"Ohmage" to amps and speakers - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 25th March 2004, 06:52 PM   #1
z is offline z  United States
diyAudio Member
Join Date: Mar 2004
Location: SW PA
Default "Ohmage" to amps and speakers

First post - impressed with the forums I've read, and other forums I've joined. This is one of the best uses of educational technology out there...real information from folks that know what they're talking about.

I'm looking to secure a new bass amp head and speaker cabinet set up. The ohm/watts ratio are really throwing me, though. I have a decent mathematical head, but when I think I've figured it out, I purchase what I think I need, and end up blowing a speaker. Don't want to do that again.

With that said, what's the relationship between amp and speaker ratings in terms of watts and ohms. Specifically, I'm looking at purchasing an amp head that puts out 300 watts at 4 ohms. I also have a line on a speaker cabinet that will handle 300 watts continuous, but the cabinet is rated at 8 ohms. Today's mathematical question - will I only be able to use half the power from my amp head, or will I get nothing out of speakers with the amp fully cranked.

Thanks for your feedback!!!
  Reply With Quote
Old 25th March 2004, 09:05 PM   #2
diyAudio Member
leadbelly's Avatar
Join Date: Dec 2002
Location: Calgary, Alberta
Default Re: "Ohmage" to amps and speakers

Originally posted by z
Today's mathematical question - will I only be able to use half the power from my amp head, or will I get nothing out of speakers with the amp fully cranked.

Thanks for your feedback!!!
It is actually not a mathematical question, if you think that V=IR is the way to solve this. It is common to see a power rating into 4 ohms that is more than that into 8 ohms in amplifiers, but it is not a specific relationship and depends on the amp design.

If you really want to know what power your amp will drive into 8 ohms, ask that question of the manufacturer. But do not worry about a bad match between amp and cabinet, the speakers will work quite fine.
The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts. Bertrand Russell
  Reply With Quote
Old 25th March 2004, 09:22 PM   #3
sreten is offline sreten  United Kingdom
diyAudio Member RIP
Join Date: Nov 2003
Location: Brighton UK
Simply put it goes like this for bass amplifiers / cabinets.

Speakers should be ~ twice the power of the head at nominal loading.

So for for your 300W/4ohm head you need ~ 600w/4ohm speakers.

Taking your 300w/8ohm cabinet, it will be fine used on its
own with the head as the head will only put out ~ 150W.
(probably nearer 200w in reality)

For best performance you need two ~ 300w/8ohm cabinets.

You can use one or two cabinets, depending on
venue, using one cabinet will not cause it to blow.

(Or just one 500W to 600W 4ohm cabinet)

  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
70cm tall, 3 way, diy speakers based on 10"/4"/1" japanese ken brown drivers. facundonu Multi-Way 34 9th March 2009 04:59 AM
12" "guitar" driver in Audio Speakers jwhit67 Multi-Way 4 11th February 2008 02:47 PM
Newb Q: How do I determine a speakers Ohmage? massappeal129 Multi-Way 5 17th February 2003 05:40 PM

New To Site? Need Help?

All times are GMT. The time now is 01:34 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2