Sony G90 manual Manufacturer’s Corner, RPG Diffuser Systems Inc., Room Optimizer

plished with gain biasing to the surround channels, either. I

set up the speakers fair and square. But clearly, the T770’s

steering in DD mode is precise and smooth.

Finally users are going to have to decide for themselves

which features they can and can’t live without. At its suggested

list price, the T770 faces some stiff competition from AVRs with

higher stated power ratings and prodigious features. Now I’m

not a big bells and whistles fan. If I want to drive fast, give me

direct input of a gated manual five speed from any era Ferrari,

not the “fly by wire” computer electronics of a clutchless Tip-

tronic. The same goes for audio and video. I want to see and hear

the unadulterated material reproduced as intended. A great

many poseurs impress with their sizzle. But as single-chassis

designs go, the NAD T770 is all steak.

M a n u f a c t u r e r I n f o r m a t i o n

NAD ELECTRONICS OF AMERICA

6 Merchant St.

Sharon, Massachusetts 02067

Tel: (781) 784-8586; fax: (781) 784-8386

Website: www.nadelectronics.com

Source: Manufacturer loan

Price: $1,699

Manufacturer’s Response

NAD would like to thank Neil Gader for his thoughtful review of the T770 receiver.

One point I would like to elaborate on is his

assertion that speaker sensitivity and impedance should be carefully evaluated for compatibility with the T770’s 70-watt x 5 power rating. While he is correct in the absolute sense, the T770 incorporates an exclusive NAD amplifier design, imped- ance-sensing circuitry, which endows the NAD with the ability to properly drive 4-ohm speakers by maintaining the correct relationship between voltage and current irrespective of the loudspeaker being driven. This is accomplished automatically, requiring no adjustments from the listener. The T770 is stable even at 2 ohms!

As Neil mentions in his opening paragraph, we rate our power for A-V products the same way we rate our stereo amplifiers, that is, all channels driven simultaneously, 10 Hz – 20 kHz, at

0.08percent THD. Most manufacturers would have rated the

T770 at 100 x 2, 20 Hz – 20 kHz at 0.08 percent THD and 100 x 5 at 1 kHz. We believe our conservative approach is more in keeping with our “music first” approach to A-V products.

GREG STIDSEN

DIRECTOR OF SALES AND MARKETING

NAD ELECTRONICS OFAMERICA

Manufacturer’s Corner

e are grateful to manufacturers Wfor correcting any errors of fact in our reviews. When we can, we also include the manufacturer’s com -

ments following a review. But sometimes space does not allow us to do that and this section gives us the opportunity to include a cogent comment while the sub - ject is ripe, rather than holding it over for inclusion in another issue.

RPG Diffuser Systems,

Inc., Room Optimizer

I’d like to commend Tom Miiller for tack- ling a very challenging task (“Revel Ulti- ma Speaker System Episode One: The Ancient Enemy,” this issue). Episode One is a wonderful attempt to raise the awareness of our community to the acoustical distortions a room can intro- duce. RPG has been conducting room acoustics research for 16 years, sharing our results with the acoustical and enter- tainment industries through peer review publications, seminars at CEDIA, NSCA, the Audio Engineering Society, and the Acoustical Society of America. Over time, it became apparent that despite the progress we have made in room- acoustic design, sound diffusion, and absorption technology, recording studios and residential hi-fi and home-theater communities were still at the mercy of the location of the loudspeakers and the listener. In researching existing pro- grams to assist in these two areas, we

found that the solution lay in a new approach that simultaneously addressed modal coupling and speaker-boundary interference response (SBIR), the two causes of low-frequency acoustic distor- tion. A technical description of this new algorithm was presented at the AES and a copy can be down-loaded from our website (www. rpginc.com). One can address this problem using wave acoustics, called the frequency-overlap method, or by geometrical acoustics, using the image model. Both approaches are difficult to apply. The rectangular room offers a unique case in which both resolve into simple and identical solu- tions. The image model, however, is the default solution, since it is time-based and can be windowed to provide the SBIR and modal responses. The issues are how to deal with the SBIR and modal coupling simultaneously and how to search the millions of possible solutions for the best one. Simultaneous treat- ment of SBIR and modal coupling was easily addressed by using the weighted smoothness (standard deviation) of both responses, and an intelligent search engine (downhill simplex, in this version) was used to search through error space for the best answer. One thing to keep in mind is that this type of problem requires optimization of many variables at one time. This type of problem con- tains the possibility of false solutions. The goal is to find the global minimum.

The starting point always affects the solutions, so the program allows for the evaluation of many random starting points. Each solution is valid and users should choose the solution that has the smallest error and the best ergonomic placement. Once loudspeaker and listen- er positions are established, the pro- gram indicates optimum positions on walls and ceiling for absorptive and diffu- sive materials to control the mid-high frequency portion of spectrum. It is important, though, to remember that the objective is envelopment in the A-V experience, and this cannot be accom- plished by sound absorption alone. The acoustical palette consists of absorption, reflection, and diffusion. The best room can be achieved by an appropriate com- bination of these. Deader is not better!

While users are generally astonished at the difference proper placement can provide, some tweak the positions the program generates. The program will find the locations that generate the best room response within its stated assumptions. While a flat room response may be math- ematically preferable, listeners have dif- ferent hearing acuity, musical tastes, and musical training. So let the Room Opti- mizer get you close, then tweak to taste. We are committed to expanding and improving the Room Optimizer, and users’ comments are welcome.

PETER D’ANTONIO, PRESIDENT

RPG DIFFUSOR SYSTEMS, INC.