Connecting multiple drivers to a crossover

[freos]

I have done some simpler two and three way crossovers, but all just including one driver for each bandwidth. Now I'm considering using some drivers I've had on the shelf for ages for what could be quite a good MI speaker cabinet.

Since the drivers have different sensitivity and impedance, to get the SPL levels to match I need to connect two mids in series and four woofers in series/parallel. However, doing this together with a crossover is new for me. If the crossover is dimensioned and made to suit the drivers at the combined impedance (series for mids and series/parallel for woofers), would this way of connecting everything work?



I.e. does the crossover "ignore" if it's an 8 ohm driver or two 16 ohm drivers in parallel or four 8 ohm in series/parallel between the crossover connections?

...or would that end in some kind of crazy result? Is it perhaps the only way to make a separate lowpass/highpass for each driver and then connecting everything in series/parallel etc?

Thanks!

[DBMandrake]

It will "work", but whether it will work well is another question. You also need to consider the bass and midrange separately, as they have very different requirements.

In the case of bass drivers, yes you can connect them in series parallel combinations, as long as all the drivers are the same model and in the same enclosure.

Driver tolerances (mostly the surround stiffness) will cause individual drivers to have different resonant frequencies, and if they were on open baffles or in different enclosures this would be a problem with series connection, because the impedance peaks of one driver would limit the drive to another driver at that frequency - their different impedance curves would interact with each other in a complex and undesirable way, so in those cases, only parallel connection would be satisfactory.

However if you mount the 4 drivers all in the same enclosure, the loading of the enclosure will cause the resonant frequency of all four drivers to be the same - so, providing the drivers are otherwise the same (which they should be for same model drivers) the impedance curves of the 4 drivers will be pulled into line with each other, allowing for a series connection. It's not a great solution compared to connecting them in parallel only, but it would work.

I would also add an extra link wire between the centre connection of one series pair of woofers and the centre of the other pair - forming a figure 8. Now you effectively have two pairs of parallel drivers connected in series, rather than two pairs of series drivers connected in parallel. Small distinction, and it will result in the same overall impedance but it will tend to equalize any small differences in the drive level between the drivers a bit better.

Don't overlook the fact that 4 woofers in series parallel combination will increase the overall sensitivity per watt by 6dB over a single driver, and by doing so you also increase the Vas four fold, so you'll need four times the cabinet volume to get the same bass alignment than with one driver. (But the payoff is 6dB increase in sensitivity, as well as a higher maximum SPL and power handling)

So depending on the driver you could be looking at a huge cabinet, or a very non-optimal bass alignment that is sensitive but has a very high cut-off frequency probably also with a large peak in the response at cut-off. (One note boomy bass...)

I'd suggest modelling the drivers response in a program like WinISD Pro Alpha - which has an option to choose the number of drivers, allowing you to see exactly the effect on the alignment with an increased number of drivers.

Midrange is a different story. In general it's not a good idea to have 2 midrange drivers. I have seen some speakers that have 2 (and 2 tweeters as well) but although they sounded great at a distance and had excellent dynamics, it's pretty much impossible to get good imaging when listening near on axis when sitting at a normal listening distance, due to severe lobing problems. When near on-axis to them there was always a phasey effect.

Depending on the size of your existing midrange drivers you might be better off looking for a single larger driver that has the required sensitivity. Even if the off axis response is not as good as a single one of your smaller drivers, at least it won't have severe lobing issues.

Without knowing a bit more about the drivers it's hard to say much else.

[DrDyna]

It doesn't really "ignore" because you've still got other electrical properties in the drivers such as inductance, but once everything is figured in it shouldn't be "crazy" AFAIK.

[tinitus]

Originally Posted by freos

I.e. does the crossover "ignore" if it's an 8 ohm driver or two 16 ohm drivers in parallel or four 8 ohm in series/parallel between the crossover connections?

almost, but not 100%
there will be small differences

but acoustic output will be very different
and is also a major 'player'

so, no, not quite the same