|Above: The woofer from my first system|
This is a nearfield measurement of a Hitachi 5" midbass. It was taken on an open baffle full range with the crossover in place. There is a small cone tweeter on the rear that might do something about the 2.5k dip. In this case I only wanted it to run up to 2k. A little EQ and this driver could behave quite well. The dip just below 800 Hz probably isn't too bad - dips are less obnoxious than peaks.
I set this mid up in a 4 way active speaker, with a waveguide loaded compression driver above 2k and a sealed Vifa woofer coming in at 400 Hz. Just one notch filter to take out the dipole peak was needed to extract reasonable performance. My original plan was to modify the driver and measure the result, but it turned out that it was good enough to try without any mods.
The crossover is the problem
Often the biggest weakness in cheap speakers is the crossover. You might have a 3 or 4 way speaker with the bare minimum of crossover components, often just a cap on the tweeter. Cost cutting is the name of the game. Many speakers never have a chance to sound decent because the crossover is so poor.
In older speakers you might also see some strange designs that include dual tweeters and dual mids side by side. It may be a good idea to disconnect or re-arrange these, since mid and tweeter drivers should never be placed side by side. Where more than one tweeter or mid is used, they should only be placed in a vertical line.
What to do with cheap drivers?
Do you have some tired old speakers collecting dust? Want to give them new life? You will need:
- basic measurement tools (mic, mic preamp, camera/mic tripod, free software)
- MiniDSP active crossover
- enough amp channels (low cost low power amps are fine)