This document summarizes acoustic testing of an Event TR8XL loudspeaker conducted in Columbia College Chicago's anechoic chamber. Frequency response was analyzed both inside and outside the chamber, showing irregularities throughout. The crossover point was found to be 1898 Hz, lower than the 2059 Hz where the driver magnitudes crossed. Polar directivity varied with frequency, from omnidirectional at lower frequencies to more directional at higher frequencies. Additional tests examined damping effects and compared results to a Shure microphone.

1. The Loudspeaker Study
Chris Nottoli
Melissa King, Joshua Roberts, Javier Forero, Frank Minella
Columbia College Chicago
Acoustical Testing I
Dr. Dominique Chéenne, Dr. Lauren Ronsse
October 16th 2013

2. Table of Contents
Abstract: ................................................................................................................................................... 3
Introduction: ........................................................................................................................................... 3
Materials: ................................................................................................................................................. 4
Frequency Response: ........................................................................................................................... 4
Crossover: ................................................................................................................................................ 8
Polar Directivity: ................................................................................................................................... 9
Conclusions: .......................................................................................................................................... 10
Additional Tests: ................................................................................................................................. 11
Introduction: ................................................................................................................................................... 11
Damping Results: ........................................................................................................................................... 11
Comparison Results: ..................................................................................................................................... 12
Appendix A: ........................................................................................................................................... 14
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3. Abstract:
The frequency response, crossover frequency, and polar directivity of an Event
TR8XL speaker were analyzed inside Columbia College Chicago’s anechoic chamber using
TEF 20. The frequency response of the speaker was also analyzed in a non-anechoic
environment. The response was relatively linear, showing many irregularities throughout
the frequency spectrum. When compared with the test conducted outside of the anechoic
chamber, the irregularities were still present. The crossover point occurred at 1898 Hz in
contradiction to where the magnitudes of the drivers crossed at 2059 Hz. The polar
directivity varied throughout the frequencies where at lower frequencies the speaker was
omnidirectional and became directional at higher frequencies.
Introduction:
The loudspeaker analysis was conducted at Columbia College Chicago, using the
anechoic chamber located in LL01 with TEF 6.0 software. Josh Roberts, Melissa King, Javier
Forero, Mike Minella, and the author of this report collaborated on this study. The
objective was to analyze the frequency response both inside and outside of the anechoic
chamber, the crossover frequency, and polar directivity. Two additional tests were
conducted to determine the frequency response as mass was added to the subwoofer and a
comparison with a Shure SM-63 microphone.
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4. Materials:

Speaker: Event TR8XL; QSC-K8

Microphone: Electro-Voice RE-55; Shure SM-63

TEF 6.0

Outline electronic turntable

Computer with TEF 20 and Outline interface

Anechoic Chamber 13’ 10” X 10’ 2” X 8’ 2”
Frequency Response:
This initial speaker used in this analysis was a QSC-K8. Preliminary steps were
taken before the frequency tests were conducted. The Electro-Voice microphone was
calibrated with TEF to .00099 V/Pascal. A test to determine if the microphone was
receiving signal from the speaker was then conducted. As seen in Appendix A-1, a
magnitude of less than 0 decibels was being obtained before the direct sound had reached
the microphone. Upon observing the frequency response in Appendix A-2, there was no
valid signal received by the microphone. Fig. 1 shows the signal flow followed to correct the
absence of a proper signal. The equipment rack patch bay had been altered since last used
and was corrected. This correction can be found in Appendix A-3 along with all other
patched connections used within these tests.
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5. Fig. 1: The output of the signal flow from TEF is displayed on the right. The input signal is displayed on
the left.
A time response, found in Appendix A-7, was conducted to again determine if the
microphone obtained proper signal. Tested at 2 feet, the direct sound arrived at 3.81ms.
The arrival of direct sound was expected at 2ms. The 1.8ms of late arrival of the acquired to
the expected direct sound explains the speaker change. This late arrival time occurs
because the QSC speaker stays on standby until a signal is present to determine if the signal
can potentially destroy the speaker by DC power. A time response was conducted on an
Event TR8XL at 2 feet. The signal reached the microphone after 1.65ms ensuring that the
results being received were accurate as seen in Fig. 2.
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6. Fig. 2: Time response on the Event TR8XL speaker at 2 feet. Direct sound reached the microphone at
1.65ms.
In obtaining the frequency response, the microphone was repositioned 1 meter in
front of the speaker as seen in Appendix A-8. Time resolution was sacrificed since the test
was conducted inside an anechoic chamber allowing for a 15 minutes sweep from 20–
20,000 Hz. The graph of the frequency response can be found in Fig. 3. The response of the
speaker was relatively linear and had many irregularities especially at 225 Hz, 360 Hz, and
550 Hz. This could be due to the size of the speaker and the tendency of the low frequency
driver to produce an inaccurate response. The speaker also rolls off at 17,000 Hz indicating
it cannot accurately reproduce the full frequency spectrum. There was also a noticeable
drop in magnitude between 2700 Hz and 5500 Hz occurring after the crossover point. The
differences between phases of the two drivers may be the cause of this phenomenon.
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7. Fig. 3: The frequency response swept 20Hz- 20,000Hz over a 15-minute period. The frequency
resolution used in the test was 11.0 Hz with a 2Hz bandwidth.
The frequency response of this speaker was also tested in a non-anechoic
environment, found in Appendix A-9. Time resolution could not be sacrificed so that
reflections off the nearest objects would not be captured in the response. The microphone
was placed 1 foot from the speaker so the time resolution will only allow the direct sound
from the speaker to reach the microphone with minimum reflections from surrounding
objects. Therefore, ten tests were conducted in octaves from 20Hz-40Hz, 39Hz -80Hz, etc.
to maximize the best possible time resolution. The graph in Fig. 4 shows the frequency
response obtained. Since time resolution could not be sacrificed, frequency resolution was
very difficult to achieve. However, many characteristics of Fig. 3 were still present.
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8. Fig. 4: Frequency response of an Event TR8XL in a non-anechoic room. Breaks in response are due to the
start/stop of each test. An overlap of 1Hz at the start of each test was used to overlay from the previous
test.
The inaccuracies of the low frequency driver were still present. The crossover
frequency can be pointed through a dip in the magnitude. The poor response of the high
frequency driver is also evident as it rolls off at 7,000Hz. The discontinuities that occur
throughout the graph are due to the 10 individual tests. It can be concluded that Fig. 4 was
an excellent representation to how the speaker reproduced sound in a non-perfect space.
Crossover:
The initial crossover point was hypothesized to occur between 2,000-3,000 Hz
where the magnitude in Fig. 3 drops roughly 3dB. Tested in the anechoic chamber, the low
frequency driver was covered with absorptive material. The microphone was then placed
directly in front of the high frequency driver. Another test was conducted covering the high
frequency driver and placing the microphone directly in front of the low frequency driver.
Results could be found in Appendix A-11. An additional test was conducted from 1,0004,000 Hz, placing the microphone directly between the high and low frequency drivers due
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9. to the lack of interactions of phase information obtained from Appendix A-12. As seen in
Fig. 5, the crossover occurs at 1898 Hz where the phase is 88 degrees out of phase.
Fig. 5: The phase test was conducted between 1,000 Hz and 4,000 Hz for 600s with a bandwidth of 2.2
Hz. Note the 30 dB drop in magnitude at 1898 Hz. As the phase is 88 degrees out of phase cancelation
occurs, which caused the significant drop on magnitude.
Additionally, the acoustic and electrical phases were not at the same frequency. The
high frequency driver crossed at 2059 Hz. This may also have occurred because the sound
was bleeding through the absorptive material, skewing the data received.
Polar Directivity:
The expected directivity of the loudspeaker was hypothesized to be omnidirectional
at lower frequencies and become more directional as frequency increases. Measured at 1
meter from the microphone in the anechoic chamber, the loudspeaker was centered on an
Outline electronic turntable. The Outline interface was set to turn every 5 degrees with
relation to the parameters in Appendix A-13 along with the speaker’s polar directivity in A14.
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10. A 3.5-minute sweep time with small interval changes were used to capture as much
detail about the directivity as possible. Below 32 Hz, the directivity was rugged looking,
which can be explained either by poor low frequency reproduction, any resonance of the
speaker itself, or both. The speaker was in fact omnidirectional between 32-50 HZ meaning
the wavelength of these frequencies diffracted around the back of the speaker housing. The
speaker then became subcardioid between 56-250 Hz. At 500 Hz, the frequencies become
smaller than the speaker where directional characteristics began to appear.
Conclusions:
The frequency response of the TR8XL loudspeaker showed a relatively linear
response from 700 Hz- 2,700 Hz. With a roll off before 100 Hz and after 17,000 Hz, the
speaker cannot accurately reproduce these frequencies. However, most of those
frequencies are inaudible to most humans and can be overlooked. The response in a nonanechoic room showed similar characteristics to the test conducted in the anechoic
chamber, but showed how it actually reproduced in a room it would most likely be used in.
Further testing of the frequency response in a studio control room would give better
insight as to how it may affect the outcome of a recording.
The crossover was found to occur at 1898 Hz where the drivers were 88 degrees out
of phase. This crossover point contradicts where the two magnitudes crossed when testing
individual drivers. Additional tests could be taken to determine how the speaker’s port
hole affects the outcome of all tests in this report. Also, using more absorptive material and
eliminating any bleed through of sound could be tested to determine if the crossover in
magnitude of each driver shifts closer to the electrical crossover.
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11. Finally, the polar directivity was found to be omnidirectional below 56 Hz,
subcardioid between 56-250 Hz, and an increase in directivity as frequency increased.
Further testing into the single hypercardioid response at 280 Hz could be investigated to
determine if a possible resonance of the table or speaker caused this to occur.
Additional Tests:
Introduction:
As an extra credit study, the frequency response of the Event TR8XL was tested
adding eight coins, more specifically quarters, to the low frequency speaker to evaluate the
effects of damping. Each quarter was taped around the speaker evenly to ensure that extra
mass affected the whole speaker as seen in Appendix A-15. The frequency response of the
speaker with and without quarters would be compared. In addition, the Shure SM-63
microphone was compared with the Electro-Voice RE-55 expecting to obtain similar results
since both are dynamic. Quarters were removed from this test, since damping was not the
concern.
Damping Results:
The results of damping were as expected seeing a 3-6dB decrease in magnitude up
until 700 Hz. By adding more mass, the speaker, seen in Appendix A-15, would have had to
exert more force in order to produce the same frequencies at the same magnitude
explaining this occurrence. As the frequency increased, the effects of damping were not as
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12. noticeable since higher frequencies stopped relaying on the size of the cone taking less
force to produce the frequencies as seen in Fig. 6.
Fig. 6: Damping with Quarter. This test foucused in between 20 Hz and 1,000Hz with a two minute
sweep. Note that the peaks at 60hz, 120 Hz, 180 Hz, etc. are due to the vibrations of the quarters on the
cone. As the crossover nears and the high frequency driver begins, these peaks become less prominent.
Comparison Results:
The frequency response of the Electro-Voice was used as a reference so that a
comparison with the Shure SM-63 can be analyzed. Many similar characteristics were
found between the two microphones; for example, the drop in magnitude between 2,7005,500 Hz was still present, as was the roll off at 17,000 Hz. The differences in the frequency
response can be due to the sensitivity of the microphones, the size of the diaphragm, and
calibration. Overall, the Electro-Voice continued to produce more accurate results that can
be easily interpreted.
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13. Fig. 7: The comparison between Electro-Voice and Shure SM-63. Sweep time of 60 s. and a 167 Hz
bandwidth were used to get a general sense of the differences.
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14. Appendix A:
Fig. A-1: Time response test conduced at 2’2”. The decibel level before the direct sound had obtained
decibels below 0 dB. In addition, the direct sound was captured at 3.66ms. This “late” arrival of direct
sound was to be investigated.
Fig. A-2: Frequency response related to Fig. A-1, showing no true signal being received.
Fig. A-3: Patch Bay connection at equipment rack. The signal from TEF goes through station two
output 3 to anechoic input 3, which in return gets set to the speaker. Anechoic 1 is the signal
received from the microphone, which gets sent to station 2 output 1 to TEF (mic A).
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15. Fig. A-4: TEF 20 connection; BNC line out to station two XLR input 3(Fig. A-5) and mic A input from
station two output 1.
Fig. A-5: Station two patch bay mentioned in Fig. A-4.
Fig. A-6: Chamber snake. Channel 1 is receives signal from the microphone. Channel 3 is the output signal
to the speaker.
Fig. A-7: Time response after patch bay correction. Direct sound reaches the microphone at 3.81ms.
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16. Fig. A-8: General set up for loudspeaker tests in the anechoic chamber.
Fig. 9: Set up for analyzing the frequency response of the loudspeaker in a non-anechoic environment.
Microphone was placed 1ft away from loudspeaker.
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17. Fig. A-10: Parameters for frequency response in a non-anechoic room. A 0.88ms delay was included in
each test to account for the 1 foot distance between the speaker and the microphone.
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18. Fig. A-11: Crossover with absorption covering each driver. The expected crossover was thought to occur
where both magnitude cross. Note that the high frequency driver appears to be producing low frequency
tones. This is due to the bleed through of the low frequency driver, which had an effect to where the
magnitudes crossed.
Fig. A-12: Crossover phase related to A-11.
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19. Fig. A-13: Polar directivity parameters.
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20. Fig. A-14: Polar Directivity graph.
Fig. A-15: Eight quarters were added to the speaker to determine the effect of damping as mass is added.
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