Series 6 - Designer Notes

Philip Bamberg said…

Sometimes a new idea is born while riding on an airplane. Such was the case for the format of Series 5 TMW. The subwoofer concept was already proven. The monitor was an existing product. All that was needed was to bring it all together as a hybrid 3-way, and freshen the styling.

...and other times I just want to start from scratch.

I wanted to do a full-range reference grade loudspeaker for over ten years, but all the specifics had not gotten out of the idea phase. Performance goals were evolutionary, not revolutionary. I am all about finding the point of diminishing returns as regards performance-per-cost, and then running hard into the knee of that curve.

Below is the cover page for the cabinet’s CAD package (and represents nearly 100 hours in cabinet CAD alone). I began this design by first laying out the acoustic geometry of a high tweeter elevation (52") together with a listening distance of 8 to 10 feet. The high monitor renders a subjectively large sound stage. This truly makes the sound seem “bigger”.

[Click for larger image:]

The subwoofer is basically the same as with the Series 5, but taller and slightly narrower. ScanSpeak dual drones reach to 18Hz with only 2.2 cubic feet of cabinet volume. I chose the ScanSpeak 4ohm woofer for higher efficiency and because it shows a smooth SPL response to 1500Hz, or two octaves above its cross point.

In my experience the ScanSpeak D2904-7100 Revelator tweeter is more reliable than their 6600 AirCirc version. The faceplate matches the style of the midrange frame. Its high efficiency also mates favorably to that of the dual midranges. This SD-2 tweeter is known for that "hear-through" transparency that delivers a relaxed and refined treble, or what I call "shoulder droop treble".

While I have favored single mid-woofer designs of late (or at least 2.5-way crossover dual-woofer designs), I returned to the D’Appolito MTM configuration based on dual 6” [15cm] midrange drivers. I really wanted the cone area of a single 7” [18cm] woofer, because that provides the acoustic drive in the power region (200-400Hz octave). Conversely I wanted a narrow baffle with well contoured edges around the midranges and tweeter so that the monitor easily disappears behind the acoustic image.

Because of my love of sound from the Skaaning 18cm mid woofer in a 2.5-way tower that I developed for Imperium Acoustics, I selected Skaaning’s purpose-built 15cm (6”) midrange unit (C-Quenze p/n 15 H 52 12 06 SDKM). Each midrange is on its own sub-baffle, and is canted forward 5 degrees above and below the ScanSpeak D2904-7100 tweeter. Therefore, in the 8 to 10-ft distance window, the listener is perfectly on axis of all three drivers, and hence there can be no smearing of the signal from the two midranges.

What I think is clever is the top which is sloped down by 5 degrees. By simply flipping the monitor upside down, the reference axis is also aimed down 5 degrees. This is the setup for the 8’ distance, while the “right-side up” monitor is used for 10’ distance or greater. The reference axis angle can even be further fine-tuned with the flexible floor spikes system.

As always, the crossover can be implemented in many ways – hybrid passive/active (like the Series 5 TMW), all-DSP-active, hybrid/line-level-passive, etc. We shall see which sounds best.

This speaker will be finished fully painted. Here is a somewhat crude rendering of that, but this image at least shows the styling better.

[Click for larger image:]