I have three points to make. First is that it doesn't actually matter what impedance you choose because the level that you hear will ultimately be based on on the current through the coils from F=BIL. So if you have identical 8 and 4 ohm units, they will have different nominal efficiencies for 2.83V, but they will have the same output for a given amount of current. Second, it is perhaps not a question of whether USB has been implemented correctly but, if it has not, whether the components inside can bear the extra current draw. I don't know what the output impedance of a USB port is but those peak draws will anyway initially come from your reservoir caps so I would have thought that averaging out the demand with larger caps was probably critical to keeping the average draw down. Thirdly, and I think this hold the solution to your implementation, is to remember that efficiency and lf bandwidth trade off against each other. So if you find some super efficient units with low mass and high B field then you prpobably going in the right direction. Because efficiency is also related to acoustic impedance the larger the surface area the better. This could mean a 2 or 3 inch tweeter - which is no bad thing - and a 4 or 5 inch bass, in some very light paper. Another root to this might be to do a mini folded horn.
Edit
I did mean to mention that, notwithstanding ther above, the boosted supply idea is a good one. Delta I will be lower and so will losses.
Edit II. Delta I will be the same cos it's at the lower V. Losses will be lower though.
Hope this helps
Edit
I did mean to mention that, notwithstanding ther above, the boosted supply idea is a good one. Delta I will be lower and so will losses.
Edit II. Delta I will be the same cos it's at the lower V. Losses will be lower though.
Hope this helps
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