Making of M2
By Man-Sun Huh
21 Feb 2000
5th step: Crossover network design
Crossover network design is the heart of loudspeaker building. Impedance and sound pressure level of each units are necessary and It's already measured in step 4. Also time delay of woofer unit is necessary. It can't be measured directly with LMS(MLSSA can measure time delay quite exactly and probably Clio can also measure time delay directly too.). So I measured the difference between top plates of each unit and It gives quite reasonable result. I took 60 micro seconds for the delay.
At first, I selected acoustically 4th order Linkwitz-Riley X-over around 1,800Hz. But during optimization I changed X-over frequency to 1,650Hz.
Then what is good x-over? Listed below is my criterion of good x-over.
- Flat sound pressure response over full frequency range.
- Steep dip at x-over frequency when tweeter polarity is reversed.(It means that phase matching at x-over point is good.)
- Minimum Impedance phase angle difference over full frequency range.(less than +-45 degree is recommended)
- Too low Impedance must be avoided.(You can break your amp!!)
- The fewer x-over element, the better
- High quality capacitor for tweeter network.
- 1% tolerance resistor is recommended.
To meet all those criterion, I simulated more than 1 month for optimization. Fig. 9. The X-over network is the final schematic diagram of X-over. And Fig. 10. Picture of the X-over network shows photos of x-over.
6th step: Final test & fine tune
Fig. 11. SPL result of M2 and Fig. 12. Impedance result of M2 show the final test result of M2. In Fig.11, curve numbered 1 is the total sound pressure response. It's quite flat with +-1dB tolerance. Curve numbered 2 and 3 are response of each units and 4 shows response when tweeter polarity is reversed. Steep dip of curve 4 means that phase matching at X-over frequency is excellent. In Fig.12, We can see impedance curve is smooth and have friendly load for amp.
Till now, I didn't feel any fine tuning for x-over. Instead, It's sound seems to be quite dependent on the sound absorbing material. I have used simple polyester(used for pillow) and Dacron. I think Dacron is much better. Some people have recommended me to use poly wools but still I didn't tested those material yet. I recommend you to adjust kinds of sound absorbing material and quantity to fine tune bass quality.
7th. step: Happy listening!
For mid-high frequency, M2 can't be surpassed by any other loudspeakers. Especially It has extremely precise imaging which can never be obtained with big multi-way system. Though M2 doesn't have high Sensitivity, It plays quite loud with my Jeff-Rowland Model 2 (75Watt) power amplifier.
M2 is a best speaker for near field listening in a small room. And It doesn't make me think to make another small 2-way loudspeaker.
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