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DIY・自作 管共鳴( QWT / TQWT ) スピーカー パート1 - 10年前の工作 / DIY QWT ( TQWT ) Speakers Part 1 - A 10 years old craft

DIY・自作 管共鳴( QWT / TQWT ) スピーカー パート1 - 10年前の工作 / DIY QWT ( TQWT ) Speakers Part 1 - A 10 years old craft

今日は少し志向を変えて以前の職場のBBSから10年ほど前に自作したスピーカーの写真をせしめたので紹介したいと思います。1枚目は現在の姿で、2枚目は発掘された時の姿です。Quarter Wave Tube (1/4波長管)という種類の構造で、菅の共鳴を使って低域を補助する設計です。現在はサブウーハーと一緒に使っていますが。
Today, I'd like to show some photos I got off of my former job's BBS, which is about a set of DIY speakers I built some 10 years ago. The first image is what it looks like today, and the second image is what it looked like when I excavated it. It's a design called a Quarter Wave Tube which is a structure that uses pipe resonance to reinforce low frequency. It's being used with a subwoofer now though.
As you can see the cone of the speaker was originally white, but the years have made it discolored like a treasure map from Indiana Jones. So I dyed the cone with a speaker cone dying agent that I bought, but it really smelled like "Bokujyuu" (the ink that you use with your brush to do that calligraphy). I might as well just get one of them from a dollar shop then it would only have cost me a dollar. Maybe I'll try that the next time I have the chance.
The speaker unit from Fostex and goes by the name FF85K, it's discontinued now but if you are interested in small HIFI units, you might want to look into its successor FF85WK. Anyway, this is how it first arrived. Man, that jogs up a lot of memory. By the way, although you won't see almost any of it, the speakers were built at the house that we are renovating in the articles.
まず部品が全部揃っているか仮組をします。下の方に写っている小さい材はは材です。画像が荒くてすみません。なんせ大分前のものなので。ご覧の通り板材はTokyu Hands購入でカットと配送を依頼しました。QWTと書いてありますがTWQTとの違いはテーパー(板を斜めについで開口をだんだん大きくする)があるかどうかです。1回折り曲げの構造で折り曲げた後ろの開口部がある方が面積が大きいので動作上テーパーと共通する部分はあります。これに対してトランスミッションライン型は逆に開口部に向けて小さくなっていきます。
First, you place it as  it will be assembled to see if everything is there. Please excuse me of the small images. It was quite a while ago so you know. As you can see the wood was bought / cut / delivered by Tokyu Hands. The title says QWT, and the difference between TQWT (Tapered Quarter Wave Tube) is that the pipe structure isn't tapered. But as you can see, the opening side of the pipe has a larger cross section so the in function it resembles a tapered tube. A Transmission Line will have the opening side narrow down in cross section opposing to this.
カットが正しいかと木材に欠品が無いかを確認 Confirm the cut size and if any missing piece(s)
Use the speaker unit as a template to mark the screw holes. 
Like so.
On this build, I used some metal inserts and bolts instead of the included tapping screws.

Mark the center of the screw hole using a gimlet. 
Measure the insert's diameter and use a slightly smaller drill bit to drill a hole.
Since the plywood is thick in proportion to the speaker units' size, I shaved off some of the edges for it's breathing.
This is how it looked before. 
And after. So you may ask, why not use a thinner plywood to start with, which is a good question but if you use thin material, the plywood will vibrate too much and ruin the sound quality.
As a matter of fact, if I was to build a new one today, I will likely use a thicker wood or double layer everything so it would have more than 15mm. Even though an 8cm unit, the cabinet vibrates when you have it moderately loud. Even though the unit is small, it handles the same soundwaves as bigger ones so you know.
As you can see, I have left where the inserts so the structural rigidity won't be compromised. To be continued !


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