1)What makes one speaker image better then another one? If it is the lack of harmonics being produced and the lack of reflections being produced that are not in phase then why don't manufacturers run FFT on the output and publish it?

2)How does the output of a speaker change when many simultaneous frequencies are being produced. For example let's take an extreme, one (fictitious, full range) driver and let's say you play a tone of 400hz, then you add another tone of 1100hz, the another one of 1400hz and so on. How does the output change in terms of distortion, seperation, and volume of those sounds?

1. Two big components of this are the phase coherency of the drivers and the directivity of the speaker (which determines how it interacts with the room).
2. What you are talking about is called intermodulation distortion or IMD. Ideally, the driver reproduces the tones as the input signal but in reality, some non-related tones are generated.

my question is if these characteristics are quantifiable why aren't they published by speakers manufacturers nor by any establishments that conduct testing on speakers, it seems to me like very important parameters?

1)What makes one speaker image better then another one?
In my experience having acoustic treatment at the first reflection points is key to good imaging. Not which speakers you use. Yes, speakers can have an effect too, and that's a function of their off-axis response. But that still gets back to suppressing the strength of reflections!

2)How does the output of a speaker change when many simultaneous frequencies are being produced.
Ideally it will not change at all, and each frequency should be reproduced the same whether the other is present or not.

--Ethan

my question is if these characteristics are quantifiable why aren't they published by speakers manufacturers nor by any establishments that conduct testing on speakers, it seems to me like very important parameters?

Ha ha ha ha ha.

Speaker makers don't publish anything useful because they don't want you to know how bad they are. And Yes, I am dead serious. They do not publish distortion, or polar (directivity) plots, and usually even the frequency response graphs are so highly "averaged" as to be mostly useless. When I wrote my Front Wall Absorption (http://www.realtraps.com/art_front-wall.htm) article, I had to use professional speakers because those are the only ones with the guts to show off-axis response!

--Ethan

Ethan, then the question becomes if they are all so bad and I would think common knowledge among speaker manufacturers wouldn't the ones with better characteristics want to differentiate themselves by publishing these specs.

I guess I just feel a little WTF!!!

Who will set the standard for measurement and who decide how it is to be interpreted? Which measurements will translate directly into better sound? Now that the United States has become a secondary market (ask yourself who gets the new gear first?) will the Japanese and Germans willingly adopt an additonal set of standards?

Years ago outrageous or misleading claims by amplifier makers finally caused the FTC to set a standard for claims of amplifier power (both channels driven, resisitve load etc.). There is still dispute over the absolute worth of this standard in purchase decisions because most consumers do not understand the relationship between output Watts and sound presure levels, as well as the usefulness in surround sound applications. Nothing in the standard addressed the fact that there is no proven relationship between output power and sound quality nor the effects of speaker efficiency and room setting.

Polar plots of off axis power and distortion measurements for speakers are very difficult to relate to the sound or imaging of the speakers. Is 10% distortion at 40 Hz discernable with program material? Will 8% sound better? Should the distortion measurement be averaged across the speaker's range or weighted to account for a set of standard ears? If the measurements are taken in an anechoic chamber or on a tower out doors, will the numbers have clear meaning in your setup?

There are a small number of test labs that will measure speaker polar response in their anechoic rooms. They will do this to 5 degree resolution for on the order of $1k. As Ethan said, there are relatively few companies that measure and make this data available - mostly just the pro sound reinforcement folks.

Regards,
Terry

1)What makes one speaker image better then another one?

Good frequency response tracking between the pair, uniform frequency response in each speaker, uniform polar response so early reflections result in the same image shift at all frequencies, and reduced reflections off nearby objects due to controlled dispersion.


2)How does the output of a speaker change when many simultaneous frequencies are being produced. For example let's take an extreme, one (fictitious, full range) driver and let's say you play a tone of 400hz, then you add another tone of 1100hz, the another one of 1400hz and so on. How does the output change in terms of distortion, seperation, and volume of those sounds?

Low frequencies at higher output levels add audible IM distortion.

wouldn't the ones with better characteristics want to differentiate themselves by publishing these specs.

But then how would a company that sells speakers for $20k each justify 10 percent distortion at bass frequencies? :D

--Ethan

Part of the problem is (from the manufacturer's perspective) is that the majority of the market place wouldn't understand what the numbers meant and know how to apply those numbers to their application. ... besides the fact we'd get into a new, meaningless, number war similar to the nonsense we see with CR numbers in projectors.

The typical user wouldn't know what to do with those plots. And in a polar plot -- do you want wide dispersion, covering a large area, or narrow dispersion, reducing side bounce? Depends on the room and application. Near-field monitors are narrow, and PA monitors are wide, on the pro side. Consumer speakers have to trade off to some average situation.

Unfortunately, we can't measure the FFT or impulse response of a speaker, then look at it, and say "this will sound good/bad" -- the sound quality we perceive is not yet well enough understood to make the appropriate measurements.

Part of the problem is (from the manufacturer's perspective) is that the majority of the market place wouldn't understand what the numbers meant and know how to apply those numbers to their application.

The typical user wouldn't know what to do with those plots.

Yes, but that's still no reason to not publish the data. For example, Stereophile magazine publishes data that is not useful to many, such as speaker impedance versus frequency. So why not distortion? Everyone understands distortion.

Some of us do understand this stuff, including polar plots, and we're the ones our friends come to for advice. So I say "Bring it on!" :D

--Ethan

Oh, I would LOVE to see that. Bring it on indeed! But they won't.

The typical user wouldn't know what to do with those plots. And in a polar plot -- do you want wide dispersion, covering a large area, or narrow dispersion, reducing side bounce? Depends on the room and application. Near-field monitors are narrow, and PA monitors are wide, on the pro side. Consumer speakers have to trade off to some average situation.

Unfortunately, we can't measure the FFT or impulse response of a speaker, then look at it, and say "this will sound good/bad" -- the sound quality we perceive is not yet well enough understood to make the appropriate measurements.

I am somewhat echoing Ethan here but it would benefit many people to publish these things. When choosing a speaker for home theater versus music, or choosing a speaker that fits with your rooms acoustics. As far as people reading them, they are free to disregard the info and I would think that a majority of people who spend serious amounts of money on equipment would read the plots and if not they would learn to read these plots because everyone wants the most bang for the buck, that is why this forum has so many members.