Speakerplans.com Homepage
Forum Home Forum Home > General > Newbie Discussion
  New Posts New Posts RSS Feed - Matching speaker ratings to amp power
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Matching speaker ratings to amp power

 Post Reply Post Reply Page  <123
Author
Message
mini-mad View Drop Down
Old Croc
Old Croc
Avatar

Joined: 13 July 2012
Location: london
Status: Offline
Points: 6903
Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 19 August 2017 at 3:21am
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.
If it sounds like a gorilla is trying to escape, turn it down.
Back to Top
fatfreddiescat View Drop Down
Young Croc
Young Croc
Avatar

Joined: 15 October 2010
Location: N.E.Wales
Status: Offline
Points: 1081
Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 19 August 2017 at 9:32am
This paper should give you a good idea of how to match amps and speakers:



Back to Top
charlysays View Drop Down
Registered User
Registered User
Avatar

Joined: 16 June 2015
Location: Wales
Status: Offline
Points: 413
Post Options Post Options   Thanks (0) Thanks(0)   Quote charlysays Quote  Post ReplyReply Direct Link To This Post Posted: 19 August 2017 at 11:22am
Originally posted by jngggggggg jngggggggg wrote:

That leads to my next question. Why is it so detrimental to run an amp at 2 ohm? Jumping from 2 to 4 ohm essentially doubles my power costs so it's a significant bump


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.
Back to Top
jngggggggg View Drop Down
Registered User
Registered User


Joined: 27 April 2017
Status: Offline
Points: 88
Post Options Post Options   Thanks (0) Thanks(0)   Quote jngggggggg Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2017 at 6:06am
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?
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10920
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2017 at 6:44am
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
Back to Top
charlysays View Drop Down
Registered User
Registered User
Avatar

Joined: 16 June 2015
Location: Wales
Status: Offline
Points: 413
Post Options Post Options   Thanks (0) Thanks(0)   Quote charlysays Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2017 at 9:44am
Originally posted by toastyghost toastyghost wrote:

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.


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.
Back to Top
hydrus View Drop Down
New Member
New Member


Joined: 01 October 2012
Status: Offline
Points: 2
Post Options Post Options   Thanks (0) Thanks(0)   Quote hydrus Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2017 at 10:01am
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.

Back to Top
 Post Reply Post Reply Page  <123

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.06
Copyright ©2001-2023 Web Wiz Ltd.

This page was generated in 0.078 seconds.