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Thread: Sound waves and smells

  1. #1
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    Default Sound waves and smells

    Just to confirm .... Alan will be there 18-21 May at the Harbeth distributor's stand (Input Audio).

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    Default Another Munich tale {or horror story?}

    So, on Saturday afternoon I started my tour of the show, just like any other punter. It was rather humid and many of the company demonstration suites were quite well air-conditioned, especially if there were not too many sweaty audiophiles filling the seats. It was nearly closing time and the strains of “Take Five” caught my ear. Seeing that it was coming from an almost empty room full of comfortable-looking seats I dived in, choosing a place near the optimum stereo seat.

    This was a company which has had a fair bit of (mainly good) publicity over the last year or so, which makes high quality audio electronics. It's name will not be divulged for it was immediately apparent that we were listening on their >30k speakers OUT OF PHASE! I enquired of one of the minders if he spoke English and, upon receiving an assurance that he did, mentioned the slight issue I had noticed. My concern was acknowledged with a shrug so I returned to my comfy seat to await developments.

    Nothing happened for about five minutes when it became apparent that other mignons, wearing the company T-shirt, were poking around behind the curtains examining wiring and stuff. After a further five minutes someone sat down beside me and announced that he was the R&D manager of the company and was I the gentleman who had mentioned the out of phase problem? Informing him I was, he promptly confirmed that I was correct and thanked me for pointing this out. I enquired how long he believed the system had been in this state to which he admitted, with a look that said “poo”, probably most of the show so far – which meant one trade/press day and one public day. He asked me if this would be a good time to switch off and correct the problem which he did, and what followed for the next fifteen minutes or so was one of the better sounds I heard at the show.

    Full marks for the R&D man and his honesty in not trying to fob me off, but how on earth does a significant company (and believe me, this lot are on the radar right now) get two complete days into the world’s premier home audio show without ANYBODY noticing, and commenting, that SOMETHING was wrong? Unbelievable. It will be most interesting to see what the press eventually have to say about this company’s efforts – whether they report that something was “not quite right” or thought the room a bit peculiar or whatever. This will be a fascinating test of the aural perceptiveness of many audio journalists - and the public.

    Depending on what The Papers eventually say, I may or may not reveal the name of the company in question but for the time being we will just wait and see.

    {Moderator's comment: Maybe the problem was the room tuning crystals?}

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    Default What does out-of-phase sound like?

    Pluto...

    How did you know it was wired out of phase? What does that sound like? Maybe many visitors wouldn't know either. I don't think I would know what that sounds like, I'd probably think things just didn't sound very good - but I don't really know. Could I try it out with my P3ESR? Any advice anyone?

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    Default The basics of out-of-phase (useful for speaker burn-in, and burn-out?)

    Quote Originally Posted by GregD View Post
    Pluto...

    How did you know it was wired out of phase? What does that sound like? Maybe many visitors wouldn't know either. I don't think I would know what that sounds like, I'd probably think things just didn't sound very good - but I don't really know. Could I try it out with my P3ESR? Any advice anyone?
    I would think the effect would be most apparent in the bass frequencies, i.e. that's where you'd get the most cancellation of signal. The frequency balance in the room must have been bass-light, if nothing else.

    Back in my "audiophile" days, I once "broke in" a pair of speakers by wiring them out of phase to each other, turning the "mono" switch on the amp (or I might have used a mono recording, I don't remember), putting the speakers face on toward each other, a couple of inches apart. Most of the output disappears through cancellation, especially in the lower frequencies. Throw a blanket over them and you can leave them playing at moderately high output level but hear very little unless you're right next to them.

    (BTW, this was not my idea - I'm fairly sure I read it as a recommended procedure in some audiophile publication. Luckily, the speakers survived it without harm.)

    Not that I would do anything so silly these days, but the cancellation effect is quite pronounced. Even with the speakers a normal distance apart, I would think it would affect the frequency balance to a noticeable degree.

    I have a pair of "noise cancelling" headphones that I believe operate on the same principle - i.e. an out-of-phase signal is fed to each ear. They're nice on airplanes. There's noticeably more cancellation in lower rather than higher frequencies, but it takes away a lot of the background "rumble" you hear sitting on a jet.

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    Default Out-of-phase: a DIY test

    If the speakers are in phase then a mono voice will sound like its coming from a point between the two speakers. If the speakers are out of phase it will be difficult to tell where the voice is coming from. To try it simply reverse the connection to one of the speakers. i.e. instead of red to + and black to - connect the one speaker end of the wire red to - and black to +.

    It should be very evident when its out of phase.

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    Default Smelling sound ....

    I'm really interested that this very reasonable question should come up 5+ years into the Harbeth User Group's life! Does it mean that the effect of out-of-phase sound is so obvious that it's a subject we don't need to dwell on - and if that's so, why did hundreds of trade, media and public pass by a speaker system and not notice? Or did they but were too polite to say so?

    Let's step back a pace of two and look at this out-of-phaseness. I suppose that there have to be a couple of pre-requisites that are necessary before out-of-phase (OOP) is generally detectable by the average listener using his ears only not test equipment:

    1) There has to be more than one speaker playing at the same time

    2) The two (or more) speakers playing have to be relatively close to each other, which normally means that they have to be in the same room and probably 2-3m apart (a guess)

    3) The speakers have to be playing the same or very similar sounds of similar energy balance and loudness. Out-of-phase condition probably isn't detectable if one speaker is playing a solo bamboo nose flue and the other speaker playing Mahler's 4th symphony. Because the two sounds are so completely different in energy, there is little acoustic 'overlap' and detecting out of phase by ear alone would be extremely difficult if possible at all.

    In a stereo two speaker system conditions 1, 2 and 3 above are normally true. That is, the two speakers are playing simultaneously, they're relatively close to each other and they are normally playing a stereo recording where aside from some few instruments panned hard left or hard right, most of the sound stage is concentrated around the centre stage between the speakers. That's certainly true for the omnidirectional lower frequencies, which in the concert hall have no real vector and would be picked up by numerous microphones regardless of whether those mics fed the left or right channels.

    What is a sound wave? Nothing more than a travelling barometric pulse from the speaker to your ear. If your pen-chart barometer was somewhat more sensitive and faster acting sound waves in the room could actually drive the pen arm up and down - then the barometer would be called a microphone. See picture.

    Important point! Imagine the worst, nastiest smell that you have ever experienced. Rotten cabbage? Yesterday's left-over curry take away? Sour milk? Ok, suppose that we have two identical normal rooms in an apartment block. They have exactly the same sealed-box* speakers and audio equipment except that the gear in room A is playing rock and roll music really, really loud and in room B, the speakers are turned off. Divide the smelly substance in half and place one next to a speaker in room A and the other half against a turned-off speaker in room B. Turn on A's speakers at absolute maximum volume. Moving between room A and B and sitting at your normal sweet spot, can you smell any difference?

    Comments?

    *Let's use sealed boxes so we are not considering the effect of the port in a vented speaker.
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    Default Smelly sonics...

    Quote Originally Posted by A.S. View Post
    Imagine the worst, nastiest smell that you have ever experienced. Rotten cabbage? Yesterday's left-over curry take away? Sour milk? Ok, suppose that we have two identical normal rooms in an apartment block. They have exactly the same sealed-box* speakers and audio equipment except that the gear in room A is playing rock and roll music really, really loud and in room B, the speakers are turned off. Divide the smelly substance in half and place one next to a speaker in room A and the other half against a turned-off speaker in room B. Turn on A's speakers at absolute maximum volume. Moving between room A and B and sitting at your normal sweet spot, can you smell any difference?

    Comments?

    *Let's use sealed boxes so we are not considering the effect of the port in a vented speaker.
    OK, I'll bite. I really don't know the correct answer, so I'll rank the responses in the order I consider most likely:

    1. No difference. There are two equal amounts of two equally-noxious substances in two identical rooms, so both will smell equally bad. The fact that one room has loud rock music playing is irrelevant, because that involves a difference sense (hearing rather than smell).

    2. The room with the loud music will not smell as bad. There'll be a kind of "masking" effect and the smell won't be perceived as strongly because the brain will already be flooded with the sensory input of the very loud music.

    3. The room with the loud music will smell worse. The loud music will overcome the body's and brain's defences, and everything will be perceived more acutely, even the bad smell.

    I know that there's an important point that's going to be made here; I'm just completely clueless about what it is.

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    Default Sound and smell - together?

    Quote Originally Posted by EricW View Post
    ...I'll rank the responses in the order I consider most likely:

    1. No difference. There are two equal amounts of two equally-noxious substances in two identical rooms, so both will smell equally bad. The fact that one room has loud rock music playing is irrelevant, because that involves a difference sense (hearing rather than smell).

    2. The room with the loud music will not smell as bad. There'll be a kind of "masking" effect and the smell won't be perceived as strongly because the brain will already be flooded with the sensory input of the very loud music.

    3. The room with the loud music will smell worse. The loud music will overcome the body's and brain's defences, and everything will be perceived more acutely, even the bad smell.
    Good answers and I can imagine that all three could be correct in certain circumstances, but they're not quite what I'm looking for.

    OK, thinking cap on again. We could have placed the smell-sources anywhere in the room, but notice that we placed them right next to the speakers. Room B with the silent speakers was the 'control'; but room A with the speakers playing really loud is the one we're curious about.

    Let's make this rather personal. Have you been in the company of someone suffering from severe halitosis but who is unaware of their condition? Have you noticed that when they talk normally that proving that you are a short distance from them that you are not troubled by the odour? Do these two observations of the room + speakers and the halitosis sufferer tell us anything about how smell permeates in a room in the presence of a sound wave? Is it counter-intuitive? Is it what we would experience standing on a windy but silent city street in the restaurant district?

    Once we have the solution to this worked through I hope that it will make the point about out of phase very clearly.
    Alan A. Shaw
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    Default What does "out of phase" sound like?

    Quote Originally Posted by GregD View Post
    How did you know it was wired out of phase? What does that sound like?
    Why not do a basic experiment yourself? Assuming you have standard passive speaker wiring (that is, one power amp output feeding a single pair of terminals on a speaker via a single cable), the speaker terminals are usually identified by colour (typically black/red) or symbol (+/-).

    We are admonished to take great care to wire our speakers correctly in phase, red to red, red to + etc. Temporarily reverse the connection to one speaker only and you will have a system that is out of phase. Listen to some simple mono speech - the sound will be vague and you will be unable to locate a point of origin. I find this quality almost nauseating; this phenomenon simply does not occur in nature hence it sounds unreal and decidedly unpleasant.

    Oddly enough, an out of phase condition is easier to detect on narrow, near-mono, material than super-duper wide stereo. I haven't the time to write up an explanation of this at the moment but suffice it to say that stereo consists of mono material (in phase) plus the addition of controlled amounts of additional out of phase material. The trick for good, wide, stereo is to ensure that the latter is prominent but not dominant. More later!

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    Default Molecules in motion?

    Quote Originally Posted by A.S. View Post

    OK, thinking cap on again. We could have placed the smell-sources anywhere in the room, but notice that we placed them right next to the speakers. Room B with the silent speakers was the 'control'; but room A with the speakers playing really loud is the one we're curious about.
    OK, I get it - I think. I'm fortunate not to know anyone with severe halitosis, but having been in Toronto a couple of summers ago in that city's garbage strike, I recall that (not surprisingly), the smell was worst on windless days.

    So I'm guessing that perhaps in the room with loud music playing, and the noxious substance right next to the speaker, the output of the speaker would perturb and disperse the molecules from the smelly substance such that it wouldn't smell quite as bad as the same substance in the quiet room.

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    Default Thoughts on out-of-phase

    Thank you for the interesting responses everyone - I will wire up my P3ESR O.O.P. later today, can't right now because I'm really enjoying some Albinoni Oboe Concerti!

    Alan, I've had some thoughts on your two points here, initially I assumed that room A would appear less smelly due to some kind of assumed masking or sensory distraction effect. After all, this can happen. When you are hurt in sports you can carry on and get carried away in the sporting event, but afterwards with no distractions it hurts like hell. I tore an ankle ligament playing football once, it hurt but I carried on another 10 minutes until the end of the match running about, even making tackes with the bad foot. When I walked off the pitch suddenly I could barely stand! Perhaps that's a different phenomena?

    However, I've changed my mind on that theory for this example. It seems somewhat logical that the increased air currents in room A could help to spread the smell around more - like stirring milk into a cup of tea using a spoon. If you don't stir it, the milk takes a lot longer to fully mix, if at all.

    So with the speakers in Munich, I would posit that O.O.P. wiring works to stop the sound from fully reaching us to hear it because the waves are partially cancelled by an equal opposite force from each speaker, which I would say must affect the lower frequencies more because the treble tends to be more "beamed" at us so would be less affected by the equal opposite signal some distance away, coming from the other speaker.

    I think I can see that using OOP material would improve spacial perception and give a better sense of an acoustic space, since the microphones would pick up direct in-phase sound from the instruments and also OOP sound from the wall reflections, the same as ours ears would if we attended the recording session. Is this how we perceive space? Without OOP sound it would sound like an anechoic chamber wouldn't it A.S or Pluto?

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    Default "Air currents?"

    Quote Originally Posted by GregD View Post
    ....However, I've changed my mind on that theory for this example. It seems somewhat logical that the increased air currents in room A could help to spread the smell around more - like stirring milk into a cup of tea using a spoon. If you don't stir it, the milk takes a lot longer to fully mix, if at all....
    Ummm. And what makes you think that there would be, in your words, "air currents" in room A? Surely an 'air current' is another word for 'wind'.

    And where would that 'wind' be coming from then? I can't visualise the source of the wind ..... (the rooms are windowless, the doors of A and B are closed). What did you have in mind?
    Alan A. Shaw
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    Post Sound waves moving the air: Isn't that an air-current?

    Quote Originally Posted by A.S. View Post
    Ummm. And what makes you think that there would be, in your words, "air currents" in room A? Surely an 'air current' is another word for 'wind'.

    And where would that 'wind' be coming from then? I can't visualise the source of the wind ..... (the rooms are windowless, the doors of A and B are closed). What did you have in mind?
    The speakers in room A are moving air around the room with by moving their drive-unite aren't they? I guess the loud sound in room A means the air is subjected to more force/pressure and therefore will move the air around the cabbage further out towards us, taking the smell with it. That's what I meant by air-currents - the air being forced around the room by the moving drive-units, not wind. I suspect from your above answer Alan, that I totally misunderstand the physics!

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    Default The wind trap?

    Quote Originally Posted by A.S. View Post
    Ummm. And what makes you think that there would be, in your words, "air currents" in room A? Surely an 'air current' is another word for 'wind'.

    And where would that 'wind' be coming from then? I can't visualise the source of the wind ..... (the rooms are windowless, the doors of A and B are closed). What did you have in mind?
    Ah, Alan. You set that particular trap by implanting the suggestion of wind, did you not? (last sentence of penultimate paragraph in posting #8)

    I know about traps - it's a professional requirement. What I don't know is the way out of this one, but it appears it can't be wind or air currents. Hence, unless you're presenting a complete red herring, I suppose it must have to do with localized variations in air pressure caused by the loud music playing through the speakers?

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    Default Polarity, Phase and Sound waves

    Quote Originally Posted by GregD View Post
    Pluto...

    How did you know it was wired out of phase? What does that sound like? Maybe many visitors wouldn't know either. I don't think I would know what that sounds like, I'd probably think things just didn't sound very good - but I don't really know. Could I try it out with my P3ESR? Any advice anyone?
    Pluto, shouldn't we be using the term polarity instead of phase? When we connect the speaker wires reversed in the case of a stereo system then we will have a general out of phase sound. However, whether the sound will be out of phase or not depends on identical signal(not necessarily of the same strength) being fed to both speakers simultaneous. In this case, both left and right drivers must move in unison either forward or backward so that we will have the image in between the speakers, if that was intended by the recording artist/engineer. That's when we will have the instruments or vocals in focus. Otherwise, it will be everywhere without an apparent localization.

    So the question is whether can we detect stereo speakers connected with interchanged polarity? I made the mistake long time ago and continued to listen without realizing what was wrong, though I felt something wasn't right. On the second day, I used recordings which I was very familiar with and immediately knew I have misconnected one of the speakers' polarity. It is most likely I wouldn't be able to tell if the speakers' polarities were crossed connected between left and right speakers if I were to listen to an unfamiliar western classical orchestra without individual instrument rendition. I would probably like the artificially expansive sound.

    Quote Originally Posted by A.S. View Post
    ... Turn on A's speakers at absolute maximum volume. Moving between room A and B and sitting at your normal sweet spot, can you smell any difference?...
    As you had mentioned, it shouldn't make any difference to the intensity of the smell in either room. Sound do not travel by blowing or creating wind or air current. It is vibration of molecules (local oscillations) and they do not travel like waters in a garden hose. The air in front of the speakers remain where it was before and after the sound. Here is the animation from Dr Dan Russell of Kettering University Applied Physics to explain how sound really travels.

    http://paws.kettering.edu/~drussell/.../wavepulse.gif .


    ST

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    Default Fill your room with water?

    Quote Originally Posted by STHLS5 View Post
    As you had mentioned, it shouldn't make any difference to the intensity of the smell in either room. Sounds do not travel by blowing or creating wind or air current. It is vibration of molecules (local oscillations) and they do not travel like waters in a garden hose. The air in front of the speakers remain where it was before and after the sound....
    Exactly so. Let's go over this to be sure we grasp this one ...

    1.
    Sounds do not travel by blowing or creating wind or air current
    Essential point. The loudspeaker is not like a desk fan. It is not producing a wind, does not producing a rush of air. If you turn on a 100W desk fan - see picture - and stand 2m away, you can feel the air rushing over your skin. If you turn on a 1 million watt PA concert hall speaker stack - see picture - can you feel the sound flowing over your skin even if you stand 2m away? No. You will feel no air flow because their is no air flow, no wind. The fan agitates the air in the room; the speakers do not.

    2.
    It is vibration of molecules (local oscillations) and they do not travel like water in a garden hose.
    Agreed. Sound does not flow like water. The speaker does not pour sound into the room from a tank. If you seal the room and put the hose pipe into it and connect it to a water supply, the room will fill up with water until it the walls burst. But you can play your speakers in the sealed room really loud all day and all night there will be no change in the quantity of air in the room, or its quality.

    3.
    The air in front of the speakers remain where it was before and after the sound.
    Agreed. That's because in 2. above, we said that the desk fan stirs or agitates the air in the room and the speakers do not.

    which means that 4. ....

    There should be little or no difference in the smell that we detect sitting at the sweet-spot in room A (playing the speakers really loud) or in room B (speakers disconnected) because the speakers are not stirring the air molecule particles. If we replaced the speakers in room A with desk fans and turned them on, then we would surely agitate and stir the air in room A and wherever we stood in the room the smell would be equally noxious. We cannot achieve that stirring effect with (sealed) loudspeakers no matter how big or how loud we play them. But if the speakers are vented, which means that they have a hole or port which acts as an air-pump, then some stirring is possible.

    So if we agree that the sound generated by the loudspeaker is not a gust of air, how does sound actually radiate from the speaker - or the birds high in the trees? Clue? What do barometers measure? (We hinted about this a few posts back...)

    >
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    Default Concentrate and observe

    The answer dear readers is here.

    Pick any molecule in the medium and concentrate on it. Watch how it moves when the hands clap. As you move your mouse around the graphic you can see an explanation of various parameters. So how does the molecule move with the sound wave? And how does the initial at-rest position compare with the final at-rest position after the sound has passed through the medium? And how does that relate to the noxious smell in the room?

    I'm now off to London to show our overseas visitors around - pictures to follow in a few days.
    Alan A. Shaw
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    Default Pressure Peaks Travel; Air Mass Doesn't

    Quote Originally Posted by A.S. View Post
    And how does the initial at-rest position compare with the final at-rest position after the sound has passed through the medium?
    It moves closer to neighbouring molecules. Then it moves back to its original position.

    Quote Originally Posted by A.S. View Post
    And how does that relate to the noxious smell in the room?
    I don't know!
    Ben from UK. Harbeth P3ESR owner.

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    Default Detecting out of phase

    Quote Originally Posted by STHLS5 View Post
    When we connect the speaker wires reversed in the case of a stereo system then we will have a general out of phase sound.
    Correct.

    Quote Originally Posted by STHLS5 View Post
    However, whether the sound will be out of phase or not depends on identical signal (not necessarily of the same strength) being fed to both speakers simultaneous.
    Equally true - for the output of the speakers to be be truly and mathematically out of phase with one another, they must be fed with identical material.

    This is precisely why it is easier to detect a "reverse polarity" [your words] condition with mono programme material. As I mentioned earlier, stereophony consists of mono material plus the additional information required to convey directional clues to the ear-brain of the listener. The former of these two (which we call the M component) is, by definition, fed identically to each loudspeaker. The latter (which we call the S component) is, by definition, fed to the right loudspeaker in reverse polarity compared to the left.

    So it stands to reason that listening to pure mono material allows for the easiest detection of a "reverse polarity" error. The more stereophonic the material, the more S (out of phase) content has been intentionally added to provide directional clues that the listener perceives as "stereo".

    So if your pre-amp has a mono button, use it. This button, in effect, removes any S component by mixing two equal and opposite signals together resulting in total cancellation. Identifying a reverse polarity state on very wide stereo music can be tricky and ambiguous, hence you need to practice and be very aware of the sonic difference between correct and incorrect polarity. Like so many things in life, training combined with experience will get you there!

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    Default Stereo sound

    So then, stereophony isn't simply differences in instrument loudness between left and right? That's what I always thought it was.
    Ben from UK. Harbeth P3ESR owner.

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