Wiring 2 different set of speakers with different ohm's??

[Thea-masta]

Ok, so i was reading through some articles about matching speaker ohms to amp ohms and come across some quite frightening facts..the question im going to ask is, How do i connect 2 8ohm speakers and 2 4ohm speakers to a 4 channel amp?
on the back of the amp its says ' CAUTION each speakers impendance is 8ohms at A+B position' i know i can have either speakers A or B on but does it change the impendance or something and will it damage my amp if not wired correctly?

sorry i having trouble putting this into words as its quite confusing.

If anybody can help me i would be much appreciated, and if you need any pictures just let me know.

[Kevin P]

Ok, first question, is this "4 channel amp" really 4 separate channels or is it a 2 channel amp with A and B speaker outputs?

If it's 2 channel with A & B, do a quick test. Connect a pair of speakers to the A outputs. Leave the B outputs disconnected. You should hear the speakers when the selector switch is in the A position, and silence in the B position. But what happens when you move the switch to the A+B position? Do the speakers still play, or do they go silent?

If they still play, the A and B outputs are in parallel, so if you have 8 ohm speakers connected to both A and B, the amp will see a 4 ohm load with both sets of speakers on. If the back panel says "use 8 ohm speakers minimum with A+B" then the amp is designed to handle a 4 ohm load. But you won't want to use 4 ohm speakers in this configuration, as this will overload the amp, plus the 8 ohm pair will play really softly since the 4 ohm pair will draw most of the power. Running an 8 ohm speaker parallel with a 4 ohm speaker will present a 2.67 ohm load on the amp, which is too much (too low an impedance) for most amps.

If the amp goes silent in the A+B position, the speakers actually get connected in series in the A+B position. In this instance you can run 4 ohm speakers in A+B, since then the amp would see an 8 ohm load, or in your example of 1 pair of 4 ohm + 1 pair of 8 ohm, it'll see a 12 ohm load. The speakers won't play as loud, but they'll play and the amp won't fry, overheat or shutdown.

[Thea-masta]

Hey, i did the test and when i turn speakers B on sounds keeps playing from A. On the back of the amp it says when i have both speakers A+B switched on its 8ohms' now what i was wondering, is it safe playing music through speakers A (which are both 4ohms each) and through speakers B (which are 8ohms each).

Also is there a way to get all speakers at 4 ohms too make it louder?

[Kevin P]

If speaker A still plays in the A+B position with the B speakers disconnected, then you're presenting a parallel load on the amp, and with 4 + 8 ohm speakers, the amp will see a 1/(1/4+1/8) = 2.67 ohm load. This will overload the amp, especially if you turn the volume up.

If the amp says "A+B 8 ohms" that means the amp can handle a 4 ohm load, so you can drive 1 pair of 4 ohm speakers, or 2 pairs of 8 ohm speakers. But running anything < 8 ohms in parallel will result in something below 4 ohms to the amp which will overload it.

I see 4 options if you want to run the 2 pairs of speakers together: (1) replace the 4-ohm pair with a set rated at 8 ohms, (2) add a 2nd amp, so each amp has 1 pair of speakers on it, (3) get a speaker switch box with built-in impedance protection, or (4) if you're always going to use both pairs, wire them in series and connect to the A outputs only.

[Thea-masta]

Ah, thats kinda left me up s**t creek then....im guessing the damage is done my DM110i's dont seem to have the ''oomf'' they used to have. :cry: :cry: :cry:

[Kevin P]

Are the DM110i speakers the 8 ohm pair, or the 4 ohm pair?

Unless you overheated the amp, you didn't damage anything permanently. Run the DM110i by themselves and you should get the "oomf" back.

I edited my above post and added 2 more options you can try.

[Thea-masta]

The Dm110i's i measure at 7.4 (8ohm) and the acoustic solutions are 3.7 (4ohm), but i just noticed on the back of the av-120's it says 4-8ohms???

[Kevin P]

That just means the AV-120s fall somewhere between 4 and 8 ohms depending on frequency.

You'll probably find that the DM110is drop in volume more when you switch to A+B, because the AV-120s are drawing more power from the amp.

Are you planning to run the speakers together (A+B) all the time, or will you sometimes be switching to just A or B? If you're planning on staying in A+B all the time, try wiring the speakers in series and see what happens:

1. DM110i (+) wire to A speaker (+) terminal on amp
2. Splice DM110i (-) wire to AV-120 (+) wire, with a wire nut or electrical tape
3. AV-120 (-) wire to A speaker (-) terminal on amp

Set speaker switch to A. Give it a listen and see how it sounds.

[Thea-masta]

Well ive wired 1 of each speaker and i can notice a considerable amount off bass in the DM's now, but, is this good for the amp? should it perform better than it did?

[Kevin P]

It's not the ideal solution but wiring in series puts less load on the amp. The impedances are added together, so 4 ohm + 8 ohm = 12 ohm.

When you had them in parallel, it was loading the amp harder (it was seeing <3 ohm load), plus with one pair at 4 ohms was drawing most of the power so the DMs weren't getting as much, causing the loss of volume/sound quality in the DMs.

If it sounds ok to you, it won't hurt anything. The ideal solution is separate amps/channels for each pair, then there's no interaction or interference between the DMs and AVs at all.

[Thea-masta]

Yh i think im going to invest in an amp for the Av's, trouble is..which one
They are acoustic solutions av-120, if you could find an amp suitable for these nothing extreme, that would be excellent, as im an amateur into home hi-fi

But thank you soo much for your help and preventing further damage to my hardware! :T

[Thea-masta]

Wow, followed your wiring advice, and by god does it kick out some power now..

[Chris D]

Success! :banana: