To: Editor, Speaker Builder Magazine

From: George E. Short III, President - North Creek Music Systems

Subject: SB Review of the North Creek Borealis

We would like to thank Mark Florian, Dr. Joseph D'Appolito, and Speaker Builder for their thorough review of the North Creek Borealis loudspeaker, and also for this opportunity to comment.

The North Creek Borealis is the least expensive North Creek - designed loudspeaker we offer. The price for the loudspeaker system, single wired and with "soft matched" drivers, is $695.00 per pair. As provided to Mark Florian, bi-wired and with broken in, hand matched "perfect pair" drivers, is $782 per pair. The cabinets are available separately, factory direct from Lee Taylor and Co. for $675 per pair.

This is a fair amount of money for a loudspeaker kit, but still represents an excellent value. The Scan-Speak drivers are beautifully made units that offer both subjective and objective performance that is far superior to most other drivers. They are hand made using the latest technology, they are very expensive and they are worth it. Likewise, the North Creek crossover components were developed by ear to match the Scan-Speak drivers, and together with our construction techniques and extensive subjective design process allow the drivers to perform to their full potential. The retail cost of this loudspeaker would be three to five times the kit price.

Mr. Florian and Dr. D'Appolito brought up a few aspects of the loudspeaker which we feel deserve further discussion. First of all, the crossover:

The tweeter network is a simple attenuated second order network with a resonance trap. The purpose of the trap is to minimize dome excursion around the tweeters fundamental resonance by creating a frequency-specific short circuit across the tweeter leads. In essence, this trap is a frequency specific electrodynamic "brake". A side benefit of the trap is that it also flattens the impedance the rest of the crossover network sees, so tweeter high pass electrical slope will remain a smooth second order throughout the stop band. The combination of the crossover's electrical slope, the drivers natural roll off, and the boundary conditions created by the cabinet front result in a smooth high pass transfer function that is approximately third order.

The woofer crossover is a damped third order topology but is more precisely viewed as two cascaded first order networks with a shelving function. This is possible because the Scan Speak 18W/8545 has a perfect L+R impedance at high frequencies. L2 then acts as a simple first order low pass, but the impedance the network sees before L2 on is still a simple L+R. C1 and R1 then become an impedance compensation "Zobel" of sorts. The combination of L1 and the C1, R1 "Zobel" become another first order low pass, but by correctly tuning the C1 and R1 the transfer function is actually initially second order, shelving to first order higher in frequency. The resulting acoustic transfer function of the entire network, combined with the baffle diffraction step and the 18W/8545's rising response before roll off, is approximately third order.

One can view the individual slopes of the drivers as well as the combined response on our web site - www.NorthCreekMusic.com. We will no longer provide component values, however. In the mid-nineties we were very open about our crossover designs, but numerous infringements on our copyright and violations of our license agreement forced us to recind this policy, and in fact in the latest generation of North Creek loudspeakers the crossover networks are unmarked and cast in resin.

A second area that requires more discussion is our method of port tuning, or "the straws".

It would be nice to say that it was invented here, but it was actually discussed first in writing by Dr. Neville Thiele himself, in an ASA journal in the late 1950's. The purpose of the straws in the port tube is to force laminar air flow through the port at high volume levels. Dr. Theile found this to be more effective than flaring the port's egress, a method used by many manufacturers at the time and recently reinvented. The method we developed of tuning the port - by keeping the port tube length constant while changing the length of the straws in the port - allows the builder to control both the tuning frequency and port Q. This in turn allows the Borealis' low frequency response to be precisely tuned to the builder's listening room and electronics.

Adding straws to the port will not work with most woofers because the additional flow resistance lowers Ql and can cause the woofer to go into over-excursion, as Dr. D'Appolito points out. It works with the Borealis because the Scan Speak 18W/8545 motor is constructed in such a way that over-excursion is not an issue. The benefit of forcing laminar flow through the port is the elimination of port noise, particularly at high volume levels, which Mr. Florian confirmed.

Lastly, we would like to comment on Dr. D'Appolito's measurements and Mark Florain's subjective evaluation:

It is important to note that the North Creek Borealis (and all North Creek loudspeakers) are designed by ear. It is a relatively simple matter to design and construct a loudspeaker that measures arbitrarily flat, has a very sharp step response and low distortion. More precisely stated, "Using measurement equipment, it is easy to design a speaker that measures well." It is a much more difficult matter to design a loudspeaker that sounds "good", and harder still to design one that sounds "great", especially on an enormous variety of source material.

A North Creek loudspeaker spends 99% of its design time in the listening room, where it is evaluated and voiced by the designer and occasionally auditioned by the listening panel. To do so correctly, the design process takes months. In a limited time window, the designer must develop a loudspeaker that will be listened to and must satisfy hundreds of owners over a period of a decade or more. Such a process can not be done well fast; to do so quickly is to do so poorly. North Creek loudspeakers are measured, tested, voiced, refined, tweaked, played soft, played loud, tweaked some more, installed in the home theater, and occasionally cranked at wild parties (all in the name of science) as part of the design process. The character of the loudspeaker is thus fairly evaluated as it will be used in the home. This is why even with new drivers being introduced by Scan Speak or that we develop in-house, and the number of potential designs that could be just great, North Creek releases an average of only one new loudspeaker per year. It takes that long to do it right.

It is interesting that the Borealis measured so well in Dr. D'Appolito's lab - interesting because after the initial design stage, we do very little measuring. The fact that the Borealis has extremely low harmonic distortion, lower IM distortion than many amplifiers (!), and the lowest cross IM distortion that Dr. D'Appolito has ever measured - is particularly thrilling, because we don't measure these things at all! It is also worth noting that according to Dr. D'Appolito's measurements, the Borealis' frequency response is 39 Hz to 20kHz ± 2dB - which is better than we quote in our literature.

The Borealis is the third North Creek loudspeaker Mark Florian has built. His comments concerning the sound of the Borealis were similar to those of his earlier speakers as well as to those of the North Creek Rhythm reviewed by Dan Smith in Speaker Builder #6-1999 - that the imaging is first rate, the speakers disappear into the sound stage, vocals and instruments sound natural, and in some cases that the sound reproduced by the loudspeakers is "the best I have heard".

Thank you again for this opportunity.

George E. Short III, President

North Creek Music Systems

www.NorthCreekMusic.com

Customer feedback:

…….I'd like to order a Poseidon Subwoofer kit. Bought the Borealis a couple
> years ago, and it's been the BEST audio decision I even made. Wonderfully
> fun and rewarding to build the cabinet, and the sound . . . well, simply
> remarkable. Many thanks for designing and offering such a quality product.
>