pattonaudio Posted April 16, 2008 Share Posted April 16, 2008 Hi guys I have a mental block and need help from you all to clear this for me. We have 2x Peavy Pro15 - 250w @ 4Ohms (1st edition ones, 2nd are 300w) and 2x Peavey Pro Subs - 250w @ 4 Ohms I think, so when connected together they run at 2Ohms. But maybe I am confused, I know the sub puts out the Highpass-Out is via Speakon 2+/2- so does this connect them so that r = 4ohms not 2? My next prob is recommending an amp to suit them! Help really appreciated! Link to comment Share on other sites More sharing options...
Ben Langfeld Posted April 16, 2008 Share Posted April 16, 2008 If the sub has a passive x-over in it then it will be presenting 4R to the amp, not 2R. ;) Link to comment Share on other sites More sharing options...
johndenim Posted April 16, 2008 Share Posted April 16, 2008 4 ohms @ x2 4 ohms per side? I have always believed that link a 4ohm sub to a 4 ohm top (passive xover) you will get 2 ohms @ the amp?Is the amp able to run @ 2 ohms Rich? I am a trained sparky so to be completely honest I cant see how one coil @ 4Ohms, plus 4Ohms in series gives you 2 Ohms?Surely it would be 8 Ohms, x2 @4=8.I know it's wrong but why?After all there is twice the resistance. :) John (confused) demin. Link to comment Share on other sites More sharing options...
Ben Langfeld Posted April 16, 2008 Share Posted April 16, 2008 The load presented to the amp is the x-over, not the drivers. Take a look at a simple passive crossover circuit and all will become clear. If I'm remembering correctly, a look on wikipedia or similar at Zobel networks might help. *waits to be corrected* Link to comment Share on other sites More sharing options...
MarkPAman Posted April 16, 2008 Share Posted April 16, 2008 I am a trained sparky so to be completely honest I cant see how one coil @ 4Ohms, plus 4Ohms in series gives you 2 Ohms?Surely it would be 8 Ohms, x2 @4=8.I know it's wrong but why?After all there is twice the resistance. :) John (confused) demin. John, when you connect two speakers together it is almost always in parallel not series. Link to comment Share on other sites More sharing options...
Simon Lewis Posted April 16, 2008 Share Posted April 16, 2008 The load presented to the amp is the x-over, not the drivers. *waits to be corrected* The impedance seen by the amplifier depends upon the crossover components and the loudspeakers... Link to comment Share on other sites More sharing options...
Rob_Beech Posted April 17, 2008 Share Posted April 17, 2008 Simon is correct of course, it's not just the crossover that makes the difference. However, in your case, the amp will see a 4ohm load. Link to comment Share on other sites More sharing options...
Jivemaster Posted April 17, 2008 Share Posted April 17, 2008 If the crosover is well designed! The amp sees the load of the bass cab below the crossove point, and the load of the top cab above the crossover. If there is no crossover the amp sees the parallel load of both cabs at all frequencies. Link to comment Share on other sites More sharing options...
palantir Posted April 17, 2008 Share Posted April 17, 2008 Do you know, I reckon that's the clearest & most concise explanation of speaker impedance voodoo I've seen................. Must be wrong, then :) Pete Link to comment Share on other sites More sharing options...
pattonaudio Posted April 17, 2008 Author Share Posted April 17, 2008 4 ohms @ x2 4 ohms per side? I have always believed that link a 4ohm sub to a 4 ohm top (passive xover) you will get 2 ohms @ the amp?Is the amp able to run @ 2 ohms Rich? I am a trained sparky so to be completely honest I cant see how one coil @ 4Ohms, plus 4Ohms in series gives you 2 Ohms?Surely it would be 8 Ohms, x2 @4=8.I know it's wrong but why?After all there is twice the resistance. :) John (confused) demin. When working with speakers its almost 99% parallel thats why I am think that the top and sub (both 4) when connected is 2 Ohms, but what does the Xover do to keep it 4? A concurrent post has been automatically merged from this point on. If the crosover is well designed! The amp sees the load of the bass cab below the crossove point, and the load of the top cab above the crossover. If there is no crossover the amp sees the parallel load of both cabs at all frequencies. No this makes more sense to me! the amp is only seeing (for my dumbass sake, may not be right) 8Ohms from the sub because the Xover is increasing resistance by sendind mf/hf to top which again is only sending 8Ohms of resistance because of the Xover. Therefore Sub and top = 4Ohms resistance is increased due to Xover series connectedTop and Top = 2Ohms parallel connect Link to comment Share on other sites More sharing options...
jamesperrett Posted April 17, 2008 Share Posted April 17, 2008 If the crosover is well designed! The amp sees the load of the bass cab below the crossove point, and the load of the top cab above the crossover. If there is no crossover the amp sees the parallel load of both cabs at all frequencies. John and Richard - you both seem to be very confused here. I've quoted Jivemasters explanation because it explains things just about as clearly as they can be explained. At its simplest, a crossover will have an inductor in series with the bass cab and a capacitor in series with the top cab. The impedance of the inductor increases with frequency while the impedance of the capacitor decreases with frequency. A simple crossover will be designed so that the impedance of the inductor and capacitor are the same as the speaker impedance at the crossover frequency. So, in a system where the speakers are 4 ohms, the bass end will have an impedance of 4+4 ohms and the top will have an impedance of 4+4 ohms. Effectively at the crossover point we have two 8 ohm impedances in parallel. I hope this makes things a little clearer. Cheers James. Link to comment Share on other sites More sharing options...
pattonaudio Posted April 17, 2008 Author Share Posted April 17, 2008 If the crosover is well designed! The amp sees the load of the bass cab below the crossove point, and the load of the top cab above the crossover. If there is no crossover the amp sees the parallel load of both cabs at all frequencies. John and Richard - you both seem to be very confused here. I've quoted Jivemasters explanation because it explains things just about as clearly as they can be explained. At its simplest, a crossover will have an inductor in series with the bass cab and a capacitor in series with the top cab. The impedance of the inductor increases with frequency while the impedance of the capacitor decreases with frequency. A simple crossover will be designed so that the impedance of the inductor and capacitor are the same as the speaker impedance at the crossover frequency. So, in a system where the speakers are 4 ohms, the bass end will have an impedance of 4+4 ohms and the top will have an impedance of 4+4 ohms. Effectively at the crossover point we have two 8 ohm impedances in parallel. I hope this makes things a little clearer. Cheers James. Thanks James but I think thats what I was trying to say in that because or the Xover between sub and top the resisitance is increased! And if the xover was not there or there were 2 same xovers then the resisitance would be halved.! Link to comment Share on other sites More sharing options...
johndenim Posted April 18, 2008 Share Posted April 18, 2008 Now my brain hurts! All taken aboard thanks guys for clearing that up.Going back to the OP's question you want suggestions for an appropriate amp to power these cabs? I assume Richard that you want just one?Again, as you know it all come down to budget, is this for a customer of yours? John Denim. Link to comment Share on other sites More sharing options...
pattonaudio Posted April 18, 2008 Author Share Posted April 18, 2008 Now my brain hurts! All taken aboard thanks guys for clearing that up.Going back to the OP's question you want suggestions for an appropriate amp to power these cabs? I assume Richard that you want just one?Again, as you know it all come down to budget, is this for a customer of yours? John Denim. I will find an amp ok it gonna be only +500watts @4Ohms, just thought that when connected they would run at 2Ohms so wanted to make it all clear first thanks guys for you help Link to comment Share on other sites More sharing options...
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