Report

On Acquiring the

Frequency Response, Crossover Frequency, and Vertical / Horizontal Polar

Patterns for a an Event Electronics TR5 Loudspeaker,

Using a TEF 20 Analyzer

by

Constantin Fenton

A report submitted in partial fulfillment of the requirements for

43-3325 Acoustical Testing I

Department of Audio Arts & Acoustics

Dominique Cheenne and Douglas Jones

Columbia College, Chicago

November 10th, 2010

 

 

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ABSTRACT

Loudspeaker specifications are important to both the purposes of the end user and the

manufacturer. To obtain some technical specifications, highly specialized laboratory testing is

required. The purpose of this report is to obtain the frequency response, crossover frequency,

and vertical/horizontal polar patterns of the TR5 loudspeaker using a TEF 20 Analyzer.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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ACKNOWLEDGEMENTS

I would like to thank my team members, Marek Kovacik, David Randin, and Jeffrey

Simonelli, for their participation, hard work, and the research time they invested into the

acquisition of the desired loudspeaker specifications. I would also like to thank Dominique

Cheenne and Doug Jones for their instruction, guidance, and advice on how to properly set up

loudspeaker tests and interpret the data.

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

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TABLE OF CONTENTS

ABSTRACT………………………………………………………………………………………2

ACKNOWLEDGEMENTS………………………………………………………………………3

INTRODUCTION………………………………………………………………………………..5

PROCEDURE………………………………………………………………………………....6 - 9

RESULTS & DATA ANALYSIS…………………………………………………………..10 - 14

CONCLUSION………………………………………………………………………………….15

REFERENCES…………………………………………………………………………………..16

 

 

 

 

 

 

   

 

 

 

 

 

 

 

C. Fenton 5

INTRODUCTION

The following is a report on the analysis and acquisition of a loudspeaker’s frequency

response, crossover frequency, and horizontal/vertical polar patterns. We used a TEF 20

Analyzer to perform Time Delay Spectrometry with a speaker and microphone placed inside a

semi-anechoic chamber. We observed the response we got off the loudspeaker and used the

software to obtain a phase response which pinpointed the crossover frequency. The results were

roughly expected given the size and configuration of the loudspeaker. The polar patterns were

obtained by rotating the loudspeaker and performing a frequency sweep every 10 degrees. The

results were as expected .Our data is reliable from what we could infer from the information we

found. This report would have been aided greatly by further understanding of TDS and the TEF

software.

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PROCEDURE

Materials Used:

-Event Electronics TR5 loudspeaker

-Behringer ECM 8000 omni-directional microphone

-TEF 20 Analyzer

- Tubescence 2 channel mic preamplifier

- Goldline 6.0 TEF Software

-Adjustable mic stand

-Outline Turntable and Controller

-Semi-anechoic Chamber

Set Up:

My report team and I began by initializing the Goldline 6.0 software. We prepared the

connections for the speaker to send a signal from the TEF, and for the mic to send its output to

the TEF. The loudspeaker, microphone, and mic pre are located inside the semi-anechoic

chamber. The TEF machine, connected to a PC equipped with Goldline Software are just outside

the chamber. Since the test equipment is room separated, some minor patchwork is required. We

connected the loudspeaker test system, tested it by performing a frequency sweep, and saw that it

was in working order. The following is a basic diagram of the signal flow we used to hook up the

system (Fig1).

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Signal Flow Diagram (Fig1)

The loudspeaker is placed on a turntable approx. 1 meter (3.3ft) off the ground and the

microphone is also 1 meter off the ground. We set up the microphone and speaker so that the

tweeter was aligned with the head of the microphone and they were both 1 meter off the ground

and the tweeter was 1 meter away from the head of the mic.

Dimensions of the chamber and relative distances between mic and speaker (Fig 2)

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For the frequency response and crossover tests, the mic was on axis with the tweeter and we

placed absorbent material on the edge of the turntable and the table under the turntable (Img. 1)

in order to reduce the chances of picking up strong early reflections off the speaker’s support

structure.

Img. 1

According to Don Davis’ Basic TEF Techniques, the

correct way to obtain a frequency response is by setting up

a time response test in order to get the receive delay so

that you can enter the receive delay number into the

parameter settings for a frequency response test.

The image to the left is a screenshot of the

parameters we selected to perform the time response test.

With the frequency range from 20Hz to 20KHz, and a

sweep time of 7.25 seconds, the TEF adjusted the rest of the parameters automatically. We chose

the Hamming window because it is the recommendation made by the TEF software manual.

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Fig. 3

Fig. 3 shows the result of the time response test and it indicates that the receive delay is at

2.95ms. This value will be the value we use for all the following tests. We performed 3 separate

frequency response test, following the guidance of Don Davis’ TEF paper, in order to increase

frequency resolution at each interval. The first test was done from 20 Hz to 200Hz, the second

from 200Hz to 2,000Hz, and the third from 2,000Hz to 20,000Hz. When we overlay the results

of these three tests we get an overall frequency response and the respective phase for all

frequencies between 20Hz and 20,000Hz. For an alternate method to find the crossover, we

performed two frequency response tests. The first FRT (frequency response test) was done with

the tweeter covered so it would transmit as little energy as possible, and the second FRT was

done covering only the woofer. Comparing the two results, one can make an approximation as to

where the crossover frequency could be.

For the polar patterns we used the Outline controller and turntable, the speaker was left

standing for the horizontal polar plot, and we put the speaker on its side for the vertical polar

plot. Polar pattern test were performed with 10 degree increments for 360 degrees.

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RESULTS & DATA ANALYIS

1st TEST 2nd TEST 3rd TEST

Combined Results:

Fig. 4

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Fig. 4 Shows the semi flat line that runs along the 115 db line as the frequency response

(the overlay of the results of the three frequency response tests). Fig. 4 also shows the phase as

the jagged line that starts at the top, comes down to a point then

shoots straight up to continue on a semi-smooth downward

progression. Where the line that represents phase shoots up, this is

known as a phase shift and it is indicative of a crossover frequency

since it is at this point where one of the speaker’s driver is not

responding so well and the other driver begins to respond a lot better.

The phase shift is caused by the temporal misalignment between the

tweeter and the woofer, a product of the sheer physical differences

between both drivers. From the adjacent graph-section (Fig. 5) we

can see a closer look of the phase shift and its exact location at the

crossover frequency of 2885.6 Hz.

This result was expected since 2885Hz fell within the

frequency region that was observed to roll down when the tweeter

was covered with sound absorbent material, and observed to roll up

when the woofer was covered with a sound absorber. The region was

roughly between 1300Hz and 3000Hz.

Fig. 5

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The polar pattern test parameters for both horizontal and vertical tests were set as follows:

Fig. 6 on the next page shows the horizontal polar pattern for the TR 5. The plot displays

what can be expected of any normal loudspeaker. It is omni-directional at low frequencies, and

the refraction starts to diminish as frequency increases. For this TR5, the sound waves don’t

bend around the speaker so well starting at around 500Hz, and in front of the speaker, the sounds

seems to narrow from 8 KHz and up.

Fig. 7 on pg. 14 shows the vertical polar pattern, which again, does not show anything

out of the ordinary, except for the tiles corresponding to 2500Hz and 3150Hz. In these two tiles

you can see the almost symmetrical notches that form at the front of the polar plot but then fade

away at 4000Hz. Knowing the crossover frequency that falls in this frequency region (2500-

3150Hz), and looking at the polar plots of the two tiles, one could guess that if you listened to

the speaker standing under it at a 45 degree vertical angle, you could probably notice the

attenuation brought on by the inefficiency of the crossover in that region.

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Horizontal Polar Pattern (Fig.6)

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Vertical Polar Pattern (Fig. 7)

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CONCLUSION

The data obtained in the experimentation process of this report was what we expected to

see. Frequency response is fairly proportioned, the crossover frequency is in the expected region

between a tweeter and small woofer, and the polar patterns behave according to the laws of

physics. Nevertheless, there is plenty of room for improvement in the data synthesis portion of

this report

There are many different test parameter settings that we could have adjusted to perform

our desired tests. After some research and a lot of trial and error, my group for this report and I,

decided upon testing parameters that were drawn from suggestions and examples from Davis’

TEF paper, as well as instructions from the manual, and many parameters were simply switched

automatically by the software. I require further understanding of the TEF software and Time

Delay Spectrometry in order to provide a more comprehensive explanation of why exactly we

chose certain parameters. Further understanding of TEF and TDS would aid greatly in analyzing

and obtaining expected results. The technical accuracy of this report as well as its clarity with

regards to parameter settings would be greatly improved if I worked on my understanding of the

underlying theory.

An interesting method to test our crossover frequency acquisition skills would be to

perform the same test but with a speaker with an adjustable crossover. That way we could track

what we expect to see and actually validate it with the TEF.

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REFERENCES

-Davis, Don. "Basic TEF Techniques." Syn-Aud-Con; Audio Angineering Society (1983). Web.

10 Nov. 2010.

-TEF Sound Lab TDS – Software User’s Manual (1997) Crown International Inc.