Audio Garage Gallery

VISO 4-8-5
Altec compact high performance speakers

Measurements
Acoustical measurements are not a joke. The best solution it would be to buy a specific measurement device, like the Clio board. But it is expensive, it costs quite all together the Altec drivers I bought. A cheap, but valid solution is Speakerworkshop, a freeware using PC audio board for speaker measurements. You need to build a Jig and make an accurate calibration. And you need to use your brain during measurements, to understand if results are good or not. It is not a Clio, of course, but it is free. There are some forum and many internet pages on Speakerworkshop, Claudio Negro site in my opinion is one of more interesting.

After correct calibration, measuring impedance and T/S parameters of drivers is quite simple and affordable.

Here the measured free air impedance graph of ALTEC 416-8Z (click to enlarge).

On the left you can find the Thiele Small parameters measured with Speakerworkshop. In the table below the differences between Altec factory data and measured by me. The only significant difference is on Qms, but it is an old Vintage component, and after 20 or more years...

Model :	Xmax		Re	Fs	Vas		Qts	Qms	Qes
	(inch)	(cm)	(ohms)	(Hz)	(cu. ft.)	(litres)
416-8B Altec factory data	0.15	0.381	6.90	25.10	26.47	749.6	0.32	7.05	0.33
416-8Z Measured	-	-	6.59	25.1		735	0.33	4.22	0.36

And here the impedance measure of Altec 416 mounted inside the VISO 485 box, with the tipical double peak of a vented system.

Impedance measurement of 802-8G with horn 511 mounted.

Frequency response measurements are more critical, complex and difficult to do. I used a B&K professional phonometer, old but perfectly working, connected to the PC.I need some days to set correctly the system, and I measured as reference my old Sonus Faber speakers.

The audio board, anyway has some limits on low and high frequency, and another limit is given by the room itself (reflections, low freq. reproduction, etc.). Moreover, quite at the end of measurements, the audio board dead! So I was not able to finish all the low frequency near field measurements, particularly on the vent.

So, please consider that result below 150 - 200 Hz and over 10.000 Hz maybe are not very accurate. Anyway, I need frequency responses for crossover design, not for a commercial brochure.

Click per ingrandire

And here the frequency response of my Altec drivers: the 416-8Z, mounted in its vented box and the 802-8G with its 511 Horn.

Time to design the crossover