Matching speaker ratings to amp power |
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mini-mad
Old Croc Joined: 13 July 2012 Location: london Status: Offline Points: 6903 |
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Like running an amp near clip... the amp.becomes more unstable to put it very crudely. The amps ability to control the cone is directly related to something called the damping factor. If you run an amp at a very low impedance you will cause it to lose control of the driver and what it's doing.
Some amps handle it a little better then others but like your can run into the red on the tacho, would you really want to keep it there throughout your entire journey? Lots of factors will cause an amp to run near it's edge of control. Running low impedance loads is another one of them. |
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If it sounds like a gorilla is trying to escape, turn it down.
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fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1081 |
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This paper should give you a good idea of how to match amps and speakers: |
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charlysays
Registered User Joined: 16 June 2015 Location: Wales Status: Offline Points: 413 |
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Also remember that when impedance halves, current doubles. So cables and power distribution become more critical. If you're running off 13a plugs most amps won't be able to draw enough current and will clip prematurely. All amps will have a shorter life span running at 2r. Many amps, even those rated for 2r run noticeably hotter even just running at 4r vs 8r. At 2r some get too hot to touch - heat kills semiconductors. |
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jngggggggg
Registered User Joined: 27 April 2017 Status: Offline Points: 88 |
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so if i wanted to power four b&c 21sw152's (program 4000watt / rms 2000watt) with a single k20 i would probably run the amp at a net 4ohms per channel.
which means i would have to buy the 8ohm version of the driver and run 2 on parallel per channel. i would only be feeding 2600watts into each speaker though. do you guys see any issues w/ that?
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toastyghost
The 10,000 Points Club Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10920 |
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I hang 8 ohm B&C 21SW152 off K20 at 4 ohm loading often, its a great match.
Also using a 13A socket does not make your amp clip earlier, it has no idea what socket it's connected to – if it needs to draw more current than the socket allows, it will do so. The fuse may or may not blow, depending on how long it tries for. The same can't be said for the breaker upstream. Edited by toastyghost - 25 August 2017 at 6:45am |
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charlysays
Registered User Joined: 16 June 2015 Location: Wales Status: Offline Points: 413 |
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Noted, I'm getting confused with voltage drop. I was once running some subs and amps of a 13a which had a few other things on it (some lights etc) and found that at 8r the amp was fine but at 4r it would show it's clip lights despite the limiter being set correctly. In other places with more 13a sockets available it had been fine. If you're pushing the limitations of 13a sockets then running at lower impedances will exacerbate it as current must go up as impedance goes down. |
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hydrus
New Member Joined: 01 October 2012 Status: Offline Points: 2 |
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There is a lot of good info already in this topic, but I'm amazed nobody said anything about the cabinets themselves.
You are all speaking about driver specs of manufactures but I doubt you'll put the driver in the same cabinet as the manufacturer did to measure his driver. The power capabilities of a driver might be very different in your cabinet. Impedance matching on the electric - mechanic (amp to speaker) interface is important but so is impedance matching on the mechanic - acoustic (speaker to air) interface. "Bad" or better word: "different" impedance matching with the air will reduce your ability to put electrical power into your voice coil. One example: Think about the pass band of your cabinet, you always want to keep the power inside it. Outside the pass band your voice coil turns into a heating element really quickly. (not only in the LF, also HF) 6th order bandpass tuned from 35Hz to 80Hz but driven at max power up to 160Hz? You just made a expensive heater/power compression device. Other example: 18" on open baffle (it's a HiFi thing) you'll probably hit x-max at 50W with your 1400W rated driver. This setup sounds amazing and gets plenty loud for HiFi but you do not want to put a 200W amp and drive it up to 0dB on this combination. Both are extreme examples but this sort of thing happens in any cabinet. Now the most difficult part: There might be impedance issues in your intended pass band of the cabinet. You should be very careful with those because, it's easier to set the HPF or LPF a bit higher to give the cabinet a lot more power capability but it's harder to do when the issue is in the middle of the pass band. And after all this manufacturers chose to use all kind of different measurement techniques for both drivers and amps. If you want to get the last Watt out of your enclosure it's really not going to be easy, especially if you don't have a full on lab to measure amp/driver/cabinet combinations. One good thing is experience (aka blowing up stuff) and common sense will get you close, and it's fun. |
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