Impedance matching

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Hi,
This is offtopic, but related to home improvement and this is where I get my best information.
I want to connect my ipod -> amp -> speaker selector -> speakers
My amp is 4 Ohms (Pyle PTAU45)
My speakers are 4 Ohms (Pyle PWRC51)
But the speaker selector that I want to buy (Pyle PSS6) says "with speakers systems that are 8 Ohms minimum".
The tech guy at Pyle says that this is an OK configuration. Since I don't know anything about impedance matching and this seems to contradict the description, I'd like to ask here!
Many thanks in advance!
Sam
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Andy comments:
Post in sci.electronics.design Lots of good advice there
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Sam Takoy wrote:

Hi, Pyl, I wouldn't trust their specs. but general rule is you can connet higher Ohmage speakers to an amp than spec. says. If you connect lower one it can burn out the amp or speaker. As an example if amp calls for minimum 4 Ohm speakers, I can connect anything higher than 4 Ohms. But if you mismatch impedance it will chage power output. According to simple Ohm's law.
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wrote:

If it is a simple speaker SELECTOR (I read that as a switch) the 4 ohm system should work fine as long as you are not approaching the power limit of the switch. A 4 ohm speaker will draw more power than an 8 ohm speaker.
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On 12/21/2010 11:36 AM Tony Hwang spake thus:

Only half correct.
You can burn out the amp, but not the speaker (well, assuming you don't overdrive it). Using a lower impedance speaker than allowed will only overload the amp.
Think of a generator and a load: if you connect an excessive load to a generator (say, a 4 kW heater to a 1 kW generator), it's not going to hurt the load, but it could fry the generator.
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On 12/21/2010 11:36 AM Tony Hwang spake thus:

Only half correct.
You can burn out the amp, but not the speaker (well, assuming you don't overdrive it). Using a lower impedance speaker than allowed will only overload the amp.
Think of a generator and a load: if you connect an excessive load to a generator (say, a 4 kW heater to a 1 kW generator), it's not going to hurt the load, but it could fry the generator (or blow its fuse or breaker).
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On 12/21/2010 11:25 AM Sam Takoy spake thus:

[other advice about posting in electronics NG good; try rec.audio.tech as well]
Can't give you a definitive answer, but am curious about that speaker selector. Is it just a simple switch box? What's its configuration? How many speakers does it handle? Can you have more than one set of speakers active at the same time?
If it's really just a switchbox, then impedance makes absolutely no difference. However, it's possible it also contains some load resistors, which would make impedance matter. You could determine this by using an ohmmeter (digital meter set on resistance, for example). Test between input & ground and output & ground; it should be an open (infinite resistance). If not, then you have resistors inside.
The worst case for you would be if you ended up running two sets of 4-ohm speakers in parallel from your amp, which would present a 2-ohm impedance to the amp. The amp would probably not like this (could overheat, blow fuse or circuit breaker or release the magic smoke).
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Sam Takoy wrote:

The thing to pay attention to is the amp. The speaker selector is a passive device, and should be fine with the 4 ohm speakers. Since the guy at Pyle confirmed this, you're good to go.
Jon
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wrote:

I believe the "8 ohm minimum" has more to do with what load will be presented at the amp. If you use 4 ohm speakers instead of 8 AND have multiple sets going at the same time you will present a very low impedance to the amp. If you are running only a few sets you should be fine.
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On Dec 21, 3:55pm, snipped-for-privacy@mucks.net wrote:

Since the amp, speakers and selector all are made by Pyle, sounds like a good question to ask them. That selector has some kind of "protection" built-in to it. Possibly to prevent you from selecting too many speakers in parallel and damaging the amp. That protection might have something to do with what the minimum speaker impedance can be.
If it were me, I'd find a simple, less expensive selector. $100 sounds like a lot of money for a switch. You can get a whole Wireless N router for less money.
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On 12/21/2010 2:25 PM, Sam Takoy wrote:

We aren't matching impedances, what we are doing is making sure that the amp doesn't blow up! (Impedance matching is tube stuff)
Amps are rated for the minimum impedance they can drive without smoking. The lower impedance, the more current and more power.
There are two basic ways you can have a single amp channel drive more than one set of speakers. Cheapie stereos, put the speakers in series, when they have A and B speaker switches. That is double the impedance and half the available power.
Running speakers in parallel, is twice the current and twice the power. If you take an amp rated at 4 ohm, that would mean you could run two 8 ohm sets in parallel. No problem.
A good woofer is usually designed to be driven directly by the low impedance of the amp, so high end speakers should be wired in parallel. This will affect a number of low frequency issues related to dampening.
I'm not sure how this switch box works, you can sign up and download the manual, but I suspect it wires them in parallel and then uses some protection circuitry to limit drawing too much from the amp. That jives with the ad copy.

Keep the volume moderate and you will have no problem. Cranking the volume may put your amp at some risk, hard to really tell without knowing more.
Pyle stuff used to have some balls to it. Don't know about now.
Jeff

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On 12/21/2010 7:36 PM Jeff Thies spake thus:

Odd thing to say: actually, transistor amps care about impedance matching too. In fact, it may be even more important with solid state, as there's no output transformer as in a tube amp to isolate the load from the final stage. Very easy to smoke transistors (or to cause the angry gods to activate the shutdown circuit or blowenfusen). In transistor amps, speakers are (more or less) directly coupled to the output stage, usually with a large capacitor to block DC.
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Agreed, impedance matching applies all over the place.
As others have noted the most likely reason fo rthe 8 ohm minimum is that the selector switch probably supports turning on two pairs of speakers. And it likely does it by connectng them in parallel. That results in a 2 ohm load if you have 4 ohm speakers which some amps can't handle. But a lot of newer amps can so check your amp manual. Or don't turn two sets on at the same time.
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On 12/22/2010 7:44 AM, jamesgangnc wrote:

This is where I'd put my money. Pretty much any amp can handle a 4 ohm load (two 8 ohm speakers in parallel). Not nearly so many can handle a 2 ohm load (two 4 ohm speakers in parallel). So probably the 8 ohm speaker limitation is there merely to protect the amp from getting accidentally fried if it happens to be the more common sort.
Certainly you can run a pair (one left; one right) of 4 ohm speakers connected to that amp. What you can't do is have two sets of 4 ohm speakers because the resulting 2 ohm load will overload that particular amp.
Jay
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Odd are that if the op is looking at a speaker switch it is to allow him to connect other sets of speakers. And that would also likely to be to power sets in other locations. The manual for that amp clearly shows two pairs of 8 ohm speakers when configured with more than one set of speakers.
Even when an amp can handle 2 ohms it increases the line losses and harmonic distortion.
So the op needs to find a speaker switch that impedance matches multiple sets of 4 ohm speakers. Such switches are available but they are more expensive. That's because they are not just switches inside.
I've run 2 ohm loads on some of my equipment but it all can either handle it or has protection circuitry in the output stage.
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jamesgangnc wrote:

Downloading a manual http://www.pyleaudio.com/manuals/PSS4PSS6.pdf the speaker switch allows connecting 0 to 6 pairs of speakers at the same time. They are all connected in parallel (although the combined impedance of 4 speakers is 2.4 ohms instead of 2 ohms with 8 ohm speakers - ?). The stated impedance of 6 - 8 ohm speakers is 1.7 ohms. Maybe their amps will work with a 1.7 ohm load (if the speakers are 8 ohms).
Not obvious how Sam intended to use the switch..
If used to connect one speaker pair at a time the switch would be OK (but probably relatively expensive from another post).
If used for 2 speaker pairs at a time the amp would have to work with a 2 ohm load (as james said).
You certainly couldn't connect 6 speaker pairs at a time.
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On 12/22/2010 12:02 AM, David Nebenzahl wrote:

No, with a few odd exceptions and for a few uses not pertinent here.
http://en.wikipedia.org/wiki/Constant_voltage_speaker_system
Early McIntosh solid state amps had transformers, and some real balls too.
In fact, it may be even more important with solid state,

This is all current driven. You are absolutely correct that running too low an impedance speaker can damage an amp (I read your other posts and did not disagree). There is no matching that takes place though for almost all home systems. It's just a caution. Think rating, not matching. In general you want the output impedance of the amp and wiring to be as low as possible, to minimize losses and to keep from having dampening issues.
In

Almost. They are usually directly driven and transistor amps have a very low source resistance. A tube is an entirely different beast. It operates at a much higher voltaqe and has a much higher resistance. There are almost no tube amps that work without a transformer, just as there are very few transistor amps that do.
DC blocking caps are very rare in home amps of any money. It is much more common to have separate plus and minus supplies and there is no DC to block. A single supply will either need a cap or will need to use a bridge mode configuration where the ground lead is an output, not ground.
I fixed and built amps for longer than I care to remember. There is an awful lot I don't know, but not about this.
Jeff

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The bottom line would seem to be that:
A - Pyle makes the amp, speakers and speaker selector switch B - The amp is rated for a 4 ohm min load C - The speakers are rated at 4 ohms impedance D - The switch just selects one speaker or more than one speaker to be driven, in which case they are in parallel.
Given the above, he can use the selector to select any one set of speakers at a time. If he selects more than one set, then he has an impedance of 2 ohms. So, the store is correct, at least in part. It will work in this manner. But if you want to be able to select more than one set, then clearly you are violating the specs. Probably would still work fine, as long as you don't want to crank up the volume approaching maximum. But, I'd contact Pyle and ask them what's up. They make all the eqpt and clearly how you can use it is limited.
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<snip>

I find that interesting, 4 ohm home speakers. This is usually the realm of car audio or anything else battery operated.
Now, I don't find the OP buying L Pads, so I think this switch box is no better than one made of light switches or something similar.

The amp will probably protect itself before anything goes bad. (They usually sample current in one of the output transistors).
People were always trying to blow up Pyle stuff, think of the target audience. Pyle stuff is supposed to be tough, or at least that is how I remember it. Not greatest stuff, but tough.
What Pyle will commit to telling you over the phone, would be an interesting exercise.
Jeff Who has seen some audio equipment abused.
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On 12/23/2010 4:27 AM Jeff Thies spake thus:

Well, yeah, I'd expect most any amplifier made today to have some kind of shutdown protection circuit built in. You could probably short-circuit the speaker terminals and the thing would just turn itself off (not exactly, but that's the effect).
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