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In Reply to: RE: The forgotten factor. posted by Thorsten on July 12, 2012 at 09:09:29
- The 'Power Response' is irrelevant. You are not everywhere in the listening room, you are at a specific position, hopefully more or less in front of your speakers. Reflected waves are attenuated by the reflection surfaces, and walls in the US are semi-transparent to low frequencies. Moreover, a large part of the reflected sound is out-of-phase. The 'Power Response' matters only in a all-concrete small lab, and the response at the listener's hears would still be different.
- The floor is typically a very strong reflector of low frequencies (and sometimes of mids and highs also - wood, stone, tiles). When out-of-phase, the reflection attenuates the direct sound.
As you, I don't have the ceiling's reflection problem, but often it is less critical than the floor reflection, except when the speakers are tall, the floor above made of concrete and low.
Follow Ups:
Darn things mucking up our sound. The walls to are a issue as is the ceiling heck your body's causing issues with absorption lets get ride of that too.
If the room is big enough to have a reverberant field then you hear the power response of the speaker.
Hi,
> The 'Power Response' is irrelevant.
Interesting. Really? So room treatment is a big scam to make people pay ton's of money for stuff they do not need?
> You are not everywhere in the listening room, you are at a
> specific position, hopefully more or less in front of your speakers.
Yes the sound you hear includes all the reflections that the Haas effect integrates with the first arrival...
> Reflected waves are attenuated by the reflection surfaces, and
> walls in the US are semi-transparent to low frequencies.
Most people do not live in the US AND even in the US you find many building that are actually very solid, though typical individual houses are indeed build in ways that raise eyebrows elsewhere...
The only house I ever lived in that had non-solid surfaces for the living room was a victorian semi-detatched house in London, the floor was wood (but only a few feet above solid earth (so quite reflective at LF) and the ceiling was wood too and hence had significant leakage... In all other cases all surfaces have been and are solid.
Arguably one needs to take the room acoustics of the taret room into account when designing speakers, so for example a speaker intended for an individual house build to US code would need a very different LF behaviour to one designed for a Condo in New York or a Flat Berlin or Tokyo.
> Moreover, a large part of the reflected sound is out-of-phase.
Really, would care to substantiate that?
Surely "in phase" and "out of phase" for a given wavelet depends on the time delay. As this varies greatly so will phase, hence the result is hard to predict. Moreover, we do not as such listen to sine-waves. and the human auditory system does not as such operate like a microphone.
There where reasons that in the days when only the Crown TEF (which I had access to) could make near anechoic measurements pink noise was used measurements in room (like when setting up speaker system in a studio).
> The 'Power Response' matters only in a all-concrete small lab, and
> the response at the listener's hears would still be different.
Yet you will find that in most cases that power response dominates the actual frequency response and perceived tonal balance at the listening position.
> The floor is typically a very strong reflector of low frequencies
> (and sometimes of mids and highs also - wood, stone, tiles). When
> out-of-phase, the reflection attenuates the direct sound.
And when in-phase the reflections amplify direct sound. In a solid structure pretty much all LF is reflected back and some will be in- and some out of phase, so with sinewaves we will get a lot of comb filtering.
However as the human hearing integrates sound in the Haas Window regardless of time delay (phase) and simply registers this as increased loudness.
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
The on-axis response only predicts the spectral balance of the first-arrival sound that reaches your ears. The power response predicts the spectal balance of the reverberant energy also, and I agree with Thorsten's giving greater weight to the power response.
The floor-bounce notch is a naturally-occuring comb-filter phenomenon, and as such is subjectively rather benign. It occurs every time two people have a conversation in a non-anechoic space. I'm not saying its effect is inaudible, just that it's not a big deal. The ears do not process sound the same way measuring equipment does; the microphone sums the first-arrival sound and the floor-bounce and gets a notch, but the ears can tell the difference and so you don't really hear that deep floor-bounce notch that looks so bad on a graph as long as it is naturally induced by the room's acoustics (and neither electronically generated nor on the recording, as in either of these cases it is readily perceived as coloration of the first-arrival sound).
One of my designs happens to minimize the floor-bounce notch through driver geometry, but that's more a side-effect than a major design goal.
Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Greater weight should not blanketly be given to on axis response or power response without first assessing the other half of the equation - room response. As noted by Toole, the ultimate response heard in rooms that are more highly absorptive will be more affected by direct, on axis loudspeaker response. Those rooms that are more highly reflective will have the opposite situation in which power response plays a vital role. Blanket statements are seldom accurate in this arena. When it comes to acoustics, the details determine what the outcome will be and generalizations are practically useless - all generalizations except for this actual statement about generalizations, of course.
: )
Well yes, if the room is absorptive enough that there is little energy delivered to the ears via reflections, then obviously the direct sound matters the most. But unless you have a highly damped room or a nearfield setup, that is unlikely to be the case. In most home listening rooms, once you are beyond about 5 feet back from the speakers (this distance of course varies with speaker characteristics and room acoustics), more energy arrives at the ears via reflections than via the direct sound.Toole notes that the following factors all correlate well with subjective preference:
1.The first-arrival sound’s frequency response at the listening position;
2.The spatially-averaged response across a window plus or minus 30 degrees horizontal and plus or minus 10 degrees vertical;
3.The spatially-averaged response of the early reflections from the four walls, ceiling, and floor;
4.The sound power, or the sum total of the speaker’s acoustic energy radiation; and
5.The directivity index, which looks at the difference between the first-arrival sound’s frequency response and the sound power (summed omnidirectional response).
Note that four of the five have more to do with what's happening off-axis than with what's happening on-axis.
I have no problem with taking the room and setup and listener positions into account when choosing speakers, but without such specific information it makes sense to look at what is likely to matter in most rooms. The direct sound matters and so does the reverberant sound, and in general the role of the latter is greatly under-appreciated in part because it is generally under-reported.
Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Edits: 07/14/12
Duke said:
" The direct sound matters and so does the reverberant sound, and in general the role of the latter is greatly under-appreciated in part because it is generally under-reported."
On that, I'm sure everyone here will agree - even Thorsten.
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