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Rocket UFW-10 Build Quality

By patrick

UFW-10_AV123S_097.jpgThe UFW-10's 13 pound woofer is built within a heavily ribbed die-cast aluminum frame. It is secured to the MDF enclosure utilizing 8 machine screws clamping into steel T-nut-style inserts. Note that the woofer has a double-stack magnet structure but no shielding so caution would be advised in placing this sub close to a CRT (tube TV).

The woofer cone of this sub is a hybrid sandwich of a black-anodized aluminum, single-dish diaphragm bonded at the back to a heavy pulp substrate. This clever and expensive construction gives the non-bending "perfect piston" performance of metal while the pulp substrate damps any high frequency ringing effects of aluminum. At the same time the combination of the two materials adds substantially to the moving mass of the system which usually allows for better low end performance.

The cabinet's front baffle is just under an inch in thickness measuring 22mm (0.86"). The rest of the five surfaces appear to be closer to 18mm (0.70"). There is also an 18mm top-mounted side-to-side brace. Structurally a good idea given the pressure generated in this sealed-enclosure subwoofer.

The Amplifier Module

UFW-10_AV123S_099_sm.jpg The amplifier module is a self-contained unit utilizing a solid feeling plastic rear enclosure. This enclosure keeps the air pressure inside the cabinet from transmitting air noise through portions of the amplifier plate such as the female RCA connectors. In many less well-built HTIB subwoofers I've seen the plastic rear enclosure used on sub-amps is sometimes too thin-walled or not heavily braced. This can cause an "oil-canning" wherein the whole plastic surface acts like a diaphragm, pushing whistling air out an RCA hole. This is not the case with the USW-10's plastic enclosure. It appears very well braced and solidly made. Pressing hard, I couldn't get the large plastic back wall of the sub to budge at all.

Finally, the two sidewalls and top and bottom inside the enclosure are lined with 1/4" felt batting. Given the extremely long wavelengths of the frequencies subwoofers are meant to produce it is still curious to me when I see any type of insulation included in a subwoofer. I do know though that it seems equally odd to Chinese assembly-line workers who make many types of (full-range) speakers, all of which could really use the insulation. So the inclusion of the felt material in this subwoofer may just be an attempt to not confuse the workers who make these several types of loudspeaker cabinets. Install insulation in all models and you know you've always made the correct choice.

The UFW-10 Under Test

UFW-10_AV123S_028_sm.jpg To get decently accurate measurements subwoofers need to be tested outdoors. I used the back parking lot and the LMS (Loudspeaker Measurement System software program by LinearX) of Speaker City USA in Burbank, California. Tested outside, subwoofers can be measured very accurately using the ground plane measurement technique as seen in the photograph.

To protect the UFW-10's cabinet I placed a heavy blanket down on the asphalt. The AV123 sub was laid on its side on top of the blanket. One meter away the LMS microphone was placed on the other end of the blanket. Setting of the rear amplifier controls were as follows:

  • Input signal from LMS was plugged into the amp's XLR (marked LFE/mono) connector. (In addition to a pair of gold-plated RCA jacks, an XLR is a real rarity for a sub in this price range.)

  • Crossover switch set to "out" (LFE mode).

  • "Phase" rotary control set to 0 degrees.

  • "Gain" set to max clockwise rotation, marked as +15dB.

  • EQ (single band parametric equalizer section): the 3 controls were set as follows:

    • "Freq" > full clockwise, labeled as 80Hz.

    • "Bandwidth" > full clockwise bandwidth, labeled as 1.0.

    • "Level" > set to 12 o'clock position, labeled 0d

  With the controls set as shown above I adjusted the LMS to input 1 volt to the UFW-10. The reading I got indicated that the either the sub's input was overloading or the transducer was compressing under power. So I reduced the voltage and tried again. As I reduced the voltage input levels the UFW-10's low frequency response began to extend lower and lower. At 500mV input this little marvel recorded a frequency response of 35Hz to 100Hz at 104dB SPL! From the curve I would guess that at least 3dB of equalization boost, centered right at 35Hz, has been dialed in. This is normal practice during a subwoofer's design stage. It is this EQ boost which allows such a small-cabinet 10" 500-watt sub to extend in frequency as low as it does.

9UFW10LMS.gif

For those who would like compare the performance of this sub with that of others in this price class, here's what to be aware of when reading some other manufacturer's literature.

  • Published figures almost never tell you how far down a sub (or any speaker system for that matter) can reach and still be truly "flat".

  • Speaker engineers usually consider the "F3" or three dB down point of full-range systems as being the maximum honest amount of dB-down.

  • In the case of or subwoofers it is the 6dB down figure that is utilized in the engineering lab if a competitor's sub is being evaluated. Minus 6dB is a stretch but gives the benefit of the doubt as to the audibility of such a frequency.

  • Many company's sales literature for both full range speakers and subwoofers will not quote a "-dB" or "__dB" down point when promoting a system's lowest hearable frequency . Almost always in this case of the lacking qualifying parameter the measurement has been taken at 10dB or more down. So the actual figure quoted is of little use. It is very difficult to hear a note at the frequency extremes which is 10dB or more down in level.

In the case of the UFW-10, we've already used the ground plane measurement method so we're seeing the 6dB "boost" that wouldn't be observed in a 4pi anechoic chamber measurement. This is an honest measurement. Place your own UFW-10 on a floor, away from walls, and this is the performance you can expect. If we drop another 4dB down from our 35Hz figure we can get to the 10dB down point which competitor's marketing specs may use. For the UFW-10 that -10dB point is around 29Hz. My take is that for a subwoofer of this very small size this is excellent performance indeed.

I had a sub quite similar in many respects to the UFW-10; the non-discontinued Infinity Interlude IL100S ($499 SRP). The Infinity was a ported design, a bit larger in overall dimensions and constructed of vinyl wood-grain-covered MDF. It had a 250-watt amp as opposed to the 500 watts claimed for the AV123 product. Like the UDW-10 I used for this test, the Infinity also had a manual set-up single-band parametric EQ but no set-up kit. If you are doing it for the first time these manual single-band parametric EQ versions of both subwoofers can be fairly time consuming to set up. And to do so accurately, without any test gear, is futile.

The owner's manual included with the UFW-10 is also available on theAV123 website. In it the manual set-up procedure is specified. It is recommended that the user have the ubiquitous Radio Shack analog SPL meter along with the bass test CD called "Basszone1" available through www.stryke.com. You'll also need to set up a frequency vs. SPL grid-chart so you can plot the subwoofer's response at intervals of 5Hz or less while you adjust the "Freq", "Bandwidth" and "Level" sections of the parametric EQ. Following AV123's instructions and methodically going through the set-up procedure for the first time can seem daunting. But from my point of view taking the time to get so intimately involved with the actual sound of different low frequency tones is an incredible learning experience. You're not only calibrating your sub, you're calibrating your ear/brain listening system at the same time! Suffice it to say that inclusion of this singularly effective room-mode compensation circuit in the UFW-10 potentially makes it one of the flattest, most accurate, in-room response subwoofers at the lowest price available.

 

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