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The Metronome ML
A family of ML-QQWTs


A Metronome is an elegant quarter-wave design closely related to an ML-V (Mass Loaded Voigt Pipe)

ML-QQWT? A Mass Loaded Quadratic Quarter-Wave Tube. This 1st appeared on the scene in the form of the ConeHead (proposed by David Dlugos for the RS 40-1354). As far as i know, this has not been built -- Andy Graddon has a half-finished (& abandoned) one in Australia.
Thus remained the state of the ML-QQWT until Stephen Cresswell decided to build a set of TQWTs. He came up with the Metronome. His is an outstanding & elegant execution with high aesthetic appeal -- it is a beauty.

Just as with the ConeHead, he missed the fact that this is not a straight taper but a quadratic taper (
detail of graph below & right) and thus, in the strict sense, not a TQWT.

Running across these from a post on
diyAudio, David D. determined the detail and Scott Lindgren modeled them as built as mass-loaded. Steven performed the required modifications to convert The Metronome to an ML-TQQT and reported much better performance. It also turns out that Martin King models show that a QQWT performs much like a TQWT -- the big benefit a most elegant presentation and -- hopefully -- higher WAF.



Scott & David started playing with more drivers. Key dimensions modeled so far (most as yet unbuilt) for a number of other Metronome ML enclosures are in the Metronome Variations Tables (with examples). These tables also have some suggested starting points for BSC (baffle step compensation)

Hemp Acoustics 8" (200mm) in Metronome

FE127e Metronomes

The wider-than-deep profile lends itself well to a bipole, hence the Bipole FE126e. The FE167 & 207 came next and it turns out the FE167 works in the same box as the FE207 with only a port adjustment (and the Hemp FR8 fits too). Just as in the case of Martin King's ML-TL it looks like a number of drivers may work well with only port (& optional filter) adjustment.

Just like a regular ML-TQWT, as long as the So & Sl (start & end cross-section) remain the same, you are free to alter the aspect ratio -- if you get too radical performance may be affected, but probably not before the driver won't fit.

Have at them... if you build a set please report back. We will continue to add & improve the drawings & check out more drivers.

The original FE108eS Metronomes