Sound Advice for Agencies

Commuters, whether in the station or on board, have to respond to announcements quickly and with confidence. However, the transit environment places demands on people’s hearing not found in controlled environments such as theaters, concert halls, even cars. Those demands include sounds such as excited children, traffic noise, passenger conversation and loud music, as well as visual chaos, such as passengers moving back and forth. Even strong scents and odors can be a distraction. Add in that transit companies want to attract riders over 50, who are many times hard of hearing, and it becomes easy to see why transit designers are demanding more of loudspeakers.

An Evolution in Mass Transit Speakers

Loudspeakers are the key element in any sound system. They must be chosen carefully and specifically for the transit industry. Not too many years ago, speakers used for mass transit applications were not specifically designed for the industry. Sometimes speakers weren’t even designed for mass transit’s standard 70-volt systems.

At other times, 4-ohm automobile speakers, which consume twice the power, were used. Although great for music, car speakers have the wrong frequency response and sensitivity to deliver clear, strong announcements efficiently. And almost always, assembly of automotive speakers and enclosures created additional labor costs and altered the sound quality.

Today a new generation of speakers is available. This new generation addresses industry needs, such as better sound, improved clarity, and easier and less expensive installation.

New mass transit speakers come complete with transformer, ceiling grill and enclosure. Newer, shallower drafts are designed to fit into tighter spaces, such as the ceiling of rail cars. Custom painted, these speakers are ready to install. Tested with speaker, transformer and grill fully assembled, they deliver sound as specified.

Inside is a water-resistant cone, 70-volt transformer and 12-watt speaker which can be used with transformers rated up to 10 watts. It performs well through the voice range (300 – 7,000 Hz) and is designed for high ambient noise situations with a sensitivity rating of 90 dB SPL. The shallow depth allows it to be installed in tight spaces.

Design, Manufacturing and Quality Control

Behind every good speaker is good design, good engineering, tight control of the manufacturing process and thorough testing. Without those attributes, speakers often fail to deliver as promised.

Good design begins with a discussion between the loudspeaker manufacturer and the audio system designer of goals and how to achieve them. The objective is to identify the highest priority specifications. For example, if the system has to be loud enough to be heard clearly over high ambient noise, there are two choices – increase amplifier power into the speaker, which is expensive, or increase the sensitivity of the speaker.

Loudspeaker sensitivity is specified in dB (decibels) and SPL (sound pressure level) with 1 watt input measured at 1 meter distance. Increasing output by 3 dB to overcome high ambient noise requires doubling the power. So, a speaker with 90 dB SPL (sensitivity) would require 2 watts of power to increase its output to 93 dB SPL.

It is clear to see how a speaker with higher sensitivity requires less power and, therefore, reduces total system cost.

Attaining high performance in loudspeakers requires good design and good engineering. Using the latest 3-D modeling software and prototyping, engineers can integrate driver, transformer and enclosures to give a very accurate idea of how a speaker will perform before it’s built. For example, if a small space is required, the software may lead the engineer to use a, low-profile, neodymium magnet, the strongest type of loudspeaker magnet. These magnets are very small, yet their high energy optimizes performance.