Cabinet materials: particle board vs birch plywood

[Guest russwollman]

The Advents I have use particle board (or pressboard, as it may be) as the cabinet material.

But I also have several ARs, 2 pair of 2ax's and a pair of 3a's, and the cabinets seem to be made of birch plywood. When I rap the sides of the ARs with my knuckles, the sound is quite solid, as opposed to the sound my knuckles create on the Advents, which sound rather hollow and less substantial. This worries me. Did the guys at AR know something magical about cabinet materials?

[Guest Brian_D]

Magic doesn't exist in speaker building!

The AR guys probably knew what everyone knows about building materials, but usualy ignores when it comes to cabinets; higher mass=lower cabinet effect.

I have no clue why Advent would use PB while AR would use ply, probably just different manufacturing pracitces... Either is viable as a building material if used correctly.

"Plywood" as it's referred to here has very high mass, is extremely stiff but unfortunately is very heavy. (essentially it's solid wood with the benefit of an excelent artifical binding agent; glue!) "Particle board" is isn't as heavy, but has lower mass and lower stiffness, thus all the bracing that goes on in PB cabinets. Particle board does have the one advantage of having a much lower resonant frequency in a given surface area, making it suitable for small cabinets or for cabinets with smaller drivers.

The cabinet effects are less where Vas is less (air volume moved by the driver in question) The cabinet effects are also less where stiffness can be acheived through bracing or freqent joints. So smaller cabinets with smaller drivers can get away with low mass building materials, large cabinets with large drivers (or smaller drivers with high Vas) need higher mass/stiffer materials.

All of this goes out the window when the bean counters see that the cost for materials and transport is reduced enough to meet some secret pricing point or marketing ploy. (remember when lexan was the end-all be-all of cabinet materials? Now TEHRE's a bad idea, I can't think of a more reverberant material, maybe aluminium!) These days, the standard is particle board. (MDF or HDF or if you want to spend an arm and a leg for building materials UHDF!) Maybe Advent was just ahead of its time!

[tysontom]

>The Advents I have use particle board (or pressboard, as it

>may be) as the cabinet material.

>

>But I also have several ARs, 2 pair of 2ax's and a pair of

>3a's, and the cabinets seem to be made of birch plywood. When

>I rap the sides of the ARs with my knuckles, the sound is

>quite solid, as opposed to the sound my knuckles create on the

>Advents, which sound rather hollow and less substantial. This

>worries me. Did the guys at AR know something magical about

>cabinet materials?

>

Plywood came along earlier than particle board in the etiology of loudspeaker-enclosure construction, and hence the early AR models you mention were affected by that. The exception is the AR-3a -- and unless the speaker was supplied in "Unfinished Utility Pine" -- the cabinet material is Novaply, a type of MDF. Some other particle-board variations were also employed by AR cabinet makers. Particle board is actually denser, and usually heavier, than equivalent plywood. The primary reason that the AR-2, AR-2ax and especially the AR-3a seem more "solid" is that the cabinets are internally braced with wood strips. This tends to dampen the cabinet panels. Advent did not rely on bracing, and I suspect that they felt if you could not readily "hear" a difference there was no reason to put cleats inside the cabinet to dampen any potential cabinet-panel resonances. In actuality, there is a small measureable difference, and it might show up in certain types of music, but it is difficult to hear. Edgar Villchur was the first to use the cleats or "braces" inside the AR prototype and AR-1 cabinet, and ironically, Henry Kloss (designer of the Advent) was the one to physically locate them in the AR-1 production cabinets. Villchur knew that the pressures inside an acoustic-suspension cabinet would be substantial, and cabinet stiffness would be important.

I think that by the time the Advent was introduced, around 1967 or so, particle board was the "standard" in cabinet construction. It was much less expensive, and in most respects superior to plywood for cabinet construction. The downside to particle board is the poor way it handles wood screws (Advent used wood screws rather than machine screws to mount drivers) and its tendancy to chip or flake. If you had to remove an Advent woofer, you could probably do it once or twice before you chipped out the screw hole. AR's, on the other hand, were built to a higher standard and used T-nuts and machine screws for all speaker-mounting installations, and the cabinet material did not matter when it came to mounting drivers.

--Tom Tyson

[Guest russwollman]

Both replies have interesting thoughts. Thanks very much.