Speaker cabinet design

[eitanwaks]

As a university student I am always encouraged to think outside the box. When it comes to speaker design it might mean quite literally outside the box.

This morning I had thought. When I use metal as an enclosure material instead of wood. What are the qualities that make MDF the preferred material among speaker builders? Can these qualities be indicated using other materials? If you give me a list of qualities that MDF possesses, I might be able to synthesize a material that mimics those properties, however easier to handle for mass production or single production.

The reason I got to thinking about this is that it is much easier to build something with metal than it is with wood. At least it is for me. Also, making precise measurements and designs that are not "standard" are much easier. Another possible advantage is that you don't have to use a matrix inside the speaker to add strength since if you use the proper metals and proper technique he couldn't achieve a very strong box by itself without needing any internal support. The list goes on and on for pros and cons.

I was just curious, what are your thoughts? If you can give me a list of the properties that MDF possesses at would-be very happy to see if I can find a material that possesses similar qualities.

Eitan Waks

[Timn8ter]

MDF is "preferred" because it's cheap and easy to work with. A good void free plywood is usually mentioned first as the "preferred" material but it's much more expensive. Using metal for enclosures is not a new idea and the quality you're looking for is stiffness. Several DIY'ers have used aluminum with great success.

[eitanwaks]

Thanks for the quick reply. I was really shocked/interested/surprised to learn that people have made enclosures from aluminum! I thought they can be done however that sound quality would diminish. What are the properties that affects sound qualities in speaker cabinets? Is it only rigidity? Does a material not affects sound quality? I thought that resonance would differ from one material to another?


Eitan Waks

[Timn8ter]

Rigidity is important. You wouldn't want a material flexing at such a rate as to change the angle of the driver toward the listener, for example. A rigid enclosure may resonate but it will do so at a frequency that is essentially inaudible to the listener. This is the main goal of using braces (a matrix as you called it) inside. A short span of material will resonate at a much higher frequency than a longer span may and at a much lower amplitude than the driver output.

[eitanwaks]

With regard to your latest reply you make sense to use a material that possesses a high young modulus. I'm not sure. Familiar with this parameter. It refers to the rigidity, and toughness of material. Extrapolating from when you said that you want the material to vibrate at very high frequencies. So high that we can hear them. You make sense to use steel rather than aluminum. In fact I can think of many other materials that would be much better than aluminum or wood.

After doing some online searching, I found that most high-end speakers are made of wood however there are some exceptions. An interesting exception that I found was a B&W nautilus. It is made of some very strong, rigid resin. Do you know of any other manufacturers that use different materials such as metals in speaker cabinet design?

I still find it very difficult to believe that the material from which the cabinet is built does not have a direct relationship with the sound that the Speaker possesses. Just some day-to-day intuition tells me that if I wrap my knuckles on wood it sounds different from when I wrap my knuckles on metal. Doesn't this have anything to do with the sound in speaker has? Could the cabinet design be solely for rigidity? Well

[Timn8ter]

Just some day-to-day intuition tells me that if I wrap my knuckles on wood it sounds different from when I wrap my knuckles on metal.

Of course. If the material vibrates within an audible range you will hear it. That may seem redundant but if we call the driver output the signal (S) and cabinet vibration noise (N) what is the S/N ratio and how high would it be to have an adverse impact on the listening experience? That might be a good question for an engineering student. I can't answer that question.
I can't think of a commercial application of metal for enclosures but there are many using resins.
http://www.u-vola.com/u-speakers_eng.html

[keyser]

one major reason wood is usually used to build speaker cabinets, is its relatively low weight. some speakers are actually built from stone. most stone types make up very adequate speaker cabinets. it's usually very stiff, and strong, and has a high own resonant frequencie. the problem is, a three-way floorstander of medium size would take 3 people to lift it!
beside the fact that such high weight is inpractical, it costs a lot of money to transport the speakers.
If you're building your own speakers, using some kind of stone might be a good choice if soundquality is the only important factor.
Bricks (!) are usually easiest, but not very pretty in most cases!

[x. onasis]

Conventional thinking is that the cabinet should be inert, that is, non-resonant in the frequencies that are audible, leaving the drivers to be the sole sound producers. Rap your knuckles on thick enough wood, steel or any solid material and when you can only hear your knuckles, _ that's_ what many consider ideal.

DIY speaker builders are often interested in "appropriate materials and technologies", meaning less energy consuming and environmentally friendly techniques. Often the biggest problem we have is to produce something that looks good from the cheapest materials available. We can build cabs that sound good, making them look as good as they sound is the harder part. (IMHO)

If working with metals was easy for me, I'd be designing the combination heatsink/amp case in a modular form.

[googler]

What, if any, impact does the internal shape of a sealed cabinet have on the sonic qualities?

I have been considering making a triangular speaker. Not an equallateral by any means. Most likely a 10" baffle with 14" sides.

[Timn8ter]

Someone would have to convince me that non-parallel walls eliminate standing waves. It doesn't work in a room, why would it work inside of a cabinet?