|   "Recording polarity": something else to obsess about? | waVeman
Dec 30, 2001 9:47 PM | | This keeps appearing at other forums, well, the hi-end ones actually, and mostly just brought it up here because it sounds interesting to discuss. Personally, it sounds like another super-ultra-subtle thing that only bats can hear, if the effects exists at all.
Before clicking on the link below, please remember this:
1) Speaker crossovers DO NOT--as far as <i>I</i> know--use polarized capacitors, i.e., no negative or postive leads. Same with inductors and resistors. A music signal consists of an alternating waveform--positive/negative--so using polarized crossover elements just wouldn't work.
2) Sound waves from a speaker consist of rarifications and compressions of the surrounding air (not actual "waves" like one sees at the beach). <b>And, the space between them is <i>extremely</i> small.</b> Remember, these waves are reaching your ears (or the microphone) as "slow" as 50 times a second (for a typical piece of rock music; lower for organ music) all the way up to fifteen/twenty thousand times a second. I can't remember how small those distances are between even the slow bass waves, (MUCH less than an inch, correct?) so if anyone wants to chime in on this.........
3) How many people out there hold their head in one position, <u>never</u> moving it, during a listening session?
4) On AA, I've read that most recording engineers don't hook up their equipment in the "correct" polarity, because : (again) with A/C, there IS no correct polarity.
5) We are not talking about the <i>equipment's</i> electronic polarity as far as how it is grounded to the main power supply. We are talking about how the MUSICAL SIGNAL'S polarity could possibly affect the sound one hears in their living room--its interactions with furniture, walls, ceilings, etc.
6) Again, don't forget the recording studio used(?) a particular polarity as far as how microphones were hooked up, tape heads, the monitor speakers being used and if they were attached "red to red, black to black", etc., etc., etc.
The AA link:
http://www.AudioAsylum.com/forums/hirez/messages/49736.html |
| Wavelength | one50
Dec 31, 2001 10:46 AM | | sound waves travel throught the air @ the speed of 1130ft/sec. (344m/sec)...at sea level on a standard tempture day (which is 59 degrees Farenhite or 15 deg. Celsius) the speed of sound is independent of frequency. The physical distance covered by one complete cycle (one half-cycle of compression and one half cycle of rarefraction) of a given frequency sound as it passes through the air is called wavelentgh. Wave length is expressed by the equation
WAVELENTGH = Speed of sound / Frequency
EXP. 1130 (speed of sound) / 100Hz (frequency in Hz) = 11.3 ft
So at 100 Hz the distance betwen a "wave" or the wave length is 11.3 feet. |
| Thanks. I guess I was just a little bit off! | waVeman
Dec 31, 2001 1:40 PM | | I was thinking it was very small because I was picturing an immobile reference point that the waves were passing by. And since a complete 50Hz wave would pass by in a fiftieth of a second and a complete 10,000Hz wave in a ten thousandth of a second.......see what I mean? But I forgot to figure in the speed of the wave. |
| re: "Recording polarity": something else to obsess about? | FLZapped
Dec 31, 2001 10:49 AM | | The polarity you are talking about isn't subtle at all. WHile recording engineers don't worry about poarity in the sense that the wire doesn't care which way the signal flows, they are VERY attentive to signal polarity.
In the signal polarity case, if you were to take two microphones carrying the exact same signal and then invert one of them, you're going to null out that signal in the mix down.
In the case of your home audio reproducion system, wiring your speakers out of phase means that with identical signals, one speaker cone will be moving out while one speaker is moving in. What this boild down to is that you will create sharp nulls in your reproduced sound. The frequencies that this occurs at will depend on your speaker spacing.
-Bruce |
| Clarification | waVeman
Dec 31, 2001 1:05 PM | | (I guess this is one subject that won't work with simple "sound bites", so..........)
I know that when dealing with stereo (i.e., two microphones, two speakers) having reversed polarity on one of the devices is a definite no-no.
What I am speaking of is the OVERALL polarity of the <i>completed</i> recording compared to the polarity of the listener's <i>home playback system</i>.
Here's what bothers me: What difference would it make if a wave's rarified portion hits your ear first, then the compression portion? I can see--possibly--the bass frequncies with their long wavelengths might somehow be affected. (The bass wave interactions in a closed space like a living room, with multiple reflective surfaces (walls, ceilings) absorbative ones (drapes, furniture, carpeting) must be an extremely hairy and complicated process. But the mid and high frequencies?)
I have read where people who heard of this concept became confused and wired their speakers out of phase, and reported various things: some thought it sounded worse, some better and some said just parts of the music sounded better. I have a feeling some had their speakers wired incorrectly in the first place so of course that would explain the improvements!
I dunno, maybe I shouldn't have brought this up. This reminds me of something called "chaos theory", a potentially mind-melting thing I don't want to worry about when listening to my music!
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Speaking of music: Using one of those gift certificate things, I just bought an album by two guys who call themselves "Groove Armada". I first heard them on a public radio station, during their funky music show. The album is called <i>Vertigo</i>. It's pretty good, if you like (it's heard to describe but...) light hearted/dancy/electronic sounding/chill-out music. It isn't that techno/pounding rave stuff with monotonous drums beats and cheezy synths--I hate that drivel. These guys, with "Fatboy Slim", did that song for that Mitsubishi commercial called "I see You Baby" (it's got the chorus of <i>I see you baby, shakin' that ass, shakin' that ass.....</i>Though in the commercial I think it was shakin' that "thing")
CDnow:
http://www.cdnow.com/cgi-bin/mserver/SID=96512386/pagename=/RP/CDN/FIND/album.html/artistid=GROOVE+ARMADA/itemid=1156697
Their own website at:
http://www.groove-armada.com/ |
| Out of Phase | one50
Dec 31, 2001 2:08 PM | | You can not tell if a Stereo pair of speakers have reversed polarity unless you use equipment to test it. But if one speaker is "out of phase", it's very apparient. Now in a 5.1 music setup if the mains are reversed, again very apparient. But if all the speakers are reversed....you'll never know.
Maybe you can test it for yourself....reverse all your speakers and listen. |
| 5.1 speakers-an audiophile's nightmare | waVeman
Dec 31, 2001 2:42 PM | | Wow, all those speakers, all those speaker cables, all those microphones, all those mixing boards.......no wonder so many of them are frightened of multi-channel music. That's their loss I guess.
Well, as someone said once: "To live is to risk." |
| Clarification | FLZapped
Jan 1, 2002 7:44 AM | | Well, first of all, one would hope that the recording engineers got it all right before sending the masters off for reproduction.
However, in general, your room has reflections, these reflections are going to create situations where signals can either add to each other or subtract from each other. This will cause bumps in the response that varies by position in the room. Will it be audible. Depends.
As the frequency rises, the effect increases because of the decreasing wavelength, however, we also become less sensitive to these changes.
This has never been a simple answer. Even with all the new computer aided tools, there is still some fudging that engineers still ahve to do when installing FOH systems.
In your listening environment, there are two methods of dealing with this situation. Dispertion and absorbtion. Depending on what you are trying to achieve dictates what approach you will use, including a combinational one.
Some professional examples. In a movie theater, they go for the whole room dead. In a stage theater, they go for a "live" stage and a dead audience area. In a church, they want the entire space to be "live" or reflective. Each situation requires different treatments, yet each must maintain their intelligibility.
I hope this helps, but it probably has just made it as clear as mud...
-Bruce |
| re: "Recording polarity": something else to obsess about? | Pat D
Dec 31, 2001 11:27 AM | | It seems some polarity differences are audible and will show up in DBTs:
http://www.oakland.edu/~djcarlst/abx_pola.htm
Those auditions found that reversal of polarity with a test signal (I don't know what it was) was audible, but when some recordings of music were used, the results were simply chance.
You are correct that in electronics, musical signals are alternating current, in essence.
I agree that we would not ordinarily know whether the polarity was correct (or even consistent) on a recording, or for that matter, our equipment. I have not read Lars Fredell's article, and do not know how he determined the polarity of the recordings. Also, I do not know what listening protocols he used to determine whether he can hear a reversal of polarity on various recordings. He is quite convinced he can.
The speed of sound is about 1330 ft/sec at sea level, I believe. You can easily determine the approximate wavelength of various frequencies in feet by dividing 1130 by the frequency. Thus, the wavelength of a 50 Hz tone calculates out at 26.6 feet. To get a 1 inch wavelength, we would need a frequency of 15,960. |
| Whoops! Typo . . . | Pat D
Dec 31, 2001 11:30 AM | | 1130/50 = 22.6 |
| More debate | waVeman
Dec 31, 2001 2:30 PM | | Thanks for the info.
In another thread, they are still debating this subject. But, again, little attention is being paid to the room interaction effects.
http://www.AudioAsylum.com/forums/hirez/messages/50173.html
(I don't post anymore over there: too much animosity over what I consider a fun, but not earth-shakingly important, hobby.)
Yea, sure, <b>the overall polarity of a recording MAY cause it to sound different (especially the bass) in DIFFRENT LISTENING ROOMS</b>, but as far as it needing to be the same polarity from recording studio to the listener's home speakers to maintain good sound, this just doesn't sound right. Again, I keep thinking of how there is no "correct" polarity for an alternating sound waveform.
This really sounds like just another issue of dealing with your room's particular sonic qualities, like moving a speaker out of a corner to clean up the bass or using a throw rug on a hardwood floor to cut back on too much reverberation (a "live" room).
It may make a sonic difference, but it sounds like just something else trivial to complicate the listening experience.
I am going to start looking up material on room interactions and room treatments to improve the sound of one's system. And the ones I've seen so far seem pretty cheap and easy to deal with. I have always been fascinated with how concert halls deal with sound: at my college one hall used large tubes (@3ft diameter, and different lengths) hanging from the ceiling; another used various flat panels in seemingly random places around the room for.......breaking up standing waves? Got a lot of reading to do! |
| re: More debate | woodman
Dec 31, 2001 4:24 PM | | Waverguy:
When we speak of polarity, any given frequency's wavelength is NOT a consideration - but "phase-shift" most certainly is. The contention (by some misguided CONE individuals) that they can readily identify incorrect polarity leaves me laughing hysterically 'til my eyes water at the nearly incomprehensible gullibility of it all!
The term POLARITY has to be defined as whether a tone (frequency) begins with a POSITIVE or a NEGATIVE excursion from neutral (ground) ... period. An audible frequency waveform of whatever timbre or tonality will be symmetrical, with both halfs mirroring each other except for the fact that one of the two "started" the tone and the other followed along behind it.
To be able to identify incorrect polarity, one would have to "hear" that first half-cycle that starts the tone and be able to tell if that beginning half-cycle was a positive-going or a negative-going one! Possible to do? Are you kidding me? I would concede that it MIGHT be possible to rig a test using one single tone-burst of short duration so that a really perceptive individual might be able to discern it. But listening to real music in real time in a real listening room? I hardly think so.
As has already been mentioned - having the two channels of a stereo system 180 degrees out of phase (opposite polarity) with each other should be readily identifiable by most people. But when a home system is all polarity consistent - whichever polarity it actually is, the incoming signals will be impossible to identify as to their polarity in my view.
That's my 27 cents
woodman |
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