la bam Posted November 19, 2018 Share Posted November 19, 2018 Hi all, With so many different threads on "what would my ohmage be...?" and with a bit of confirmation needed, I thought it might be an idea to have a thread where we could put everything in one thread, also so others can reference and understand. Im sure a lot understand, but also a lot don't. Theres also different set ups, amp set ups and cab configurations. So, i'll start with...... Cab - Markbass 6x10 900w runs at 6ohms. Amp - QSC RMX1450. What will my ohmage be, running this amp in bridged mode? And is there any problem with that? Quote Link to comment Share on other sites More sharing options...
ahpook Posted November 19, 2018 Share Posted November 19, 2018 (edited) I'm not sure I understand your question....your speaker cabinet has an impedance of 6 ohms. Are you asking about power output for a given speaker impedance ? (Apologies if I'm being dense) Edited November 19, 2018 by ahpook Quote Link to comment Share on other sites More sharing options...
la bam Posted November 19, 2018 Author Share Posted November 19, 2018 no problem (ive probably not described it properly). Im wondering what ohmage the power amp will be running at, when running in bridged mode, if using a 6ohm cab, and what output in watts that would be giving. Would it be 3ohms (as the amp is bridged)? Rather than 6ohm in normal / stereo mode? Quote Link to comment Share on other sites More sharing options...
BassBunny Posted November 19, 2018 Share Posted November 19, 2018 The QSC in Bridged mode is 4 Ohms with an output of 1400w RMS. Quote Link to comment Share on other sites More sharing options...
goingdownslow Posted November 19, 2018 Share Posted November 19, 2018 Ohmage! It's disgusting! Quote Link to comment Share on other sites More sharing options...
la bam Posted November 19, 2018 Author Share Posted November 19, 2018 This is where i get confused...... If the QSC spec is 4ohm bridged giving 1400w, then using my 6 ohm cab will draw approx 1000w - is this correct? Completely confused now though for some reason i thought running in bridged mode doubled/halved (depending on how you look at it) the ohmage - so instead of 6ohm in one channel of stereo, it would use 3ohm, as both channels are being used? Any clarity appreciated! Quote Link to comment Share on other sites More sharing options...
Dood Posted November 19, 2018 Share Posted November 19, 2018 (edited) I think a better thread would be to explain in layman's terms what all of these technical phrases mean, then to demonstrate them with simple diagrams and calculations. This would allow each member to work it out and then post on the thread to ensure they are correct. For example La Bam, your question: The cabinet provides the load not the amplifier. So, you amplifier has a minimum load (in ohms) that it is happy with. I am going to assume that as above, in bridge mode you can have any impedance as long as it is higher than 4 ohms. Since your cabinet is 6 Ohms, your amplifier sees that load and thus that would be the "measured ohmage" across the output terminals. This is of course Impedance which is an AC measurement, not to be confused with Resistance which is a DC measurement that you'd make with a simple 'multimeter'. What the 6 ohms measurement does do (on paper at least) is affect the power reading of the amplifiers output. At 2 ohms difference though in this scenario, it's not worth bothering about as your 6x10 cones are moving plenty of air anyway. Edited November 19, 2018 by Dood auto-correct wrecked my post :( 1 Quote Link to comment Share on other sites More sharing options...
ahpook Posted November 19, 2018 Share Posted November 19, 2018 (edited) 59 minutes ago, la bam said: no problem (ive probably not described it properly). Im wondering what ohmage the power amp will be running at, when running in bridged mode, if using a 6ohm cab, and what output in watts that would be giving. Would it be 3ohms (as the amp is bridged)? Rather than 6ohm in normal / stereo mode? The power amp will see the 6ohm impedance at its output and deliver what it can into that load, so yes....it will deliver less than the full 1400W @4ohm that Bass Bunny quoted above. Edited November 19, 2018 by ahpook Quote Link to comment Share on other sites More sharing options...
Dood Posted November 19, 2018 Share Posted November 19, 2018 (edited) 11 minutes ago, la bam said: Completely confused now though for some reason i thought running in bridged mode doubled/halved (depending on how you look at it) the ohmage - so instead of 6ohm in one channel of stereo, it would use 3ohm, as both channels are being used? Any clarity appreciated! So, bridge mode. In the power amp there are two identical amplifier stages. Both for example will have a minimum impedance (load) you can connect to each. Lets take a 4 Ohm cabinet as our example per amplifier channel. Now, when you switch the power amplifier in to bridge mode you are combining the two modules. You will in theory get more out put, however you need to add the output impedances together. In this case, your minimum impedance cabinet (single) you can add to this bridged amplifier is 8 ohms. Sometimes you are lucky enough to find a power amplifier that will run down to 4 Ohms in bridge mode which is handy for cabinets such as yours with a load of 6 ohms. Edited November 19, 2018 by Dood Quote Link to comment Share on other sites More sharing options...
la bam Posted November 19, 2018 Author Share Posted November 19, 2018 (edited) So, if im right, will it run at 6ohm, or x2 lots of 6ohm (as its bridged) so 6/2 = 3ohm? (as im only using x1 cab). Edited November 19, 2018 by la bam Quote Link to comment Share on other sites More sharing options...
Dood Posted November 19, 2018 Share Posted November 19, 2018 Just now, la bam said: So, if im right, will it run at 6ohm, or x2 lots of 6ohm (as its bridged) so 6/2 = 3ohm? Treat bridge mode as one amp, not two modules. So the load on the amplifier is 6 ohms. Quote Link to comment Share on other sites More sharing options...
la bam Posted November 19, 2018 Author Share Posted November 19, 2018 (edited) . Edited November 19, 2018 by la bam Quote Link to comment Share on other sites More sharing options...
la bam Posted November 19, 2018 Author Share Posted November 19, 2018 Just now, Dood said: Treat bridge mode as one amp, not two modules. So the load on the amplifier is 6 ohms. ah, that is perfect. 1 Quote Link to comment Share on other sites More sharing options...
la bam Posted November 19, 2018 Author Share Posted November 19, 2018 Thanks all. I dont know where i got the information that running in bridged halves/doubles the ohmage the amp runs at, but its a relief to hear just to treat it as one amp. Thanks. Quote Link to comment Share on other sites More sharing options...
Count Bassy Posted November 19, 2018 Share Posted November 19, 2018 1 hour ago, la bam said: Thanks all. I dont know where i got the information that running in bridged halves/doubles the ohmage the amp runs at, but its a relief to hear just to treat it as one amp. Thanks. You may well find that amplifiers specify a minimum load of say 4 Ohms for each channel in standard mode, but 8 ohms minimum in bridged mode. This should be clearly marked somewhere near the speaker connections. However the ohms of a particular cabinet will be fixed and does not depend on how it is driven. Quote Link to comment Share on other sites More sharing options...
Jack Posted November 19, 2018 Share Posted November 19, 2018 1 hour ago, la bam said: Thanks all. I dont know where i got the information that running in bridged halves/doubles the ohmage the amp runs at, but its a relief to hear just to treat it as one amp. Thanks. I think where you may be slightly confused is that, when using bridge mode, each channel of a dual channel amp sees a load of half the total impedance. Your QSC will bridge into 4R, which means each channel sees a load of 2R. This pans out, because your amplifier is rated to work in to 2R stereo. You won't see a spec for each channel at 1R as this is below the minimum rated impedance for the amp, this is why you also won't see a spec for bridged into 2R. So, in your situation, with a 6R cabinet, the amp is bridged into 6R total, delivering somewhere between the 900W it produces at 8R and the 1400W it prouces at 4R. Let's go with 1200W for the sake of ease. That means each channel of the amp is producing around 600W into a 3R load. Does that clear things up a little? Either way, your cab is 6R, nothing you can do about that. Also, it's 'impedance' rather than 'resistance' or 'ohmage'. Quote Link to comment Share on other sites More sharing options...
la bam Posted November 19, 2018 Author Share Posted November 19, 2018 Thanks, I think it's becoming clearer. So, by running in bridge mode, each channel is giving 600w at 3ohm, but overall that's 1200w at 6ohm, which is perfectly safe to run at? Quote Link to comment Share on other sites More sharing options...
Dood Posted November 19, 2018 Share Posted November 19, 2018 2 minutes ago, la bam said: Thanks, I think it's becoming clearer. So, by running in bridge mode, each channel is giving 600w at 3ohm, but overall that's 1200w at 6ohm, which is perfectly safe to run at? Well, if your cabinet is rated a 6 ohms and your bridged power amplifier has a minimum load of 8 ohms, on paper, no, technically the impedance is too low. In reality though 2 ohms in the grand scheme of things is unlikely to blow up a QSC when ran within it's parameters. YMMV. Quote Link to comment Share on other sites More sharing options...
la bam Posted November 19, 2018 Author Share Posted November 19, 2018 Sorry (i know im being a pain - it will sink in i promise), but ive gone into confused mode again.... The QSC manual quotes: https://www.qsc.com/resource-files/productresources/amp/discontinued/rmx/q_amp_rmx_series2ru_usermanual.pdf "Bridged mono mode combines the power of both amp channels into one speaker, resulting in twice the voltage swing, four times the peak power, and approximately three times the sustained power of a single channel. This mode uses Channel 1's input, gain control, input filter, and clip limiter; Channel 2's should not be used. WHEN TO USE IT (OR NOT) Use bridged mono to deliver the power of both channels to a single 8- or 4-ohm load. Set switch positions 6 and 7 to "BRIDGE MONO ON." Use Channel 1's inputs, and connect the speaker as shown." There is also a picture on page 21 of a guitar set up showing everything fine in bridged mode with one cab as long as its >4ohm, which my 6ohm cab would be? Quote Link to comment Share on other sites More sharing options...
obbm Posted November 19, 2018 Share Posted November 19, 2018 Your QSC will be fine in bridged mode driving your 6-ohm cab. Some years ago I used to use a QSC PLX-1602 to drive a 3x10 (5.33-ohm cab). Never had a problem and loads of headroom. The RM-1450 has the potential to deliver in excess of 1000-watts into your cab, it just depends how far you are prepared to wind up the volume control. 1 Quote Link to comment Share on other sites More sharing options...
la bam Posted November 24, 2018 Author Share Posted November 24, 2018 Thanks to all who helped on this. Ive spoken to QSC themselves today, just querying their manual that clearly shows bridge operation being fine into 1 cab at 4ohm or greater. After speaking to them it should show that (as said above) its a 4ohm LOAD not CAB that it should show. As such, paranoia has set in, so im not going to go down this route anymore. Hence the QSC amp and x2 bridge cables will be going up for sale. On the plus side - i now have a better idea of how bridging works at last! Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted November 24, 2018 Share Posted November 24, 2018 There's no reason to sell the amp. Bridged it will handle a minimum load of 4 ohms. Minimum means that's the lowest value you may use, not the highest, nor the exact load you may use. Perhaps this will help: https://billfitzmaurice.info/forum/viewtopic.php?f=10&t=19292 BTW, there's no such term as ohmage. The term you should be using is impedance. Ohmage is the made up word used by those unaware that ohms are use not only to measure impedance but also its components, resistance, capacitive reactance and inductive reactance, either separately or in combination. Quote Link to comment Share on other sites More sharing options...
la bam Posted November 24, 2018 Author Share Posted November 24, 2018 I'm too confused to be honest. I can't work out why it isn't sinking into my brain. So - what load am I using, using a 6ohm cab bridged? Quote Link to comment Share on other sites More sharing options...
Dood Posted November 24, 2018 Share Posted November 24, 2018 On 19/11/2018 at 14:03, Dood said: Well, if your cabinet is rated a 6 ohms and your bridged power amplifier has a minimum load of 8 ohms, on paper, no, technically the impedance is too low. In reality though 2 ohms in the grand scheme of things is unlikely to blow up a QSC when ran within it's parameters. YMMV. I stand corrected having read the manual, the amp will do bridged at 4 ohms, this you can ignore my post above, save for the bit about 2 ohms difference really being a problem. Impedance changes depending on frequency as I understand it. Bill will explain more thoroughly. Quote Link to comment Share on other sites More sharing options...
Dood Posted November 24, 2018 Share Posted November 24, 2018 (edited) 23 minutes ago, la bam said: I'm too confused to be honest. I can't work out why it isn't sinking into my brain. So - what load am I using, using a 6ohm cab bridged? Take a torch as an example. It has batteries, a light bulb and a switch. When the switch is flicked, electronics flow around the loop of the circuit. When the electrons pass through the bulb, although there is illumination, the electrons encountered resistance getting across the bulb filament. The bulb in this case is your load. The resistance the electronics encounter to get through it is measured in Ohms. The battery is your amplifier, the bulb your speaker. Your speakers are the load on the amplifier. The label on the cabinet says 6 ohms, thus that is the 'resistance' the cabinet has on the flow of electrons. Now the reality of the situation is that we actually call this impedance in an AC circuit, but the word 'resistance' is a bit more meaningful in layman's terms. Hopefully I have explained this and my analogy works lol Edited November 24, 2018 by Dood Quote Link to comment Share on other sites More sharing options...
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