MDF

The meat and potatoes of loudspeaker manufacture for decades has been MDF (medium density fibreboard) which is made from compressed softwood fibres held together with resin and wax. MDF is cheap very machineable and is a reasonable material for building loudspeaker enclosures.

Ok, that's whats good about MDF but whats not so good?
MDF is simply not stiff enough and does not have sufficient mass to resist ringing. The main body resonance of enclosures built with MDF is usually between 280hz and 400hz, this is in the power range region and just above. Knowing how to brace or damp an MDF enclosure is the key to getting decent performance out of this material.

HDF or HD3

The best all round material for building loudspeaker enclosures is HDF or high density fibreboard.

It is however expensive but not prohibitively so, it costs here in Australia 7.2 times that of high quality WR grade MDF. It also has 1.6 times the mass of MDF
OK that seems like a lot more expensive but the sonic benefits it brings must be heard to be believed. Comparing two pairs of identical loudspeakers (right down to the wire and type of solder) one pair built with 18mm MDF the other pair with 18mm HDF is a revelation!

The MDF sounds glazed with a midrange humming that significantly reduces resolution and rhythmic timing.
HDF by comparison is jet fighter fast, Piano decay for instance is just incredible, the additional nuance and purity of sound is amazing.

Enclosure Bracing.

This is a very in depth and time consuming part of loudspeaker design . Many designers simply link their enclosure walls together with shelf bracing thereby raising the natural resonance of the enclosure. This approach works reasonably well but it has some problems, primarily because the negative enclosure energies are not being dealt with they are simply being shifted to a higher vibrational frequency, say from 300hz to 700hz for instance.

This approach is generally considered the way to go because it apparently reduces enclosure colorations to an insignificant level ! NOT !!!! This is where Lenehan Audio parts ways with accepted design practice.

For the past seven years we have been developing a proprietary enclosure bracing technique we call differential bracing cancellation. In short the Q profile or resonance patterns of opposing enclosure walls are arranged so as to partially cancel each other out. We do not lock together identical enclosure walls with shelf braces, this can more than double the trouble at much higher frequencies.

Enclosure Damping.

Dampening enclosures with the wrong or too soft a material is a complete waste of enclosure volume and does nothing!
very stiff and massy enclosures require specific materials applied correctly to specific areas.

We use hard bitumous layering and also Ply in various thicknesses. Ply can be used for two entirely different functions, firstly as a lamination to dampen some types of panels and secondly as a brace to mechanically raise panel resonance without significantly increasing mass.
One must remember that resonance is energy and energy cannot be destroyed ; only diverted, converted or channeled.

Internal Damping materials.
This is also a critical area, we use a proprietry material we call Stiky Foam in two different densities inside our enclosures. Reducing internal standing waves and stopping reflection back to the midrange diaphragm is of course important in stopping mid and power range colouration.