The range of Pensil speaker kits are a specific Mass Loaded Transmission Line alignment developed specifically for the Mark Audio driver range by Dr, Scott Lindgren, the plan sets are hosted over on Fugal-phile and are free to download and build yourself. This kit specific to the Pluvia 11 speaker driver has been designed to make building your own as easy as possible. Made from 18mm Baltic Birch ply and machined by CNC to provide an accurate and repeatable way for you to build this DIY full range loud speaker. Take a look over at our instruction page for this design to see how simple it is to put it together. The Birch ply timber product is a much higher quality than the MDF that speaker kits are often constructed from and the cabinets are fully braced which results in a really inert cabinet and as good a quality construction as can be found in even very high end speakers.
For those wanting to build their own from scratch you can down load an outline of the sizes here- Pensil 11 plans.
These speakers got a glowing review over on HiFi Pig, reviewed by father and son team Rob and Dave Stevenson, here are a few quotes to whet your appetite.
‘Dramatic transient speed in macro dynamics and micro dynamics, imaging and cohesiveness in the sound of instruments that is obvious with reproduction of acoustic kit and vocals.’
‘Their musical character is clean and clear with intense detailed layering and impressive dynamics’
‘coherent and seamless – meaning the individual instruments & vocals sort of hang nicely defined as fully formed separate items and make up a stage set which can extend further in all directions, up, back, left and right, out from the boxes.’
‘These beauties deliver a good spread of complex orchestral works .They have the accurate tonality required, and detailed presentation to illuminate the music’s construction and emotion’.
‘Berlioz ‘March to the Scaffold‘ and ‘Witches Sabbath’ in his Symphony Fantastique is punched out with full macabre venom’
The full review of the HiFi Pig ‘Highly recommended’ speakers can be read here and is well worth a read.
Here are a few words from Dr Scott Lindgren about the Pensil designs.
The MLTL is a variation on the vented box theme, but has a number of differences from a regular bass reflex type. The majority of bass reflex / ducted vent enclosures are derived based on Helmholtz (cavity) resonance theory, which assumes a uniform internal air-particle density, and no Eigenmodes (standing waves) present. For enclosures where the overall dimensions are relatively close to each other, this serves quite well, once the enclosure is appropriately damped. However, the assumptions begin to fail when one dimension is stretched relative to the others. In such cases, the standing waves begin to affect the behaviour of the enclosure and its output. Therefore, a quality enclosure design will account for these when developed, either attenuating, or, as is the case with MLTLs, actively using the standing waves as part of the enclosure alignment / tuning, rather than pure Helmholtz behaviour. There is no penalty for doing so (one is not ‘faster’ or ‘slower’ than the other for e.g.), and a number of advantages can be obtained.
In the case of the pensils, the enclosure has a large volume compared to a normal vented box, and the longitudinal standing wave is factored into the enclosure alignment. Without damping, the result is a large excess of enclosure gain over a relatively broad tuning compared to a typical vented box. The enclosure is then stuffed, to typical transmission-line levels, with damping material. This provides a much-flattened impedance load similar to a pure transmission line, but with relatively broad-band gain. (Note: technically, if the electrical TL analogy is to be applied narrowly, a TL would be an enclosure designed to provide the flattest possible impedance load, with no other considerations at all. The term is rarely applied so narrowly: even Bailey’s original article on the subject used the terms ‘Transmission Line’ and ‘non-resonant’ in its title, and then proceeded in the main text to describe an enclosure that was, in fact, resonant). The Mark Audio drive units have a small amount of low-frequency gain built into their responses. Under typical room conditions, this matches well to the enclosure output, and avoids the need for shelving filters. The cabinets are designed to have a removable back: the owner can then trim the quantity of the stuffing material to suit their own room acoustics and personal preferences, without needing to make physical changes to the enclosure itself.
In any enclosure that uses standing waves as part of the alignment, the position of the driver (location of excitation) affects the behaviour, most significantly the activation of harmonic modes that occur in an un-tapered line at odd multiples of the fundamental. End loading (placing the driver at the ‘closed’ end of the line) will ensure maximum excitation of the fundamental, and all the harmonic modes. By adjusting the tap location (where the driver is positioned along the axial length of the line), it is possible to reduce the excitation of these unwanted harmonic modes (which are further attenuated by the stuffing within the enclosure. Note that while it is often claimed that stuffing reduces the speed of sound in a transmission line, in fact, as proved by Augspurger, King et al, this reduction is in fact quite small). Adjusting the position of the vent can also have an effect on output; in the case of the pensils, it is deliberately located at the end, partly because they were intended to be as physically simple as possible, but also because the driver position and relatively high stuffing density are sufficient to reduce the effects of the unwanted harmonic modes without needing any offset to the vent position.