In my experience, virtually all the points made above are pretty right on. However, I would like note two reasons for the skewed (measurable and/or audible) tone balances.
I believe most tone-balance/cabinet-tuning decisions are made to offset the audible effects of a speaker having serious amounts of phase shift at every frequency, high to low.
Bass boost, no matter how obtained, is most often used to offset the sharp/overly-aggessive sound of a phase-leading treble (or equivalent woofer time lag). Doesn't happen if designers listen to live music often. You also see designers turn down the tweeter, and "pull apart" the tweeter/mid crossover point to introduce a dip (measured) but "not" audible. Until you hear it after 30 CDs... especially the ones that "work out" the crossover range.
The other factor is the type of room- large and open, vs medium and damped, etc. East coast/West coast homes... Fortunately, in hi-end, most expensive speakers can be designed for use in moderately damped rooms of 300 to 700 sq ft with listening distances between 8 and 15 feet, for a seated listener on an average sofa. That's a useful set of constraints, in my experience.
When the phase shift in a speaker is reduced to just a very few degrees of fluctuation thru the main part of the audio band, it becomes MUCH easier to
A) set the amplitude response to sound flat and to measure flat, and
B) for the speaker's tone balance to remain similar in a wide range of positions.
I think it's important to try and state why something "happens". Above it may seem like I know what I'm talking about. But can I justify A) & B) very simply?
Yes-
For A) set the amplitude response flat:
Having excellent phase accuracy/time coherence between drivers means that all the amplitude peaks and troughs from woofer and tweeter line up over each other. You get the amplitude you put in, since nothing is cancelling. No matter what the test tone or the music.
When they are out of phase, what you measure depends on HOW you measure- the type of test signal, particularly. What you hear depends on the tone range and the complexity of the music.
For B) less room dependent:
Since reducing phase shift results in a more temporally compact, succinct presentation of the music's dynamics and tones, then you can hear the speakers more clearly apart from the room's echo. Which is an echo field also then less cluttered.
If a speaker has gross phase shift from the mid down to the bass, as most of the ones discussed above do, it is usually a lag on the order of many milliseconds- which is the distance to the wall behind, or farther. With ringing at the crossover point.
Which all sound like room problems because of the long time delays. "I just moved them out 1/2" and the bass got much better!" It did- but only because of a particular interaction with the room, and your location, exaggerated by that woofer's trailing output. Slow rhythm is the clue it is not the room.
My comments here are primarily directed at dynamic speaker designs. One factor I should mention, which frankly is just as important to "coming up with" an OK tone balance is the drivers:
Multiple mids and one tweeter change tone balance w.r.t each other, as you move away.
Multiple tweeters and multiple mids change relative tone balance as you move away.
So do multiple woofers vs a single mid.
Physics and measurements support this. Apparently, most designers ignore this, looking for some other performance aspect from using multiple drivers. They should tell you the design distance/listener height.
Hope this is useful info. Nice thread.
Do all of you see a trend? Egads! That would indicate speaker design is a mature technology. No way.
Best,
Roy
Green Mountain Audio
I believe most tone-balance/cabinet-tuning decisions are made to offset the audible effects of a speaker having serious amounts of phase shift at every frequency, high to low.
Bass boost, no matter how obtained, is most often used to offset the sharp/overly-aggessive sound of a phase-leading treble (or equivalent woofer time lag). Doesn't happen if designers listen to live music often. You also see designers turn down the tweeter, and "pull apart" the tweeter/mid crossover point to introduce a dip (measured) but "not" audible. Until you hear it after 30 CDs... especially the ones that "work out" the crossover range.
The other factor is the type of room- large and open, vs medium and damped, etc. East coast/West coast homes... Fortunately, in hi-end, most expensive speakers can be designed for use in moderately damped rooms of 300 to 700 sq ft with listening distances between 8 and 15 feet, for a seated listener on an average sofa. That's a useful set of constraints, in my experience.
When the phase shift in a speaker is reduced to just a very few degrees of fluctuation thru the main part of the audio band, it becomes MUCH easier to
A) set the amplitude response to sound flat and to measure flat, and
B) for the speaker's tone balance to remain similar in a wide range of positions.
I think it's important to try and state why something "happens". Above it may seem like I know what I'm talking about. But can I justify A) & B) very simply?
Yes-
For A) set the amplitude response flat:
Having excellent phase accuracy/time coherence between drivers means that all the amplitude peaks and troughs from woofer and tweeter line up over each other. You get the amplitude you put in, since nothing is cancelling. No matter what the test tone or the music.
When they are out of phase, what you measure depends on HOW you measure- the type of test signal, particularly. What you hear depends on the tone range and the complexity of the music.
For B) less room dependent:
Since reducing phase shift results in a more temporally compact, succinct presentation of the music's dynamics and tones, then you can hear the speakers more clearly apart from the room's echo. Which is an echo field also then less cluttered.
If a speaker has gross phase shift from the mid down to the bass, as most of the ones discussed above do, it is usually a lag on the order of many milliseconds- which is the distance to the wall behind, or farther. With ringing at the crossover point.
Which all sound like room problems because of the long time delays. "I just moved them out 1/2" and the bass got much better!" It did- but only because of a particular interaction with the room, and your location, exaggerated by that woofer's trailing output. Slow rhythm is the clue it is not the room.
My comments here are primarily directed at dynamic speaker designs. One factor I should mention, which frankly is just as important to "coming up with" an OK tone balance is the drivers:
Multiple mids and one tweeter change tone balance w.r.t each other, as you move away.
Multiple tweeters and multiple mids change relative tone balance as you move away.
So do multiple woofers vs a single mid.
Physics and measurements support this. Apparently, most designers ignore this, looking for some other performance aspect from using multiple drivers. They should tell you the design distance/listener height.
Hope this is useful info. Nice thread.
Do all of you see a trend? Egads! That would indicate speaker design is a mature technology. No way.
Best,
Roy
Green Mountain Audio
