Loudspeaker EQ

In January I started to look again at my GX300 crossovers. I use a handy program called Passive Crossover Designer which I feed with measurements taken with REW v5.1, both are freeware and really good in the latest versions in my opinion. I bought a U-MIK test mic recently and downloaded the calibration curve for my serial number and it led me to do a lot of driver and speaker testing before being ill.

REW's response curves, waterfalls, and other graphs are really interesting. I've written about them before in the room acoustics context so will not digress. I started to look at the distortion analysis this time and have been measuring various speakers in my collection with the sine wave sweep and also with two tone/intermodulation tests. Very interesting, especially when comparing closeup readings with listening position. The latter picks up more of the room's contribution obviously but also shows how being off axis can reduce the closeup distortion.

On my GX300, which I still enjoy, I am toying with adding the missing inductor to make the midrange LPF third order to match the third order HPF on the tweeters. I have rigged the extra part up to listen and to measure the impact, still not sure it's worth the admittedly limited effort to make the change properly. Temptation may overcome me yet...

I did eventually rig up an A/B switching arrangement for that inductor feeding the midrange speaker. Very short cables which stayed in circuit but shorted out the new inductor.

I used a fixed position for a calibrated microphone and REW software to measure the frequency response and THD with and without. Miniscule difference, slighlty steeper rolloff and about 0.2% less THD. Which is probably inaudible. So I reverted to stock crossover, moved the test gear away, popped the inductors into one of my spares boxes, and then played more music which was nice.

Now an interesting finding: you can make a simple tone control using your loudspeakers, essentially a 'tilt' control where you subtly alter the balance of bass and treble extremes. Please don't try this if your amp's manual has warnings about speaker connections or you are nervous about breaking something by getting the wiring wrong.

I am assuming the speakers have separate LF and HF terminals and you normally link these together.

Please leave the link between the black or minus terminals in place and take out the red or positive link. You may wish to lower the volume on the amplifier first or put on standby if it is a valve amp. Check carefully that you are not shorting out the amplifier, the resistor should go where the link was between the two red/+ terminals. I take no responsibility if you do something silly or dangerous. If in doubt you shouldn't try this but take care and you may like the result.

Lets say you want to have more bass...

The opposite wiring approach applies for getting more treble than bass, the red+ plug on the cable from the amp goes to the HF+ terminal and the resistor joins this to the LF+ so there is less bass.