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Now is the time to discuss some of the DEQX capabilities. It is capable of measuring each individual driver and creating a digital correction filter for each to flatten its response and group delay curves. This process is called speaker correction. Group delay has something to do with making sure that waves of all frequencies from a given driver reach the listener at the same time and in the same phase. I have never fully understood group delay.* The DEQX is also capable of measuring the left and right channels at the preferred listening position and creating filters that parametrically equalize the room response at the preferred listening position with or without going through the 'speaker correction' process.

* While it is much more complicated than some might think—which is why Pete rightfully demurs—the long and the short for our purposes is that DEQX processors slow down on-time and early-arriving frequencies so that slower frequencies can catch up.

One of these days I plan to correct for the 21ms delay between my huge 20Hz sub horn and the rest of the system. The way I will do this is to play the sub horn directly from the line stage and the stereo three-way channels from the DEQX, delaying each of the latter by enough time to get the subwoofer wave to the ear in sync with the stereo channels. When doing this time correction I will also correct for the time delays inherent in the layout of the stereo speakers.

Once the user gets the hang of it, the equalization system is surprisingly easy to use. Smoothed left and right channel frequency response curves are shown on the computer screen along with the EQ curve. Smoothing is necessary because the response curve is basically unrecognisable hash without smoothing. Apparently our brains do a lot of smoothing to allow us to make sense of audio signals. A wonderful feature is the ability to invert the EQ curve. Once inverted it should look like the smoothed frequency response curves. We have to remember to reinvert the EQ curve or we will end up hearing something twice as bad as without EQ. There are no left and right channel EQ curves. We are required to apply the same EQ to both. But I got ahead of myself. The DEQX also has a fabulous crossover capability, offering various families of crossover filtering at various slopes. We are using linear phase filters with a slope of 48dB/octave. Using a steep slope allows us to hear the portion of the audio band a driver plays best without the portions of the band it plays worst. A steep crossover slope is much like using a paring knife to remove a worm from an apple. The user is able to set up the DEQX for a two-way system, a 3-way system or a two-way system with a sub.

This is a good place to mention the benefit of multi amping. You cannot use the DEQX without multiple power amplifiers. When you use multiple amplifiers, each amplifier operates over a limited band. This keeps the high frequencies from being played through an amp that also plays those big strong low frequencies. This reduction of intermodulation distortion is easily discernable and a good reason to use an electronic crossover like that incorporated into the DEQX. Of course there is also a huge penalty in system complexity. If you want a simple system, don’t go this route. If I have this right, each set of speaker correction curves, room measurements, crossover data and parametric EQ data is stored as a project file on a PC used to set up the DEQX and read its mind. Also, if I have this right, the project file records the crossover parameters. I cannot remember how this all works. Some of the data are stored on the PC, some in the DEQX. I’ve taken some notes on this. I personally don’t have adequate recall to work with the DEQX without frequent head scratching.

Enters the DEQXpert stage left. His name is Larry Owens. I hope Larry will forgive me if I refer to him as a middle-aged man of average build with an elfin personality, a ponytail and a wonderful smile. Larry is smart. He knows all the alleys and back streets of DEQX. He lives in the Denver area. Larry is a perfect gentleman with a great sense of humor. By Skype Larry can be in your listening room with you and with your permission remotely run your Windows computer to set up DEQX perfectly. You will have to plug in and move the microphone. If your system is simple, Larry may be able to do the job in a few hours. My Po’ Boy system has not had the benefit of Larry the DEQXpert. I have not yet implemented the DEQX speaker correction or time delay features. What I do use is the great crossover and room EQ functions of DEQX without which neither Stephæn nor I would want to deal with a full horn system. Whenever Pete plays the Po’ Boy system he is happy as a clam at high tide. Pete is almost too happy to mess with the system any further. That said, at some point if the good Lord is willin’ and the crik don’t rise, we will eventually try speaker correction and time delay.

Stephæn’s Po’ Lil’ Thing system has had the benefit of Larry the DEQXpert. Stephæn and I were present each time Larry did his magic by remote control 1.100 miles away. Wow! Larry is a pro. And he is pleasant to work with. Larry had us place the DEQX calibrated reference microphone kit ($799 including a long cable and boom stand) as many times as required and measured first the nearfield response of individual drivers, then the system response from the listening position. Larry then meticulously sought out crossover points by trial and error that allowed perfect speaker driver correction and sewed together the results with perfect stitches. During this process he parametrically equalized the response curve. He manipulated files somewhat like the guy with the three walnut half shells and beans. The file system of the DEQX is much like the old Windows file tree, not that you would ever know by reading the DEQX manual. Files can be cut and pasted from project to project. When Larry completed the work on Stephæn’s system, the system was as flat and time and phase correct as any audio system the world has ever seen. And it sounded right.

The DEQX allows the user to save a large number of projects, likely more than we will ever need. The DEQX can be difficult for some people to use. The more a DEQX is used, the easier it becomes. Multi-amplified systems are complicated but they really can deliver. If one builds a lot of speaker projects or even one important one, the DEQX can be wonderfully helpful. Most people would not know a digital system was playing if they heard a system properly set up with the DEQX. The benefits of DEQX and multi amping may in many cases, outweigh the benefits of avoiding digital.