Chained speakers signal connected in series

Unless the two loudspeakers are identical, there will be some modification of the frequency response of BOTH speakers. It does not matter which is first and which is second in the series.

The difference may or may not be small, it depends on the specifics. Try it and see what you think.

I disagree with imhififan’s opinion that the crossover points will change. In my experience, they do not. But each speaker’s frequency response will be modified by the other speaker’s impedance curve being in its signal path. If the two impedance curves are identical, then so is each speaker’s sensitivity to the other’s impedance curve, and the net frequency response of each is unchanged. But if their impedance curves are different, then there will be changes in the frequency response of both speakers.

(For geeks only: It is tempting to think of each speaker as a resistor in series with the other, thus ruining the amplifier damping factor for both and effectively doubling the woofers’ Qes, but this is also incorrect, because each speaker also has its own motor strength.  Assuming generally similar speakers the DC resistance is approximately doubled but so is the total motor strength, therefore woofer Qes is not degraded. This is a different situation from adding an equivalent series resistance, in which case only the DC resistance would be doubled [with total motor strength remaining the same], in which case the effective driver Qes would also be doubled, as predicted by the calculated degradation in effective amplifier damping factor.)

Duke 
speaker designer

Both woofer in each speaker will get much lower crossover point and the tweeter will get a band-pass filter instead of high pass.

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No it does NOT.. The impedance does not change at the driver, Only what the amp sees at the XO terminal, not the driver. The ONLY way to change the resistance is to CHANGE the resistance.. We haven’t

If that were the case then running in parallel would produce the opposite effect AGAIN. Twice the current and double the crossover point? Double the current draw but it doesn’t change AT the driver. The driver resistance hasn’t changed a bit..

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I did this 15 (?) years ago. READ ON!!

Let us say that both channels were being fed with a pure 1kHz sine wave and that both halves of the amplifier were identical in every respect.

If you connect your stereo speakers conventionally, then for each positive part of the sine wave, the amplifier drives each speaker cone forwards. For each negative part, the amplifier drives the speaker cone in the opposite direction. Each speaker then produces a 1kHz tone.

The positive speaker terminal is producing a voltage that represents your sine wave. The negative (or Common/Ground) terminal is the reference for this voltage. (across two points right)

Now, connect a single speaker across the two positive outputs and ignore the grounds. If you have identical voltages with respect to ground coming out of your terminals, then the net voltage (and hence speaker cone displacement) is zero and so you will hear nothing.

Only very very expensive amplifiers have this degree of perfect matching so it is likely you may just barely discern some sound.

Now, connect a conventional stereo source to the amplifier and what you now get is a voltage on each positive terminal that is slightly different from the other. In this case, you will hear something. Often, vocals are fairly central so the same signal is present on both channels and will cancel out. Instruments that are left or right of center (i.e. more on one channel or the other) will be discernible to a greater or lesser extent depending on the amount of stereo separation.

A Little trick to try.

Connect a pair of speakers to your amplifier but instead of the two negative wires returned to their terminals, connect them to each other. Effectively you have just connected two speakers in antiphase series across your left and right channels.

Play your tunes and enjoy "separated stereo with little or no center sound stage"!

This is not as stupid as it sounds. The A speakers, (Left and Right) are wired conventionally. The B speakers are wired as I have just described and are placed further apart than the normal speakers but slightly behind the listening position.

By running the amp with just the A speakers selected, you get conventional stereo.

By running the amp with A + B selected, I get a wider stereo effect with no additional electronic processing involved.

By connecting a suitable value resistor or variable resistor between the speaker commons and the amplifier negatives (they are usually common so you only need one connection) and allowing some of the signal to go the conventional route and some to go the "wrong way round" you can vary the WIDTH of your stereo separation.

You can go one better than this.

Use TWO amplifiers (a matching pair). Connect the source to both amplifiers using a Y splitter lead on each channel. Drive two pairs of speakers from each amp so that you have 8 speakers in total. Position four of the speakers around the lower half of your listening area. Position the other four higher up in the room so that you have the same left-right and front-rear orientation (but two layers if you like), separated by a meter or more. Ideally half a meter above and half a meter below your ear position. Do not connect any speaker grounds to the amplifiers - wire all four pairs as "antiphase series".

Now, instead of using a variable resistor on each back channel, use a 2 axis potentiometer (joystick) with the center taps of each axis connected to ground and the ends of the tracks (two per pot) connected to the junction of your speaker negatives.

You can now use the joystick to completely mess with your aural experience. Purple Haze comes to mind... "Movova, and Let Jimi take OVA"

TINKER TIME FELLA... Back to the lab.... Come on dog...

Regards

I disagree with imhififan’s opinion that the crossover points will change.

I believe the Tannoy SGM 10B has parallel crossover, if connect two speakers in series, the LF section will be #1 speaker low pass inductor --> #1 speaker woofer --> #2 speaker low pass inductor --> #2 speaker woofer.
Correct me if I'm wrong, doesn't each woofer will see two inductor and a woofer voice coil in another speaker in series?

Interesting - I spent a little time to sketch the schematic. Granted the amplifier output will see 2 inductors in series, the crossover frequency of the driver is based on the L and C values. That ratio does not change whether the speakers are connected in series or parallel. My vote is that it does not change the crossover frequency. As far as the series or parallel connection of the speakers to the amplifier, the series connection does make it typically easier for the amp to drive the load. But this is only true up to about 70% of the maximum voltage capability of the amplifier. A parallel connection of the speakers will yield a 3dB increase in SPL, if your amplifier can handle the load resistance and deliver enough current. I preferred to connect them in parallel. That being said, I frown on multiple drivers in series OR parallel, especially in the midrange and tweeter frequencies. Whether they are point source of line source drivers, the sound will lose detail and become fractured and unclear. Happy listening!

Good summary.