two speakers on one terminal

[mark32]

I was doing some work for a customer of mine and before leaving I was asked to move their stereo from one side of the wall to another. I noticed they had two sets of speakers on one terminal. In other words, the - from two seperate speakers went to one - terminal of the amp, likewise, the + did the same. In all there are four speakers (Two pairs) hooked up like this. I know this is incorrect from my days of fooling with car stereos, but what exactly can go wrong in this situation and what can be done without running new wires?

 

[Buck Parrish]

I don't see any thing wrong with it. You got two - and two + right? Two on one pair of - and +'s and two on the other. You might not have surround sound. But could still be stereo.

 

[wireguru]

(unless this is 70v line) you could blow up their amplifier. Connect two speakers in parallel like this and you cut the impedance in half. Look at the back of the amplifier for minimum impedance, then check the impedance on the speakers. If the amp says 8ohm min, and you connect two 8ohm speakers to the amp, the amp will either shut down on overload or blow up with any significant volume level. If the amp says 4ohm minimum and you connect two 8ohm speakers in parallel you will be ok.

 

[zbang]

the amp will either shut down on overload or blow up with any significant volume level..

It really really depends on the amp. I've got a couple that are happy to drive a <1 ohm load (Crowns). OTOH I'd leave to the HO/amp owner to determine if there's a problem.

 

[wireguru]

It really really depends on the amp. I've got a couple that are happy to drive a <1 ohm load (Crowns).

thats why I suggested to check the combined impedance of the speakers against the amp's minimum impedance. From the OP, it seemed like a consumer grade stereo, not a pro audio amp capable of driving fractional ohm loads.

 

[MacG]

thats why I suggested to check the combined impedance of the speakers against the amp's minimum impedance. From the OP, it seemed like a consumer grade stereo, not a pro audio amp capable of driving fractional ohm loads.

Good call. We just went to a demo of KH speakers. Their 6" boxes ere 16 ohm so they could run 4 boxes in parallel down to 4 ohm. Most professional amps have multiple ratings in their cut sheets. It is not uncommon for a sub woofer to go to 2 ohms. Remember to not let the magic smoke out of the speaker or the amplifier or it will not work any more.

MacG

 

[zbang]

From the OP, it seemed like a consumer grade stereo, not a pro audio amp capable of driving fractional ohm loads.

The DC-300A isn't consumer grade ?

 

[hurk27]

My "1979" Techniques SA-1000, is consumer grade, it will drive at 2 ohms all day long, if you can keep the voice coils from pulling out of the cones:roll:
came with a 120v 20 amp plug on it.

But my newer IC output amp pioneer won't even drive less then 8 ohms without shutting down with the Techniques SA-1000 I can drive 4 sets of speakers ,, the speaker selector will connect all 4 sets, the pioneer only has two speaker hook ups and the selector only allows one set or the other but not both. so sometimes you can look at the speaker selector knob to see if it allow both sets or just one set at a time, it will say something like A-B-A+B if both sets can run. I have a Sansuie 990 that has 4 output amps each capable of 2 sets each, but it's only 250 watts @ 8 ohms per ch x 4 .02 THD, where the Techniques SA-1000 is 760 watts @ 8 ohms per CH. @.009 THD << now thats when receivers was made.

Of course my Crown 3600 Micro-Tec trumps both:roll:

Most new stuff is junk in my book.

 

[K2X]

I remember frying an old Fender guitar amp head by hooking to many speakers up to it. Now I follow instructions.

 

[mark32]

Thank you fellows for your insight.

I failed to look for an ohm rating on the stereo or speakers (In wall). Next time I'm over there I'll check it out. I did look at the a and b selector and you could only have one on at a time. Lets say that the speaker's ohm rating in parallel are lower than the ohm rating of the stereo, is there any solution without changing the speakers or stereo?

 

[hurk27]

If they are 4 ohm speakers then wire them in series for 8 ohms, make sure you get the polarity correct.

I have seen many of these in-wall speakers rated at 4 ohm, but if they are 8 ohm then its kind of pushing the peek voltage of the outputs if you wire them for 16 ohm.

Since you didn't wire it like that I would leave well enough alone as if something does happen it wont be your fault.

 

[LarryFine]

I wouldn't place two speakers in series unless they were identical. We know from open neutrals in MWBC's what can happen if their impedances vary.

THE fix is a second amplifier for driving one of the speaker pairs. Second would be an external speaker selector/switcher with impedance protection.

 

[hurk27]

I wouldn't place two speakers in series unless they were identical. We know from open neutrals in MWBC's what can happen if their impedances vary.

THE fix is a second amplifier for driving one of the speaker pairs. Second would be an external speaker selector/switcher with impedance protection.

Placing two speakers of the same impedance in series will not be a problem, but mixing a 4 ohm with an 8 ohm would, I have done this with a 4 ohm 15" and a 4 ohm 18" sub, to stop a amplifier from over heating and shutting down because of the 2 ohm load, the speakers took it just fine, and the load to the amp was greatly reduced, but your right a selector or L-Pad that corrects the impedance would be the best way, I use this on whole house installs when a amp has more then one set of speakers on it. leviton makes a good 100 watt 8 ohm stereo L-Pad that keeps the line at 8 ohms to the amp.

 

[GeorgeB]

Placing two speakers of the same impedance in series will not be a problem, but mixing a 4 ohm with an 8 ohm would, ...

if they are the same brand and model, I would not object much, but speaker impedance is very frequency dependent and commonly varies over more than a 2:1 range. It is not unusual for an "8 ohm" to present as low as 4 ohm or as high as 16 ohm loads over the audio range. It is possible to underload an amp as well as overload one. And damping factor goes to heck ... rather than having a sub-ohm driver, each speaker has that plus the series speaker.

I'm with the poster who recommends another amp ... not really expensive in low power consumer grade stuff. (We're not talking the Crown type stuff here). Mostly for damping reasons I'm loathe to recommend series connections.

At reasonable listening levels, the 2 ohm load on the 8 ohm rated amp rarely causes any problems. And with the 40 feet of #24 wire so often used ... another 2 ohms per speaker right there.

 

[MacG]

if they are the same brand and model, I would not object much, but speaker impedance is very frequency dependent and commonly varies over more than a 2:1 range. It is not unusual for an "8 ohm" to present as low as 4 ohm or as high as 16 ohm loads over the audio range. It is possible to underload an amp as well as overload one. And damping factor goes to heck ... rather than having a sub-ohm driver, each speaker has that plus the series speaker.

I'm with the poster who recommends another amp ... not really expensive in low power consumer grade stuff. (We're not talking the Crown type stuff here). Mostly for damping reasons I'm loathe to recommend series connections.

At reasonable listening levels, the 2 ohm load on the 8 ohm rated amp rarely causes any problems. And with the 40 feet of #24 wire so often used ... another 2 ohms per speaker right there.

More speakers are ruined by an under powered amplifier than overpowered. Seems counter intuitive but the overpowered loudspeaker's distress is quickly recognized and countered by turning it down - uh, in most cases. It is the loudspeaker that is being driven by an amp that cannot deliver what the loudspeaker wants when the operator wants it to go louder that is in trouble. Think of the sine wave. The loudspeaker is being driven in and out like the wave is going up and down. In an underpowered situation the peaks of the sine wave are cut off the speaker stops traveling and holds either out or in for the duration of the plateau (that is the duration of the "clip"). This just sounds muddy and it not as quickly recognized as a damaging sound likes being overpowered is especially in a noisy environment. When this happens the voice coil does not move properly and the heat builds up and poof the magic smoke gets out and the loudspeaker won't work anymore. Great for special effects though and guys in the repair business.

MacG

 

[LarryFine]

if they are the same brand and model, I would not object much, but speaker impedance is very frequency dependent and commonly varies over more than a 2:1 range. It is not unusual for an "8 ohm" to present as low as 4 ohm or as high as 16 ohm loads over the audio range. It is possible to underload an amp as well as overload one. And damping factor goes to heck ... rather than having a sub-ohm driver, each speaker has that plus the series speaker.

Exactamundo, especially the impedance varying with frequency.

I'm with the poster who recommends another amp ... not really expensive in low power consumer grade stuff. (We're not talking the Crown type stuff here). Mostly for damping reasons I'm loathe to recommend series connections.

That was me, and again, I agree.

At reasonable listening levels, the 2 ohm load on the 8 ohm rated amp rarely causes any problems. And with the 40 feet of #24 wire so often used ... another 2 ohms per speaker right there.

As I mentioned in another thread, amps don't automatically overload speakers with lower power capability, unless you over-drive the speaker. Unlike electricity, we have an output-voltage (volume) control.

As with electricity, the speaker current will depend on the output voltage and the speaker (and wire) impedance, and the resultant power will depend on that current and the voltage at the speaker terminals.

If a speaker has too low an impedance, the amp's power supply will run out of current before maximum voltage is achieved, and if the impednace is too high, the output voltage will peak before maximum curerent is achieved.

Either scenario results in less than maximum power being available. Too much output current will overheat the amp, and too much voltage will drive the amp's output transistors to clipping and cause tweeter damage.

 

[LarryFine]

Since Mac brought up clipping, too, I'll explain what it is.

A transistor's emitter-collector resistance varies with the base ("input") voltage (current, really). When driven too high, the output stops increasing with an increase in the base signal, and the transistor is said to be saturated.

Picture a sine wave with the peak cut off in a straight line. The two 'corners' of what is normally a smooithly-varying signal become a source of extremely high-energy square wave, which drive extreme currents through the tweeter.

 

[egnlsn]

Thank you fellows for your insight.

I failed to look for an ohm rating on the stereo or speakers (In wall). Next time I'm over there I'll check it out. I did look at the a and b selector and you could only have one on at a time. Lets say that the speaker's ohm rating in parallel are lower than the ohm rating of the stereo, is there any solution without changing the speakers or stereo?

Keep them in parallel, but place a 4 Ohm, 100 Watt resistor in series with the + terminal. That will bring your impedance close to 8 Ohms, and 100 Watts should be sufficient for the power rating of the amp. Just to be safe, you would want the resistor to be at least 20% higher than the rating of the amp.

 

[Sierrasparky]

Impedance needs to be correct.
One way to place more speakers in paralled is a speaker distribution box. It can take care of the impedance issue,.

 

[hurk27]

if they are the same brand and model, I would not object much, but speaker impedance is very frequency dependent and commonly varies over more than a 2:1 range. It is not unusual for an "8 ohm" to present as low as 4 ohm or as high as 16 ohm loads over the audio range. It is possible to underload an amp as well as overload one. And damping factor goes to heck ... rather than having a sub-ohm driver, each speaker has that plus the series speaker.

I'm with the poster who recommends another amp ... not really expensive in low power consumer grade stuff. (We're not talking the Crown type stuff here). Mostly for damping reasons I'm loathe to recommend series connections.

At reasonable listening levels, the 2 ohm load on the 8 ohm rated amp rarely causes any problems. And with the 40 feet of #24 wire so often used ... another 2 ohms per speaker right there.

The problem with this is it doesn't matter when both coils are electrically the same, if both coils are 4 ohms they are electrically the same, if one is rated 100 watt and the other 10 watts, this would be like series a 100 amp fuse in-line with a 10 amp fuse, of course the lower watt coil would open first if the peak wattage of it is exceeded. but again both coils will electrically see the same frequency and wattage. 8 ohms is 8 ohms. Is this a good way to run a set of speakers? No, and normally I wouldn't do it. but in a pinch I have, like I said to keep a show going.

More speakers are ruined by an under powered amplifier than overpowered. Seems counter intuitive but the overpowered loudspeaker's distress is quickly recognized and countered by turning it down - uh, in most cases. It is the loudspeaker that is being driven by an amp that cannot deliver what the loudspeaker wants when the operator wants it to go louder that is in trouble. Think of the sine wave. The loudspeaker is being driven in and out like the wave is going up and down. In an underpowered situation the peaks of the sine wave are cut off the speaker stops traveling and holds either out or in for the duration of the plateau (that is the duration of the "clip"). This just sounds muddy and it not as quickly recognized as a damaging sound likes being overpowered is especially in a noisy environment. When this happens the voice coil does not move properly and the heat builds up and poof the magic smoke gets out and the loudspeaker won't work anymore. Great for special effects though and guys in the repair business.

MacG

Very correct statement, clipping an amp is one of the biggest reasons of speaker failure, and especially high frequency drivers.

A speaker that has a rating of 100 watts RMS, will have a rating of 400 watts peek. this is 6 db over rating, this 400 watt is a very short duration peek rating.

For every 3 db you increase you effectively double in power.
Clipping an amp is driving the amp to produce a non sinusoidal DC output that is 6 db over the rating of the amp, remember this amp is now sending a 6 db "DC" voltage to your speakers, that would mean if we were to drive those 100 watt speakers with a 50 watt amp, and you turn it up to the point of clipping, you are effectively sending a 200 watt DC signal to a coil that can only handle 100 watts continuous RMS.

So you always allow a 1.5 to 1 head room over the rating of your speakers, to drive any amp into clipping is just shear madness.

This is the science behind blowing speakers with a amp that is two small.