Time coherence - how important and what speakers?

Roy,
Thanks for the long response. Here are a couple links that show interesting data on the above topics:

www.t-linespeakers.org/projects/tlB/radresponse.html

This has impedance data which shows a remarkable impedance flattening at the 1/4 lambda frequency at quite reasonable stuffing densities, in addition to a dramatic reduction in the driver resonance peak itself.

www.t-linespeakers.org/projects/martin/focal/test_line.html

This also shows a dramatic drop in the 1/4 lambda resonance at normal stuffing levels (using Dacron), and also has several other interesting results. One is that the reduction in speed of sound is far less than Bradbury etc's data on wool and fiberglass. You are likely correct that the microscopic fiber characteristics have a major role in this. Also, note that at the higher frequency peaks, the experimental data show near-perfect correspondence with the theoretical numbers, suggesting that there is effectively NO air-mass coupling to the cone at these frequencies. This one plot is what convinced me that there is indeed a strongly frequency-dependent air-mass coupling.

I will still take issue with your (implied) statement that added mass is not a problem. I understand the games that can be played with mass and compliance, but only at the expense of cabinet size and/or efficiency. I also understand that one can say that "you can always make the magnet bigger." But therein lies the real-world problem: you would like to keep the efficiency as high as possible (within reasonable limits), and the cabinet at a reasonable size, while being limited by the reality of the relatively weak magnetic fields achievable with fixed magnets. So added mass does not come without penalty. In addition, my passion for a long time now has been for 2-way systems, so my perspective tends to be skewed by that reality without my realizing the need to state it, and I should have prefaced my comments with it.

Again, thanks for the extraordinary effort you have put into this thread. It has been very enjoyable.

Gmood1-
I am glad to know you do not generalize based upon the design of the speakers. Ears should lead the way- So play an extremely wide variety of music and recordings (old/new/audiophile/distorted) until you hear what the speaker cannot do, as if you don't find those faults in the store, you will find them in the home at some point.

And when you find a flaw- such as "too peaky sounding on bluegrass", that means not only can you not play bluegrass, you'll find you cannot stand the sound of the massed, slightly dissonant strings that a 20th-century composer such as Samuel Barber or Morton Gould used to great effect, or soprano voices, or a Vienna Boys Choir disc, or realize the effect which comes over you hearing a Rachmaninoff piano concerto at full tilt, or appreciate more fully the genius of Hendrix, or the delicacy of touch required for ragtime piano, or Dixieland, or the inflections of Billie Holiday, or Janis Joplin, or Creedence Clearwater, or Chris Whitley, or King Crimson, or No Doubt, or Massive Attack, or Metallica, or Screamin' Jay Hawkins, or appreciate the real differences between...

So you play only the 'approved' audiophile recordings, of rather bland music.

You are wrong however, when you say there is no "best way to design a speaker" I could assume you are talking about basic decisions like woofer size, port or transmission line, six tweeters or one, but actually I really don't know what you mean with that statement.

There is a best WAY to design a speaker, which I'm sure you hadn't known, nor would I expect anyone to. It's the scientific methodology used to think through and then test and build and test and... And that method is for the designer to always start with the listener's location and the room around him and the SPL required and the bandwidth desired and the coverage angles. Those are exactly the parameters any professional concert-sound designer starts with. Then he's paid to work backwards to the drivers which will deliver that desired sound. Time coherence is only part of the equation, an important part.

And this approach to design is contrary to the way most all home speakers are designed- most of their designers got a wild hair and said something like, "the d'Appolito configuration is the way to go!" and never went beyond that, into understanding what happens because of that decision out at the listener's location. They began their designs at the cabinets instead of at your ears. This explains why so many high-end speakers are bought and then sold- the dissatisfaction.

So again, I'm not sure what you meant- maybe it was "don't trust any designer". Fine- in fact an excellent idea! But as you use your ears, don't do yourself a major disservice by listening to only audiophile recordings to find the best speakers. Happy listening!

Karls, thanks for the links- I've had a look, but will not respond here, as this is not the thread for that, and I probably have not the time to say anything useful. I do see, at first glance, what appear to be some wrong assumptions about what the impedance curve peaks mean vs. the 1/4-wave line lengths. But I'm likely wrong- their measurements do not go low enough below 20Hz to reveal the errors.

Phasecorrect- you make some good points about design execution, and bear in mind most speaker designers are nowhere near fully trained. Fortunately, no permanent harm comes from bad speakers, so those designers can "get away with it". You just wouldn't want them to engineer your car or medicines or food-handling machinery or house.

If I seem mean-spirited or overly critical- I am sorry, but what I've said about poor design methods is true- I have spoken to `way too many designers, while great guys, well-intentioned, smart and hard-working, simply never slogged through the graduate calculus and fluid dynamics, thermodynamics and the mechanical engineering it takes to make a speaker that performs well on most all music, in most rooms, with most amplifiers. And reviewers support those halfway design decisions saying, "These speakers really need tubes." or "They really can't play a distorted recording." While those are accurate statements, they put the blame on something else in the chain, and not the speaker. What a disservice to you, the listener! But then reviewers are usually not technically trained, so it's only natural. I would hope that anyone reading these submissions of mine here and on that European link I gave will see how basic physics applies to speakers and how that explains what we hear and also the discrepencies between measurement and hearing.

Best regards,
Roy

Roy,
Whats up with the Green Mountain Audio website???

There's been no spare time to finish the last few pages (for the new speakers), as we take care of orders/existing customers. However, it shouldn't be too much longer `till we can get back to it and get it published. Thanks for checking!
Best,
Roy

New Speakers?

Are you designing or upgrading any new bookshelfs?........