Anyone know much about speakers? Voltages and waveforms, not audio quality.

[prv]

I'd like to have a horn on Ariam. I already have a speaker up the mast, and I'm soon going to be adding a button to the binnacle anyway for something else, so it's just a matter of something to make the actual horn signal.

In my box of bits I found a small circuit-board which I vaguely remembered as being a signal generator. And indeed, connected up to my new $20 USB oscilloscope, it seems to be emitting a slightly scruffy square wave at about 11v:

Luckily, I have a duplicate of the mast speaker in my shed (accidentally got filled with water when the mast was down, I assumed it was ruined and replaced it, actually seems to be fine). It's a 30 watt 4 ohm horn speaker. Connected up to the wave generator board, it makes a loudish tone. The generator has a frequency control on it, which I've adjusted to something that doesn't sound horrible. I also tried to measure the current going into the speaker and think it was about half an amp.

My knowledge of analogue electronics in general, and speakers in particular, is basic in the extreme. So, questions:

1) Is this waveform into the speaker likely to do it any harm? It should really be smoother, shouldn't it?
2) Though it's irritatingly loud in my study, I suspect this combination will be a bit anaemic on the water. Am I likely to be able to get more noise out of the same speaker, presumably by increasing the voltage? If so, what would be a good way of doing that? I don't really want to involve a packaged amplifier, though a small module would be ok if that's the easiest approach.

I have 5v Arduinos on hand if that would make a better signal source than the wave generator.

(I don't want to just mount an off-the-shelf horn sounder somewhere; I want to use the speaker I already have nestling neatly underneath the radar. I also don't want to get sidetracked into an argument over whether a sailing boat should have a horn in the first place, and will waggle an animated yellow bottom at anyone who tries )

Pete

 

[BERT T]

What is the existing mast speaker connected to at present?

 

[VicS]

I'd like to have a horn on Ariam.

Pete

ultimately this is the sort of thing you have in mind I assume?

HI diddle dee the most appropriate if you have to limit your self to just one tune.

Dont forget you will also need a bell

 

[elton]

A square wave won't damage your speaker. You may find altering the frequency to match a resonant frequency of the speaker, will dramatically increase the sound level. If the circuit is an astable multivibrator (a very common configuration https://en.wikipedia.org/wiki/Multivibrator#Astable_multivibrator), the frequency can be altered by changing one (or optionally two) resistor(s). Changing it to a variable resistor or a preset pot, will allow experimentation.

 

[William_H]

A square wave won't damage your speaker. You may find altering the frequency to match a resonant frequency of the speaker, will dramatically increase the sound level. If the circuit is an astable multivibrator (a very common configuration https://en.wikipedia.org/wiki/Multivibrator#Astable_multivibrator), the frequency can be altered by changing one (or optionally two) resistor(s). Changing it to a variable resistor or a preset pot, will allow experimentation.

I think you probably mean set it to a "resonant" frequency of the speaker. ie that frequency which makes the speaker really squawk which unfortunately will probably sound the most horrible.
Yes square waves will not hurt the speaker. You could get a lot more power out of the speaker if you fed the generator into a bridge type amplifier of 4xMOSFET switches (2 N channel and 2 P channel) so the waveform becomes 0 to near 12v pos then 0 to near 12v -ve or 24v PtoP. more power more sound. good luck olewill

 

[prv]

the frequency can be altered by changing one (or optionally two) resistor(s). Changing it to a variable resistor or a preset pot, will allow experimentation.

Yep, the module already has a variable resistor to do this. It runs from audibly-distinct clicks to a high-pitched squeak. I've set it to a suitable-sounding tone. There didn't seem to be any point where it resonated and got louder, at least within the range of notes I'd want it to make.

Pete

 

[prv]

You could get a lot more power out of the speaker if you fed the generator into a bridge type amplifier of 4xMOSFET switches (2 N channel and 2 P channel) so the waveform becomes 0 to near 12v pos then 0 to near 12v -ve or 24v PtoP.

So one thing I was trying to find out was what sort of voltage range would be normal for maximum volume on this kind of speaker, without being high enough to cause damage. Any idea?

Pete

 

[fredrussell]

At the risk of having an animated yellow bottom waggled in my direction, would a car horn not be easier? I assume they're waterproof.

 

[prv]

At the risk of having an animated yellow bottom waggled in my direction, would a car horn not be easier? I assume they're waterproof.

Strictly speaking, the bottom is only for discussions on whether to have a horn at all

The argument against a dedicated 12v sounder is that I don't want to hang more junk off the rig than necessary, and I also don't want to have to climb the mast to fit one, run a cable (which would have to hang loose in the main section of the mast as the two wiring channels are now full), fish it out through the mast foot, take the headlining down to get it from the mast back to the wiring bay, etc etc. Using the existing speaker and cable is neater aloft, and just breaking into the existing cable where it passes through the wiring bay, to add a DPDT relay and sound-generator board, makes a far easier installation job.

That's why

Pete

 

[lw395]

30W 4 ohm.
Vsquared over R = power, so Vsquared = P.R, = 120
That gives V = 10.95
That's V rms, Vpk to peak is twice that for a square wave or twice that x square root of 2 for a sinewave.
Peak current will be peak volts/R. So 2 or 3 Amps.
I don't necessarily agree that shoving full power square waves up a speaker will do no damage, 'it depends'. I would filter off the worst of the harmonics to get a bit more like a sine wave personally, or back off the power.
Since you want to run off 12V, your easiest route is a bridge amplier, which puts a signal on one side of the output and the same signal in anti-phase on the other side, as opposed to the return side being grounded.
Maybe something like this:
http://www.st.com/web/en/resource/technical/document/datasheet/CD00000124.pdf
or maybe a class D amplifier would get you a little more power and efficiency.

There may be built pcbs on ebay?


http://www.ebay.co.uk/itm/DC-12V-2A...699782?hash=item25b7b23646:g:p3YAAOSwECZUm7be

You'd need a few r's a nd c's to get the input level and lop the harmonics down a bit.

 

[Spi D]

This includes ability to PA over the mic, so also would allow you to entertain

Several variants - would it be too simple? Eg.
http://www.ebay.co.uk/itm/12V-Loud-...252655?hash=item2a4f407c6f:g:mdYAAOSwWnFV-BaE

 

[prv]

This includes ability to PA over the mic, so also would allow you to entertain

Already got that through the VHF, as well as automated fog signals etc. In theory it can do manual horn blasts as well, but you have to go through about three levels of menu first. An idiotic piece of design by someone who wasn't thinking about how it would actually be used. If they'd put a pair of terminals on the back for a horn button, or even a button on the RAM mic, this whole exercise would have been avoided.

(And your suggested item has the amplifier built onto the back of the speaker so has all the mast-climbing, cable-running problems of Fred's idea.)

Pete

 

[prv]

So it seems that the thing I'm trying to build is a common item in the US, known as a "siren driver" and used in fire and burglar alarm systems:

The board above is a couple of dollars, and there are lots of others like it. Sadly I cannot find anything similar anywhere outside the US; I guess as in many other fields their way of wiring alarm systems is unique, meaning that these items aren't applicable elsewhere. But rather than continue faffing around with bits of veroboard and cobbling together modules that do almost the right thing, I'm going to bite the bullet of exorbitant shipping costs and buy in one of these. Thanks for the suggestions.

Pete

 

[pvb]

Interesting! Let us know how it works out.

 

[rob2]

Frequency and sound pressure levels are set out in Annexe 3 of the Colregs -

250 - 700 Hz, for a vessel less than 75 metres in length.

Rob.

 

[William_H]

Just one last word on this. You need to know the impedance of the speaker and the max power rating of the speaker.
Typical speakers are 8 ohm and may take 20 watts which is ok for the amp /drivers referred to.
The max power available in watts is limited by the supply voltage so as said about 20w produced by a bridge type amp or 10 w for a single ended amp on 12v. But the voltage will always be limited to 12v peak to peak for single ended or 24v p to p for bridge amp. Hence it is a question of how much power the speaker takes.
So makers of car radios realised that with limited voltage they needed to have lower impedance speakers so we see 2 ohm speakers. The other alternative is to have a switching power supply to produce 100v DC to get 100w or so of power into 8 ohms.
Don't let all this worry you as sound pressure is perceived in a logarythmic manner so lower power may be ok. good luck olewill

 

[prv]

Just one last word on this. You need to know the impedance of the speaker and the max power rating of the speaker.

4 ohms, 30 watts, as stated in the original post.

The American siren board I've ordered specifies a 4 ohm speaker and states 60 watts of available power. I'm assuming this is like the current rating of a power supply, and the speaker won't draw more than it needs.

Pete

 

[nigelmercier]

Assume this one? It might have been worth doing a group buy ...

 

[bedouin]

A square wave won't damage your speaker. .

In general square waves can blow speakers but it depends on the speaker design, but probably not an issue in this case.

But in any case I don't think a square wave is the best form for a horn, it is not a pleasant sound and it probably doesn't carry as well as a form with more power in the lower frequencies.

 

[lw395]

4 ohms, 30 watts, as stated in the original post.

The American siren board I've ordered specifies a 4 ohm speaker and states 60 watts of available power. I'm assuming this is like the current rating of a power supply, and the speaker won't draw more than it needs.

Pete

No, if you turn up the input to a an amp rated at "60W into 4ohms", then a "30W 4ohm" speaker will get 60W.
Give or take the fact that speaker impedances are complex and amplifier manufacturers often exaggerate their power.
So, you'd want to keep the volume turned down some.

Also, most speakers designed for music or PA won't like being used at a high duty cycle, it's a peak rating, not continuous. Probably no issue for normal yacht fog signals.