I am designing a two way monitor for SB Acoustics that will eventually lead to a full documented Kit. This thread will show how i work from unpacking the drivers to measuring them, constructing the crossover and the cabinet.
When the speaker is ready it would also like to discuss the subjective impressions how they sound.
When the speaker is ready it would also like to discuss the subjective impressions how they sound.
The drivers came well packed and presented, full intact. The woofers are 6 1/2 " and on the market since some month. The tweeter is brand new. When i unpacked them, there was some protection silk over the membrane. when i took it away i saw why. They are so new that the membrane was still a bit sticky from the coating but not so much as to collect dust.
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Interesting Drivers Joachim! I'd not seen these ones before. I've got some SB12MNRX25-4's and am most impressed with the build quality and the closeness to factory specs! Unfortunately a house purchase and renovation has got in the way of completing that project for the time being. I will be very interested to follow this thread! 
Tony.
Tony.
I will make my own impedance measurements today.
One first commend : The cones of the mid woofer are trumped shaped and from a paper material that contains papyrus fibers. That makes the cones very stiff. Together with the impedance compensation that results in a very extended bandwidth up to 10kHz, as good as many wide band drivers. There is a small hole in the response at ca.1.3kHz. That comes from the very low mechanical damping of the rubber surround. It would be easy to take that away by using a high damping surround or edge coating but that would have increased mechanical losses. It was decided that good dynamic behavior is more important then a small and benign hole in the response. I will measure the units i have here of cause. The data sheet is only priliminary and i am using the 4 Ohm version that may behave differently.
One first commend : The cones of the mid woofer are trumped shaped and from a paper material that contains papyrus fibers. That makes the cones very stiff. Together with the impedance compensation that results in a very extended bandwidth up to 10kHz, as good as many wide band drivers. There is a small hole in the response at ca.1.3kHz. That comes from the very low mechanical damping of the rubber surround. It would be easy to take that away by using a high damping surround or edge coating but that would have increased mechanical losses. It was decided that good dynamic behavior is more important then a small and benign hole in the response. I will measure the units i have here of cause. The data sheet is only priliminary and i am using the 4 Ohm version that may behave differently.
I measured the impedance curves by holding the drivers with my hand.
The woofer has very low mechanical losses. You can see that the peak at the fundamental resonance is sharp and narrow. That translates into a high Qms.
The edge resonance at 1kHz is just visible in the phase of the impedance curve as a small wrinkle. For such a low loss driver this is very well controlled and looks better then the preliminary data sheet. I do not care much about the small hole it may create in the frequency response at that frequency but undamped there would be a rise in distortion too. There is a sharper discontinuity at somewhat under 4kHz. That seems to be the cone break up frequency. A very high frequency for a paper cone so it is quite stiff. The driver should be very useful until 3kHz.
The tweeter looks simply perfect. Low, symmetric and well damped fundamental resonance. Both drivers have a very flat impedance curve so they must have some copper in the magnetic gap. Actually this kind of low rise is a rare sight so modulation from changing inductance over lever is very well controlled. Inductive modulation is a very nasty type of distortion so i am very happy to see this eroded here.
The woofer has very low mechanical losses. You can see that the peak at the fundamental resonance is sharp and narrow. That translates into a high Qms.
The edge resonance at 1kHz is just visible in the phase of the impedance curve as a small wrinkle. For such a low loss driver this is very well controlled and looks better then the preliminary data sheet. I do not care much about the small hole it may create in the frequency response at that frequency but undamped there would be a rise in distortion too. There is a sharper discontinuity at somewhat under 4kHz. That seems to be the cone break up frequency. A very high frequency for a paper cone so it is quite stiff. The driver should be very useful until 3kHz.
The tweeter looks simply perfect. Low, symmetric and well damped fundamental resonance. Both drivers have a very flat impedance curve so they must have some copper in the magnetic gap. Actually this kind of low rise is a rare sight so modulation from changing inductance over lever is very well controlled. Inductive modulation is a very nasty type of distortion so i am very happy to see this eroded here.
If the kit includes a flat-pack cabinet then some extravagant affair is fine. If not I'd stick with a standard box, boring I know, but if it's to be build-able by the majority then that's pretty much necessary I think.
I'm looking forwards to how this turns out + additional measurements of the tweeter. It's going to be interesting to see how it justifies itself in the face of the already very nice standard version.
I'm looking forwards to how this turns out + additional measurements of the tweeter. It's going to be interesting to see how it justifies itself in the face of the already very nice standard version.
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