...same thing goes for the self-interference notch off the back wall too. That kind of is a little more intuitive, since the reflection off the back wall is generally in line with the listener. There's not usually a large angle of incidence. But still, it's probably worth mentioning that the biggest notch I see is at the frequency where the speaker is spaced 1/4λ from the back wall, not necessarily where path length difference is 1/2λ. It's usually the same thing in this case though, or close to it.
but they are delayed by 10ms and reduced in volume so our brain can distinguish.
Yes, but when the speaker is 1/4λ from a boundary, the reflected wave is 1/2λ away.
Hello,
Isn't is obvious? In small rooms within the ears integration time there is more energy at the treble than in the recording venue which is usually larger acoustic space. Because in small room the reflection pattern is more dense. And because at lower freqs the integration times are longer so the effect does not show up as it does in treble. That's why to perceive the same 'flat' treble must be attenuated (smoothly).
- Elias
Isn't is obvious? In small rooms within the ears integration time there is more energy at the treble than in the recording venue which is usually larger acoustic space. Because in small room the reflection pattern is more dense. And because at lower freqs the integration times are longer so the effect does not show up as it does in treble. That's why to perceive the same 'flat' treble must be attenuated (smoothly).
- Elias
Sorry, it wasn't clear to me that you were specifically talking about the frontal wall.
I promise I'll have a listen.
Adding a single reverb at 11ms isn't going to recreate the dipole experience in room. Perhaps I'll make an omni recording for you of a monopole vs dipole.
Even in large auditoriums, the direction of the reflections is very important. Researchers now use multiple microphones to measure the angle and intensity of the reflections. The desire is to maximize the lateral ones and minimize the vertical and frontal ones. I know of no instance in room acoustics where it is deemed desirable to have frontal reflections.
Maybe I'm nit-picking, but it's still not clear to me that the reference is only to the front wall. I would consider any enclosing surface, be it front, back or side wall, floor or ceiling to be a boundary. Small rooms could have the closest boundary (outside of the floor) be the side wall depending on placement. The 1/4λ spacing example would not result in the same patterns at the listening position for anything other than the front wall.
Dave
The front wall or the floor. These are two boundaries that are often around one meter away from the sound source.
I regularly measure ~120Hz floor bounce notch, and this is from the self-reflection interference from the floor. I can see it outdoors with no other boundaries present. If the speaker is ~one meter up, there will be a pretty deep notch in this region. That's where the sound source is 1/4λ away from the ground, so the reflection is 1/2λ. Naturally, the notch is pretty deep.
The thing is, the path length delta creates a notch too. I find it much less deep, so little in fact, that sometimes I can't find it. The one that's deep is the one where the boundary is 1/4λ away. I have always assumed it is because the sound is omnidirectional at this frequency, so the interference is strongest from the radiation where the reflected angle of incidence is zero.
This is different from the vertical nulls, which are formed from path length deltas. Of course, the sound is much more directional at that frequency.
In the case of a guitar... I prefer indoors to the semi anechoic outdoors especially during 6-8 months of the Canadian climate.
..... heading outdoors now.
Measuring my current room seems to agree strongly with this...which does surprise me somewhat, compared with measurements in previous rooms I've had.
I have the midbass driver of my speakers 70cm off the floor, and of course notice a significant notch in the response between 100-150Hz. 1/4 wavelength is 123Hz...
Just recently I decided to try a little experiment - I pulled one of my 12" woofers out of storage and propped it up on the floor beneath the left speaker, (which is on a small table) completely unbaffled, with a 300Hz 12dB/oct low pass filter, driven in parallel with the main speaker.
The hole around 123Hz (which actually extends from 100Hz to 150Hz or so) is completely filled in - an increase of about 8-10dB.
There is also a bit of a hole in the 200-300Hz range which roughly corresponds to the calculated floor bounce with a listening distance of 3 metres and ear level of 1m.
This hole is only improved about 2dB with the floor mounted woofer in place - true, it's near it's crossovers low pass frequency, but even without a filter the change was less than I expected. All other frequencies show little or no change in the steady state response.
So this measurement agrees with your suggestion - the higher frequency floor bounce cancellation sees a moderate improvement but the big improvement occurs at the 1/4 wavelength frequency for driver height, which falls much lower in frequency, and is listener position independent.
The cure in both cases is the same - a low mounted woofer, but the 1/4 wavelength cancellation requires a lower woofer than that calculated from unequal path length floor bounce alone, so I might have to revise my idea of what the ideal height is...(mind you with a 12" woofer the cone itself is so large compared to the potential height off the floor that I've found the exact height becomes a lot less fussy)
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Big difference between making music and reproducing music and what works for a hall may be exactly the opposite of what is needed for a music room.
In reproduction, we don't want to hear or otherwise locate the speakers. As a goal, the speakers should be completely undetectable no matter how you listen or turn your head, etc.
The speakers are just transducers to put motion into the air that the listener can posit as an orchestra in a hall. We want to have a phantom image of something else, not a veridical image of the speakers.
Some particulars can never be well reproduced by two speakers and fortunately, we can readily settle for a kind of loosey-goosey version without the sound seeming ambiguous. The gut-feeling of ambience is that way.
Other factors, like left-right position, our brains are pretty particular about and so the cues leading to left-right perceptions have to be very consistent, stable, etc. (Heard a Gilbert and Sullivan operetta on PBS last night - very clear voices but they sure could wander about the stage fast. I think that was because they would face or face-away from the mics while trying to be good actors on the stage and that ended up in my perceptions in my music room as motion across the stage.)
My 2-cents
In reproduction, we don't want to hear or otherwise locate the speakers. As a goal, the speakers should be completely undetectable no matter how you listen or turn your head, etc.
The speakers are just transducers to put motion into the air that the listener can posit as an orchestra in a hall. We want to have a phantom image of something else, not a veridical image of the speakers.
Some particulars can never be well reproduced by two speakers and fortunately, we can readily settle for a kind of loosey-goosey version without the sound seeming ambiguous. The gut-feeling of ambience is that way.
Other factors, like left-right position, our brains are pretty particular about and so the cues leading to left-right perceptions have to be very consistent, stable, etc. (Heard a Gilbert and Sullivan operetta on PBS last night - very clear voices but they sure could wander about the stage fast. I think that was because they would face or face-away from the mics while trying to be good actors on the stage and that ended up in my perceptions in my music room as motion across the stage.)
My 2-cents
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And my 2-cents on dipoles - and as an ESL fanatic: dipoles (or ESLs) have certain virtues that adherents LOVE. Adherents are prepared to compromise on other virtues which might be important to other people, and vice versa.
I was the last guy on the block to go to stereo, prefering to afford one great mono system rather than two mediocre stereo speakers. Others on this forum might have done the same.
Yes, there are legitimate differences in personal values in sound reproduction. Until speakers are perfect in all aspects, there will be personal choice about what matters most.
You'd have to rip the Dayton-Wrights from my cold, dead hands before I'd consider using blocks of heavy cardboard to create music.
I was the last guy on the block to go to stereo, prefering to afford one great mono system rather than two mediocre stereo speakers. Others on this forum might have done the same.
Yes, there are legitimate differences in personal values in sound reproduction. Until speakers are perfect in all aspects, there will be personal choice about what matters most.
You'd have to rip the Dayton-Wrights from my cold, dead hands before I'd consider using blocks of heavy cardboard to create music.
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David, didn't catch this post at first. What do you want to prove with those files?
Same for me. The early reflection from the side wall near
the speaker is good for nothing IMO.
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Also for the (opposite and later) lateral reflections:
They may increase spaceousness but are they "needed"
for "good" reproduction ?
I'd like to see reflections
(due to delay, intensity, direction) in terms of
"some are less detrimental".
Listening room reflections cannot be useful for
reproduction. They exist and we have to make the
best of it, ecspecially as our living rooms are not
control rooms usually.
Somewhat higher broadband directivity is an approach
to have a higher direct/reflected ratio even for larger
listening distances.
Dominant frontal reflections are detrimental
(especially if too early and intense), agreed.
A dipole produces predominantly frontal reflections
if placed/toed wrong.
The usual "panel parallel to front wall" placement is
nonsense and only introduced because with many
designs the highs fall off off axis:
With such designs you have to choose between
"pestilence and cholera" as we say in german.
(Dull sound or unbalanced modal excitation of
the room including detrimental frontal reflections.)
Dipoles having a consistent coverage from midrange
to highs - only very rare designs - give you the
opportunity to choose where you want the reflections
to come from predominantly.
So are we discussing preferred direction and delay of
listening room reflections or having another
dipole/monopole discussion ?
As i said: Dipoles (and more cardioids) are the speakers
which offer the listener to choose and also treat
the room more selectively.
If someone likes excessive combing and dominant
frontal reflections, he can misuse a dipole speaker
to achieve that.
It's in the mix, don't you think ?
The monopole box can just claim to circumvent that
misuse, by allowing no choice. But solving a
problem is different, which makes a cardioid attractive
IMO.
Since we were discussing dipoles and I was voiceing a concern about extra full range energy that would bounce off the front wall, while others were saying "so what", I thought I'd do a reasonable simulation of it. Dipoles 5 ft in front of a wall were suggested so that would be a reflection delay of about11 ms. Rear output is out of phase (which sounded like it lowered all the resonance pitches when I did that in the simulation).
The only other variable would be the attenuation of the back bounce which is a combination of extra distance, actual radiation angle and wall reflectivity. I think the 5dB reduced reflection is realistic for a dipole in front of a non-absorbtive wall.
Cool Edit Pro
David S.
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