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DIY・自作 管共鳴 ( QWT / TQWT ) スピーカー パート 8 - このスピーカーによる10年間の実験で分かったこと / DIY QWT ( TQWT ) Speakers Part 8 - What I learned with this 10 years experiment with these speakers

DIY 管共鳴 ( QWT / TQWT ) スピーカー パート 8 - このスピーカーによる10年間の実験で分かったこと / DIY QWT ( TQWT ) Speakers Part 8 - What I learned with this 10 years experiment with these speakers

I have mentioned a bit on the prior post but after looking over, I found out that this craft was done around 2008, so we know now that this is a 10 years old craft. Originally it was done as an experiment, so if we take it from that perspective this could stand also as a 10-year span experiment. So I would like to write some conclusions inclusive of the years.
These speakers were just left at the corner of a room but the cone was clearly discolored. The same FF85K model bought as spare had not gone through the discoloring (wrapped in a plastic bag and boxed). Maybe we'd see some difference with a perfectly new unit, but by itself, I could not tell the difference. So it seems we could say that it would stay as it should with less humidity.
The stored spares are pristine till this day.
The dying of the cone by this agent I bought hasn't changed the sound almost at all likely because the agent only gave a negligible layer. I also tried it on a sheet of paper but it was very runny and did not give any thickness to the paper after it was dry, seeming it does not have damping properties of any sort.
The surface of the wood does not show any mold or smell. It's smooth to the touch and does not show any changes over the 10 years. Of course, it passed through 3.11 and fell over so some of the corners are chipped and such. One thing we can say is that the Bokujyuu is a pretty long-lasting coloring agent.
Next will be about the structure, but when you want to add a tweeter, basically you would like to have the unit that crosses with your tweeter to be as close to each other as possible, and that means mounting that unit close to the top edge of the box as possible. So, in this case, I wanted to know how far I can go. People that have ever designed a speaker might think that it's too close to the top panel, but that was my intent. The other point is that I wanted it as slim as possible.

There are many say about where a unit should be mounted on a Quarter Wave Tube but it seems there is no clearly established theory that the majority will be comfortable to agree on. Another reason why I wanted to have it mounted as close to the top is, as you can see in the photo, this enables us to have the rear panel some 200 mm away to minimize primary reflection. This is an effort to try avoid making it sound like it's in a small box.
Above is the measurement of the frequency response of the speaker. The measurement range is 20Hz to 20kHz, the orange being without a subwoofer and the blue being with the subwoofer. Normally the pipe should have a resonance of 47Hz or so, but since the speakers are crammed into corners, it seems to be resonating at a lower frequency. The dip from 160 Hz to 200 Hz is from the standing wave of the room. Even if it wasn't there the frequency response is declining toward the left and could clearly use more bass, so it seems for this length of pipe, a 10 cm (4 inch) unit or a 12 cm (5 inch) would be more adequate. But if you aren't shy of using subwoofers, this being a very slim speaker the stereo image is pretty outstanding so for those people 8 cm is also a good choice.
Just for your information, the subwoofer used was a Fostex PC-SUBmini2. Not like I planned to use Fostex, but simply it was small and cheap here. I have no problem with the quality of this product, but you might like to note that this will likely not be able to keep up with larger speakers. In any case, I am satisfied to have a quite high level of sound quality in this restricted space. Movies, games, and music are all very enjoyable so I would recommend if anyone thinks about trying. Recently there are good sounding Class D amps cheap as chips like starting from 20 bucks or so, and the speaker will probably outlast many of your digital gadgets.


So in the end, what would I do differently if I was to rebuild this model?
1. I would use thicker plywood or have it double layered such as two layers of 12 mm instead.
   You can feel the vibration from the box when it is at a considerable volume
2. Use a better terminal (speaker connectors)
   I would like to use one that has a better contact area to the cable.
3. Connect the front and rear panel all the way from the bottom to top
   For more structural rigidity
So basically since it went very well for an experiment, if I am to rebuild with the same concept I would want to simply spend more resources on it.


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