PRECISION CROSSOVER ALIGNMENT

As anyone knowledgeable in speaker design will tell you, the crossover is the heart of the system. A crossover is an electrical circuit that separates the different bands of the audio spectrum and directs each band to its appropriate driver. All SP Technology products are designed with crossover alignments that include the "acoustic" response of the individual drivers in the final transfer function. Textbook approaches are never blindly taken as each and every design is painstakingly researched, repeatedly tested and modified to obtain the ideal summed driver responses. As much (if not more) time is invested in this single aspect of design as in any other area.

Filter theory has been researched extensively over many years and is now, for the most part, a complete science. It has been shown that each alignment has its own individual advantages and disadvantages. Our position is to use what ever works the best in a given application. While it is true that we prefer to use the Linkwitz-Riley alignments due to their superior phase properties, we will not be restricted by academics in our quest for excellence.  From time to time we may choose to use other alignments as well — form always follows function. Natural Law will not permit any other approach and we ARE bound by it both philosophically and practically.

It is a costly and very time-consuming fact that we go to extremes in order to guarantee that every aspect of performance under the control of the crossover is optimized. Impedance compensation at critical points is always implemented. Often this has secondary benefits in the area of power handling that is often overlooked by those who consider such techniques to be of minimal value. Thermal time constants are modeled and conjugate solutions are implemented where appropriate and practical. It is at this point we will invoke our privilege and limit any further specific details, as we are not intent on educating the competition. The final response is all that matters to you, the prospective customer, anyway.

In practice, textbook formulas almost never give accurate results. Some would argue that the point is moot and to a certain degree, we agree. We only make mention of the fact for the benefit of those that are of legalistic persuasions. In the end, all that matters is that the final system response is linear and at crossover the drivers exhibit minimal phase difference. This requirement is often in stark contrast to many designs on the market.

It is a common observation that many consumers and apparently designers, believe that a flat frequency response on-axis is all that matters, overlooking the effects of dramatic frequency response variations off-axis. As a result one often sees designs that exhibit excessive inter-driver phase differences, which leads to poor off-axis frequency response/vertical polar response.  It is our design objective to produce products that exhibit a wide vertical polar response and this can only be achieved if inter-driver phase is minimal and/or the drivers are in phase at the crossover frequency.  It appears as though this might not bother some listeners who seemingly don't mind sitting in the proverbial "sweet spot," with their head in an imaginary vise. Arguably, we can scarcely imagine paying good money for a loudspeaker that demands such a committed audience though.

But even if this weren’t an issue, then an even greater problem occurs when the drivers are not in-phase or nearly in-phase at crossover. Whatever the entire radiated spectrum of sound may be… you can be sure that the surfaces of the room will be reflecting it. That energy ultimately returns to the listener in the form of a reverberant field. If the reflected energy of the reverberant field does not have a similar spectrum or "signature" as that of the direct energy from on-axis, a very artificial soundstage will be the result.

Many a novice and “would be” home recording engineer has found this out the hard way. It would be curious to know how many hours have been spent installing and then shortly thereafter removing most of the acoustic foam, egg cartons and carpeting from the walls of garage recording studios. Countless young zealots have made the mistake of thinking they had to "deaden" the room to make a quality recording. A speaker that has a flat response on-axis but uses drivers that are not in-phase (or nearly so) will exhibit an erratic off-axis response and produce a similar, albeit less dramatic of an effect as in the “novice studio” scenario above.

In stating this, we would be remiss if we gave the impression that a flat frequency response was not an important objective. Quite the contrary, a response free of significant frequency amplitude variations is vital in any product being promoted for professional use. Where we take issue is that with all of the modern analysis equipment at an engineer's disposal, it should not be as difficult as it appears it must be to achieve a flat magnitude response within the pass-band of the loudspeaker. To be honest, we're not playing fair here though. Our waveguide technology and its inherent linearity make it relatively easy for us to offer an extremely flat frequency response, amongst a few other critical characteristics.

Oh, lest the reader think that simple measurements are our only criteria, we would be remiss if we failed to mention the great effort we have expended in procuring the finest crossover components and internal wiring available.  Mundorf™ of Germany, known for their unsurpassed component quality, supplies all components used to construct our crossovers.  We offer a “standard” version crossover for all models but different degrees of optimization and upgrades beyond this are available upon request.  It must be noted that due to the added size of the components involved, upgraded crossovers are only available as externally mounted units and are provided in elegant matching enclosures that can be placed beside or behind the speakers.

All components are hand soldered and inspected before installation in the system. Final crossover adjustment to achieve a response of +/- 2dB (typically +/- 1dB) is performed on the production line for each and every enclosure and loudspeaker pairs are matched for frequency response.

Finally, every driver is connected to its respective crossover point via custom designed wire by R.A. Smith Ltd.  Each wire is specifically engineered to match (as closely as possible) its respective driver’s load impedance and the crossover’s source impedance.  SP Technology is the only OEM manufacturer authorized by R.A. Smith Ltd. to use their superior wire in loudspeaker construction.  Copper wire is offered in the standard version, but Mundorf Silver-Gold wire is available upon request.

As you can see, we take crossover design and internal wiring very seriously.  Next to the drivers themselves, the crossover is the most important component of any design.  Once you’ve experienced the difference they make for yourself, you’ll understand our obsession.

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