# Measuring a loudspeaker's diaphragm

• escaldon
In summary, the displacement of the loudspeaker's diaphram is 0.034 mm, the velocity is 190 mm/s, and the acceleration is 9,76 mm/s^2.
escaldon
Hi all,

First of all, thank u for ur time and sorry about my english.
I have measured a loudspeaker's Sound Pressure Level from a distance of 1 m. At the same time, I've measured, with a accelerometer, the displacement, velocity and acceleration of the loudspeaker's diaphragm. I've found that when the SPL is 60 dB and the frequency is 80 Hz (loudspeaker radiating a pure tone) the displacement is 0,034 mm, the velocity is 190 mm/s and the acceleration 9,76 mm/s^2.
1) First wrong that i found is that, i know the magnitude of displacement is d=A, so d=0,034 mm, then the velocity is v=w·A=17,1 mm/s, and acceleration is a=w^2·A, so a=8,59 mm/s^2. The most different is about the velocity (17,1 mm/s so far from 190 mm/s).. any idea?
2) i start slowing the SPL, and i find that the velocity and displacement decreasing also, however, the acceleration keep constant.. about 9,7 - 9,8 mm/s^2. When the SPL is 42 more or less, the acceleration start decreasing (at 42 dB is 2,1 mm/s^2) until almost zero at 39 dB.. is not a bit rare?

Thank u very much.

You might want to post this in the Engineering section, or find an acoustic website specializing in such things. Good luck though, perhaps someone will answer it.

Thanks Dan, i'll do it.

escaldon said:
Thanks Dan, i'll do it.

The engineering section on PF is rather small though. You're question is somewhat busy for physics folk, who like to see things boiled down to a little data and basic theory.

ok, i see, so I'm going to post in another web. Thanks

Question 1 . What type of speaker are are using?
The reason I am asking is the displacement of 0.034 mm. 1 mm is about the thickness of a sheet of paper, and you are even less. This must be a very small speaker.

Question 2. Why do you assume that velocity is w·A and acceleration is a=w^2·A. Is your accelerometer measuring maximun velocity and acceleration.

Question 3. where is the accelerometer palced on the speaker?

Your speaker gives out a pure tone at 80Hz and the sound waves travel as a sine wave.
The speaker diaphram displacement is aslo a sine wave . Likewise the velocity and acceleration.

256bits said:
Question 1 . What type of speaker are are using?
The reason I am asking is the displacement of 0.034 mm. 1 mm is about the thickness of a sheet of paper, and you are even less. This must be a very small speaker.

Question 2. Why do you assume that velocity is w·A and acceleration is a=w^2·A. Is your accelerometer measuring maximun velocity and acceleration.

Question 3. where is the accelerometer palced on the speaker?

Your speaker gives out a pure tone at 80Hz and the sound waves travel as a sine wave.
The speaker diaphram displacement is aslo a sine wave . Likewise the velocity and acceleration.

1 mm? You mean 0.1 mm?

Thanks for ur reply 256bits. I'm measuring a low-frequency loudspeaker.

0,034 mm is a rare value, i know.. and that occurs at 60 dB.. i think I'm doing something wrong when i measure with the accelerometer.

i was a bit confused about maximum values.. i see is a sinusoidal wave. i should integrate the displacement to get the velocity and so on with acceleration.. is ok? well, really, with my accelerometer is possible to get the three parameters but, there is something wrong.. starting with a displacement of 0,034 mm..

i place the accelerometer close the dust cap, in the cone..

thanks

## What is the purpose of measuring a loudspeaker's diaphragm?

The purpose of measuring a loudspeaker's diaphragm is to evaluate its performance and ensure that it is producing accurate and high-quality sound. This measurement can also help identify any potential issues or defects with the diaphragm that may affect the overall sound output.

## What tools are needed to measure a loudspeaker's diaphragm?

The tools needed to measure a loudspeaker's diaphragm include a measurement microphone, an audio interface, and a software program for analyzing the measurements. A calibrated sound source may also be necessary for accurate measurements.

## What parameters are typically measured on a loudspeaker's diaphragm?

The most common parameters measured on a loudspeaker's diaphragm include frequency response, distortion, sensitivity, and impedance. These measurements can provide valuable information about the diaphragm's performance and characteristics.

## How do you interpret the results of a loudspeaker's diaphragm measurement?

The interpretation of the results will depend on the specific parameters measured and the desired performance goals. Generally, a flat frequency response, low distortion, high sensitivity, and consistent impedance are desirable characteristics for a loudspeaker's diaphragm.

## How often should a loudspeaker's diaphragm be measured?

The frequency of measurements will depend on the intended use of the loudspeaker and the manufacturer's recommendations. In general, it is recommended to measure the diaphragm when it is first installed and periodically thereafter to ensure optimal performance and identify any changes or issues that may arise over time.

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