Connecting an 8 ohm svc sub to a 4 ohm amplifier - diyAudio
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Old 7th May 2010, 04:26 PM   #1
kaadye is offline kaadye  United States
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Default Connecting an 8 ohm svc sub to a 4 ohm amplifier

Hi
I have an 8 ohm jl audio 8wo-8 sub and a 4 ohm 2 channel amp from sound stream. is there any way i can connect this 8ohm sub to the 4 channel amp
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Old 7th May 2010, 04:51 PM   #2
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You can use an 8ohm speaker on the output of a 4ohm amp with no problems except for a loss of maximum power. If you are willing to use both channels you can bridge them quite safely, and get 2 x the 4 ohm power into the 8ohm sub.

The (quite old) Soundstream amps I've got (Reference R200s) all support bridging 2 channels with a switch. If yours have the same feature you can simply follow the instructions to get a good bump in output power.

HTH

Stuart
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Old 7th May 2010, 05:49 PM   #3
kaadye is offline kaadye  United States
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Thanks Stuart
Yeah i can bridge my amp. but i was really concerned whether that 8ohm sub can be safely driven with this 4 ohm amp when bridged.
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Old 7th May 2010, 06:40 PM   #4
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Bridging halves the impedance an amp 'sees', so yes you should be able to drive an 8Ohm sub but probably not a 4Ohm sub.
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Old 7th May 2010, 07:05 PM   #5
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Quote:
Originally Posted by kaadye View Post
Yeah i can bridge my amp. but i was really concerned whether that 8ohm sub can be safely driven with this 4 ohm amp when bridged.
The driver will stand a much better chance of surviving if overloaded with a clean waveform by an amp which is too powerful (unless taken to extremes) than an underpowered amplifier driven into clipping

The first distortion you would hear would be from the driver which isn't too bad & you simply turn it down a bit. The first distortion you hear from an underpowered amp is the amp clipping, this puts DC accross the voicecoil & it heats up incredibly rapidly & probably soon fails..
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Old 7th May 2010, 09:10 PM   #6
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Any amp that you should even consider bridging should have DC protection.
And you can only deliver so much power from a clipping amp before it goes into protect. But you should have turned it down way before so any damage would be your own fault.
Some amps when bridged will output huge amount of DC into the load if one side would go into protect.

I read somewhere that most amps that came in to that workshop for repair where bridged. And many had taken speakers with them. (think it was a thread over at speakerplans forum)

But it's your choice.
From the stories I have read I would not bridge unless I am 100% sure it would be inside SOA and I really need the higher rail voltage.
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Old 7th May 2010, 09:22 PM   #7
Slowmo is offline Slowmo  Latvia
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What kaadje wants to hear is that amplifier states minimum allowable impedance of speakers that can be connected to it. You can always connect higher impedance speakers safely. Yes, you get half of the power when doubling the impedance, but on the other hand, amplifier can control speakers better (better damping factor).
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Old 7th May 2010, 09:25 PM   #8
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It is just like saying "can I use a 50W bulb/lamp on a circuit capable of and rated at 100W?"

Yes, of course you can, but it may not be as bright (loud).
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Old 14th May 2010, 09:06 AM   #9
kaadye is offline kaadye  United States
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So here are the specs
the amp specs - rms(not peak) - 45x2 and 120x1 @ 4 ohm
the sub specs - 75w rms @8 ohm
so my question is whether i can safely connect these without screwing up the amp or the sub
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Old 14th May 2010, 10:34 AM   #10
AndrewT is online now AndrewT  Scotland
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The 45+45 into 4r0 does not fit with 120 into 4r0 when bridged.
Similarly 45+45 into 8r0 does not fit with 120 into 4r0 when bridged.
Can you check the specifications again?

What are the supply rail voltages when the amp is idling?
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