US2071153A - Acoustic horn - Google Patents

Description

Feb. 16, 1937. A. 1. ABRAHAMS ACOUSTIC HORN Filed May 7, 1935 rlfrinr:

lNvENToR BY MMM A oRNEY Patented Feb. 16, 1937 UNITED STATES PATENT CFFICE 3 Claims.

This invention relates to a hygroscopically impervious method and means of suppressing the frequency-amplitude peaks of a resonant surface.

An object of this invention is to provide a horn 5j of reduced weight which can eiliciently handle large values of energy.

Another object of this invention is to provide a mode of construction of such horns wherewith substantial rigidity is attained.

lo Another object of this invention is to incorporate with such mode of construction means Where- With the sundry resonance peaks, normally associated with the ordinary metal or other thinwalled horns, are suitably damped or smoothed out.

Another and incidental object of this invention is to have such means used in providing the above objects hygroscopically impervious.

These and other objects as will become apparent 20,;111 the description following are secured by means of this invention.

The invention resides substantially in the construction, combination, location and relative arrangement of parts, together with the method employed therewith, as more fully described below, as shown in the accompanying drawing, and as finally pointed out in the appended claims.

Referring now to the drawing, wherein like characters refer to the same or similar parts:-

Fig. 1 is a side elevational view in vertical crosssection of a horn made in accordance with this invention.

Fig. 2. is a similar view of a reducing section adapted with a ferrule suitable for use with the horn of Fig. 1 when the mouth of the speaker unit is such as to require same.

Fig. 3 is a similar view of an alternate construction of section.

Fig. 4 is a conventional View of a speaker suitable for use directly with the horn of Fig. 1.

Fig. 5 is a conventional View of a type of speaker requiring a ferrrule and reducing section as shown in Fig. 2.

When it is necessary to have air-propagated sound waves reach a substantial dist-ance at suitable intensity level, a large modulating chamber of proper design is generally required for transmission; and in combination with a microphone or other such device, also found very useful in reception.

If such chamber is made of ordinary metal, experience teaches that: (1) to avoid wind reverberation and wave-form distorting resonances,the walls should be fairly thick; (2) with such thick 65 walls, a highly undesirable Weight factor is introduced; (3) if the wall thickness is reduced to avoid seemingly excess weight, the disturbing resonances and reverberations are brought within the working frequency range, and the rigidity likewise suffers. 5

On the other hand, a horn made of plastic material to avoid the metallic resonances must necessarily have a heavy wall. Here wall thickness for proper rigidity has to be balanced, not only against contending weight, but also against 10 that of resiliency and brittleness.

Such conflicting factors have called for design compromise which at best has resulted in horns of acoustical and/ or mechanical efficiency leaving much to be desired. 15

A careful study of this problem has led to a solution, found efficient and practicable in every way, and now forming the subject matter of these Letters Patent.

In accordance with this invention, the wall en- 2U velope is made composite, and preferably in sections. It has been found that if a shell of thin gage metal is reinforced with an overlying or underlying surface of fabric, paper, or other such initially pliable material suitably treated before 2- and/ or after application, a chamber of low weight, of great rigidity, suicient resiliency, and highly damped resonance characteristics free from humidity variations results.

As evident from Figs. 1, 2. 3, in conformity with 30 advanced practice, the corresponding parts of tandem sections are represented by the same letters with a subscript indicating their ordinal position in the complete assembly. So also, a discussion applicable to all sections is accomplished 3- by considering the general or nth (ordinal) section. Thus, with nzl, 2, 3, In and On are the inner and outer Walls, and Cni and Cu2 are the anterior and posterior collars of the typical section. This being the nth section, the suc- 40 ceeding one will be the (11+1)th, and will have C(n+1)1 and C n+1 2 as its anterior and posterior collars. In joining the nth and (it-l-Dth sections, the posterior of the former and the anterior of the latter are brought together; and the cooperating flanges will thus obviously be Cn21C n+i 1 (e. g. C22IC31 in Fig. 1).

More specifically, and with particular reference to Fig. 3 for purpose of illustration, a very thin (18 gage, say) metal sheet In is spun, cut, or 50 otherwise formed into a frustumed envelope (usually of rectangular or circular cross-section exponentially increasing along the sound axis). One important advantage of constructing a horn in sections is that the cost of preparing such component shells is greatly reduced without deleterious effect on acoustic performance.

With such thin metallic shell as a base for a section, the pliable material (e. g. fabric) is suitably cut to permit a snug contacting fit, and stily drawn over said shell. Such material may be impregnated before and/or after mounting by a hardening and waterproong compound such as Varnish or the like and either air-hardened or baked, as more fully set forth in my U. S. Patent 1,878,360 led Sept. 26, 1931, and issued Sept. 20, 1932.

The construction of the section is completed by securing fianges Cui and Cnz to the ends thereof by rivets R or the like. The taper of the sections and dimensions of cooperating flanges C1L2=C n+1 i is preferably such that a substantially continuous and smooth horn interior is attained; the consecutive sections being held t0- gether by suitable bolts B. Though not essential, a terminal collar Ca2 (Fig. l) may be provided if desired.

When the mouth of the speaker-unit, microphone, or other device used in conjunction with such horn requires it, an initial section (Fig. 2) with a suitable ferrule C11 is used.

Fig. 3 shows an alternate form of construction wherein the hardened material is made the inner wall I rather than the outer wall On of an nth section of horn.

It is obvious that sundry changes in the details of construction and relative sequence of steps will readily occur to those skilled in the art. I am aware, for instance: that the composite-wall envelope may be prepared in one piece and then cut into sections; that the pliable material may be formed and partially or Wholly hardened on a mould before mounting on the metallic shell; and that fastening means other than metallic iianges or of the type shown may be employed; all without departing from the spirit and scope of my invention. I do not, therefore, desire to be limited to my disclosure of the invention as given for purposes of illustration, but rather to the invention as dened in the appended claims.

The word contacting as herein used signifies underlying or overlying.

The word electrophone will be used to designate a device capable of converting electricall modulations into sound modulations (such as a speaker unit) or sound modulations into electrical modulations (such as a microphone).

What I claim is:-

1. The method of manufacturing an acoustic horn which incorporates the steps of constructing thin metallic frustums of suitable taper, reinforcing said frustums by a contacting nonmetallic and initially pliable material, treating said material so as to leave same in a hygroscopically impervious and hard state, and mounting suitable connecting flanges on corresponding non-integral sections.

2. The method of manufacturing an acoustic horn which incorporates the steps of constructing thin metallic frustums of suitable taper; providing means integral therewith adaptable to joining said frustums with other similar sections, and reinforcing said frustums by a contacting nonmetallic and initially pliable material treated so as to leave same in a hygroscopically impervious and hard state.

3. In an acoustic horn, a detachable section comprising a frustumed envelope with a wall of thin gage metal substantially reinforced by a contacting non-metallic and initially pliable material treated so as to leave same in a hygroscopically impervious and hard state, and means for joining said section with other similar sections.

ALEXANDER I. ABRAHAMS.

Images