[Housteau]

I have a very basic speaker builders question to ask.  Lets say that you have a three driver speaker using an external crossover.  The drivers could be all 4, or all 8 ohm, it doesn't really matter.  But, because of their odd number no combination of series and/or parallel wiring would have it come out to a nominal spec of either 4, or 8 ohms.  Most if not all speakers have that nominal rating.  Are resistors added to create that 4, or 8 ohm spec?  If so, what kind are they? 

[Speedskater]

With a crossover each speaker is operating in a different frequency range. So the basic series and parallel formulas don't apply. I's way more complicated.
But with a correct crossover and all three drivers (woofer, mid & tweeter) of the same impedance, the total load will be about that impedance. 

[Housteau]

With a crossover each speaker is operating in a different frequency range. So the basic series and parallel formulas don't apply. I's way more complicated.
But with a correct crossover and all three drivers (woofer, mid & tweeter) of the same impedance, the total load will be about that impedance.

Thank you for your reply, but no.  You read a bit too much into what I was asking.  My question is simply based on an enclosure with three of the same drivers all covering the same frequency range.  Lets say it is an upper bass module.  The crossover is external to the unit and is not part of the equation.  I just want to know if resistors are often used along with the drivers parallel and/or series wiring to create that nominal 4, or 8 ohm load measured at the speaker terminals.  If so, of what type is most common?  For example:  Would it be a power resistor?

[Speedskater]

Oh in that case, yes the series and parallel rules do apply. Three is an difficult number, the only solutions are: all 3 in parallel or all 3 in series. Resistors will make a mess of things. That's why you will never see 3 drivers.

[opnly bafld]

Like Focal (others?) make/use drivers with an impedance that will work.



 

[Housteau]

Oh in that case, yes the series and parallel rules do apply. Three is an difficult number, the only solutions are: all 3 in parallel or all 3 in series. Resistors will make a mess of things. That's why you will never see 3 drivers.

Well, actually there are such speakers.  I have a set and I think I have solved my mystery.  This upper bass module is part of the VMPS RM-V60s.  It supports the tower V section.  You can see them in my Gallery.  An option was offered adding a second upper bass module which I did not do.  Now I have access to empty cabinets and the original drivers.  It is a Misco 6.5".  My driver is not currently listed with them as it was and is a special order.  Those that they do offer are similar and at either 4, or 8 ohms.  My current bass modules measure to be at 4.2 ohms.  That was the reason for my original question.  How did Brian Cheney get to that 4 ohm reading using three 4, or 8 ohm drivers?  The answer is he didn't.

My mistake was assuming my driver was 4, or 8 ohms.  It isn't.  It is 6.3 ohms and probably why it is a special order.  Two of those in series and in parallel to the third makes 4.2 ohms.

[Speedskater]

Like Focal (others?) make/use drivers with an impedance that will work.

I think the there is a lot more going on inside the box, than just connecting drivers in parallel.
* * * * * * * * * *
Back to the original question:
three 4 Ohm drivers is series is 12 Ohms and any amp will be happy.
three 8 Ohm drivers in parallel is 2.7 Ohms and only a few amps will be happy.

[Housteau]

I think the there is a lot more going on inside the box, than just connecting drivers in parallel.
* * * * * * * * * *
Back to the original question:
three 4 Ohm drivers is series is 12 Ohms and any amp will be happy.
three 8 Ohm drivers in parallel is 2.7 Ohms and only a few amps will be happy.

Yes.  See my reply to your post above.  You combine series and parallel circuits.

[Speedskater]

I had some VMPS tower speakers and some sub-woofers. Spoke to Brian Cheney (RIP) on the phone a few times. He was thinking outside the box. He was also doing work for other loudspeaker manufactures.

[Housteau]

I had gotten the chance to get to know Brian.  I miss him.

[Speedskater]

From December 1986, I found the instructions for the VMPS Tower II/R loudspeakers. There is a large power resistor in series with the smaller magnet woofer.

[FullRangeMan]

Try a crossover calculator:
http://www.erseaudio.com/CrossoverCalculators

[Russell Dawkins]

The answer is he didn't.

My mistake was assuming my driver was 4, or 8 ohms.  It isn't.  It is 6.3 ohms and probably why it is a special order.  Two of those in series and in parallel to the third makes 4.2 ohms.

Only problem with this solution is the two in series would get collectively half the power going through the series parallel system because they would represent a 12.6Ω load. So, each of those drivers would handle 1/4 the power that the single parallelled 6.3Ω driver would handle.

[Speedskater]

Try a crossover calculator:

The VMPS crossovers don't look like crossovers in loudspeaker books.
Things like, two different sized woofers, one with a resistor in series.

[planet10]

I just so happen to be having thot experiemnts on a 3-driver speaker.

All FR wired in series with a big cap shunting 2 of them. That leads to only 1 driver working at high frequencies (so no combing) and much less excursion & 3 times the cone area at low frequmcies. The drivers are nominal 4Ω so the end result is 4Ω up top & 12Ω at the bottom.

dave

[planet10]

Try a crossover calculator:

Crossover calculators are not very useful with real world loudspeakers.

dave

[FullRangeMan]

Crossover calculators are not very useful with real world loudspeakers.

dave

What do you could suggest to the OP calc the resistance value to 3 woofers to linearize the impedance?

[Housteau]

It looks like in order for me to know for sure exactly how he wired these drivers I will need to remove one and look inside.  I will do that if I decide to build up that second set of upper bass units.

[mrhyfy]

I think what is confusing us is that we are assuming drivers are 4 ohm or 8 ohm.     If the speaker maker uses custom drivers , say 2 or 3 ohms  OR say 16 ohms...then they can series or parallel as desired.

[FullRangeMan]

The best option would be three 16 ohms woofers to:
16/3=5.3ohms
A manageable impedance to a nominal 8ohms speaker.