Acoustics – Sound-modifying means – Intensifying horn
Reexamination Certificate
2001-03-20
2003-03-11
Nappi, Robert E. (Department: 2837)
Acoustics
Sound-modifying means
Intensifying horn
C181S177000, C181S030000
Reexamination Certificate
active
06530451
ABSTRACT:
FIELD OF THE INVENTION
The present invention regards a system of components for the diffuision of sound, which is particularly suitable for permanent or semipermanent installations in venues dedicated to the production or reproduction of music, speech, sounds or vibrations, outdoors, in cinemas, auditoriums and in all indoor rooms in general.
BACKGROUND OF THE INVENTIONS
New digital technology in the sound recording field has made it possible to record part of the sound spectrum with absolute fidelity, such as the low and especially infra-low frequencies, those below the levels which are audible by the human ear and are perceptible by the body as vibrations.
This technology is also characterized by the absence of distortion of the original wave shape at a much higher sound level than was and is possible with analog systems. Particularly, in analog systems adding to the pickup problems Insurmountable mechanical and electromagnetic limits which are found during the storage or recording phase of the program on magnetic tape or vinyl records, it is absolutely impossible to exceed a certain level of dynamics, especially in the frequency bands in question, and to contain the distortion and therefore the degradation of the original signal within negligible limits.
In short, present digital systems enable the recording and the reproduction of a much wider dynamic range than is usually audible or necessary for the sensitivity of the human ear, maintaining great fidelity with features of low distortion and useful passband.
However, although this possibility is now widely accepted during recording and future development is looking to record further infinitesimal qualitative details, the possibility of reproducing the dynamic range by means of a modem amplification system is not as widely achieved.
In fact, in spite of the extensive technical/scientific literature on the subject, I'm not aware of any product capable of reproducing such a dynamic range, at least as far as the low or infra-low frequencies are concerned, which are the most difficult to reproduce in terms of power. This hoped for result is often unachievable due to environmental acoustics, which too often are not up to the reproduction system'standard, or at any rate don't allow the original sound quality to be fully respected.
It must not be forgotten that for the sensitivity curve of the human ear, the difference between the loudness level at the center of the audible band (e.g. taking a value of 90 dBSPL and 1,000 Hz) and the level necessary for the same loudness at the bottom end of the audible band, 20 Hz is no less than 30 dB SPL.
Now since 30 dB (logarithmic measurement unit) are equivalent to 1,000 times in power, this means that when 1 Watt of power is applied to its terminals, a given loudspeaker is capable of reaching (for example) a level of 90 dBSPL at 1,000 Hz; to obtain the same loudness at 20 Hz, it's necessary to use another loudspeaker with the same efficiency at the latter frequency as that of the former loudspeaker at 1,000 Hz, as well as a power capacity and mechanical construction able to support no less than 1,000 Watts applied to its terminals.
Although material and adhesive technology has now enabled the construction of loudspeakers with voice coils capable of supporting 1,000 electric Watts even for long periods without burning out, thanks also to ingenious cooling systems, this in fact occurs at relatively high frequencies, up to the transducer's maximum effidency zone, usually at frequencies of between 100 and 200 Hz; however, this same technology definitely does not make this practice possible at gradually lower frequencies, even from 100 Hz: the entire loudspeaker is mechanically destroyed in a very short, regardless of the capacity of the voice coil to hold power without burning out.
This occurs because a loudspeaker's diaphragm movement, necessary for the reproduction of low and infra-low frequencies at a high sound pressure levels, is almost always incompatible with its own intrinsic geometry or mechanical construction.
Moreover, even overlooking the fact that any loudspeaker which is capable of holding a sound signal applied to its input terminals with a power of 1,000 Watts would reproduce this signal with such a high distortion that no ear could bear i for a significant time, a larger quantity of loudspeakers, in a ratio of at least 1 to 10 or higher, according to the radiation conditions under which these units would have to operate, would have to be used to compensate for this enormous difference in efficiency, which is typical of woofers when reproducing low frequencies rather that those in the central band.
The premise is so generalized that it is possible to see with increasing regularity sound reinforcement systems using a section for the reproduction of low and infra-low frequencies composed of a large number (even ten) single high-power units linked together.
This is because of the need to obtain high sound levels which are distortion-free or almost when reproducing music, nowadays routine practice in all the types of related events; dubs, live concerts or even classical music reproduced live in stadiums for thousands of listeners, with the digital amplification of a large symphonic orchestra, or even modem films' soundtracks which, thanks to digital recording, are able to recreate the sound's level and quality in a captivatingly realistic manner.
All this obviously leads to a significant rise in costs and consumption due to the use of a large amount of electricity for powering numerous units together, as well as a rise in maintenance costs because of the greater possibility of repair work.
However, realistic high-level sound reproduction even for low and infra-low frequencies isn't the only problem that prevents the intrinsic quality of modem sound production and/or recording techniques from being achieved.
In fact, rooms delegated mainly to the reproduction of music and speech (e.g. movie theaters, projection rooms, etc.) very often have architectural characteristics which considerably change the original sound played back inside them, even more so if levels must be kept high for the degree of realism required.
Walls that are parallel and often reflective, lack of homogeneous, well-distributed absorption for achieving optimal reverberation times for the venue and the type of program being reproduced lead to the concentration of greater energy on some frequency bands rather than others in certain positions in the room, according to the studies and statistics that have stood the test of time for decades.
In relatively small rooms, it's even possible that so-called well-known stationary waves occur at low frequencies, greatly altering reproduction quality, masking medium and high frequency bands, whose intelligibility is indispensable to enable speech to be understood when there is an often extremely complex music program.
Generally speaking, rooms built in the past, but also nowadays, for the reproduction of the film soundtracks (e.g. movie theaters), often for budget reasons, have classical parallelepiped layouts with parallel walls, regardless of the fact that there are also the so-called “balconies”, even if these are less frequently built for cost reasons.
Moreover, apart from the necessary insulation towards the outside, internal acoustic treatment which should be very accurate to obtain the required reverberation curve according to the hall's frequency and dimensions, is generally limited to the ceiling and (for reasons Intrinsic to the function) to the area of the floor on which the audience's fabric-covered seating is installed.
Walls are rarely suitably well treated. “Flutter” echoes, “slap” echoes, unwanted reflections and stationary low-frequency waves often considerably worsen reproduction of soundtracks and speech in theaters screening films.
SUMMARY AND AIMS OF THE INVENTION
A first aim of the present invention is to overcome and solve the aforementioned problems regarding reproduction of low and infra-low fr
McGlew and Tuttle , P.C.
Nappi Robert E.
Outline S.N.C. di Noselli G. & C.
San Martin Edgavdo
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