# Questions on Loudspeaker Diaphragm Movement

1. Oct 12, 2007

### rockerboi

Good day to all!

I just want to ask if someone here knows some data or measurement of speaker diaphragm movement(distance moved by the diaphragm relative to its resting position) of any speaker(any type or brand) when a certain frequency and volume is applied to it. I just badly need the information.

Thanks

2. Oct 13, 2007

### NoTime

The amount of diaphragm movement will vary based on type or brand as different speakers have different efficiencies.

This is a problem whether by volume you mean power applied to the speaker or sound pressure level (SPL).
Edit: If you measure SPL in the near field you can make an approximation.

Even having a speaker mounted in an enclosure or sitting on the floor will make significant changes.

If you need to know then you will need to measure the movement.

Last edited: Oct 13, 2007
3. Oct 15, 2007

### rockerboi

I don't have the instruments to measure the speaker's movement that is why I am looking for a data regarding that. Perhaps a loudspeaker manufacturing company can provide me one. Do you know a company that may give me such data that i need? thanks

4. Oct 15, 2007

### Staff: Mentor

It's pretty easy to measure. Put in earplugs, then shine a laser pointer at the speaker cone, near the middle and at an angle of 45 degrees. Then turn up the volume, and measure the left-to-right size of the spreading of the red dot (hold your ruler just in front of the moving cone, without touching it). Then use a little trig to figure out what the front-to-back displacement is.

Typical displacement is on the order of 1cm for medium volume 12" speakers, IIRC.

5. Oct 21, 2007

### rockerboi

Thanks berkeman.

But if a speaker vibrates and moves very fast, how would I be able to measure the displacement of the cone with regards to a specific frequency and volume?

Do you know where I can find a data of speaker movement for any speaker? Thanks Ü

6. Oct 21, 2007

### NoTime

1) Berkeman's idea will work for any frequency and volume.

Quiz question. How could you use just a ruler and your ears to measure speaker cone displacement.

7. Oct 21, 2007

### rockerboi

ok. But what I mean is what is the cone's movement,example, per 1 millisecond. Such that per millisecond there is a varying frequency and loudness. What I am looking for is a some kind of graph or line graph showing the cone's movement with varying frequency and loudness for certain time duration. Sorry if my question is a little vague

8. Oct 22, 2007

### Staff: Mentor

If you put in a sine wave for the voltage drive to the speaker, the displacement of the speaker will also be sinusoidal with respect to time. So if the input is a 1kHz sine wave, and the peak-to-peak displacement front-to-back for the speaker is 1cm, then the displacement can be described by the following equation:

d(t) = 1cm sin(2*Pi*1000Hz*t)

9. Oct 22, 2007

### Staff: Mentor

Hmmm. That's a hard quiz question. Is it still a non-contact technique?

10. Oct 22, 2007

### NoTime

No

11. Oct 22, 2007

### Staff: Mentor

Interesting. Okay, that narrows it down some. I'd assume that the non-no-contact contact needs to be light enough not to distort the measurement (or hurt the speaker cone), so that narrows it more. I have one picture in my mind, but there's a resonance in the non-no-contact thing that will give me the wrong total deflection. Gotta think about other possibilities....

12. Oct 22, 2007

### rockerboi

Thanks berkeman..now i understand.

Is an audio signal always sinusoidal or there are flat turns or edges? If it is not sinusoidal, how can I predict its displacement for a particular time?

13. Oct 24, 2007

### NoTime

There are many possible wave shapes.
Each with a coresponding equation.

Music or voice will not be sinusoidal.
In these cases you could digitize the source to a graph.

14. Aug 6, 2009

### orangeberet

Hello people. What you want is, for example, "Eminence Designer", which let you know what is the cone displacement of any speaker (introducing the TS parameters previously) in any box.

Greetings from Spain!