comparison of objective and subjective observations on music rooms

THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA VOLUME 27, NUMBER 4 JULY, 1955

Comparison of Objective and Subjective Observations on Music Rooms JosEPH BLANKENSHIP,* R. BERNARD FITZGERALD,* AND R. N. LANEi

The University of Texas, Austin, Texas (Received February 21, 1955)

This paper presents a comparison of the physical and acoustic measurements in several music rooms at The University of Texas with the subjective reactions of the musicians working in these spaces. Emphasis is placed on the musicians' viewpoint in regard to desirable room characteristics.

HE functional effectiveness of music rooms may be considered from several viewpoints which in- clude that of the architect, the acoustician, and the musician (both as performer and listener). It may appear that these viewpoints should coincide to the extent that the combined effort of the architect and

the acoustician might be assumed to satisfy adequately the needs of the musician. However, this is not neces- sarily true in view of the fact that psychological factors which exert a strong influence upon the musician may not be considered or understood by the architect and acoustician. In the past the opinion of the musician has rarely been sought or considered in such matters and little has been done to establish valid procedures and terminology for obtaining this opinion.

The purpose of the present study was as follows:

1. To explore procedures and techniques and to define terminology enabling the musician to express his evaluation of music rooms.

2. To evaluate specific music rooms in terms of their adequacy for music performance.

3. To integrate the contribution of the musician with that of the architect and acoustician with regard to the construction of music rooms.

Items 1 and 3 concern information which is obtain-

able to some degree by objective acoustical measurements. Item 2 provides a means for a general evaluation and is important not only because it indicates a subjective judgment but also for its significance when related to the judgments in items ! and 3. The relationship and comparison of subjective judgments and objective measurements is highly desirable in order that the results of such studies may be interpreted more ac- curately and completely.

A consistent response pattern for the three items provides a cross reference concerning the implications of the respective items and their effect upon musical performance. In the interpretation of the ratings poor, fair, good, and excellent the line of demarcation between fair and good represents a wider range than might normally be assumed since any rating less than good cannot be accepted as really satisfactory.

The study was divided into two sections involving the following areas:

1. Practice rooms and studios in the Music Building at The University of Texas.

2. Rehearsal rooms and auditoriums at The Uni-

versity of Texas.

One of the primary problems encountered in this project concerned determining a suitable terminology which would be understood and interpreted similarly by discriminating musicians and also have meaning for the architect and acoustician. [-Although the ap- proach to the selection of procedures and terminology was done independently of any previous studies in this field, a subsequent comparison with the terminology used in evaluating the acoustics of the Royal Festival Hall I in London, England (1951) indicated a rather close parallel with regard to definition of terms and the items included•.

The final form of study involved an independent rating by each subject of the following items: 1. Room reverberation too much satisfactory too little 2. Suitability for music

performance poor fair good excellent 3. Room frequency response poor fair good excellent

A. Tone quality B. Dynamic range C. Ensemble balance D. Clarity of inner parts

* Department of Music. $ Defense Research Laboratory. • Parkin, Allen, Purkis, and Scholes, J. Acoust. Soc. Am. 25,

246 (1953).

All of the rooms evaluated have been in use for a

period of more than ten years and were judged by members of the music faculty and music students who were thoroughly familiar with the music rooms.

PRACTICE ROOMS AND STUDIOS IN THE MUSIC BUILDING AT THE UNIVERSITY OF TEAXS

The purpose of this study was to aid in establishing some satisfactory acoustical characteristics of music practice rooms. Economy usually requires that music practice rooms be kept to a minimum size. Such rooms are, therefore, usually too small to afford the most desirable acoustics for musical performance. It is intended that this study should aid in revealing a means for adjusting the interior of a room to make it more satisfactory musically.

The practice rooms used for this study are on the third floor of the Music Building of The University of Texas. Figure 1 shows a view of the construction and furnishings of the rooms. This room has an 8-ft ceiling and is approximately 6 ft wide and 9 ft long. In addi- tion, two other identical rooms were used for the study.

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MUSIC ROOMS 775

Musician subjects were asked to perform in the room and then to rate each room according to items which will be presented shortly. In all, twenty subjects were used and the areas of specialization which were repre- sented are as follows: piano, voice, flute, oboe, clarinet, bassoon, trumpet, trombone, French horn, violin, viola, cello, and string bass. Of the twenty subjects, ten were faculty members, and ten were students of the Depart- ment of Music of The University of Texas.

Each subject performed in one room just as it is pictured. Then the rooms were acoustically treated in several ways with panels 3 ft wide and 7 ft long. These panels were constructed with a wooden frame, filled with Fiberglas Aerocor, and covered with a

FIG. 1. Interior of practice room in Music Building, The University of Texas.

loosely-woven glass cloth. The Fiberglas filler was left out of one panel in order to introduce •n extra experi- mental factor--in other words it was a dummy panel, similar in appearance, but not altering the acoustics of the room appreciably. The rooms were used then with the following arrangements' a room with one dummy panel, a room with one good panel, a room with one dummy and one good panel, and a room with two good panels.

Figure 2 is a comparison of room 316 (no extra treatment) with room 318.1 (one good panel). First an explanation of the chart is in order. Observe the letters across the top line; P stands for poor, F--fair, G--good and_Emexcellent. In Item 3, M stands for too much,

Room No. $/6 Room No. $18.1

P F G E P F G E

I. Tone Quality o. High (• ! g 6. b. Low p F g f 6'

2 Dyhomic Range o. Low Level p F' f 6.

b. High Level C•) f g f 6'

5. Reverberation Af m $ ....

FiG. 2.

S--satisfactory and L--too little. If there are definitely more responses under a certain rating it is shown as a capital letter. If one or more ratings are about equal they are shown with a small case letter, but if one of these is slightly better it is circled. It is intended that the capital letter shows the greatest tendency of the subject data, while the lower case letter shows an off-shoot or tail in its direction. Notice on this chart that the addi-

tion of one good panel caused the ratings of all items to concentrate under G--good and the reverberation rating moved to satisfactory.

Figure 3 shows a comparison of room 316 (no extra treatment) and room 318.2 (two good panels). It is observed here that two panels made an improvement but some deterioration is evident. The f's are almost as strong as the g's and reverberation, while it is still satisfactory, has a tail in the opposite direction from that shown in Fig. 2.

Figure 4 is a comparison of room 318.1 (one good panel) and room 318.2 (two good panels). This chart

Room No. $/6 Room No.

P F G F' p F G E

I. Tone Quality o. High I• f g F' g b. Low p F g f 6.

. ,

•. Dynamic Range o. Low Level p F' f g ß

b- High Level (•) f g f 6.

5. Reverberation Af $ I

FIG. $.

Room No.$18.1 Room No.$18.•

P F G E P I r G E .,

I. Tone Quality

o- • igh ß .

..

b. Low f

2. Dyno'mic Range o. Low Level f 6' f g ß

b. High Level f 6. f 6.

Too Much I '• Little TOO Much .• Too Little 3. Reverberation ............

FIG. 4.


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776 BLANKENSHIP, FITZGERALD, AND LANE

Room No. $/4. / Room No. $/4,2

P F G E P F G E

I. Tone Quality O. H•gh - - G - f G

b. Low - F' g - G

2 Dynamic Ronge o. Low Level f g f g

b. High Level f g G

3. Reverberation m s $ /

Fro. 5.

Room No. $/4.,_P Room No. $/•. /

P F G E P F G E

I. Tone Quality o. High b. Low

2. Dynomic Ronge o. Low Level

b. High Ledel

3. Reverberotion

Fro. 6.

is presented in order to show a more direct comparison of the effect of one panel and the effect of two panels.

Figure 5 shows a comparison of room 314.1 (one dummy panel) and room 314.2 (one dummy panel and one good panel), and shows the effect of the visual presence of the dummy panel. From all outward ap- pearances the dummy panel was the same as the good panels, but it was not filled with Fiberglas. The dash marks after item one, tone quality, indicate a diffusion in the responses. Many subjects indicated verbally that they could not detect much difference between room 314.1 (dummy panel) and room 316 (no treatment), but they were reluctant to score it that way on the data sheet. It seems that the visual presence of a panel caused some confusion in what was heard.

Figure 6 shows a comparison of room 314.2 (one dummy panel and one good panel) with room 318.1 (one good panel). Here again the presence of the dummy panel caused the subjects to show some uncertainty in their ratings, but the two rooms are judged essentially equal. It may be of some significance here to note that the musician subjects gave a more consistent evaluation on items number one and two, which are musical terms, than they did on item three, which might be considered to be more of an acoustical term.

Figure 7 shows a comparison of room 314.2 (one dummy panel and one good panel) with room 318.2 (two good panels). The results here bear out what was previously shown to be the effective difference between one good panel and two good panels except for the tail branching off under reverberation. However, this tail may perhaps be attributed to the visual presence of the dummy panel.

Figure 8 shows the reverberation curves for these practice rooms. The top curve shows the room response with no panels, the center curve with one panel, and the bottom curve is with two panels.

The musician evaluates a room by ear, of course, but probably his ability to adjust musically to the room greatly affects his evaluation of the room. From the results of this study it seems that these practice rooms are best when treated with one panel but with two panels they are slightly on the dead side for most instruments.

To the acoustician this information is important in the design of the interiors of practice rooms as long as they are about the same size as the ones tested. It should be noted that these rooms were designed to be live and "brilliant" with control of the low frequencies achieved by resonant, randomly supported plywood wall panelling. The floors were wood on suspended con- crete, and the ceilings were hard plaster. The design aim was achieved but after several years of use the consensus of opinion now indicates that for these small rooms, a uniform frequency response with a shorter reverberation time of approximately 0.4 to 0.5 second is to be desired.

THE TEACHING STUDIOS

The individual teaching studios in the Music Building at The University of Texas are for the most part of two sizes, both considerably larger than the practice rooms. These rooms were designed by C. P. Boner in 1940 and reflect all the fundamentals of proper acoustic design

Room No. 3/4. 2 Room No. 3/•'.2

P F G E P F G E

I. Tone Quality o. High b. Low

2. Dynomic Ronge o. Low Level

b. High Level

3. Reverberation

E'och Pone/ $• 7',r /" F/berg/os.

io

0.8 0.6

04

02 • i I I i I

IOO iooo

Frequency In cps

FIc. 8. Practice room, The University of Texas.

IVo PoneIs One

•Two PoneIs

ioooo


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MUSIC ROOMS 777

FIG. 9. Interior view of large teaching studio in Music Building, The University of Texas.

for teaching studios. The ceiling is splayed, the walls are of randomly braced -}-in. plywood, the opposite ends of the room are nonparallel plywood and the liveness of each room may be individually adjusted by the draperies. Figure 9 shows the large size studio with an 11-ft ceiling, 13 ft 2 in. in width, and 18 ft 3 in. in length. The sound isolation between rooms is exceptionally good and averaged 78 db from 125 to 4000 cycles per second.

Figure 10 shows the amount of reverberation control afforded by the adjustable draperies. Each studio can be adjusted from a rather brilliant room to one which has a uniform time with frequency of approximately 0.6 second. Notice that with the draperies extended the rooms have a uniform reverberation time similar to the

recommended characteristic for the practice rooms but with a longer average time.

Figure 11 shows the subjective reactions to a comparison of Room 204A (small studio) and Room 204C (large studio). All subjects stated that both of these rooms were far superior to all the practice rooms; therefore, this chart presents only a comparison between the small and large studios. Again, though both studios are rated very highly, the large studio is better liked. The larger studio may be approaching an optimal size for teaching studios, since larger studios may be an uneconomical use of space.

1.4

.0 I

C)B ! 0.6

0.4 oz

• • Oropes es Extended

iil i i i i i ii I I

IOO IOOO IOOOO

Frequency /ncp$

Fro. 10. Teaching studio 206A, The University of Texas.

Room No. 204,• Room No.204C

P F G E P F G E

I. Tone Quality o High G e

b. Low G e g

'2.' Dynamic Ronge o. Low Level G e g E'

b. H,gh Level g e

ß

3. Reverberation $ i $ _

FZG. 11.

REHEARSAL ROOMS AND AUDITORIUMS AT THE UNIVERSITY OF TEXAS

The second section of this study concerned three large music rooms at The University of Texas' Hogg Auditorium, the Music Building Recital Hall, and Rehearsal Room 200 in the Music Building. Seven members of The University of Texas music faculty participated in this part of the project and their opinions represent a cross section of instrumental and vocal specialists which includes soloists, chamber music performers, and the conductors of the university band, orchestra, and choir.

Each faculty member indicated his evaluation of the room independently following an explanation of the method and purpose of the study. As noted in the ac- companying illustrations each of the rooms was evaluated concerning three types of music performance: solo, chamber music, and large groups. It will be observed that the ratings on suitability for music performance vary in these three categories even though the evaluation of room reverberation has a more consistent

pattern. This serves to indicate that satisfactory room reverberation is not the only factor to be considered. The results of this study are summarized in the illustrations which follow and, as in the previous study, the opinions of the subjects are indicated by the use of capital and lower case letters.

Some variance in the opinions of the music faculty

FIG. 12. Five-hundred seat recital hall in Music Building, The University of Texas.


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778 BLANKENSHIP, FITZGE'•RALD, AND LANE

ROOM REVERBERATION SUITABIL)TY RESPONSE TOO S TOO Much L,tt le P F G E P F G E

Solo $ œ • e ..

Chomber Music $ E' • e _..

Lorge Groups S 6. •, e

Fro. 13. Recital hall.

members might be expected since the evaluation of each individual will reflect knowledge of his special field (vocal or instrumental), and experience with the respective categories (solo, chamber music, large groups). However, the scores indicate a consistent pattern with minor deviations except for Rehearsal Room 200.

It should be noted at the outset that the Recital Hall, Fig. 12, was specifically designed for solo and chamber music performance and that the ratings for these categories are consistently good or excellent (Fig. 13).

the situation by making it possible to adjust and control the sound reflection of the stage area to some extent.

In Hogg Auditorium, Fig. 14, it should be noted that opinion is somewhat less consistent for the three types of performance in regard to both reverberation and suitability (Fig. 15).

Large choral and instrumental groups require a stage ceiling for satisfactory performance conditions due to the large open area above the stage and the use of stage risers or platforms ranging from 12 in. to 36 in. in height is very desirable for satisfactory sound projection. Soloists and chamber music groups must be placed near the front of the stage for satisfactory results. Performance conditions are best when the stage curtains and draperies are removed since their sound absorption results in a deadening effect. An adjustable plywood stage ceiling in four sections is used with very satisfactory results.

Results obtained for Rehearsal Room 200, Fig. 16, not only indicate a diversity of opinion of the subjects

Fro. 14. Fourteen-hundred seat Hogg Memorial Auditorium, The University of Texas.

The opinion that the room is not large enough to be considered ideal for large instrumental groups is indicated by a rating of good rather than excellent under suitability. The partially enclosed stage area is a dis- advantage for band and orchestra since the sound of instruments placed near the walls and corners of the stage is reflected to the extent that the tonal balance of the group is affected. In the experience of the conductors the placing of the French horns and drums has proved to be a special problem. A larger stage area would tend to improve this condition and a removable stage extension is used. However, this extension does not provide sufficient additional space to make it possible to seat large groups so that the drums and French horns can be placed a sufficient distance from the reflecting wall surfaces which enclose the stage area. It is felt that the installation of adjustable draperies across the back of the stage would improve

ROOM REVERBERATION SUITABILITY RESPONSE ...

TOO S TOO Much Little P F g E P F G E

Solo S (2) 6' f

Chomber Music $. (•) F' f L. orge Groups $ 6' f

Fro. 15. Hogg Auditorium.

(see Fig. 17), but also suggest the presence of disturbing acoustical conditions. Notice that the rating with regard to room reverberation shows a widely varying but evenly divided opinion among the musicians. How- ever, the ratings of the other two items do not reflect a similar lack of agreement since the majority considered the room unsatisfactory, rating only in the poor and fair columns. While it is obvious that this room is con-

sidered less satisfactory than the other two rooms,

Fro. 16. Rehearsal room in Music Building, The University of- Texas.


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MUSIC ROOMS 779

there is also lack of agreement as to why it is unsatisfactory. It would appear that the shape and size of this room may be major factors contributing to the con- fusing acoustical conditions.

Experimentation has shown that Room 200 is much more satisfactory acoustically if large groups are seated facing toward one end of the room rather than toward one side. However, the room is too narrow to use con- ventional seating arrangements when the group is seated facing toward one end of the room and the players at the rear of the room are located too far from the conductor for best results. Part of the acoustical

difficulty seems to be due to the fact that large groups must occupy nearly the entire floor area and that players seated near the walls find it more difficult to coordinate their playing under these conditions.

Figure 18 represents a detailed comparison of the room frequency response ratings for the three rooms, the average room frequency response ratings being shown in Figs. 13, 15, and 17.

Room 200 was rated rather consistently as unacceptable, with Hogg Auditorium on the borderline between good and fair, while the Recital Hall was considered to be satisfactory.

, .

ROOM REVERBERATION SUITABILITY RESPONSE

Too S Too Much U,tt le P F G E P F G E

5olo (• $ / F F

:bomber Music (• $ I (•) ( e F

.orge Groups t• $ I I•) f F

Fro. 17. Room 200.

In Room 200 low tone quality, dynamic range, and clarity of inner parts were definitely unacceptable and may have contributed to the lack of agreement concerning the room reverberation shown in Fig. 17.

In general the acoustical measurements carried out in the three rooms studied in this paper supported the subjective judgments of the musicians. For example, the Recital Hall, which was rated excellent, has no measureable acoustic defects, no echoes, no side wall flutter, and has a uniform reverberation characteristic

RECITAL HOGG ROOM 200 HALL AUDITORIUM

P F G E P F G E P F G E

Tone Quolity

8. LOw P E f •'

Dynom•c Ronge A. Low Level •' f e f g 8 H•gh Level F g e f g e

Overoil Ensemble Bolonce f • • e G

Clor•ty Of Inner Ports F' g e F

1.6 1.4

I0

0.8 0.6 o• o•

E'm p f• W/fh .•00 People (Co/cu/ofed)

Frequency In cps

Fro. 19. Recital hall, The University of Texas.

very near the recommended optimum time for a hall seating five hundred people (see Fig. 19). The hall also has a deeply coffered ceiling and diffusing panels on the side wall.

Hogg Auditorium, which was designed several years before the Recital Hall, received a borderline rating between good and fair, which was due in part to a rather nonuniform reverberation characteristic with

'" I IIIIii

1.8

IIII

,.o j

IIIIIII I I IIIIIII I Ill 0'43 456 81 2 J 456 81 2 J 456 81

I00 I000 I0000 Frequency /• cps

Fro. 20. Hogg Auditorium, The University of Texas.

frequency (see Fig. 20), and lack of proper reflecting surfaces near the stage and in the ceiling. Diffusion is achieved along the side walls by draperies hung on windows, and there are no objectionable echoes. There- fore the acoustic design of this auditorium might also be considered to be between fair and good.

1.6

1.0

0.8 0.t5

0.4 03 >

i I ! i i i•11 IOO iooo IOOOO

Frequency In cp$

Fro. 18. Room frequency response. Fro. 21. Ensemble room, The University of Texas.


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780 BLANKENSHIP, FITZGERALD, AND LANE

The Rehearsal Room, Room 200, does not appear to have any acoustical defects which could account for the bad rating it received by the musicians. The reverberation characteristics, shown in Fig. 21, are relatively uniform and the average reverberation time is not a great deal over the optimum time for a room of this volume. The lack of clarity might be improved by de- creasing the reverberation time, but the unsatisfactory dynamic range and low frequency quality might not be

improved at all. Since sufficient diffusion of sound is accomplished by the plywood diffusers on all four walls and tilted ceiling panels, it may be that the chief trouble with the room results from its use with groups which are entirely too large for the physical space.

The preceding studies are the result of cooperative effort by the Music Department and the Acoustics Division of Defense Research Laboratory at The University of Texas.


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comparison of objective and subjective observations on music rooms

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