The Tempest

By Scott C. Blaier
31 Mar 1996

Objective Listening Tests and Evaluation

Upon initial listening tests two things were apparent. First, in comparison with Craig's 2-way (we will call them Brand X so I am not sued) commercial loudspeakers (8.0 inch woofer and 8.0 inch passive radiator) the Tempests sounded "bass shy" when listening to rock and roll and heavy metal music. I surmised that the X's had an emphasized mid bass at the expense of low bass extension. In fact, many people have grown accustomed to overemphasized midbass, often using their receiver's loudness control to further boost this range. Many listeners associate speakers that have emphasized midbass as having good bass; and that is fine; who am I to judge. Indeed, most music does not contain much bass below 40 Hz., and extended low bass response is generally less noticeable than emphasized mid bass. Loudspeaker manufactures have known this for years, and often design high "Q" acoustic suspension, or nonflat (peaked response) vented enclosures to make their speakers "saleable". They know that "the general public" will buy a mid-bass heavy loudspeaker over a loudspeaker with taut extended bass response.

So, I pulled out my sound pressure level (SPL) meter and sine wave generator and did some measuring. Sure enough, the X's had a pronounced bass peak at around 55 Hz., and rolled off rapidly below that frequency. I measured the Tempest, and found the NHT 1259 woofer to be flat in response to around 30 Hz. It rolled of gradually below that point, but still had output into the 20 Hz. region. Not leaving good enough alone, I fed a 30 Hz. sine wave into the Tempest to achieve an output level of over 105 dB to demonstrate its low bass capabilities. The NHT's exhibited no audible harmonic distortion, just a pure and VERY powerful fundamental 30 Hz. This driver has an amazing throw ! In fact, the 1259 actually modulated my voice at this output, an effect similar to talking into a fan. In comparison, the X's cones slapped at the air violently at 30 Hz., but could only produce harmonic overtones (sounding like a motorboat "put put"). This is not to criticize Brand X loudspeakers, which are very popular, and own a "lion's share" of the commercial loudspeaker market. However, they were clearly outmatched in low bass capability.

This led to a tweak. We removed the 3.0 lbs of polyester stuffing to "plump up" the midbass by decreasing the "apparent box volume". Although stuffing lowers Qtc and box resonance frequency, we discovered the tradeoff was a significant loss in overall efficiency because of frictional losses associated with the woofer working (pushing air) against the surface area of all that polyester fill. There are techniques to minimize such losses, such as not putting the damping too close to the rear of the woofer basket or using a buffer of loose damping directly behind the woofer, grading into more compressed damping in the rest of the enclosure. All I can say is experiment for yourself by changing the box volume with solid fill material and/or experiment with different quantities of acoustic damping material. In this design you can subjectively alter the bass quality, to some degree, in order to make it "sound" the way you like it. The bass sounds "right" now, but going "cold turkey" and kicking the "peaked midbass" habit in favor of flat extended bass can take some getting used to.

First listening also revealed a slightly forward sound in this listening room, and the loudspeakers sounded better with the midrange and treble slightly attenuated (hence the addition of the tweeter and midrange l-pads). The attenuation yielded a softer, laid back sound. Indeed, the sound of these loudspeakers is very dependent on the source. These loudspeakers can be merciless on bad recordings, and reveal everything you "never wanted to hear". On a positive note, they can also reveal "good" sounds you never heard before. I realized I could not build a loudspeaker that will sound "the same" in any conceivable listening environment. Therefore, the addition of the l-pads gives some control over uncooperative room acoustics.

Conclusions
We believe this loudspeaker sounds very good! Bandwidth is near flat and borders both subsonic and ultrasonic. Its wide dispersion presents an excellent and very large sound stage that everyone can enjoy, regardless of seat. The Vifa midrange and tweeter are detailed and dynamic, and of course, the NHT 1259 produces a tremendous amount of low-distortion, low frequency bass. And for you Rock and Rollers and home theater enthusiasts, these loudspeakers can absorb a tremendous amount of power, and play EXTREMELY loud (without distortion) while doing so. They are not some fragile, "don't play me loud ... I only image" loudspeaker. They will blow you house down man ! And if you are interested in the home theater/surround sound thing, these nicely compliment the Esquires. So if you want to build a loudspeaker that does not cost a fortune, and is just plain fun to listen to, perhaps a pair of Tempests is the ticket for you. We think the finished product is commensurate with the effort. Good Luck.

Scott Blaier

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