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richgrohl
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Amp and Speaker matching impedance

Hi,

Previously I posted looking for speakers and amplifier recommendations for my Audio Technica AT-LP160 turntable. Now I just like to ask if the speaker and receiver that i decided to buy are compatible.

 

Speakers : Pioneer SP-BS22 Bookshelf speakers (6 ohms / 80w / 2.83V: 85dB)
Receiver : Harman Kardon HK-3390 Steareo Receiver (8 ohms / 80w x2)
 

I have read somewhere that I should not match a speaker with lower impedance rating than the amplifier. I just like to check with people in this forum because I'm afraid that I may have the wrong understanding of matching amp and speaker ohms.

commsysman
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AMPLIFIER

Actually, the ideal is to have an amplifier with very very low output impedance (less than 0.5 ohms) and speakers with a much higher impedance.

This insures that 80% or more of the audio signal voltage appears across the speaker, and very little is dropped by the internal impedance (also called output impedance) of the amplifier.

This also ensures that the variations in speaker impedance at various frequencies do not cause major non-linearities in the frequency response of the entire sound system.

It is desirable that a speaker system have a constant impedance at all frequencies, but that is not a realistic design goal.

This is one reason that high-power amplifiers are very desirable. The high power may not actually be needed, but higher power capability usually means a lower output impedance, and THAT is what is really the most important thing.

I am sure that the output impedance of your amplifier is much less than one ohm, and there is certainly no incompatibility there.

Very high-quality power amplifiers, like my Musical Fidelity M6PRX, have an output impedance of 0.1 ohm or so, and that is ideal; especially for large speakers that can have an impedance of 3 ohms or less at some frequencies.

To really understand the operating impedance of any speaker system, you need to get a GRAPH of impedance VS Frequency, since the impedance varies widely at different frequency. The "6 ohms" or what ever is specified, is often an inaccurate generalization that tells you very little.

In the "Measurements" section of the Stereophile review of your speakers, you will see from the impedance graph for those speakers that they have an impedance of 4.5 ohms at 115 Hz and go above 20 ohms at several parts of the audio frequency range.

JoeE SP9
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What he said

In essence commsysman said that the HK3390 will have no problems driving those Pioneer speakers. FWIW, I agree with him.

For most contemporary speakers and receivers/amps there is no need to be concerned about whether a speaker is an impedance match. In addition, I'll add that speaker wattage ratings are for the most part worthless. As long as you pay attention to signs/sounds of distress and lower the volume when they are present you can safely use just about any amplifier/receiver with just about any speaker. All things considered more power is almost always better.

If you're under powering the speakers the amplifier will sound strained----Turn down the volume.

If you're overpowering the speakers the speakers will sound strained----Turn down the volume.

commsysman
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Amplifier Impedance

In the quote below, you imply that 8 ohms is the "the impedance rating" of the amplifier section of the receiver.

This is absolutely not true. What it says is that the amplifier was tested, as the US government requires, to see how much power it will put out to an 8 ohm RESISTOR connected across its output terminals. This is a standard test mandated by the FTC. ALL amplifiers are tested with an 8 ohm load for power output. THAT DOES NOT MAKE THEM 8 OHM AMPLIFIERS!

The actual output impedance of the amplifier is probably between 0.5 ohms and 1 ohm, which is as it should be; MUCH LOWER than the impedance of the speaker it will drive. WE DO NOT WANT THE IMPEDANCES TO MATCH.

The only place "impedance matching" is desirable is between an antenna and a transmitter, at radio frequencies, so that maximum power transfers to the antenna at one specific frequency. This principle does not apply in audio.

In audio we are not after maximum power transfer, but trying to maintain a fairly constant power transfer to the speaker over a wide range of frequencies. The concepts and applications are completely different.

QUOTE:

Speakers : Pioneer SP-BS22 Bookshelf speakers (6 ohms / 80w / 2.83V: 85dB)
Receiver : Harman Kardon HK-3390 Stereo Receiver (8 ohms / 80w x2)
 

I have read somewhere that I should not match a speaker with lower impedance rating than the amplifier. I just like to check with people in this forum because I'm afraid that I may have the wrong understanding of matching amp and speaker ohms.

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