Since I came up with the idea of experimenting with hollow sound columns, I have been thinking about what materials to use. I found that drilling holes in the middle of wooden sound columns and bamboo pipes were not very meaningful. Finally, I decided to try carbon pipes and copper pipes. Carbon pipes are easier to find. I asked a fishing friend for a scrapped fishing rod. The fishing rod has a taper, but it is not very obvious within the length of the sound column. I chose to cut it off at a diameter of 6.3 millimeters, with a small head of 6.2 millimeters. The carbon fishing rod wall is relatively thin because it has a taper that can be nested into two layers, reaching a thickness of 0.3 millimeters. Carbon pipes are very brittle and cannot be cut with saws or knives during processing. Only mixed files can be used to ensure that they will not split.    

After testing, carbon tubes have been found to significantly increase volume and vibration. After installation, the volume is very high and the vibration is very abundant, especially for chords or diphthongs, which vibrate very strongly and are suitable for playing strong and powerful music. The drawback is that the sound feels slightly dry and not soft enough, possibly due to the hard and easily vibrating carbon tube, which has a significant improvement effect on instruments with low volume and poor vibration.

I couldn't find the brass tube, and the copper tube was too soft and not suitable. As a result, I found a hero signature pen lead, a very hard stainless steel tube with a diameter of 5.9 millimeters and a wall thickness of 0.16 millimeters. I tried it first. Before processing, I searched online for an empty heart sound column to see if anyone had tried it. As a result, I found a patent information. In 2005, someone in Inner Mongolia tried a metal sound column and did not say what material was used. They could drill holes on it, which was said to improve sound quality and applied for a utility model patent. I also drilled three holes in this stainless steel tube, which is very hard and thin and not suitable for drilling. I first used a small round file to horizontally file out a groove when it was about to pass through, and then used the tip of the small round file to pierce through and screw out a small hole. To avoid damaging the piano board, I glued a layer of printing paper (maybe kraft paper is better) on both ends of the sound column with 502 glue. After installing it, I plucked the strings and felt that the residual sound became very long. When playing, the sound became quiet and melodious, with a significant improvement in volume and vibration. The noise was very low, and the friction between the bow hair and the strings was almost inaudible. I tried to block the small holes with adhesive tape, and the result was like a flute. Every time I opened or blocked a small hole, there would be a different sound quality effect. Finally, it was determined that opening two small holes on the same side would have the best effect. But this metal column is exactly the opposite of the carbon column, with a sound that is too quiet and appears somewhat mediocre. It lacks a pine aroma and feels a bit like a flute. When playing stress, especially chords or double notes, it lacks that surging feeling.

Conclusion: Both carbon and metal sound columns have a significant improvement effect on the volume and sound quality of mid-range pianos that are not ideal, and are worth a try. But at the same time, it should also be recognized that improvement is based on the original foundation, and it is impossible to change mid to low end pianos into high-end ones.