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
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
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..
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.
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.
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).
Sorry messed up with my specs from another amp:
these are the specs that i have on the box and manual
4 Ohm [14.4V] 55W x 2 [20-20kHz, 0.08%THD]
2 Ohm [14.4V] 75W x 2 [1kHz, 0.8%THD]
Bridged[4 Ohm] 150W x 1 [1kHz, 0.8%THD]
Frequency Response [+0dB -3dB] 5Hz-50kHz
Signal to Noise Ratio 95dB
Input Sensitivity Control 0.2V-5.0V
Please let me know if i can connect the sub and the amp.
these are the specs that i have on the box and manual
4 Ohm [14.4V] 55W x 2 [20-20kHz, 0.08%THD]
2 Ohm [14.4V] 75W x 2 [1kHz, 0.8%THD]
Bridged[4 Ohm] 150W x 1 [1kHz, 0.8%THD]
Frequency Response [+0dB -3dB] 5Hz-50kHz
Signal to Noise Ratio 95dB
Input Sensitivity Control 0.2V-5.0V
Please let me know if i can connect the sub and the amp.
55W into 4r0 is ~14.8Vac into the load.
75W into 2r0 is ~12.2Vac into the load.
The output has lost 1.7dBV when changing from 4r0 to 2r0.
This amplifier may be able to drive a 2r0 load without blowing itself up. I would never class an amplifier as low impedance capable if it loses 1.7dBV.
A good amp should lose less than 1dBV when driving a load resistance of half the recommended speaker load.
An excellent amp would lose <0.5dBV when driving that resistive test load.
Your amp is struggling to drive a 4ohm load properly because it is current limited.
It can drive resistors as the spec shows, but it will make a bad job of driving reactive speakers.
Use one channel rated for 55W into 40hms to drive one 8ohm speaker. With luck it should cope with this load OK. You will probably have about 30W maximum into your 8ohms speaker.
75W into 2r0 is ~12.2Vac into the load.
The output has lost 1.7dBV when changing from 4r0 to 2r0.
This amplifier may be able to drive a 2r0 load without blowing itself up. I would never class an amplifier as low impedance capable if it loses 1.7dBV.
A good amp should lose less than 1dBV when driving a load resistance of half the recommended speaker load.
An excellent amp would lose <0.5dBV when driving that resistive test load.
Your amp is struggling to drive a 4ohm load properly because it is current limited.
It can drive resistors as the spec shows, but it will make a bad job of driving reactive speakers.
Use one channel rated for 55W into 40hms to drive one 8ohm speaker. With luck it should cope with this load OK. You will probably have about 30W maximum into your 8ohms speaker.
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I am actually faced with the same dilemma. I have a dual 4 ohm sub I would like to run at 8 ohms on a ppi pc2600.2. I know 8 ohms bridged will be around 300 watts, but does it hurt the amp at all? I have heard conflicting stories on this. Also, does running at 8 ohms lower the THD at all? Thanks for posting this question.
The two power specifications above show the amplifier cannot drive a 2ohm speaker load and will struggle to properly drive a 4ohm speaker load. It simply cannot deliver sufficient current to drive reactive loads.
If you bridge two of these amplifiers
Instead of 55W into 4r0 you will get 110W into 8r0
and instead of 75W into 2r0 you will get 150W into 4r0.
But the same advisory limitations apply that I gave you earlier.
110W into 8r0 will struggle to drive an 8ohm reactive speaker.
150W into 4r0 cannot drive a 4ohm speaker.
You will get better performance using the 4ohm amplifier driving an 8ohm speaker and since you have two of these 4ohm amplifiers you can drive two 8ohm speakers for a total of ~60W of maximum output power.
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