ScanSpeak 15S/8530K01 MTM

[Jimmy154]

Hello friends,

By coincidence I'm trying to build a speaker similar to this one, but with Seas 27TDFC tweeters:

http://www.northcreekmusic.com/Catam...amountInfo.htm

Is this part of the page true?:

The original design was targeted to be an 8-ohm plus system, to be compatible with typical tube amplifiers and SET’s as well as the latest generation of OTL’s. As there are virtually no true 8-ohm woofers, my first attempts were to connect a pair of 4-Ohm woofers in series (Scan Speak 15W4530G00’s). This was successful to some extent – certainly in terms of high system impedance and bass extension, but compared to my reference systems, the two-woofers-in-series prototypes did not remotely approach the level of midrange clarity of any other North Creek loudspeakers…perplexing as the 15W4530’sound great when driven solo. Among my reference systems are the Okara II – 9500 and the Eska mini-tower, both of which are built with Vifa P13 5" woofers, where the Okara II is a single and the Eska is an MTM with the P13’s in series. Directly comparing the Eska to the Okara II, there was no loss of midrange purity when going from the single driver to the series-wired MTM. Hmmmmmmm…….

Both the Scan Speak 15W4530 and Vifa P13 are manufactured by Danish Sound Technology and the build quality is comparable, but there are significant differences in technological innovation. Other than the enormous motor employed by the Scan-Speak driver, the major difference is three Faraday rings that encase the Scan-Speak motor’s center pole. Faraday rings perform an interesting function – they protect the motor’s center pole’s magnetic field strength from being modulated by the current through the voice coil, which greatly reduces midrange intermodulation distortion. However, the voice coil current is still modulated by voice coil motion, voice coil inductance, and the driver’s low frequency resonance, and it is this modulated current that drives the second woofer down the line.

The only conclusion I was able to reach regarding why it was not audible through the Vifa P13’s, yet clearly audible through the Scan Speak 15W’s, is that because the Vifa P13’s do not have Faraday rings the modulation is symmetric (that is, they modulate both themselves and the next woofer), where with the Scan Speak 15W’s do have Faraday rings so the modulation is asymmetric (that is, they modulate only the second woofer).

After discussing this with another loudspeaker designer, who observed the same phenomenon with SEAS Excel drivers (which incorporate a similar motor to Scan-Speak’s), both of us concluded that it is Faraday-ring related. Unfortunate as to the best of my knowledge, this is the first time a Faraday ring has proved to be detrimental to system performance.

At the same time, I was trying to run a string of Aurum Cantus G1's in series as the tweeter line, and they also failed to approach the performance of a single Aurum Cantus G1 (in fact, they did not even come close). This I attributed to all of those impedance matching transformers run in series.

Because of this, North Creek has dropped the development of a Scan-Speak - Aurum Cantus based line array.

I think this only applies to drivers wired in series, eh?

[Jimmy154]

After further reading and pondering, I'm pretty sure this distortion only occurs when wiring drivers with these rings in series. I wanted to delete this thread, but couldn't