Hey all,

Let me introduce myself first. My name is Adam Pelz, and I am the individual who calibrated Ken's cinema. I have done quite a bit of work with Dennis Erskine, and am one of a few who he brings on to calibrate his exceptional work. I help teach some classes now and then with the HAA, and I also work for many dealers through out the country (and Mexico and Canada) as a freelance audio and video calibrator. I am also a big consumer of scotch, so this may tend to ramble a bit.

Hrm...where to begin? How about some design philosopy..Dennis has already explained quite well about why subwoofers are important, and how multiple subwoofers are critical to achieving smooth and similar bass response across a listening area, and he provided some basic references for such. Go ahead and read that sentence again please! If you happen to have a dedicated listening room, with 1 chair, or 2 very close together, then only read further if you are the curious sort. If you all need is for 1 seat to be great, then most of that can be achieved with proper positioning of the listener, mains, and subwoofer. You might achieve something good without using a sub, but the absolute physics of small room acoustics make it unlikely. Everything below is geared toward multiple seating positions, although the primary listener certainly does not suffer from these tools.

In reality, most of us prefer our music and movies to be social events, to experience and share with others. Insert your favorite dramatic music score here. Suddenly, we are faced with lots of problems that almost guarantee some compromises. Murphy clearly requires that for you, the primary listener, to have smooth bass response in your favorite chair, then the one occupied by your spouse will be in the middle of modal peaks, which are capable of being upwards of 15dB higher. Your neighbor, sitting next to you, happens to be in a null; Both of them think you are insane. No need to raise your hands, as I can spot you from here.

Compromises then. The papers referenced by Dennis suggest multiple subwoofers are in order. Another gentleman, Gerry Lemay, teaches a "virtual subwoofer" technique in his extremely valuable hands-on classes. In either case, some very important prerequisites are needed, starting with proper listener positioning, and putting your speakers in optimal locations. In other words, don't put your couch up against the back wall, keep the mains away from boundaries, insist that your center channel is the same speaker as your L&R, and not some horizontal bastardization, keep them out of cabinets, only use dipoles for surrounds if you absolutely must...and a bunch of other things I am sure the forum members here already know to avoid.

So reading from above, nearly all of those compromises involve the room. Direct sound vs indirect sound. The reflected sound clearly dominates direct sound. If any of you need, I can get into the math in another post, although it would be best in another thread entirely. So what we hear is very dependent upon the off-axis response of the speakers, which directly correlates to the type of acoustical treatments installed. Many of you would be shocked at how badly some very highly regarded speakers are when you measure the off-axis response, yet that reflected sound greatly dominates what we hear. Bad off-axis response? Absorb the first reflections, which will increase Focus, but greatly diminish Envelopment. Bad off-axis response will also decrease the accuracy of speaker Response, and possibly Clarity. And we haven't even begun to explore poor listener positioning, modal responses, boundary gain, and other room specific effects.

The goal of this is to present how much impact the room has on what we hear. Far more than most would assume. Having the right tools to overcome the obstacles the room alone presents will often outweigh the latest and greatest pre-pro, amplifier, or speaker selection. I am in no way trying to diminish high end audio companies! I myself have a room of very expensive kit from Linn. But I have participated in many manufacturer demo systems, where I have hidden some 3rd party DSP under the table, which allowed me to add PEq, very precise gain controls, shelves and other filters, none of which is currently available in any consumer grade components.

So back to compromises... I perfectly understand, and in some cases completely agree with some push-back on using professional grade 3rd party DSP solutions. Unfortunately, at this time, those are the best tools available. Certainly, there will be some losses in resolution, but I firmly believe that the benefits outweigh the costs.

My favorite anecdote involves a movie scene, Star Wars, Episode II, opening sequence I think. Large ship headed to land, accompanied by two smaller craft. In one system, until we had the bass dialed in correctly, the whining engine sound of the two smaller crafts was largely masked. The loss had nothing to do with speaker or pre-pro choice, and only to do with proper calibration of the system.

This particular system also exhibited some curious pre-pro design problems. When implementing crossovers, there must be a x-over setting for the mains, and one for the subwoofers. The first determines the slope and frequency applied to the lower end of the main speakers, and the second applies to the upper range applied to the subwoofers. Ideally, they should both be the same. If the mains are crossed at 80Hz, 24dB/octave, then the subs should also be crossed at 80Hz, 24dB/octave. This particular system changed crossover slopes depending on the DSP mode selection, ie, movies, music etc. The room certainly did not suddenly change; why should the speaker setup change? Simply because the component designer wanted it that way. You would be amazed at how often this occurs, in very highly regarded components.

I did not cover even a small portion of what I intended, but this has rambled on enough. I will answer any questions or comments when I have the time. Essentially, my point is that there are many compromises that need to be made when designing a system. Compared to all of the things I can fix with an offboard DSP processor, the bonuses will far outweigh the compromises made.

Adam
Acoustic Mafia 'Hear No Evil'

Adam
Acoustic Mafia 'Hear No Evil'