April fools day aside, I have heard interesting reflection effects in the natural world many times. Here are a few.
Pink noise at the beach: as a wave comes in it has a noise spectrum. Do deep knee bends and you will hear a pitch effect that changes with ear height.
Hold a piece of paper over a hard surface such as a desk. Constantly rustle or crinkle the paper to create noise, while moving the paper up and down above the surface of the desk. You will hear distinct pitch effects that varies with paper distance.
Reflections off of a picket fence. These are interesting. I've heard distinct multiple relections off of fences with multiple slats. Due to the geometry the pitch changes as the contribution from farther slats arrive. I think the pitch goes up with time, kind of a "boink" sound. Best I ever heard this was at a tennis court where every ball hit excited it.
I frequently hear reflections with pitch in listening rooms, when pink noise is playing and you receed from the speaker, you will hear distinct pitches. Floor and ceiling bounce is a big contributor, the pitch will go up as you move away.
Room noise/mailing tubes. The roar of the ocean we hear when listeing to a shell is just the outside world's noise fed through the resonance filter of an enclosed volume. A cardboard tube held to the ear will have this from the usual pipe resonances. You can hear the difference between closed end and open end.
People at a cocktail party? Yeah you'd probably hear that too, especially if you can get them to move nearer and farther from the boundary. These effects are generally more audible when they vary. Less audible when stationary.
David S.
There was nothing "sloppy" in my writing or in anyone else's, we just disagree with your definition. And Yes, you do see this terminology in JAES. "Distortion" does not mean "added tones", look it up. (From Wiki: "A distortion is the alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation. ") Because you choose a more limited definition is your perogative, but it is arrogant to impose that definition on others and then criticize them when they don't, especially when yours is the one that does not stand up to scrutiny.
There is a long tradition of talking about "linear distortion" and "nonlinear distortion". We may tend to think of distortion as something that happens to a waveform. i.e. added harmonics, but clearly academics have long used the term linear distortion to refer to frequency response effects.
It is a proper usage.
David S.
It is a proper usage.
David S.
Earl, I recognize that JAES lets this stuff get by. My comment was that JASA would not not put up with that.
Now your argument is that "wiki" says its okay. Probably not a reassuring thought.
My definition is not limited, it is simply what is taught, has always been taught, in any linear systems class. I understand that others can get confused. In your case, however, you were trained as a scientist and talk to other scientists. I have higher expectations and can not understand why you are defending this.
Let's agree to disagree and leave it that.
neat!
You can have a real quick test by visiting here.
Ambiophonics Demos
It worked fairly well using the built in computer speakers on my mac.
Although I'm sure there are a number of things that affect perception of depth in a recording, if by depth you mean getting a sense of size, scale, and distance of the auditory scene behind the speakers, (as opposed to Left-Right stereo localization) then I would suggest that the range between ~100-300Hz is a very important factor.
In particular, big holes in the response in this range can tend to collapse the depth of an image so that it sounds like it coming from a plane which is at or just behind the speakers.
Not surprisingly, floor bounce can cause issues in this range, and it's generally been my observation that speakers which deal with floor bounce (low mounted woofer, or vertical array of woofers or other methods) can - all other things being equal - give a much more convincing effect of depth on some recordings than a speaker whose only source of bass through the floor bounce region is a high mounted driver.
It's not a stereo effect either, because you can switch the playback to dual mono and the sense of depth remains. (or the lack of depth as the case may be)
As discussed in another post within this thread I've been playing around with adding a narrow band floor level woofer to help fill in floor bounce cancellation whilst making as little change elsewhere as possible and the effect is quite interesting.
As it's an un-baffled driver there is essentially zero change in bass response below 90Hz, the hole around 100-150Hz is filled in, and a dip around 200-300Hz is also improved. Above 300Hz there is no significant measured effect.
One of the most noticeable changes when switching it in or out is a much more convincing sense of depth and also scale in some recordings when switched in. Something that can't be achieved by simply trying to EQ the high mounted driver.
The effect can be quite subtle on some recordings, and not present on others - on some recordings the only change is a bit more weight in male vocals or a bit sharper attack on bass instruments - both of which can be attributed to the improved response in the upper bass 100-200Hz range.
I've noticed similar effects before when comparing the same set of drivers working in 2 way and 3 way, but since I was switching from an 8" driver acting as mid bass to a 12" driver providing bass up to 300Hz and the 8" only providing midrange, some of the change could easily have been attributed to the different bass characteristic of the two drivers - essentially a completely different driver is handling everything below 300Hz in one mode, so too much is changing to narrow down what's important and what's not.
However in this more recent test the 8" driver is still operating right down to ~40Hz as a mid bass driver, providing the vast majority of the bass, with the floor mounted "helper woofer" only operating from 100Hz to 300Hz, and only really having a measurable effect where floor bounce related holes are occurring. (Due to it being somewhat less sensitive) Therefore the "fill in" is quite specific to only the regions where cancellation from the floor is occurring for the higher mounted mid bass driver.
The same (admittedly subjective) improvement in sense of depth and scale is present in this configuration as it is in a full 3 way system with low mounted woofer, which tends to confirm my feelings that those frequencies from 100-300Hz are important for depth, and need to be well balanced and without significant holes at the listening position for a really convincing sense of depth.
With the woofer near the floor some male vocalists at times sound like they are at a different height when using a 300-350Hz LR2, what I preferred for quite some time. I chose this to minimize the midrange floor bounce issue from the start.
The reason I originally moved the woofer up was subjectively determined, it was my first 3-way attempt years a ago when I was first starting, so part of the problem then could have been my crossover work and was not related to image. I had a temporary 12" x 24" box. In the room I could not get good quasi-anechoic measurements in its range, of course. The box and low mounting position I used at the beginning allowed me to temporarily re-position the box for driver height. The best response is where I have mounted a single unit since. It turned out somewhat close to what was used in the old Hales Audio Revelation 3-way systems as far as positioning, not that this was intended.
For as much as I can, I prefer to do things objectively, but it simply did not sound correct until I made that change. That system had a Dynaudio 17WLQ as midrange, but in later systems with the same woofer I used smaller, pure midrange units.
Much as I'd like to rely purely on measurements, at times I still end up making small adjustments to satisfy myself for what I hear, but I go to measurements and software to make most changes. Bass and mid-bass are the areas on which I have not been able to rely purely on measurements to determine the actual change needed. I probably just haven't tried hard enough.
Dave
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For those folks experimenting with raising or lowering the woofer from the floor.
Certainly, one of the things you are doing is changing the time of floor bounce (the additional propogation delay). This of course will change the comb filtering (due to the delay-and-add). But there is another confound to consider. The floor is providing a boundary. This boundary is augmenting the low frequency response (similar to placing speakers in a corner, to get a benefit from corner loading).
This will certainly be a real effect, I won't guess as about its strength in your particular case. The notion that a height cue is being created, however, is on pretty shakey ground.
Certainly, one of the things you are doing is changing the time of floor bounce (the additional propogation delay). This of course will change the comb filtering (due to the delay-and-add). But there is another confound to consider. The floor is providing a boundary. This boundary is augmenting the low frequency response (similar to placing speakers in a corner, to get a benefit from corner loading).
This will certainly be a real effect, I won't guess as about its strength in your particular case. The notion that a height cue is being created, however, is on pretty shakey ground.
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I notice it with the woofers primarily with baritones. The image is somewhere between the woofer and mid/tweeter. Almost everything else has the image at the height of the mid/tweeters. This is, again, with a 300-350Hz Fc W/M.
Dave
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To me, position of the midrange or midwoofer is what largely sets the apparent source of vocalists. Panning between stereo channels sets horizontal (L/R) position and height of the sound source location sets vertical position. I'm sure other factors come into play, but those are the biggest things.
But my long time favorites - the constant directivity cornerhorn and the matched-directivity two-way with flanking subs - both deal specifically with boundary reinforcement and self-interference. I've studied these specific issues a lot. What I've concluded this far is the floor bounce notch is significant on any point source loudspeaker that is elevated off the ground more than a foot and a half or so. I've also found that the techniques that mitigate this notch always make the speaker sound much better, although admittedly, these techniques accomplish other useful things in addition to just smoothing the floor bounce notch.
I think you probably remember the discussions on AudioRoundTable.com about five years ago about modal smoothing and multisubs. I was a big proponent of flanking subs because that was a way to smooth the floor bounce notch. It seemed to me that there was more emphasis on the modes below 100Hz - which are admittedly very important - but to smooth the nearest reflections from the floor and possibly the nearest wall, flanking subs or helper woofers or some other kind of less distant array are needed, in addition to modal smoothing subs placed further away.
- Search list for "multiple subs" on AudioRoundTable.com
- "Speaker Placement - the Subwoofer Thing", one of the threads that discusses multisubs and the difference between the lower modal range (20Hz - 100Hz) and the transition region (100Hz - 200Hz)
- "Sub placement", another thread that discusses multisubs (and I see a post from you in that one
)
I agree with you on this point, that you cannot say whether adding flanking subs to a two-way waveguide loudspeaker system sounds better because floor bounce notch is smoothed or or some other reason. If you move the whole loudspeaker up and down, you can't say whether it's the floor bounce notch moving in frequency or the boundary reinforcement changing the response, interacting with baffle step to create a continually changing response as the speaker is moved up and down. There is more than one issue in play here, as you've said, "another confound to consider".
But one thing you can say, and that's the effects are clearly measurable. You can see the floor bounce notch when a midwoofer speaker is raised off the floor, and you can see the absense of one when it's on the floor. You can see the floor bounce notch created by a speaker on a stand go away when a flanking sub is placed on the floor, nearby, and blended through the lower midrange, up through the floor bounce notch frequency around ~150Hz or so.
Another thing I have noticed is an almost universal attraction to speakers that have some mechanism that mitigates floor bounce. I won't start a list of speakers that do this (either by design or accident) although I started to and then changed my mind and decided to delete it. It would probably be bad form. But I have noticed that there are a handful of manufacturers that have included 2.5-way or truncated arrays or other techniques that create midbass/midrange sound sources that mitigate floor bounce. They are almost always preferred over similar speakers that use a point source in the 100-200Hz range placed on stands or otherwise elevated to ear level.
Wayne, I think you had a couple of questions in there. So let me answer by, in turn, posing a couple of questions. This regards the psychoacoustic discriminablity of the topic in question (this is my area of expertise, so perhaps I can be helpful).
1. What is the accuracy that humans demonstrate in resolving position along the median plane (height)?
2. The acoustic cues used for such discrimination are in what spectral region?
So we both agree that raising the woofer off the floor will change various aspects of the resultant waveform (hard to disagree with that one). Whether the resulting comb filtering is audible, in a particular case, would depend .....
However the notion that this is a technique to alter the appearant height of the sound source is on shakey ground (within reasonable limits, using the woofer). This is me being tactful.
1. What is the accuracy that humans demonstrate in resolving position along the median plane (height)?
2. The acoustic cues used for such discrimination are in what spectral region?
So we both agree that raising the woofer off the floor will change various aspects of the resultant waveform (hard to disagree with that one). Whether the resulting comb filtering is audible, in a particular case, would depend .....
However the notion that this is a technique to alter the appearant height of the sound source is on shakey ground (within reasonable limits, using the woofer). This is me being tactful.
I'm not sure about that. The floor bounce is in a transitional region where localization cues start to emerge.
Perhaps "emerging" but not very strong. The stronger cues will be higher in frequency.
And this whole "floor bounce" discussion ignores the simple, and almost ideal, solution of just using a thick rug at just the right place. This leaves the ceiling reflection, but thats a different issue in most cases. Its not always wise to try and get the speakers to correct for all the rooms issues. From what I know, the floor bounce is one that is better dealt with in the room than in the speakers.
For a long time I had a system that consisted of 2 stacks cabinets, a 12" woofer in the lower, 8" full range in the cabinet above it, and ribbon tweeter on top of that, and as well as being able to switch them to different configurations (full range, 2 way, 3 way) I could turn the cabinets 90 degrees to change driver heights slightly, and slide them back and forth to try different z axis alignments.
I found that with the right crossover adjustment the height of male vocals were not lowered by having the low woofer in operation. If I used a 6dB/oct 300Hz crossover (or even 200Hz) on the woofer invariably the vertical position would be "smeared" with some vocals sounding like they were half way between the woofer and midrange - much as you describe.
I can only assume that this is a result of excessive higher frequencies being produced by the woofer up into a range where the ear is more easily able to localize height, as well as excessive overlap between the drivers. Below certain frequencies the ear can't distinguish height, (except perhaps due to effects of floor bounce notches) but of course a crossover is not a brick wall filter, so doesn't completely eliminate frequencies above the critical range, whatever it is. (Somewhere between 300-600 Hz I suspect)
However with 12dB/oct at 300Hz I didn't find this to be a problem, even with the woofer quite low.
Interestingly, when I tried to bring the woofer cabinet forward (about 40mm) to time align the woofer and midrange driver the problem returned even with the 12dB/oct filter. For some reason I don't quite understand, putting the woofer slightly behind the midrange driver (it's natural z axis misalignment due to driver depths) was actually beneficial in avoiding vertical smearing of the image location.
Perhaps there is a "precedence" effect in operation, where in the overlap region the driver whose sound arrives slightly sooner tends to dominate our sense of localization. Before anyone jumps on me over this - yes it is just speculation, I don't have any references to back it up.
Likewise I found it essential in the crossover adjustment that the woofer didn't "over power" the midrange driver. In other words it was important the woofer level at the crossover was not even slightly greater than the midrange - equal or slightly less gave the best result. I ended up using a deliberately over-damped low pass response on the woofer.
The reason I asked was because when I converted your 19" into metric (48cm) it rung a bell. It sounded a lot like what I found to be near optimal height. For a long time I had my 12" woofer at 30cm (floor-centre) for practical reasons, and while it solved the floor bounce I always felt there was a bit too much response at 200-300Hz, which made it quite difficult to roll off and cross over without an excessively complex passive filter, or active EQ. (Which I ended up using)
From memory I found the optimal range to be 40-50cm floor to centre for that woofer on a wide baffle. It reduced the lower midrange response enough to make the crossover a lot more manageable without significantly reducing the floor bounce benefits.
Any lower than about 40cm and the midrange started to slope up significantly, any higher than 50cm and floor bounce cancellation started to return.
While it might be possible to come up with measurements to describe this situation, measuring on axis anechoic response alone is not enough information, nor is pseudo-anechoic measurement spliced with near-field.
No one would argue that changing the height of the woofer on a large 3 way system doesn't affect the bass, floor bounce effect, and lower midrange (if crossed that high) in a big 3 way, and yet anechoic measurements (taken far enough away to minimize phase and angle changes with woofer height) will show no change in the response with the woofer location - clearly not the case.
If anything it just shows a good example of where a purely anechoic measurement is insufficient - and that below 200-300Hz the interaction of the room can't be ignored especially the nearest boundary.
At least with a floor standing design you can make the floor boundary a part of the design - a tall floor standing design is always going to be placed on the floor, even by non-technical listeners, so the distance from each driver to the floor is known and can be accounted for in the crossover.
A smaller bookshelf size design is always at the mercy of the listener as to how high it's placed - you can suggest all you want that your speaker go on an 70cm stand but at the end of the day you can't force anyone to do so...
Agreed.
Are you serious ? How many rugs do you know of which have significant attenuation at 200-300Hz ? None that I'm aware of. A thick bean bag filled pillow, yes (I've tried that before, placed at the mirror reflection point on the floor) a rug ? No way...
Also this ignores the lower frequency notch pointed out by Wayne occurring at ~100-200Hz, due to the reflection from the floor directly below the speaker - no amount of rug is going to do something about that frequency, even if you put it under the speaker...
If you can think of any practical way to deal with floor boundary cancellation only in the room treatment, please share it. As far as I'm concerned the cancellation we're talking about can only be solved in the speaker design with driver placement.
Designing a speaker without any consideration of the nearest always present (in the case of a floor standing design) room boundary seems doomed to mediocre results to me..
Provided the woofer is rolled off adequately low and steeply enough (see my previous posts) then I agree, the woofer doesn't seem to affect the apparent source of the vocalist. 300Hz at 12dB/oct seems to be a comfortable minimum.
A significantly higher crossover frequency or lower slope seems to start to smear the image between the woofer and midrange driver for male vocals.
This has always been my major complaint with conventional (and now seemingly ubiquitous) "satellite/sub" systems, where you typically see a narrow, tallish floor standing speaker with all woofer(s) high up off the ground, crossed over with a sub below 80Hz.
It seems to be common audiophile wisdom that such a system can perform as well as a more conventional large 3 way system with a low mounted woofer, but it does absolutely nothing for the hideous floor bounce notch such a speaker will have.
Try as you might, with a 80Hz crossover that small speaker is never going to sound like a large speaker. It's really rather surprising just how much of the oomph and sense of scale and power of a large speaker design comes not just from the low bass, but also from the neglected floor bounce cancellation range in the upper bass/lower mid.
Often the limitation of a smaller higher driver design is not so much a lack of low bass, but a lack of being able to deliver upper bass at the listening position.
I wouldn't go so far as to say almost universal, as there's too many ways to screw up a design even with a low mounted woofer, but in a speaker that's otherwise an excellent design and takes care of the other important issues, dealing with the floor bounce does add some "magic sauce" that's difficult to appreciate until you do hear it well done.
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Of course I'm "serious". I'm not here to play games.
I use a futon, about 3 " thick and then cover it with a rug. Unless you are right on top of it, it just looks like any other rug. And no, this is not completely effective at 100-200 Hz, but it gets very effective above that. And since you already agreed that the image situation was at much higher frequencies I am not so concerned with the first notch, and the rest are completely removed.
Yes, I'm "serious".
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