INTRODUCTION

Since we opened our audio specialty salon several years ago, we have featured our own augmented stereo transmission line sub woofer for our clients who wanted the most deep ranging and the most natural bass response possible regardless of the price. While this system was designed by us from some classic transmission line concepts, we modified the system for better performance and to insure highest quality control in construction and near zero unit-to-unlt variability.

To date each unit has been one-off; a custom unit. Each is meticulously built, and the finish is applied to the client's specifications. Our fee for this is $1400. This is quite a bit more money than any other bass speaker on the market. The price is not a reflection of its single unit production, nor of its being a piece of fine furniture. For as we prepare to market this unit nationally, we will continue to sell the speaker for $1400. The reason has nothing to do with any inherent magic or any exorbitant priced parts. The reason is that the unit costs a miniature fortune in labor for several reasons: (1) it is made with heavy, bulky parts which cabinetmakers find take considerable time to place carefully; (2) it is built in sections with great lengths of time needed for glue to dry; (3) it is made with rather precise measurements which take patience and skill to lay out; (4) it is heavy to move while being built; and (5) it is exceedingly expensive to deliver to a client. These are five very important reasons.

If you are (1) patient, (2) willing to personally absorb our five reasons as listed above, (3) are a fairly skilled person in carpentry (nothing too difficult), (4) are fairly careful in making measurements and drawing lines, you can have this same unit with the very same performance for about $300 in materials and the sweat of your brow.

Each channel of the stereo transmission line has an effective length of 12 feet for a 1/4 wavelength of about 21 Hz. Since the initial length of the first section of the line is 6 feet, it is possible to absorb much of the back wave reflection which might cause a problem at 64 Hz. Fillets are used throughout to insure rigidity. The corner of the transmission line, while easy to construct, has been designed to augment the output of the system. This becomes one of the most efficient genuine sub woofers you can own. The "in-line" resonance of the woofer is about 12 Hz, and this together with the highly damped resonance results in very low low frequency distortion.

Those who have heard or have purchased the $1400 version of this sub woofer admit it is the deepest ranging, yet most accurate bass reproducer they have ever heard. Some audio cognoscenti who have listened have stated that the only deeper ranging bass reproducer they ever heard were infinite baffle enclosures of brick and concrete of far greater size than the PERFECTIONIST AUDIO SUB WOOFER.

There are other sub woofers in production which look like large acoustic suspension loudspeakers. There are others which look like end tables. There is no doubt that ours is larger. However we have taken care in design to make the unit function as a large serving table or credenza. When finished with an appropriate wood veneer or plastic laminate, the unit is less obtrusive in the listening room than any of the other sub woofers on the market. As with any sub woofer, be it a box or an end table or our credenza, it will only be optimized when positioned properly to interact least with room resonances. Our credenza functions more flexibly in most rooms than do other units.

We invite you to read this manual carefully several times before beginning construction. We think the plans will go together in your mind's eye very easily. Once the task at hand is grasped, begin to look forward to a very rewarding result.

SPECIFICATIONS

FREQUENCY RESPONSE: (4 pi measurement)

TOTAL HARMONIC DISTORTION:

FREQUENCY RESPONSE VERSUS DISTORTION: (worst case)

EFFICIENCY :

MAXIMUM SOUND PRESSURE LEVEL:

POWER HANDLING CAPABILITY:

DIMENSIONS :

INSTRUMENTATION FOR MEASUREMENT:

PERFECTIONIST AUDIO SUB WOOFER: CONSTRUCTOR'S MANUAL & INSTRUCTION MANUAL
Available only from Perfectionist Audio Ltd.

ASSEMBLY INSTRUCTIONS: PERFECTIONIST AUDIO SUB WOOFER

These general instructions list all basic materials including lumber for building a "state-of-the-art" sub woofer system. This system is an augmented stereo transmission line. There is a separate line for each channel. It is designed so that the bass sources can be placed close to the mid-treble sources making phase and transient response adjustments possible. (Center channel sub woofers by definition, must ignore phase and transient response considerations.)

GENERAL CONSTRUCTION

Construction has purposely been made simple by the design, which avoids sharp bends and angles. The size of the cabinet makes tuning of the system rather uncritical when built to these specifications. The diagrams supplied in the Appendix should be self-explanatory. The lumber recommended is 3/4" minimum. It can be built from larger stock, but you would have to adjust all measurements from our drawings to the scale of your larger stock. Some lumber yards will cut your large pieces to your order.

There are only two primary considerations which make this woofer second only to some units in concrete enclosures. The design is large enough to eliminate worry about proper tuning or loading. Upper most must be (1) rigidity and (2) air tightness.

All joints of all large boards including the baffle boards will be braced with 2" wood fillets, screwed in place every three inches and finally caulked for an air tight seal. In each channel there is a wall which divides the top and bottom of each transmission line. This wall must be fitted in place with rabbet joints for cabinet rigidity. As this wall is fitted in place in its rabbet joint, it must first have been liberally coated with epoxy glue. All places where wood joins must be spread with epoxy glue. After each piece is fitted, wherever there is a wood joint, use the silicone caulk liberally for a seal. If you purchase the caulk in black, after sealing you might hold 8 portable light behind the seal and inspect the joint from the other side. If you see light, re-seal the joint.

Careful attention must be given to the installation of the 1" birch dowel rods. If not properly installed, they will resonate. After locating the centers for the birch dowels on the cabinet's center divider wall which divides the two channels, drill holes completely through this board. Locate the same centers on the front and rear walls (outer walls) of the cabinet and drill a hole just 3/8" deep. Cut your dowels to fit flush with the interior of the cabinet's center divider wall and fit all the way through to the countersunk hole in the front or rear of the cabinet. Now you are ready to install the dowels. Push the dowel in place. This should be a tight fit. After the glue is dry, apply a small bead of silicone caulk around the circumference of each dowel at the center divider wall of the cabinet and at the countersunk hole where it is recessed. This exercise may appear necessary only when elephants tap dance on your cabinet, but we assure you that it is not strength which counts here, it is rigidity and air tightness. A cabinet which is not rigid, as rigid as you can possibly make it, will make its own resonances when the speaker is played. This is especially important in woofers. For the resonances in the woofer interacting with the resonances of the cabinet will lead to peaks and dips in response, not to mention differences in the response of the actual transmission line system from the response of the radiated response of the cabinet. With our directions followed, you are assured the cabinet will have no sound of its own. The only sounds produced will be those of the program input.

When joining any large boards in this project, and most are large, you must take the time to carefully brace these boards and clamp them until the glue is dry. This takes time, but the rewards are worth it.

For the exterior cabinet walls veneered chipboard may be used; or veneer applied later. For a greater variety of finishes and for greater durability a wide selection of plastic laminate is available from Pionite, Wilson-Art and Formica. For cosmetic appeal grilles should be installed at each end to cover the drivers and their respective ports. Note that the driver baffle boards are recessed so that a grille can be installed in the recess. Leave, at least 3/8" between the driver face and the back of the grille, so that the driver will not flop against the grille on strong bass wave fronts. We recommend that the framework for the grille have its perimeter completely surrounded with Velcro for a tight fit and for freedom from resonances.

SPECIFIC CONSTRUCTION STEPS

Step A.

Assemble all of the tools you will find necessary for this project. There is nothing more aggravating than trying to go on to the next step only to find you must borrow or buy the necessary tool the next day.

This manual is designed to use the simplest of tools. We suggest you use tools with which you are familiar. If you are more familiar with tools of greater sophistication than we suggest, use them to accomplish the tasks outlined more easily.

MINIMUM TOOL LIST:

Step B

Purchase all of the materials (read: all) you will need to build the PERFECTIONIST AUDIO SUB WOOFER. You will find some of the most minor parts will be the most difficult to locate. Shop! Look for good deals at building supply houses, as you will most likely take a bath on the foam. You are to buy the least expensive polyurethane foam used by upholsterers. We would like to say cheapest, but in relation to other parts of this speaker the foam is one of the most extensive parts. If you do purchase the foam from an upholsterer, do yourself a favor by paying him the extra five to eight dollars to cut the material to size. This is a time consuming, messy chore. Have access to all of these materials before you begin to build the speaker.

Step C

Take all measurements from the drawings in the Appendix of this construction manual. Lay out all measurements before you do anything else. It is possible to make this sub woofer from four sheets of chipboard only if you lay out all measurements in advance. One false move, and you must buy an additional sheet. Care in taking these measurements and laying them out now will save untold time and emotional grief later

Setp D

Using the edge guide and following your lines carefully, cut the largest pieces from each sheet of chipboard. Change blades frequently. Cut carefully as chipboard enjoys living up to its name. You will find this order of cutting will make the smaller sections easier to cut.

Locate the two transmission line tunnel plates. One end edge of each must be trimmed to an angle of 85 degrees as these pieces are cut from the chipboard stock. This is important for later construction.

Step E

After cutting all of the large sections from the 4' x 8' sheets, with just as much care and attention cut the smaller sections from the remaining pieces, You now have cut the major structural parts of the speaker.

Measuring carefully to allow for the counter sink in the front or rear of the speaker and for the width of the cabinet's center divider board, cut all 1" dowel rod to size. The sizes will be (2 pieces 11 3/8" each) and (26 pieces 11 3/4" each).

Finally, cut the wood fillets to size from the dimensions given. Careful! These are tight fitting. There may be some final trimming necessary. N.B. Never glue and screw a fillet in place unless you are sure it will not be too big for the allotted space. If it is glued and is too big, the damage is irreparable. If it is fitted and trimmed before it is glued, there should be no problems.

Step F

Take measurements from the Routing Guide in the Appendix beginning at the top of each panel. Next check those measurements. Note that there will be no fillets at the tunnel plate of each channel as enough cabinet volume has already been used. The tunnel plates are routed and recessed. It is essential that the tunnel plate routed channels provide a snug fit. The tunnel plate line must be even and level. Rechecking measurements is not being too careful. Finally, check one board against another to make sure lines to be routed will line up with one another.

Take the same care and attention to locate the lines in both the top and bottom of the speaker which will be routed to hold the cabinets center divider board.

Measurements done, carefully route a 3/4" line where indicated to the standard 3/8" depth.

Step G

In both the front and rear panels of the speaker, locate the exact centers into which the 1/2" birch doweling will be counter sunk. Note that the measurements are the reverse for each channel as the channels fire from opposite ends of the speaker box. With the power drill and an arbor, you will make a counter sink of 3/8 " for each dowel.

A helpful hint! Locate a depth of 3/8" on the arbor. If you take some masking tape and carefully wrap it about the end of the arbor many times, the arbor will have a depth guide for 3/8".

Take measurements for the exact centers of the dowels on the speaker cabinet's center divider board. These holes will be drilled all the way through the chipboard. It is easier this way. Just make sure the measurements are correct.

Step H

You are now ready to begin cabinet assembly. Note that all joints,with few exceptions, are butt joints braced with 2" square fillet. The fillet is glued with epoxy, as is the joint in which the fillet fits. Next each fillet is screwed in place with 1 1/2" flat head wood screws every three inches. Seams on either side of a fillet will be sealed with silicone (RTV) caulk for air tightness. Do not spare the caulk. Do not believe the myth that epoxy glue dries immediately. Leave plenty of time for the glue to dry and time to wipe away excess epoxy glue. Large sections should be clamped and left to dry for 12 hours or longer.

Words of caution. Every place wood pieces join, epoxy glue will be used. In most circumstances only reasonable care need be exercised in applying the glue as excess glue will squeeze under pressure and can be wiped away. The exception to this is the routed channel in the top and bottom of the speaker which will be fitted with the speaker's center divider board. At these two locations, it is essential that only a minimum of glue be applied with something like a finger of a rubber glove or finger cot well into the groove; but with no excess glue. Excess glue can build up in this area and prevent completion of the speaker cabinet as a result of a hump in this area of the speaker.

A helpful hint! These fillets are going to require that you earn a set of sore arms and shoulders and a blistered set of hands. If you have access to a power drill with a variable speed chuck, you can drive all the screws with the drill.

When attaching any board to another via fillets, drill starting holes for the wood screws and counter sink those holes before you begin any of the gluing, screwing or sealing.

In the same light, remember to drill wood screw starter holes and counter sink them on the top and bottom of the speaker where the cabinet's center divider board will be attached. This must be done before beginning this assembly step.

When completed, these fillets will establish primary bracing for the bottom of both end panels and the bottom edges of both the front and rear panels of the speaker. All of this is being done in the name of air tightness and rigidity.

Step I

Locate the front and rear boards of the cabinet. Designate the bottom edge of these panels.Mount the fillets which will secure these panels to the bottom of the speaker. Follow STEP H.

Step J

Locate the cabinet's center divider board. This board will be 69" long. We will be preparing this board for final construction.

Step K

This is one long set of steps which should be done at one time. It deals with the installation of the center divider board.

Step L

This step is to prepare the cabinet for lining with damping material.

Step M

This step will line the cabinet with damping material.

Step N

Along the end edges of both the front and rear of the speaker drill holes and counter sink them every 3" for fillets. These fillets will be mounted as per fillet mounting instructions in STEP H. These fillets, when dry, will be used to secure the end of the cabinet. Care should be taken here to make sure the edge of the fillet to meet the speaker top is 90 degrees.

Glue the fillets in place and attach with screws. Use silicone seal on the edge bounded by the front and rear of the speaker.

Step O

This step will prepare and mount the end panels (baffle boards) of the cabinet.

Locate where the driver is to be mounted on each baffle board. With each driver comes a template with directions for the necessary rebate to be routed to allow flush mounting of the driver. Make a 7/16" rebate for the driver. CAREFUL: This must be precisely done. Sloppiness here may break the speaker mounting holes or prevent proper alignment of the speaker on the baffle.

Drill the holes necessary and as indicated on the KEF instructions for the T nuts.

Glue end panels in place. Drill holes every 3" for wood screws. Counter sink holes. Firmly screw end panels to fillets on the front and rear of the cabinet for this purpose.

Step P

Trim foam blocks to fit the end of each channel. When trimmed to fit, attach with white glue to the inside of the speaker cabinet in each channel.

Step Q

Mount the top of the speaker to the assembled box. Be sure to screw and glue the top to each edge it meets: i.e., the front, the rear and the center divider board.

Be sure to use glue sparingly lest the cabinet top bow.

Attach screws very firmly as this board cannot be sealed with silicone, because the joint cannot be reached.

Step R

Mount the base of the speaker to the bottom of the speaker cabinet as shown in the Appendix.

Because of the size and weight of this speaker cabinet, it highly advised that castors be added. Since castors come in many sizes, it is difficult here to make any hard fast rules about installation. Make sure the castors purchased are rated at 400 pounds per set. Be sure to purchase the appropriate castors for your application: i.e., units are available for carpet or for hard surface floors.

The castor should stick out from the base of the cabinet just enough to move the speaker. If needed, you may add plates to the base of Speaker to create a raised surface for mounting the castors. Generally, the castor should extend just 1/4" below the speaker cabinet base.

Step S

The finish for the cabinet will now be added. Be it wood veneer or plastic laminate apply according to directions supplied by its manufacturer. Use router veneer trimming attachment to make edges flush.

Speaker ends may be veneered or may be painted flat black.

Rough edges of the ends of the cabinet will be slowly built and filled with wood spackle or wood putty and sanded smooth. When completely dry, these edges will be veneered or painted also,

Step T

On the rear of the speaker cabinet and near the bottom, you will mount the cannon XLR connectors. With an arbor, drill holes to accept the XLR connectors. Properly in phase (copper on pin l and silver on pin 2) for each channel, attach the wires from inside the speaker cabinet to the XLR connectors. Through the hole which will accept the driver, tighten the XLR connector in place, then seal with silicone seal. Seal thoroughly.

Step U

Finishing touches.

Step V

Paying great attention to detail, attach the hot wire to the hot pin on the KEF driver for each channel. Attach the silver lead to the driver in each channel to the remaining pin.

Using the supplied T nuts attach the KEF drivers to the baffle boards. WARNING: Great care must be used to start the T Nuts into the shipboard. If too much pressure is attached these "ears" for holding the driver in place will break. Slightly tighten each of the four screws. Only after the driver is pulled rather tightly to the baffle board is it safe to secure the drivers as tight as possible. This must be done in this manner.

Step W

Turn to the instruction manual portion of this book to find out how to hook this sub woofer system to your existing system. Instead of taking any more directions, after connecting the PERFECTIONIST AUDIO SUB WOOFER to your system, you can give it some orders and directions. You will be surprised how well the sub woofer obeys, if you have followed directions.

PERFECTIONIST AUDIO SUB WOOFER: INSTRUCTION MANUAL

Your dual channel sub woofer is now ready for set up and testing. Preferred set up is with an electronic crossover and a separate stereo power amplifier, with the levels set for the lowest frequency at which the mid-treble speakers can handle bass transients flat. While this woofer system is flat to beyond 600 Hz, a low crossover point assists in the important steps of transient testing. Additionally, it makes no sense at all to use a sub woofer for reproduction of the mid range. We assume you bought the mid range speakers because you liked them for that purpose.

For speakers like the ROGERS LS3/5A, JR 149, SPENDOR SA-l and speakers capable of even deeper bottom end, we recommend a crossover point of l00 Hz. For speakers like the BRAUN Output C, ADS 200, VISONIK D-30 or D-50, we recommend a crossover point of 125 Hz. Finally for speakers with good, but not deep ranging bottom end like the SPENDOR BC-l, QUAD ESL, FRIED MODEL R. we recommend a crossover point of 80 Hz.

We recommend a crossover with a steep slope of about 18 dB per octave, as a general rule. While there is argument about whether one uses Butterworth filters or some other configuration. It must be noted that the argument cannot overlook the fact that any crossover induces some phase shift; Butterworths on the order of 90 degrees per pole (6 dB increment). A well designed electronic crossover of any type will be easier to live with than a poorly designed one of a specific type recommended by some well wishing engineer. Please remember that both high and low signals pass through the crossover. If the crossover is designed to sound like a $200 receiver, then no matter how good the preamplifier is that you are using the music will be degraded to the level of the quality of the crossover.

We unreservedly recommend the Mark Levinson Audio Systems LNC-2 Electronic Crossover. It is excellence without par, but is expensive. The performance is unsurpassed with this woofer. Also interesting and useable are crossovers from Janis Audio Associates, DB Systems and R.A.M, Audio. At the time we go to press these are the units we have tested and approved. At no time could we recommend the use of an AUDIO RESEARCH vacuum tube electronic crossover with this woofer; models EC2, EC-4 and EC-3. They will provide an inaccurate, woolly bass response unless their respective power supplies are heavily modified. This is true of that company's SP-2 and SP-3 preamplifiers in conjunction with this woofer system.

ADVANTAGES OF BIAMPLIFICATION

There are, at least, three advantages to biamplification. One is acoustical. It allows you to use your mid-treble speaker to its optimum parameters without audible stress when you try to produce natural bass from it. It allows the bass driver of your mid-treble unit to work less and produce greater accuracy, thus greater definition.

There is an efficiency advantage to biamplification. Since biamplification gives a four fold increase in effective power, there is little chance you will need behemoth amplifiers, which usually sound less accurate than smaller ones. While dynamic range capabilities are increased, there is little possibility of clipping. Since each amplifier works in its own much more limited frequency range, there is far lower distortion of an intermodulation type produced in the amplifiers and by the speakers.

Finally, biamplification requires electronic crossovers which by their very design eliminate large power losses of the passive crossovers. Damping is retained intact with electronic crossovers. These active devices have no loss or gain in damping factor; important when using this sub woofer. Electronic crossovers usually allow the user to match levels precisely between the mid-treble drivers and the sub woofer system. In a passive crossover this is difficult to accomplish, and when accomplished often leaves a great deal to be desired. Electronic crossovers when designed well allow the blending of the mid-treble drivers and the woofer at the crossover point with respect to phase to remain intact. In fact a good electronic crossover provides for linear response through the crossover point.

ELECTRICAL PHASE: MID-TREBLE AND SUB WOOFER

Since this is a stereo sub woofer system being used in conjunction with a pair of fine stereo speakers, electrical phasing should be a simple matter. First, check that both drivers of the sub woofer system are wired in phase; i.e. copper to hot and silver to ground. Trace these leads back to the power amplifier to see that the left driver is connected to the left output and the right driver is connected to the right output. Check the bass amplifier inputs to see that the right channel input leads to the right channel output of the electronic crossover. Do the same for the left channel input to the bass amplifier to the left channel output of the electronic crossover. Finally check to see that the left channel input to the electronic crossover is plugged in to the left channel output of the preamplifier. Do the same for the right channel. While simplistic, this needs to be stated as it eliminates 90% off all problems in this area caused by incorrectly connected leads.

The stereo mid-treble speakers you will be using might be in phase. We say might, because some units are intentionally wired out of phase at the factory for reasons only the manufacturer knows. So assume that the stereo pair of speakers are internally in phase. Perform the same checks of leads from the speaker (each one separately) back to its amplifier. Then check the leads from the amplifier to the electronic crossover. Finally check the leads from the electronic crossover to the preamplifier output as was done for the woofer system.

In 99 cases out of l00 your speakers are now correctly in electrical phase.

ACOUSTICAL PHASE: MID-TREBLE AND SUB WOOFER

Much is being said lately about phase and hearing. Several speakers are marketed employing special features to eliminate phase distortion (cancellation). This is not electrical phase as discussed above, but is acoustical and is related to the placement of the speakers, the speed of the speakers and the characteristics of the listening room. We intend to discuss optimization of the PERFECTIONIST AUDIO SUB WOOFER with virtually any speaker in a box and those of a bipolar response like Magnepan, Magneplanar and QUAD ESL. There has been much said on this subject in the past few years. Much has been true. We will explain the truths again, and put the myths to their well deserved rests.

In your listening chair, you should have all of the music arrive at your ears within the same time frame (phase) in which it was recorded. We will not deal with multi-track multiple mono discs here. There are some who would have you believe that to place your main (mid-treble) speakers in phase with your sub woofer is an unachievable Herculean task. This is not true for woofers. Woofers produce notes with long enough wavelengths that make this task rather uncritical.

This phasing task while uncritical will take time and patience. It is best to have the mid-treble speakers and the woofer on the same plane as you look at them. However since this is a woofer installation, you may have the mid-treble drivers removed from the woofer by as much as three feet. While this may sound shocking to phase fanatics, one need only listen to a set of Magneplanar Tympani III speakers. While the voice coil of the speakers are nearly perfect planes, there are two sets of drivers; mid-treble and woofer. The typical set up of Tympani III speakers is mid-treble to the right and mid-treble to the left with the woofer panels about three feet to the rear and in the center.

We say all of this, because balancing the system is far more critical than placement when our general guidelines are followed.

BALANCING THE SYSTEM

THE ROOM

We will present several approaches to balancing the system. One will be directed toward the technically oriented person with great amounts of technical equipment available who would object if we did not include this approach. The other approach will be geared toward the non-technical or semi-technical music lover who has little test equipment at his disposal, and involves little more than utilization of a record or test tape and some careful listening. For this non-technical balancing approach a Sound Pressure Level Meter is not needed, but could be used (C weighted or Flat.)

In balancing, with all the directions we will be giving, it would be nice to know what it is that we are trying to achieve. We will be seeking the optimum placement of the mid-treble speakers and the sub woofer for the flattest response and best stereo imaging through the crossover point. Why the crossover point? If your midtreble speakers have poor linear response, there is little that balancing can do for them. The same is true for the woofer. However if we balance the two sets of speakers for ultimate smoothness, flatness through the crossover point, it should be virtually impossible to detect when one set of speakers is playing and the other is not.

To begin, all rooms have waves. All rooms! Despite what you have been told lo these many years, waves are not bad in all cases. Your room will have four corners where the floor meets the walls, and four corners where the walls meet the ceiling. Standing waves are not necessarily bad. They result from the boundary conditions at these corners. These standing waves are more critical for mid-treble speakers than for sub woofers. Sub woofers create wavelengths of over 10 feet and are less critical. But a brief understanding of this will assist you in room placement of your speaker system.

With woofers there is less opportunity of standing waves to be excited by reflections from walls because of the long wavelengths. This does not mean that placement of a woofer along a wall will have little effect on the woofer, but rather more important is how that wall is bound by its corners. The standing waves relevant to bass frequencies are called eigen frequencies (tones) and are dependent upon the shape, dimension and furnishing of the room. The desire is to distribute these standing waves evenly. This is accomplished more easily in a rectangular room than in a square room. It is accomplished best in a room where no two walls are parallel. This creates a standing wave atmosphere where standing wave frequencies are never clumped together, but are spaced irregularly.

In a room where standing waves are allowed to be produced in clumps in some areas and free in other areas there are problems created. Music is periodic. When music is produced in clumps it creates nodes. These nodes create peaks in response. Of course that same room with nodes will have, by its very nature, anti-nodes which create dips in response.

To examine this phenomenon yourself, place your sub woofer along one wall and walk about the room while playing some program source with deep bass. You will easily notice that bass in some areas of the room is more profound (visceral) in some areas and rather lacking in others. Our task is to eliminate as much as possible this phenomenon.

The standing wave for a particular mode is excited the most when the sound source is placed at the particular anti-node and excited least when placed at the position of the node. The best suggestion is to place your sub woofer at the anti-node. In most rooms this will be three feet from the nearest corner. It will generally be one to two feet from the nearest wall.

BALANCING THE SYSTEM: THE TECHNICAL WAY

To balance the system with test equipment, you will need the following equipment or its equivalent: General Radio Pink Noise Generator, General Radio Noise and Vibration--Analysis Meter, B & K Calibration Microphone.

Place the music system where you assume it will perform best. Then apply pink noise to a level where 0 dB = 85 dB SPL on the Noise and Vibration Analysis Meter. From the listening position, sweep the room for eigen tones with 1/3 octave centered bands. For greater accuracy, sweep with 1/10 octave bands. Record your information.

Since an 18 dB per octave crossover will still have the woofer producing some output at 200 Hz and the mid-treble unit producing some output at 75 Hz, this area would be the most critical for your concentration. However should you notice any strong nodal or antinodal indications from 10 Hz to 240 Hz, you should reposition your speaker systems to eliminate them. Each time you move the speakers, re-sweep the room.

After the speakers are optimally placed, and frequency distribution noted through the crossover point, adjust your electronic crossover to add or subtract bass or add or subtract treble to smooth the response. After each change, re-sweep the system. Do this until the system is virtually flat from 75 Hz to 240 Hz. To fine tune the system, do the same procedures to smooth response from 10 Hz to 25 KHz.

BALANCING THE SYSTEM: THE NON TECHNICAL (EASY) WAY

We have found that most music lovers are not extremely technically oriented. Those who are usually do not have access to the kinds of test equipment we mentioned above. Our non-technical method for balancing the system is performed with far greater ease. Believe it or not, when conscientiously performed, it yields the same results within 1 or 1 1/2 dB.

An important note for any sub woofer user: Sub woofers are seductive devices. It is easy to try to balance a woofer with a selection of music which has awesome bass. But do we know how that bass was equalized? No! Do we know whether that particular selection actually sounds real? No! Most manufacturers of sub woofers recommend that sub woofers be balanced with recorded material which contains little bass response below 60 Hz. This will surely take you below the crossover point for balancing purposes, but will have very little opportunity to overwhelm you. We have an ultimate test record to recommend in this light: After The Ball: A Treasury of Turn of the Century popular Songs on Nonesuch H-71304. We have swept the record and found that side one, cuts one and two contain no notes below 60 Hz.

Turn on your system. Play the Nonesuch record, side one, cuts one and two. Turn up the bass until the piano notes or the singer begin to sound as though they have just a bit too much bass response; are too heavy. Then turn the crossover back just a slight amount until this disappears. To double and triple check by this method only makes the balancing more accurate. Your system should now be completely balanced. Should you have noticed some holes in bass response or treble response while performing these tests, you might move your speakers until this changes, then perform the balancing tests again.

Happy listening

ADDENDA

What do you do if you try to balance the woofer with the midtreble units and find the crossover does not have enough latitude to permit perfect balance?

This is no problem. It is a result in a slight mis-match from your power amplifiers. Each power amplifier needs so many volts in for so many volts (so much power) output. If your amplifiers have gain controls, you can adjust for this imbalance with the gain controls, then re-balance the system.

What power amplifiers does PERFECTIONIST AUDIO recommend for use in a biamplified system?

We feel the choice is wide open. However our biases (pun intended) go something like this. We would never put a vacuum tube amplifier on this sub woofer, because they seldom have the damping factor capable of controlling it. For the sub woofer we would easily recommend one of the many fine medium power amplifiers: Dunlap-Clarke 250; Bryston Pro 3B; Quatre DG-250 Gain Cell, or just about anything Linear, clean, and capable of producing bass to below 10 Hz. in the 100 watt per channel area into 8 ohms.

The mid-treble amplifier will be very dependent upon the amount of power the mid-treble units are capable of using without being destroyed. You be the judge. Among our recommendations for accuracy, transparency and definition are the following: Audio Research Dual 76A; Audio Research Dual 76; Futterman H-3; Paoli 60 M; Quatre DG-250 Gain Cell; Marantz 9 in pairs;Marantz 8B; Bryston Pro 3B; Stax DA80, and etc.

Most classic transmission lines are damped with long fiber wool. Yours is not. Why?

Transmission line technology has blossomed with our English friends. They had access to large amounts of long fiber wool at reasonable prices. In an English transmission line the purpose of the long fiber wool is to effectively damp all rear wave resonances from the woofer. If any rear waves escape from the port, they are to be in phase with those emanating from the driver itself. Long fiber wool did this job well because of its variable length and variable density. These are its primary properties. However long fiber wool is supplied in balls like cotton. The long fiber wool must be carefully spaced within the line, glued in place, then combed out like the hair on a longhaired dog. This is touchy. It can lead to great amounts of unit-to-unit variability because of placement, amount and the amount combed out. Far worse is another problem. In use the wool has a tendency to grow limp. When limp, the original properties are virtually gone. The only remedy is to recomb the wool in the line.

We opted for lightest weight urethane foam in our sub woofer. Frankly, any damping material will work when properly designed into the speaker. We find this light weight urethane does everything the long fiber wool does, but never needs readjusted. It has all of the pluses and none of the minuses. Additionally, it is available in the United States at reasonable cost and few are alergic to it. Long fiber wool is available from only a few sources in the United States at a price of $5 or $8 per pound. We feel we have chosen a very viable alternative. Since our sub woofer was designed for use with light weight urethane foam, we do not recommend substitution of wool for foam. We could not claim any performance with that substitution.

SOURCES FOR KEF DRIVERS

SOUND ADVICE
536 State Road
Emmaus, Pennsylvania 18048

TRANSLINE SOUND
452 Poplar
Wyandotte, Michigan 48192

CUSTOM SOUND SERVICE
8460 March Road
Algonac, Michigan 48001

J.P. Enterprises
P.O. Box 458
Placentia, California 92670

E & E Audio
2816 Church Avenue
Brooklyn, New York 12226

AUDIONICS
8600 N.E. Sandy Boulevard
Portland, Oregon 97220