The Siren Board

So I've made the frame to ANOTHER siren, which I'm calling the 88 (8 horns, 8 drivers(all the horns are 30W respectively, meaning there will be a total of 240W)). It's big, and it's bulky, (even without the horns on!) but I've come to a predicament:

"Should I use 100/70V speaker horns or standard horns, and if so, where should the amplifiers go?"

Post your solutions below, and as usual, thanks in advance for your advice!

Use 8 ohm or 16 ohm PA horn drivers from Atlas Sound or similar - do not use pro-audio compression HF drivers. Also, do not use 70/100V drivers. Wire the horn drivers so that they present a net impedance of between 4 and 8 ohms. For drivers connected in series, the impedances of each driver add together, and then for multiple groups of one or more drivers wired in parallel, with the same configuration of drivers per group, the result impedance is the impedance of each group divided by the number of groups.

Suppose you have 8-ohm drivers, and you have a total of eight units. Wire them together in four series-wired groups of two drivers per series group, giving you 16 ohms per group. Then wire the four groups in parallel, dividing 16 by 4 to give a final impedance of 4 ohms. Most amplifiers can drive this load safely.

If you have two amplifier channels available, but they are only rated to support 8-ohm impedance per channel, then wire two of the above-described 16 ohm series groups in parallel to give an 8 ohm load from a set of 4 drivers, then do the same for the other two groups, and connect each 8-ohm set to a different amplifier channel.

If you have the same group of 8-ohm drivers, you can wire them together in two groups of four drivers wired in series for total impedance of 32 ohms, then you can wire the two 32-ohm series groups of drivers in parallel to give a 16 ohm impedance, which most amps can tolerate but your power output will be reduced by half so you will need a higher power amplifier. The benefit to the higher impedance load is the amp will run cooler.

Keep in mind, if you have a two-channel amplifier, you can NOT just strap the two channels together at their outputs to give a single set of positive and negative outputs. This will result in one channel of the amp driving the low output impedance presented by the other channel, parts will burn out, and the amp will be ruined.

I hope this helps.

Okay. I have made a change to the system: I'm using 16 15W horns, which will amount to the same total wattage. With this said, will I need to get an amplifier for each and every horn (since I gather from your excellent advice, having 2 horns on a dual channel amp will fry the amp's components due to the load)?

Rather than using 16 15w drivers, I would recommend using 4 of these along with these drivers.

One tiny hitch... I have called off the project, owing to the fact that my school are waiting to replace their system of 1981 fire alarms, so this siren would be useless, and I am based in south east England, so I am not willing to part my (not so) strong British pounds to pay for overseas shipping. Sorry, but thanks for your advice!

Chem_Boffin_6589 wrote:One tiny hitch... I have called off the project, owing to the fact that my school are waiting to replace their system of 1981 fire alarms, so this siren would be useless, and I am based in south east England, so I am not willing to part my (not so) strong British pounds to pay for overseas shipping. Sorry, but thanks for your advice!

Are you getting the speakers from the fire alarms?

No, The fire alarms there are getting replaced. I am getting them, and I'll be incorporating them into my house alarm. As for the siren, I was going to use standard 15W passive speakers (these are also used on my mini electronic siren).