Speaker impedance

[Hokiefyd]

I have an older Teac AG-V1020 in our entertainment center. I have always had two bookshelf speakers hooked to it, a pair of older KLH speakers that put out good lows, but poor highs. I want to add a set of set of speakers for highs to help fill in. I have speakers from a Panasonic boombox I was playing with these weekend. The KLH speakers are of an unknown impedance (though probably 6 ohm or thereabouts) and the Panasonic speakers are 2.7 ohm.

The Teac receiver is designed for 4-16 ohm impedance.

There are two sets of speaker outputs on the receiver, A and B. If both are selected, it says that it runs them through the surround sound circuit in the receiver (I have the Teac owner's manual). With the Panasonics connected to the A outputs and the KLHs connected to the B outputs, I heard only the Panasonics. It's like the KLHs weren't even on. When I turned A speakers off, then it's like the B speakers turned on and I could hear them then. So I got to looking at running both speakers from the A output.

It appears to me that I want to connect the speakers in series...that is:

+ on the Teac to + on the Panasonic speaker
- on the Panasonic speaker to + on the KLH speaker
- on the KLH speaker to - on the Teac

If I connect them in series, the impedances are additive, right? So my total impedance would be the 2.7 ohms on the Panasonic speaker plus whatever the impedance is on the KLH speaker; say it's 6 ohms...it'd be 8.7 total ohms, right? Which would be fine.

But if I connect the speakers in parallel, that is the +/- inputs on the Teac going to both the +/- input on the Panasonic speaker and the +/- input on the KLH speaker, then the total impedance is reduced by the inverse of both, right? It would be in THIS situation that I could burn up the amplifier in my receiver unit due to too much power being sent to the speakers, right?

I am pretty clearly not looking for an audiophile system here...just something with a little more balance (the KLHs are good on lows only) for when we're watching a football game or a movie.

Thanks!

 

[NateDN10]

Originally Posted By: Hokiefyd

If I connect them in series, the impedances are additive, right? So my total impedance would be the 2.7 ohms on the Panasonic speaker plus whatever the impedance is on the KLH speaker; say it's 6 ohms...it'd be 8.7 total ohms, right? Which would be fine.

That's correct.

Originally Posted By: Hokiefyd

But if I connect the speakers in parallel, that is the +/- inputs on the Teac going to both the +/- input on the Panasonic speaker and the +/- input on the KLH speaker, then the total impedance is reduced by the inverse of both, right? It would be in THIS situation that I could burn up the amplifier in my receiver unit due to too much power being sent to the speakers, right?

Total resistance for parallel resistors is 1/((1/R1) + (1/R2)). Which is what I think you were saying. So in your case it'd wind up at about 1.9 ohms.

If you connect them in series, the power they'll get is in proportion to their impedance. If your system is rated for 50W RMS per channel at 8 ohms, that means 20V RMS output. Then the 2.7 ohm speakers would get 14.3W, and the 6 ohm speakers would get 31.7W.

In parallel, they'll each see the full 20V, so the 2.7 ohm speaker will get 148W and the 6 ohm speaker will get 66.7W. Of course that's way over the system's rated power so you'll burn something up or hit a limiter before you get that high.

 

[440Magnum]

I wouldn't connect them in series- the impedence isn't just a number, it varies over frequency (its a vector, in other words, with a magnitude and a phase.)

In a nutshell, what happens is that if you wire in series, one speaker will dominate at some frequencies, and the other at other frequencies. Or the higher impedance speaker will just dominate and it'll be the opposite effect to connecting them in parallel.

Basically you want all the speakers to be closer in impedance than what you have.

 

[bepperb]

Yes, I suppose you would want them in series and definitely you don't want them hooked up in parallel. Your math is for DC, the actual impedance will vary greatly over the AC frequencies they will work at.

 

[ARCOgraphite]

Are these the KLH's?

 

[ARCOgraphite]

You want to connect the panaheadache speakers to the KLH with a crossover network - just to start you could use a high voltage electrolytic between 4 and 10 uf. Its fruitless to connect the speaker in parallel or series as they differ to greatly in efficiency (sensitivity) and impedance.

Think of using an inexpensive automotive style add on tweeter kit to add some highs instead?

 

[NateDN10]

Originally Posted By: 440Magnum
I wouldn't connect them in series- the impedence isn't just a number, it varies over frequency (its a vector, in other words, with a magnitude and a phase.)

In a nutshell, what happens is that if you wire in series, one speaker will dominate at some frequencies, and the other at other frequencies. Or the higher impedance speaker will just dominate and it'll be the opposite effect to connecting them in parallel.

Basically you want all the speakers to be closer in impedance than what you have.


This is true, and something all my numbers didn't take into account.

 

[Hokiefyd]

The speakers are KLH AV2000.

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=6874

Do you think the reason I could not hear the KLHs when hooked to the B outputs is because they have such a different impedance than the Panasonics (on the A outputs) have? Could/should/would those two circuits be connected within the amplifier, and the Panasonics were receiving all the power, even though both speaker buttons were depressed (to power both pairs)?

In the case where I cannot use the Panasonics, and that's looking like that may be the case, I would probably try to find a set of used speakers in the same impedance range as my KLHs.

 

[ET16]

Another thing to consider might be that few amplifiers can handle loads below 4 ohms well. Have you tried such speakers with your amp?

 

[Gotch]

Not a great idea to mix and match speakers with different impedance, esp, if played at higher listening levels. The crossovers can cause instabilites in the amp and other speaker. Best practice for multiple speakers is the same impedance and similar SPL ratings to minimize this. Also, as stated above, the impedance is not a static number and moves around as frequencies change. A 8ohm rated speaker could go from 4 to 12 ohms across the frequecy range and average at 8ohms. If the two speakers dip into the low end at the same time, you could be looking at 1ohm loads on the amp...not good.

 

[RF Overlord]

Originally Posted By: 440Magnum
I wouldn't connect them in series- the impedence isn't just a number, it varies over frequency (its a vector, in other words, with a magnitude and a phase.)

In a nutshell, what happens is that if you wire in series, one speaker will dominate at some frequencies, and the other at other frequencies.
Quoted for truth.

I had speakers in different rooms with a common amp. I tried connecting them in both configurations, and in series I could hear a definite colouration of the sound on the main set in the den. Parallel is where it's at if the amp can support the low impedance.

 

[Propflux01]

What about replacing the tweeter with a more modern mid-tweeter? I know most speakers of that era were cone type and not known for high output in the higher ranges. You should be able to find a decent one to match the dimensions you have on yours now.

 

[aquariuscsm]

You could always get a pair of piezo tweeter horns (piezos require no crossovers) and just set them on top of your KLH cabinets.

 

[Hokiefyd]

Thanks for the continuing suggestions. I will look at replacing the tweeters in the KLH cabinets.

For what it's worth, here are the specs on the Teac amplifier:

Quote:

F.T.C. Rating: 100 watts RMS per channel minimum,
both channels driven into 8 ohms from 20 Hz to 20
kHz with no more than 0.08% total harmonic
distortion (U.S.A./Canada)
DIN Power: 75 watts (Eurpoe/U.K.)
RMS Power (20 - 20 kHz):
100 watts 0.04% (U.S.A./Canada)
70 watts 0.08% (Europe/U.K.)


There is also a 2-position impedance selector switch on the back. One position is for 4 ohms to less than 8 ohms, and the other position is for 8 ohms or more. If both A and B speakers are used together, the switch goes into the 8 ohms or more setting.

I take this to mean that the receiver really prefers 8 ohm speakers (nominally), and that driving 2.7 ohm speakers with it is probably out of its operating range.

http://www.kpsurplus.com/buy/teac_ag_v1020_audio_video_stereo_receiver/62344

At one time, I had the full component system...including 5-disc CD changer and dual recording tape deck! Ha ha. I've sold off the CD changer and tape deck, but receiver still works great...as long as I don't blow it up!

 

[Propflux01]

Originally Posted By: Hokiefyd
....I take this to mean that the receiver really prefers 8 ohm speakers (nominally), and that driving 2.7 ohm speakers with it is probably out of its operating range.


You are correct. However depending on usage you might be able to get away with it as long as your not cranking the tunes to eardrum-splitting level, continuously, for long periods of time. I am thinking a Movie soundtrack/dialog probably would be OK. I have even older equipment with similar specs and have regularly used 4Ohm speakers without issues.