Correct connectin of multiple loudspeakers 1

[voltair]

I have to connect loudspeakers in a seater coach. Each double seat has an 8 ohm 20W speaker. There are 7 such speakers on each side,each side being connected into an amplifier with 20 per channel, 4 ohms impedance.

There are many combinations of series/parallel arrangements to get close to 4 ohms. For instance, connecting No. 1 and 2 in parallel, 3 and 4 in parallel, 5 and 6 in parallel. This gives 4, 4, 4 and 8 ohms. Then connecting all three 4 ohms in series giving 12 and 8 ohms. Finally connecting 12 and 8 in parallel, giving < 5 ohms.
My question is, what about the power from each speaker. Will they be balanced or will some of them be louder than others.
What other considerations are important.

Best regards,
Voltair

 

[Lewish]

The short answer is - they will not all be the same loudness. But, given the environment, the difference may not matter. This may be only be able to be determined by trying it. And then trying a different combination.

 

[ghb]

follow your plan as above except with the 7th speaker place an appropriate load in shunt generating 4 ohm impedance

place 2 groups in series to achieve 8 ohms impedance

place the 8 ohm groups in shunt to achieve the 4 ohm impedance

connect to amp

of course you'll dump some power into the load
however you won't have a mismatch at your amplifier either

good luck

 

[bob98009]

this type of problem has arisen before. the solution is to use transformers. you make no mention if all the speakers are the same or what thier sensitivity is. do you have a impedance meter? using a 70 or 25 volt trans, then paralleling them, taking into account phase the load will be higher than 4 ohms. the power amp will be very happy and run forever plus one day. does this scheme work? yes, and very well. distributed systems are common in commercial audio work.

 

[peebee]

Or add/subtract a speaker if you can. 2x3 = 6 speakers or 2x4 = 8 speakers would work better than the 7 you're trying to install.

TX is the best solution for 7 speakers, most power output.

Resistor is cheapest way to evenly distribute power.

No TX + no resistor + seven speakers = severe mismatch in power output.