How can I quickly save and load my mixer settings for Speaker Workshop?
What is a full-duplex sound card; why do I need one?
What are the exact hardware requirements for Speaker Workshop?
What is the best sample rate and sample size to use?
Why are my impedance charts wrong?
Why are my acoustic measurements wrong?
What is an MLS signal?
What is an FFT?
How can I improve the memory management?
How can I make my crossover work correctly?
I need help with my impedance jig design

How can I quickly save and load my mixer settings for Speaker Workshop?

Setting your mixer up for use with Speaker Workshop is a rather tedious affair. Luckily someone (Martin Saxon) has built a neat little program called QuickMix that lets you do this easily. Check out his web page.

What is a full-duplex sound card and why do I need one?

A full-duplex sound card is a sound card that can record and play at the same time. That is required for all Speaker Workshop measurements. If your sound card is not full-duplex the program will produce a "Can't open sound" error message when you try to record.

What are the exact hardware requirements for Speaker Workshop?

Speaker Workshop requires Windows 95. It also requires a full-duplex sound card. In addition the program is very RAM and CPU intensive so 16MB of RAM (40MB of virtual memory) and a Pentium are recommended minimums. You can use a 486 with less ram but performance will suffer (reduce your sample size).

Speaker Workshop files can get pretty large - each dataset uses up 8 x [number of points] bytes - about 1MB for a 128K sample size - so have disk space available and consider reducing the sample sizes. Remove leftover datasets before saving.

What is the best sample rate and sample size to use?

There is no best size - selection is a compromise between increased frequency resolution (more sample points or lower sample rate), noise immunity (more sample points), and performance (less of everything).

For woofer impedance testing (to get Q and resonance) use the largest sample size and lowest sample rate possible. Note that sample rates below 44KHz are not correctly filtered by most sound cards and will cause aliasing (frequency response imperfections).

For acoustic measurements and crossover design a lower sample size is often adequate, but use a 44KHz sample rate to have woofer and tweeter response with the same frequency range.

For passive component testing a lower sample size is often adequate.

We recommend using 8K to 16K sample size and 44KHz sample rate for most tests. Lower sample sizes won't be significantly quicker - but noticeably less accurate. Lower sample rates will be more accurate but noise levels will increase dramatically due to the filtering issue.

Why are my impedance charts wrong?

The first step is to try switching right/left in the Options/Preferences Measurements tab. If that doesn't help recalibrate your impedance jig. Ensure that the jig works with a resistor load (using passive component measurement). If not (or the input impedance is very low), unplug any connection between the Sound Card and the CD-Rom sound output - not the CD-Rom control lines, this is usually a three-wire connection.

Why are my acoustic measurements wrong?

The first step is to try switching right/left in the Options/Preferences Measurements tab. If that doesn't help ensure that your acoustic levels are correct. Microphones have limited dynamic range. Set your amplifier volume and microphone spacing to achieve a maximum 8-16K level (using Sound Record to check absolute levels). Below 2K Speaker Workshop is unable to reliably sense the start of input acoustic data. Above 32K there is data clipping which will cause all sorts of anomolies. Also, manually adjust the mic volume in your sound mixer - we can't programmatically.

What is an MLS signal?

An MLS (Maximum Length Sequence) signal is a pseudo-random noise signal with the happy coincidence that after some serious processing it looks like a pulse, but with much more energy - lower noise levels - than a standard pulse. If you remember any electrical engineering: a pulse contains all frequencies and if you know the pulse response of a circuit (speaker) then you know the frequency response of the circuit. Hence, Speaker Workshop uses MLS signals exclusively for impedance and frequency response testing.

What is an FFT?

An FFT (Fast Fourier Transform) is a quick way to convert time data to frequency data. After finding the pulse response of a circuit, an FFT of the time data produces the frequency response of a circuit. An FFT of a sine wave is a single peak at the sine frequency - with leakage to nearby frequencies. As implemented in Speaker Workshop, FFT's only work with powers of 2 data sets (e.g. 1024, 4096, ...).

How can I improve the memory management?

Speaker Workshop uses a lot of memory for the undo buffer. Each undoable transformation takes 8 x [number of points] bytes. To make it easier to clear this memory, the undo buffer is emptied when you save (and undo is no longer available). Save - to reduce memory requirements, to run faster, and to fix out-of-memory issues after running for long periods of time.

How can I make my crossover work correctly?

Gee this is a tough one. Crossovers are heavily dependent on the frequency response and impedance charts for each driver.

• Ensure that all driver acoustic responses are in the same dB ballpark (use Transform Scale to make them the same, subject to efficiency differences).
• Make sure that driver impedance charts cover the full frequency range of the speaker - frequency resolution is less important for crossovers so use a 44KHz sample rate and medium (8K-16K) sample size for final impedance and acoustic measurements.
• Enable individual frequency response charts (in the network preferences dialog) and examine each driver's response to determine the anomaly.
• Finally, don't expect a stock crossover to work well without significant tweaking - drivers don't have flat impedance and don't have flat frequency response curves.

I need help with my impedance jig design?

Check out the well targeted discussion at Eric Wallin's web site..