speaker ohms

[ozboater]

i realise that this isn t an electrical question but it relates in some way ( i guess) :)... i have a new set of outdoor speakers that i want to connect to an old sony mini hifi... the sony has a pair of 6 ohm speakers and the amp is about 40 watts RMS... i d like to connect the second set of outdoor speakers with a speaker selector switch...one that will allow me to select A / B and A+B...

anyway, the outdoor speakers are 8 ohm... are there any potential problems hooking up speakers with different ohms ???

thanks for any advice / help

cheers

oz

[domwilson]

What is the impedance of the other set of speakers? Are you planning on playing both sets simultaneously? Are you planning on playing them loud? Some amps become unstable or can be damaged with too low of impedance speakers. This is a complex topic. I can answer you better with more detail.

[Jeff Wohlt]

You can go that way with a switch. 8 ohm is fine if it really is a 6 ohm set up...which is kinda odd. You will only notice the 8 ohm slightly lower in volume.

Now with out a switch and you add speaker in para then a 4 ohm system then becomes a 2 ohm and that can burn amps. My kid did that with his little room stereo and after you play it hard and loud it will shut down.

If you drive both A&B at the same time I would not play it loud or try to push any big watts thru them.

Of course, if you are playing Bethoven (SP)and all that kind of music then it will burn up anyway

It will be just fine as long as you play classic rock from the 60s-80s....har-har-har.

[Flying Scotsman]

Douggie the HiFi "expert" will try to explain...speakers rated with a low ohm rating are easier to drive than those with high ohm rating. Car speakers are a perfect example, they are usually rated at 4 ohms and can be driven to high volumes with a crappy transistor amp but can not produce realistic base boom boom ...look inside and you will see chips that provide the amplication, not good. the ohm rating changes dramitically upon the frequency response...low frequency creates the highest demand on the amp. That is why a speaker with a high ohm rating and a low hertz rating requires a quality amp to produce the best overall sound. You will put a huge demand on that amp running 4 speakers

Douggie

[ozboater]

thanks gents...

the old speakers and i presume amp is rated at 6 ohms... the new outdoor speakers are 8 ohms...

yeah, i plan to use them together mainly (A + B)... occasionally i ll run them as pairs, either the outdoor ones in the garden and the old sonys in the man cave.... mainly playing together tho...

it s mainly to listen to internet streaming radio from australia so cranking it up doesn t really come into the picure... mainly talk radio etc... 702 sydney... great stuff... abc.net.au/streaming

i ll crank the rock upstairs on the big jbls and polks...

so you blokes reckon i ll be ok then... any idea where i can pick up a stereo selector switch ?? i ve seen on at radio shack that allows the hook up of four sets of speakers but i m not sure if it ll allow you to play two or more sets together... plus i only want two sets of speakers hooked up - not 4...

thanks again for the help men... much appreciated

oz

[domwilson]

You should be ok as long as you don't crank it. Speaker impedance is a nominal figure as speakers present a very complex load to the amplifier. But just like boats, Watch the temps...

[egneg]

All you need are 2 DPST switches and a plastic box to make it yourself.

http://www.radioshack.com/family/index.jsp?categoryId=2032278&allCount=91&fbc=1&f=PAD%2FProduct+Type%2FDPST&fbn=Type%2FDPST

http://www.radioshack.com/product/index.jsp?productId=2062279

[Flying Scotsman]

As an aside, most mass market amp specs are rubbish and all they can do is drive a resistor at 8 ohms. In the real world they fail to live up to their promise, and as has been mentioned speakers and amps, like FE motors depend on the setup to live up to their credentials

Douggie

[ozboater]

you blokes are awesome... thanks heaps... that looks like a good solution egneg, unfortunately i have no idea how to solder it together... soldering i can handle but the hook up has me baffled... any chance you could draw me up a quick wiring diag?? big ask i know but without one i m shot... sure looks like a cheaper and better solution than the 4 way radioshack thing i was looking at... plus it ll save me about 35 bucks...

with the dpst stiches i ll be able to run the speakers in the A / B , or A+B set up yeah ??

cheers

oz

[egneg]

Yes you can choose a/b or a+b. Give me a bit of time and I will draw up the diagram.

[Flying Scotsman]

i realise that this isn t an electrical question but it relates in some way ( i guess) :)... i have a new set of outdoor speakers that i want to connect to an old sony mini hifi... the sony has a pair of 6 ohm speakers and the amp is about 40 watts RMS... i d like to connect the second set of outdoor speakers with a speaker selector switch...one that will allow me to select A / B and A+B...

anyway, the outdoor speakers are 8 ohm... are there any potential problems hooking up speakers with different ohms ???

thanks for any advice / help

cheers

oz

It is very easy to wire think and what switch. Yes I am being nasty

Dougggie

[ozboater]

cheers egneg, i apprectate it... i could get it eventually but it d need to be resoldered at least 35 times... good on ya mate..


douggie

[egneg]

Here it is Oz.

[ozboater]

cheers egneg... awesome... i reckon i got it now... i ll post ya the results..

[linnmajik]

OK, I'm glad I found this thread. I've gone to school for electrical engineering and have actually installed home theatre systems that sold for over $200,000. Let me begin by helping to reduce some confusion. I may repeat some things that were already said but this should be very helpful in summing up everything in one thread.


I don’t have time to write this perfectly so some parts may be point form.
This paragraph is my basic answer to the thread (I will expand and explain afterwards):

There is no problem with hooking up speakers with different ohm ratings as long as the total load impedance doesn’t drop below what the amplifier is designed for. The safest way to do the switching is to buy an impedance-matching speaker switcher. You can buy one that will allow the Sony to “see” 6 or 8 ohms - even when you are running both sets of speakers at the same time. I believe companies like Q.E.D. and Russound have these switchers.

Ohm’s law: As resistance (or in AC circuits - impedance) decreases, current increases.

As impedance drops, the circuit gets closer and closer to being shorted. This increases the current demands from the amplifier. Most amplifiers are current-limited and are not stable driving low impedance speakers (or a combination of speaker pairs that allow the amp to “see” a low impedance circuit) Since Sony mini systems have almost no current reserve, keeping the impedance high is much easier for the amplifier to drive.

Two sets of 8 ohm speakers switched on in a series circuit, the amplifier sees 16 ohms. Two sets of 8 ohm speakers switched on in parallel, the amp sees 4 ohms (current demand is 4 times that of the series circuit - but more voltage is required)


Ohm rating is nominal, impedance fluctuates with frequency. An 8 ohm speaker can be as low as 3 ohms at a certain frequency and some have been measured as high as 70 ohms at certain frequencies. At low ohms, the amplifier needs to swing large current, at high ohms, it needs to apply high voltage (to make up for the large voltage drop across 70 ohms)


Douggie,

Low impedence speakers are HARDER to drive than high impedence. Car speakers are 4 ohm because high impedence causes voltage drop and the power supply “rails” in a car amp operate at a lower voltage than a house amp. LOW ohm rating and low frequency is the most difficult - massive current demands and the amp has to control a larger moving mass with more back EMF. You are right about the specs of mass produced amps - it got even worse when home theatre came out - An amplifier that draws 150 watts from my wall outlet can’t put 110 watts out to each of my 5 speakers at the same time. Its all lies. And, in most situations, power has absolutely no bearing on performance. It all demands on how well the amp was made. I’ve heard great sounding 20 watt amps and terrible sounding 100 watt amps.

Jeff,

8 ohm speakers are not lower in volume than 6 ohm - their volume has to do with input power and efficiency, not their impedance. Current does not provide loudness, the product of current and voltage is power, which, combined with the speaker’s efficiency make it play at a certain volume.

If someone does have low impedance speakers, it is better if they have high efficiency.
A 90db speaker will require half the amount of power to get to the same volume as an 87db speaker. (A 90db speaker at 50 watts will play as loud as an 87db speaker at 100 Watts.)

A 4 ohm 90 db speaker can sometimes be as easy to drive as an 8 ohm 87db, but there are a lot of variables.

Egneg,

Your diagram is a parallel connection with no impedance matching, switching A + B and running at the same time, the Sony will see 3.4 ohms, "high-end" Sony ES amps can barely handle this.


Keep volume very, very low. (Which could be difficult outdoors)


I wish I was a better writer, but I can expand on everything later, I have to go.