What I mean is because the wavelength of all these various freq component vary, even if they start all at a specific zero crossing and go positive at the speaker, by the time they get to your ears the phase has changed due to the distance/time of flight.
So the various freq components, that started out the same, now have a whole soup of phase shifts with respect to each other. Suppose you sit at 3m from the speaker. The freq with a wavelength of say 3m just has completed 1 wave and is back to zero, the one with say 6m wavelength now is also at zero but opposite phase, the one with 40cm wavelength is now at 240 degreess, going up. Etcetera.
And when you move to a different distance, it is different again.
Jan
The argument that was previously expressed in here (not by me, and I can't find it, so paraphrasing), is to imagine silence. Then the guy hits the drum. Assume a positive wavefront sets out from the drum, it will hit your ears as positive first as it arrives, regardless of where you are. Does this sound different if it's absolute pressure is inverted?
The bit I don't get in this is that the initial 'thwack' of a drum has a fairly broad band response and I have heard say that studio types are known to boost the 1-3kHz response to get more thwacky goodness. Now this corresponds to the area where quite a few speakers have their crossover regions so there will be a significant phase shift around that area. (180 or 360 degrees in many cases).
Or is this what the full range mob harp on about?
Or is this what the full range mob harp on about?
For mixing commercial records, one issue is that many small speakers can't reproduce very low kick drum fundamental tones. Therefore is it common to boost maybe somewhere around 1-3 kHz to bring up the click of the beater hitting the kick drum head. The idea is at least there will be something people can hear that will still convey a little something from the kick drum, maybe to help maintain some sense of groove in dance music. The exact frequency boosted depends on what beater click frequencies sound good, and if a hole or a dip in the mix frequency spectrum is available to drop in some beater sound without undue masking or other new issues arising.
Regarding absolute phase, sometimes when a kick drum head is struck, there is an initial puff of air from a hole cut in the resonant head, or from a cylindrical port installed in the head called a "kick port."
When a single puff of air is produced, the resultant waveform may look kind of like a step with a slow ringing decay. If there is any absolute polarity to the puff, rather than thinking of it as a wave, if sufficiently LF, a more intuitive model might be something more like an electric cooling fan. A fan can project a stream of air a long way on the pressure side, but on the suction side it pulls in air from all around, so the airflow pattern and pressure pattern is not symmetrical on both sides of the fan.
To the extent a very LF drum hit, or initial transient, might be similar to a fan model, it might make more sense to expect there could be some resulting perception of absolute polarity possible in some listening situations.
When a single puff of air is produced, the resultant waveform may look kind of like a step with a slow ringing decay. If there is any absolute polarity to the puff, rather than thinking of it as a wave, if sufficiently LF, a more intuitive model might be something more like an electric cooling fan. A fan can project a stream of air a long way on the pressure side, but on the suction side it pulls in air from all around, so the airflow pattern and pressure pattern is not symmetrical on both sides of the fan.
To the extent a very LF drum hit, or initial transient, might be similar to a fan model, it might make more sense to expect there could be some resulting perception of absolute polarity possible in some listening situations.
Sorry for the close quote, but I think these words are important. A step response is wideband by definition, so the question still is which frequency band is the absolute phase important for.
If he strikes the drum head opposite you then the mallet is moving toward you, so presumably the initial wavefront is compressive as it travels toward you. If he strikes the drum head on the side nearest you the initial wavefront will have the opposite polarity. If you close your eyes can you tell which side of the drum he is striking?
Or he is just using one mallet and only striking one side of the drum. Does it sound "natural" to people on one side of the street but "unnatural" to folks on the other side?
Don't like marching bands? OK travel back in time to watch Gene Krupa playing "Sing Sing Sing". He is hammering away on a couple of floor toms, each of which has two heads. When he strikes the top head the membrane moves down presumably causing a rarefaction, but the bottom head also moves down presumably causing compression. Which one are you hearing?
These claims about absolute phase and percussion just seem silly to me.
You want broadband? Try a nice Zildjian cymbal. When it is struck it vibrates and last time I checked both surfaces were exposed to the air in the room. So what is the correct absolute phase of the wavefront which is traveling in all directions from both sides of all parts of the cymbal, from the cup to the edge?
I still don't understand, Jan.
Because all the components of the signal, whatever their frequencies travel at the same speed, for the listener, they will arrive at the same time. With their respective phases. Unchaged, as I said.
.
The phase is not the same at a given moment for different listeners situated at a different distance from the speakers, but who care ? We are alone in our brain.
About absolute phase of the speaker's assembly, I do think many can find a slight difference. Specially with powerful low frequencies transients, like Kick drums. Reason why so many amplifier propose a button to allow phase reversing.
But, may-be it is just because most of our electro magnetic speakers are not at all symetrical in the plane of their moving coil ?
Kick drums have components in all the listenable bandwidth up to the highest frequencies you can hear.I love the term "low frequency transient". Especially the fast one.
Like 30Hz transient or so
And even at 30Hz (or the fundamental frequency resonance of the skin where is most of the energy ) the signal is *very unsymmetrical*: A big half of a period during the time the 'Kick' push the skin, followed by a fast decay due to the skin's resonances.
In studios, they use often kick drums opened with only one skin and heavy pillows on it to dump their skin resonances.
Even this first half period 'pulse' is modulated in frequency (not sinusoidal at all) by the decreasing kick speed during the time it pushs the skin, while the signal return to 0 at the skin resonnance frequency.
Is-it a funny English's mistake (Pr Tournesol is not anglo-saxon) to call half a period a "transient" ?
Tryphon.
Last edited:
- Status
- Not open for further replies.