[floobydust]

 I would imagine that many of the folks lurking here have heard of the "Golden Ratio" theory which defines a relationship between the 3 internal dimensions of the speaker enclosure. Skipping the Greek history lesson, in simple terms it defines the ratio as 1.6:1.0:0.6 (approximate). Applied to a theoretical design requiring 960 cubic inches, you would have an internal width of 10 inches, a height of 16 inches and a depth of 6 inches. By definition this "Golden ratio" should reduce standing waves and unwanted reflections in the enclosure itself.

 This implies that the front baffle has a size of 10 inches x 16 inches (internal dimensions) plus the thickness of the sides, top and bottom panels. This makes a pretty large surface overall compared to the relatively shallow depth, ie, the sides, top and bottom are much smaller. I've seen numerous design plans on the net which adhere to the "Golden ratio" and of course many more which don't.

 So I would pose two questions for the group:

1- Has anybody implemented similar designs (same driver, construction, materials, internal volume, etc.) which have a golden ratio version and a non-golden ratio version to test the theory and have some identifiable differences?

2- While adhering to the golden ratio design, has anyone tried moving the driver to one of the other panels (ie, use the side or top/bottom) as the front baffle and if so what, if any differences where identifiable.

 Regards, KM


 

[Ed Schilling]

Kevin,
1. yes. years ago.
2.yes. no difference to speak of as long as the cabinet was "proper" in all other areas.

Again, this area is just one part. It is just as easy to screw up a "golden ratio" cabinet as any other. There are many more important things to consider, I think. While internal standing waves are not to be taken lightly they can be dealt with in many ways and I'm not so sure the "golden ratio" is needed or wanted in many circumstances.

Just my opinion.

Ed

[Kevin Haskins]

I agree with Ed.    There are a lot of things going on in a loudspeaker.   Your problems in the room are going to dwarf your standing wave issues inside the box.    And... you can damp those with materials, put braces in the box to change the internal dims if necessary.       

[floobydust]

Kevin,
1. yes. years ago.
2.yes. no difference to speak of as long as the cabinet was "proper" in all other areas.

Again, this area is just one part. It is just as easy to screw up a "golden ratio" cabinet as any other. There are many more important things to consider, I think. While internal standing waves are not to be taken lightly they can be dealt with in many ways and I'm not so sure the "golden ratio" is needed or wanted in many circumstances.

Just my opinion.

Ed

 Hi Ed,

 Thanks for the response.... most of my speaker building days go back to the 70's... and mostly with Kef drivers and Decca ribbons (we were dealers for both). We did some internal bracing and damping to help reduce standing waves and experimented plenty with various damping materials, densities, etc. and had a nice recording studio and measurement equipment to test them with. One of the best setups we did was a B139 driver in a TL which to this day still delivers low frequency response that is exceptional. The guy I sold my pair to was still using them after more than 25 years.... possibly still as I lost track of him.

 I also agree with Kevin (like talking to myself) on the effect of the room. My main speakers are still Quad ESL 63 US Monitors and provide an excellent reference for anything else. When setup properly they really disappear acoustically in the room but setup can be tricky and there is a definite "sweet spot". The original Quad ESLs (had access to these too back in the 70's as I built a pair up for a buddy that got them in pieces on a "deal") had a much tighter "sweet spot" and more limitations on dynamic range and frequency response but were simply amazing in what they deliver sonically.

 I will be working on a enclosure design for the Fostex F120A and hopefully have something meaningful before year end.

 Regards, KM

[chadh]

Okay, this is probably a silly question, but whenever these golden ratio issues come up (in discussions about room dimensions, or cabinet sizes or whatever), I wonder the same thing.

I appreciate that using the golden ratio dimensions will reduce resonances and standing waves.  But there's essentially no way you're ever going to get the golden ratio exact, is there?  I think the dimensions are irrational.  So, given that you're always going to be estimating the golden ratio, do you have any reason to believe that getting "close" to the golden ratio gets you performance that's "close" to that of the idealized cabinet?  There are lots of simple looking dynamic systems that exhibit extreme sensitivity to initial conditions, and to changes in defining parameters.

I know chaos theory isn't fashionable anymore, but maybe someone could give me a quick idea about why I don't need to worry about that kind of thing here.

Chad

[Ed Schilling]

Kevin,
Since the 70's little has changed as far as those pesky laws of physics and enclosures. Drivers have gotten "better" but even that is on a unit to unit basis. All the new fangled ways of "designing" a cabinet all lead back to the same thing. A proper sounding TL will be just that regardless of whose math you  use.

Everything you knew and did then is just as valid today and if it worked then it will today and if it didn't well then.......

The real thing is that single driver speakers are very difficult to make work. 2 way speakers are MUCH easier. Much of what works with multi speakers in the way of cabinets is not going to work well for a single driver if you want both SPL and LF extension. No amount of math is going to fix this and where those two meet is what you live with.

I've looked at the 120. The MMs and low (ish) sensitivity ruled it out for me. But that is another story! And everyone's goals are different.

Good luck in your quest.

Ed

Chad....you posted as I was typing. Good one. You pretty much nailed it. There are probably just as many bad "golden ratio" speakers as there are good ones. The ideal cabinet (speaker system) is one that sounds good (to you).

[Wayner]

The Biblical proportions of the golden rule have become too expensive in the modern age. They also result in a no-traditional look, not that that really matters. I have built a speaker with the same exact dimensions using a SEAS 6 1/2" woofer. After fooling around with all of the formulas and junk like that, it sounded the best with a 1" port in the back, covered with some open cell foam (no tube). the design is called a "boom-box" which is similar to the Dynaco A25 series of speakers. They have great bass and mine ain't bad for a little 6 1/2" woofer. Fairly uniform on a low freq sweep, too.

As always, the ear is the ruler when it comes to speaker design IMHO.

Good luck, have fun

Wayner

[JLM]

I guess is that the golden ratio speaker cabinet doesn't matter because:

A)  The dimensions are so small that only very high frequencies would be affected;

B)  Those high frequencies are very directional so they would have to reflect several times before they could come out through the cone and thus eliminate the issue;

C)  Those high frequencies have much, much lower energy levels so the cabinet walls could absorb more of them;

D)  Most driver cone materials wouldn't transfer high frequencies through to the front.


But this does raise an important idea, that of what happens to all the sound (not just pressure) that goes inside the cabinet.  There's just as much sound inside the cabinet as out.  One concern is cabinet vibration.  Some cabinets have been measured to emit more sound than the driver due to thin walls/baffle and lack of proper bracing.  This makes every note sound like the cabinet (some designers design with that in mind for better or worse).  The other concern is sound that reflects back to, and through, the drivers.  Driver material is not acoustical imprevious, in fact they are quite the opposite.  Just hold a piece of typing paper against your mouth and hum. 

So a more important factor in cabinet design is to skew the back wall, thereby directing the direct reflection away from the back of the drivers.  Note that quarter wave tuned pipes, transmission lines, rear loaded horns, and of course open baffles all do this.

[Tliner]

Hi Ed,

I have been designing speaker systems mainly transmission lines since the late 1950's. I still have TL speakers with the KEF B139 bass drivers playing at the moment. When I A/B them with the latest design they are yesterdays speakers. There has been a lot of progress and refinement during the last 40 years.  They still work well and provide bass that is excellent. But modern drivers provide better slam and general dynamics. Today TL speakers can be designed so they are much smaller than the old KEF (Bailey) designs and sound better even though they are mostly 2 way. Every deign that worked well in the '60's still stands up today. In some respects nothing much has changed. 

The "golden rule" is scaleable to some extent and the smaller the enclosure the tighter the building tolerances. That said; different drivers have their own "specialities" and some drivers used in a TL speaker even buck the rule usually drivers with high SPL and Bl. The dimensions of the chamber directly behind the driver may have to be altered to attenuate standing waves and to give the driver sufficient breathing space. It is a juggling act to say the least!

But the dynamics of the listening room play the biggest part in the way music is perceived by the listener. I use  three different listening rooms to test speakers. One room is large and uncluttered and tends to accentuate the bass and the smaller cluttered room the speaker tends to sound dull and doesn't have the musicality in the bass and lower midrange. Long ago I stopped trying to design speakers for specific listening rooms and now design good all round performing speakers letting the owner to figure out their own room problems with a little guidance.

Good luck and keep the debate going.

Laurie.

[jules]

Something that hasn't been discussed so far is that the golden ratio tends to give cabinets with a wider baffle [as against the currently fashionable narrow and deep cabinet].

This can reduce the frequency at which baffle step compensation would be required by maybe a couple of hundred HZ and at the same time allow the driver to be placed somewhere closer to 1/3 of the way across the face of the baffle rather than close to the centre. This placement is supposedly an aid in diminishing nasty abrupt baffle step problems according to my limited understanding of such things.

What do you think?

jules

[JLM]

jules,

Depends of course on which two dimensions you pick to define the front baffle.  A small cabinet, say 8" x 13" x 21" could have front baffles of 8x13, 8x21, or 13x21.  In any of these cases the smallest dimension only varied by no more than the golden ratio of 1.61.

BTW the "golden ratio" is an invention of the ancient Greeks to reduce echos in those stone temples.  If you're constrained by retangular shapes its the best.  But speakers (even rooms) don't have to be.  We use retangles out of practical concerns of constructability and so they have become the best understood.  If you think about it, its one of the worst shapes for acoustics. 

Parallel sides promote standing waves, so non-parallel sides (especially the major panels) are preferred.  Thats why pipes (transmission lines, quarter wave pipes, horns, etc.) or a sloped baffle design should work best.  Again, most underestimate how much sound comes through the cone from inside the driver.  Just consider the term "paper thin walls" and you'll begin to understand.  Add to that the spls inside the cabinet (20 - 30 dB higher than outside) and you'll grasp the importance of avoiding standing waves inside the cabinet altogether.

[jules]

Yes, of course you're right. The issue of which face you choose as the front baffle is an entirely different topic.

Interesting origin for the "golden ratio" ... thanks

jules

[Scottmoose]

An old favourite was to use a ratio where height = 1.414 x width & width = 1.414 x depth (based on an old industrial design philosophy that was big in modernist & brutallist architecture). Both that and golden ratio tend to promote as even a particle density & minimise standing waves as far as it's possible to within a monkey coffin.

Does it make a difference? Yes, it can make an improvement but with many reservations IMO. A mediocre design is a mediocre design, period. Using golden ratio dimensions isn't going to turn it into a good design -it might reduce the mediocrity slightly (if you're very lucky). Conversely, it will improve a cabinet that's already good (it certainly won't hurt), providing of course that it doesn't take you away from your design goals. For e.g., assuming you wish your driver to be at ~ear height, and changing the dimensions to suit the aforementioned ratio moves it away from that, you've probably done more harm than good. YMMV, as ever.