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Pages
1 System Introduction
2 2nd step: Measurement of Unit characteristics
3 4th step: Measurement
4 5th step: Crossover network design
5 Part List

Figures
1 Picture of the finished M2
2 Enclosure design plan
3 Impedance measurement of woofer unit
4 Impedance measurement of tweeter unit
5 Treatment for woofer frame resonance
6 Ground plane method
7 SPL of woofer (W/O X-over)
8 SPL of tweeter (W/O X-over)
9 The X-over network
10 Picture of the X-over network
11 SPL result of M2
12 Impedance result of M2

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Making of M2

By Man-Sun Huh
21 Feb 2000

System Introduction

Over one year has passed after I finished making M1. At that time I already planned to make M2. M2 is another 2-Way small monitor system. It uses Seas Excel woofer and Scan-Speak Revelator tweeter. I decided to go to bass-reflex system because of the limited bass performance of Seas woofer Fig. 1. Picture of the finished M2.

This time I will show the procedure to make M2 and I hope It will be helpful to who want to build one's own Hi-End loudspeaker.

1st step: System concept & Unit Selection
Small, precision Hi-End small monitor is always my concept. M2 is not an exception. It uses Scan-speak D2905-9900 Revelator tweeter. I already used D2905-9300 for my M1 and quite satisfied with 9300. At first, I was not so certain that more than 2 times expensive tweeter than 9300 can be justified. The result was more than satisfaction. In every respects, Revelator surpasses 9300 with great margin.

Revelator has no ferrofluid in the gap between voice coil and magnet. Ferrofluid is used to dampen resonance at natural frequency and to cool the heat of voice coil. So, In general, tweeter with ferrofluid has higher power handling and requires simple X-over network. And almost every hi-fi tweeter has ferrofluid in the magnet gap. But It can be harmful to sound quality. Scan-speak knows it well and make their flag ship tweeter without ferrofluid. Scan-speak suggests second order or higher filter at no lower than 2.5kHz as well as an LRC resonance conjugate network for Revelator. If M2 were a commercial design, I might have followed their suggestion. But I used second order filter around 1.65kHz without an LRC resonance conjugate. (I already remarked the benefits of low crossover frequency at an article of M1) Up to now, two pairs of M2 are working well more than half year without breaking a tweeter.

Woofer is a SEAS Excel W17E002. Of course It's a one of highly regarded 6.5inch woofer. I chose this unit because It seems to produce very detailed sound. And It looks great!! It uses magnesium as a diaphragm. It's material is quite different with Scan-speak 18W8545 woofer which uses pulp as a diaphragm. Sound of SEAS is somewhat different with Scan-speak. SEAS has more detailed sound in mid-high, Whereas Scan-speak has more open sound in mid-bass.

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