2-Way Ribbon Tweeter Speaker
I've always heard great things about ribbons tweeters - their small moving mass is supposed to leads to effortless high frequencies. From my limited sampling of speakers, I've found that in prolonged listening I like soft domes more than metal domes. How will ribbons compare?
Ribbons come in all price points with the high end units running well into 4 digits left of the decimal point. At some point I read a recommendation for the Pioneer ART-57D and I bought a pair from Martin Sound Products. This was many years ago and I recall that they were under $20 each. The driver's exterior is mostly plastic and is driven by a built-in transformer. I haven't seen these drivers online in many years and it's a shame because they are great value for the money.
The woofer is a Vifa M18WO-09-06 7-inch treated paper driver with a rubber surround, long throw design and a magnesium basket. These are the 6 ohm versions; they also come in 4 and 8 ohm. I got these from Madisound for $28 on a closeout sale many years ago. I previously tried to use these in a transmission line design but that didn't work out.
Here are the specs for the M18WO-09-06 as published by Madisound at the time of the sale.
- Nominal Impedance: 6 ohms
- Nominal Power: 90 Watts
- Sensitivity: 88.4 dB 1W/1m
- Frequency Range: 35 - 3000 Hz
- Free Air Resonance: 35 Hz
- Voice Coil Diameter: 40mm
- Voice Coil Height: 14mm
- Air Gap Height: 6mm
- Effective Diaphragm Area: 132 cm^2
- Moving Mass: 17.5 g
- Force Factor: 7.5 Bxl
- Vas: 29.1 liters
- Qms: 6.24
- Qes: 0.35
- Qts: 0.33
Both images below are from printed catalog pages. The first is for the 8 ohm version of the woofer. The second is for the Pioneer ART-57D
Here are some LAUD plots I made of the woofer and tweeter in their baffles. Somewhere I have 1 meter plots of the final speaker but I can't find them.
For the overall speaker, I wanted something that I could tweak over time. So the plan was for the woofer and tweeter to sit in their own boxes. The crossover would live externally so it could be modified or even bypassed if need be.
In the current speaker, the vented box measures 9 (wide) by 12 (deep) by 18.5 (tall) inches externally. This is 7.5 x 10.5 x 17 internal or 1338.75 cubic inches or 0.77 cubic feet (not counting some internal bracing, port and driver volume). The round port is 2 inches ID and 6.8 inches long. PerfectBox calculations are Fb = 39.7 Hz, -3dB at 43Hz.
The woofer box has a terminal cup installed on the top for direct access to the woofer. The tweeter doesn't have a box (it has a closed back).
The tweeter is mounted to an 8 inch (wide) by 6 inch (tall) MDF baffle. This was my original teststand and I've continued to use it this way. The crossover is mounted on the rear of the tweeter assembly.
The woofer crossover is a second order electrical LP at 1.5KHz with a 1.2 mH inductor and 7.8 mfd (2 x 3.9) capacitor. The tweeter is a second order electrical HP at 3KHz with a 4.3 mfd capacitor (3 + 1.3) and 0.56 mH inductor (2 x 0.28). There is also an attenuation network consisting of a 2.7 Ohm series resistor (14 || 6.8 || 6.8) and 7 ohm parallel resistor (14 || 14). These frequencies may seem a little funny but it's what sounded best to my ears.
The speaker in its current setup has been like this for several years. I had every intention of making more changes - replacing the crossover with an active one, trying different tweeters (I have some Alisson domes I'd like to compare). And maybe some time in the future I'll get around to it. But I recently realized that with so many other projects on the backburner, it would likely be a while before I had a chance to play with this speaker. And since I like them so much, I took a weekend and covered up the MDF box with black paint and rosewood veneer. Note that the differences in color in the picture is strictly a lighting effect. The actual color is more like the speaker on the right.
These speakers are currently wired to an Onkyo TX-4500 Mk II from the late 70's. They are marvelous. The high end is not tiring and the low end is robust. And no, there are no grills planned.