Could someone explain impedance to me?

[mhjmhj]

Hello and thanks for looking.

I'm in the process of shopping for a new AV receiver. I think I may have broken my ho-hum Panasonic SA-HE100K receiver (100 watts per channel x 2 (into 6 ohms, 40 Hz to 20 kHz, with less than 0.9 percent THD); 100 watts per channel x 6 (into 6 ohms, 40 Hz to 1kHz, with less than 0.9 percent THD)) by using it to power some Acoustic Research AR-3a speakers (4 ohm impedance). Now I'm looking into getting a new receiver and I don't want any problems down the road because I am asking it to do too much.

So my questions are:
-what is a basic explanation of what impedance is with regard to receivers/speakers?
-can I damage a receiver (say one that is "110 Watts x 7 (20Hz - 20 kHz, 8 ohms, .09% THD FTC)" like a Pioneer that I'm looking at) by hooking up the 4 ohm AR-3As to it?

[markw]

You seem to have the needed numbers available. Good. I'll give you some general pointers to keep in mind.

The basic rule is that the lower the impedance of the speaker, the harder the amp has to work.

Amps are rated at a certain impedance rating. They will most likely work, to some degree, with a lower impedance but it's working hard to do so.

A lower impedance speaker on an amp not rated for that low an impedance may work at low levels but, when pushed hard, may do bad things or, possibly nothing at all. ...as you seem to have discovered.

AR3's are notoriously inefficient and hard to drive. they suck up a LOT of watts, particularly when pumping out bass. The fact that that poor amp lasted as long as it did is a miracle.

Also, remember, the AR speakers aren't designed to accept constant amounts of high power. They are not made to be played at ear-splitting levels.

If you try pump megawatts into 'em long term, they may just burn a coil and it's game over for them. They were made in the days when a "real" 50 wpc amp was a monster and they were generally driven by tubes, which have a much more "polite" way of clipping than transistors do.

As for amplifier power: to get a barely audiable three decible increase in loudness, you need to double the amp's power. i.e. you need to go from fifty watts to 100 watts and the difference will only be barely audiable on peaks.

To get an apparant doubling of loudness, you need ten times the power. That fifty watt amp now needs to be a 500 watt amp.

[mhjmhj]

Thank you for your response, Mark. I think I understand.
When you say I "have the numbers needed" do you mean that that Pioneer I'm looking at can handle the AR-3As?

[spasticteapot]

Most vintage speakers are 8-ohm, so your "100 watt" reciever suddenly becomes a 40-watt reciever. (I'm guessing on this - if it were a properly designed 100 watt-into-2-ohm amplifier, it should only put out 25 watts at 8 ohms.)

Odds are, your reciever was not actually capable of what it was sold as being able to do. If you want to drive those speakers, you need a monster of an amplifier - try for a vintage amplifier (they usually work much better on the amp-hoovering speakers you have than any modern products for twice the cost) of good quality, perhaps a Sansui, Pioneer, or Marantz of some sort. I'm buying a Sansui 7900z, one of the last decent Sansui recievers before they became crap, for only $40 - while the tuner is nothing to write home about, these are very low distortion amplifiers capable of 100 watts at under .1% distortion. However, some vintage amps do not like 4-ohm loads, and if you want the best in vintage amplifiers (a Sansui 9090 or au9700), be prepared for a hefty pricetag.

The AR-3As are amazingly inefficient speakers, too - it's a wonder your amplifier could make them produce any noise at all. Most people reccomend massive amplifiers for this speaker, which is famous for only sounding good when you've got the equivalent of an electrical substation driving it. Amplifiers between 150 and 300 watts per channel are reccomended, with 100 watts per channel being a minimum.

Alternately, you can get a paralleled LM4780 gainclone kit at Audiosector.com that will work marvellously. Run in parallel, the 4780 can drive a two-ohm load without breaking a sweat - so don't worry about impeadance. And if the 60-90 watts you'd get by running parallel into 4 ohms is not enough, try bridging it - with a little luck, you can get well over 100 watts.

Alternately, buy two kits, and run two bridged modules per side in parallel. This will result in a freakishly powerful amplifier that could also serve duty as an arc welder.

[markw]

Thank you for your response, Mark. I think I understand.
When you say I "have the numbers needed" do you mean that that Pioneer I'm looking at can handle the AR-3As?

I should have said "you know what numbers to look at", at least for a start. Pretty, yes, but, what do they mean in the real world?

You quote the specs for eight ohm loads. What does it say about four ohm loads?

And, odds are that the specs quotes are valid only when TWO channels are driven, at most. What does it say about when all channels are driven?

When all channels are driven you would be surprised at how quickly that wpc figure drops. Remember, you've only got limited power available from the power supply and it must be shared with all driven channels.

Yes, Quoting power like that is legal. Honorable? Well, what's love got to do with it. It sells receivers, doesn't it?

If you're bound and determined to push these speakers to their limit, and perhaps beyond, then start looking at separate preamp/power amp combos or integrated amps like NAD, Rotel or other "real" stereo amps.

[markw]

Most vintage speakers are 8-ohm, so your "100 watt" receiver suddenly becomes a 40-watt receiver. (I'm guessing on this - if it were a properly designed 100 watt-into-2-ohm amplifier, it should only put out 25 watts at 8 ohms.)

Actually, in a perfect amp, the power it puts out would double as the impedance decreases by half.

i.e assume an amp pumps out 50 watts @ 8 ohms. At four ohms it would be pushing 100 watts, at two ohms, 200 watts, ad infinitum until the poor amp dies of being overworked to death.

As for bridging amps, what many people overlook is the simple fact that when you do that, the bridged amp pair "see" the speakers impedance as one half what it really is. So, a bridged pair would "see" a, eight ohm speaker as a four ohm load and a four ohm speaker as a two ohm load.

[mhjmhj]

Wow, thank you all for the informative responses. You must all be electrical engineers.
I'm not a big fan of those "for dummies" books, but this might be what I need in this case. But the responses are truly helpful and appreciated

OK, so now I've got lots more questions:

1. What is "bridging" and what is "parallel" ?

Before I ask any more questions, let me tell you what my goal is:
I want to have a HT system (5.1 is all I'm wired for) where the front speakers are also my main stereo music listening speakers as well. I figured the AR-3As are the best speakers I own, so they should be my front speakers. As complicated as all this is, I'm wondering if I should just sell them and get something more compatible with today's receivers (but let's not go there yet).

Alternately, you can get a paralleled LM4780 gainclone kit at Audiosector.com that will work marvellously. Run in parallel, the 4780 can drive a two-ohm load without breaking a sweat - so don't worry about impeadance. And if the 60-90 watts you'd get by running parallel into 4 ohms is not enough, try bridging it - with a little luck, you can get well over 100 watts.

That looks like a fairly easy fix. Now is that like a component that I can just "hook up" to my stereo or is that something that needs to be "installed" inside the receiver itself?


I'm sure I'll have more questions, but I don't want to be a pest.

[mhjmhj]

You quote the specs for eight ohm loads. What does it say about four ohm loads?

And, odds are that the specs quotes are valid only when TWO channels are driven, at most. What does it say about when all channels are driven?

this is all it says in the Pioneer specs:

Power:
Surround Power: 130W x 7 (20Hz-20kHz, 8-ohms, .09% THD FTC)
Stereo Power: 130W x 2 (20Hz-20kHz, 8-ohms, .09% THD FTC)

[Resident Loser]

Actually, in a perfect amp, the power it puts out would double as the impedance decreases by half.

i.e assume an amp pumps out 50 watts @ 8 ohms. At four ohms it would be pushing 100 watts, at two ohms, 200 watts, ad infinitum until the poor amp dies of being overworked to death...

...in a perfect world, and with an amp that has high-current capabilities...It's a rare bird these days that can double it's 8 Ohm output with with a nominal 4 Ohm load...even less so with the multi-channel HT cr@pola...more like 100Wpc @8 Ohms and maybe, maybe 140Wpc @4 Ohms...and that's if it's even rated for that load by the mfr.

And for the OP, those ARs are acoustic suspension speakers which do require more power than newer, ported models, but the original spec is for a minimum of 25RMS Wpc...Generally speaking, even the more inefficient loudspeakers generally draw only 3-5 Watts when listening at reasonable levels say 80-85 dB or so...When applied within reason, more power really can't hurt and in some cases less power can (due to overdriven distortion levels) but, IMO 100 clean Wpc should be more than sufficient...unless, of course, you want your ears to bleed...

And while I have no experience with any sort of outboard bridging devices, I'd offer a word of caution...don't...some amplifiers will not tolerate any sort of bridging schemes unless designed for that purpose...

jimHJJ(...hey mark, how was your holiday?...)

[Resident Loser]

...as per the Pioneer website, the OM for the VSX-82TXS states the speaker spec @6 to 16 Ohms and requires a user reset for the 6 Ohm rating...a 4 Ohm speaker may cause problems e.g. activation of protection circuits at the very least...maybe worse...

jimHJJ(...you may want to contine searching for a more load-friendly amp...)

[markw]

this is all it says in the Pioneer specs:

What's it say about four ohm loads? If it says nothing, then that alone should tell you something.

[Carl Reid]

I really hate to be the Prophet of Doom and Gloom... but If I'm understanding your problem correctly... you might be better off selling the AR-3a's and getting speakers that are easier to drive...

It sounds like (unless I'm mixing up threads) if you want to use a receiver to drive multiple speakers in different rooms to a reasonably high volume... and on top of that the mains are already most amps worst nightmare....

If you really want to use one receiver to drive numerous speakers you might be better off with easy to drive speakers all around OR if you really love the AR-3a's then you might want to consider a multichannel pre-amp and using different monoblocks to handle each speaker or at least seperate amps for the AR-3a's....

As for using the Panasonic as a pre-amp (I think someone mentioned that)... does it have pre-outs? I had a Technics Receiver (which they later renamed to Panasonic, when they scaled back the Technics line) that had the same ratings 100Wx5 @ 6 ohms, but it didn't have pre-outs...