Table of Contents
General Speaker Technology
An electronic audible alarm produces an audible warning sound using electronic means. This is in contrast to electro-mechanical alarms that produce sound by mechanical means. Examples of electro-mechanical alarms include the old clapper type alarm clocks, school bells, and car horns. Examples of applications that use electronic audible alarms include smoke detectors and microwave ovens.
Electronic audible alarms may utilize piezoelectric transducers, electromagnetic technology, or speaker technology. Most electronic audible alarms utilize piezoelectric or electromagnetic technology, but speakers are used when:
- Loud low frequency sounds are required (less than 1 kHz).
- Human voice is required.
- Multiple frequencies are required (such as music).
Using a speaker is a more expensive solution than using a piezoelectric transducer, so speakers are typically only used when piezoelectric technology will not meet all application requirements.
Bare speakers do not contain any acoustic sound chambers, so it is up to the user to mount the speaker properly. Mounted speakers not only are pre-mounted, the housing contains an acoustic chamber which affects the sound characteristics. See the description of an acoustic chamber in the SOUND FAQ Section below.
Electrical Application Issues
No. You can connect the speaker drive signal across the speaker terminals either way. If the speaker comes with bare wires or a connector, the speaker is still non-polar and you can connect to the wires or the connector either way with the voltage signal.
Speakers are not driven the same way as piezoelectric transducers. Speakers are rated in Ohms and Watts are typically driven using audio amplifier integrated circuits.
The answer depends on what kind of signal you are applying. Speaker power is rated in watts, so you must calculate or measure the average and maximum power being applied to the speaker. Oscilloscopes and other audio measurement equipment can provide these numbers. If a simple signal is being applied to the speaker (such as a sine or square wave), these values can be calculated manually: Speaker Wattage = (Vrms * Vrms)/Impedance
Mechanical Application Issues
Mallory's circular bare speakers do not have any mounting holes. Customers typically mount the speakers by laying the speakers on a ledge or into a housing that does not touch or obstruct the mylar cone material, and then either use glue or silicone adhesive to secure the speakers to the housing or ledge. Also, care must be taken that the glue or silicone adhesive does not get onto the mylar cone material which could dampen the sound level.
No, the bare speakers are not offered standard with wires. However, Mallory does offer the same models with a twisted wire cable assembly and a Molex Microfit 3.0 connector. The suffix “-MX” indicates that the circular speaker comes with this cable assembly.
Molex Microfit 3.0 Model No. 43025-0200.
The mating connector that needs to be used is Molex Model No. 43020-0201.
The speaker cone does mechanically flex, so some room is needed in front of or behind the speaker cone to allow for this physical movement. If the design calls for placing something very close to the speaker cone, contact Mallory to verify enough room is available for the speaker cone to flex properly.
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Soldering & Washing Issues
330°C for 1.5 seconds or 270°C for 4 seconds.
Sound level is measured in decibels (abbreviated dB). The dB scale is an arbitrary scale that reflects the loudness of the sound that is being measured. It ranges from 0 dB (threshold of hearing) to 130 dB (threshold of pain). For a better understanding of the decibel sound level scale, see Technical Application Guide, "Decibel Sound Level Scale".
The audible alarm should be at least 10 dB louder than the ambient back ground noise so that it can be easily heard. You can estimate the ambient background noise by using the chart found in the Technical Application Guide, “Decibel Sound Level Scale" or you can use a sound level meter to measure the actual ambient noise level.
Every time the sound level increases by 10 dB, it will sound twice as loud to the human ear. For example, an alarm specified as 90 dB at 2 feet will sound half as loud as one specified as 100 dB at 2 feet.
Sound level falls off over distance. We intuitively know this because we have to talk louder (or even shout) when people are farther away. The rule of thumb is that every time the distance doubles, the sound level drops off by 6 dB. For example, if an audible alarm measures 60 dB at 2 feet, by the time it reaches 4 feet, it will only be 54 dB. By the time it reaches 8 feet, it will only be 48 dB, and so on.
On Mallory’s Technical webpage, there is an Excel spreadsheet that enables the calculation of sound level across different distances and wattages.
Most people can only distinguish a sound level change only when it increases or decreases by 3 decibels. For example if a person was listening to an audible alarm that changed from 90 to 92 dB, that person would most likely say that the alarm did not get louder. If the sound level changed from 90 dB to 93 dB, the person would say that the sound level is slightly louder. If the sound level changed from 90 to 96 dB, the person would say that the sound level is significantly louder. If the sound level changed from 90 to 100 dB, the person would say that the sound level is twice as loud as before.
Pulsing tones are more easily distinguished than constant tones. Also, pulsing tones convey typically convey more urgency to a person than a constant tone. On the other hand, it takes more electronic circuitry to make a tone pulse, so pulsing audible alarms are usually more expensive than constant tone alarms. If a more pleasant sounding tone is needed, a chime sound may be preferred.
You can listen to the various sounds that Mallory audible alarms make on our SOUNDS webpage.
dB is the abbreviation for decibels which is how the sound level of audible alarms is measured. The “a” in dBa means that the sound level was measured on an A-Weighting scale. The A-Weighting scale was developed to compensate for the fact that the human ear is not a perfect microphone. By applying the A-Weighting scale to sound level measurements, you put the different frequencies (pitches) that the audible alarms produce on an even basis (i.e. comparing apples to apples). Mallory always uses A-Weighting for their sound level measurements, but not all audible alarm manufacturers are this diligent.
Mallory Sonalert has worked with Professors at Rose Hulman University in an attempt to model the sound chamber using Helmholtz equations, but these equations do not work well in predicting the resulting sound characteristics of the alarm. When Mallory Sonalert engineering designs new audible alarms, we rely on past designs and experience to give guidance on a starting point. However, the final design of the sound chamber is based on careful process of building prototype after prototype in order to find that sweet spot in sound performance."
The acoustic sound chamber of audible alarms includes the area inside the housing that is in front of the sounder element and includes the front hole opening.
The sound chamber does not work like organ pipes. In organ pipes, there are standing waves of different size depending on the frequency generated. This is why the organ pipes are different lengths. If the standing wave principle was used for electronic audible alarms, the alarms would have to be many inches or feet in length.
Perhaps the best way to explain how the acoustic sound chamber works is to think of it using a more visceral medium. If you think of the air sound waves being replaced by water, the sound chamber would work by providing an efficient shape for the water to move out of the housing without being obstructed by eddies, reverse currents, and dead spots. Essentially, the acoustic sound chamber provides a low impedance path for the air pressure wave to escape the housing with maximum intensity.
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Mallory is not aware of anyone who has ever had a shelf life issue with our alarms. That being said, some alarm models contain aluminum electrolytic capacitors. The recommended shelf life for these capacitors is 5 to 10 years depending on how they are used. Our application of these capacitors is not especially sensitive to the shelf life issues of these components, so we would expect that they would last 8-10 years or longer in our alarms just sitting on the shelf (no voltage applied during that time).
Mallory Sonalert Products alarms, buzzers, and speakers do not require an ECCN Number. However, if you absolutely need to assign an ECCN Number, use EAR99 (which means that our product is not regulated).
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Design Engineering uses a variety of tests during the verification and validation design phases. These tests can include: surge voltage, reverse voltage, hot & cold life tests, room temperature life test, humidity, vibration, shock, salt spray, and terminal strength. The Environmental Tests for each alarm are listed in that alarm’s Environmental Durability PDF available on the website.
MSL 1 (Unlimited)
That is a loaded question. Mylar speakers are typically called water resistant. While water won’t hurt the speakers, the speakers are not designed to be submerged in water for extended lengths of time. If possible, the speakers should be shielded from direct water sprays. If the speaker is mounted in a housing, the housing should be mounted down or drain holes should be added to remove any standing water promptly.
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