Properties of Speakers

[Sheep]

Hey ya, thats not even the right graph...

Thats the EP600..

SheepStar

 

[Buckle-meister]

First of all, sorry for the delayed response WmAx. Last time I looked at the thread, Sheep hadn't a clue.

...your attached graph is not comparable to the Axiom graph. Please note the dB scales of both graphs.

Shoot! Yes, I should've spotted that myself. Sorry 'bout that.

So, given that roll-off exhibits a non-linear slope (x-dB/Octave = linear decrements of dB for a halving of frequency), is it correct to say that when the scales/limits of graphs that're being compared are compatible, both the theoretical and actual response (with the latter a little more 'ragged' looking) would be a straight line plateaux and at its lower end; a smoothly (with ever increasing slope) curved roll-off?

EDIT: Shoot! Just remembered that the response is typically plotted using a logarithmic scale!

Also, regarding speaker drivers, now and again I hear of folk talk of perfect driver motion as being 'pistonic'. Now I know what a piston is, but I was wondering whether what was meant by pistonic literally referred to the same type of motion as a car engine's pistons where the locus of the cylinder head over time would show a sinusoidal curve, or whether what was meant was a square-wave type of graph of a perfect driver moving backwards and forwards over time?

 

[jaxvon]

First of all, sorry for the delayed response WmAx. Last time I looked at the thread, Sheep hadn't a clue.



Shoot! Yes, I should've spotted that myself. Sorry 'bout that.

So, given that roll-off exhibits a non-linear slope (x-dB/Octave = linear decrements of dB for a halving of frequency), is it correct to say that when the scales/limits of graphs that're being compared are compatible, both the theoretical and actual response (with the latter a little more 'ragged' looking) would be a straight line plateaux and at its lower end; a smoothly (with ever increasing slope) curved roll-off?

EDIT: Shoot! Just remembered that the response is typically plotted using a logarithmic scale!

Also, regarding speaker drivers, now and again I hear of folk talk of perfect driver motion as being 'pistonic'. Now I know what a piston is, but I was wondering whether what was meant by pistonic literally referred to the same type of motion as a car engine's pistons where the locus of the cylinder head over time would show a sinusoidal curve, or whether what was meant was a square-wave type of graph of a perfect driver moving backwards and forwards over time?

You'd want pistonic in the automotive sense. The goal of any driver is to track the incoming sinusoidal signal as precisely as possible. Now, keep in mind that the musical signal will look almost nothing like a single tone sine wave, as music consists of hundreds if not thousands of different waveforms of differing frequencies and amplitudes summed into a single signal (one for each channel). Your speakers' drivers must then move as best they can to replicate that wave. To better stress the point, I've included a simple visual.

Here is your basic sine curve with amplitude A:

If you are playing a test tone of say, 1kHz, the input should look like the above graph. The equilibrium of a sine curve is the line where A=0. In the above graph this line is the t axis. This is where the greatest rate of change takes place. How does this translate to driver movement? With an input of voltage V and current I, a driver will exhibit a given output that corresponds to that input. The movement of the driver can be expressed by the same sine wave. When the driver is at rest, it is sitting at the equilibrium point. When moving with input signal of f=1000Hz, it should ideally move back and forth, perfectly tracking the sine wave, with the greatest velocity occuring when the driver passes the equilibrium point during its stroke.

 

[Buckle-meister]

You'd want pistonic in the automotive sense. The goal of any driver is to track the incoming sinusoidal signal as precisely as possible...Your speakers' drivers must then move as best they can to replicate that wave.

Are you sure? Aren't we getting confused by what the input signal to the driver is versus what behaviour we would ideally have the driver possess?

I understand that music can be built up from the sum of a multitude of sine waves - this is the basis of digital recording is it not. However, say we introduce a square wave to a driver, unless I am mistaken, the driver will not be able to play it perfectly because the simple act of moving backwards and forwards will lend the driver momentum (which does not form a part of the input) and so the 'square' part of a square wave input cannot faithfully be reproduced. In other words, even when the input stops, because of momentum no driver can ever stop at the same instant.

Now consider the opposite case. Here we have a (theoretical) driver that can exactly reproduce a square wave type input. Such a driver would have the capacity to 'turn on a hair's breadth' so to speak would it not? Thus my argument that pistonic driver motion would actually take a square wave form in terms of driver capacity, but that it is the source input of sound that is (comprised of) sinusoidal (components).

Does this make sense, or is it still completely wrong?

 

[ChrisJam]

Just for reference, it's spelled "ya'll". Keep in mind that "ya'll" is singular. The plural of "ya'll" is "all ya'll"

I may be a newbie to HT and its related components, but now we're in *my* ballpark! <cue evil laugh: muhahaha>

As a full-time writer who does some freelance editing, I can assure you that the correct spelling is "y'all." The contracted word is "you," which puts the apostrophe between "you" and "all."

Don't belive me? No problem! Check this well-respected American English usage book: _Garner's Modern American Usage_, from the Oxford Press, 2003. Even my handy-dandy desktop dictionary has "y'all," not "ya'll."

You are right--well, almost <s>--about the plural. It involves another "all": the plural is "all y'all." Now it gets fun if we go to the possessive of the plural: "all y'all's."

OK, enough of the off-topic stuff. I now return control of your TV set to you. (Oops, I was having an "Outer Limits" moment.)

BTW, jax, I'll probably be asking more audio newbie questions, and look forward to having you help me again. Best wishes!

 

[ChrisJam]

Sorry about the double post

I saw strange lines in the bottom part of my reply, and tried fixing them. It didn't work. But you can read my words, which shouldn't have had any strike-out lines through them. I don't know where they came from. Maybe this is something else I can learn from the audiophiles at this forum.

 

[ChrisJam]

Thanks, mulester7

Mulester7 told me in a PM how to remove my double post. I took the advice and, voila, the extra post is gone. Thanks! I still don't know where the strike-out lines in my original post came from. I hope it's as readable on your computers as it is on mine.

But hey, I'm still right about the spelling of "y'all."


Chris

 

[WmAx]

So, given that roll-off exhibits a non-linear slope (x-dB/Octave = linear decrements of dB for a halving of frequency), is it correct to say that when the scales/limits of graphs that're being compared are compatible, both the theoretical and actual response (with the latter a little more 'ragged' looking) would be a straight line plateaux and at its lower end; a smoothly (with ever increasing slope) curved roll-off?

You may have to clarify what you wish to inquire about. But if you are asking if the graphs shown are correct(as would be expected to be predicted by a typical calculation), then yes, they are.

Also, regarding speaker drivers, now and again I hear of folk talk of perfect driver motion as being 'pistonic'. Now I know what a piston is, but I was wondering whether what was meant by pistonic literally referred to the same type of motion as a car engine's pistons where the locus of the cylinder head over time would show a sinusoidal curve, or whether what was meant was a square-wave type of graph of a perfect driver moving backwards and forwards over time?

So far it seems that the typical/common reference to pistonic is not being used in this thread in the correct perspective. When one refers to 'pistonic' behaviour, they usually mean a diaphragm that moves as a single, solid unit. In real life, most diaphragms have a degree of flex due to stress past a certain frequency[where the driver enters break-up mode(s)], or when the driver is under very great pressure/stress(such as a LF driver at high excursion/incursion) where the stress exceeds the mechanical stiffness to retain a solid shape. The edges of the diaphragm will not be moving in exact unison/phase with the center, for example.

-Chris