The difference in volume of your amp into a 4Ω load from an 8Ω load will be hardly noticeable. You don't need to get every last watt out of your amp.
Perhaps this will be even more helpful. If you have an low powered amp that is rated for 4 ohms minimum. The way to maximize performance is to used two identical 8 ohm speakers instead of one 4 ohm speaker. A solid state amp will typically make more power with the 4 ohm speaker, bit often the 4 ohm speaker will be slightly less efficient than the 8 ohm speaker.
When you pair cabs that are identical, you get acoustic coupling in the low end. Near perfect acoustic coupling occurs across the frequency range in which driver spacing is within approximately 1/4 wavelength. Essentially this helps the drivers couple to the air more efficiently, so they produce more SPL. The general rule is adding a second speaker will give you +6dB over the SPL one speaker would make with available power. But we need to keep in mind when we hook up the second speaker, the power sent to the first speaker usually drops.
With a tube amp the total power remains the same as long as the amp sees the expected load. This means when you plug the second speaker in, the power will be split equally between the two 8 ohm speakers. So if you start with 300W, each speaker will get 150W. Here is a rule:
When power is cut in half, SPL drops by -3dB. When power is doubled SPL increases by +3dB.
Let's assume the speakers have 97dB sensitivity rating.
With one speaker receiving 300W the SPL =122dB
When you add the second speaker the power is split evenly between the speakers
With one speaker receiving 150W the SPL =119dB
Then when you have both speakers packed together, you get +6dB from mutual coupling.
119+6dB=125dB
So you see, you get a net +3dB if the total power remains the same when you add the second speaker. The SPL of the first speaker dropped -3dB when the power was cut in half, but then mutual coupling with the second speaker provided +6dB. So the net is -3+6=+3dB
If you have a solid state amp that can double the power when the load drops from 8 to 4 ohms, you get to entire +6dB from mutual coupling. The power doubles, but is then split evenly between both speakers. So the first speaker continues the receive the same power when the second speaker is added.
Since most solid state amps don't double the power when the load drops from 8 to 4 ohms. Expect to get +3- to 5dB
Let's do the figures for the OP's amp
44W at
96dB sensitivity = 112dB
This is for one 4 ohm speaker with a slightly lower sensitivity rating than the 8 ohm speaker
33W at
97dB sensitivity = 112dB
This is for one 8 ohm speaker
22W at 97dB = 110dB+6dB=116dB
This is for two 8 ohm speakers splitting 44W. The 110dB is the SPL of one speaker at 22W. The +6dB is the gain in efficiency from mutual coupling.
Notice the single 4 ohm speaker is not louder than the single 8ohm speaker. This is partly because the 8ohm speaker has a 1dB higher sensitivity rating. Also the dB difference from 44W to 33W is only about 1.24dB, so the amp was barely able to make up the difference in the lower sensitivity of the 4 ohm driver. In this case there is no benefit to running the amp at 4 ohms. Also the amp will be more stressed at 4 ohms, so maybe you're better off running the 8 ohm speaker.
Another rule:
It's generally accepted that the smallest change in SPL you can hear is 3dB. Taken in context with the previous rule on power doubling: If the 4 ohm speaker has the same sensitivity rating as the 8 ohm speaker and the amp doubles power when the load is dropped from 8 to 4 ohms, you will barely hear a difference (+3dB).
Notice the dual 8 ohm setup is 4dB louder than the single 8 ohm setup (116-112=4), and it is 4dB louder than the single 4ohm setup (116-112=4).
Also, because perfect acoustic coupling only occurs in the low end, using a second speaker will sound fuller in the low end. Ask yourself if this is desirable.
Many people wind up buying a 4 ohm speaker, with the idea of getting maximum power from their amp. Later when they don't have enough headroom they don't have the option of using an extension speaker to further expand the capabilities of their rig.
I used the Watts to dBm calculator for dB conversions.
Watts to dBm conversion calculator You can not use the calculator directly because it is set to calculate dBm not SPL (dB). Here is how I fudge the math, since I don't know how to actually do it.
In the calculator, 1 Watt = 30dBm. So to figure out how loud a speaker will play, you need to know the speakers sensitivity at 1W. Input the amp's wattage at the speaker's impedance into the calculator and subtract 30 from the figure. This is calculating the decibel difference which is the same for SPL and dBm. Finally, add the result to the speaker's sensitivity rating.
For example. Your amp will make 33W at 8 ohm. 33W is 45.185dBm per the calculator. I rounded this down to 45 and subtracted 30 = 15. This answer is the decibel chance from 1W to 33W (15dB). We were using a 97dB sensitivity rating, so add 97 to 15 = 112.
Speaker sensitivity ratings are typically expressed something like this:
Sensitivity 97dB 1w/1m. This means 1W was applied and the 97dB measurement was taken at a distance of 1 meter.
One thing to be careful of is sensitivity ratings are sometimes given at 2.83V instead of 1W. This makes the 4 ohm speaker appear to have a 3dB higher sensitivity rating because 2.83V at 4 ohms is 2W, and 2.83V at 8 ohms is 1W. Since you know that doubling the power results in a 3dB change, you can just subtract 3dB from the 2.83V at 4 ohm sensitivity rating to get the 1W sensitivity rating.
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