| Author |
Topic: Speaker impedence |
Steve Richter
From:
Neenah, WI USA
|
Posted 3 Feb 2005 6:05 pm |
|
Question for you electronic gurus out there. Since wiring 2 speakers in parallel cuts the total impedence in half, can you change the impedence of a speaker by putting a resistor in parallel?
probably a silly question .. but ..
thanks,
steve |
|
|
 |
Ken Fox
From:
Nashville GA USA
|
Posted 3 Feb 2005 6:15 pm
|
|
You will change the load the amp sees. However it best be a foot long or more power resistor (200 watt rating recommended) or a fire will result. I use a 200 watt resistor in my shop, rated at four ohms to test amps. Even it gets hot as a match!
You would not change the impedance of the speaker by putting a resistor of the same impedance(AC resistance) in parallel with it, you would just lower the impedance to 1/2 that the amp sees. Power would be shared equally across the two parallel loads.
|
|
|
|
Harold Dye
From:
Cullman, Alabama, USA
|
Posted 3 Feb 2005 7:44 pm
|
|
| In order to hook two speakers together in parallel what is necessary ? I have two 8ohm speakers cabs and I want to use them together to achieve a 4 ohm load to match my Amp. I assume I can put another jack in one and run a cable from it to the other but how do I wire it in. Your help is appreciated. |
|
|
|
Bob Metzger
From:
Waltham (Boston), MA, USA
|
Posted 3 Feb 2005 8:53 pm
|
|
Connect the second speaker in parallel with the first. For two 8 ohm speakers, this will result in a 4 ohm load.
That means hot connects to hot, ground connects to ground. The parallel connection can be inside the amp, if there are two speaker jacks. For two jacks wired in parallel: a wire connects the two hots lugs on the jacks together and a wire connects the two ground lugs on the jacks together.
Or there can be a jack in one/either of the cabs to chain the two cabs/speakers together (Hot on the jack goes to hot on the speaker; ground on jack to ground on speaker). If two jacks are in a cab, they are wired as above, hot to hot, ground to ground.
Now you just have to double-check that your two speakers are playing in phase with one another. Then you're done.
Bob M. |
|
|
|
Steve Richter
From:
Neenah, WI USA
|
Posted 4 Feb 2005 4:43 am
|
|
| Thanks, Ken. I thought that the size of the resistor might be a problem depending on the power rating of the amp. Just a thought that crossed my mind while cruizin'. |
|
|
|
Harold Dye
From:
Cullman, Alabama, USA
|
Posted 4 Feb 2005 4:48 am
|
|
Bob M,
Thanks for the info. |
|
|
|
John Daugherty
From:
Rolla, Missouri, USA
|
Posted 4 Feb 2005 5:49 am
|
|
Steve, Please note that Ken said "the power is shared by the 2 loads".
To clarify this: You will only hear half of the available power if you use a resistor. The other half will be dissipated as heat from the resistor. Not a good way to match the load.
The only beneficial way to match the load is to use two 8-ohm speakers in parallel,plus to plus & minus to minus,which wires them in-phase. |
|
|
|
David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
|
Posted 4 Feb 2005 11:22 am
|
|
Harold if you are running a single amp (e.g., a head cabinet, or a combo with the internal speaker disconnected) to two separate cabs, each with an 8 ohm speaker, the simplest thing is to get a Y adapter (one in, two out) and plug it into the amp internal speaker jack. Then just run a separate speaker cable from the Y adapter to each speaker cabinet. If you want to use the internal speaker and one external speaker, plug the Y adapter into the internal speaker jack, then plug the internal speaker into one of the adapter's out jacks, and the external speaker into the other adapter out jack.
The above is the manual way to connect speakers in parallel. Many amps have an internal speaker connection, and a separate external speaker jack. This ext. jack may be either a series or a parallel connection. You will have to consult the spec. sheet or the circuit diagram fo the amp to figure out which type yours is. |
|
|
|
Harold Dye
From:
Cullman, Alabama, USA
|
Posted 4 Feb 2005 12:26 pm
|
|
| David thanks for the response. I use a MM head sometimes and that has 2 speaker jacks wired in series. It has the switch which allows for choosing either 4 or 8 ohms. When I use my two 4 ohm cabs I set it at 8 ohms and I'me good to go. When I want the 8 ohm I can only use one of them. I was looking for a way to connect the two in parallel, set the switch at 4 ohms and go for it. BTW the 4 ohm cabs are 12" speakers and the 8's are 15's....thats why I would like to use both 8's at the same time. |
|
|
|
Dave Grafe
From:
Hudson River Valley NY
|
Posted 4 Feb 2005 8:18 pm
|
|
Steve, you said:
| Quote: |
| Since wiring 2 speakers in parallel cuts the total impedence in half... |
This is true only if the two speakers have equal impedance.
When wired in parallel the total impedance equals the reciprocal of the sum of the reciprocals, as (for two 8 ohm speakers): 1/8 + 1/8 = 2/8, the reciprocal of which is 8/2 or 4 ohms total load. For one 8 ohm and one 4 ohm speaker: 1/8 + 1/4 = 3/8, the reciprocal of which is 8/3 or 2.6666 ohms (the 4 ohm speaker will receive twice the power as the 8 ohm one).
For impedances wired in series the total is the sum of the parts, as: 8 + 8 = 16 ohms or 8 + 4 = 12 ohms (all speakers will receive the same total power).
For a case such as Harold's where the amp speaker outs are wired in series, you might consider making a series wye adapter for the two 4 ohm cabs (making 8 ohms total for the pair), a parallel wye adapter for the two 8 ohm cabs (making a 4 ohm pair) and then plug both combos into the amp for a total 12 ohm load. Set the selector for 8 ohms and let 'er rip. In this case, all speakers will receive the same power from the amp.
Bear in mind that you can't hurt your amp with too high an impedance, only too LOW a load will heat it up and cost you money.
Also note that if you have speakers from different manufacturers (or even the same manufacturer but different years) you cannot count on simply wiring them alike (plus to plus, etc.) to have them operate in phase with each other.
Once you have your speakers wired up, hit the strings over the pickup with the palm of your hand to make a big thudding sound (or you can use any other manner at hand of generating a big low frequency impulse) and visually check to see that the cones are traveling in the same direction. If any of your speakers are NOT traveling in synch with the others reverse the wires to that speaker and check again.
Older JBL speakers (and some others as well) produced rearward travel with positive volts applied to the red terminal, which is the opposite of what many other manufacturers do. I understand that the newer JBL voice coils produce FORWARD travel with a positive voltage applied to the red post, which I believe is also the norm for BW.
It doesn't matter which way your speakers move, as long as they move together (i.e. in phase with each other).
As always, please let me know if I can confuse the issue any further for you.
dg[This message was edited by Dave Grafe on 04 February 2005 at 08:58 PM.] |
|
|
|
Eric Pritchard
From:
Berkeley Springs, West Virginia, USA
|
Posted 10 Feb 2005 9:55 am
|
|
If you put two 8-ohm speakers in parallel then you will have 4-ohms. If your amp can drive 4-ohms you have no problem. If it can't drive 4-ohms, then the speakers need to be in series, unless you use a matching transformer. This will give you maximum power output, if the amp can not drive 4-ohms.
Have a great day,
------------------
Eric Pritchard
Pritchard Amps
www.pritchardamps.com |
|
|
|
