mirror-textfiles.com/fun/q&a

     THE MOST COMMONLY ASKED QUESTIONS ABOUT BUILDING ENCLOSURES

Many JBL users build their own loudspeaker enclosures.  Their audio 
skills range widely from novice to expert.  From the thousands of 
letters and calls we have received addressing the subject of 
loudspeaker enclosure construction, we have determined the most common 
questions and present the following Questions and Answers.  The 
particular questions listed attempt to answer as many questions as we 
feel are necessary to provide enough information to build an enclosure 
which will allow your JBL loudspeaker to operate to its potential.  The 
questions selected here concentrate on vented "bass reflex" enclosures, 
since low frequency horns are fairly complex, and many good tested 
designs exist.  Also, it is often more econonomical to buy a bass horn 
enclosure than to build one.  Vented box enclosures are by far the most 
popular enclosure type.  Vented boxes are finding increasing use by 
touring sound companies, displacing existing horn enclosure designs 
because of the greater low frequency power output and extended low 
frequency capability they offer when used in arrays.  In addition to 
their simple design requirements, vented loudspeaker enclosures offer 
flexibility of design in shape, weight and component complement, and 
usually produce the best results obtainable from modern loudspeaker 
drivers at the lowest cost.

[1]
Q: What makes a good vented enclosure?

A: Basically, an enclosure serves to partition the front and rear of 
the driver's cone, preventing the opposing air pressure changes 
produced by cone motion from cancelling, and allowing the radiation of 
sound from the front of the driver only.  In addition, vented 
enclosures allow the compressibility of the air inside the enclosure to 
work as a more active part of the "system" consisting of driver and 
enclosure.  Beyond these two basic functions, a low frequency 
loudspeaker enclosure should do absolutely nothing, that is, it should 
add no effects of its own--no vibration, no tonality, no motion--
nothing to interfere with or absorb acoustic energy produced by the 
driver.

[2]
Q: Is it possible to get low, punchy bass from a small enclosure?

A: Yes, if the driver in the enclosure is designed for low bass 
operation in a small enclosure.  Unfortunately, it's usually a small 
driver that can work properly in a small enclosure, and that dictates 
that lower sound levels will result from the small amount of air such a 
small driver can move.  Larger boxes (with larger bass drivers) produce 
more bass, smaller boxes produce less bass.  It's a fact of life, like 
the fact that it takes a bass viol, a tuba, longer piano strings, or 
very large organ pipes to produce bass energy in the air.  Low bass 
requires that more air move, and bigger boxes contain more air that can 
be put to work making low bass.  

[3]
Q: Can I get more bass from my enclosure by installing a bigger driver?

A: A given enclosure will not automatically produce more bass when a 
larger driver is installed, in fact the opposite is often the result.  

[4]
Q: What about putting two drivers in the enclosure to increase bass?

A: Placing two bass drivers in an enclosure designed for one will 
usually produce less bass and more midrange output, and will upset the 
operation of the driver-enclosure system because each driver will 
behave as though it is installed in an enclosure which has only half 
the internal volume of the original enclosure (with one driver).

[5]
Q: What should I do to use two drivers (for more bass)?

A: There are two alternative possibilities.  When using two identical 
drivers, you can build an enclosure with twice the internal volume of 
the original enclosure that contained one driver, or you can duplicate 
the original enclosure and stack the two.  As the latter alternative 
suggests, when building the double enclosure, it's necessary to treat 
the enclosure as if it were two enclosures--you must double the porting 
used on the single smaller enclosure--although it is not necessary to 
divide the volume of the double enclosure unless two different driver 
models (e.g. E130 and E155) are used and their interaction would be 
undesirable.  A usable example of this might be a 227 liter (8 cubic 
foot) enclosure divided into two chambers so that the E130 occupies 57 
liters (2 cubic feet) and the E155 occupies 170 liters (6 cubic feet).  
In this case, the ports tuning either chamber to the same desired 
frequency will be quite different.

[6]
Q: What does port or enclosure "tuning" mean?

A: In exactly the same way the resonant note from a bottle can be 
raised and lowered by adding or pouring out liquid to change the 
bottle's air volume, enclosure tuning is affected by the ratio of air 
volumes in the port (the bottleneck) with its attendant flow 
resistance, and the enclosure interior volume.  Tuning of loudspeaker 
enclosures is a result of manipulating the differences in effective air 
mass between the enclosure interior and the air in the port.  The 
bottle-like nature of a vented enclosure is known as a "Helmholtz 
resonator."  The ports or ducts in a vented enclosure work only over a 
narrow band of frequencies near the chosen tuned frequency, producing 
the same effect noted when blowing across a bottleneck--a single 
distinct pitch.

[7]
Q: Is it always necessary to use a port for good bass?

A: JBL uses vented enclosure designs because they are superior to 
sealed enclosure designs in several important ways--as long as it is 
possible to tightly control the loudspeaker driver parameters in 
manufacturing as JBL does.  Vented designs produce lower distortion at 
the lowest operating frequencies, afford the driver protection against 
mechanically destructive large cone excursion, and better enable the 
driver to absorb and utilize its full power rating from an amplifier 
when operating at low frequencies.  It is important to keep in mind 
that porting and tuning an enclosure provides air loading for the bass 
driver down to frequencies just below the Helmholtz frequency, but does 
not provide any loading for the driver at frequencies below that, such 
as subsonic turntable rumble, record warp or microphone wind pickup.  
If you intend to operate a sound system at high power levels, we highly 
recommend an electronic high-pass filter to eliminate subsonic input to 
the power amplifier(s).  This will substantially increase the available 
useful power from the amplifier which will then only operate in the 
audible frequency range.  Such a filter is the UREI model 501 Sub Sonic 
Processor, or the built-in sub-sonic switches of the JBL Electronic 
Frequency Dividing Network model 5234A.

[8]
Q: Where should I locate the port(s) with respect to the woofer?

A: Bass reflex enclosures are usually designed to tune from about 100 
hertz and down.  The length of sound waves at these low frequencies is 
over 11 feet, so port placement is not critical.  Ports may be located 
anywhere on the baffle with no change in bass performance; some designs 
even locate ports on the back of the enclosure which works well as long 
as the enclosure is not close to a wall (a couple of port diameters 
away) and there is an unobstructed air path between the woofer and the 
port.  Overall, it's safest to locate the port somewhere on the baffle 
with the woofer(s) far enough away from side walls to avoid interaction 
between port and enclosure wall or the fiberglass insulation on the 
wall.

[9]
Q: What should the ducts be made of?  Is round better than rectangular?

A: Port ducts may be made of anything rigid, such as paper cardboard 
with about a 1.5 mm (1/16") or larger wall thickness.  They can be any 
shape, square or rectangular (such that port area remains constant) and 
made of wood or other suitable material.  It is not necessary to use 
PVC pipe for port tubing, particularly when most carpet stores throw 
away large amounts of heavy carboard tubing of between 3 and 4-1/2 
inches inside diameter.

[10]
Q: What is the relationship of duct length to port area?

A: When port area is increased, independently of other factors, 
enclosure tuning is raised.  If duct length is increased, independently 
of other factors, enclosure tuning is lowered.  To keep the same tuning 
(Helmholtz frequency) you will need to increase duct length as you 
increase port area. 

[11]
Q: How big should the port be?

A: The bigger, the better.  Any port causes some resistance to air 
movement, and so introduces unavoidable losses in output to the system 
as a whole.  The ratios of port area and length and enclosure volume 
determine the Helmholtz frequency tuning.  Mechanical reactance 
elements, stiffness and air mass, control the effective air mass 
ratios.  At very low operating levels, where air in the port does not 
move very fast, a small short port will behave the same as a large 
longer port as far as enclosure tuning is concerned.  At high power 
levels however, the restricted air flow of the smaller port will 
produce output level losses, some de-tuning and at high enough levels a 
small port will cause the enclosure to behave like a sealed enclosure 
with little or no contribution from the port.  To minimize resistive 
losses, the largest practical port should be used.  Computer listings 
of port choices calculated to limit air velocity inside the port duct 
will list duct sizes which are normally impractical.  A 380 mm (15 in) 
diameter port is not an unreasonable choice for a 380 mm bass driver, 
however the necessary length would dictate that such a port might 
itself have a volume of many cubic feet, sometimes equal to or larger 
than the original enclosure.  A good rule of thumb would be to avoid 
ports whose circular area is smaller than at least 1/3 the diameter of 
the driver such as a 127 mm (5 in) diameter port for a 380 mm (15 in) 
driver.  This will usually provide sufficient port area so that the 
port will not "whistle" when the system is operated at high power 
levels near the helmholtz frequency--a sure indication of severe system 
losses and potential power compression and low-frequency output 
limiting.

[12]
Q: Can I use several smaller ports instead of one big one?

A: Yes, however there is a phenomenon associated with air resistance 
resulting from air drag on the internal surfaces of port ducts and 
turbulence at the ends of the ports that requires a duct length 
correction when several ports are used.  For example, when using four 
100 mm (4 in) tubes instead of one 200 mm (8 in) tube (which has the 
same port area but one-quarter the internal surface area), the length 
needed will be slightly less than that needed for the single 200 mm 
tube, perhaps 5% to 10% less, depending on overall enclosure volume.  
These effects exhibited by port ducts is exaggerated by proximity of 
the duct to enclosure interior surfaces or any other type of boundary 
that may cause air turbulence near the end of the duct, therefore it's 
important to keep duct ends away from the rear of the cabinet or other 
obstructions by an amount at least equivalent to or larger than the 
dimension across the port.  If you are using a rectangular port that 
has as one of its sides, an enclosure wall, you might have to use some 
correction.

[13]
Q: Is there a simple mathematical way of designing proper enclosures?

A: Yes, a JBL scientist, D.B. Keele Jr., simplified the work of A. 
Neville Thiele and Dr. Richard Small so that anyone with a pocket 
calculator and a ruler or straight edge can design the right enclosure 
volume and choose the right port or duct for a given loudspeaker 
driver.  JBL offers, at no cost, a four-page "kit" containing detailed 
step by step instructions, written specifically for non-mathematicians, 
showing how to use published Thiele-Small driver parameters in 
enclosure design.  Examples are shown with their results graphically 
represented.  An enclosure design flow chart and enclosure venting 
nomograph are included. 

[14]
Q: Should the enclosure's baffle be removable?

A: This is a question of mechanical strength and rigidity.  All 
enclosures, particularly those intended for rough portable use, should 
be constructed with all sides permanently fixed by glue and screws, and 
sealed air-tight by virtue of well cut and glued joints.  It is 
preferable to mount loudspeakers from the front of the baffle board to 
eliminate the possiblity of reflections from the inside of the 
loudspeaker mounting hole, thus it becomes unnecessary to provide for 
removing the baffle.  Woofer openings are usually large enough to reach 
through in order to work inside the box, for example, to install other 
components.

[15]
Q: Is there a preferred shape for loudspeaker enclosures?

A: There are a number of shapes that improve performance and some that 
cause distinct degradation in performance.  For single, full-range 
drivers (e.g. JBL's LE8T) a sphere is the ideal shape for an enclosure 
because the curved surfaces avoid the diffraction effects of cabinet 
edges, which bend sound waves in a manner dependent on frequency.  For 
multi-way loudspeaker systems, spheres are usually impractical because 
of the large size needed and because of the precise orientation 
required for optimal listening.  Conventional enclosures work best 
mounted flush into a wall where diffraction is controlled by virtue of 
the wall surface, and for free-standing enclosures, tilting, angled and 
curving surfaces may be employed to help reduce or control edge 
diffraction.  The overall shape of the enclosure is relatively 
unimportant except where the shape makes it difficult to build a rigid 
enclosure.  It is best to avoid enclosure dimensions that are multiples 
of each other, such as 1 X 2 X 4 ratios, and strive to use dimensions 
that have somewhat unrelated ratios such as 1 X 1.23 X 1.41.

[16]
Q: What is the best material to use for building enclosures?

A: For home and permanent installation use, high density particle wood 
is the most cost-effective material for general enclosure construction.  
The best wood to use for portable enclosure construction is 14 to 20 
ply per inch Finland birch type.  Birch plywood is very expensive 
however, and a carefully braced enclosure made of high grade void-free 
fir plywood can do the job just as well in most cases.  The thicker you 
can make the cabinet walls, the better the results will be because of 
reduced wall vibration and resonance, but the tradeoff is cost and 
weight.  Enclosure walls should be cut so that edges form an air-tight 
seal when glued together.  Cleats and caulking can also be used if 
needed to insure a good fit and tight air seal.

[17]
Q: Is bracing necessary?  How much should be used?

A: Bracing should be added to the enclosure interior to minimize 
enclosure wall vibration.  Enclosure walls simply cannot be stiff 
enough since wall vibration indicates that energy is being wasted to 
move enclosure panels rather than moving air.  25 X 76 mm (1 X 3 in) 
pine bracing fixed on edge with glue and screws to the enclosure walls 
will help provide the minimum necessary stiffening without affecting 
the internal volume significantly.  If you are building large subwoofer 
enclosures, bracing with two-by-fours works better, though you should 
take the bracing volume into account since a 3 m (10-foot) length takes 
up 12.9 liters (0.36 cubic foot) of enclosure volume.  

[18]
Q: How should I mount drivers on the baffle?

A: Mount drivers on the front of the baffle whenever possible to avoid 
the reflections from inside the mounting hole.  Heavy drivers should 
normally be front-mounted using Tee-nuts and machine screws or JBL's 
MA15 clamps.  If Tee-nuts are used, apply a bit of Bostic or Pliobond 
type rubber glue to the inside of the nut flange to help avoid losing 
the Tee-nut inside the enclosure when installing the driver.  Baffle 
board construction is much easier if all baffle parts are assembled 
prior to final box assembly.  

[19]
Q: Do I need fiberglass inside the enclosure?

A: JBL uses a 25 mm (1 in) padding of 1/2-pound density fiberglass 
stapled to the enclosure interior on all surfaces except the baffle.  
You should use 100 mm (4 in) thick dacron or 25 mm (1 in) fiberglass on 
at least three of the surfaces of parallel interior walls.  Keep sound 
absorbing materials away from the port(s) as the air velocity inside 
the port can be sufficient to tear off bits of the material and squirt 
them out of the enclosure.  It is not necessary to cover the inside of 
the baffle, but doing so will rarely degrade system performance.  The 
enclosure exterior may be covered with your choice of any suitable 
finish or decoration; this will not affect bass performance and in some 
cases (as with Formica) may help stiffen the enclosure walls.

[20]
Q: Does Fiberglass significantly affect enclosure tuning?

A: No, not unless the enclosure is stuffed full of fiberglass, in which 
case the apparent volume of the enclosure increases by 12% to 20% as 
seen from the point of view of the bass driver.  Stuffing the enclosure 
full with fiberglass is not recommended because it introduces system 
losses, is expensive and interferes with port operation.  The exception 
to this would be a sealed "air suspension" type system enclosure where 
more virtual volume is needed and actual volume is not available, 
and/or where box dimensions which are multiples of each other can't be 
avoided and the fiberglass stuffing will help absorb the internal sound 
reflections.

[21]
Q: What is needed to mount a midrange on the baffle with the woofer?

A: For cone-type midrange drivers, a sealed sub-chamber should be used 
to prevent interaction with the enclosure's bass driver.  JBL drivers 
suitable for sealed-chamber midrange use require only 10 to 40 liters 
(.3 to 1.0 cubic foot) of chamber volume to operate at typical midrange 
frequencies, above 200 hertz.  Subchambers should be constructed 
solidly and liberally lined with fiberglass.  As in the case of 
enclosure shapes, avoiding multiples of dimensions, subchambers should 
be built so as to avoid square and cube shapes in favor of non-related 
numerical ratios.

[22]
Q: Is there any special procedure for mounting a horn in an enclosure?

A: Use of a horn/compression driver does not require any subchamber 
since these devices form their own air-tight seal.  JBL horns such as 
the 2344, 2370, MI-291 and 2380 horn family also seal their own cutout 
opening in the enclosure when properly mounted on the baffle.  Better 
compression drivers are quite heavy, so a brace should be provided to 
cradle the driver to prevent driver movement during shipping.  In 
combination with the length of a horn as a lever, driver mass can cause 
the assembly to tear off the baffle or break the horn if the enclosure 
is handled roughly or dropped.  Driver mass can also tear off the horn 
throat if cabinets are dropped on their backs.


                 CONVERSION CONSTANTS and USEFUL DATA
                ____________________________________


LITERS   FEET^3   INCHES^3  METERS^3     MILLIMETERS  INCHES   METERS
___________________________________    _____________________________
   1.00 =   .03531 =   61.0 = .001          1.00  =    .039  =  .001
  28.32 =  1.00    =  1,728 = .02832       25.40  =   1.000  =  .0254
1000.00 = 35.31    = 61,016 = 1.00       1000.00  =  39.370  = 1.000

TO FIND SOUND WAVE LENGTH: divide velocity of sound by frequency (Hz)
  (SOUND VELOCITY = 344 m/s, 1130 ft/s or 13,560 in/s)

AREA OF CIRCLE = 3.14 x (radius squared)   Note: radius = 1/2 diameter

TO FIND THE DIAMETER OF A CIRCLE WITH EQUIVALENT AREA:
  2 x square-root of (area divided by 3.14)  
  example: area of 9" tube = area of 8" square duct calculated:
  (area) 64/3.14=20.37, square root = 4.51 x 2 = 9.03 (diameter)

VOLUME OF CYLINDRICAL DUCT = circular area x length

VOLUME DISPLACED BY JBL LOUDSPEAKERS: 8" = .05 cu ft, 10" = .1 cu ft, 
12" = .15 cu ft, 15" = .2 cu ft, 18" = .3 cu ft.

JBL LOUDSPEAKER MOUNTING HOLE AND BOLT CIRCLE DIMENSIONS:
mounting holes:
8" = 7-1/16"   10" = 9"   12" = 11-1/16"   15" = 13-31/32"   
18" = 16-13/16"

bolt circles:
8" = 7-5/8"   10" = 9-3/4"   12" = 11-9/16"    15" = 14-9/16"    
18" = 17-3/8"


             BIBLIOGRAPHY of RECOMMENDED AUDIO REFERENCES
            ____________________________________________

FOR AUDIO NOVICES:

BOOKS:

David B. Weems, "Building Speaker Enclosures,"  Radio Shack 
publication, stock# 62-2309

"The CAMEO Dictionary of Creative Audio Terms," Creative Audio & Music 
Electronics Organization, 10 Delmar Avenue, Framingham, MA 01701

F. Alton Everest, "The Complete Handbook of Public Address Sound 
Systems," Tab Books #966, Tab Books, Blue Ridge Summit, PA 17214

David B. Weems, "Designing, Building & Testing Your Own Speaker 
System," Tab Books #1364 (this is the same as the Weems book above)

Abraham B. Cohen, "Hi-Fi Loudspeakers and Enclosures," Hayden Book Co., 
0721

Alex Badmaieff and Don Davis, "How to Build Speaker Enclosures," Howard 
W. Sams & Co., Inc., 4300 West 62nd Street, Indianapolis, IN 46268

Bob Heil, "Practical Guide for Concert Sound," Sound Publishing Co., 
156 East 37th Street, New York, NY 10016

PAPERS:

Drew Daniels, "The Most Commonly Asked Questions About Building 
Enclosures,"  JBL Professional, 8500 Balboa Blvd., Northridge CA, 91329 

Drew Daniels, "Using the enclosure design flow chart," JBL 
Professional, 8500 Balboa Blvd., Northridge, CA 91329 

FOR EXPERIENCED AUDIO PRACTITIONERS AND HOBBYISTS:

BOOKS:

Jens Trampe Broch, "Acoustic Noise Measurement," Bruel & Kjaer 
Instruments, Inc., 185 Forest Street, Marlborough, MA 01752  (617) 481-
7000

Howard M. Tremaine, "The Audio Cyclopedia," 2nd Edition 1969, Howard W. 
Sams & Co., Inc., 4300 West 62nd Street, Indianapolis, IN 46268

Arnold P. Peterson and Ervin E. Gross, Jr., "Handbook of Noise 
Measurement," General Radio, 300 Baker Avenue, Concord, MA 01742

Martin Colloms, "High Performance Loudspeakers," A Halstead Press Book, 
1978 John Wiley and Sons, New York and Toronto.

Harry F. Olson, "Modern Sound Reproduction," 1972, Van Nostrand 
Reinhold Co., New York.

Harry F. Olson, "Music Physics and Engineering," Dover Publications, 
180 Varick Street, New York, NY 10014

Don and Carolyn Davis, "Sound System Engineering," Howard W. Sams & 
Co., Inc., 4300 West 62nd Street, Indianapolis, IN 46268

F. Alton Everest, "Successful Sound System Operation," Tab Books #2606, 
Tab Books, Blue Ridge Summit, PA 17214

PAPERS:

Drew Daniels, "Notes on 70-volt and distributed system presentation,"  
for the National Sound Contractors Association Convention, September 
10, 1985, JBL Professional, 8500 Balboa Blvd., Northridge, CA 91329

Drew Daniels, "Thiele-Small Nuts and Bolts with Painless Math," 
presented at the 70th Convention of the Audio Engineering Society, 
November 1981 AES preprint number 1802(C8).

FOR ENGINEERS:

BOOKS:

Harry F. Olson, "Acoustical Engineering," D. Van Nostrand Co., Inc., 
250 4th Street, New York 3, NY 1957 (out of print)

Leo L. Beranek, "Acoustics," Mc Graw-Hill Book Co., New York 1954.

Harry F. Olson, "Elements of Acoustical Engineering," D. Van Nostrand 
Co., Inc., 250 4th Street, New York 3, NY (1st ed., 1940, 2nd ed., 1947 
both out of print)

Lawrence E. Kinsler and Austin R. Frey, "Fundamentals of Acoustics," 
John Wiley and Sons, New York and Toronto.

N.W. McLachlan, "Loudspeakers: Theory Performance, Testing and Design, 
Oxford Engineering Science Series, Oxford at The Clarendon Press 1934, 
Corrected Edition, Dover Publications 1960.

PAPERS:

Don B. Keele, Jr., "AWASP: An Acoustic Wave Analysis and Simulation 
Program," presented at the 60th AES Convention in Los Angeles, May 
1978.

Fancher M. Murray, "An Application of Bob Smith's Phasing Plug," 
presented at the 61st AES Convention in New York, November 1978.

Don B. Keele Jr., "Automated Loudspeaker Polar Response Measurements 
Under Microcomputer Control," presented at the  65th AES Convention in 
London, February 1980.

R.H. Small, "Direct-Radiator Loudspeaker System Analysis," Journal of 
the Audio Engineering Society (JAES), Vol. 20, p. 383, June 1972.

Mark R. Gander, "Ground Plane Acoustic Measurement of Loudspeaker 
Systems," presented at the 66th AES Convention in Los Angeles, May 
1980.

"Loudspeakers," An anthology of articles on loudspeakers from the pages 
of the Journal of the Audio Engineering Society, Vol. 1 through Vol. 25 
(1953-1977).  Available from the Audio Engineering Society, 60 East 
42nd Street, New York, NY 10165  Telephone (212) 661-8528

A.N. Thiele, "Loudspeakers in Vented Boxes," Proceedings of the IREE 
Australia, Vol. 22, p. 487 August 1961; republished in the JAES, vol. 
19, p. 382 May 1971 and p. 471 June 1971.

Fancher M. Murray, "The Motional Impedance of an Electro-Dynamic 
Loudspeaker," presented at the 98th Meeting of the Acoustical Society 
of America, November 19, 1979.

Mark R. Gander, "Moving-Coil Loudspeaker Topology As An Indicator of 
Linear Excursion Capability," presented at the 64th AES Convention in 
New York, November 1979.

Garry Margolis and John C. Young, "A Personal Calculator Program for 
Low Frequency Horn Design Using Thiele-Small Driver Parameters," 
presented at the 62nd AES Convention in Brussels, March 1979.

Garry Margolis and Richard H. Small, "Personal Calculator Programs for 
Approximate Vented-Box and Closed-Box Loudspeaker System Design," 
presented at the 66th AES Convention in Los Angeles, May 1980.

Fancher M. Murray and Howard M. Durbin, "Three Dimensional Diaphragm 
Suspensions for Compression Drivers," presented at the 63rd AES 
Convention in Los Angeles, March 1979.

R.H. Small, "Vented-Box Loudspeaker Systems," Journal of the Audio 
Engineering Society, Vol. 21, p. 363 June 1973, p. 438 July/August 
1973, p. 549 September 1973, and p. 635 October 1973.

JBL TECHNICAL NOTES:

The following are available at no cost from JBL Professional:

Vol. 1, No. 1 - "Performance Parameters of JBL Low-Frequency Systems"

Vol. 1, No. 2 - "70-Volt Distribution Systems Using JBL Industrial 
                 Series Loudspeakers"

Vol. 1, No. 3 - "Choosing JBL Low-Frequency Transducers"

Vol. 1, No. 4 - "Constant Directivity Horns"

Vol. 1, No. 5 - "Field Network Modifications for Flat Power Response
                 Applications"

Vol. 1, No. 6 - "JBL High-frequency Directional Data in Isobar Form"

Vol. 1, No. 7 - "In-Line Stacked Arrays of Flat-front Bi-Radial Horns"

Vol. 1, No. 8 - "Characteristics of High-Frequency Compression Drivers"

Vol. 1, No. 9 - "Distortion and Power Compression in Low-frequency 
                 Transducers"

Vol. 1, No. 10- "Use Of The 4612OK, 4671OK, And 4660 Systems In Fixed 
                 Installation Sound Reinforcement"

Vol. 2, No. 2 - "JBL/UREI Power Amplifier Design Philosophy"

Instruction Manual - "Motion Picture Loudspeaker Systems: A Guide to 
                      Proper Selection And Installation"

"JBL Sound System Design Reference Manual" ($15)