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Old 18th June 2013, 05:46 AM   #151
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Originally Posted by dumptruck View Post
I would be shocked if floor bounce is among the most objectionable, frankly. Not saying it isn't, necessarily, just saying I would be a bit shocked. I know in cases where you end up with an especially bad lower midrange / midbass cancellation, you can hear it pretty well and it's not good, but it also seems less bad than it measures, and (at home) it's often in the range where vertical room modes are also getting in on the fun so that makes amateur analysis kinda difficult.

Anyway, my point is our brains grow up hearing everything bouncing off the ground/floor all the time, and we evolved with a ground too (and probably to at least some extent, a floor). It's the most normal reflection. Or, maybe it would be more accurate to say it's the expected (by the brain) reflection?
I think the self-interference notch from the wall behind the speakers is probably the worst offender in the lower midrange. The floor bounce notch can appear on the same frequency range, depending on speaker height and distance to the listeners though, and so mitigation of both can be achieved by the same mechanism, in many cases. And I agree with you that the vertical modes tend to start in this same low-midrange band, so all can be dealt with using helper woofers or flanking subs to good effect.

Another thing I hate is HF ceiling reflections. I call that ceiling slap because that's exactly what it sounds like. It makes a pinging sound, sort of like flutter echo, but it happens even in some rooms that are pretty well carpeted. It seems worse in rooms with gabled ceilings, probably because they reflect more into the center of the room. Speakers with tall vertical radiation sound really cluttered in rooms like that, sort of like a tinny radio in the bathroom. Speakers with narrow vertical HF beamwidth really help. In my experience, the worst part seems to center around 4kHz, so as long as the radiation pattern above ~2kHz prevents much energy at the angle of reflection back to the listeners, that particular problem is greatly reduced. It isn't a hard goal to achieve, but speakers that provide too tall vertical beamwidth in some rooms sound bad to me.
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Old 18th June 2013, 09:40 AM   #152
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Thanks for the clarification. Seems to conflict with my experience... more than a little bit. How large of a room were they emulating? Did they try different spectral content for the reflections for determining the level of detection? Should I just go look this up somewhere?

Http://www.aes.org/e-lib/browse.cfm?elib=7673

He basically did two generations of the test. Initial tests used a simple cardioid model for the speaker and its off axis curves. A later test used actual measured curves for the response of each reflection's radiation angle. i.e., if a side wall reflection was caused by a ray 30 degrees off axis to the loudspeaker, the actual 30 degree response was used in the simulation.

He did find that where the more realistic model had higher directivity the threshold of detection for those reflections was higher (reflections less audible). Since the level of detection was already above the natural level it was of no consequence.

As reflection levels were varied, test subjects noticed differences in source direction, loudness and timbre (frequency response). As reflection levels were reduced, timbre changes were the last to disappear. Tests were done with speech and pink noise. Pink noise was more revealing.

The natural level for most reflections in his typical room were 10 to 15 dB below the direct sound. This was due to the off axis level of the speaker, the increased air travel distance and the loss at each boundary. Noise was more revealing than speech as a test signal, but still had detection levels 3 to 9 dB higher than the natural level, except for the first front floor bounce.

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Old 18th June 2013, 09:44 AM   #153
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Originally Posted by Wayne Parham View Post

Another thing I hate is HF ceiling reflections. I call that ceiling slap because that's exactly what it sounds like. It makes a pinging sound, sort of like flutter echo, but it happens even in some rooms that are pretty well carpeted.
I've heard this as a comb filter effect. Move nearer and farther from the speaker and the pitch changes. You can also hear significant treble bounce off of most thin carpet.

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Old 18th June 2013, 10:22 AM   #154
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So it looks like off-axis response is important. But, how do we measure its effect on localization, timbre and spaciousness?
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Old 18th June 2013, 10:52 AM   #155
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So it looks like off-axis response is important. But, how do we measure its effect on localization, timbre and spaciousness?
You are still jumping to the unproven conclusion.

You will not measure its effect because it is a perceptual issue. You have to do what Soren Bech did, find a way to vary the off axis part only and then search for thresholds of detection or just noticable difference levels.

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Old 18th June 2013, 11:06 AM   #156
AllenB is online now AllenB  Australia
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Originally Posted by speaker dave View Post
For most of the reflections the real life levels were found to be lower than the level of detection.
I was most disappointed when I discovered this when with speakers toed toward the opposite walls at hotter than the speaker's listening axis, 2" of rockwool 3'x3' made only a slightly noticeable difference.

When you ask the question 'how important is speaker directivity?', I'm sure it has driven many to make inadvertent improvements including better baffling, keeping sound away from room clutter, even the change to compression tweeters.

It wouldn't be the first time a mass misconception with illogical reasoning has led to better speakers.
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Old 18th June 2013, 11:27 AM   #157
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Originally Posted by speaker dave View Post
You are still jumping to the unproven conclusion.
Lipshitz's conclusions:

"1) Flat power produced at the expense of non-flat axial response
produces a colored overbright and definitely 'wrong' sound in the
case of loudspeaker #1. The effect is worse in the smaller
listening room.
2) Flat power together with flat axial response is still colored and
overbright in the case of loudspeaker #1, but less so than in (1)
above. In the case of loudspeaker #2 no midrange coloration
results, only excess brightness.
3) The midrange coloration in the case of Experiment 3 appears to be
caused by the unbalanced reverberant power put into the room due to
the sway-back nature of EQ3. In principle, this should have exactly
compensated for the complementary power curve of the
forward-pointing 'monopole'. Clearly the spatial distribution of
the reverberant power must be important, and hence presumably the
loudspeaker's directivity index curve does affect the perceived
coloration.
4) If the directivity index curve is monotonic the impression of flat
power is purely one of excess brightness and some delocalization.
5) In all cases, flat power into the room appears undesirable. As
previously argued, rolled-off highs on axis are also undesirable,
and so we are led to conclude that for domestic use a loudspeaker
should have a smooth monotonically increasing directivity index as a
function of frequency. Precisely what the shape and ultimate rise
should be remain to be investigated. Probably the best that one can
do is to find a range of acceptable contours. Personal preferences
and listening room acoustics as well as loudspeaker positioning will
also affect the decision.
6) A flat power 'dipole' is less objectionable than a flat-power
'monopole'.
7) Adding spectrally neutral reverberant power to the room produces a
somewhat bright sound.
8) It follows that the frequency balance of the reverberant sound is
perceptually significant.
9) These effects are greater in smaller, acoustically more reflective
rooms.
10) A small power dip in the crossover region is relatively innocuous,
whereas a peak is audibly undesirable. Although our conclusion
referes to reverberant power peaks and dips, it is consistent with
Bücklein [7].
11) Consequently, the perceived tone color is a product of both the
direct spectral balance and that of the early reflections, and not
of the direct sound or of the reverberant sound alone.
12) Unbalancing both the direct and reverberant spectrum produces
colorations broadly similar to, but more pronounced than, spectrally
unbalancing only the reverberant sound.
13) A more directional loudspeaker is less affected by the room.
14) The greater the delocalization the less pronounced is the effect on
the perceived tone quality." (AES Conv. Paper 2301)

Unproven? Pretty much the same others have found.

Quote:
Originally Posted by speaker dave View Post
You will not measure its effect because it is a perceptual issue. You have to do what Soren Bech did, find a way to vary the off axis part only and then search for thresholds of detection or just noticable difference levels.

David S
If we can correlate reflection patterns to perception, we can "measure" perception. That's what psychoacoustics is all about.
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Old 18th June 2013, 11:55 AM   #158
lolo is offline lolo  France
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Originally Posted by markus76 View Post

If we can correlate reflection patterns to perception, we can "measure" perception. That's what psychoacoustics is all about.
it has been done already, have a look at Yoichi Ando's work.
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Old 18th June 2013, 11:56 AM   #159
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Originally Posted by markus76 View Post
Unproven?

I think it is somehow unproven, because what is the optimal power response, for example, for the speaker depends mostly on how the music recording was created and which kind of power response the original monitor speakers once had.

If they had falling power response then sure the same recording sounds bright with constant power response speakers.


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Old 18th June 2013, 11:58 AM   #160
Juhazi is offline Juhazi  Finland
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I have messed around a dipole speaker project with numerous measurements. For a sanity check I measured also my 2-way BR speaker, a variation of MarkK's ER18DXT. I can verify that in my conventional living room with RT around 0.3 - 0.5, The dipole spekers produce significantly more accurate and pleasant sound. Reflections, seen as spectral decay up to 300ms are markedly less with the dipoles (one speaker's measurements shown here.
Click the image to open in full size.
Attached Images
File Type: png AINO vs ER18DXT dir 100ms.png (166.4 KB, 188 views)
File Type: png aino%20vs%20er18dxt%20decay%20spectr.png (587.6 KB, 183 views)
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