Shema Yisrael (Hear, Israel) strongly implies that acoustics is fundamentally important to the design of Synagogues.

What do we want to hear?

What do we want to hear in a synagogue? Prayer is both spoken and sung by the congregation; prayer is both spoken and sung by the prayer leader; Torah is chanted in Hebrew; sermons and announcements are spoken in English. What are the acoustical requirements for these various functions, and what do they imply for the architecture?

Congregational singing and prayer require a certain amount of acoustical feedback: sound reflecting back to the worshipers from nearby hard surfaces. Hard pew backs help create this "singing in the shower effect." Without this support, you feel as if praying in isolation.

Generally in an Orthodox synagogue, the chazan chants with his back to the congregation. Without hard surfaces to reflect sound back to the congregation, his voice will sound weak and indistinct. In addition, he needs the support of sound coming back to his ears, otherwise he may push and strain his voice.

One must be careful with the amount and location of hard surfaces within a synagogue, however. Too much hard surface area will make for an overly reverberant space, thus undermining speech intelligibility: a very high priority, especially for sermons and announcements in English. On the other hand, the musical quality of sound of the service is also important. To my ear, this calls for a certain amount of reverberance. A delicate balance must be struck in the architectural acoustics, as it is in the liturgy.

The layening of the Torah, in particular, is a characteristically brilliant method of clearly presenting information in a beautiful package. Speech intelligibility is extremely important in reading the Torah. However, mere information is not enough; this information should be presented in a beautiful manner. The chanting of the Torah transcends decoration; it also aids intelligibility of the text. By slowing down the pace of the words, and by exaggerating the pitch range, chanting allows for-even takes advantage of-reverberance to enhance both the intelligibility and the beauty of the text.

The women's section

In an Orthodox synagogue, women sit separately from the men. Often there is a mechiza between the men's and women's sections. Since the women often sit to the side, or to the back, and since they do not participate directly in the service, it is imperative that they have the best possible conditions for hearing and seeing. They should have better sightlines than the men. In particular, the mechiza should be designed so that it interferes as little as possible with the hearing and seeing. Any solid material, such as lucite, should be avoided, since it will block sound.

Elevating the women's section accomplishes two desirable goals: It makes the women's section less visible to the men below; and it offers superior conditions for hearing and seeing to the women. In fact, the origin of the mechiza was a balcony added to the Bais Hamikdas during the celebration of Sukkos so that the women could have a better view.

Sound systems

In an Orthodox synagogue, amplified sound is not permitted on the Sabbath. As an acoustician, I wholeheartedly agree with this prohibition. I am not a scholar; my objection to the use of sound systems is based on what I hear. Amplified sound does violence to the tranquil spirit of the Sabbath. Sound systems distort the sound of the human voice; they introduce a barrier between speaker and listener; they encourage poor speaking habits; and they discourage courtesy and attention. In my experience, sound systems are often more of a hindrance than a help to speech intelligibility. We should be heartily thankful for the halakhic proscriptions against their use on the Sabbath.

Noise control

Strict noise control is the most important aspect of good acoustical design for speech intelligibility. Noise can come from a variety of sources: traffic, people in other parts of the building, people within the room, lights, and -usually the worst culprit-mechanical ventilation.

We take noise in our environment for granted. But even noise that is not noticed by the untrained ear will have a pernicious effect on the understanding of speech (see The Secret of Architectural Acoustics Revealed). The effect can be compared with looking through a dirty window. The dirt is not noticed, but once the window is cleaned the improvement in clarity is striking.

Nothing can be done directly about noise created by other people at the service. However studies have shown that when mechanical and environmental noise is minimized, people will control their own noise to a surprising extent. This has been borne out by the author's experience.

A source of noise peculiar to synagogues is the additional space that can be opened to the sanctuary on occasions such as the High Holy Days. These spaces are often closed off with a movable partition. These partitions are never perfect noise barriers, but people in the additional space often do not realize that they can be heard in the sanctuary. It is worthwhile to use a partition with a high noise rating. Correct installation is critical, since even a small gap can severely compromise noise isolation.

Hard-of-hearing worshipers

Any synagogue will have a number of members with impaired hearing. They fall into two groups: those whose hearing is starting to go, but who do not use a hearing aid; and those with hearing aids.

Fortunately, conditions that improve speech intelligibility for those with normal hearing-low background noise, strong early sound reflections, and relatively low reverberance-will also help those who are hard-of-hearing. Background noise levels below the hearing threshold for hard-of-hearing listeners will encourage others to curtail extraneous noise, thus improving matters for the hard-of-hearing.

People who are hard of hearing have a much lower tolerance for reverberance than do those with normal hearing. I do not believe, however, that sanctuaries should be designed to be extraordinarily non-reverberant. A certain amount of reverberance is beneficial, as we have discussed. The proper balance is bet worked out for each individual case.

Another aid to the hard-of-hearing is to provide seating from which it is easy to see as well as hear people speaking from the bima.

To leave this subject on an optimistic note, older congregants with poor hearing are likely to be familiar with liturgy, which can be read in the Siddur-a great aid to understanding. Perhaps sermons and announcements in English could also be printed as well.

Congregation Degal Israel

Let us consider and example of a synagogue that is generally considered to be acoustically successful, both by its congregation and by several professional acousticians: Degal Israel of Lancaster, Pennsylvania, designed by S. Z Moslowitz of Wilkes Barre, PA, in 1963.

The sanctuary is a simple rectangular box of modest scale. It is 42 feet wide; the farthest rear seat is only 44 feet back from the bimah. The ceiling, at 21 feet, is high enough for a little acoustical "breathing room," but low enough so that sound reflections off the ceiling arrive early enough to support, rather than mask, voice coming from the bimah.

You would call this room neither reverberant, nor "dry." It has enough reverberance so that the shofar can resound a bit; the sound of the congregation blends pleasantly in prayer; words form the bimah are supported by the room, yet not covered up by reverberance. This is due to the room's dimensions, and to a judicious blend of hard and soft surfaces. The wall behind the bimah, for example, is a large area of hard wood. This surface, along with the plaster wall and ceiling, serves to reflect sound from the bimah out to the congregation. This is especially important when the chazan is chanting with his back to the congregation. (Note: further improvement could be had here by removing the carpet from the bimah.)

The backs of the pews are hard, providing some acoustical support for worshipers, and allowing them to blend with their neighbors. Thick carpet in the aisles, on the other hand, cuts down on the buildup of later sound reflections, which would tend to obscure speech.

There is room for improvement here, mainly in the area of noise control, but a lot of the elements we have dealt with in this essay are just right. I regularly attend services here and am fond of the acoustics.

The role of the acoustical consultant

When considering building a new sanctuary, or renovating an old one, it is important to get the advice of an acoustical consultant at the earliest stages in the process. For instance, the acoustical consultant should help select the architect. Nearly every design decision affects the acoustics; it is an art to strike the proper balance.

Noise control in particular-fundamental to acoustical excellence-should be considered as early as possible, since costs for noise control depend heavily on how early in the design it is taken into consideration. Air handling units, for example, are often mounted on roofs or directly under the sanctuary. Controlling the noise from such locations is costly and cumbersome. Mounting such noisy equipment away from the sanctuary makes noise control much easier and less expensive.

Parting thoughts

Perhaps, after all, acoustics is not the sovereign concern in synagogue architecture. A synagogue is a not a concert hall, nor is it a lecture hall, but a house of prayer and study. Much of what goes on is known by heart by many of the congregants, or can be read out of the Chumash or Siddur. However a pleasant sound and good speech intelligibility are blessings that will make the experience of the worship service more enjoyable, and create a precious opportunity to hear the human voice partaking in that most human activity, prayer.