Cheeseweasel Posted August 29, 2011 Share Posted August 29, 2011 A company I work for has a stock of 8 ohm PA horns which are hired for outdoor events. They produce acceptable results when only a few are used and cable runs are kept short, but for larger events, e.g. providing PA for an agricultural fair, they are pitifully quiet (we used 16 of them on a job at the weekend, wired in series/parallel combination with about 300m of cabling and the level was so low that we had to hire in 100V horns from elsewhere to do the job properly). I'm looking to convert the existing horns to run on 100V, as the company already has a nice 100V amplifier and suitable cabling. What I'm asking is, does there exist some sort of converter that I can buy and bolt onto the back of the 8R horns so I can use them as 100V speakers (i.e. a transformer in a box)? I would prefer to buy a ready-made product than build something myself. I haven't had much luck with looking online, and I wondered if anyone on here has experience of doing this? Link to comment Share on other sites More sharing options...
paulears Posted August 29, 2011 Share Posted August 29, 2011 never seen a ready built one, but a plastic box, couple of glands and a transformer isn't too much of a pain to build. I guess there's no real demand for a ready made one? Link to comment Share on other sites More sharing options...
Cheeseweasel Posted August 29, 2011 Author Share Posted August 29, 2011 never seen a ready built one, but a plastic box, couple of glands and a transformer isn't too much of a pain to build. I guess there's no real demand for a ready made one? I appreciate that, and I'd be happy to build them myself. I doubt that the company would be happy to pay me for a day or two's work + materials though. And it would be nice to have something purpose-built, ideally with a switch to select different taps and a couple of connectors for chaining the horns together neatly. Link to comment Share on other sites More sharing options...
Jivemaster Posted August 29, 2011 Share Posted August 29, 2011 It's even possible that the cable entry housing already has space for a transformer inside the box. However that could be a permanent change - they become 100v line horns permanently! It's by far the neatest option. Research your brand and model of horn on-line, see whether the option exists to buy them as 100v line units, if so then there may well be space to retrofit a transformer. Alternatively look at upgrading the connecting wire that you use, bell wire is fine for line speakers but 2.5mm^2 twin is better for 8 ohm speakers. For an individually calculated option consider looking for an amp that has a rating for 16 ohm speakers and account for 8 ohms in the cable and 8 ohms in the driver -perfect if calculated and measured each time - suicidal if not or your calcs are wrong. For a non related purpose, I have run out a 800m length of bell wire and it measured out at about 90 ohms. My purpose coped yours would not. Link to comment Share on other sites More sharing options...
boatman Posted August 29, 2011 Share Posted August 29, 2011 If one exists Richard Tait of Comtech (ex Tait Components) in Glasgow will know about it. Their phone number used to be 0141 564 4644 before Comtech took over, so that might be worth a try. Their old website address http://www.tait-components.com/ now points to Comtech and doesn't give a phone number. Link to comment Share on other sites More sharing options...
dbuckley Posted August 29, 2011 Share Posted August 29, 2011 I have a few such boxes, home built. Link to comment Share on other sites More sharing options...
Jivemaster Posted August 29, 2011 Share Posted August 29, 2011 A brief cost/benefit calculation should tell the firm whether your time would be well spent or they should buy more speakers (100v) or continue the sub hire system Link to comment Share on other sites More sharing options...
Cheeseweasel Posted August 29, 2011 Author Share Posted August 29, 2011 Thanks everyone. I've found a product that will do the job. It's a 100v transformer in a watertight box with selectable tap via a rotary control. It only costs a fiver, so I guess I'll get one and try it out. All I need to do now is build a splitter box for each cluster of horns with a couple of parallel speakons on it so we don't have to mess around with twisting bits of wire together. Link to comment Share on other sites More sharing options...
TomHoward Posted August 29, 2011 Share Posted August 29, 2011 Is that an off the shelf product, if so are you able to provide details or a link? Link to comment Share on other sites More sharing options...
Cheeseweasel Posted August 29, 2011 Author Share Posted August 29, 2011 Is that an off the shelf product, if so are you able to provide details or a link? Sure, here's a link. I'm slightly worried about how cheap it is so I've just ordered one for the time being to try it out before I commit to buying the other 15. Link to comment Share on other sites More sharing options...
TomHoward Posted August 29, 2011 Share Posted August 29, 2011 Thanks, they look interesting. Searching shows that that's an Adastra part, no 952.797. We have a mixture of 8ohm and 100V stuff, so they may be useful if we ever wanted to include a couple of 8ohm boxes in a 100V run. Of course you can get other transformers in higher ratings (CPC listings) but none of them are boxed up like that, you'd have to box them up in a weatherproof enclosure with connectors etc. Be interested to hear your thoughts about it - especially how it performs with an 8ohm box speaker as well as a horn if you got round to trying it. Link to comment Share on other sites More sharing options...
Cheeseweasel Posted August 29, 2011 Author Share Posted August 29, 2011 Thanks, they look interesting. Searching shows that that's an Adastra part, no 952.797. We have a mixture of 8ohm and 100V stuff, so they may be useful if we ever wanted to include a couple of 8ohm boxes in a 100V run. Of course you can get other transformers in higher ratings (CPC listings) but none of them are boxed up like that, you'd have to box them up in a weatherproof enclosure with connectors etc. Be interested to hear your thoughts about it - especially how it performs with an 8ohm box speaker as well as a horn if you got round to trying it. It's certainly far cheaper than what I could build one for, and if it's made by Adastra to go with their existing 8 ohm horns it must be useable. Another useful feature, looking at the zoomed-in image, the tap selector switch seems to have an 8 ohm setting (i.e. transformer bypass), so there's no reason why you couldn't have it on every horn, giving you the option of running them at low impedance or 100V. I'll keep you posted and if I can dig out a small hifi speaker from the warehouse I'll give that a go too - might be a good way to do an indoor paging system on the cheap or make a 100V 'listen' monitor. Link to comment Share on other sites More sharing options...
dbuckley Posted August 30, 2011 Share Posted August 30, 2011 Theres better information here, and in particular the wattage ratings of the transformer. Just a note on 100V horns and transformers; apply a high pass filter to get the bass out of the amplifier feed, as it is the bass energy that will saturate the transformers. Horns don't have an extended low frequency response anyway, so theres no sonic loss. I note they are intended for "rock" speakers; I have some drainpipe speakers in my garden that would probably benefit from being fed at 100V... (I have a big garden) Link to comment Share on other sites More sharing options...
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