Measuring the loudspeakers parameters...Arta/LIMP guide...
SK | EN
Often, mainly in car hifi, we meet loudspeakers without any TS-parameters provided by the manufacturer, even though they are important for enclosure design. If we have recommended enclosure parameters, we still cannot be sure these are right four our particular loudspeaker (loudspeakers can differ even if they are the same model). Or what if we have some special requirements?
This all is why we might want to measure TS parameters of our loudspeaker. What do we need?
- - PC with MS Windows 98/Me/2000/XP/Vista/7 OS and a sound card
- - 2 pcs. 3.5mm jack, some wire and precisely measured resistor (about 100 Ohms)
- - weighed play-dough (or anything similar - sticky and able to hold its shape)
The first thing we have to do is to download software package from www.fesb.hr/, which includes ARTA, STEPS and LIMP. Install it after downloading. It is a shareware, but the only restriction is that we won't be able to save our measurements directly in application
The next step is creating the measurement device. It's not difficult at all, here is the simple scheme:
We use one of the soundcards output channels, which is connected tu to resistor. Both ends of the resistor are connected to the soundcards input, one to the right channel, the other to the left one, through the resistor is also connected our measured speaker to the output of the soundcard. The resistance of the resistor doesn't have to be 100 Ohms exactly, but for the safety reasons don't use smaller value
After connecting the device to the sound card, let's run LIMP, we accept to continue in demo mode. First click on the Setup/Audio Devices and select devices we want to use for the sound output and input. Of course we have to configure the sound settings in windows correctly (select the correct input in recording devices, it can't be muted). Then, in setup, we can set the measuring method, if we will use using the stepped sine (short interval tones of given frequency), or it can compute using fast Fourier transform (pink noise on the output, result is calculated from the spectrum) - FFT method is faster. In this window we also set the reference channel and the exact value of the resistance of our used resistor.
We have the configuring done, now we can proceed to the sound card calibration. That's how we ensure the same output level on both input channel - we do this with the load (speaker) disconnected. Click on the record -> calibrate and there on "Generate" button. We can see the level of signal on the input channels, both levels should be similar, if it's not, something is set wrong, check the Volume settings in windows. If both levels are similar, we should set the output and input level of output and input, so the level bar would stay under the red value (but should be high enough). Then, click "Calibrate" and the calibration is done.
We can continue with the measurement itself. Connect the measured loudspeaker to our device, click the "Start rec" icon. Wait until the response is smooth and with a clear impedance peak, then click "Stop rec". This is the measured impedance response of our speaker. If the values are higher than they should be (for example the minimum impedance is over 100 ohms), we have swapped reference channel in settings.
Now we can also get the inductance value by setting the cursor at 1kHz (by left clicking).
Click on Overlay - Set as overlay.
Now we proceed with adding the measured weight to the speaker cone, it's better when it holds itself on the cone.
Click at Start rec again. Another response will show, with lower resonance. So now we have two curves, click at Analyse -> Loudspeaker parameters -> Added mass method. We fill the fields with the DC resistance (measured by ohmmeter or multimeter, of course take the resistance of the wire leads into consideration), cone diameter (measured with 1/3 of the surround) and added mass (weight) and click on the "calculate TSP. We will get the TS parameters, which we can copy & paste into text editor (notepad for example).
For precise measuring we need good sound card (onboard codec isn't enough, doesn't have enough "strength" on the output), properly made measuring device (short & thick wire leads) and a silent room, noise also has some effect on the measuring.
We also need to choose the right weight of the added mass, if the speaker has big and massive cone, or stiff surround, the height has got to be higher. We need to get the Frequency shift (displayed in the table where the measured parameters will show) in between 20 to 50 percent.
TS parameters are changing with the age of the speaker, mostly in the first few days of speaker working - surround and spider will get softer, that's why it's good to do a burn-in.
When measuring loudspeaker parameters like described, we must have the speaker out of the enclosure!
Final measured impedance response of the speaker (yellow) and with added mass (green), the grey one is the phase response.
Another, smaller peaks in the response which may occur in the second measurement are caused by the added mass, for example when it has some moving or resonating parts or when it's only put on the cone, not holding itself. Therefore I recommend to measure the speaker in vertical position, with added mass holding itself on the cone with large enough area.
I will be grateful if you send me your measured parameters (with the trademark and model of the loudspeaker and your name or nickname) to my e-mail:
My measured parameters