Double Refined MDF

[stevem]

I started a new speaker project last week, and I bought my MDF from a mill-work company instead of Home Depot. As I began to cut the parts out, I realized that this MDF was noticeably harder and felt a little heavier and more rigid than what I was used to. When I looked at my invoice copy it said "Double Refined MDF sheet". I searched the net to find that this board is denser than standard MDF and has more glue in it. It is used by mill-work companies for doors and other building products because it machines better.

My question is, for speaker building, is this stuff a good or bad thing? I like the solid rigid feeling of this material, but it also seems to make more noise when you hit it. It looks like it's somewhere between standard MDF and HDF (Masonite). Has anyone had any experience with this stuff?

[SEAWOLF97]

I had some Epicure cabs made of that stuff ....heard no diff .... (but no fun to cut)

in one of my old posts , it got called HDF

http://www.audioheritage.org/vbullet...l=1#post185242

[Lee in Montreal]

I wasn't aware about "double refined". But I have once used 1" HDF to build some transmission line cabinets. Heavy and solid like a rock. ;-)

BTW I don't think that HDF is also called Massonite. Massonite is more porous and has much less density.

[stevem]

Thanks, I appreciate the responses. Anyway, I'm almost finished the enclosures, and they look nice and solid. This material seems about the same as regular MDF to work with. By the way it is the 1 inch thick stuff.

[doodle6]

I started a new speaker project last week, and I bought my MDF from a mill-work company instead of Home Depot. As I began to cut the parts out, I realized that this MDF was noticeably harder and felt a little heavier and more rigid than what I was used to. When I looked at my invoice copy it said "Double Refined MDF sheet". I searched the net to find that this board is denser than standard MDF and has more glue in it. It is used by mill-work companies for doors and other building products because it machines better.

My question is, for speaker building, is this stuff a good or bad thing? I like the solid rigid feeling of this material, but it also seems to make more noise when you hit it. It looks like it's somewhere between standard MDF and HDF (Masonite). Has anyone had any experience with this stuff?

The material that you have has been around for a long time. It was used routinely for outdoor signage for a couple of decades because it stands up to the elements well with very small shrink and swell numbers - around 3% if memory serves. Lately it has become popular with cabinet makers because of the way the core takes finishes. With standard MDF, the core is so porous that it wicks finishes right in and continues to look porous (shows roughness instead of slickness on the finish surface) even after three or four finish coats. The finisher has to apply multiple coats to fill the machined areas until a top finish begins to build which provides a slick, smooth surface. The double refined board that you bought eliminates almost all of that problem so that even on machined areas the first finish coats aren't sucked in, instead lying on top and smoothing out, thus eliminating a lot of labor in the finishing process. This makes it possible for manufacturers to cut out MDF panels, then machine the faces in such a way that the panel takes on the appearance of a frame and panel, five piece door. With standard MDF, the same thing COULD be done, but the only affordable way to finish those doors was to vacuum press a thick layer of "foil" membrane, an almost half mm. thick PVC coat onto the cabinet door after machining. The big problem with that approach is that that coating was so thick that it didn't follow small machined profiles very closely, instead smoothing them out a lot so that they lost their sharp shapes, transforming very crisp and sharp machined profiles into very rounded profiles in their final appearance after application of the top coat.

I don't see why any of that should affect the performance of that board in the application that you intend.

[Mannermusic]

I started a new speaker project last week, and I bought my MDF from a mill-work company instead of Home Depot. As I began to cut the parts out, I realized that this MDF was noticeably harder and felt a little heavier and more rigid than what I was used to. When I looked at my invoice copy it said "Double Refined MDF sheet". I searched the net to find that this board is denser than standard MDF and has more glue in it. It is used by mill-work companies for doors and other building products because it machines better.

My question is, for speaker building, is this stuff a good or bad thing? I like the solid rigid feeling of this material, but it also seems to make more noise when you hit it. It looks like it's somewhere between standard MDF and HDF (Masonite). Has anyone had any experience with this stuff?

If you have a good lumber yard, you can specify the "press" specification of the MDF. Generally, 40 psi is the normal good quality, 70 psi is the next and 90 is also available if you don't mind burning up your router. The higher the press, the denser, stronger, stiffer the material.

[stevem]

Thanks everyone, this is some really god information. It also makes a lot of sense since I bought this from a mill-work company. They probably use it for making doors.

I almost hate to ask what the press quality of the stuff from home depot is.

[duaneage]

I got double refined MDF free of formaldehyde from Russel Plywood in New Castle Delaware. They stock 1 inch and can get up to 2 1/8" special order. 240lbs a sheet. I like the double refined since it is consistently solid all the way through and holds screws well. It IS hard on tools, I end up replacing a router bit after a pair of speakers.

[stevem]

I liked working with this material because it routes precisely, and makes a very strong and ridged enclosure. Too bad your supplier is a little far away for me or I'd buy from them.