There are frequent discussions on what measurements to take when designing a speaker system. I started out using only on-axis measurements. Normal, I suppose. After a time I found that I didn't get the sound I expected from the resulting system optimization.
At the same time, I was experimenting with methods of reducing raw driver variations (those pesky peaks and dips which never seem to show up on published specs). Much has been written about flush-mounting drivers and offsetting them laterally, expecially the tweeter. So I started measuring at 15° left and right to see what the off-axis looked like, as this has a significant impact in the overall sound of a system.
Next I obtained a router to flush-mount drivers . I flush-mounted the tweeter on an existing system, measured and redesigned the crossover. This prompted tests using tweeters laterally offset, which was reputed to reduce baffle edge diffraction effects. The results of these tests showed the worth of this to me. That is the only way I would construct a system today.
Then one day, I averaged three measurements, on-axis, left and right. I then imported this into the optimizer, designed a crossover, then tested and listened. The difference was dramatic to me. I had finally achieved the sound for which I was looking (well, at least a lot closer!).
This section shows the raw measurements of a system I have built for my brother. He wanted small and inexpensive. The woofer is in a 4L closed box as he'll use it with an active crossover with a subwoofer. It'll also be close to a wall or on a bookshelf, so the bass rolloff will be lessened.
The tweeter used is the one used in the previously mentioned experiments. It is mounted in an upper corner of the baffle.
Each screen shows the axis and angle of the measurement microphone. All are at a distance of one meter.
I plan to continue expanding this site. I'll be putting up the full design of this system. It's not necessarily the best design, just one which sounds good to me and fits the needs of my brother and his wife.
It'll be quite limited as a 2-way, although placed against a wall it has a surprisingly pleasing sound without the sub. It will be quite limited in absolute output, as I use no highpass on the woofer. Therefore the bass signal will not be attenuated unless a highpass circuit is applied to the input of the amp (the intended situation).