Rock Mountain Way (2-Way) Prepared for: Transducer Theory Prepared by: Kenneth Stahl, Designer February 15, 2011 Proposal number: 000-0001 Ontrack Inc. 2109A Woodmar Drive Houghton, MI 49931 T 906-231-2939 [email protected]www.kennystahlrock.com Ontrack Inc.
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Rock Mountain Way (2-Way)
Prepared for: Transducer Theory
Prepared by: Kenneth Stahl, Designer
February 15, 2011
Proposal number: 000-0001
Ontrack Inc. 2109A Woodmar Drive Houghton, MI 49931 T 906-231-2939 [email protected] www.kennystahlrock.com
To build a set of Hi-Fi studio quality mixing monitors. Keeping in mind the lifestyle of a recording engineer size matters, trying to keep them transportable is important. Also it will be important to produce High-SPL’s.
Overview
* Develop an understanding for Sound Pressure Levels and what will be the average listening level.
* Examine the design trade-offs that exist in loudspeaker design
* Developing a standard for low frequency response.
* Compare Box-Types.
* Develop a system to minimize diffraction
* Examine Various Woofers (Simulate).
* Examine Various Tweeters.
* Determine Box Size and Makeup.
* Dealing With Standing Waves (Bracing).
* Build Ideal Crossover and examine summations.
* Accounting for a budget and making economically sound choices.
Design Proposal 1
Ontrack Inc.
Introduction
The last chain in a recording studio is no doubt the listen medium. A biased listen
medium is detrimental to the success of a project, studio, engineer, and to the music itself.
Unfortunately most reasonably priced monitor systems are not suitable for actual studio
use. With mass production and profits as a motivation it is no real surprise that this is the
case. The Rocky Mountain Way loudspeaker system is an economical alternative to what
is currently on the market and provides unbiased sound reproduction.
SPL’s
First off defining the SPL capability is the first part of the lengthy design process.
SPL’s or Sound pressure levels are is defined as the physical intensity of sound relative to a
standard reference value. Also know as the measurement of how loud a system is and is
measured in deciBels (dB). In the planning stages of developing a loudspeaker system, it is
necessary to determine what the desired output or how loud? With the design objective in
mind, building studio monitors, an average of measurements was first observed at a com-
fortable mixing level. After which the next step was to push the volume until the level was
both too quiet and too loud. The averaging process for each level was taken by three
measurements throughout the day and can be seen with the following results:
Design Proposal 2
Ontrack Inc.
RESULTS
COMFORTABLE SPL: 89.33 DB
WHAT IS TOO LOUD: 96.66 DB
WHAT IS TOO QUIET: 72 DB
OBSERVED SPL (DB)
DATE COMFORTABLE LEVEL TO LOUD TO QUIET
1-19 @ 4:00PM
1-19 @ 11:00PM
1-20 @ 10:00AM
89.0 98.0 75.0
92.0 99.0 75.0
87.0 93.0 66.0
0
25.0
50.0
75.0
100.0
Comfortable Level To Loud To Quiet
66.0
93.087.0
75.0
99.092.0
75.0
98.0
89.0
KENNY’S SPL TESTS (DB)
1-19 @ 4:00pm 1-19 @ 11:00PM1-20 @ 10:00am
SPL TESTS
A loosely coined listening environment would to listen from 1 meter from the “Rocky
Mountain Way” system because they will likely be on a desk at that distance from the in-
tended listener. Therefore the above tests were performed at roughly 1 meter from a loud-
speaker system, listening to a high-definition recording of Donald Fagen’s “Morph the Cat”.
The results show that the comfortable listening average is 89.33 dB.
Design Proposal 3
Ontrack Inc.
When accomplishing High-SPL’s in a loudspeaker design it is important to
understand the relationship between an amplifiers output power and the relative SPL
change. According to the Speaker/Watt relativity concept for each doubling of power you
add 3 dBw SPL’s 1. Therefore it requires double power to get an additional 3 dB’s out of a
loud speaker system, this will come in handy when looking at the desired SPL in the later
stages of the design process. In the following example amplifier power is shown in relation
to the relative SPL change.
1
2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
0 10 20 30 40
Power vs. SPL dBw
SPL (dBw)
Power Watts
Power (Watts)
1
2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
SPL (dBw)
0
3
6
9
12
15
18
21
24
27
30
33
36
39
Design Proposal 4
1 Plummer, Christopher Personal Interview. 11 January 2011
Ontrack Inc.
Design Trade Offs
In loudspeaker design there are three major areas of interest, bass response, size
and SPL capability. Identifying higher importance to one of the areas will result in the other
two being less appealing. Taking these principals and applying them to a pie-chart of a
fixed size it becomes apparent. By shifting each piece of the pie to a larger section you
would be indicating that particular design criteria is more important and the the other two
sections would suffer2. Below there are four pie charts indicating the various difference
between these three categories. Note: In this example when the size is smaller than the
Coming to a decision on the tweeter was difficult because of the similarities of the
frequency response between the three. The big question is does the 27TDFC have the
same apparent width of sound field as the or D2904 or the E0047. The answer to that
question is something that is not found on a technical specs sheet. The only real way to
find out is to purchase all of the tweeters and decide. That not being an option the
27TDFC is the tweeter that will be in this loudspeaker system. A decision not made lightly,
the choice was made both on price but also Madisound’s recommendation. Other soft-
dome tweeters were in the top 10, however due to higher resonant frequencies they were
eliminated.
Design Proposal 22
Ontrack Inc.
100 1 000 10 000
100
95
90
85
80
75
70
65
60
55
50
50
40
30
20
10
0
Frequency [Hz]
*IEC 268-5, via High Pass Butterworth Filter 2500Hz 12 dB/oct.SEAS reserves the right to change technical data
MagnumT29MF001
E0047
The frequency responses above show measured free fi eld sound pressure in 0, 30, and 60 degrees, mounted in a 0.6m by 0.8m baffl e. Input 2.83 VRMS, microphone distance 0.5m, normalized to SPL 1m. The impedance is measured without baffl e using a 2V sine signal.
SPL
[dB]
Impedance [ohm
]
ET29-004Dec 2005-1
Nominal Impedance 4 Ohms Voice Coil Resistance 3.5 OhmsRecommended Frequency Range 2000 - 25000 Hz Voice Coil Inductance 0.03 mHShort Term Power Handling * 200 W Force Factor 3.0 N/ALong Term Power Handling * 90 W Free Air Resonance 500 HzCharacteristic Sensitivity (2.83V, 1m) 92.0 dB Moving Mass 0.35 gVoice Coil Diameter 26 mm Effective Piston Area 8 cm2
Voice Coil Height 1.1 mm Magnetic Gap Flux Density 1.9 TAir Gap Height 2.5 mm Magnet Weight 53 gLinear Coil Travel (p-p) 1.4 mm Total Weight 0.61 kg
The T29MF001, “MAGNUM” is a 25mm magnesium dome tweeter with a patented Neodymium based magnet system. It is the tweeter of choice for those who seek extremely precise and realistic sound reproduction combined with a relatively low crossover frequency.
A unique HEXADYM patented magnet system based on 6 radially magnetized NdFeB magnet blocks. Effi cient ventilation and damping of every potentially resonant cavity behind the dome, surround and voice coil. Moderate magnetic stray fi elds present no problems in AV installations.
A generously underhung voice coil ( + and - 0.5mm ) ensures low distortion even with low crossover frequencies.
An optimally shaped magnesium dome membrane which behaves like a piston throughout the audible frequency range and shows a controlled break up above it.
A homogenous, linear surround manufactured by SEAS from SONOMAX, a soft polymer material of high climatic stability.
Flexible lead-out wires which ensure a good connection between voice coil and terminals. This arrangement also helps to prevent lead breakage due to the large excursions encountered when low crossover frequencies are used.
Low viscosity magnetic fl uid which provides excellent cooling while maintaining a low resonance frequency.
6,0 mm machined aluminium front plate with a moderate horn loading characteristic which ensures linear frequency response, and a stiff and stable connection to the cabinet.
A substantial injection-moulded rear chamber made from zink eliminates unwanted chamber wall resonances and conducts heat away from the magnet system.
Box, Size, and Layout
Physical Space of the woofer will greatly determine the size of the box. Using a 10”
speaker is going to mean a larger box than using a 6” speaker. Taking that into considera-
tion the H1411 woofer measuring 10.5” with flange will require at least 1-2” on each side
for proper mounting. As explained in the woofer section the best comprise of results for
the woofer is to build a box that is 2 cubic feet. Taking into consideration the golden ratio
of speaker building the internal dimensions of 2 cubic foot box should be 24.46” x 15.12”
x 9.38”. However trying to reduce the hight of the speaker and to provide for extra volume
lost for parts inside the cabinet, the dimensions would need to be modified. Therefore the
size outside of the box size will be 24 1/2” x 15 1/4” x 14” and 23” x 13 3/4” x 12 1/2”
inside the 2 layers of wood.
Using two layers of wood will be essential for the completion of this design for a
number of reasons. First of which is to try to reduce the cabinet resonances using only one
board. By having two types of wood it will increase the cabinets rigidity and increase the
mass of the walls. This will effectively lower the wall vibrations which helps to eliminate the
unwanted cabinet effects. In the North Creek Cabinet Handbook they recommend using 3/
4” MDF and 3/4” Baltic Birch Plywood. It states that this the Plywood composite panel will
Design Proposal 23
Ontrack Inc.
be 4 times as stiff as one layer of MDF and in combination they will greatly reduce panel
resonances.12 Below is a general fold out of how the cabinet will look.
Design Proposal 24
12 North , Creek. Cabinet Handbook. Old Forge New York: North Creek, 1992.
Ontrack Inc.
LEFT RIGHT
BAFFLE OUTSIDE
BAFFLEINSIDE
11PLY MDFBLACK HOLE
BACKOUTSIDE
BACK INSIDE
SIDE OUTSIDE
SIDE INSIDE
TOP/BOTTOMOUTSIDE
TOP/BOTTOMINSIDE
Bracing
Bracing is as it sounds taking wood and adding braces between the sidewalls. This
is a technique used to eliminate standing waves inside a cabinet and to reduce the cabinet
resonance. The main thing is to use a wood that is different than the internal walls.13 The
implementation will include at the very least one brace with an approximate hight of 3-4
inches. The position of the brace will be above the slightly above the woofer as to not
introduce reflections out the front of the woofer. It will be fastened into a brace and glued
that is glued into the sidewall. It will also include an assortment of 1/2”-1” holes to
minimize the amount of cabinet volume lost by adding the brace.
Crossover
In a multiple driver loudspeaker systems crossovers are almost necessary. A cross-
over controls the overlap of frequencies between multiple drivers.14 Tweeters are small
drivers that produce high frequency signals (think violin). W/O crossovers the full spectrum
of sound would be transmitted to the tweeter and would cause the tweeter to fail. Similarly
low-frequency woofers cannot reproduce high frequency sound sources but rather low
* Katz, Bob. "Level Practices (Part 2) (Includes the K-System)." Digital Domain. 01 September 2000
* Plummer, Christopher Personal Interview. 11 January 2011
* Green, Grant. "Frequency." Contrabass. Available from http://www.contrabass.com/pages/frequency.html. Internet; accessed 20 January 2011.
* Noakes, Cameron. "Diy Audio Corner." Enclosure Dilemma: Ported vs Sealed. Available from http://diyaudiocorner.tripod.com/dilemma.htm. Internet; accessed 20 January 2011.
* Dickason, Vance. Loudspeaker Design Cookbook. Peterborough, New Hampshire: Old Colonial Sound Lab, 2006.
* Ludwig Sr., Arthur. "Silcom." Loudspeaker Construction. Available from http://www.silcom.com/~aludwig/Loudspeaker_construction.html. Internet; accessed 20 January 2011.
* North , Creek. Cabinet Handbook. Old Forge New York: North Creek, 1992.