Amplifier Power and Speaker Loudness - Why does 15W sound louder than 60W?

[tscan]

Hello everyone, I'm running into a problem that I can't seem to find the answer to. I have a 2x15W amp that gets much louder than a 60W mono amp. The 2x15W amp is pushing two 8 ohm speakers. The 60W mono amp is pushing one 4 ohm speaker. I have them both in sealed boxes and you would think that the 60W would be significantly louder than the 2x15W but that just doesn't seem to be the case. I know double the power does not equal double the loudness, but from everything I've seen the 60W should be about 20% louder than the 2x15W. I have no way to accurately test the power of either amp, but during low bass tones I never see my power supply pull more than 1A @ 19V when using the 60W amp. This would lead me to believe that it isn't operating near its rating?

I have the 2x15W amp connected to two ND90-8. The 1x60W amp is connected to one RS100-4. The RS100-4 is a more efficient speaker than the ND90-8 so none of this is making any sense. Is my 60W mono amp not really a 60W mono amp?

2 x 15W Amp: http://www.parts-express.com/sure-el...-only--320-330

1 x 60W Amp: http://www.parts-express.com/wondom-...bles--320-3519

I am running the Wondom board in mono mode because I ordered it directly through them in PBTL configuration. This lets you do one speaker at double the power.

Any idea what is going on?

[kevintomb]

This is what we call "Apples versus Oranges"

You are comparing things, with too many differences, to isolate down to just one thing.

Input sensitivity, different speakers, and a few other things factor in.

[mzisserson]

This is what we call "Apples versus Oranges"

You are comparing things, with too many differences, to isolate down to just one thing.

Input sensitivity, different speakers, and a few other things factor in.

Ill second this. Way too many variables. Sometimes increased distortion will make sound seem louder. If the 2x15 is running at 8 ohms. You are likely getting nowhere near full-band 15Wrms with even a couple of dB overhead, so what may seem "loud" is your impression of higher distortion. All to many times we blame speakers for ills of the system as a whole.

[Millstonemike]

The gain on the 60w amp is set to 20dB. If you using the AUX input with a mp3 player or phone, your not driving it with a strong enough signal to realize the full power out. If so, try using a PC to drive it, the volume should go up with the stronger signal.

BTW: it's not really a 60w amp, maybe 40w rms in PTBL mode at 19v with the RS100-4 ).

[tscan]

The gain on the 60w amp is set to 20dB. If you using the AUX input with a mp3 player or phone, your not driving it with a strong enough signal to realize the full power out. If so, try using a PC to drive it, the volume should go up with the stronger signal.

BTW: it's not really a 60w amp, maybe 40w rms in PTBL mode at 19v with the RS100-4 ).

I'm actually using the onboard bluetooth. Is there any way to increase that signal? The onboard aux creates a terrible ground loop. Why are you saying that it's not really 60W with that speaker?

[Millstonemike]

I'm actually using the onboard bluetooth. Is there any way to increase that signal? The onboard aux creates a terrible ground loop. Why are you saying that it's not really 60W with that speaker?

The wattage rating in the ad is not qualified. Many budget amps list peak music power and other "nefarious" ratings - marketing hype. When you see a spec such as "100w rms into 8 ohms with <0.1% THD", then you have a qualified power rating for an amp. The most power you can get with a 19v PS is nominally ~45w rms into 4 ohms - physics.

The BT module should be driving the chip to full power. Other's have used this amp without issue. I would double check the mono mode wiring, perhaps independently wire the RS100 on each channel as a test - the manual isn't very clear on mono mode. In fact the way, I read the manual, I believe it is wrong in that regard. The 2x30w board uses the TI TPA3118 chip. I've have successfully used its sister chip, the TPA3118, in mono PTBL mode. That's the same chip used on the Sure 2x50 BT amp and the chips are essentially the same except for thermal dissipation.

[tscan]

The wattage rating in the ad is not qualified. Many budget amps list peak music power and other &quot;nefarious&quot; ratings - marketing hype. When you see a spec such as &quot;100w rms into 8 ohms with <0.1% THD&quot;, then you have a qualified power rating for an amp. The most power you can get with a 19v PS is nominally ~45w rms into 4 ohms - physics.

The BT module should be driving the chip to full power. Other's have used this amp without issue. I would double check the mono mode wiring, perhaps independently wire the RS100 on each channel as a test - the manual isn't very clear on mono mode. In fact the way, I read the manual, I believe it is wrong in that regard. The 2x30w board uses the TI TPA3118 chip. I've have successfully used its sister chip, the TPA3118, in mono PTBL mode. That's the same chip used on the Sure 2x50 BT amp and the chips are essentially the same except for thermal dissipation.

If I have a 19V @ 5A power supply then why would you not be able provide 60W? Even at 90% efficiency I should be fine yeah? I would still expect a large amount of distortion out of the RS100 at max volume given that the power rating is 30W but it doesnt even seem like its being pushed to its max.

[djg]

The THD % is given at 10 watts output, at 1 khz only, the classic earmark of dodgy specs. The power spec does not specify what THD % is, and at what range of frequencies. A hifi spec would be, as mentioned above, 30 watts @ 8 ohms, at whatever THD %, from 20 to 20,000 HZ. This amp can out put 30 watts / channel at some frequency at some level of distortion. The 30 is essentially a meaningless number.

[gdmoore28]

The THD % is given at 10 watts output, at 1 khz only, the classic earmark of dodgy specs. The power spec does not specify what THD % is, and at what range of frequencies. A hifi spec would be, as mentioned above, 30 watts @ 8 ohms, at whatever THD %, from 20 to 20,000 HZ. This amp can out put 30 watts / channel at some frequency at some level of distortion. The 30 is essentially a meaningless number.

djg is giving you the straight scoop. Bottom line is in the specifications that most manufacturer's DON'T tell you.

[Millstonemike]

If I have a 19V @ 5A power supply then why would you not be able provide 60W? Even at 90% efficiency I should be fine yeah? I would still expect a large amount of distortion out of the RS100 at max volume given that the power rating is 30W but it doesnt even seem like its being pushed to its max.

Your power supply can supply the juice, but there are other limiting factors.

The nominal power output per channel is ultimately limited by the supply voltage (19v in this case) and the impedance of the speaker (4 ohms). The nominal rms power rating for a given supply voltage into a speaker of X ohms is (in BTL mode as with this amp):

W rms = (V² / 2) / X ohms = (19²/2) / 4 ohms = 45.125w

Of course, the PS has to have the current capability as you mention (weakest link in a chain).

The amp's digital chip is rated at 30w +30w rms. This is a thermal limitation of the TPA3118 chip - the amount of heat it can dissipate. The chip is designed to dissipate heat via the PCB's copper ground plane. It's sister chip, the TPA3116 actually has a pad on top of the chip to attach a finned heat sink. This facilitates its higher heat dissipation rating of 2 x 50w or 1x100w. Both these chips can output there maximum power rating given a sufficient PS voltage at less than 0.5% THD.

The 60w rating in mono mode, is the same heat dissipation maximum as 2x30w. However, the amps mono mode (unlike bridgeable car amplifiers) is simply alternating the use of each channel to allow one speaker to draw the heat dissipation rating of both channel's. You'll still only get a maximum of 45.125w rms into the same RS100-4 at 19v.

It doesn't appear that the board makes use of the chip's built in PBTL (e.g., mono mode) capability where both outputs are tied together in parallel (R+ to L+ and R- to L-). That's why the manual says to connect to R+ and L- for mono mode (not ideal).

This is probably not your problem, your not getting 45w given your initial description, something else seems wrong. Please try driving the RS100 with only one channel instead of the mono mode wiring to eliminate that as a the cause. We've seen issues with other chip amps using this R+ & L- mono mode kluge (sometimes works but not ideal).

If the output doesn't improve with using a single channel, then I would eliminate the BT section as the cause. I would try to drive the AUX input with a PC line out as my next test (not an mp3 or phone as the source).

[Pete Schumacher]

Could be that the 4 Ohm speaker has a sensitivity that is lower than the 8 Ohm speakers.

Two 8 Ohm speakers will have 3dB more output than a single 8 Ohm speaker, and if each is more sensitive than the 4 Ohm speaker, you get a BIG increase in output per watt making the 15W seem like much more.

Put the 8 Ohm speaker on the 60W amp and see how it compares with the 4 Ohm speaker.

[tscan]

Your power supply can supply the juice, but there are other limiting factors.

The nominal power output per channel is ultimately limited by the supply voltage (19v in this case) and the impedance of the speaker (4 ohms). The nominal rms power rating for a given supply voltage into a speaker of X ohms is (in BTL mode as with this amp):

W rms = (V² / 2) / X ohms = (19²/2) / 4 ohms = 45.125w

Of course, the PS has to have the current capability as you mention (weakest link in a chain).

The amp's digital chip is rated at 30w +30w rms. This is a thermal limitation of the TPA3118 chip - the amount of heat it can dissipate. The chip is designed to dissipate heat via the PCB's copper ground plane. It's sister chip, the TPA3116 actually has a pad on top of the chip to attach a finned heat sink. This facilitates its higher heat dissipation rating of 2 x 50w or 1x100w. Both these chips can output there maximum power rating given a sufficient PS voltage at less than 0.5% THD.

The 60w rating in mono mode, is the same heat dissipation maximum as 2x30w. However, the amps mono mode (unlike bridgeable car amplifiers) is simply alternating the use of each channel to allow one speaker to draw the heat dissipation rating of both channel's. You'll still only get a maximum of 45.125w rms into the same RS100-4 at 19v.

It doesn't appear that the board makes use of the chip's built in PBTL (e.g., mono mode) capability where both outputs are tied together in parallel (R+ to L+ and R- to L-). That's why the manual says to connect to R+ and L- for mono mode (not ideal).

This is probably not your problem, your not getting 45w given your initial description, something else seems wrong. Please try driving the RS100 with only one channel instead of the mono mode wiring to eliminate that as a the cause. We've seen issues with other chip amps using this R+ & L- mono mode kluge (sometimes works but not ideal).

If the output doesn't improve with using a single channel, then I would eliminate the BT section as the cause. I would try to drive the AUX input with a PC line out as my next test (not an mp3 or phone as the source).

I am unable to try just one channel. The board comes wired differently from Sure Electronics and I have no way to turn PBTL mode on or off unfortunately. Currently I have R+ and R- tied together and L+ and L- tied together. If I try to use just R+ and R- I get no sound. R+ and L- doesn't seem to yield a higher output.

[Sydney]

You can use a test signal of known level ( CD or download ) to feed the amplifier.
Measure the output voltage and compare the ratio ( However there can be differences in input sensitivity ).

[Millstonemike]

I am unable to try just one channel. The board comes wired differently from Sure Electronics and I have no way to turn PBTL mode on or off unfortunately. Currently I have R+ and R- tied together and L+ and L- tied together. If I try to use just R+ and R- I get no sound. R+ and L- doesn't seem to yield a higher output.

Yes, the amp doesn't support the TPA3118 built in PTBL mode. R+ & R-, :+ & L- tied together doesn't make sense to me - that's shorting each channel's speaker outputs. You may have a bad channel.

[tscan]

Yes, the amp doesn't support the TPA3118 built in PTBL mode. R+ & R-, :+ & L- tied together doesn't make sense to me - that's shorting each channel's speaker outputs. You may have a bad channel.

The product page says to connect both of them together for best efficiency:
PBTL (Mono) Mode Configurable
The JAB series amplifier boards offer the feature of parallel BTL operation with two outputs of each channel connected directly. To operate in this PBTL (mono) mode, apply the input signal to the RIGHT input and place the speaker between the LEFT and RIGHT outputs. Connect the positive and negative output together for best efficiency.

Here is where I took that from: http://store3.sure-electronics.com/aa-ja32472-1751

When I play a left right test I hear both the left and right come out of the single speaker so I don't think I have a bad channel?