Extension Speaker Jack questions - NUBIE

[HackRabbit]

I have been a lurker at this site for a while and I have learned a great deal; but as you will see from my questions, I am just not that smart.

I have a Blackface Fender Bassman head.
On the back there is a 'speaker' jack and an 'extension speaker' jack.
It is my understanding that the 'speaker' jack should be connected to a 4-ohm speaker cabinet configuration.

Here are my questions:
1.) If connecting to both 'speaker' jack and an 'extension speaker' jack to separate speaker cabinets. What should the ohm of each cabinet be?

2.) I understand that head generates more than 50 watts.
For the sake of argument, assume the head generates a maximum of ~50 watts. When two identical 50-watt 4-ohm cabinets are connected to the head, one cabinet using the 'speaker' jack and the other cabinet an 'extension speaker' jack; does that mean each cabinet is 'sent' ~25 watts each? Or is the wattage ratio 'drawn' based on the speaker cabinet configuration criteria?

3.) I understand that cutting the wattage in half does not cut the volume in half. Is it possible to reduce the volume a tad by connecting the 'extension speaker' jack to a dummy load of the proper wattage and impedance? Using the prior example, connecting a 50-watt 4-ohm cabinets to the head using the 'speaker' jack and connecting a 50-watt 4-ohm dummy load to the 'extension speaker' jack; will that cut the wattage going to the actual speaker cabinet in half or are the electronics more complicated than that? If so, will the volume reduction be noticeable?

Thank you in advance.

['67_Plexi]

I have been a lurker at this site for a while and I have learned a great deal; but as you will see from my questions, I am just not that smart.

I have a Blackface Fender Bassman head.
On the back there is a 'speaker' jack and an 'extension speaker' jack.
It is my understanding that the 'speaker' jack should be connected to a 4-ohm speaker cabinet configuration.

Here are my questions:
1.) If connecting to both 'speaker' jack and an 'extension speaker' jack to separate speaker cabinets. What should the ohm of each cabinet be?

2.) I understand that head generates more than 50 watts.
For the sake of argument, assume the head generates a maximum of ~50 watts. When two identical 50-watt 4-ohm cabinets are connected to the head, one cabinet using the 'speaker' jack and the other cabinet an 'extension speaker' jack; does that mean each cabinet is 'sent' ~25 watts each? Or is the wattage ratio 'drawn' based on the speaker cabinet configuration criteria?

3.) I understand that cutting the wattage in half does not cut the volume in half. Is it possible to reduce the volume a tad by connecting the 'extension speaker' jack to a dummy load of the proper wattage and impedance? Using the prior example, connecting a 50-watt 4-ohm cabinets to the head using the 'speaker' jack and connecting a 50-watt 4-ohm dummy load to the 'extension speaker' jack; will that cut the wattage going to the actual speaker cabinet in half or are the electronics more complicated than that? If so, will the volume reduction be noticeable?

Thank you in advance.

Hi,

Just because you don't know the answers to the questions doesn't mean you are not smart. There's no such thing as dumb questions only dumb people that won't ask qustions.


1) The outputs on your amp are paralleled together meaning they are connected to the same tap. This means the total speaker load the amp should drive is 4 ohms. Two 8 ohm speaker cabs in parallel would give you 4 ohms. That said I've seen many instances where these Fender amps have driven the stock 4 ohm speaker plus say a 16 ohm or even an 8 ohm cab as well. Tube amps are a little more tolerant about driving a LOWER impedance load than they are a higher impedance load. The exact opposite to a solid state amp. Whenever you drive a different load than the tap is designed for, apart from risking saome issues, the frequency response of the amp changes, as does the feel of it.

2) The power distribution depends on the loads. Electricity always prefers to take the path of least resistance. So more power will distribute through a lower load than a higher one. If the output power is 50W and the load of each speaker is the same, then yes basically 25W will be distributed to each speaker. In reality it is a little more complex because we are dealing with AC signals, not DC. What this means is that the impedance of the speaker 'seen' by the amp isn't a constant figure but changes quite dramatically depending on the frequency of the signals. Impedance is AC resistance and is a product of DC resistance, Capacitive Reactance and Inductive Reactance. Both reactances have a frequency dependant component to them , so because not every speaker is exactly the same the power distribution may not be exactly 50/50. Bottom line is give yourself a bit of room by having speakers that can handle more than half of the output power of the amp.

3) Yes, but you will affect the feel of the amp. Because part of the power is being distributed in to a purely resistive load, that means that regardless of frequency that dummy load is always a contant impedance. For a purely resistive load, Impedance = DC Resistance. You could use an attenuator designed to emulate the response of a speaker.

As a side note wattage and volume (sound pressure) are not the same. Related yes, but not the same. The amount of sound pressure you hear also depends on the sensitivity of the speaker. A speaker with 100dB sensitivity only requires half the power a 97dB speaker would to acheive the same sound pressure (Volume).

Alan.
Carol-Ann Amps.

[HackRabbit]

Alan.
Thank you so much for taking the time to response.
Your response has answered my questions.
Again thanks,
Peter