In many ways, the Fiesta and Casita represents a departure from the traditional North Creek style loudspeaker design. It is not that we have raised, lowered, or in any way revised our standards. Rather, the Fiesta and Casita are built around the SEAS W18NX-001 Nextel-coated paper cone woofer, and unlike any other driver previously made, the W18NX has the unique ability of sounding naturally musical regardless of the quality of crossover components or amplification via which it is driven. The SEAS W18NX is such an inherently forgiving driver that one can make considerably compromises upstream and still get excellent results.

The SEAS W18NX is built on SEAS traditional 18mm aerodynamically optimized cast magnesium frame. The motor is built with an enormous ceramic magnet with the pole encircled with three Faraday rings and extended beyond the top of gap with a machined chrome phase plug. Together with the Nextel coated cone, soft rubber surround, extended voice coil and Klippel optimized suspension, the W18NX is the most advanced and visually striking driver to date from SEAS.

Fundamental resonance is 40Hz and the frequency response is gently and steadily rising from 300Hz to the upper roll off point at 4kHz.

Matching the SEAS W18NX, we have chosen our standard overachiever in the budget priced tweeter field, the North D25-06S 25mm silk dome, and are recommended upgrade to the North D28-06S 28mm dome with Faraday sleeve. Both tweeters are an excellent tonal match for the W18NX, as the inherent nature of silk domes is to be naturally musical and forgiving. The D25 offers wider dispersion whilst the D28 significantly more resolution and higher power handling.

The photo above is the North Casita in a Parts Express #302-724 cabinet. This is a nicely made 0.5 cubic foot box with a 3/4" MDF shell and single figure-8 brace, veneered on sixe sides, and comes with a pre-shaped fascia and grille. The fascia shown in the photograph was actually made here as a replacement for the stock PE fascia. The new fascia is made from 1/2" birch plywood laminated to 1" MDF. The additional modification to the PE box is to cut out the center section of the figure 8 brace, install the crossover, then replace the brace section with plywood. These changes make the PE cabinet much more substantial while requiring minimal effort and maintaining the internal volume. The North Fiesta can also be built in the Parts Express #302-75x family of one cubic foot cabinets with similar recommended improvements.

The photo below left is the Fiesta in the Tower cabinet, which has a one cubic foot air volume for the woofers and a secondary chamber in the bottom where the crossovers are installed and the volume filled with sand for ballast.

Crossover Design and Execution

The Fiesta and Casita crossover development took place from March to November of 2005.

Long familiarity with the North D25 and D28 tweeters made the high pass filter design very simple, as as written elsewhere, both of these tweeters benefit from an absolute minimum of circuitry. The target crossover frequency was 1641 Hz. The crucial element of the crossover designs became properly voicing the woofer low pass crossover to perfectly match the tweeter. One would think this would be relatively unproblematic with a woofer with smooth, rising frequency response such as the SEAS W18NX-001, but in practice the situation becomes considerably more complicated because the combination of an extremely light cone and extremely large magnet makes the 'NX very difficult to nail down. Whether this was the goal of SEAS or not, the light cone/large magnet mix means a woofer with a very low Qts, and as those who are long familiar with the sound of a range of Qts woofers in a vented box, a low Qts woofer can have very clean and detailed low bass, but lacks the visceral punch that most listeners find ultimately rewarding.

Traditionally what one would do in this situation is decrease cabinet volume and raise the tuning frequency such that there would be more punch in the mid-bass and less deep bass, so that overall the system would sound better balanced. But here rather than sacrifice deep bass, we decided to lose a little efficiency and pick up the low end by incorporating a large value air core inductor of a very fine wire gauge. It seems counterintuitive that a finer gauge of wire would lead to more bass, but in practice it works quite well.

The low pass network is a textbook third order acoustic, and combined with our acoustic third order high pass and staggered poles, for both the Fiesta and Casita, overall frequency response is 41 Hz to 20kHz ±2dB. Likewise the antiphse null for both systems is nearly -30dB, indicating perfect on axis blending and antiphase cancellation.

North Creek Casita Frequency Response Spread

North Creek Fiesta Frequency Response Spread

System sensitivity is 85dB for the Casita, which is a true 8-Ohm loudspeaker, and 90dB for the Fiesta, which is 4 Ohms. System input impedance with and without the optional impedance equalizer "Twister" circuits are shown below:

North Creek Casita Frequency Input Impedance

North Creek Fiesta Input Impedance

The SEAS W18NX has an unusual sound quality. It sounds spectacular with top notch electronics and the best recordings (as most good woofers do), but it also sounds just wonderful with so-so recordings and average electronics. The low end is quick and tight, while the mid-bass and midrange is smooth and clean. The crossover region is seamless, and going to the top end, the North silk domes work their usual magic. Overall, the Fiesta and Casita are excellent matches for Audio and A/V systems where movie soundtracks, digital radio and MP3's are sometimes used as a source, as the forgiving, naturally musical nature of the drivers seems to get the most from these formats yet still excels with top quality two channel.

Casita - D25 Project Consists of matched SEAS 18WNX001 woofer and North D25-06S tweeters, assembled woofers network built with 16 AWG air core inductors, electrolytic capacitors, North power resistors, assembled tweeter networks built with Zen and Harmony metallized caps, 16 AWG inductors, North power resistors. All crossover components are hand matched to ±1%, TefFlex AG an Lex OFHC internal wiring, single wired with Texas binding posts; everything required to build the loudspeaker system except the wood.
Casita - D25 Project ...$695 per pair

Casita - D28 Upgraded Project Consists of matched SEAS 18WNX001 woofer and North D28-06S tweeters, assembled woofers network built with 16 AWG air core inductors, Zen high frequency film capacitors, North power resistors, assembled tweeter networks built with Cascade-Bypassed Crescendo film and foil capacitors, 14 AWG inductors, North power resistors. All crossover components are hand matched to ±1%, TefFlex AG an Lex OFHC internal wiring, single wired with Texas binding posts; everything required to build the loudspeaker system except the wood.
Casita - D28 Upgraded Project ...$retired.

For Casita Contents and Cabinet Plans in .pdf, click here

Both the Parts Express 302-734 cabinet and the Madisound MD02 cabinet are  compatible with the Casita.

Fiesta - D25 Project Consists of matched quad SEAS 18WNX001 woofer and North D25-06S tweeters, assembled woofers network built with 16 AWG air core inductors, Zen bypassed with Harmony high frequency film capacitors, North power resistors, assembled tweeter networks built with Zen and Harmony metallized caps, 16 AWG inductors, North power resistors. All crossover components are hand matched to ±1%, TefFlex AG an Lex OFHC internal wiring, single wired with Texas binding posts; everything required to build the loudspeaker system except the wood.
Fiesta - D25 Project ...$1129 per pair

Fiesta - D28 Upgraded Project Consists of matched quad SEAS 18WNX001 woofer and North D28-06S tweeters, assembled woofers network built with 16 AWG air core inductors, Zen bypassed with Crescendo high frequency film capacitors, North power resistors, assembled tweeter networks built with Cascade-Bypassed Crescendo film and foil capacitors, 12 AWG inductors, North power resistors. All crossover components are hand matched to ±1%, TefFlex AG an Lex OFHC internal wiring, single wired with Texas binding posts; everything required to build the loudspeaker system except the wood.
Fiesta - D28 Upgraded Project ...$retired.

For Fiesta Contents and Cabinet Plans in .pdf, click here

The Madisound MD02 cabinet is  compatible with the Fiesta. Fascias are not available yet, please ask.

Working with the SEAS W18NX has been a unique experience. Unlike the W18E Magnesium cone we use in the North Pegasus and Prometheus, which has both the highest resolution of any mid-woofer ever and is completely unforgiving of any errors in recordings, electronics, and crossover design, the W18NX appears to be completely forgiving of just about everything. In essence, it is an anti-W18EX. The only other driver that seems to share this ability is the Scan Speak 15W8530K series, with the sliced paper cones, and these sound completely different in the low end.

After spending two years with the SEAS W18E magnesium cones, working with the Nextel cone was a breath of fresh air. Using the pre-built Parts Express cabinets with upgraded fascias and a few simple mods made the cabinet work a breeze. A simple third order crossover design using standard components went together relatively quickly, and the end result was two new loudspeaker designs that are easy to listen to and sound great on all types of music.

I have come to think of the Fiesta and Casita as audiophile loudspeakers for non-audiophiles. They are not picky of electronics, sources, and cables, nor do they that picky about set up (other than toe in). As long as the rear of the speakers are two feet or more from the back wall, the bass fills out and the soundstage opens up nicely. These are the optimal loudspeakers for those individuals who wish to build, set up and hook up their new audio system, then sit back and enjoy while moving on to the next project.

-George E. Short III, ©January 2006

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