Working with MDF
In the World of Design and Fabrication, you will Come across many different and Sometimes exotic materials. But the most common has to be MDF or Medium Density Fiberboard. MDF is a material with some wonderful properties for use in the Audio and Acoustics world. It’s easy to find, cuts and routs well, is uniform and usually available in many different thicknesses. It’s also dense making it fairly acoustically dead, meaning it’s less prone to ‘Ringing’ a phenomenon where the material will vibrate and cause abnormal sounds and cancellation at certain frequencies and amplitudes. This makes it the first choice for many novice and seasoned Builders.
However, for all of MDF’s strengths, it also has its weaknesses. And this can be a major challenge for someone who hasn’t had the experience of working with MDF before, or someone who hasn’t worked with it often. Firstly, MDF is particle board and because it’s made from lots of very tiny pieces it has a very high internal surface area and acts like a wick. When introduces to liquids like water it will rapidly soak them up and the material will swell and lose its bond. I often see this with enclosures that have been mounted in trunks or left in areas that have rapid and extreme environmental changes ‘for example I lived in Florida for many years a place where the humidity often stays at 90% for days at a time’. It also means that sealing MDF is a must for longevity, oil-based primer or paint is generally the simplest way to do this and must be done before any other finish is applied.
One other downside is that although MDF is very dense it doesn’t really hold screws well and is very prone to splitting or cracking if not predrilled with the correct bit. This means it needs to be bonded together chemically. This is usually done with PVA glue, also known as polyvinyl acetate. The correct way to glue MDF together ‘for a bond that will last longer then the speaker going in it’, is to score and pre-wet the surfaces that will be in contact. This can be done with some lite sanding and a precoat of glue allowing for some of the glue to soak into the surface before adding the bulk of the glue and joining the parts together. The best practice when gluing, ‘and this goes for any wood product’ is to clamp the surfaces together with as much force possible without damage to the materials. With MDF you can also use 18 gauge brad nails to clamp the parts together, but if the box is correctly glued and braced the nails will only be there to clamp and orient until the glue is cured. Wood Glue is a chemical bond, and as such, is much stronger then the mechanical bond of nails or screws. Often the wood will fail before the glue in test’s.
In conclusion, MDF is a popular choice for speaker building due to its relatively low cost, and ease of use. It also offers a decent level of acoustic performance, making it suitable for both home and professional audio applications. However, it is important to be aware of some of the drawbacks of MDF, such as its tendency to absorb moisture and its relatively low strength. I hope this helps anyone considering MDF for their next speaker enclosure. - Tha Boy Genius
More info on this topic will soon be available in the ‘Designers Space’ section of the website. “Thank you for reading”.