Although I don't have the room optimization experience that most of the others have had, I'd like to offer one small but I think significant point.
Particularly once you get above bass frequencies, tuning the room for flat frequency response using a test cd, microphone, etc., is not necessarily going to get you the best sound, and in fact probably won't. The microphone is not going to discriminate very well, if at all, between early arrival sound (the direct path from the speakers to the listening position) and later arriving sound (reflected off of walls, ceiling, etc). But your ears will!
I believe that some of the more sophisticated (and expensive) equipment that does this sort of thing can help to take arrival time into account, in a meaningful manner, but a Radio Shack sound level meter used with test tones from a cd will not. Although I think you will get meaningful results that way in the deep bass region, because of the long period and wavelength of the tones, and the consequent lack of timing sensitivity and directionality of our hearing at low frequencies.
Regards,
-- Al |
In the bass, the arrival/decay times are more easily measured and corrected whereas at higher frequencies room mode interactions approach randomness. Thus, at those higher frequencies, only FR adjustments are feasible. Yes, at higher frequencies only FR adjustments are feasible, but the point I was trying to convey is that making those FR adjustments on the basis of measured flat frequency response, in response to continuous tones monitored only in the frequency domain, will not provide best results. Listening to music provides the last (and most important) word in that part of the spectrum, it seems to me. Arrival times in the deep bass assume importance particularly because of reinforcement and standing wave issues, as everyone probably realizes. Which causes the measured (and heard) amplitude of deep bass to vary as a function of frequency and location in the room, and which can be more easily corrected on the basis of measurement, as you indicated. Regards, -- Al |
Newbee -- I don't think you are missing the point, you are just making some additional points.
To re-state my basic point, room effects at mid and high frequencies are heard differently by microphones + sound level meters than by the human hearing mechanism. The human hearing mechanism tends to some degree to "latch on" to the leading edges of transient waveforms, and give them greater emphasis than what may follow a few milliseconds later. I think that is pretty well recognized. But a microphone + sound level meter monitoring a continuous frequency sweep, or a series of tones covering the different parts of the spectrum, will not do that -- the late arriving sounds at any given frequency will be taken into account, so to speak, simply based on their amplitude. Therefore, whatever the desired tilt of the fr may be, tuning the room or the system to provide it on the basis of that measurement technique will not give the desired result when listened to by a human.
Regards,
-- Al |
The human hearing mechanism tends to some degree to "latch on" to the leading edges of transient waveforms, and give them greater emphasis than what may follow a few milliseconds later. Re my earlier comments on this issue, in a post in a different current thread Shadorne referenced a Wikipedia writeup on the "Haas Effect," which is what I was referring to without knowing its name: http://en.wikipedia.org/wiki/Haas_effectA brief excerpt from that article: When two identical sounds (i.e., identical sound waves of the same perceived intensity) originate from two sources at different distances from the listener, the sound created at the closest location is heard (arrives) first. To the listener, this creates the impression that the sound comes from that location alone due to a phenomenon that might be described as "involuntary sensory inhibition" in that one's perception of later arrivals is suppressed.
The Haas effect occurs when arrival times of the sounds differ by up to 3040 ms. As the arrival time (in respect to the listener) of the two audio sources increasingly differ beyond 40 ms, the sounds will begin to be heard as distinct. Thanks, Shadorne! Regards, -- Al |
Good info, Kal, thanks!
To put all this in perspective, we should keep in mind that as a rough approximation sound propagates through air at around 1 foot per millisecond, varying somewhat with temperature, altitude, and other factors.
Regards,
-- Al |
most speakers display the sharp roll off in the highs above 10K. I think mostly because you are comparing your 'in room specs' with anechoic measurements made by the manufacturer either 1 or 2 meters from the speakers. I wonder if treble beaming could be a factor as well, assuming the tweeters are pointed straight ahead. Should be easy enough to check, by toeing the speakers in a little, and re-measuring. I had looked at the specs for the speakers, and they specify a horizontal dispersion covering a 60 degree arc (meaning +/- 30 degrees from straight ahead). Which would make toe-in especially important were they to be moved further apart. It's unfortunate, though, that it's impractical to move them further apart; I agree with Newbee that it would be likely to improve imaging considerably. Regards, -- Al |
Shadorne -- Thanks for the good explanation and the good reference!
Regards,
-- Al |
Al: the speakers are indeed facing straight ahead. I gather beaming refers to high freq, right? Shadorne's [very interesting] explanation seems to suggest beaming in the mids. I have no clue what the dispersion of the mids driver is. Anyway, as Newbee said, at 11 ft away it would seem dispersion would be wide enough, right? My understanding is that a driver will tend to beam as its diameter approaches or exceeds the wavelength of the sound it is radiating. According to a quick calculation I did, the one inch diameter of your dome tweeter corresponds roughly to the wavelength of a 12 kHz note. So at or near that frequency, and higher, it could be expected that the tweeter's dispersion would narrow considerably, and progressively with higher frequency. The speaker is spec'd for +/- 30 degrees dispersion, which your listening position clearly satisfies, but we have no way of knowing how rigorously that spec was defined, e.g., if it was intended to cover all frequencies up to 20kHz. In principle, a similar concern could exist with respect to the mid-range driver, given its 6 inch diameter and 4kHz upper crossover frequency. But I would have higher confidence that the manufacturer's spec for dispersion would be accurate for the mid-range frequencies, than for say 15 to 20kHz which most people can't hear anyway. So that is the background on why I raised the question, but I think that Shadorne's good response pretty much puts the issue to bed. Regards, -- Al |
