HohlFlute Single Driver Transmission Line Speaker System
| Introduction: When we moved into our house, we found a hideous shelf occupying an entire wall of the living
room. However, it was made of what I surmise must be some very old plywood. In addition, the living room needed a low-profile means of music reproduction. Fortunately, the shelf had been finished in nearly the same stain as had the wood trim of the entire living room. So I decided to build some speakers out of them. I'm a huge fan of transmission line style speakers, so I looked around for a design which would please both me and my wife; not an easy task, I assure you. It occurred to me that if I sacrificed deep bass reproduction, I could satisfy my desire for hifi reproduction, at least from the midbass up, and I could satisfy my wife's desire for a low-profile design with a slender, elegant design. Judge for yourself. Click on the thumbnail pictures for a more detailed picture. |
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| The Idea: What could be a more elegant, low profile, and still whimsical TL design than mimicking one of those wooden organ stops? |
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| Detail: So I crawled into the crawlspace, took one out, and studied the detail. |
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| Technical Study: I studied what actually makes a "Hoehlfloete" resonate. |
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| Modeling the Driver: Martin J. King offers his mathcad worksheets free of charge. I modeled the TangBand 881S in a couple of virtual pipes. |
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| Prototyping: The one of the right modeled much better, well-below 100Hz, but it was declared "too fat" for the living room. I disagreed, but you see that I was already building the real thing... |
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| Prototyping II: This is the second, more slender of the two. This was to measure the enclosure in real air instead of in simulations. I wanted to make sure that something so small actually could reproduce 100Hz. |
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| Measuring: I built the Eric Wallin Jig II, learned to use Speaker Workshop (it should be offered as a course for credit at the university) and measured the response. |
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| The Graph Lies: It's kinda humpy at 200Hz, eh? Well, I can tell you--and those of you who know how Speaker Workshop works can attest to this--this is a graph of several other graphs combined, so the graph is a distortion of several measurements. It is, indeed, kinda humpy here and there, but my ears are telling me that this thing sounds really good down to 150Hz or so. |
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| Little Driver, Big Sound: Yes, this thing really does sound that good, with a little help. Stay tuned for that! |
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| Dimensions: The interior measures a scant 24 inches in length, then 2.5 by 4 inches depth and width. |
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| The End is Near: The fulfillment of the shelf is at hand. |
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| Panels: The shelf is now a speaker. All the remains is glue and further preparation. |
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| Preparation: I used to always forget actually installing the interior wiring. Not this time! |
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| Preparation II: I also learned to tack the interior wire for easy access later on. |
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| Preparation III: Pause for some liquid refreshment, a cold Samuel Adams, the choice of this Frugalphile. |
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| Frugal Woodworking: I wanted both the angled port area and to show the interesting plywood assembly. It proved a challenge with my miter saw kit, but I eventually prevailed, especially after some creative sanding. |
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| Sealing: Apply and let cure for 72 hours to let the gases dissipate. |
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| Shaving: Using a razorblade, I shaved the silicone down to about a millimeter uniformly, allowing the driver to sit almost flush against the wood with an impenetrable seal. |
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| Glued: All the enclosure pieces, properly speaking, are assembled, drying, and waiting to be detailed. |
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| Modification: In the meantime, I bought a modification kit from Mark Mckenzie at Madspeaker (McKenzie Acoustical Design), specifically designed for this particular driver. This driver sounds as good as any I've heard! |
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| Finished: The product met my expectations. |
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| Profile: From a different angle. |
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| Detail: This is detail of the port area. The steel machine screws, I have been informed, shall be replaced with brass. |
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| More Detail: This really came out according to plan. I'm very pleased with the design and the sound. |
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| Installed: The Hohl Flutes and my dear patient wife, along with me, wish you a Merry Christmas in 2004 and a prosperous 2005. |
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Hohlflutes |