[irlsanders]

Quote:

Idealy the transients should be reproduced on the same driver that makes the fundimental and harmonics of the note. Speakers and headphones are inherently limited in repoducing real instruments. Real intruments make all their own frequencies. headphones and speakers try to make all the instruments frequncies at the same time. This leads to one instrument doppler shifting the sound of another. Most headphones, and some speakers, at least have the advantage of each intrument's sound coming out the same driver. On headphones and bass: Headphones can never reproduce bass properly. Like islander and others have said, bass is not just an ear thing, it is a body thing as well. Also it is difficult to properly reproduce a bass note in a typical living room since the reflection hits you too soon. You'd need low frequency absorbing walls to get close and this isn't simple (cheap) to do. Sitting on a subwoofer is no answer, it vibrates the wrong body parts. Life is a comprimise, so is sound reproduction. There is no right answer, just the one that works best for us. [/B]

Well said, Dk. Although, most instruments do make sound from more than one place - just try micing a double bass. There's the buzz from the bow, the free air vibration of the strings, fingering sounds on the neck, and the full sound amplified by the resonating wooden body. A very complex accoustical system! That the whole system of mic-record-playback even works at all is astounding! Hardly seems right for us to gripe about it at all.

 

[dknightd]

Quote:

Originally posted by Spad Someone ought to breakout a hammer and chisel for this. You should consider using it for a sig, dknightd.

I don't get it

<edit> I get it now. My mind must
be tired. Better rest and listen to some tunes

 

[Dusty Chalk]

Well, I'm obviously not preaching to the choir on this one, so I'll just stop.

All your points about bass reproduction are wrong, though. Sound is sound is sound. Whether it was created by instruments, or created by speaker or headphone elements, it still ends up the same way by the time it gets to the ears -- highly localized pressure variations. Whether it was generated by one instrument or multiple instruments, they don't "doppler" each other. That's just wrong. I understand what you're trying to say, but what you're addressing is the problem of mixing. Whether that happens in air (as in on a mic-ed recording of multiple live instruments) or in electronics (as in seperately recorded instruments mixed by a recording engineer) -- this isn't something that one needs to worry about. The speaker or headphone element only has to successfully reproduce the net result, and then it has done its job (no mean feat, but the sort of problems you are discussing are beyond this).

I understand what you are trying to say about the body -- and that is a point, you don't wear your headphones on your abdomen -- but surprisingly minor when your ears are convinced. If your ears don't want to be convinced, then no amount of words will convince them, so I'll just quit.

But you really ought to give a pair of Beyer DT770's -- properly amplified -- a try before you come to any conclusions. You'd be surprised how little you miss.

 

[dknightd]

Quote:

Originally posted by Dusty Chalk Whether it was generated by one instrument or multiple instruments, they don't "doppler" each other. That's just wrong. I understand what you're trying to say, but what you're addressing is the problem of mixing.

I respectfully disagree. Lets consider a simple
example; a string bass (or any instrument) playing
a 50hz tone, and another instrument
playing a 5Khz tone. If the instruments are
making the tones, then there are two seperate
sources, and the sound simply reaches your ears
"mixed" as you describe.

Now what about when these two instruments are
recorded and we ask a speaker (or headphone) to
reproduce this sound. In order for the speaker
to produce both sounds at comparible volume it
has to move more to reproduce the 50hz signal than it does to reproduce the 5khz signal. The 50hz
signal causes the speaker cone to move toward
you for 1/100 sec, then away for 1/100 sec, etc.
Superimposed on that is the 5khz frequency the
speaker is also asked to reproduce. But the movement of the speaker cone
caused by the 50hz signal is
Doppler shifting the 5khz signal. During the
1/100 sec the driver is moving toward you the
5khz signal has its frequency shifted slightly
higher. Then in the 1/100 sec the speaker cone
is moving away from you the 5khz signal has
its frequency shifted lower. Obviously this
is more of an issue with a speaker than with
headphones because the cone has to move more
in a speaker. I wonder if this is why headphones
(and large panel speakers) are thought to have
cleaner upper midrange than most speakers.

This is all part of required comprimises. We
want all the sound from a speaker to come from one
driver if possible, but, if we do that there
can be a problem with Doppler shifting frequencies
especially at high volumes. Or we can use lots
of drivers, but than phase issues become more
problematic (partly because then crossovers
are required).

I wonder, if a person listened only to
quartets perhaps each instrument could be
recorded seperately. Then at home each instrument
would be recreated on its own speaker. A new
sort of "quadraphonic" recording. The home
user could even move their 4 speakers around
to change the placement of each instrument on "stage"

 

[kwkarth]

Ok,
I'm going to jump in here and straighen both of you guys out, that way you can both be mad at me and be friends with each other

Dusty, conceptually, Dknight'd is correct about doppler distortion except in one small misstatement.

dknightd you said "In order for the speaker to produce both sounds at comparible volume it has to move more to reproduce the 50hz signal than it does to reproduce the 5khz signal."

Actually the 50 Hz signal does NOT require the speaker to move MORE. The amplitude of motion is entirely dependent upon the amplitude of the signal, not the frequency. Frequency equates to speed of motion only, and amplitude of sound equates to the distance or amount of driver excursion.

Other than that, you're absolutely correct, a 5kHz wave riding upon a 50Hz carrier will indeed be doppler modulated at the rate of 50Hz. Assuming of course that both sounds are reproduced by the same driver. The effect is quite audible and I am sure that is one of the reasons that large panel radiators or multiple driver arrays sound so clean in some respects.

Cheers!

 

[dknightd]

Quote:

Originally posted by kwkarth Ok, I'm going to jump in here and straighen both of you guys out, that way you can both be mad at me and be friends with each other

I don't *think* anybody is getting mad. I know I'm not. But thanks for stepping in...

Quote:

dknightd you said "In order for the speaker to produce both sounds at comparible volume it has to move more to reproduce the 50hz signal than it does to reproduce the 5khz signal." Actually the 50 Hz signal does NOT require the speaker to move MORE.

Hmmm. I was always under the impression that low
frequencies required greater cone excursion to create the same percieved volume. Certainly tweeters do not move near as much as woofers.
Play a 50hz signal and a 5khz signal on the
same speaker at the same percieved volume -
for 50hz you can see the cone
move, for 5khz the cone doesn't appear to move
near as much (if at all, but clearly it is).
I have atributed this to the lower sensitivity
of the ear at low frequencies, and, the less
effective coupling of a speaker to a room volume when the speaker size is smaller than a wavelength.
Of course I could be wrong! It wouldn't be the
first time!

I wonder now for example if sound volume is related
to the rate of pressure change. In which case low
frequencies would also require greater cone excursions than high frequencies. Maybe I'll look
into this someday.

Maybe somebody will step in who knows this,
but, as you note, it is not critical for our
understanding of Doppler shifting in speakers
(although if lower frequencies do not require
more cone excursion it would make the effect
much less noticable).

regards

 

[Dusty Chalk]

Quote:

Originally posted by kwkarth Dusty, conceptually, Dknight'd is correct about doppler distortion except in one small misstatement. ... Other than that, you're absolutely correct, a 5kHz wave riding upon a 50Hz carrier will indeed be doppler modulated at the rate of 50Hz. Assuming of course that both sounds are reproduced by the same driver. The effect is quite audible and I am sure that is one of the reasons that large panel radiators or multiple driver arrays sound so clean in some respects.

I thought that was whole speakers, not a problem with the elements. Oh, well, learn something new every day. Thanks, kwkarth!

 

[kwkarth]

Actually, as you no doubt know, this is not a simple subject.

Yes, dnightd, woofers typically do move more than tweeters, but it is for two reasons... One, the amplitude of low frequency information is virtually always greater by far in most music, and two, you are correct in surmising that the typical woofer has to work hard to move enough air because of coupling or acoustic impedance matching of the driver to the air in the room.

Dusty, you are also correct that doppler distortion can and is attributed to entire speaker systems, in extreme cases, and not just single drivers, but the effect of modulating a HF wave with a LF wave is much more severe or pronounced if both soundwaves are emanating from the same driver. This fact, in and of itself is a good arguement for multi-way speaker systems as opposed to single driver systems.

 

[irlsanders]

The other reason we don't see mids and tweeters moving (so much) is their higher frequency - I wonder at what freq our eyes actually stop being able to resolve mechanical vibration?

A friend and I once mounted a small laser diode to a damaged 5" driver in college. When driven with audio, we got an instant disco style synchronized light show projected on a blank wall - a fun way to visualize audio. The reverse process is actually used these days to measure driver performance - by aiming a laser at a moving diaphragm and measuring the way it scatters the light.

It's neat that a little post aimed at subwoofer advocacy has turned into a pleasant acoustical theory discussion.

Re: Doppler - if the original instruments were both recorded with one mic, that diaphragm was already "Doppler modulated", and if the signal is played back on a single driver, no additional modulation should occur. The problems begin occurring when signals from multiple mics are combined and then played back through a single driver. The worse case scenario I can imagine is when your have no subwoofer in your HT system, and the LFE channel is played back through your mains. As already stated, the effect is pretty minimal, otherwise all recorded music would sound like poo.

On that note, I just had the most amazing opportunity to hear a film score performed live to picture at the 20th Anniversary premiere of ET. John Williams conducting a Los Angeles film orchestra in the Shrine Auditorium. Live music is such a fabulous release and reference point. I dare say the money spent on a live concert is a better investment that any new pair of headphones!

 

[dknightd]

Quote:

Originally posted by irlsanders Re: Doppler - if the original instruments were both recorded with one mic, that diaphragm was already "Doppler modulated", and if the signal is played back on a single driver, no additional modulation should occur.

Good point! I never thought about that. Assuming things are linear, and I'm not missing something, it does seem that the Doppler shifting should cancel out. Cool

Of course if the engineer messes with the signal, or, you playback through multiple drivers, then the problem returns.

Maybe that helps explain why I'm enjoying simple two mic'd recordings so much lately.

 

[irlsanders]

Quote:

Originally posted by dknightd Maybe that helps explain why I'm enjoying simple two mic'd recordings so much lately.

That, and the fact that there are no phase anomalies produced by instruments leaking into multiple mics at different distances. I love recordings done with a single pair of coincident mics. This is only feasible for small ensembles in great spaces, but it's a thriller when done right.

 

[Dusty Chalk]

Quote:

Originally posted by irlsanders Re: Doppler - if the original instruments were both recorded with one mic, that diaphragm was already "Doppler modulated", and if the signal is played back on a single driver, no additional modulation should occur. The problems begin occurring when signals from multiple mics are combined and then played back through a single driver. The worse case scenario I can imagine is when your have no subwoofer in your HT system, and the LFE channel is played back through your mains. As already stated, the effect is pretty minimal, otherwise all recorded music would sound like poo.

Poo -- heh-heh.

Actually, this sounds a lot like what I was trying to say Re: "mixed in air" vs. "mixed in electronics". Was I at least half right in that stuff that gets mixed via "air" does not have the doppler problem? And if so, how is it that electronics could possibly add that problem, since what they are doing is analogous to what happens in air? I'm missing something, please educate me... Quote:

On that note, I just had the most amazing opportunity to hear a film score performed live to picture at the 20th Anniversary premiere of ET. John Williams conducting a Los Angeles film orchestra in the Shrine Auditorium. Live music is such a fabulous release and reference point. I dare say the money spent on a live concert is a better investment that any new pair of headphones!

I've seen both Koyaanisqatsi and Dracula performed live (the soundtrack, that is) -- wonderful experience.

 

[irlsanders]

Quote:

Actually, this sounds a lot like what I was trying to say Re: "mixed in air" vs. "mixed in electronics". Was I at least half right in that stuff that gets mixed via "air" does not have the doppler problem? And if so, how is it that electronics could possibly add that problem, since what they are doing is analogous to what happens in air? I'm missing something, please educate me...

I'd love to nail down this Doppler discussion, but I fear my wording will be crude and diagrams would help alot. Lemme take some time to get the wording straight befroe I reply.

Did you catch the use of Pohwaqqatsi (let's see what my spell checker makes of that!!) in The Truman Show? Pretty effective.

 

[Dusty Chalk]

Oh, really? No, didn't see that movie, but heard that it was original music...oh, well...

And it's Powaqqatsi. (No, biggie; it's really hard searching for Koyaanisqatsi on eBay when even the sellers don't know how to spell it.)