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In Reply to: RE: Ideal frequency response curve posted by Inmate51 on June 17, 2015 at 22:19:25
In your post you say "And, so, yes, a roll-off at upper frequencies is desirable, and is one of the things which acousticians consider when designing or renovating rooms for music."
However, what if the room is acoustically dead or one's high frequiency hearing is beginning to roll off? Its much easier to correct in room response with a speaker whose response is flat across the entire spectrum than one that is rolling off in the high end.
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In most rooms, the frequency response you hear at the listening position is dominated by the overall power response radiated by the speaker into the room and how it interacts with the room. The overall power response is never flat.
Suppose you design a speaker that is perfectly flat when measured at 1m distance on the tweeter axis in an anechoic chamber, which is a design target for some companies. Unless the speaker has perfect constant directivity (none does), the response off the tweeter axis will not be flat. The dispersion characteristics of most speakers lead to an off-axis response that slopes downward with frequency, with the slope increasing as you move further off axis. Hopefully it's a smooth curve without any major peaks or suckouts, but few speakers achieve that. And the peaks and suckouts vary depending on whether you are moving off axis horizontally or vertically.
Also, as you move out from 1m distance, the on-axis response will change too. It will become generally down sloping, with some peaks and dips. This change with distance occurs even under anechoic conditions.
Good speaker designers pay as much attention to the off-axis response as the on-axis response, making trade-offs between flatness of the on-axis response against the shape of the total power response. If you chase perfectly flat on-axis pseudo-anechoic response and take what you get off-axis and at distance, the result ends up sounding colored in-room.
Now suppose you were to design a speaker that is both flat on-axis and you try to control off-axis response by limiting directivity as much as practical. The result will have a flatter power response, but will also sound unnaturally bright. Because music isn't being produced with that kind of target response in mind.
I concur that there is no such thing as a perfectly flat speaker. I just don't like designs where they purposely try and roll off the high end.
As has been pointed out several times in this thread, flat does not sound correct. Everybody designs for a roll-off. The question is how much top end roll-off is right in a speaker, and there is no objective answer because the end result is dependent on external variables such room, listening distance, positioning, and so on.
That's where the B&K and similar curves come into play. The B&K curve is one attempt to capture what response sounds the most natural. A designer who accepts the B&K curve as a reference will try to achieve a power response that follows the curve in a typical room. Of course, deciding what is "typical" is guesswork.
You seem to be hung up on thinking that there is an objective standard that you can measure loudspeaker frequency response against and there really isn't.
One might be forgiven for thinking that an objectively good speaker is one that measures flat on-axis at 1m in an anechoic chamber, but that is neither necessary or sufficient. It is a somewhat arbitrary design target. I can design two speakers that both measure flat on-axis at 1m pseudo-anechoic, but with very different power responses, one that rolls off slowly with increasing frequency which sounds too bright and one that rolls off rapidly and sounds too dark.
Similarly, I could design a speaker with an intentional rise or dip in the on-axis 1m anechoic response which compensates for a falling or flaring off-axis response such that the response at the listening position 3m away is smoother and flatter than if I had designed it with a flat on-axis 1m anechoic response.
"Good speaker designers pay as much attention to the off-axis response as the on-axis response,"
Seriously?!!
And this is news to whom?!
:)
"...or one's high frequiency hearing is beginning to roll off?"
What did you say? Could you speak up - I can't hear you. ;)
It's well-known that a reverberation characteristic which is somewhat longer at the low end and shorter at the high end generally provides a more desirable room sound for music. It gives a greater sense of "fullness" or "body" to the sound. Whether or not this is related to our reduced sensitivity to lower frequencies, I don't know - I haven't ever studied it from that angle - but I'd suspect that it is.
With regard to acoustically "dead" rooms, that's an interesting point. If you've ever been in a really nice studio control room, you know what a pleasure it can be, even just for conversing with another person - forget the music, just talking sounds great! Here'e the funny thing, in a small-ish, dead-ish room, there really isn't a "reverberation time" per se. This is because the "reverberation time" is so short that the sound never gets to what we would call a "steady-state" level from which we can measure an RT60. This is not to say that the quality of the reverberant field isn't important - it is! - but it takes another set of skills to do small-ish dead-ish rooms well, and that's something which I haven't done in YEARS.
Hearing loss: Oddly enough, adding more high frequency content to the room makes things worse, not better. What we want is more detail, and adding more high frequency energy to the reverberant field doesn't accomplish that. This brings up the issue of speaker output, and how it affects the sound we hear, in the room we're in.
Does that answer your questions?
Based upon your questions, you don't appear to be a neo-audiophile.
Fess up. :)
:)
I'm a crusty objective engineer..an audiophile's nemesis or nightmare. :)
My definition of speaker detail would be a speaker's ability to faithfully reproduce the signal without adding a voice of its own by either smearing phase relationships or by emphasizing or de-emphasizing (if that's a word) a single or a band of frequencies. Distortion also plays a significant role in this and I'm going to be looking at Floyd Tooles work on linear and non linear distortion and how humans perceive it. I want to understand this.
Adding more high frequency energy in a deadish room would help make the high end sound more available but in a lively room would hurt the high end. I would think that its easier to correct for a flat response whether you have to emphasize or de-emphasize the highs without affecting neighbouring frequency bands.
Its nice debating this with you BTW. :)
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