Light Console Posted November 20, 2006 Share Posted November 20, 2006 5 years ago, I installed a sound system in a Church, and now they are expanding. We already have a flown EV rig for the main part of the Church, but now the area to the left of the dais is to have a mezzanine floor installed. This means we will need some fill speakers for the two levels. There is no budget for this really. I have left on permanent hire an old HH amp (VX-300) which gives us 150W per channel at 8 Ohms. I have 2 pairs of Ariston MSX-03 which are only rated at 50W 8 Ohms. Question is, how do I wire them up so that I don't damage anything? My guess is in series, but I don't know how that will affect the wattage side of things. Is this why some amps only have their attenuators at 50%, cause as I understood it, the amp works at full pelt regardless, it just requires more input signal to get to maximum output?I would much rather get JBL Control 1s or the like, but I think the problem will remain.Sorry, but as I don't know what this is called, it was hard to find anything with the search!It was easy with the EV rig, we bought the amp that used to drive them at the same time as the EVs! Link to comment Share on other sites More sharing options...
saturnx21 Posted November 20, 2006 Share Posted November 20, 2006 Hi if you simply wire one speaker in to one channel of the amp and the other speaker into the other channel of the amp and just back off the volume of the amp alittle you should have no problems what so ever! HTH *edited for type'os!!!! Link to comment Share on other sites More sharing options...
MarkPAman Posted November 20, 2006 Share Posted November 20, 2006 I have not been able to find a "proper" spec for these speakers but:Suitable amplifier power rating: 15~35 watts (rms)and similar figures can be found on e-bay. :) So, be very careful with your 150W amp, you could easily fry the speakers if you use one channel for each speaker.As you suggested, wiring the speakers in series & using only one side of the amp would be better (I assume that you only want mono anyway). That leaves you an amp free for something else! :D Link to comment Share on other sites More sharing options...
J Pearce Posted November 20, 2006 Share Posted November 20, 2006 I'm currently driving my 50Wpk hifi speakers with a 300W a side amp. Just don't turn it up as loud! To moron proof it you could put a limiter before the amp and then prevent access to the limiter's controls. Link to comment Share on other sites More sharing options...
MarkPAman Posted November 20, 2006 Share Posted November 20, 2006 To moron proof it you could put a limiter before the amp and then prevent access to the limiter's controls.Why spend money on a limiter to protect £10 (e-bay) speakers? The money would be better spent on some proper speakers. Link to comment Share on other sites More sharing options...
Ynot Posted November 20, 2006 Share Posted November 20, 2006 I have left on permanent hire an old HH amp (VX-300) which gives us 150W per channel at 8 Ohms. I have 2 pairs of Ariston MSX-03 which are only rated at 50W 8 Ohms. Question is, how do I wire them up so that I don't damage anything? My guess is in series, but I don't know how that will affect the wattage side of things.It's not as simple as that.Roughly speaking:Two 8 ohm speakers in parallel will give you a 4-ohm total impedance.Two 8 ohm speakers in series will give you a 16-ohm total impedence.That's assuming that they're simply speakers with nothing else in the way, like crossovers etc. However, if you have 2 speakers rated for just 50w each, I doubt that there are any configurations that you could come up with that will let you connect them to a 150w output without blowing the drivers, and possibly the amp output stages! Is this why some amps only have their attenuators at 50%, cause as I understood it, the amp works at full pelt regardless, it just requires more input signal to get to maximum output?This intrigues me...I'm assuming the amp is a straight in/out model ?? Does it not have a level control (or two)? Link to comment Share on other sites More sharing options...
Rob_Beech Posted November 20, 2006 Share Posted November 20, 2006 Please bear in mind there are 2 pairs of these speakers..... My suggestion would be have 2 speakers in series off of each channel and keep the channels turned down. Make sure that the speakers are not being overdriven when you are the necessary operating volume for the main system. you would benefit from blocking access to these controls aswell (already mentioned). Rob Link to comment Share on other sites More sharing options...
Light Console Posted November 20, 2006 Author Share Posted November 20, 2006 Thanks for the posts so far folks, to clarify a little...Ideal would be for some decent speakers, but at the moment, there is no budget, we have just spent it on getting some lighting bars installed, and the new floor!There are 2 sets of speakers, so a pair upstairs, and another pair downstairs. The system is run in mono anyway, so was thinking of up/down on channels 1/2 respectively. There is nothing in the way of crossovers in the speaker path.Two attenuators are present on the amp, and work ok. My ramblings about attenuators at 50% was me trying to remember college work from years ago on power amp circuits. As I remember, the amplifiers work flat out all of the time, the attenuators are in the input stage of the amp, so turning them down has no affect on output power. I might be barking up the wrong tree!I think that the way forward might be to try and get hold of an old Hi-Fi amp to run them, matched to the speakers. Another problem which has just come to the floor is turning the whole system on and off. We need to make it off just one switch, which will play havoc with inrush currents et al. This is because the only place left for the amps is in the false floor with "The Great Escape" style hatches from the floor above as access, so no chance of getting to the power switches and attenuators. Maplins used to sell 4 way relay units that sequentially turned things on, but I can't find them now. Link to comment Share on other sites More sharing options...
Ynot Posted November 20, 2006 Share Posted November 20, 2006 Please bear in mind there are 2 pairs of these speakers.....Still only 100w max...However, using some (rather rusty) ohms law, I make the max power usage for the 2 x 8 ohm speakers as 76w in series, but 306W in parallel! VERY coarse calculations, but it does serve to demonstrate the need for caution with speaker usage! Speakers don't tend to comply 100% to the basics of Mr Ohm, but it's probably close enough!(And don't start on whether it's peak or rms ratings you're quoting....!! :)) Link to comment Share on other sites More sharing options...
Light Console Posted November 20, 2006 Author Share Posted November 20, 2006 Thanks again folks,Problem 1 solved, they managed to adjust the budget for the new floor, so matched amp and speakers were added. :)Problem 2 solved, old speakers and amp to be used as Vestry and Altar monitors, until they blow up, used at reduced levels. :D :) Problem 3 solved, electrician to install four switches to be turned on in sequence by user. :) :) :) What a good evening! Link to comment Share on other sites More sharing options...
BlueShift Posted November 23, 2006 Share Posted November 23, 2006 In fact speakers dont comply at all with mr. ohm in that sense That version of ohms law is the simplistic version for pure resistors. But speakers have impedance (essentially a complex resistance) and this also varies over the frequency range (massivly) so while those kind of calculations will do for rough checks, dont be using them for anything precise because u need to start using things like phasor manipulation of the various impedances which will just get messy :-) Link to comment Share on other sites More sharing options...
lightsource Posted November 23, 2006 Share Posted November 23, 2006 In fact speakers dont comply at all with mr. ohm in that sense But in this instance, it can be used as a 'general rule of thumb', after all the OP did ask a basic question. And it was answered by the most basic of answerers ..... more funding :) Link to comment Share on other sites More sharing options...
Ynot Posted November 23, 2006 Share Posted November 23, 2006 In fact speakers dont comply at all with mr. ohm in that sense That version of ohms law is the simplistic version for pure resistors. But speakers have impedance (essentially a complex resistance) and this also varies over the frequency range (massivly) so while those kind of calculations will do for rough checks, dont be using them for anything precise because u need to start using things like phasor manipulation of the various impedances which will just get messy :-)Er, which is why I placed the caveat on my post that it was VERY coarse and just for demonstration purposes!!:) Link to comment Share on other sites More sharing options...
Tom R Posted November 23, 2006 Share Posted November 23, 2006 Two attenuators are present on the amp, and work ok. My ramblings about attenuators at 50% was me trying to remember college work from years ago on power amp circuits. As I remember, the amplifiers work flat out all of the time, the attenuators are in the input stage of the amp, so turning them down has no affect on output power. I might be barking up the wrong tree! You are right in theory but it would not really affect you in this situation! You would seriously struggle to get 100% output out of your amp if its attenuated to 50%, I believe you're talking about running your amps at about 3/4 and using the headroom on the desk to maximise gain before clipping? Wouldnt really be applicable here though... Obviously attentuating the signal will always affect the output though, and attenuating the signal (by default) will make it quieter! 2x50W speakers on 150W amp (assuming both figures are RMS) would be fine if you just turned the amp down - just be careful! Link to comment Share on other sites More sharing options...
Rob_Beech Posted November 25, 2006 Share Posted November 25, 2006 Still only 100w max... I was referring to the impedance differences with there being 2 pairs rather than the power rating. 2x50W speakers on 150W amp (assuming both figures are RMS) I think we established the 50w of the speakers is a peak rating, and the specs show an amplifier up to 35 watts is more apt. It does however seem to be sorted now with some new gear, so that appears to have worked out nicely. Rob Link to comment Share on other sites More sharing options...
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