I'm a total noob to this and only have basic understanding of electricity and audio.
I install siren/pa and emergency equipment in vehicles for volunteer 1st responders and part-time police.
The industry standard siren speaker is a 100w 37w rms 11 ohm and the 125db siren is, as it should be, very loud.
My question is what are some options I have to reduce the output to something that is extremely quiet for testing/installation purposes. It can be crude and will only be used temporarily.
I thought maybe I could put an L-pad pot in line before the speaker to be able to adjust the output without destroying the amp.
My other thought was since I have a couple 6 ohm 50w resistors maybe I could put those in series prior to the speaker as a temporary fixed volume solution.
Thanks in advance for the help.
I install siren/pa and emergency equipment in vehicles for volunteer 1st responders and part-time police.
The industry standard siren speaker is a 100w 37w rms 11 ohm and the 125db siren is, as it should be, very loud.
My question is what are some options I have to reduce the output to something that is extremely quiet for testing/installation purposes. It can be crude and will only be used temporarily.
I thought maybe I could put an L-pad pot in line before the speaker to be able to adjust the output without destroying the amp.
My other thought was since I have a couple 6 ohm 50w resistors maybe I could put those in series prior to the speaker as a temporary fixed volume solution.
Thanks in advance for the help.
Assuming it's just a speaker?, and fed from a conventional amp?, then you can't damage the amp anyway - even with no load at all (that only applies to valve amps).
A simple L-Pad attenuator is all you need - and probably not even that - but you'll probably be surprised how much attenuation you need to make it 'sensibly' loud 😀
Why do you think it's 11 ohms?, is that what you measured on a meter? - if so it's probably 16 ohms.
Personally I'd use a 16 ohm 50W resistor as a dummy load, then take a 100 ohm resistor off that to feed the speaker - and you might find that's still too loud 😀
Going back a LONG time one of my wife's cousins bought our young daughter a toy phone for Christmas (in revenge for us buying their daughter one!) - the beeps from the buttons were incredibly loud and annoying, and while I can't remember the value of resistor I put in series with the speaker I remember been amazed at how high it was!.
A simple L-Pad attenuator is all you need - and probably not even that - but you'll probably be surprised how much attenuation you need to make it 'sensibly' loud 😀
Why do you think it's 11 ohms?, is that what you measured on a meter? - if so it's probably 16 ohms.
Personally I'd use a 16 ohm 50W resistor as a dummy load, then take a 100 ohm resistor off that to feed the speaker - and you might find that's still too loud 😀
Going back a LONG time one of my wife's cousins bought our young daughter a toy phone for Christmas (in revenge for us buying their daughter one!) - the beeps from the buttons were incredibly loud and annoying, and while I can't remember the value of resistor I put in series with the speaker I remember been amazed at how high it was!.
Try this fixed attenuator.
I designed it for the typical "5W tube amp" which is still way too loud for appartment use if you crank it, but you should change values a little to suit your siren speaker.
Replace R1 with 2 x 15 or 20 ohm 25W resistors in series, and R2 can be 0.47 ohms as shown or lower: 0.33 ; 0.22 or 0.1 ohms.
I suggest these values because they are typical power amp emitter ballast resistors , inexpensive and easy to find.
Volume attenuation will still let you hear your siren but be *much* more bearable.
I designed it for the typical "5W tube amp" which is still way too loud for appartment use if you crank it, but you should change values a little to suit your siren speaker.
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Replace R1 with 2 x 15 or 20 ohm 25W resistors in series, and R2 can be 0.47 ohms as shown or lower: 0.33 ; 0.22 or 0.1 ohms.
I suggest these values because they are typical power amp emitter ballast resistors , inexpensive and easy to find.
Volume attenuation will still let you hear your siren but be *much* more bearable.
Great! thanks guys. I appreciate the input.
I'm not afraid of experimenting, but if I made a mistake in this case it could be costly.
Your diagram confirms the method I was thinking is possible. However I'm just concerned with the resistor values. I think 50w may still be way too loud for my needs, these sirens could make your ears bleed in a closed in space. I'm looking for an equivalent db output as a cell phone speaker from a few feet away for example....just loud enough to make sure the tones are working properly.
Nigel, I don't know what you mean by conventional amp but just from what I've read it seems that if I use a speaker with the wrong impedance I can toast the control unit....perhaps that's not correct?
I haven't ever bothered to put a multimeter on any of the speakers, if I were to I'd assume they would read less than 11ohm anyway because of the method used to test it. As I mentioned, 100w/11ohm is the industry standard for the speakers themselves so I'm just going by those specs. I don't know enough about electricity to know why that is but all the amps and speakers from manufacturer to manufacturer have the same specs in both one and two channel variations.
I'm also open to using a different, lower wattage speaker instead of the siren speaker if that makes any difference. I'm sure I have PC type speakers laying around, but I wouldn't know what value resistors to use to attenuate properly without damaging the amp or speaker
Thanks!
I'm not afraid of experimenting, but if I made a mistake in this case it could be costly.
Your diagram confirms the method I was thinking is possible. However I'm just concerned with the resistor values. I think 50w may still be way too loud for my needs, these sirens could make your ears bleed in a closed in space. I'm looking for an equivalent db output as a cell phone speaker from a few feet away for example....just loud enough to make sure the tones are working properly.
Nigel, I don't know what you mean by conventional amp but just from what I've read it seems that if I use a speaker with the wrong impedance I can toast the control unit....perhaps that's not correct?
I haven't ever bothered to put a multimeter on any of the speakers, if I were to I'd assume they would read less than 11ohm anyway because of the method used to test it. As I mentioned, 100w/11ohm is the industry standard for the speakers themselves so I'm just going by those specs. I don't know enough about electricity to know why that is but all the amps and speakers from manufacturer to manufacturer have the same specs in both one and two channel variations.
I'm also open to using a different, lower wattage speaker instead of the siren speaker if that makes any difference. I'm sure I have PC type speakers laying around, but I wouldn't know what value resistors to use to attenuate properly without damaging the amp or speaker
Thanks!
No one has suggested 50W, that wouldn't be any quieter.
You can't damage the speaker anyway, and the only way to damage the amp is to connect too low an impedance to it.
JMFahey's solution doesn't maintain the correct impedance load, but there's no real need to - my main concern with his approach is the difficulty of getting it quiet enough, and the relatively 'crude' steps available by using standard very low value resistors.
Thanks. This stuff is so far over my head, I knew you guys here would be able to help.
By that I only was referring to the two 25w resistors in series, my mistake.
I can't damage a speaker if it's too low of a wattage you're saying?
Ok, now your original suggestion makes more sense to me.
I thought it was bad for both parts if the impedance was off in either direction.
If you still feel that would be a good route to take could you clarify that for me? you lost me with the last half-sentence.
What would be the result of two 50w 6ohm in place of R1?
thanks again for bearing with me.
Nigel said:
By that I only was referring to the two 25w resistors in series, my mistake.
I can't damage a speaker if it's too low of a wattage you're saying?
Ok, now your original suggestion makes more sense to me.
I thought it was bad for both parts if the impedance was off in either direction.
If you still feel that would be a good route to take could you clarify that for me? you lost me with the last half-sentence.
What would be the result of two 50w 6ohm in place of R1?
thanks again for bearing with me.
if it's like siren/pa horns i've encountered they're dual units siren triggered by DC voice band page speaker with a common ground for both. are you looking to attenuate the siren?
It's a single speaker siren and pa with radio repeat. I'm looking to attenuate everything coming through said single speaker, by ~90%.
thanks
Sorry, I was thinking about getting a *total* load impedance of 15/20 ohms (simply because it seems to be far easier to get 10 ohm power resistors instead of 7 or 8 ohms ones) and wrote "15/20 ohms each". 🙁 OMG
And of course I stand corrected.
1) As of the attenuation, the siren will never get 50W out of this but respectively:
with 20/0.47 ohms= 20 mW ... which should be loud enough to know the system works but VERY listenable in a silent workshop .
with 20/0.22 ohms= 5 mW
with 20/0.1 ohms= 1 mW
truly "cellphone on the table a meter away" levels 😉
In fact, the 0.47 ohms resistor level will be fine.
This has been tested lots of times and the "3 AM" label is confirmed by happy customers 🙂
As of why I chose a shunt attenuator instead of high value series resistors is because in practice sound remains closer to the unattenuated one, while series ones cause a buzzy annoying sound, reason being that speakers have a very far from flat impedance, and the constant current type drive caused by high value series resistors (10X nominal impedance and above) enhance the worst traits of speakers.
That´s why most earphone outs (which just get 100 to 470 ohms in series) are horrible.
Also didn´t suggest a variable level setup with a rotary switch or something, simply that if 0.47 ohms is *still* too loud (given the siren speaker high efficiency) there´s the option of setting it even lower.
Try it, you can build it in 5 minutes, for peanuts.
Post results 🙂
EDIT: in case it got lost in translation 🙂 , "50 W" is what resistors will *stand* ... reasonable thinking that your amp supplies "37 W" ... but the siren will get milliWatts .... "cellphone levels".
And of course I stand corrected.
1) As of the attenuation, the siren will never get 50W out of this but respectively:
with 20/0.47 ohms= 20 mW ... which should be loud enough to know the system works but VERY listenable in a silent workshop .
with 20/0.22 ohms= 5 mW
with 20/0.1 ohms= 1 mW
truly "cellphone on the table a meter away" levels 😉
In fact, the 0.47 ohms resistor level will be fine.
This has been tested lots of times and the "3 AM" label is confirmed by happy customers 🙂
As of why I chose a shunt attenuator instead of high value series resistors is because in practice sound remains closer to the unattenuated one, while series ones cause a buzzy annoying sound, reason being that speakers have a very far from flat impedance, and the constant current type drive caused by high value series resistors (10X nominal impedance and above) enhance the worst traits of speakers.
That´s why most earphone outs (which just get 100 to 470 ohms in series) are horrible.
Also didn´t suggest a variable level setup with a rotary switch or something, simply that if 0.47 ohms is *still* too loud (given the siren speaker high efficiency) there´s the option of setting it even lower.
Try it, you can build it in 5 minutes, for peanuts.
Post results 🙂
EDIT: in case it got lost in translation 🙂 , "50 W" is what resistors will *stand* ... reasonable thinking that your amp supplies "37 W" ... but the siren will get milliWatts .... "cellphone levels".
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Perfect! thank you very much, I look forward to trying this.
Just so I don't end up using the wrong product by accident, could you provide a link or a pic to a product page?
Again correct me if I'm wrong, but your proposed method uses shunt type resistance only?
thank you
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