• Registered: 2011-05-30
  • Posts: 85

Topic: Ohms / Watts?

Hey! I've got a noob question re: PA system.  I have a Carvin StageMate S400D -- a small PA.   

Spec sheet indicates 60 watts RMS @ 8 ohms.   100 Watts RMS @ 4 ohms (with 8 ohm extension speaker). 

http://www.carvinguitars.com/manuals/76 … 00-web.pdf

The Carvin extension speaker is $200 and am wondering if I can instead get something more affordable.  Should I be looking strictly for 100 Watts @ 8 ohm extension speaker?

http://www.carvinguitars.com/products/810

Any insight and/or recommendations on more affordable extension cab speaker are greatly appreciated.  Thanks!!

  • From: Probably Somewhere
  • Registered: 2010-12-09
  • Posts: 2,446

Re: Ohms / Watts?

Ohm my gosh watt are you talking about?

I have no idea about the answer but I couldn't help myself with the easy pun.

  • Registered: 2011-05-30
  • Posts: 85

Re: Ohms / Watts?

Thanks.

  • From: Western Oregon,US
  • Registered: 2008-07-22
  • Posts: 2,498

Re: Ohms / Watts?

Speakers are fun..... once you have some understanding of how things work.

This link will take you somewhere that has a pretty good tutorial on resistance and power....  http://www.prestonelectronics.com/audio/Impedance.htm

Either way your extension speaker should be 8 ohm (4 ohm total load in parallel with the 8 ohm speaker in the amp) and I would likely size it at the 60Watt RMS which is the output of the amplifier (or a bit higher for headroom). Bear in mind that the 100 Watts referenced in your spec is now split between 2 loads (or 50 Watts per speaker).

Watts is Watts, Amps is Amps, to my mind the more important thing is the frequency response and range of the speaker.... that is what really matters in music, the part you hear.  Volume is a function of size, not power, and you will try to get something loud without losing the high frequencies...... do your homework and check those numbers as well.  You should be able to find something in your price range that will serve you well without "letting the smoke out" of your amp.

Take Care, and Good Hunting!
Doug

"what is this quintessence of dust?"  - Shakespeare
  • Registered: 2011-05-30
  • Posts: 85

Re: Ohms / Watts?

Thanks a lot, Doug!  I've seen a few things written about watts vs. amps, but this helps a lot.  Thanks again.

  • Registered: 2006-03-04
  • Posts: 2,662

Re: Ohms / Watts?

Here's a quick and easy link that should be helpful as well.

http://www.ohmslawcalculator.com/ohms_l … ulator.php

Give everything but up.
  • From: Western Oregon,US
  • Registered: 2008-07-22
  • Posts: 2,498

Re: Ohms / Watts?

Ohm's Law:   Volts X Amps = Watts.  simple algebra lets you solve for whatever value you are concerned with (generally you try to limit Amps. Amps is a another term for current, ).  Why is that important? So you don't have to run huge conductors to your speakers in an effort to reduce heat and burning up your wires (or the house), not to mention that they are cheaper and easier to carry around.

I would say that most Amplifiers push voltage to the speaker array at around 1/2 of your mains, example: my little Fender measures 59 volts (actual, with my Fluke Voltmeter)  Incoming line voltage hovers between 115-118 VAC here in the States.  Higher the voltage, the lower the Amperage for the same Wattage output. 

An interesting note:  Most Home Stereo speaker cabs are 16 Ohms....  which explains the dainty wires you can easily hide without much fear of setting fires or getting yourself fried if you get across them when they are powered (still not recommended).

Hope I didn't thoroughly confuse anyone yet...

Doug

"what is this quintessence of dust?"  - Shakespeare
  • From: Scott County, Virginia, U.S.A.
  • Registered: 2008-03-19
  • Posts: 794

Re: Ohms / Watts?

Doug, you didn't confuse me - I was already confused. The only thing I know about electric is - you can touch "this" wire without getting zapped and you can touch "that" wire without getting zapped, you just can't touch "this" wire and "that" wire at the same time.

Live in the "now" - a contentment of the moment - the past is gone - the future doesn't exist - all we ever really have is now and it's always "now".
  • From: The Land Of Song
  • Registered: 2007-12-10
  • Posts: 5,702

Re: Ohms / Watts?

i've been buying and using PA's and speakers since the 70's. as has been mentioned above leave a little head room, eg; 100 watt amp - 150 watt speakers (combined) for clarity of sound and avoidance of blowing the cones. back then we'd try to get the lowest ohmage to be able to push out the greater wattage. but with the last set of speakers i bought it seems to be the other way round?
must remeber that the size of your connecting leads also adds resistence, so the thicker the better.

EACH 8 OHM SPEAKER YOU ADD REDUCES THE OHMAGE ; 1 - 8 OHM SPEAKER = 8 OHMS. 2 8 OHM SPEAKER = 4 OHMS. 3 8 OHM SPEAKERS = 2.66 OHMS (or something like that).

best thing is to check out on-line tutorials if your still confused, i've tried to make it simple.

Ask not what Chordie can do for you, but what you can do for Chordie.

Phill Williams's Website

  • From: Western Oregon,US
  • Registered: 2008-07-22
  • Posts: 2,498

Re: Ohms / Watts?

You have a good grasp of things Phill, but you mentioned that the last set you bought it seemed the other way around?  My guess is that that latest addition (pair?) might have been wired differently.  Normal is wired in parallel, but they can also be wired in series.... series wiring adds the sum of ohmage rather than halving.

So you could have two 4 Ohm speakers wired so the resulting resistance equals 8 as opposed to 2. Usually you find the series/parallel wiring useful when building cabinets where you have multiple speakers for accurate sound rendering.  Base, Mid, & Tweet.... there will also be high and low pass filters in the line to protect them each from waveforms that are beyond their capacity to "make" without physical damage.

That's kinda why I mentioned the 16 Ohm home stereo speakers.... because they are available cheaply used, and can be wired in such a way as to make them compatible with your PA system to get by on until you have funds for upgrade.

Doug

"what is this quintessence of dust?"  - Shakespeare

11 Reply by ee

  • ee
  • Member
  • Offline
  • Registered: 2017-05-20
  • Posts: 11

Re: Ohms / Watts?

You can connect multiple speakers in a parallel configuration to attach two or more speakers, doing so will decrease the overall resistance provided by the system. You can use this calculator to find the equivalent resistance of two or more components in parallel automatically here.
http://www.electricalcalculators.org/pa … alculator/
Alternatively, you can use Ohm's Law to find the power for any resistance/current value.
http://ohmlaw.com/ohms-law-calculator/

Ee