Speaker impedence question ....
- Thread starter maug2122
- Start date
Securb
One of Jerry's Kids
Yes, it depends on how you wire the speakers. Two 8 ohm speakers wired in parallel result in a 4 ohm load. If you wire them in series you will get 16 ohms. Think of amps and speaker cabs as glasses of water. You do not want to pour 8 oz (amp ohms) into a 4 oz (cab ohm) glass. If you pour 8 oz (amp ohms) into a 16 oz.(cab ohms) glass you will be fine. With the cab being twice the ohms of the amp it will not be as efficient in pushing the cab, but seeing you have a 100-watt head you should be plenty loud enough.
With Solid-State amplifiers, the impedance is not usually an issue unless you go below the rated impedance for that amp. Most ALL SS amps are good down to 4 ohms. They are a direct transfer of energy device. They do not care if the speaker impedance is 12.5 ohms or if it is 5.5 ohms. It will convert X voltage across that impedance to produce X watts of power. You may notice that most ALL SS amps state perhaps 100 watts @ 4ohms and then 50 watts @ 8ohms and then 25 watts @ 16ohms, this is because the amp produces a fixed voltage for it's output power. The conversion of that voltage into watts is determined by the speaker impedance. 8ohms is half of 16 ohms, so it will double the wattage dissipated. 4ohms is half of 8ohms so it will again double the wattage dissipated.
That being said ALL amplifiers have a minimum impedance that they can drive. In most consumer-grade amps, it is usually 4ohms. Given the THD ( total harmonic distortion ) rating that the specs state, I would venture a bet that the 150 watts and 75 watts respectively is because of the fact that they only showed you the max power it would produce, hence a higher THD. Powering an 8-ohm load out of the stereo out would simply cut your peak wattage in half and your THD would go from 10% to 4% or something like that. If you look at the back of the Power-Block, you will see next to each output that it says 8ohms MIN, or 4ohms MIN. This simply means that in Bridge mode, the MINIMUM impedance you can drive with that amplifier is 8ohms. So you must have an 8ohm speaker or higher to safely power it. For stereo operation, you cannot go below a 4ohm speaker cabinet for either channel.
Tube amplifiers have a different requirement and should only be connected to a speaker that matches the impedance selection set on the amplifier. That is a different subject though.
That being said ALL amplifiers have a minimum impedance that they can drive. In most consumer-grade amps, it is usually 4ohms. Given the THD ( total harmonic distortion ) rating that the specs state, I would venture a bet that the 150 watts and 75 watts respectively is because of the fact that they only showed you the max power it would produce, hence a higher THD. Powering an 8-ohm load out of the stereo out would simply cut your peak wattage in half and your THD would go from 10% to 4% or something like that. If you look at the back of the Power-Block, you will see next to each output that it says 8ohms MIN, or 4ohms MIN. This simply means that in Bridge mode, the MINIMUM impedance you can drive with that amplifier is 8ohms. So you must have an 8ohm speaker or higher to safely power it. For stereo operation, you cannot go below a 4ohm speaker cabinet for either channel.
Tube amplifiers have a different requirement and should only be connected to a speaker that matches the impedance selection set on the amplifier. That is a different subject though.
Securb
One of Jerry's Kids
I did not know the Power Block was stereo. You should be fine. It pushes stereo 75W RMS per side @ 4 ohms. That is fine going into each 8-ohm speaker if the cab is wired for stereo and the speakers are rated to handle the power. If it is not stereo you can retrofit it with a Marshall jackplate, you can find them on eBay. I did this with my 2x12 to give me 150 watts @ 8 ohms per side for my JC 120 head, I flip the switch and run it in mono for my Marshall.
maug2122
New member
I have two Crate Power Block , one is going into a early1980's Laney half stack loaded with two Fane and two Celesion Greenbacks.
The other CPB is going to a old Peavey 2x12 loaded with Sheffield speakers.
Both Crate Power Blocks are hitting my cabs with 150 watts each.
The other CPB is going to a old Peavey 2x12 loaded with Sheffield speakers.
Both Crate Power Blocks are hitting my cabs with 150 watts each.
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