Audio experts help Decibel output.

While doing what you are proposing may increase the longevity of the amplifier, chances are you'll get less volume, not more, unless the amp is pretty much unable to function in a reasonable manner with the 4 ohm load.

Each of the series connected speakers would see half of the voltage that is being put out by the amp at any instant of time, resulting in each speaker receiving 1/4 of the amount of power that it would receive if the full output voltage of the amp at that instant were applied across it. So the total power delivered to both speakers (in each channel) would be only 1/2 as much as it would be if the full output voltage of the amp were applied across a single speaker.

The only way in which a volume increase would result is if the maximum output voltage that the amp can provide into 4 ohms (and that it can sustain, for some amount of time that depends on the kind of music you are listening to) is much less than what it can provide into 8 ohms, which would be indicative of a weak design.

I am assuming, btw, that you are referring to a solid state amp, not a tube amp.

Also, btw, keep in mind that for good sonic results series connected speakers should, in general, be identical models.

Regards,
-- Al

Would the characteristics of the signal coming off the amp be changed as it passes through the first speaker into the second? In other words, hooking two four ohms nominal rated speakers up in series isn't as simple as 2 times 4 equals 8.

Hi Bruce,

Yes, the signal seen by one speaker will be affected by the presence of the other speaker. However, if the two speakers are identical models, as I indicated they should be, their impedance vs. frequency characteristics will presumably match very closely. Given that, the effect will simply be that each of them will at any instant of time see a voltage equal to the output voltage of the amplifier at that instant divided by 2, which in turn will cause the amount of current flowing through them to also be divided by 2, relative to what it would have been without the other speaker being present. Since for a given load power is proportional to voltage x current, the two factors of 2 result in a four-fold reduction in the amount of power delivered to each speaker, as I had indicated.

Another consideration is the effect of the series connection on damping factor. Although it seems counter-intuitive, that is not an issue, as explained in this paper, which I must credit A'gon member Kijanki for calling to my attention a couple of years ago.

Why not just stick a high power 4 ohm resister in series with just one speaker?

That would waste half of the power being put out by the amp, since all of the power consumed by the resistor would be converted into heat, rather than some of it being converted into sound.

Last point - a 30 watt amp is a pretty low power amp. If the OP winds up overdriving the amp, it may clip.

Good point, especially of course if the speakers are relatively inefficient.

Best regards,
-- Al

Hi Bruce,

What will double, as seen by the amplifier, is the impedance that each speaker has at any given frequency. "Impedance" reflects the combined effects of resistance, inductance, and capacitance at that given frequency. Assuming that the two speakers have the same impedance (as each other) at all frequencies, half of the voltage that is put out by the amplifier at any given frequency at any given time will appear across each speaker. Think of the output of the amplifier as the summation of many different frequencies occurring simultaneously. Half of the voltage corresponding to each of those frequencies will appear across each speaker. The summation of all of those halved voltages, appearing across each speaker, will be the same as what the amplifier is putting out, except scaled down by a factor of 2.

Something that may help to clarify this would be to consider what happens if a voltage at some frequency is applied across two series connected resistors, or alternatively across two series connected inductors, or alternatively across two series connected capacitors. In each case, half the voltage appears across each of the two series connected components. And likewise if the components are a complex impedance consisting of some combination of resistance, inductance, and capacitance, such as a speaker. And in each of those cases the phase angle between voltage and current at any given frequency will be the same as if only one of the two components were present, since the two components have identical phase characteristics.

Concerning parallel connection, if the amplifier is solid state and therefore has a negligibly small output impedance, the speakers essentially become independent of each other, and have no effect on each other even if they have different impedance characteristics. The load on the amplifier will be increased, of course. In the case of a tube amplifier that has significant output impedance, paralleling non-identical speakers having significantly different impedance vs. frequency characteristics could result in some alteration of the frequency response of each speaker, because the voltages appearing at the output of the amp would be affected by the relation between the amp's output impedance and the total load impedance.

Viral, no, you would need an amplifier rated at 100 watts into 8 ohms to put 50 watts into each of two series connected 4 ohm speakers. If the 100 watt amplifier is solid state and therefore has negligibly small output impedance, and is robustly designed and is capable of supplying lots of current, it would be able to put 200 watts into a single 4 ohm speaker. The 1/4 factor is the relation between the power into each of two series connected 4 ohm speakers (50W in this case), and one 4 ohm speaker (200W in this case, provided by an amplifier that is rated at 100W into 8 ohms, but is presumably and hopefully capable of providing 200W into 4 ohms).

Whether or not you would want to put 50 watts into the speakers is a separate question, of course, which depends on their efficiency, the listening distance, the kinds of music, your volume preferences, etc.

Best regards,
-- Al