Speaker and Amplifier Wiring Please Help!

As you can see I have a car amp and some speakers, can anyone with speaker or amp knowledge please tell me (or even better draw a diagram :D) of the best (most efficient / loudest) way to wire all these up, the specs are as follows…

2/1 channel amplifier
Max power – 400 watt
4 ohm stereo – 2 x 75 watts RMS
2 ohm stereo – 2 x 100 watts RMS

ROUND SPEAKERS (midwoofers)
4 ohm
25 watt

4 ohm
4 watt

Thanks for your help!
(P.S my plan is to build a portable sound system powered by a car battery)

Picture of Speaker and Amplifier Wiring Please Help!
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gmoon5 years ago
Probably the best way to approximate your optimal load from four speakers (per channel) is combination series/parallel wiring. Four 4 ohm speakers would combine for a total load of 4 ohms. Maybe that load isn't quite optimal for the maximum power the amp can provide (75 watts / channel vs.100 watts for 2 ohm load), but it's usually accepted that multiple speakers have a higher SPL, and "sound" louder, so it's a wash.

-- There isn't a way to combine four 4 ohm speakers (symmetrically or otherwise) to get a 2 ohm load.

-- Two speakers in parallel would yield a 2 ohm load, but the power rating for both would only be 50 watts total, far below the 100 watts/channel (and see the note below).

-- Be careful with the output, even with four speakers per channel. Rated at 25 watts, together they can handle a total of 100 watts.

But often in practice it's best to have speakers rated for double the output power, because peak power output can exceed the "continuous" power rating. Your "Max Power" of 400 watts is probably an indication of this. It depends somewhat on how the amp manufacturer measures output power...

You could combine all 8 speakers for an optimal load of 2 ohms and 200 watts power capabilities...but you'd need 8 more speakers for the second channel.

mpilchfamily is right about the crossovers. But those can be considered an "add on" to the main speakers...
superrob (author)  gmoon5 years ago
Thanks gmoon, taking what you and mpilchfamily have said I have a few ideas -

First getting rid of the tweeters sounds like a good idea - less messing with crossovers, different types of speaker, odd numbers of speakers etc...

A possible setup I have come up with then is this? (see idea 1)

Also you were saying about the amp giving too much power for the speakers to handle, I can get hold of more of the round midwoofers so would this work? (see idea 2). That would create somewhere between a 2 and 3 ohm load right? (im trying to get technical now aha)

Thanks for your help so far!
gmoon superrob5 years ago
No worries, sr'b.

If you can find four more identical speakers, the "idea 2" schema will have a load of 2.667 ohms. That will have more output power as it's closer to the optimum load of 2. It should be capable of handling 150 W of peak power. And more speakers are generally louder/better anyways...

Here's a great calculator for speaker wiring combinations: Shavano Music impedance calc. You can even mix and match impedances, but that complicates the power handling capabilities.

Note that calculating the max power depends on all the speakers having the same specs. If not, then the power handling should be calculated based on the lowest wattage speaker, 'cause that will be the one to blow. So five 25 watt speakers mixed with one 10 watt speaker would be safe only to 60 watts, not 150W.

RE: The max peak power-- it depends not only on the amplifier (SS amp manuf's tend to inflate the numbers), but the speakers themselves might even have two power ratings, one continuous and one peak. And how the amp is used, too. So a speaker setup that's "safe" for one person might be inadequate for another...
superrob (author)  gmoon5 years ago
That "Shavano Music impedance calc" is very useful, I will bookmark it for any furute projects.

Luckily ive got 4 more identical speakers (almost sold them!) so "idea 2" it is!

Now just to build some sort of enclosure, my very rough idea (see picture) is 6 separate compartments, each with 2 speakers and one tube (port?)

any advice on building my enclosure would be greatly appreciated?

Again, thanks for your help!
I'm not sure but you might not be able to connect all of that to the amp. You may have to settle for 3 mids per channel so you can include the tweeters. Or dump the tweeters so you can use all the mids.

But you will want to build a crossover unit for them. A crossover unit will direct divide and direct the frequencies to the correct speakers. This way the tweeters are only getting the higher frequencies giving you a crisper sound. Learn more about Crossovers.