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The Speaker Project




The Main Speakers







The Main Speakers - Start to Finish

The Monitors - Overview
Selecting Drivers
Test Drivers
Designing the enclosure
Build a prototype
Design a crossover
Listen to the prototype
Build templates
Build enclosures
Finish the enclosures
Final Test
Parts List

  Speaker Workshop Project
Monitor - Test Drivers

The first phase of driver testing fulfills two purposes.

1. Testing lets you check the drivers to make sure that they are within specification.

2. Testing lets you design an enclosure for the woofer.

A free air impedance test is the most critical test here. Perform this by tightly clamping the driver (preferably upright with no surfaces nearby) and then test the impedance using Speaker Workshop.

Tweeter Test

We test the tweeter by simply doing a free air impedance test. This verifies Q and FS . For the XT tweeter the free air impedance test looks like

After doing the test, do a Driver / Estimate Parameters to see what Speaker Workshop considers to be the driver parameters based on the impedance tests. Don't forget to set the driver's DC Resistance manually before doing this (Driver / Properties). You can compare the tested impedance to the .Estimate dataset to see if they match and to find irregularities in the tweeter impedance curve.

For the tweeter we get an FS of 550Hz and a QTS of .601. The Vifa spec for the driver is an FS of 500Hz and a QTS of .55. We are well within spec (and as usual both FS and QTS are high - perhaps because the driver hasn't been broken in).

Woofer Test

To test the woofer we have to perform two impedance tests. One in free air and one with added mass or in an known volume enclosure. These two tests between them capture all the information needed to verify the woofer is good, and to calculate FS, QTS, and VAS - the three important Thiele/Small parameters.

Here are the two woofer impedance tests I did. Earlier in the project I used added mass, so here I did a sealed box test. The box was the bottom part of the two-woofer prototype (sealed off). These measurements were taken at a sample rate of 48KHz and a sample size of 256K with 3 samples to give good frequency resolution and low noise near resonance.

You may note the "hash" around 500Hz in the sealed box curve. This is caused by reflections from the box sides or internal box resonances. Here's a close-up of that part of the chart. Notice how the "hash" is only evident in the red (Sealed Box) dataset.

Anyway, Speaker Workshop does the Estimate Parameters using these settings and comes up with values of

Spec Measured A  Measured B Factory
FS 45.3 Hz 43 Hz 38 Hz
QTS 0.44 0.40 0.34
VAS 17.2 L 18.5 L 25 L

As usual, QTS is high and VAS is low - the typical non-broken-in results. Agreement with factory spec is actually quite good. The B result is a different, more broken in, PL18.