| Usher Be-718 Bookshelf Speakers with Beryllium Tweeters |
| Written by John E. Johnson, Jr. | |||||
| Tuesday, 13 November 2007 05:45 | |||||
Introduction Specifications
Usher makes some big heavy speakers. We reviewed a pair of these - the floor-standing CP-6381s - a few months ago. They weigh 137 pounds each. The Be-718s are bookshelf monitors. They are about the same size as most bookshelf speakers, but are much heavier than average, nearly 40 pounds each. They are beautifully finished on all sides, with the enclosure being made of an acrylic material, and with Birch wood side panels. You can choose either black or white for the acrylic. Usually, one sees speakers that are either sealed (no port) or with a round port in the front or back. The Be-718s are slot-loaded, meaning that the "port" is a long thin slot rather than a round hole. One other thing - the most important - makes the Be-718s unique: the tweeter is made of beryllium, which is a very light, very strong metal. In fact, beryllium has an atomic weight lighter than aluminum, yet it is much stronger. What this means is that the tweeter dome can be made very thin (the factory heats it to 7000 Fahrenheit), and this results in low distortion because there is less tendency for the tweeter dome's mass to interfere with its moving back and forth. One problem with beryllium is that it is very difficult to work with (it's brittle and toxic if it gets on your skin), and so is very expensive to manufacture. In the past, companies have gotten around this by using alloys (mixtures of two or more metals). Finally, though, pure beryllium tweeter domes have emerged, through special manufacturing processes that have been developed. Nevertheless, only a few companies make them, partly because it is still a dangerous substance to work with. The tweeter on the Be-718 is 1.25" in diameter. It is covered with a stiff metal mesh grille to keep fingers off of it. A close-up photo is shown below. You can see the gray beryllium dome beneath the mesh. A conventional cloth grille covers the entire front of the speaker.
The woofer is 7" in diameter, and from the way air was coming out of the slot during low frequency tests, I would estimate that it has a very long excursion capability.
All in all, these are some of the most beautifully made speakers I have ever seen.
The Sound
On the Bench
At 1 kHz, the woofer was still the output device, but THD+N was now down to 0.25%, which is excellent.
At 10 kHz, the tweeter was outputting the sound, and distortion was still low, at 0.22%.
With 10 kHz and 11 kHz sine waves, the A+B peak at 21 kHz was 47 dB below the fundamental, while B-A at 1 kHz was 65 dB below the fundamental.
This, to me, is the most important graph, as it shows distortion at all the audible frequencies. I first set 1 kHz to output at 100 dB with the microphone at 1 foot, then measured the spectrum. THD+N is off scale below 33 Hz, and comes down rapidly to stabilize around 3% from 50 Hz to 150 Hz, then goes down again to be about 0.2% - 0.3% from 500 Hz up to 20 kHz. Notice that it goes up to nearly 0.5% just above 2 kHz, which is the crossover frequency. The fact that it stays around 0.2% from 500 Hz up to the limits of audibility gives the speaker a very neutral sound. If there were more variability, the speaker might sound harsh, tinny, overly sibilant, and otherwise some sort of skewed sound quality that would take away from being neutral. Like just about any speaker, the Be-718 will benefit from having a good subwoofer, using a crossover (judging from this graph) of about 50 Hz.
This graph shows the room response at 1 foot and 1 meter. Look how flat it is (1 meter) from 50 Hz to 20 kHz. This is terrific!
The impedance appears to be 8 ohms nominal, and dips to 4 ohms at about 3 kHz. Electrical phase stays within + 400 and - 600. The impedance peaks at 20 Hz and 65 Hz are from the woofer interacting with the slot and the enclosure. The upper peak at 65 Hz occurs when the woofer suspension and enclosure air spring are combined with the woofer's moving mass (tighter spring). The lower peak at 20 Hz is created when the woofer and air mass in the slot form one moving mass acting against the woofer suspension (heavier mass). The peak at about 1.8 kHz is due to the crossover. The free air resonance of the woofer is probably about 40 Hz.
Conclusions Comments (3)
what about an amplifier that costs less then the speakers
written by Steve Rogers , July 01, 2008 That power amp costs $7500 and puts out 12000 wats according to a stereophile spec I found on it. would like to know how then sound with a "normal" amp that costs same or less then speaker Write comment
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If there is a Maurice Ravel piece that just about everyone is familiar with, even if you are not a fan of classical music, it is "Bolero" (this particular recording is Telarc SACD-60601). It starts out so soft, you wonder if your audio system is even turned on.
John Pizzareilli has a very interesting trio, as there is only the guitar, bass, and piano (no drums). He sings while mostly playing rhythm on his guitar. It lets one really hear the various instruments along with a baritone voice. Of course, they have to play like mad to make up for no percussion, but it works.
I am not necessarily a big Richard Strauss fan, but this recording (Telarc SACD-60661) is really something. I suppose it has at least a little bit to do with the fact that Telarc does not compress their recordings, and this one is SACD.
This recording (Telarc SACD-60592) has all kinds of artists, not the least of which is The Manhattan Transfer, and songs like "Stompin' at the Savoy".
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