Alembic Guitars Club

Connecting => Miscellaneous => Topic started by: phylo on December 30, 2006, 07:59:54 PM

Title: Ohms
Post by: phylo on December 30, 2006, 07:59:54 PM

I have a pair of old Acousitc Research speakers.  My dad bought them in the early 70's.  The label on the back says they are 4 ohms.  Can anyone tell me what the impact of this is?  Standard receivers are now 8 ohms, right?  Will these work with an 8 ohm receiver?  I also have the AR receiver, but it needs repair.  Anyone know if this worth repairing?
Thanks!

Title: Ohms
Post by: alembic_doctor on December 30, 2006, 08:09:44 PM

You need to find out what the minimum impedance is on the amplifier.  Ifthe amplifier has a minimum of 8Ohms on it, then it is not recomended that you hook up a pair with a 4 Ohm impedance.  You can probably do a google search of the equipment model and find a manual or spec sheet.
 
My $0.02

Title: Ohms
Post by: alembic_doctor on December 30, 2006, 08:31:35 PM

http://www.grc.nasa.gov/WWW/K-12/Sample_Projects/Ohms_Law/ohmslaw.html
 
http://www.the12volt.com/ohm/ohmslaw.asp
 
Here's a couple of links pertaining to Ohms Law for the geeks or anyone who cares.
 
Another thing to remember is that a speaker is a reactive load.  The impedance can actually go much lower depending on the Frequencies applied to it and the volume at which those frequencies are disseminated.  
 
I also recommend that you find out the RMS power rating of the speakers.  You want to be sure that the amplifier you are  hooking up to it has sufficient power.  Due to the fact that it is easier blow your speakers by under powering them than over over powering, You should have an amplifier (receiver)that puts out at least the RMS rating of the speakers.  We always double the RMS and sometimes (depending on application)we'll double the Maximum(usually subwoofers).  
 
another $0.02

Title: Ohms
Post by: inthelows on December 31, 2006, 10:29:21 AM

There are so many kinds out there now you need to see if the model is collectable or not. This will determine if you want to invest in repairing it or not. Between $75 and $150 if the parts can be found.
The ohmic value as simple as it is on a speaker should be as close to the amp output. This keeps the speaker from getting a lethal dose of current that fries open the voice coil.  
The good doctor has it right. Although I personally haven't heard of blowing them up by under powering the fact that most amps have a little room either way.  
Since the power rating is the real factor I would heed the doc's advice. Mismatched impedance can make for higher distortion levels and can cause damage to both speaker and amp.
Good luck!
NLP

Title: Ohms
Post by: keith_h on December 31, 2006, 10:59:37 AM

NLP,
The problem with an under powering a speaker deals with clipping. The smaller the amp the more likely one is to drive it into clipping. By using an amp over the rated power of the speaker you are less likely to drive the amp into clipping and therefore less likely  to cause speaker damage.  
 
Keith

Title: Ohms
Post by: alembic_doctor on December 31, 2006, 02:13:16 PM

And amplifiers can clip without you hearing it.

Title: Ohms
Post by: inthelows on December 31, 2006, 02:25:37 PM

Well I sit corrected! Thanks for the info.
Most dealings I have had the amps have enough room for accommodating impedances 2 to 16 ohms.
Now granted only the acoustic 370 was able to handle that range w/o adjusting the settings.
Most audiophiles have amp to spkr impedance dead on unless using electrostatic types with matching transformers which do the job.
Thanks again for the input.
NLP

Title: Ohms
Post by: phylo on January 03, 2007, 10:06:55 AM

Thank you.  Very useful.  Hopefully they aren't blown already