This section is from the book "The National Capitol. Its Architecture Art And History", by George C. Hazelton, Jr. Also available from Amazon: The National Capitol Its Architecture Art and History.
Passing through Washington in 1821, I was requested by the architect of the Capitol, and subsequently (1827) by the Secretary of State, to give an opinion on the causes of the difficulty of hearing in the Hall, and the means of remedying the defect. On these requisitions, I submitted two papers on the subject to these gentlemen, wherein was discussed the theory of acoustics, (as regards the laws of sound) and the application of its principles to the peculiar circumstances of the Hall of Representatives : explanatory diagrams accompanied these papers, showing the design of the room, and the practical effect of two modifications of plan. These papers were referred to by the architect of the Capitol in his last report; but, laying down a theory totally at variance with that he had assumed as the correct one, they were never brought forward.
On a visit which I made the Seat of Government in 1830, I took the liberty of calling the attention of the House to the substance of my communication to the Secretary of State in 1827, which was referred to a committee; who, after investigating the plan submitted, made a favorable report to the House. With a view, in part, to test the correctness of the principle upon which the proposed improvements were based, a temporary partition was directed to be constructed in the gallery, so as to form an unbroken line of wall behind the columns and parallel therewith. A very sensible difference, both in hearing and speaking, was experienced by the members and audience from the execution of this part of the plan, though of a temporary character. Another essential part of the design could not be tested during the sitting of the House, namely, raising the floor, but the committee was satisfied that it would be effective in its operations to answer the object in question. The House not making any appropriation for carrying the plan reported by the committee into execution, the partition which had been put up, was taken down in the recess, and the Hall restored to its original state as it now stands. This circumstance will enable those who were members of the House in the last Congress to judge of the difference in effect between the two modifications of plan.
Every day's experience satisfies me of the correctness of that theory I have advocated associated with the conveyance of sound, and upon which I have based all my plans of rooms intended for the accommodation of deliberative bodies. The opportunities which I have had of testing the principles of this theory by actual practice, in the construction of several rooms of large dimensions, (one of which is greater in area than the Hall of Representatives,) enables me to speak with confidence on this subject ; and I therefore do not hesitate in saying that it is practicable to give to the present Hall all the advantages in hear, ing and speaking of which it is susceptible.
The plan of the Hall of Representatives was adopted as the best form of room to answer the demands of a deliberative assembly. This form was selected by the French Government for its Chamber of Deputies on the recommendation of the most eminent architects of France. The theatres both of Greece and Rome were all on the semi-circular plan ; and, in the construction of our modern theatres, the same form is adopted. In the execution of the plan of the Hall of Representatives some radical errors were committed, which have almost defeated the object of its design. The first error was the breaking of the circular line of wall by running the colonnade above, and in addition to this, breaking the circular line of wall back of these columns into irregular surfaces. The second error consisted in sinking the floor or raising the dome beyond their proper relative position to each other. The third error lies in the location of the Speaker s chair, and, consequently, the seats of the members.
To remedy the first error, I have proposed to construct a wall behind the third seat in the galleries, so as to keep up the circular line complete and parallel to that of the columns.
By reference to my letter, printed by order of the House in 1830, accompanied by diagrams of explanation, the reasons upon which this part of the plan was based will be seen.
Sound being subject to the same general laws which govern light, viz. radiating from a centre every way from its original source, and subject to reflection and refraction, it follows, that, in the construction of a room for speaking or hearing to the best advantage, the form should be such as to give the greatest number of consonant echoes, or, in other words, that as few of the rays of sound (or reflections of the voice) should cross each other as practicable. Now the circular form is that best adapted to produce the fewest dissonant echoes, and to give the most distinct sound of what is spoken.
The second error, which consists in the too great loftiness of the room, I have proposed to remedy by raising the floor to the general level of that of the prostyle behind the Speaker's chair, or as high as would be consistent with propriety, having reference to the columns encompassing the Hall.
It is a fundamental principle in acoustics, that, where a room to speak in (to be distinctly heard) is covered with a domical or cylindrical ceiling, the point describing the curve line of the same must be below the ear of the speaker or hearer ; and if this point is below the floor, the ear will be less sensible of the return of the voice. If this rule is not attended to, and the point describing the curve is above the ear of the speaker, the ring of echoes or reflected sounds from this ceiling, will cross each other above the ear, and produce a sensible echo. That the point describing the dome of the Hall is above the floor, is proved by standing in the axis and centre of the plan of the room, (just in front of the clerk's desk) and stamping the foot or clapping the hands : for a distinct repetition of the original sound will be heard.