Speaker Design: choices vs limitations

[adLuke]

Hello all,
I am starting to learn a bit about the incredibly huge world of sound science.
Out of my ignorance a lot of questions, but one is bugging me the most:
Clearly sound waves are 3 dimensional. And I understand we represent them in 2d for our understanding.
But why most designs for speakers look at 2 dimensional problems?
The baffle (ok, probably that one I get), the diffusers inside, and also most speaker designs are just a box as if you want to tackle waves just one plane at a time.
Is this a choice because modelling 3d is too complex or is it because it is an extremely good approximation to what is needed?
Personally I am attracted to speakers that are curved, have angles and are not boxy (I own the JBL Ti2ks and Ti6ks and love the design).
But willing to enter the DIY world I would like to know if I should stick to boxy speakers and not venture into anything else.
Thanks everyone for their piece of mind here.

 

[ppataki]

I can try to comment on the question about the boxy speakers:
Standing waves usually get formed between two parallel surfaces
A room - and a traditional speaker box too! - has three of these parallel surfaces so the situation is pretty bad
These standing waves inside a speaker cabinet can create unwanted resonances, colorations, etc.

However there are shapes that have fewer parallel surfaces or none at all, for example a sphere or a square based pyramid
If you build your cabinet in of these shapes there will be no standing waves formed inside the cabinet

Having said that due to practical considerations I guess very few people venture into that domain....

 

[RayDunzl]

Never saw a Ti6k before.

Made in Denmark.

JBL - Ti1k - Ti2k - Ti6k - Multiple models - Speaker set

An eye catching superb surround set from JBL Ti-k series, consider these are the most beautiful speakers ever designed by JBL, solid built quality with modern design, due to high sensitivity and 6ohm it will fit into any surround receiver nowadays, all speakers has been fully tested and pain in...

www.catawiki.com

 

[adLuke]

Never saw a Ti6k before.

Made in Denmark.

JBL - Ti1k - Ti2k - Ti6k - Multiple models - Speaker set

An eye catching superb surround set from JBL Ti-k series, consider these are the most beautiful speakers ever designed by JBL, solid built quality with modern design, due to high sensitivity and 6ohm it will fit into any surround receiver nowadays, all speakers has been fully tested and pain in...

www.catawiki.com

Yes indeed. Made in Denmark. Beautifully I think, but don't have a lot of experience.
I was awestruck back in early 2000s when I bought them.

 

[adLuke]

I can try to comment on the question about the boxy speakers:
Standing waves usually get formed between two parallel surfaces
A room - and a traditional speaker box too! - has three of these parallel surfaces so the situation is pretty bad
These standing waves inside a speaker cabinet can create unwanted resonances, colorations, etc.

However there are shapes that have fewer parallel surfaces or none at all, for example a sphere or a square based pyramid
If you build your cabinet in of these shapes there will be no standing waves formed inside the cabinet

Having said that due to practical considerations I guess very few people venture into that domain....

Thanks, that was my guess as well. And I was wondering why I don't see more pyramid-like cabinets given that curved surfaces are much more complex to obtain and, I bet, to model.

 

[Jazzman53]

Have you considered omitting the box entirely? OB's are popular in the DIY community.
DIY ESL's are pretty awesome too.

 

[Deleted member 46664]

But why most designs for speakers look at 2 dimensional problems?

Short answer? Because the speaker cone is moving linearly in only 1 dimension. Thus the sound pressure tends to be a result of the cone motion actually changing the size of the room and/or the box it's in.

The speaker kicks out... a wave of travelling pressure is created. It's complex, like the wave on a beach... but it is still only moving in one dimension.

 

[DVDdoug]

Clearly sound waves are 3 dimensional.

I'm not sure what you mean or how that relates to speaker shape.

The sound wave hitting your ear is simply a pressure wave could be described as one-dimensional or it can be defined in two dimensions as amplitude & time (like the wave you see on an oscilloscope or in an audio editor). If you record that sound with a microphone, those two dimensions completely capture all of the information. But with one ear we don't hear "time" since there is only one pressure intensity at any instant in time. We perceive the pressure changes as pitch or frequency which is time-related. With both ears you get time & phase differences (related to the speed of sound in air) as directional cues.

I would describe regular stereo as one-dimensional... It's a "line" between the left & right speakers with a "phantom center" and an (imperfect) illusion of a soundstage in-between. Regular surround is two dimensions (where sounds can appear to come from any direction in a plane). Atomos adds the 3rd dimension of height.

 

[DVDdoug]

Speaker design & construction involves many compromises and design choices. In fact, most good speakers & monitors are "simply boxes", often with special attention given to the way the soundwaves from the tweeter reflect off of the baffle, and sometimes there is a waveguide or horn.

And some speakers are designed to be omnidirectional or to otherwise interact with the room instead of just "shooting the sound" toward the listener. Of course with more room interaction the performance is more unpredictable in any random room.

Every speaker manufacturer will tout their design choices & as a benefit or advantage.... That could be enclosure shape or cone material or ported or sealed, etc. But usually they are just decisions & compromises and another manufacturer could get the same performance with different choices.

 

[DVDdoug]

And I was wondering why I don't see more pyramid-like cabinets

My home-built speakers are trapezoid... The front & back are parallel but the sides tilt-in so the bottom is wider than the top. This was a purely cosmetic decision. The speakers are tall and main speakers stack on top of the larger subwoofers to make a larger trapezoid.

 

[Jazzman53]

My home-built speakers are trapezoid... The front & back are parallel but the sides tilt-in so the bottom is wider than the top. This was a purely cosmetic decision. The speakers are tall and main speakers stack on top of the larger subwoofers to make a larger trapezoid.

Share a pic?

 

[adLuke]

Have you considered omitting the box entirely? OB's are popular in the DIY community.
DIY ESL's are pretty awesome too.

I am still a novice but yes, I'm considering that as well. Only downside would be they're not really as good looking as some cabinets out there..

 

[adLuke]

I don't understand how we can consider the sound waves as one-dimensional or two (considering time).
To me it's clear that sound expands in 3 dimensions like a sphere: consider hitting a spoon on a glass.
That sounds goes out in all directions whether you're right or left, front or back, above or below the glass.
So if sound radiates in all 3 directions, it bounces off on all surfaces.

 

[Deleted member 46664]

I don't understand how we can consider the sound waves as one-dimensional or two (considering time).
To me it's clear that sound expands in 3 dimensions like a sphere: consider hitting a spoon on a glass.
That sounds goes out in all directions whether you're right or left, front or back, above or below the glass.
So if sound radiates in all 3 directions, it bounces off on all surfaces.

On a speaker you have only one surface radiating sound ... and it's omnidirectional only for a very small portion of the frequency range. In each case -- woofer, squawker, tweeter-- as the wavelength of the sound gets closer to the size of the cone it becomes increasingly directional.

 

[Another Bob]

If you build your cabinet in of these shapes there will be no standing waves formed inside the cabinet

An organ pipe has no parallel surfaces and resonates like crazy. Not quite the same thing, obviously, but the point still stands.

There is a ton of research out there - by the professionals as well as the DIY community - on enclosure shapes. I think it can be summarized as: yes, it makes a difference, but 1) not as much as you might think, 2) some shapes that intuitively look promising are worse than rectangular solids, and 3) it's probably not worth the added manufacturing complexity. Standing waves of the frequencies present inside speaker cabinets can be satisfactorily dealt with through absorbtion. If you want to complicate your build, you're probably better off focusing on rounding the front baffle to deal with diffraction (you need a pretty big radius if you want to address more than the top octave) and bracing to address panel vibrations.

 

[adLuke]

Thanks so much @Another Bob .
I would appreciate if you could give me some idea of where to find some of the research.
All I am trying to do is get something that is pleasing to the eye without messing the sound!
I think the JBL TiK series did that pretty well.

 

[Jazzman53]

I am still a novice but yes, I'm considering that as well. Only downside would be they're not really as good looking as some cabinets out there..

Maybe, maybe not:

Jazzman's DIY Electrostatic Loudspeaker Page

DIY electrostatic loudspeakers

jazzman-esl-page.blogspot.com

 

[Another Bob]

I would appreciate if you could give me some idea of where to find some of the research.

Unfortunately, I can't. I remember one AES paper in particular that measured many midrange enclosure shapes, but that was probably 20+ years ago and I have no idea what the title was or who the author was. And much of the DIY stuff tends to be buried in threads with titles that don't help the search. Hopefully some of our other members can chime in, as we have both skilled DIY practitioners and commercial speaker manufacturers in this forum. The main thing, of course, is to stick to content where the authors have actually built things and measured the results. As with many audio topics, there's a lot of nonsense out there being repeated as fact.

Edit: A little more searching led me to this thread: https://www.diyaudio.com/community/threads/midrange-enclosure-internal-shape.369316/
It may be that those Jim Moriyasu articles in Speaker Builder were what I remembered as an AES paper.

 

[captainbeefheart]

"Sound waves" or pressure waves in regular atmosphere follows the same equations as fluid dynamics. The equations show how nonlinear this mechanism is, basically the peaks are higher energy portions of the wave and the trough are the lower energy portion. These localized pressure changes distort themselves, the wave travels faster during the high energy phase vs the lower energy phase.

This is why I feel people tend to describe single ended amplifiers as natural sounding because the nonlinear distortions (even harmonics) is what we hear in nature.

Moving backwards to the speaker cone which creates these localized pressure changes, think of the speaker as a motor, the motor moves in one dimension in and out, like a pump if you will.

 

[dc655321]

"Sound waves" or pressure waves in regular atmosphere follows the same equations as fluid dynamics. The equations show how nonlinear this mechanism is, basically the peaks are higher energy portions of the wave and the trough are the lower energy portion. These localized pressure changes distort themselves, the wave travels faster during the high energy phase vs the lower energy phase.

Got a reference for that?

That does not sound like acoustic physics I am familiar with. At least not below shockwave phenomena.