You would actually get better performance by cutting the Bass below ~100hz.
Trying to reproduce Frequencies below 100hz with a tiny Speaker will just result in lots of Distortion.
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Before getting the last response, I did tune my circuit to make the RC filter formula equal to 7.2 Hz. Experimentation leads me to think C1 and R7 make a high-pass filter. Maybe I am better off to take new advice of setting a higher cutoff frequency because when I used some cheaper speakers (about the size of 3 loonies stacked like pancakes), you can't really hear bass.

 

As I have been telling you since post 2. You will also blow that speaker up if you feed it more than about 1W of power. Your project is doomed without a better speaker. You can't turn a sows ear into a silk purse.

 

You will also blow that speaker up if you feed it more than about 1W of power. Your project is doomed without a better speaker.

Even when my speaker I'm using is rated at 4.5W 8 ohms?

 

The power ratings on cheap speakers like that are pure fiction. It might be able to handle 4.5W for a fraction of a second at sone frequencies, but not continuously.

You still haven’t told us how you intend to use it, what sounds it will be producing, so it is hard to tell what might be needed.

 

Do the Specs on your Speaker say 4.5-Watts-RMS Power Handling ?,
if it doesn't, then they are talking about "Music-Power", usually measured at ~1000hz,
which is really just 2X the real RMS Power, ( but only when they're being honest and feeling generous ),
and, of course,
China has their own special rating system that starts-out at 100-Watts, and goes all the way to 10,000-Watts,
( just subtract 3-decimal-places to decode the Chinese-Power-Rating-Method ).
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I got another thing on my plate before speakers. I'm trying to get at least 7V P-P if possible using most common components. So I changed the pre-amp to a common-base configuration but it seems my values are way off because the waveform is flat at top and not
proper at the bottom. When I increase R7, the top of the waveform looks better but the bottom looks like it could be sortof more pointier. Is there some equation I should be aware of for a common-base amplifier? It would be nice if I can take an input voltage of say 1V p-p (or lower) and make the output waveform a perfect copy of the input waveform but larger so it's 7V p-p.

 

You use only one slow diode for D1 instead of two fast diodes. Then at low levels there is crossover distortion that sounds like buzzing:

I don't see the need for fast diodes - normally the bias voltage has a capacitor across it to keep the voltage stable.
Voltage drop is important, and the random difference between diode voltage and Vbe means that the bias setting is also fairly random. Three diodes would be better, with emitter resistors each dropping about 0.3V means the bias could be set more accurately, but at the expense of another 0.3V loss from the output.

 

The other day when I presented high value capacitors, you told me they're too high. So you're saying the 100 ohms + 22uF capacitor make up a high-pass filter?

Calculate it yourself f=1/(2πRC)

Wouldn't the 1N914's or 1N4148's more likely to blow up compared to the 1N4007's? I mean to get max voltage peak-to-peak I probably will be using more current.

No, there is very little current through that part of the circuit - output current divided by Hfe

capacitor that connects to the speaker? Then I'm asking to use a bit too much current and possibly transistors that will go as hot as an oven goes when a thanksgiving turkey is 100% done.

Nonsense - 90% of amplifiers are designed that way.

 

You are using a low current 8 ohm speaker. Car speakers are 4 ohms for double the power.
With a 14.4V supply, the peak voltage in the 8 ohms is about 6.5V then the peak current in each output transistor is 6.5V/8 ohms= 813mA. The minimum hFE of the output transistors is 25 then the base current of the output transistors is 813mA/25= 32.5mA. The peak current in the biasing diodes is a little less at about 20mA. The maximum allowed peak current in a fast 1N4148 diode is 200 to 400mA. Then you do not need very slow very high current 1N4007 rectifier diodes for biasing.

A speaker needs to have an enclosure designed for the detailed spec's of the speaker. A small speaker produces not much bass but when in a ported enclosure the bass from a half-decent 4" speaker can be very good down to 55Hz and lower frequencies are produced but mot as loud.

Get rid of the new common-base input transistor.
There is high distortion because the AC negative feedback through R9 is killed by R11 and R6.
Of course the capacitor in series with R7 makes a highpass filter even when the capacitor in the previous negative feedback loop is grounded.

Here are the spec's of a half-decent 4" speaker that costs only as much as one meal in a restaurant:

 

I'm trying to see if I can simulate the push-pull action by changing V3 from 0.01V to 2V (2V being the biggest positive value of the peak) and it seems like the voltage offsets are close to 0.7 in each instance. Maybe these waveforms are correct?

And I still can't figure out how exactly to calculate the output wattage. I want to use LTspice to pick up the largest current so I can multiply by voltage to get wattage.

 

Bootstrap capacitor C2 uses the output AC voltage swing to "boost" the voltage at the base of the TIP41 to be above the positive supply voltage. Then the positive output voltage can swing very close to the positive supply voltage. The output cannot swing close to ground because the emitter voltage of the TIP42 PNP output transistor is about 0.8V more positive than its base.

You should look at the DC output of the amplifier to see the DC voltage swings, not the AC output at the speaker.

To calculate the output power the output signal should have no distortion. Then divide the peak-to-peak output voltage by 2 times the root of 2 (2.828) to find the RMS voltage. Then square the RMS voltage and it is divided by the speaker impedance (8 ohms) to calculate the true continuous low distortion output power.

Feeding 2VDC to the base-emitter of a silicon transistor will very quickly destroy it. The simulation software knows nothing about things that are severely overloaded like that.

 

ok so I am getting cleaner output here.

Then divide the peak-to-peak output voltage by 2 times the root of 2 (2.828) to find the RMS voltage. Then square the RMS voltage and it is divided by the speaker impedance (8 ohms) to calculate the true continuous low distortion output power.

So I'm guessing p-p output voltage here is 13? (14 for the top part of the wave, and 1 for bottom part and subtract the 2?)

So 13 divided by 2 times 2.828 = 18.382 (RMS voltage)
Then 18.382 squared divided by 8 = 42.23W?

Wait.... don't my resistors have to be 10ths of ohms to draw 42 watts? Your math or something is throwing me off...

 

No and no.
1) The peak-to-peak is 14V - 1V= 13V.
2) 2 times the root of two is 2.828.
3) 13Vp-p/2.828= 4.6V RMS.
4) 4.6V squared= 21.16, divided by 8 ohms= 2.65W.

Now use a bridged amplifier like in a car radio. A bridged amplifier is 2 amplifiers, an amplifier for each speaker wire but one amplifier inverts the signal then the speaker gets almost double the output p-p voltage and almost double the current.
Then the max undistorted power into 8 ohms when the supply is 14.4V is about 9.3W or about 17W into a 4 ohms speaker.

You probably do not need R11. Bias the output to be near half the supply voltage by adjusting the value of R9.

 

That should be enough to blow the Voice-Coil straight out through the center of the Cone of that 4.5" Speaker.
You had better roll-off the Bass response really hard if You expect the Speaker to survive.
But at least You won't have to worry about "Clipping" the Signal.
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The cheap 2.5 inch "2W" speaker has absolutely NO audio specs and NO manufacturer's name. If it is true, The "2W" is the maximum amount of heating it can survive.
Bass will not hurt it since its suspension is very stiff, and its cone does not move much at low frequencies.

The 4 inch 10W speaker costs 4 times as much but it also produces no bass. It has a cheap foam surround that fails soon.

 

I'm probably better off avoiding the bridge and accepting the 2.6W output because I am on a budget. and doing the bridge will take almost double the parts and likely double the heatsinks and of course better speakers.