Rocket UFW-10 Calibration and Dual Setup
Okay, time to set-up for the flattest bass response at the listening position. We're trying for the highest overall SPL using the least amplifier power. Subwoofers need lots of spare power available.
If your HT set-up is in a living room corner like mine and you're starting with a single UFW-10, placing the sub into that corner can give you a potential of as much as an 18dB gain. This is free low frequency boost! (Qualification time: 18dB is the maximum theoretical gain that can be achieved when going from a 4pi anechoic chamber environment, which is like suspending a speaker in a spherical space, to a room corner which is basically a 1/8th pi environment)
Note that since this AV123 sub has the single-band parametric room-mode correction the dire warnings we've all read regarding corner placement of a sub go right out the window. Yes, corner placement does get you a lot of free gain but it will also typically generate a pretty good-sized room-mode bump. With the built-in single-band parametric EQ, however, the room mode will be tamed as the bass energy is more uniformly re-distributed across the low frequency spectrum during the calibration procedure described in AV123's Owner's Manual. You'll now be able to hear, perhaps for the first time, smooth, delineated, bass.
If your system set-up falls into the more common flat front wall placement, a single or even double subs at the one third point of the wall on either side of the center channel should also work well. Wall placement can give a 12dB boost in frequency though, like corner placement, in the real world the gains are usually less than the theoretical 12dB and 18dB maximums.
One critical step is to mount the Radio Shack meter on a tripod and situate it at exactly your ear level in the primary listening position. And pay attention to the dB correction values given for the Radio Shack meter in the instructions. The strength of a room mode at your listening position does not mean you can skip the tripod and just lay the RS meter on your sofa. The measurement won't work as well. So take the time to help the set-up procedure work correctly and you'll be rewarded with tight, tuneful and well differentiated bass! When you hear a really well recorded DVD such as "Heat Wave" from the "Standing in the Shadows of Motown" disc you'll be absolutely amazed that you put up with that one note bass for so long!
Rating Speaker System Performance
I'm going to divide the five star rating system Audioholics has been using for their electronics and loudspeaker reviews so far into half or quarter stars. I do this for several reasons:
- The five star systems we've used at Audioholics tend to bunch all manufacturer's products toward the top four to five stars, even when using half stars. In the case of electronics, with audible differences so small as to be unnoticeable between, say, the sound of a $1000 receiver and a $2000 receiver, this rating system makes a lot of sense. After all, a receiver's measurable frequency response differences are on the order of tenths of a dB at most. A loudspeaker on the other hand can have huge differences in frequency response. It is these differences which are most notable in some very low priced systems. And hopefully less audible with a measurements-based speaker manufacturer who strives to put out the most musical and accurate speaker at each given price point.
- In listening double-blind in Harman's Multichannel Listening Lab we used a 10 point system. Using the10 point system was useful in that we trained listeners could place a speaker system in a hierarchy of sorts that rewarded higher points for speaker systems which actually performed in a manner superior to other systems. (i.e. Smooth, measurably flat frequency response.)
- As Sean Olive noted in his AES paper which described the scores of trained versus untrained listeners, trained listeners as a group would tend to score lower performing speaker systems toward the bottom of the range (0 to 3.5 or 0 to 1.75 stars) while good performing speaker systems would score toward the middle of the range (3.5 to 7.5, 1.75 stars to 3.75 stars). This left the top performing systems, usually the most well engineered (and costly) to post scores of 7.5 (3.75 stars) and above.
- In the case of subwoofers I have a pair that I currently use in my home theater which I plan to use as my "references". As a pair, in my home theater, I would give these two systems, calibrated with their single-band parametric equalizers specifically to my listening position, a cumulative score of 8.0 or 4 stars. Very, very good but still room for improvement. (More subs or a more refined system to better integrate the subs/listening space could edge the score higher.)
- Regarding subwoofers, and contrary to the generalized pronouncements within the audio community which says that once the bass is flat it should all sound the same, I will disagree. And I will explain my reasons for disagreement in this and subsequent subwoofer reviews.
My first reference subwoofer is the ( now discontinued) Infinity Intermezzo 1.2 12" acoustic suspension sub with the R.A.B.O.S. single-band parametric EQ and 850 watts dynamic power (originally $1800). The second sub is the currently available Infinity Beta CSW-10 10" acoustic suspension sub with R.A.B.O.S. and 650 watts dynamic power ($1000). The Intermezzo 1.2 is mounted in the corner behind my Sanus equipment rack atop which sits my 40" Mitsubishi TV. As measured and plotted manually, this sub has a virtually flat ±1dB, 20Hz to 80Hz frequency response, at the listening position 10' away. The CSW-10 is mounted behind the listening position and 8' from the listening position.
Since I would be using one or two front mounted UFW-10's for this listening comparison it was decided to leave the CSW-10 unplugged and to compare the single or dual CSW-10's to the single, reference Intermezzo 1.2. Here's what I found out during initial calibration of both the single and dual UFW-10 subs:
- Using the removable, IEC three-conductor (grounded) 14-gauge power cord that came with my review samples resulted in a 60Hz buzz on my system. Installing a $0.50 gray, two-conductor "cheater plug" made the buzz go away. Since there are no UL, CSA, or other approval ratings on the back of amp plate I would guess that by selling the UFW-10 with a UL-approved three-conductor power cord AV123 is saving thousands of dollars in certifications and passing the savings on to the consumer.
- Setting up a single UFW-10 sub to the left of the Sanus rack and using the Room Adaptive Bass Optimization System (R.A.B.O.S.) accessory kit that comes with some Infinity subs I was able to get the AV123 sub within ±2.5dB from 35Hz to 100Hz. I was able to achieve virtually the same ±2.5dB resolution and frequency response when I later set up the second UFW-10 sub symmetrically, to the right side of the Sanus rack.
- It is important to note that when setting up dual subs automatically with the newer S.O.S. UFW-10 version, that symmetry be maintained with your subs' placements with respect to room boundaries and the distances to your listening position. Going out of symmetry can give rise to slight phase differences in the arrival times of specific frequencies at your listening position. But since you run both subs in setup mode at the same, and it's done automatically, "pretty close to symmetry" is usually good enough.
