Do lower frequencies travel farther?

[Robert Gift]

http://www.whelen.com/outdoor/warnfaq.htm

Quoted from Whelen Engineering FAQ:

"The frequency of a warning tone used in rating a siren's Sound Pressure Level is critical in evaluating the performance of an outdoor warning siren, where the siren's warning tones are expected to carry over great distances.

Whelen siren systems are designed to optimize the production and projection of low frequency warning tones. It is documented that higher frequency tones attenuate (lose power) more over distance than low frequency tones.

A warning siren capable of producing 124 dB at 100 feet with a 500hz warning tone will be more effective than a siren producing 124 dB at 100 feet using a 1,000hz warning tone. This factor should be considered in planning a warning system.

Consider this example of the attenuation of higher frequency tones that is apparent in our everyday life..................

As you are standing out in your yard, your neighbor's teenage son has the stereo in his car blasting as he is coming down the road toward your house. The earth seems to shake as the "boom, boom, boom" of the low frequency bass notes are felt beneath your feet and on your ears. It is not until the car is very near to you that you can hear the high frequency acoustic guitar and voices. As the car
passes you, these high frequency tones seem to disappear, but the pounding and
thumping of the "boom, boom, boom" bass can still be heard and felt.

This scenario clearly demonstrates that ability of the lower frequency tones to be heard at a farther distance than the higher frequency tones.

In short, remember that not all 124 dB (at 100 feet) sirens are alike."

Why dual-tone sirens?
Do some produce Resultants to have a farther reach?

[q2bman]

In my opinion the low tones do cary farther. This is not based on any scientific fact just me hearing distant ambulances. I can hear the low end of the wail better than the high end. But, in you example of the car stereo, one would have to remember that low frequencies like those from a subwoofer are omnidirectional. The highs from the speakers are very directional and may tend to "bounce" arround the interior.

The Whelen's here in Ft Worth went off the other day as I took cover in a parking garage. I walked to the exit to hear the sirens. I could hear the whelens in the town a few miles west of me clearly. The the siren about a block came on and blasted me away! I could hear the low end of the wail from the whelens more clearly than when the reached peak.

I think yes. Low frequencies seem to travel father distances with more spl.

[Whelen Rules]

In my opinion the low tones do cary farther. This is not based on any scientific fact just me hearing distant ambulances. I can hear the low end of the wail better than the high end. But, in you example of the car stereo, one would have to remember that low frequencies like those from a subwoofer are omnidirectional. The highs from the speakers are very directional and may tend to "bounce" arround the interior.

The Whelen's here in Ft Worth went off the other day as I took cover in a parking garage. I walked to the exit to hear the sirens. I could hear the whelens in the town a few miles west of me clearly. The the siren about a block came on and blasted me away! I could hear the low end of the wail from the whelens more clearly than when the reached peak.

I think yes. Low frequencies seem to travel father distances with more spl.

I second this opinion. I believe lower frequencies travel further as well. I live a little less than a mile east of a Whelen Vortex now and I can hear it and others over 2 miles away in town clearly! The closet one to me (less than a mile) is the loudest and I ESTIMATE its dB rating is 74. I can hear others in town that are over a mile and a half or two miles from me at a reconizable hearing level of about 60-63 dB.

[Castlevania2006]

the wail tone on any siren cycle through the sound frequencys, some hear the higher parts better then the lower parts some hear the lower parts better then the higher parts.

[Robert Gift]

the wail tone on any siren cycle through the sound frequencys, some hear the higher parts better then the lower parts some hear the lower parts better then the higher parts.

The siren frequency range is well within the range of normal hearing.
As we age, we lose high frequencies, but we still hear well way below those lost frequencies. (Except for some rockers who have damaged their hearing from loud music.)
My wife and I both detect the bottom sweep of a distant barely-heard electronic siren wail before we detect the higher arc.
As the ambulance gets closer, the higher part then also becomes audible.
But is the siren speaker putting out the same dB at the higher frequencies as at lower?

[JasonC]

But is the siren speaker putting out the same dB at the higher frequencies as at lower?

Not at the same wattage at least. A speaker outputting a 10w 1000Hz tone will have a higher dB level than the same speaker outputting 10w at 500Hz. It takes more energy to produce lower frequencies. Thats why 100 watts can drive a police siren that can be heard over a long distance vs a home subwoofer, which can be felt more so, but travels less far. You can take 100 watts of power only a few feet form a sub, but not in front of a higher pitched police siren.

[q2bman]

I would be interested in a DB per foot per frequency study. Maybe the DB equals that of a higher pitched frequency at a certain range. It does seem the low frequency from a electronic siren carries farther. Even if the wattage remains the same as on a police siren. SO if 100W at a high frequency is louder close up maybe its not as loud as the 100W low frequency at the 100 Ft mark or even a mile off.

[Nelso90]

Throw this one around...
Maybe the reason low frequencies travel farther, is that the wavelengths are longer. If they are more widely spaced, they'd have less of a chance to become interfered with. They could skip over objects on the ground.

[kagome122885]

http://www.whelen.com/outdoor/warnfaq.htm

Quoted from Whelen Engineering FAQ:

"The frequency of a warning tone used in rating a siren's Sound Pressure Level is critical in evaluating the performance of an outdoor warning siren, where the siren's warning tones are expected to carry over great distances.

Whelen siren systems are designed to optimize the production and projection of low frequency warning tones. It is documented that higher frequency tones attenuate (lose power) more over distance than low frequency tones.

A warning siren capable of producing 124 dB at 100 feet with a 500hz warning tone will be more effective than a siren producing 124 dB at 100 feet using a 1,000hz warning tone. This factor should be considered in planning a warning system.

Consider this example of the attenuation of higher frequency tones that is apparent in our everyday life..................

As you are standing out in your yard, your neighbor's teenage son has the stereo in his car blasting as he is coming down the road toward your house. The earth seems to shake as the "boom, boom, boom" of the low frequency bass notes are felt beneath your feet and on your ears. It is not until the car is very near to you that you can hear the high frequency acoustic guitar and voices. As the car
passes you, these high frequency tones seem to disappear, but the pounding and
thumping of the "boom, boom, boom" bass can still be heard and felt.

This scenario clearly demonstrates that ability of the lower frequency tones to be heard at a farther distance than the higher frequency tones.

In short, remember that not all 124 dB (at 100 feet) sirens are alike."

Why dual-tone sirens?
Do some produce Resultants to have a farther reach?

The dual tone sirens were designed at the time when single tone sirens were used for fire alarm purposes. This is so the public could distinguish between the two. Maybe that is the reason why sirens needed to be dual-toned to recieve federal funding back then.