4ohm speaker with 8ohm amplifier

Hi
I've got an old amplifier (Pioneer SA-2001), it's got 4 channels (65w/channel). On the back, it says that it supports 8 and 16 ohm speaker and that you need to see the manual for 4 ohm use. I looked up the manual online, but can't seem to find anything. For years, I've used 4, 4 ohm speakers without a problem (the amplifier has watt-meters on the front panel so as long as they don't exceed 65w continuous, this shouldn't be a problem, I guess)

Now, I want to connect 2 4 ohm speakers and 2 8 ohm speakers.. I haven't tried it yet, but my guess would be that at a certain volume level, the 4 ohm speakers would be way louder than the other ones. What could I do to fix this?

Regards

Add series 4Ohm resistance with the 4ohm speakers? Just a guess, I don't know how it will affect the group delay for example.

so as long as they don't exceed 65w continuous, this shouldn't be a problem, I guess

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If the transistor power dissipation is the limiting factor, the available continuous output power is less than 65W/2.

Hi,

An audio amplifier is a voltage amplifier.
A 4Ohm speaker draws twice the current than an 8 Ohms speaker at the same input voltage.
This increases power dissipation.
In worst case this violates SOA of the amplifier's power resistors - but this is not very likely.

I don't expect much influence on the sound - at least at low and medium levels.

Regarding loudness between 4Ohms and 8Ohms: mathematically this is just a deviation of 3dB
But if you compare true speakers (not math) of different brand 8Ohms with 8Ohms then you will recognize deviation in sound level of 3dB, too.

Klaus

Cecemel said:

see the manual for 4 ohm use.

Click to expand...

It's possible they advise stringing two 4-ohm speakers in series. This creates the equivalent of 8 ohm. Thus less risk of burning up your power amplifier. Observe correct phase polarity connections.

Hi,

From fidelity view connecting speakers in series makes no sense...it will cause very unlinear frequency response, especially when different types of speakers are connected in series.

Klaus

A speaker has a strong low frequency resonance and more resonances at higher frequencies. A modern solid state amplifier has a spec called its "damping factor" which is its extremely low output impedance that reduces a speaker from resonating like a bongo drum at one low frequency and shrieking at the higher frequency resonances. Some amplifiers have a damping factor of 1000 which means when it drives an 8 ohm speaker its output impedance is 8/1000= 0.008 ohms. If you connect a resistor or even worse, another speaker the same in series then the damping is almost none, bong bong.

Your amplifier is designed for speakers no less than 8 ohms per channel. If you connect a 4 ohm speaker then it could be destroyed because the current is doubled. Its Watt meters do not measure Watts because they think your speakers are 8 ohms, instead they measure voltage. If the meter shows 65W when driving a 4 ohm speaker then the actual output power is trying to be 130W.

Our hearing's sensitivity to loudness is not linear, it is logarithmic so we can hear a very wide range of loudness. The difference between 20W into an 8 ohm speaker and 40W into the same but 4 ohm speaker is just a small loudness difference. 10 times the power sounds twice as loud, 1/10th the power sounds half as loud.

Perception of loudness has lots of limitations; we have a peak sensitivity close to 1000-4000Hz (depends on age) with a time constant of about 1/2 sec. Therefore the pressure levels, the frequency and the durations are all to be considered. With age, low frequency sensitivity declines and many modern amplifiers have a bass boost (that artificially enhances amplification of low frequencies) which is often useful.

Connecting speakers in series is NEVER recommended unless the audio quality is not a concern (speakers are not resistive devices and they are more like electric motors).

If you are not going to turn the volume knob to the end, 4 Ohm speaker will work just as fine as a 8 Ohm speaker. At the same setting of the volume control, a 4 Ohm speaker will be slightly louder compared to a 8 Ohm speaker (at lower volumes, the 4 Ohm speaker will deliver about twice the power: but do not forget the motor analogy). My personal advice: just try and experiment. Positioning the speakers at the right place in a room is the key (and the listener is at the center). In a real case, you do not have much choice about position of the speakers and the listeners and trial and error is the only effective solution.

Admittedly stringing speakers in series is non-ideal. An L or T pad could be a better solution. As I understand it, if properly adjusted it presents an 8 ohm load to the amplifier, yet drives a 4 ohm speaker.

An L pad is a volume control at the speaker. If an 8 ohm speaker is used it always presents 8 ohms load on the amplifier and a variable damping ratio to the speaker. A T-pad maintains a load of 8 ohms to the amplifier and a source of 8 ohms for poor damping of an 8 ohm speaker. They were used when vacuum toob amplifiers were used with an output transformer. They are also used with modern PA amplifiers that have an output transformer.