[Wind Chaser]

The geometry of enclosure can make huge differences.

Enclosure Shape Effects - Dr. Harry Ferdinand Olson - Acoustical Engineering, page 23

[Daryl]

Why stainless steel? While it is possible to make a good enclosure out of MDF, stainless steel is vastly harder, stiffer and denser. In short the result is extremely low distortion, excellent bass and midrange tone with the absence of coloration.

1" stainless steel is stiffer than 1" MDF.

Sheet metal on the other hand will have issues of it's own.

There is nothing wrong with a properly built MDF enclosure.

Now vastly increasing cost and complexity without realizing a functional benefit is fine if it pleases you, but you shouldn't use it as a basis to make others appear foolish.

It can backfire on you.

[Wind Chaser]

What's sheet metal got anything to do with this?

[Christof]

It seems that an egg shaped enclosure and front baffle would be nice...no parallel walls or similar measurements anywhere.  A sphere might be strong but wouldn't there be some inherent troubles with the shape?  What about a Bean?



oops....this thread is about materials.  I have had the best luck, regardless of the enclosure shape when I employed Constrained Layer Damping construction methods and dissimilar materials, 3/4" MDF + Lossy Material + 1/2" Baltic Birch for example.

[Wind Chaser]

Now vastly increasing cost and complexity without realizing a functional benefit is fine if it pleases you, but you shouldn't use it as a basis to make others appear foolish.

The difference here is one person is talking from the experience of doing and the other isn't.

[Daryl]

Any enclosure shape or type is perfectly suitable for any level of performance.

That is to say there is nothing special about transmission lines or aperiodics that cannot be achieved in a simple sealed enclosure.

Horns, vented and any other style can be used to achieve any performance level as well.

Proper damping can control any internal resonace so specific ratios of internal dimensions are not necessary.

Often you see folks go to rediculous measures to handle backwaves and they will tell you it is necessary.

That is to say the B&W Nuatilus enclosure no matter how impressive looking offers no advantage over a sealed box like the one shown below.

[Wind Chaser]

It seems that an egg shaped enclosure and front baffle would be nice...no parallel walls or similar measurements anywhere. 

http://www.soundstagelive.com/factorytours/waveform/

[whubbard]

Well there seem to have been a very good number of responses, but lets try to keep it on topic, as I think it would be a nice thread to reference in the future when building projects.

Winder Chaser, I think you idea of building the cabinet out of metal was interesting, but at the end of the day it doesn't seem like a realistic choice over MDF. I am very glad you shared you conclusions on what happened when you used the steel, and that great, but unless there is more to add, I think it's a silly thing to fight about on this thread.
Daryl, It's not worth fighting about...neither of you will win, and it will just distract the point of the thread. Lets be friendly here 

The chart about the different enclosures and their respective frequency response graphs is very useful, thanks for posting it. I think it proves one thing though, at least for now, there is no perfect shape for a cabinet. (which is why I went OB).

A bean speaker would also be interesting, has anyone tried this?

I would say the overall message is that the cabinet should be a dampened and rigid as possible, no matter what material is used.

Lets keep this going as I think there are some great things being discussed.

-West

[Daryl]

I would say the overall message is that the cabinet should be a dampened and rigid as possible, no matter what material is used.

Harebeth uses relatively light flimsy enclosures because lighter/less stiff walls are easier to damp.

Something to keep in mind.

Material choice is not very important though you will need to make different engineering choices depending upon what you use.

Enclosure shape also not very important except the baffle which was what the above chart was about (it had nothing to do with internal waves if anyone was unsure).

Myself I like big baffles the size of a door or just mounting the enclosure flush into a wall like in a studio.

[Wind Chaser]

Winder Chaser, I think you idea of building the cabinet out of metal was interesting, but at the end of the day it doesn't seem like a realistic choice over MDF.

...there is no perfect shape for a cabinet. (which is why I went OB).

Metal is costly, however if one wanted to go the metal route, I'd recommend aluminum as it is a much easier material to work with than stainless steel.

I'm in total agreement with you; the best enclosure is no enclosure.

[Daygloworange]

DGO,

That you "work with metals quite often" isn’t tantamount to fabricating speakers out of metal.  Make that same speaker out stainless steel and 1”MDF and compare the two.  Until then, whatever you think you might know pertaining to how they sound or what it takes to dampen them is neither scientific, nor objective or useful.

Windchaser, I don't know why this discussion has turned into a debate with you. I'm not interested in arguing.

This could be a very informative thread, let's keep it positive and informative.

I think you assume you know a lot about me and all the work that I do, when in fact, you don't. I have worked with metals for many years, and done work for a number of companies, and know quite a bit more than you might think I know. Here are just a few quick samples of some extrusions that were handy. There are others that I can't show due to NDA's.



I don't have to "make" speakers out of metal to understand the simple physical properties of different materials. Over the years I've worked with many metals, alloys, and composites.

What I do know about materials is scientific, objective and useful to this thread.

Metal is costly, however if one wanted to go the metal route, I'd recommend aluminum as it is a much easier material to work with than stainless steel.

Aluminum? You mean like this?



Don't rely on what you think you might instinctively know about metals, and search for information. It's out there....



http://www.tms.org/pubs/journals/JOM/0511/Burleigh-0511.html

Cheers




 

[shaynet]

While almost impossible to describe the myriad of combinations one could make, I would like to offer these facts:

 - metal enclosures typically have a much higher resonance "Q" - that is the amplitude tends to be higher, but over a narrower range of frequencies.  The advantage to this is that it tends to be easier to engineer a damping solution that more greatly damps the resonance peak (as opposed to broadband dampening).

- For the same thickness, metals will be stiffer than mdf (though working with metals as thick as we do mdf would be impractical).

- The shape of an enclosure makes a HUGE difference on the resonance modes of the panel.  Curved panels are stiffer than an equivalent sized straight panel. (with same bracing).  PSB is doing an excellent job of taking advantage of this in their enclosures.  The Waveform utilized fairly thin aluminum in the egg (a casting) to good effect (replacing the use of stacked indidually sliced pieces (like Magico Mini).

- moving a resonance up in frequency does not by itself make it harder to excite (take more energy).  However, it makes it less likely that a driver may provide the necessary energy.  For example, a woofer is not likely to provide a lot of energy at 1k to excite a mode.

It is amazing how often a single material trait is touted as being the "key" to performance.  It is also interesting to see how many vendors point to their "heroic" construction techniques as being the "only"
real way.  lol.  I personally prefer to see the simplist construction technique that yields the desired result.  (very easily measurable)

BTW, yes the Wilson material is a phenolic.  The company that makes it for them also makes materials for skate ramps and cutting surfaces - at least they did a few years ago.

[Wind Chaser]

Waveform utilized fairly thin aluminum in the egg (a casting) to good effect....

Actually those Waveform aluminum eggs are not that thin.  If anything they are over built.  I consulted with John Ötvös a few times before I went ahead with my stainless steel cylinders.  As he told me the proof is the pudding.  So there's no point in trying to persuade those self-styled experts who imagine they know everything.





MDF is cheap and easy to work with, and for that reason it is almost exclusively the only material used in enclosure design.  The vast majority manufacturers do not experiment, or even consider for that matter other materials.

In contrast, Krell is one of the few manufacturers who dared to challenge the status quo and realized the superiority of steel in their LAT series.

Metal is costly, expensive and challenging to fabricate; but the pay off is in the performance and those results are unattainable with MDF.

[JLM]

In engineering terms, material stiffness (stress versus strain) is called Young's modulus, or just "E".  Wood is about 1200 pounds per square inch (psi), structural steel is 29,000,000 psi, etc.  As mentioned above, stiffness is a factor of thickness squared and then squared again (to the 4th power).  So all else being equal, doubling the thickness results in an 8 fold increase in stiffness.  Stiffness/deflection increases in direct proportion to width, mass, "E", or the applied pressure loading.  Increasing mass has the additional benefit when considering conservation of momentum, so as the cone/air mass moves forward the speaker must move backwards.

Also consider that the decibel scale is logarithmic, so doubling the perceived sound pressure level (volume) requires a 10 fold power increase.  Again, the internal cabinet pressures are 100s/1,000s of times greater than those in the room.  You can even feel the "wind" at ports under high spls of deep bass. 

Yet cabinet design (shape/bracing) can be more important than choice of material or mass.  While the deflection of a cantilever (unsupported wing) of given length/width/thickness is 48 times that of a piece of material bonded at both ends of the same length/width/thickness, the harmonic (resonant) difference between the two is even larger.  Deflections of insupported length in either case are a factor of length to the 4th power.  So all else being equal, tripling the length results in a 81 fold increase in stiffness/deflection.


To sum up...

Linear factors:  material width, stiffness (Young's modulus), material density (mass)

48 to 1 factor:  wings vs. supported panels

4th power factors:  unsupported length, material thickness

Logarithmic factor: sound pressure level, frequency

In all this keep in mind that energy levels go up as frequency goes down and that cabinets primarily only effect frequencies below 300 Hz (the bottom 4 octaves).

[shaynet]

Excellent post, JLM.

I believe that the Young's modulus for MDF is 530,000.  It is still considerably less than steel or aluminum (aluminum is around 10,000,000).

Adding mass is always an interesting topic and one that I am experimenting with variables on.  The only downside to an evenly distributed addition of mass is that it moves the resonant frequency down (for the panel), where, as you pointed out, there is more energy to excite the resonance (i.e., a higher forcing function).  I am looking at the effects of asymmetrical mass addition to see if I can get the benefits, while minimizing the adverse impacts.

My comment about "thin" aluminum in the egg for the Waveform was relative to the thickness of an mdf enclosure.  The Waveforms, in general, were extraordinally engineered and over-constructed.  : ).

I have to disagree that cabinets really only have an effect below 300 hz.  I have heard (and measured) many a design with resonances up to 1k that caused audible impact.

Working with steel/aluminum does not have to be THAT expensive per unit.  however, the initial costs can be rather high.  I screwed up the design of an extrusion for a speaker baffle before (trying to make the speaker "pretty"), which cost me 3k for the new die.  Argh.  however, the production costs of the extrusion itself was not bad at all.  The key is quantity. 

There are some very clever uses of material out there.  The Rockport speakers are examples of design to the nth degree (I don't know if it is necessary, but the designs are possibly as good as it gets relative to minimizing vibration).  Paradigm is making using of steel in their Signature series.  We mentioned the Waveforms.  Relative to the price, I am not that impressed by the Krell.  They appear to be using thick extrusions.  PSB, as I mentioned before, is using formed MDF with great results.

To reiterate what JLM said, the design can have much more impact than the materials.  There are quite a few mdf enclosures out there that are really quite good.  There are a few that are excellent.  Some don't pay attention to the details.  Heck, PVC can make an excellent enclosure when used right.  Conversely, you can make a horrible cabinet with alternate materials.  I have seen flimsy, high vibration designs that utilized "good" materials.  Use of a high stiffness material does not guarantee success.

[JLM]

Thanks, I should have worded differently, that cabinets are designed to only affect frequencies below 300 Hz.

[sbrtoy]

I think there are a lot of people who would love to use exotic materials in their speakers, but with the current costs of aluminum, steel, plastics etc. skyrocketing it makes it pretty cost prohibitive. 

Driver costs have gone sky-high as well due to currency and market fluctuation, so it is a question of where you get more value. 

[sbrtoy]

BTW...isn't Waveform now defunct?  I think like many speaker manufacturers the difficulty is doing something labor intensive in small volume and making it pencil commercially.

For hobbiests it is a different story...obsession over common sense. 

[Wind Chaser]

BTW...isn't Waveform now defunct? 

It happened like this...  stress, divorce, health issues, more stress, then retirement.

[shaynet]

I didn't realize that he had gone through that.  His products were stellar - comparable to all the mega-priced gear that I have heard.

Unfortunately, convincing audiophiles to go with an active system, especially a large speaker system, is difficult.