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Construction and setup detail for Drew Daniels' high-efficiency loudspeaker system.

(Portions of text excerpted from Audio Critic article.)

Loudspeaker column design, built and tested as proof-of-concept demonstration by Drew Daniels, Senior Technical Staff member of Walt Disney Imagineering R&D department and electroacoustical consultant to the Walt Disney Company, February-March of 1990.

Loudspeaker system component complement:

(4) 2242H subwoofers (2.1% conversion efficiency each or 8.4% in tandem)

(4) 2227H high-efficiency 15" woofers (one pair each side, about 17% efficient each pair)

(2) 2123H high-efficiency 10" midrange (3.5% efficient each)

(2) 2382A horn with 2450H compression driver (30% efficient each)

Efficiency or "conversion efficiency" is defined here as the ratio-expressed as a percent-of the acoustical output obtained for a given electrical input. Thus a transducer that delivers 5 acoustical watts to the air when fed a 100-watt electrical input signal is said to be "5% efficient."

In case you're wondering if the poor 10" mid with its mere 3.5% efficiency, can keep up with the horn, rest assured I needed 10 dB of attenuation on the mid to get flat frequency response.

For amplification, I used two BGW SPA-3 triamplifiers. BGW was happy to set up the triamplifiers to provide high-pass filtering for the two 15's at 80 Hz, band pass for the 10" midrange from 300 Hz to 1200 Hz, and band-pass and horn EQ filtering with the lower end of the high frequency band at 1200 Hz. The crossover slopes are Linkwitz-Riley type 24 dB/octave.¹ The amplifier's input section also includes switched attenuation and built-in signal delay to adjust the acoustic time of arrival for acoustically aligning the cones and compression driver. Although the amplifiers are each only 5.25 inches of rack space, they each produce up to a total output of 1000 watts, providing 600 watts for each pair of fifteen's, 200 watts for the mid and 200 watts for the horn. This represents an average of around 30 dB of headroom above normal living room listening levels, which generally range in milliwatts for these speakers. Even though this much headroom and power seem to be overkill, I assure you that is not the case. I include here a table from my Audio Engineering Society workshop on basic audio-it includes the results of about 130 hours of measurements I did of live and recorded material using a $7500 Brüel & Kjær true-RMS voltmeter and a $40,000 Brüel & Kjær audio analyzer to record the peak-to-average power ratio of various signals. (1997 note: these are no longer available except on special order. I recommend using four solid-state amps of your choice-my choice is Adcom-and building a 48 dB/octave (8th order) Linkwitz-Riley crossover).

In order for untrained listeners to perceive no obvious squashing of dynamics, audio reproduction systems should be capable of the following peak-to-average ratios for these stimuli:
SOURCE MATERIAL CREST FACTOR
ROCK MUSIC 10 dB
HORNS (legato notes) 10 dB
REEDS (legato notes) 12 dB
STRINGS (bowed) 15 dB
SPEECH 20 dB
PIANO 30 dB
POP MUSIC 40 dB
STRINGS (plucked) 40 dB
DRUMS 40 dB
ORCHESTRAL MUSIC 50 dB
INDIVIDUAL PERCUSSION INSTRUMENTS 60 dB
GENERAL HIGH-FIDELITY REPRODUCTION 60 dB

¹ Linkwitz-Riley 24 dB per octave (fourth-order) or 48 dB per octave (eighth-order) crossover filter slopes produce flat acoustic energy summation through the crossover frequency region.

The BGW SPA-3 turned out to be the elegant and simple alternative to a large rack of gear. Having done similar projects many times in the past, I can honestly say I would not go back to the racks and cabling and connectors and ground-loop chasing always necessary as long as the SPA-3 is available to eliminate all the little gremlins that tend to pop up when one builds up complex systems.

Note to builders: I don't recommend trying to build passive crossovers for these units. Acoustic time-of-arrival delay of sufficient time is not practical with passive devices and system performance really suffers without it. Additionally, to obtain anywhere near the performance of the tri-amped system using coils, caps, power resistors and such, the crossover would be far more expensive than a pair of SPA-3's and would probably weigh somewhere in the neighborhood of 100 pounds-because of all the huge coils.

There have been many questions in the letters I've received about doing this project some other way, with modifications, with different components etc., perhaps to accommodate someone's favorite component or fit some particular space or budget. I cannot address these questions individually without addressing the particular goal of the individual asking. I can do this-it is in fact, my livelihood-I will be happy to design a custom system for you, but be aware that this must be done on a consulting time basis. This project however, is what it is, and as such, it pleased all the audio golden ears at Disney enough that they insisted on using my lab pair for the yearly Halloween show with an audience of 2500 people spread over an outdoor area covering 235 degrees, as well as company meetings with Eisner and Wells in huge tents with thousands of people in the audience. This with a sizable company inventory of all manner of THX-rated large theater systems, rock-concert boxes form various manufacturers, etc.

THE MAGIC HORN FIX

There are some tricks that are essential for eliminating horn "honk." The first is to use the cone driver placed just below the horn, all the way up to a frequency where it begins to "beam" due to the relationship of sound wavelength and cone diameter. At a frequency where the resulting Q-factor (directivity) of the cone matches that of the horn, the transition from cone to horn will be smooth, and not abrupt-as it can be in systems where the cone is too large and the horn is too small. If this condition is met, and the frequency response of the cone is good well beyond the frequency up to which it is used (a well-behaved upper end rolloff), then the horn will enjoy a seamless transition from the cone and will not honk, assuming its frequency response is good and uniform over its output angle. This latter condition is referred to as being "power-flat" and is very important to the transparent operation of the speaker system in rooms, with their concomitant acoustic implications. If the speaker system is power flat, the sound in the room will be as good as that particular room will allow it to be.

THE MIDRANGE

The midrange driver must be a cone, unless you live in a theater and don't mind a 4-foot high horn (I crossed my mid at 300 Hz into the woofers). As it turns out a mid cone supplying 300 Hz to 1200 Hz gives the proper effortlessness with very little power, and thus has extremely small cone excursions and low distortion. As I mentioned earlier, I had to trim the 2123H mid cone back 10 dB on the amp's gain control to get the response through the band flat. The power absorbed by the mid cone driver amounts to milliwatts most of the time, which helps to hold harmonic distortion to very low levels, typically well below 1% THD up to dangerously loud volume.

I experimented with a dozen midrange drivers before I was confident that the 2123H with its high efficiency and limited excursion linearity would produce sufficiently low distortion. It is a wonderfully transparent driver and a large part of the reason this speaker system sounds like listening to live music rather than loudspeakers. Note: as of 1995, JBL is manufacturing a new even higher power 10" driver called the 2012H. If you can obtain 2012H's, performance will increase even further.

The driver is mounted on the baffle as close to the horn as I could get it with my inexpensive mid chamber geometry. You could do better if you are willing to cut the shape of the mid driver's frame into the lower lip of the horn and snug the mid frame up into the cutout and, of course, figure out a mid chamber arrangement that would clear the horn and driver behind the baffle, but this is not measurably better than just a touching fit.

The enclosure for the mid cone consists of a 10-inch diameter concrete casting tube made of plasticized paper. Such tubes are made by Burke Tube and Sonotube and no doubt many other regional paper products manufacturers. The tube is mounted to the baffle by gluing into a counter-bored shoulder cut-out, routed in the back of the baffle around the mounting hole. The tube is about 12 inches long (deep), it is filled completely but loosely with a "jelly roll" of unbacked fiberglass house insulation cut from a roll about 4 feet long. The back end of the tube is sealed air-tight with a disc of 1-inch thick medium density fiber board-the same material used to build the rest of the box.

Please, even if you hate handling fiberglass, don't substitute other absorbing materials for it. Fiberglass is unique in its physical properties and substitutes will not work as well. Just get some long heavy rubber gloves to handle the stuff, and shower off with cool or cold water when you're done.

One letter I received inquired about using the JBL three-inch throat midrange compression driver and horn. The horn itself is 44" wide by 42" high and with the driver attached, is 42" deep and weighs 82 pounds. The letter also asked about horn-loading the two 2227 cone drivers for greater efficiency. Let me explain why I chose the geometry I did, so that those of you inclined to even higher efficiency can decide how to proceed from an informed set of criteria: First, one of my design goals was the use of the typically small space behind the perforated theater screens in the new smaller multi-cinema complexes being built around the country and in Disney attractions that have such screen spaces. Even at Disney Imagineering, it would have been impossible to argue successfully for the space behind the screens required for horn loaded systems, and in fact, this column design (once tested and listened to) proved that horn-loaded systems were not necessary to play even the loudest ear-splitting explosion effects in theaters of 200 or 300 seats. Second is the issue of acoustic impedance. Simplistically, acoustic impedance is the ratio of radiation resistance to the acoustical load. Radiation resistance varies with the size of the acoustical aperture (source size) and the acoustical load is the air in the room in which the source is operating. The source drives the load, and so if we wish to avoid transmission line conditions where we must match the source and load to obtain proper power transfer and flat frequency response, we must provide a source of low acoustic impedance (small source size) so that the source output is sufficiently robust to essentially ignore the load conditions. What we lose doing this is some efficiency and sound pressure level capability; what we gain is flatter frequency response and freedom from such effects as the deterioration of performance when we move furniture around or close or open a door or window. The real bottom line, however, may be that this little column is simply more practical perhaps, than some other designs.

THE WOOFERS

The 2227 fifteen-inch cone driver should be thought of as a low-midrange-not really a woofer. Yes it's a big driver with a big voice coil. In fact, I use two of them in my bass guitar rig, but its QTS and moving mass are so low that when you put it through Thiele-Small calculations and plot curves on a computer as I did countless times, the device ends up looking more like a midrange itself. To be accurate, the Keele exponent-corrected program I use (because it gives me systems that measure the same as the model predictions) calls for about 1.5 cubic feet per driver, tuned to about 85 Hz-not exactly organ pedals. I ended up opting for a slight over-damping of two units in a 3 cubic foot volume tuned to 80 Hz. Even so, the unassisted output of the box is flat to 65 Hz and droops only slightly at 40 Hz, in the middle of a 40,000 cubic foot room (my test lab at Imagineering R&D).

Be sure the high-pass filter on the amplifier driving the two 2227H's is set to 80 Hz and rolls off at a rate of at least 18 dB per octave. The 2227H drivers are high-efficiency, limited linear excursion devices (in fact, they are one of the highest efficiency cone drivers made anywhere). The crossover frequency of 80 Hz is the design target to limit cone excursion and produce a good transition to the subwoofers.

The enclosure is built as rigid and non-resonant as possible and then lined with fiberglass over the entire interior surface area, except around the ports where air turbulence might tear off pieces of fiberglass and spray them around. The woofer portion of the enclosure is the only real structure. The midrange tube is extremely rigid and exceptionally non-resonant. My goal in designing the woofer section was to minimize spurious panel-vibration and acoustic output-within reason. There is more panel output, in fact, from the thick, ribbed metal back cover of the compression driver.

I used four two-by-fours for bracing inside the woofer compartment. These were counter-drilled for wood screws and glued with aliphatic resin glue, on-edge, to the compartment panel interior surfaces. I tried to space the braces at random-so that no two unbraced panel areas were the same size-thus randomizing panel section resonances. I also glued the two cutout discs from the woofer holes to the outside of the back panels to make the total panel thickness 2 inches, plus braces!

SETTING UP THE SYSTEM

This can be tricky. I used a TEF analyzer and a $40,000 1/24th-octave Brüel & Kjær real-time analyzer and intensity probe set of phase-matched microphones (another $14,000). First, I did energy-time measurements to set the delays in the amplifier. This proved to be difficult, since I had to take distance ranging measurements of each driver separately to make sure I was looking at arrival times from the intended measurement object. After I got the delays set, I checked frequency response the best I could in the space available, then resorted to the real-time analyzer. Be aware that the frequency responses you get with these two methods are very different because TEF windows its measurements to try to exclude reflections and examine only direct sound from the source, while real-time analysis includes all returning room energy information along with that from the speaker. I like a balance of both measurement methods, because one lets you fine tune the energy output of the speaker, and the other lets you adjust large trends like the general "too-bright" high end you will likely notice if you try to obtain flat output to 20 kHz from the direct-sound readings of a truly power-flat or "constant-directivity" horn. Such horns produce more high frequency energy in the first place because they distribute the energy over a larger angle, that is to say, if one equalizes such a horn for flat response, then more high frequency energy will be pumped into the listening space than would be the case for other types of horns. Most people are not used to listening to power-flat top-end, and will find it too brassy. Only minimal-miked big-band recordings will sound right with the system adjusted this way.

For your playback system head end, I recommend that you use an extremely low-noise preamp with simple Baxendall type "tone controls." The bass and treble turnover frequencies are a matter of taste, but 100 Hz and 10 kHz or 200 Hz and 5 kHz seems to work well to adjust this system to music on recordings. To my ear, parametric equalization is less pleasing and is certainly prone to putting more phase aberrations in more audible frequency ranges than are simple tone controls. One-third octave "graphic" equalizers are completely useless for high fidelity use and one-octave units are even worse-avoid these. They introduce horrendous phase shift problems of their own, and if not properly analyzed with the system they are driving, will virtually always degrade performance.

Begin adjusting with the amp master gains set low, and turn the preamp all the way up. Slowly advance the amp gains until you can achieve proper balance and slightly louder than necessary output. This will ensure that you will have the least possible amplifier hiss from the speakers. Amplifier hiss is a phenomenon that rarely troubles owners of low-efficiency speakers, but these monsters are efficient enough to make the transistor junction noise of poorly designed amplifiers quite audible.

If any of you reading this decide to build this system, it will cost around $10,000 including amps and all. If you get that serious, if you are rich and adventurous and don't care what stereo salesmen think, you are the type of person who would really enjoy this system.

SUBWOOFERS

The Subwoofers should generally occupy the space between your main speaker systems. The reason for this preferred location is the so-called propagation delay of low frequency sound from the sub units.

All loudspeakers are natural electromechanical filters and as such, they produce a delay of some size between their input signal and their acoustical output response-there is no exception to the natural laws that cause this type of delay-despite what commercial manufacturers put on their literature.

In more technical terms, the amount of delay depends on the filter bandwidth and the amount of attendant phase shift inherent in the filter's band-limit or envelope shape and other characteristics. For example, a simple single-order or "single-pole" filter produces 90 degrees of phase shift at the frequency, where the signal passes through the half-power (-3 dB) frequency point. Thus a subwoofer whose high-pass characteristic is a single pole filter will exhibit a 6 dB per octave rolloff below its operating band. If we use a sealed-box with a 30 Hz lower band limit defined by the -3 dB or half power point, then we will have 90 degrees of phase shift or a delay of 8.3 milliseconds at 30 Hz. This delay is equivalent to roughly 9 feet of sound travel through air.

At the crossover frequency of 80 Hz we are imposing on this system, sound waves are 14.1 feet long. We will want to know what order our crossover will be. We will assume the subwoofer upper band limit is way beyond 80 Hz and will not add significant phase shift to the crossover, (in fact the 2242H driver described could be used as the low end of a three-way system up to 300-400 Hz with no special consideration except that its conversion efficiency is low). For the sake of example, I will use the common 18 dB/octave crossover slope and calculate the position correction estimate needed. First, each 6 dB/octave forms what we referred to as a "pole" for the calculation. Three poles gives us 270 degrees of phase shift or three-quarters of a sound wave at our 80 Hz crossover frequency. Three fourths of 14.1 works out to be 10.6 feet.

Fortunately for us, there is also delay in the column's low-frequency output due to the high-pass function and the built-in delays in the amplifier we have adjusted to get our acoustical alignment between cones and horn. This means we will not have to place the subwoofers 10.6 feet forward of the columns. In fact, because of the ear's forgiveness, you'll find there's a "window" of space for physical placement that allows a good deal of flexibility in setting the speakers into your listening space.

WHAT YOU HAVE WHEN YOU'RE DONE

These loudspeaker systems could easily be used behind a perforated movie screen, providing sound to an audience of hundreds of people in a small movie theater (the original design intent). They are also equally capable in a home listening room setting, of causing you permanent hearing loss, and doing so quickly.

I have two tips for you and I urge you to pay heed:

First, play music at no more than realistic levels. I assume that if you choose to build these things, you've done so because you're interested in fidelity of the reproduced sound to the originally recorded sound. You will get the best representation of the original sound if you play the reproduction at the original sound level. Playing too loud is as detrimental to fidelity as playing too softly.

If you play predominantly rock music, there is no such thing as an original sound level-since all the recorded material comes out of a little electronic box or was derived by sticking a microphone somewhere you would never purposely put your ears.

In either case, you need to keep a sound level meter handy. You can get a perfectly adequate SLM at your local Radio Shack store for around fifty bucks, and for your ears sake, don't ignore this advice.

These speakers make so little distortion that you will be tempted to believe that the 120 dB sound you are listening to is only playing at 90 dB. This is not good. You will lose your hearing. Don't let this happen.


Otologists and other hearing Experts all warn that persistent ringing in your ears for several hours after causative auditory events is an absolute certain indication you have suffered permanent hearing loss!

If you find that the clean sound causes your favorite rock artist to be emasculated, you can go out and get an Aphex Aural Exciter to add distortion back in so that it sounds loud again. (Seriously)

Here's a "parts list" in case you get ambitious.

FOR THE COLUMNS:

(2) BGW model SPA-3 triamplifiers (contact the BGW factory to custom order).

(2) JBL 2450J compression drivers.

(4) JBL 2227H cone transducers.

(2) JBL 2382A horns.

(2) JBL 2123H cone transducers.

(3) Sheets, MDF (Medium Density Fiberboard) 60" square 1" to cut parts for two boxes.


(2) Six-position barrier terminal strips (8-32 screws or larger).

(1) Package, #10-14 spade lugs and professional crimper.

(1) Length, 12-gauge twisted pair wire to hook up transducers.

(1) Small box, 2" drywall screws.

(1) Large bottle (16 oz.) Aliphatic Resin wood glue.

(1) Quantity two-by-fours, to make eight 30" pieces.

(1) Concrete casting tube, 10" I.D. 3 feet.

(32) 10-32 2" Philips pan head machine screws.

(8) 10-32 1.5" Philips flat head machine screws.

(24) 1/4-20 2" black Philips flat head machine screws.

(40) 10-32 1/2" T-nuts.

(120) square feet of R-19 unbacked pink fiberglass (for columns and subwoofers).

REAR VIEW OF FINISHED CABINET WITH TOTAL CABINET DEPTH = 16.0"

WOOFER CHAMBER BACK REMOVED

FOR THE SUBWOOFERS:

(4) JBL 2242H cone transducers.

(6) Sheets, MDF (Medium Density Fiberboard) 60" square 1" to cut parts for four boxes.

(1) Length, concrete casting tube, 8" I.D., to make four 15" long pieces.

(1) Quantity two-by-fours, to make forty 24" pieces.

(4) Two-position barrier terminal strips, (10-32).

(32) 10-32 2" Philips pan head machine screws.

(32) 10-32 deep T-nuts.

Cut four pieces of tube at 15" length.

Rout baffle counter bore for tubes to O.D. of tube, 1/2" deep in back of baffle.

Cut eight panels for baffles and backs, 29" square.

Cut eight panels for tops and bottoms, 29" 27"

Cut eight panels for sides, 27" square.

Attach two pieces, two-by-four, 24" long to each panel, screwed and glued on edge as for columns.1

Butt-join all pieces together using cabinet clamps.

Line all five surfaces except the baffle, completely with fiberglass. Take care to keep the fiberglass away from the vent duct end or it may be sucked in and sprayed into the room by the air turbulence at the inside end of the duct.


1 note: make sure brace pieces on the different panels clear each other when the box panels are assembled.


Construction diagram for subwoofer cube(s).

The Subwoofers pictured here, should generally occupy the space between your main speaker systems. The reason for this preferred location is the so-called propagation delay of low frequency sound from the sub units.

All loudspeakers are natural electromechanical filters and as such, they produce a delay of some size between their input signal and their acoustical output response-there is no exception to the natural laws that cause this type of delay-simply because sound waves vary in size.

In more technical terms, the amount of delay depends on the distance (in time) between the zero-crossing and the maximum pressure formed in the air by loudspeaker diaphragms along with the filter bandwidth and the amount of attendant phase shift inherent in the filter's band-limit or envelope shape and other characteristics. For example, a simple single-order or "single-pole" filter produces 90 degrees of phase shift at the frequency where the signal passes through the half-power (-3 dB) frequency point. Thus a subwoofer whose high-pass characteristic is a single pole filter will exhibit a 6 dB per octave rolloff below its operating band. If we use a sealed-box with a 30 Hz lower band limit defined by the -3 dB or half power point, then we will have 90 degrees of phase shift or a delay of 8.3 milliseconds at 30 Hz. This delay is equivalent to roughly 9 feet of sound travel through air.

At the crossover frequency of 80 Hz we are imposing on this system, sound waves are 14.1 feet long. We will want to know what order our crossover will be. We will assume the subwoofer upper band limit is way beyond 80 Hz and will not add significant phase shift to the crossover, (in fact the 2242H driver described could be used as the low end of a three-way system up to 300-400 Hz with no special consideration). For the sake of example, I will use the common 18 dB/octave crossover slope and calculate the position correction guess needed. First, each 6 dB/octave forms what we referred to as a "pole" for the calculation. Three poles gives us 270 degrees of phase shift or three-quarters of a sound wave at our 80 Hz crossover frequency. Three fourths of 14.1 works out to be 10.6 feet.

Fortunately for us, there is also delay in the column's low-frequency output due to the high-pass function and the built-in delays in the amplifier we have adjusted to get our acoustical alignment between cones and horn. This means we will not have to place the subwoofers 10.6 feet forward of the columns. In fact, because of the ear's forgiveness, you'll find there's a "window" of space for physical placement that allows a good deal of flexibility in setting the speakers into your listening space.

"NEAR-FIELD" SUBWOOFING

There is an alternative to the four expensive monster sub cubes, but it takes some getting used to; both in terms of the concept and the execution. Near-field subwoofers can be used near (directly behind) the listening position. Placing the subs close to your ears offers three advantages:

1. Smoother low-end frequency response, because of the direct-to-reflected ratio of the sound you actually hear. Standing waves create huge peaks and nulls in response depending on your room characteristics, but if you can get really close to the sound source, your proximity alone swamps out the peaks and nulls because of the lower the output level of the subs required to compensate the inverse square law distance losses. If you are listening to only (or mostly) direct sound and not room reflections, then you will hear sound as smooth as the loudspeaker can provide.

2. Since you're using less power (typically about a quarter as much) you can get away with smaller devices-maybe one cube or a custom box with a pair of cheap 12" subwoofer drivers inside. You will have to ensure that the box itself produces good, flat response, but even this is easier to get-and down to a lower frequency-when you use a near-field arrangement.

3. Your neighbors and your family will appreciate not having their teeth loosened by massive bass penetrating the entire house. Bass carries the most because its long waves are so much harder to absorb or bend. You've probably noticed (in L. A. we sure do) how the cars with monster audio systems only seem to make bass as they pass on the street outside. Bass carries like a fog horn, and near-field subwoofers can reduce the amount of sound energy you initially pump into the air.

Of course, careful balancing will have to be done to match levels with the front loudspeakers, and you will need a good audio delay line to delay the subwoofer signal between 5 and 50 milliseconds. I recommend using something like a pair of Plye 12" subwoofer drivers in a sealed box shaped something like a low boy table, placed directly behind your couch. The box should be about 10 cubic feet internally, and it should be stuffed loosely but completely full of R-30 fiberglass to ensure that it is over-damped. If you're serious about the project, you should also get a 1/3rd or a 1/6th-octave graphic equalizer to flatten out the box from the listening position.

ADDENDA

Speaker cabling:

Prepare speaker cabling for the high frequency horns only from multiple twisted pair Spectrastrip high-speed computer data ribbon cable. You can parallel as many conductors as you like to obtain the equivalent of a 14, 12 or 10 AWG. This method produces the finest performance available from wire-of any kind, at any price! You may also use pairs of single 10-gauge stranded wires which you can twist using an electric drill motor. Twisting conductors around each other places the current paths (and resulting surrounding magnetic fields) closer to right angles to each other which in turn reduces inductance-the main property of speaker cabling that can cause a loss in high frequencies in the amp-cable-speaker system. You can use any 10 or 12-gauge wire pairs for the mid and lower frequency drivers or even as small as 16-gauge if cables are short.

Terminate the three pairs of wires into a screw-terminal barrier strip mounted on top or on the back of the woofer chamber. From there, continue with the same wire to the amp. Place the amp nearby (it happens to be the same width as the speaker cabinet) and keep speaker cables short to minimize resistance and capacitance. This is the best you can do to insure that wire is not playing a degrading role in your audio system.

It is essential that good connections with low contact resistance be made at each connection. Use of crimped lugs is recommended if the certified crimp tool is used to install the lugs. High-cost gold-plated hardware which offer good mechanical connections are acceptable if they can be made to provide a low-resistance connection to the wire itself, and may offer additional benefits in avoiding contact "poisoning" due to the molecular migration of dissimilar metals across the connection. Periodic checks of connections will, in any case, avoid chemical connection problems.

This project is expensive enough already. Don't listen to any hair-brained morons who may try to tell you "special" speaker wire will make any difference. It's not true-it's only mysticism. If there were any actual advantages, such wire would have found its way into the engineering mainstream for large military projects, and satellites where billions in research would surely have revealed the benefits and resulted in at least some documentation. PERCEIVED benefits are exactly that-perceived-as a direct result of psychological inclination to rationalize and justify the absurd expenditure of money for what amounts to nothing more than prestige.

Lastly, if you're totally into perfection, I can highly recommend the Sigtech AEC 1000 Acoustic Environment Correction System. It is a serious engineering tool developed from the technology of radar image enhancement. The box (and a PC) measures and stores the total transfer function of the loudspeakers and the room, convolves huge DSP filters (2470 filter poles) from the stored measurement, and processes your audio at 250 million operations per second to produce corrections from up to four listening positions. You are left with smoother frequency response with a vastly closer match between left and right, and smooth phase response in the bargain since the correction is done in the time domain. No other device even comes close to the power this thing provides. You could turn one of your speakers toward the wall so that its output is reflected back to you later and with wider dispersion and added absorbtion, and the box is capable of correcting so thoroughly that the stereo image will be pulled right back to the center as if everything was normal! I used this thing at Disney to make Hi-Fi through tubes! And it worked!! It will cost you between $6500 and $8500 depending on whether you want the whole analysis system or are content to have an engineer set it up for you. For more information about the Sigtech, e-mail me at drewdaniels@worldnet.att.net.


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