Reducing Speaker Volume for Siren Testing

Henry455

Member
For the Whelen and the Federal (brw/org, black/wht) these wires go to the white connector on the RIGHT of the picture POLARITY IS NOT AN ISSUE. The signal from the siren is AC not DC . The only time "polarity" of the speaker wires is relevant is when using 2 speakers in parallel for proper phasing.
 

CVengence

Junior Member
Our test sirens are just flipped upside down on a thick rubber mud flap off a cement mixer. Dumbs it down enough to not kill your ears.


Sent while driving.
 

rofowacker

Member
OK, Radio shack near me has nothing in any of the ranges shown here. I am in a crunch and the siren on the Gator needs to be reduced tomorrow through Sunday as it will be in a high population of people on foot at a huge event.


is it the ohms or the watts that is the key here? I am not eletronics stupid, just challenged on most days. So a 900 Ohm 3 watt vs a 10 watt 50 ohm (i think they had this one. Someone please school me! Nicely.....
 

Henry455

Member
The higher the ohms, the less volume you will get AND a lower wattage resistor can be used. here are a few examples.


Ohms law: Amps= voltage divided by resistance


Most 100 watt sirens produce 33 volts RMS output.


33 volts divided by 11 ohms (100 watt speaker impedance) = 3 amps. 3 amps X 33 volts = 99 watts


Say we put a 900 ohm resistor in series with the 11 ohm speaker.


33 volts divided by 900 = .036 amps. .036 amps X 33 volts = 1.2 watts. the speaker output would approx 1 watt and you would need a 2 watt resistor.


Say we used a 450 ohm resistor in series with the 11 ohm speaker


33 volts divided by 450 ohms = .073 amps. .073 amps X 33 volts = 2.4 watts. The speaker output would be approx 2 1/2 watts and you would need a 5 watt resistor.


Probably clear as mud but I hope it helps.
 

rofowacker

Member
Henry that makes a lot more sense now. I guess the looming question is now how many watts do I want as an output and work it to find the resistor needed.
 

Henry455

Member
In your application I would guess 10 watts would be plenty. Most car alarms sirens are 5 to 10 watt output for comparison. That would require a 110 ohm resistor rated at 15 watts. 220 ohm resistor rated at 7.5 watts (or higher) would give you 5 watts.
 

MtnMan

Senior Member
Henry455 said:
In your application I would guess 10 watts would be plenty. Most car alarms sirens are 5 to 10 watt output for comparison. That would require a 110 ohm resistor rated at 15 watts. 220 ohm resistor rated at 7.5 watts (or higher) would give you 5 watts.

Henry, your double L-pad design is great, but I have to disagree with your math here. Your calculations give the correct total power output, but most of power is going to be dissipated by the resistor. The actual power to the speaker would be 0.8 W and 0.2 W in these examples (let me know if you're interested in the details... I suspect everyone else has tuned out).


The good news for rofowacker is that human hearing is quite insensitive to power levels, and about 1 W should be fine for demo purposes. Get the 2-pack of 50 Ohm, 10 W resistors from Radio Shack, put them in series, and you've got a a 100 Ohm, 20 W. Put that in series with the speaker and you should be good to go.
 

Henry455

Member
MtnMan you are correct, my bad. The voltage drop across each resistence has to be taken into account. Sorry for the confusion on my part.


Tim
 

Skip Goulet

Passed Away
rofowacker said:
OK, Radio shack near me has nothing in any of the ranges shown here. I am in a crunch and the siren on the Gator needs to be reduced tomorrow through Sunday as it will be in a high population of people on foot at a huge event.

is it the ohms or the watts that is the key here? I am not eletronics stupid, just challenged on most days. So a 900 Ohm 3 watt vs a 10 watt 50 ohm (i think they had this one. Someone please school me! Nicely.....

Just curious to know why you want to scale back on the volume just because you're in a large crowd. Experience has taught me that with a large crowd, the louder the better if you need to get through the crowd.
 

MtnMan

Senior Member
Skip Goulet said:
Just curious to know why you want to scale back on the volume just because you're in a large crowd. Experience has taught me that with a large crowd, the louder the better if you need to get through the crowd.

I'm guessing this is some kind of demo, not for actual emergency use.
 

Thomas1234

Active Member
I recently acquired a AS-250 (-NL Dutch) siren module from Federal Signal. I would love to try this out together with a TS24 siren speaker.
But without annoying neighbors, is there any way to lower the volume, example remove the cone or else? Help appreciated!
 

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prty

Newbie
put it in the closet and pile a bunch of clothes on top maybe? or put it face down on foam and put something on top?
 

Thomas1234

Active Member
Oke, thanks again..what is just did, put a sock inside the cone of the speaker, put the whole in a plastic (ikea) box, and made sure some old blankets are in the horn itself. Now i can hear finally the sound at around (typically dutch Hi-lo police sound) ..dont you just love those mini sunday evening projects! ;-)
 
Although there have been great suggestions presented for reducing the volume of sirens, I believe this one is the most versatile. It's a 100 watt stereo 8 ohm Lpad wired to give a 200 watt 16 ohm mono Lpad. This gives you the ability to adjust the volume from very low to full volume with a twist of the knob. Because of being an Lpad the sirens sees a fixed impedance from low to high. I chose the 200 watt version because I have been using a 100 watt 16 ohm Lpad but with a 100 watt siren and the pad turned to very low volumes it heats up very hot. Applications include man caves, parades, car shows, Emergency Equipment sales demos, etc. The Lpad costs $25.00 so it is not as inexpensive as some of the other solutions. The Lpad part # is 260-264 and can be found at Parts Express: the #1 source for audio, video & speaker building components. Below are some pictures and a short demo video. Click on top picture for video.


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Henry, The solution you provided above seems like exactly what I need to do on a Gator. We recently purchased a gator and someone installed a 100-watt Powercall on it. We run it through crowds of people at the county fairground, and other public events, and we find that the 100-watt is obnoxiously loud and startles people walking in front of us. It is honestly even too loud for us and we are used to loud sirens. Last year, we stuffed towels in to the speaker and it was much better. I'd like to see a more professional way to achieve this and be able to make the siren louder when in other areas such as parking lots (this gator is a medical transport gator that takes people to the parking lot where ambulances are waiting).

Question for you is, can you repost your wiring diagram for this LPAD? It appears that they got removed. Thanks in advance!
 

shues

Lifetime VIP Supporter
The video above shows a 500k Ohm pot. There's not much useful adjustment range for siren volume reduction on a pot with such a high value. @Henry455 suggested more suitable values in his post above. He also suggested using an L pad, which helps to ensure an impedance match between the siren and the speaker throughout the entire adjustment range.
 
I make mine using 3.3K ohm 1/4watt resistors. I was offering them soldered, heat shrink, connectors and shipped for $10 for a while. Everyone said they worked great. I will post a demo. They work great and the volume is perfect for inside. Not loud at all to the ears.

 

shues

Lifetime VIP Supporter
Each of the red circles represents one channel of what is sold as a stereo L-pad. Remember that audio is AC, so there are no positive and negative terminals to be concerned with. The terminals marked 2 are connected to what is known as the wiper arm of the ganged potentiometers that make up an L-pad. The wiper arm is the moving part. The wiper arm can be placed electrically closer to or farther from the source, in this case the siren output at the terminals marked 3. The lower the resistance between terminals 2 and 3, the higher the resistance between terminals 2 and 1. This inverse relationship helps to ensure the siren sees the same load at any given time, regardless of how much that load is provided by the speaker itself and how much of it is provided by the L-pads' circuits between terminals 2 and 1.

There is some introductory information about audio L-pads available here: http://www.colomar.com/Shavano/lpad.html
 

trucky14

Lurking Newbie
I make mine using 3.3K ohm 1/4watt resistors. I was offering them soldered, heat shrink, connectors and shipped for $10 for a while. Everyone said they worked great. I will post a demo. They work great and the volume is perfect for inside. Not loud at all to the ears.


Ok, I like this idea. I am in the need to take a few BLET training cars for a local community college into "track mode". The drivers training track is next to a residential area. So the cars when learning pursuit driving on the course can not have an audible outside speaker. They want a small speaker in the console that can be switched to track mode when being used at the college, or normal when they get to drive at the old runways of a retired airport. My question to you is will this heat up substantially over time causing issues? These cars will be on track for at least 5-8 hours a day.
 

shues

Lifetime VIP Supporter
Yes, your resistors will need to dissipate a lot of heat. You will need to build a network of resistors, likely either with heatsinks or by placing the setup in an oil bath.

You could also play a recording of a siren in the car using its existing stereo and speakers, which could probably be controlled from the siren's original controls with a little creativity.
 

MtnMan

Senior Member
My question to you is will this heat up substantially over time causing issues?
Depends on the value of the resistor. A 500 Ohm resistor in series with the speaker would be about right for your use, and will only dissipate about 2 Watts. Use a 5 Watt or higher rated resistor and you’ll have no problems.
 

shues

Lifetime VIP Supporter
The 1/4 watt 3.3k ohm resistors in the quoted post are probably underrated for the application.
 

zxsas

Newbie
Although there have been great suggestions presented for reducing the volume of sirens, I believe this one is the most versatile. It's a 100 watt stereo 8 ohm Lpad wired to give a 200 watt 16 ohm mono Lpad. This gives you the ability to adjust the volume from very low to full volume with a twist of the knob. Because of being an Lpad the sirens sees a fixed impedance from low to high. I chose the 200 watt version because I have been using a 100 watt 16 ohm Lpad but with a 100 watt siren and the pad turned to very low volumes it heats up very hot. Applications include man caves, parades, car shows, Emergency Equipment sales demos, etc. The Lpad costs $25.00 so it is not as inexpensive as some of the other solutions. The Lpad part # is 260-264 and can be found at Parts Express: the #1 source for audio, video & speaker building components. Below are some pictures and a short demo video. Click on top picture for video.


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I wish those pictures were still available. This is exactly what i need. I need to be able to lower the volume on my siren for parades and demonstration. If im at a children's home at their bday party full volume is a little too loud. Does anyone have any pictures of adding a two 100watt l-pads with volume control.
 

Layne6288

Newbie
I have a BP100 that I'm going to keep around the shop to test sirens on. I want to reduce the output. Is there something commercially made that I can put inline on the speaker wire to do this? Or can someone tell me how to make something to do it?


I recall an install on an engine where they had the feature via a switch on the dash. I'm looking to do something like that.
I learned to use a lightbulb, splice one wire from your speaker on the side of a lightbulb then the other end on the bottom. Lower the wattage bulb the quieter.
 

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