed to get it to be less prominent. I don't want to be bothered messing around replacing strings so I won't do anything about it. The rest of the piano is just magnificent.

Going OEM is certainly a viable option I didn't mention but cross your fingers that you don't get another pair of "Friday afternoon shift" strings that you seemed to get in the first place. I have always liked Kawai's and this seems so below them from the pianos I've seen.

Well, just a few more thoughts...

One of the first things I always check on pianos like this is bearing on the bridges. The 2nd thing is the angle of the bridge pins.

Or, something laying on the sounding board in that area, loose from the rim, a slight crack in the board are a couple of other thoughts, Picture frames on the walls, heat vents... Anything is possible without seeing the piano..

Jerry:
I completely disagree with you here...Just kidding ha ha ha, have a nice day!

Thank you for all of your great answers about the piano position in the room and room acoustics. I'm looking forward to know more on questions 1 to 5.
Best, Zeh

I just thought of one more addition to check. On occasion, I've discovered a string that isn't going around both of the bridge pins by passing one of them. That will certainly give that twang sound...

ZeH,
I have learned from Dr Sanderson a little about L mode issues that give very practical and relatively simple solutions.
First you need to properly diagonse the L mode.
It will feed on energy from the 7th or 9th partials and be audiable around the 14th or 18th partial. Try it identify the offending partial. Isolate the strings and listen to only one at a time. If the noise goes away it is more likely a mismatch with the strings and that requires replacing both strings of the unison with a more closely matched pair.
If the noies is specific to one string or both strings individually you can further identify L mode by slightly de-tuning the individual string. The pitch of the offending partial will not change as the string is brought above and below the correct pitch.
Now that you have done this you need to contact a string maker like Arledge and tell him the problem. The solution is to slightly alter the strings inharmonicity and Jim will do it for you.
Usually changing the length of the exposed core that does not have winding on it will alter the inharmonicity considerably without altering the tension much. Changing the strings inharmonicity will force the L mode above or below the partials that are feeding it energy. You may never be able to completely get rid of it but you can make it much less audiable. Yes, this will also require new strings.