What is louder (dB rating)?

[der Papst]

I was disappointed by the video of a unit looking similar to the HLS which indicated a mere 100 dB at a mere 20 meters from such a unit. Either the sound level meter had a bad battery, the meter was defective, or the siren's air supply was low.

I know the Video you are talking about.
It was a real HLS, even one of the most powerfull.
The Name of the manufacturer is Rickmers-Werft, the rarest HLS in Germany.

At first, if you emit Sound with >160 dB, you don't have to care about dead zones because even the reflection of the sound is louder than any other normal siren. It's very usefull to concentrate the sound to a very small "donut" because the direct radiation is only needed at very big distances - because of that, the SPL-meter will have been hit only by reflections.
A wide angle of emittation would hit near objects directly, causing damages to the near people and also to fragile objects.

I know a Pintsch-Bamag with reduced airpressure because the siren destroyed several windows at the first test at full power.
Maybe that's another reason - the recorded siren is on the yard of a school, maybe the air pressure has been reduced because of the children.

[acoustics101]

The 160 dB rating you are quoting would have to be at 1 meter. At a distance of 30 meters (100 feet), from which most warning sirens are rated, the SPL would drop by 30 dB to 130 dB, yet the meter was indicating a mere 100 dB from a said distance of only 20 meters. There is definitely something wrong with this picture.

The SPL of any non vertically arrayed omni source should not fall off by 30 dB from the on axis SPL at something like only a 45 degree angle from the source. I could possibly see it occuring from an extreme angle of 90 degrees (directly under the siren). I could also see it occuring at a shallower angle it if it were a tall stacked array, such as a Whelen WPS2910, but not from just a single array of horns.

With its single horn array, the HLS would not be that highly directional of a unit (thus more acoustical output for a given dB rating at 100 feet). There are laws of physics dictating the directivity index vs the physical size of the radiator vs the wavelength.

If there was not something wrong with the setting of the sound level meter, such as it being set on its high sensitivity setting with a maximum reading of around 100 dB, I vote that this unit was not operated at its full output. When measuring loud devices up close, you must always use the low sensitivity setting, which allows readings in excess of 130 dB on this type of meter. Cheap Radio Shack meters max out at slightly above only 120 dB. In either case, you need to be familiar with their operation in sound fields of high level.

I was disappointed by the video of a unit looking similar to the HLS which indicated a mere 100 dB at a mere 20 meters from such a unit. Either the sound level meter had a bad battery, the meter was defective, or the siren's air supply was low.

I know the Video you are talking about.
It was a real HLS, even one of the most powerfull.
The Name of the manufacturer is Rickmers-Werft, the rarest HLS in Germany.
quote]

[System 7000]

According to the H?rmann HLS manual that der Papst posted a link to, here are the sound ratings for the HLS273:



In Imperial:
.......30 m = 98.425 ft
.......60 m = 196.85 ft
.....120 m = 393.70 ft
.....240 m = 787.40 ft
.....480 m = 1,574.8 ft
.....960 m = 3,149.6 ft
..1 920 m = 6,299.2 ft
..3 940 m = 12,926.5 ft

Regards,
Jerry.

[acoustics101]

http://a.imageshack.us/img692/2986/42357368.jpg
This is very useful information, but it does not appear to be for the same HLS model. That's the same impression I got when originally posted. The siren looks completely different and the maximum level given is 124 dB at 30 meters. I like the fact that they are not derating these with distance by the arbitrary 10 dB/doubling the distance as seen in most siren literature. The figures shown are believable and are obviously based on actual measurements.

At 160 dB at 1 meter (130 dB at 30 meters) the model shown in the original photo should be a full 6 dB louder. I wonder if these units are no longer being made? It would be quite a siren!

[der Papst]

The head of the HLS273 and similar models is 0,5m high, the other heads are 3-4 m high and have very big horns.
The size of a horn is very important for the SPL.

The HLS is not longer made because:
1.) The cold are is over since 30 years.
2.) The HLS is the most complex siren ever built which makes expensive maintanance necessary.

I think i'll have time to write an article about the parts of the system and the controller.

A short description:
Because the siren can't produce the needed air amount in real-time, the air storage has to be always under full pressure and the batteries mustn't loose their voltage.

The diesel-engine drives a dc-generator and a compressor, connected by a clutch.

If the pressure sinks under its threshold, the controller starts the diesel-engine and switches the clutch on to enable the compressor.
After the pressure is on its maximum, the controller switches the clutch off.
The diesel-engine doesn't stop until the batteries are fully charged.

[BIGMIKE SOCAL]

While doing my research if found these specifications:

Pintsch Bamag HLS pneumatic high-performance data (level with head):
Manufacturer: Pintsch Bamag
160dB @ the horn
156dB @1 meter.
131dB @30 meters.

Chrysler-Bell Siren:
Manufacturer:American Blower
Three stage centrifugal type compressor stiff shaft unit
43 inch OD cast iron housing
22-3/4 inch OD cast aluminum heat treated alloy impellers
Rated speed 4,600 RPM
Discharge volume 2,610 CFM
Discharge pressure 6.95 psig
Discharge velocity 35,000 fpm (400 MPH)

171dB @ the horn.
138dB @ 30 meteres.
Single Tone, 460 Hz

[der Papst]

Pintsch Bamag HLS pneumatic high-performance data (level with head):
Manufacturer: Pintsch Bamag
160dB @ the horn
156dB @1 meter.
131dB @30 meters.

Where did you find that?
That would be more SPL at 30m and less SPL at 1m than the small H?rmann-head - how's that possible?

Meassurement at the horn is completely senceless and i've never read something like that. How is it defined?
Fixing the microphone into the horn? LOL

The official rating is 163dB/1m @ 16bar.
Since the air is delivered from an air storage, the SPL depends on the pressure.
The most HLS fill the storage to 16 bar. Sirens near buildings often use less pressure but its possible to use more than 20 bar.

[BIGMIKE SOCAL]

Pintsch Bamag HLS pneumatic high-performance data (level with head):
Manufacturer: Pintsch Bamag
160dB @ the horn
156dB @1 meter.
131dB @30 meters.

Where did you find that?
That would be more SPL at 30m and less SPL at 1m than the small H?rmann-head - how's that possible?

Meassurement at the horn is completely senceless and i've never read something like that. How is it defined?
Fixing the microphone into the horn? LOL

The official rating is 163dB/1m @ 16bar.
Since the air is delivered from an air storage, the SPL depends on the pressure.
The most HLS fill the storage to 16 bar. Sirens near buildings often use less pressure but its possible to use more than 20 bar.

Pintsch Bamag HLS info came from a staff member from the Ministry of Defence of the Federal Republic of Germany office in Berlin (via Email).

[der Papst]

Info came from a staff member from the Ministry of Defence of the Federal Republic of Germany office in Berlin (via Email).

163 to 156 dB is a big difference, maybe that's how they configure the siren near buildings.
I also doubt of their exactly knowledge^^
The HLS have been mounted during cold war and at its end, the most sirens in germany have been unmounted...
Especially the HLS is a forgotten system in germany. Some have been "bought" by the communitys or fire brigades for a symbolic DMark.

Today, only electronic sirens or E57 are mounted where needed, the HLS is dissapearing everywhere.
And just a small part of the HLS in germany is active...

[acoustics101]

Thanks Mike! This is the most useful information yet about the Pintsch Bamag HLS pneumatic siren.

First and foremost, the most important reading is the SPL at 30 meters (100 feet). There is some confusion about the measurement at the mouth of the horn and at 1 meter. Normally you would measure the SPL at 1 meter from the throat of a horn and not from its mouth, as apparently was done here. In the case of a very large horn, such as the horn of a Thunderbolt, you may still be inside it! I would not trust a reading there.

In summation, a reading of 131 dB at 30 meters omni is as much, if not more total acoustical power than the 180 HP Chrysler siren's 138 dB at 100 feet unidirectional output.

While doing my research if found these specifications:

Pintsch Bamag HLS pneumatic high-performance data (level with head):
Manufacturer: Pintsch Bamag
160dB @ the horn
156dB @1 meter.
131dB @30 meters.

Chrysler-Bell Siren:
Manufacturer:American Blower
Three stage centrifugal type compressor stiff shaft unit
43 inch OD cast iron housing
22-3/4 inch OD cast aluminum heat treated alloy impellers
Rated speed 4,600 RPM
Discharge volume 2,610 CFM
Discharge pressure 6.95 psig
Discharge velocity 35,000 fpm (400 MPH)

171dB @ the horn.
138dB @ 30 meteres.
Single Tone, 460 Hz