I want to buy my sister a new reciever. She has about 5 sets of speakers in her house, all wired through a speaker splitter. The ones that she has the most trouble running are TWO pair of Polk Audio outdoor speakers (8 ohm, 85W) which are always used at the same time and her Bose 201 (8 ohm, 10-120W) bookshelf speakers. There are three other sets in her house which she doesn't have any problem with. She can turn off the speakers in each room.

Do I need a high power reciever since she'll be running several sets of speakers at the same time or one made for lower amperage? I am looking at the Yamaha RX-V650, 100W per channel and the Onkyo TX-SR502 which is 75 W (8 ohm) or 110 W (6 ohm). Both were highly rated in Consumer Reports magazine.

Which reciever would be better for her system? Or is there something else that would be better?

Paul

What exactly is a "speaker splitter"? If you do mean that these things are truly in parallel, she's going to have serious issues trying to push that many speakers at once.

I guess a speaker splitter has the ability to deliver the signal to multiple sets while internally maintaining the impedances of the load?

She is 1500 miles away so I can't look at what she has, but I looked at a speaker splitter at local electronics store, it looks like it just sets up the different circuits in parallel that you can hook lots of speakers up to, but it says is has protection for the reciever built in. Maybe it's got a big resistor built in to prevent the impedence from getting too low or something.

I am just trying to figure out if this Onkyo may be better suited to do the job than the yamaha high power reciever.

Power won't help. A 1000 W amplifier is exactly as likely to fry than a 10 W one of you hook 5 pairs of speakers to it. Stereo amplifiers can stand two pairs of 8 Ohms, or one pair of 4 Ohms.

In general, audio amplifiers are designed for specific requeriments (power and load impedance)....

Any 8 Ohms amplifier (for example) was designed only for this... if you force this requeriment is very probably that your amplifier will be damage...

Many sets of speakers in parallel down the impedance a lot!!

for example: speaker A is 8 Ohms.. and speaker B is 8 Ohms too..
speaker A in parallel with speaker B resulting in 4 Ohms for total impedance!!!

Three 8 Ohms speakers in parallel resulting in (8/3)=2.67 Ohms!!!

The splitter is not good because is only a switch, only connections.. The switch not compensate this effect..

Lower impedance implies more current to flow in the output transistors of the amplifier, as consequence the amplifier probably will be destroyed..

Well, the Onkyo unit appeared to handle lower impedences better so I ordered that one. My sister's speaker system may destroy her recievers with low impedence, that may be why she needs a new one. If it ruins this one I'll talk to her about changes she could make to the system to safeguard her reciever, but for right now she won't listen to me. She and her husband see that some of her speakers aren't very loud and they didn't pay much for thier current reciever so they think thier reciever sucks and they need one with more power. Anyway, I've learned a lot in doing the research.
Thanks,
Paul

There are setups made for just this application with several moderate amplifiers in 1 box or stackable. That way 1 amp isn't trying to drive way low impedance.

I found this simple diagram to show her how to hook up speakers in series, and thus eliminating the impedence load problem: http://shop.store.yahoo.com/mobile-emotion...wtoprophoo.html

Within reason, you can also combine series and parallel connections to drive more speakers without loading the amp. Consider that two (nominal) 8 ohm speakers in parallel will show the amp 4 ohms. Two four ohm speakers in series will show the amp 8 ohms. So take two pairs of eight ohm speakers, each wired in parallel (4 ohms) and wire the pairs in series and you're back up to eight ohms, a safe load for almost any amp. If all the speakers are identical they'll all play at the same volume, if they're different they won't, so you'll have to experiment.

Yes, it's true... but, it's very very important that the "series" combinations are for IDENTICAL speakers..

If the speakers don't have a uniform resistive impedance across the audio spectrum they will affect each other's frequency response. edit: identical speakers probably ok too... I just have some vague doubt that with a reactive load the power factor may shift.. but haven't put it to paper.

Any theoretical effects of power factor or one set of speakers changing another's response are going to be swamped by other factors (low volumes, probably incorrect placement, not the highest-fi speakers to begin with) in the original poster's application.
It's a lot more likely there would be problems with smaller speakers playing too loudly in comparison with the honkin Bose and Polk boxes, but experimentation would probably come up with a workable plan. If the OPs speaker selector box includes some sort of protection it's all irrelevant anyway. It'd be easy to find out, just short any set of speaker leads and if the receiver doesn't go up in flames it's probably OK

Very good point

I believe that not problem...
Very important !!!: ONLY ONLY for IDENTICAL SPEAKERS !!!!

Any speaker is a complex impedance, and this changes with the frequency...

For example, for a test frequency (1 Khz):
Speaker A is the same like Speaker B...

Speaker A is: c + dj;
c = resistive component of the impedance...
d = reactive component of the impedance...

Speaker B is: the same like A.

Angle of the impedance = arc tan (d/c), this defines the power factor and reactive component of the complex impedance... (in each speaker)

Speaker A in series with B: (c+dj) + (c+dj) = 2c + 2dj
arc tan (2d/2c) = arc tan (d/c)!!! the same like Speaker A or B, the power factor not change

Speaker A in parallel with B:


arc tan ((d/2) / (c/2)) = arc tan (d/c) !!! the same like A or B.. in this case the power factor is the same too.

The equations are the same for any audio frequence, because the impedance change equal in both speakers...

If Speaker A is IDENTICAL to Speaker B:

CONCLUSION: The power factor not change, is the same for both combinations of speakers (series or parallel), and for only speaker too.

Power Factor = cos [arc tan (d/c)]

> I believe that not problem...
> Very important !!!: ONLY ONLY for IDENTICAL SPEAKERS !!!!

I've been out of school for a long time and don't speak equations any more. Where is the part where it says what that is bad happens if you dare to try this with non identical speakers? Do they sound bad? Does the amp blow up?

Because I've done it on numerous occasions over the years with probably hundreds of different speakers without encountering any problems other than mismatched volume, and I'm wondering what I've missed.

Many (most?) speakers have dips and peaks in their impedance vs frequency graph.. generally corresponding to crossover points or some mechanical resonance. If 2 speakers are in series and only speaker (A) has a dip at a partiicular frequency, then speaker (A) will have relatively less voltage across it than (B) at that freq compared to others. That means that speaker A will change the frequency response of B and vice versa.


On the power factor wrt identical speakers, I had a feeling everything would add up the same and balance out, but wasn't positive.

>Many (most?) speakers have dips and peaks in their impedance vs frequency graph..
>generally corresponding to crossover points or some mechanical resonance. If 2
>speakers are in series and only speaker (A) has a dip at a partiicular frequency, then
>speaker (A) will have relatively less voltage across it than (B) at that freq compared to
> others. That means that speaker A will change the frequency response of B and vice
> versa.

Possibly, but in real life such changes would often be trivially small compared to the large amount of input power change required to produce an audibly different sound from a loudspeaker. Moving your head or the loudpeaker six inches one way or another is liable to have a greater effect.

"Speaker splitters" sound like a gimmick to me, the way it's done in the trade is simply by daisy-chaining them in parallel.

You will sometimes run into problems if you're running a lot of big speakers off a small amp. I probably would aim to only have as many watts on a channel as the amp can cope with, as opposed to excessively under-rating the amp.

You don't mention the configuration she's using them in, but obviously running two 85W 8-ohm speakers off an amp which is not rated for 4-ohm operation is asking for trouble.

Incidentally, as I understand it if you run two speakers in series you can problems with unequal Back-EMF which will lead to phase difference and other nasties. There's a reason it's hardly ever done .