Increase total Speaker Impedance -- Potential Solution

Thanks Al. Nice to have expertise on the board.

Hello! Thanks all for your input and thanks  @almarg  for your expertise again!

The reason I needed to figure out a way to increase the impedance of my DIY unit is that the Zero Autoformers will soon have another use. I purchased a tube amp to be used with my Martin Logans and I heard the electrostatics' impedance drops really low and a pair of Zeros will help big time. Hence, the Zeros will now be connected to the electrostatics instead.

I'm not ready to chip up another $500 for another pair of zeros since if that's the case, I'd rather just sell all my drives and just buy another pair of speaker and kiss the DIY goodbye. Luckily, I found a creative way to re-wire the speaker so the impedance is now 4 ohm instead of 1.6 ohm.

How I did it:

Originally, almost all of them have separate crossovers and wired in parallel. Now I have three crossovers:

1x 2 way crossover at 2000hz
1x 1 band-pass 800-5Khz
1x low pass 800hz

Speakers:

1x Dynaudio D76AF
1x Dynaudio 15W75 Esotec
1x Dynaudio 17W75
1X Morel Supreme Tweeter (forgot model number, but ideal crossover I recall was 1800hz)
1X Dynaudio MW172 (8 inc)
With the exception of MW172, the rest are 8 ohms

2 way crossover high-pass connection goes into Morel Tweeter. The same crossover, low-pass connection goes into 15W75 and 17W75 wired in series. I understand they are not identical, but I see they have similar frequency response plots. Then, still using the same low-pass connection, wire the MW172 parallel to the 15w75 and 17w75 series, along with a series 1.5 ohm resistor. So in the end, I have all the woofers on the same low-pass connection of the 2 way crossover. However, the MW172 is crossed over a second time with the 800 low-pass filter. The D76AF stands along with the band-pass filter. Overall impedance showing in my multi-meter is 4.1 ohm.

Question is will the somewhat high output impedance of the amp still affect the bass negatively?

Probably not, unless slightly enhanced bass is seen as a negative. It won't be by much though.

Overall impedance showing in my multi-meter is 4.1 ohm.

That is the DC resistance and is only the drivers that don't have a cap in series with them. To really know the **impedance** (as opposed to resistance), you need a different test, since impedance often relates to frequency and can be quite different from resistance!

You'll need a variable resistor that might cover the range of the drivers. A 50 or 100 ohm potentiometer should do the trick. You'll also need a sine wave generator which will drive the speakers. We're not talking about any power here. You might be able to find an app for your phone that will do the job. You'll also need your DVM.

Set the frequency at which you want to measure. Put the potentiometer in series with the speaker. You'll only be using the center connection and one side.  Apply the signal. set the control so that the AC voltage drop across the speaker is the same as the control. Switch to Ohms and measure the control (out of circuit is best). That is the impedance of the speaker at that frequency. Continue to do this for all frequencies of interest.


You'll see that there is a low frequency impedance peak, followed by a lower impedance which then rises as frequency is increased. There might be dips at crossover frequencies. Check the areas of interest (crossover frequencies and then 500Hz above and below each crossover frequency). Then you can draw this all out and see what you got.

As a general rule of thumb when you put drivers in series they really should be the same kind of driver for the reasons Al points out above!