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Impedance Matching

 

New member
Username: Seanm909gmailcom

Churton Park, Wellington New Zealand

Post Number: 1
Registered: Oct-14
Hi Guys,

New to forum, not very clued up on impedance matching etc. I am assisting someone with installing speakers in a small clubhouse and don't want to mess up the system.

The clubhouse has an existing 45 watt / 4 ohm PA amplifier. They want to connect 2 or 4 x 100 watt/6 ohm speakers to it (depending on whats possible). The output section of the amp has 2 terminals (screws) with 4 ohms written above it and 2 terminals (screws) 100V written above it.

Can this type of amp safely drive 2 or 4 of these speakers or none at all ? If it is possible, how would I wire in the speakers - series, parallel to get the best result.

Any assistance is appreciated.

Thanks,
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17990
Registered: May-04
.

Do you have an owner's manual for this amp? It should give a better explanation of proper operation than do the numbers you've provided. The retailer who sold the amp should also offer after the sale service.

From your description, I assume you are not fully aware how amps and speakers operate together. There are no "4 Ohm" amplifiers nor "6 Ohm" speakers. The spec "45 watt / 4 ohm PA amplifier" intends to say the amp is capable of 45 watts output when it is working into a 4 Ohm resistive load. It will produce higher or lower wattage when the load value is raised or lowered. Typically, a solid state amplifier (direct coupled rather than transformer coupled) will produce about half its 4 Ohm power when working into an 8 ohm load.

The "load" is what is important since a "6 Ohm" speaker is not a resistive load but rather a reactive load. The difference is in how the amp is measured (resistive load) and how the amp must operate in the real world (reactive load). Loudspeakers as a "load" do not remain at only one impedance value and most "6 Ohm" speakers will have a low point in their impedance which may dip beneath 4 Ohms and rise above 8 Ohms. This reactive load will vary with frequency and can make for unpredictable results when assessing proper amp/speaker pairings.

I'm going to assume the "100V" labelling means the amp can be connected to the speakers via a transformer with a "100V" primary winding. This application would normally be for a much more complex system than two speaker pairs. Now I'm assuming when you say, "They want to connect 2 or 4 x 100 watt/6 ohm speakers to it ... ", you are saying one or two pairs of speakers. Your lack of clarity here is what is making a direct answer more difficult to provide. Further, you do not give any informaton about how the speakers will be used; all playing together, each set playing independently but with similar music/vocal signals, with a difference in volume between the pairs, etc.

If you are connecting two pairs of speakers of an identical model, wiring them in parallel will essentially half the impedance load seen by the amplifier. Given that a "6 Ohm" speaker will likely drop beneath 4 Ohms at some frequency, this is a less than desirable connection. Wiring the speakers in series also presents problems since the speakers cannot be controlled independently and the total impedance will rise by approximately twice the "nominal" (or stated/average) impedance of each speaker. This would put the total impedance load for the amp at an average of 12 Ohms. Since power output drops as impedance rises, this series connection would be expected to produce approximately ten watts from your amplifier. Given the minimal amount of information provided, either parallel or series connection will pose certain problems for this amp/speaker pairing.

I would say make the parallel connection to begin with. Play the system at moderate volume levels and check the warmth of the amp by placing your hand on the top of the case. If the amp doesn't have sufficient air flow around it, the amp might get quite hot. If the amp feels overly warm, this is a sign the amp doesn't care for this parallel connection. A series connection is probably not going to provide enough power to adequately drive the speakers. Therefore, the next move would be to a speaker selector switch box with a "protection" switch. Something like this; http://www.crutchfield.com/p_190SS4/Niles-SS-4.html?tp=2997&awkw=75619818985&awa t=pla&awnw=g&awcr=47439082225&awdv=c

The "impedance magnification" protection is just a large value load resistor and the connection is still in parallel. This is, however, the least expensive way to connect your proposed system and not endanger the amp. If you require independent volume control over the speaker, you can buy a selector with volume controls.

Ideally, you would make your connection via an "autoformer". This sort of control comes in a selector switch box alone, a switch box with volume controls or you can buy in wall speaker volume controls with autoformers. http://www.russound.com/speakerselector_overview.php An autoformer based connection will always show the amp a constant load no matter the varying impedance of each speaker. This is your "best" connection in that it is the safest connection. It is, however, the most expensive way to make the connection.

If, in the end, none of this makes sense to you, contact Russound and discuss this with their representatives. Without much more information, there isn't a better answer to be given IMO.



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