Those of us in the audio design field begrudgingly accept the fact that the loudspeaker is the weakest link in any audio system. Amplifiers and source units have achieved a degree of accuracy that makes any induced distortion inaudible to even the most critical listener. Loudspeakers, on the other hand, are assembled with imprecise mechanical components and passive electrical components that contribute significant distortion to the audio signal.

No matter how high the price or defined the engineering, a traditional passive loudspeaker is going to add substantial distortion and frequency response errors, so that sonics never sound quite right. Combine this fact with necessary compromises in amplifier power, proximity of boundaries and speaker placement, and it?s no wonder that listeners become frustrated with having to sit in the ?sweet spot? to achieve reasonable sound quality.

DSP speaker correction solves the ?sweet spot? issue by removing inherent driver distortions, resulting in a system with flat frequency and power response, so that the drivers produce the lowest distortion of which they are capable. Or, in plain English, the sonic image ? where instruments and voices are placed in the soundfield ? remains accurate regardless of speaker placement or the listener?s place in the room.

Passive Loudspeakers: Always a Compromise

Of all the audio disciplines, loudspeaker design is one of greatest compromise, since the designer is forced to assume a variety of applications and environments. Manufacturers tailor output to suit the lowest common denominator, requiring consumers to then experiment endlessly with placement and other options to obtain the best possible sound in the widest area.

Passive speakers use passive crossovers, which leads to sub-par performance. Crossovers, which send high and low frequencies to the appropriate drivers (tweeter, mid, woofer), are subject to wide differences based on temperature and output. At the risk of getting overly technical, the steepest-slope design possible (for both cost and design reasons) is 24dB per octave, and far more common is second order or 12dB/octave. Using shallow slope crossovers causes the drivers to produce sound beyond the limits of their ideal operating range, either increasing distortion or compromising the off-axis frequency response of the system. The wide overlap between drivers means that they work well together only in a small area (the sweet spot), and/or that their sound is highly dependent on the room in which they are placed.

Active, or powered speaker systems provide known amplifier power for better control of the entire system, but internal filters still add distortions to the frequency response.

Whether designing a passive or an active speaker system, the designer is forced to find the best balance between on- and off-axis system response, system size and power handling to achieve realistic performance. Some are better than others, but nonetheless, all represent compromises in design and none achieve perfect sonic output.

DSP Speaker Correction: Why and What For

Mention DSP and the most likely reaction is, ?No fake hall effects, please.? DSP (digital signal processing) gets a bad rap from being associated with unnecessary features on a/v receivers, but DSP-based speaker correction is the future of home loudspeaker technology for several indisputable reasons:

DSP offers high resolution with distortion characteristics similar to ultra-high end audio components
Elimination of the ?sweet spot,? providing a broad, accurate soundstage from virtually anywhere in the listening room
Simple, pre-set equalization settings to allow speaker placement on shelves or walls as well as on stands
True plug & play operation
An upgrade path for future DSP solutions, such as room correction and distortion reduction
A small and compact cabinet, taking as little space as possible while offering high output

When properly executed, speaker correction promises unparalleled resolution and precise control of each individual woofer and tweeter, allowing the system to play louder than any previous compact design to date. The broad sonic dispersion with real time correction of delay and other anamolies makes it exceedingly flexible in terms of placement and the listeners? sitting position.

For example, in NHT?s new DSP speaker-corrected system, NHT Xd, there are two satellite speakers, both of which include two amplifiers; one each for the tweeter and midwoofer. The crossovers are programmed into the outboard DSP processor, providing available slopes that allow the crossover point between tweeter and midrange to be quite low without distorting the sound. A bass module, or woofer, incorporates two active, opposed, 10 inch drivers, a PowerPhysics 500W Class D amplifier, and minimal controls; specifically, a ?bass trim? and voltage selection.

High Tech, but Easy to Use

A DSP speaker corrected system is as plug & play as the most basic home audio products, but with dramatically improved results. When done right, there is a minimal number of controls on the front panel of the processor, encouraging the user to ?set once and forget.? The consumer only needs to select the proper setting for each speaker?s placement in the room, and even this Boundary control offers equalization settings for only four room positions ? corner placement, near one wall, on top of a TV, or free standing in the room away from walls.

Placement of the bass module may require some experimentation based on respective room layout and other considerations.

DSP Correction: The Future of Loudspeaker Design

The dramatic benefits and improvements that result from DSP speaker correction are potentially market shattering in virtually all categories of sound reproduction — home, car and in the recording studio. Although the first generation is priced like all first generation releases ? meaning at the high end — prices will certainly fall as production scales up in volume. However, a DSP speaker system can be future proof if, like the NHT Xd, it allows for easy software and firmware upgrades via a USB port.

The comparison of performance between a DSP corrected system and a traditional passive system is so dramatic that even the untrained listener will immediately appreciate the difference. The software interface is easy to use, so designers not only have a 100-fold improvement in their pallet of design tools, but the time it takes to bring a new product to market can be significantly shorter than more common, less impressive models.

Music and movies should provide pure enjoyment. DSP speaker correction offers the most advanced technology to let listeners simply enjoy home audio.

Since it was founded in 1986, NHT? has continually challenged the notion that the very best sound reproduction must come at a premium price. NHT takes pride in designing and marketing loudspeaker systems that provide a lifetime of listening pleasure. Its products from past to present speak volumes of NHT?s dedication to sonic excellence. For more information, visit NHT (Now Hear This) is a brand name of Rockford Corporation?. Rockford Corporation is based in Tempe, Ariz. and is a publicly traded company under the NASDAQ stock symbol ROFO. NHT?s website can be viewed at and