Cabinet materials - why not more diversity?

Status
Not open for further replies.
Jump to Latest
#23
Advent used to have a couple of speakers that had expanded foam cabinets and perforated aluminum grills. The outer layer of the foam was much denser and harder than the internal layer, and the boxes were not much lighter than wood, though I think they were cheaper to manufacture. I owned a pair of them (an Advent II maybe?) and thought they sounded sweeter and less boxy than standard Advents, but they were also dramatically less easy to integrate into the average decorating scheme, since they were white with silver grills. This was ok in the 70s, maybe, but probably less popular later.
The later Bozaks -- made in Taftville, not Norwalk, and using conventional drivers -- had regular appearing cabinets but the actual enclosure was half of a sonotube (the cardboard tubes used as forms for poured concrete columns) built into the box with the gaps filled with poystyrene foam. I have a pair of these, but can't comment on the sound because a part of the midrange contouring circuit was fried, leading to a dead short in both midranges.
I can't find any information about component values and so I suppose I have to unwind the coils, and reproduce them. What a pain. Anyone know what happened to the people who worked there -- I think the designer was named David Luchs -- I sure would like to find out the values of the coils.
 
#24
Nat Eddy said:
Advent used to have a couple of speakers that had expanded foam cabinets and perforated aluminum grills. The outer layer of the foam was much denser and harder than the internal layer
Click to expand...
I'm a strong advocate for soft on the inside, hard on the outside for mid-range enclosures and chocolates. Hard and rigid is perfect for bass but, usually, too reflective for mid-range. It also breaks your teeth.

Steve
 
#25
7V said:
I'm a strong advocate for soft on the inside, hard on the outside for mid-range enclosures and chocolates. Hard and rigid is perfect for bass but, usually, too reflective for mid-range. It also breaks your teeth.
Click to expand...

The phrase you're looking for is "constrained layer damping." I'm afraid I don't like constrained layer chocolates, preferring the Corian variety (dark chocolate with mint chips).
 
#27
A company called Wilhams Insulations in Hastings used to make an MDF/bitumen/MDF sandwich which was used by JBL. Another company called Rowntree makes a dark chocolate/minty goo/dark chocolate wafer, but its temperature stability is poor and it's only available in quite small tiles.
 
#31
Re: Blackpool Rock

Da5id4Vz said:
WS Slater makes a very tasty sucrose composite. It likely doesn’t have any purpose related to speaker building, but they will extrude batches with customized lettering embedded in the core.
Click to expand...

Not so. Here's an example. PMC is the Professional Monitor Company, they make some rather splendid loudspeakers, and when I bought a pair of MB1 for work I was worried that I might need to buy a pair for myself.
 

Attachments

  • pmc.jpg
    pmc.jpg
    18.9 KB · Views: 557
#33
at one of those gift stores like sharper image or brookstone there was a novelty shelf system that used INFLATED speaker enclosures, made of the same kind of transparent plastic sheet material they use for beach balls and other things. not hi-fi. probably not even lo-fi. but a conversation piece nonetheless.

/andrew
 
#36
Here's the full griff...

Dave, many thanks.

OK. The top and bottom are each made of two sheets of 19mm MDF. One piece fits inside the smaller half-ellipse, the other inside the larger half ellipse. The angle aluminium and MDF make a frame (seen from the front) to which the aluminium can be folded round and secured. You now have a box, but the gap between the aluminium sheets is unfilled. The original design that 7N7 worked to was slightly different (read "not as good"), so I can't give filling details that are tried and tested, but I would be inclined to drill a hole in the MDF to squirt the foam in. The foam is that stuff people use for bodging houses.

The shape of the box is very rigid, and doesn't cause reflections (satisfying 7V's reservations). The traditional "knock" test sounded good. The front panel is boringly flat (makes it easier to mount the loudspeaker), but should have profiled edges to reduce diffraction.

For the mathematical whizzes amongst you. I did an Internet search to calculate the perimeter of an ellipse. There are approximations and an exact series that converges frighteningly slowly. In the end, I made a pair of aluminium templates, used them to mark out the MDF. Carefully cut the MDF and measured it with a steel tape measure. That's how impractical the formulae were! (Bear in mind that a 1mm error in 400mm was not acceptable.)
 
#37
Re: Here's the full griff...

EC8010 said:
For the mathematical whizzes amongst you. I did an Internet search to calculate the perimeter of an ellipse. There are approximations and an exact series that converges frighteningly slowly. In the end, I made a pair of aluminium templates, used them to mark out the MDF. Carefully cut the MDF and measured it with a steel tape measure. That's how impractical the formulae were! (Bear in mind that a 1mm error in 400mm was not acceptable.)
Click to expand...

My CAD program reads out a 28,000 mm^2 interior cross-section area.

dave
 
#38
So, EC8010, I gather that there's aluminium on the inside and outside with foam in the wall. Is that right? Please excuse the question, it's just that I'm denser than your cabinet.

Also, what do you use for drive-units and how does it sound?

By the way, how near London and which direction?
 
Status
Not open for further replies.
Top Bottom