Does impedance matter or the load matters more ?

[jst]

Does impedance matter or the load matters more ?

Here's the system I use :
- 2.1 amplifier kit, tpa3116d2 (ZK-TB21) , with 19volt vaio adapter (7Amperes).
- Satellite : 4 inch Full Range open baffle (8 ohm) and a tweeter (8 ohm)
- Subwoofer : Double coil 6 inch with Miniscoop box design, it can be set to 2 ohm parallel both coils, 4 ohm using only one coil, 8 ohm using series.

I usually use 4 ohm with ony 1 coil, but yesterday I watched a video about test load to tpa3116d2 and it can draw 72 watt of power at 2 ohm iirc.
At my usual listening volume with subwoofer set at 4 ohm using only 1 coil, it's already quite loud, it only draws 2-4 watt of power (checked using both dc and ac watt meter).
Since 2-4 watt of power is FAR from 72 watt which this chip is capable of, today I changed my sub to 2 ohm and connect the double coils in parallel.

With that being said, my question is with the subwoofer. I use this system as my pc's multimedia speakers so it's left ON the whole day from the moment I wake up till I sleep, so around 16h a day. Will changing the sub to 2 ohm stress the system too much for both the amp and the speaker ? Because at 2 ohm I notice the load is still FAR from 72 watts which it's capable of, which is only 2-8 watts now. Mostly only 4. It doesn't seem much difference from 4 ohm before, but the sub sounds noticeable stronger.

I'm fine with the wear and tear but I dont want it explode at random time, and ppl seem to emphasize that 2 ohm is dangerous. So is it the load that matters or the impedance ? Because the amp is not even warm, only slightly just like usual when it was set to 4 ohm.

 

[solderdude]

mains power meters don't measure short peaks very well.
To judge how much power is present you need a real peak meter or O-scope on the actual output of the amp.
That is a bit tricky because these amps are usually balanced.

 

[SSS]

Use what sounds best. I don't think that the amp will be overloaded at medium listening levels. At high levels the question is whether the amp can deliver the needed current which is of course more compared to the 8 ohm circuit. At the 8 ohm circuit the coils are in series which means that the voice coil damping may be different which explains that the 2 ohm version sounds better.

 

[wwenze]

Since you don't intend to change the loudness of your sub, the power that goes into the sub is going to be the same anyway. So the load impedance arrangement only decides the ratio of current and voltage that you need to get that same loudness.

Anyway most typical amplifiers are designed to work best with one particular load impedance, and in the case of home speakers and amplifiers that value is 8 ohm for lower distortion and 4 ohm for more power. You can see the reviews on this site for confirmation. Note that going even less ohms will not further increase the maximum power available from the amp, but will instead reduce it.

 

[audio_tony]

I performed some power tests on a generic TPA3116D Class D board.
Results:
At 20v 2amps it produced 34w into 4 ohms (resistive load) at the onset of (visible) clipping @1kHz (so probably 1% or so THD)
At 25 volts 2.7 amps it produced 59 watts into 4 ohms (load as above)

I didn't try a 2ohm load.

According to the datasheet, my measurements vs PSU voltage are pretty close.

Additionally - running it into a 2 ohm load appears to require a pre filter (PBTL mode)

 

[jst]

mains power meters don't measure short peaks very well.
To judge how much power is present you need a real peak meter or O-scope on the actual output of the amp.
That is a bit tricky because these amps are usually balanced.

For the oscilloscope, tpa3116d2 is quite common and there are ppl that measure it using oscilloscope on youtube, and it can provide around 72 watt at 2 ohm iirc. That's why I use that 72 watt as a guideline, since my normal listening volume's load is only less than 10 watt then I think this 2 ohm is still safe and still far within the limit, but need confirmation if my method can be used to judge whether it's safe or not.

Use what sounds best. I don't think that the amp will be overloaded at medium listening levels. At high levels the question is whether the amp can deliver the needed current which is of course more compared to the 8 ohm circuit. At the 8 ohm circuit the coils are in series which means that the voice coil damping may be different which explains that the 2 ohm version sounds better.

Yea, I think I'll use this 2ohm for now and see for later, that's also what i thought but not quite sure.

There are many videos on youtube that show this chip tpa3116d2 can provide close to spec which is 50 50 for stereo or 100 for mono, and since my load even with 2 ohm is only less than 10 watt, I assume that it's safe, can I assume it like that ? Because 10 watt is far from the spec and at average it's even less than 5 watt.

 

[jst]

I performed some power tests on a generic TPA3116D Class D board.
Results:
At 20v 2amps it produced 34w into 4 ohms (resistive load) at the onset of (visible) clipping @1kHz (so probably 1% or so THD)
At 25 volts 2.7 amps it produced 59 watts into 4 ohms (load as above)

I didn't try a 2ohm load.

According to the datasheet, my measurements vs PSU voltage are pretty close.

View attachment 401055

Additionally - running it into a 2 ohm load appears to require a pre filter (PBTL mode)

View attachment 401056

If my listening volume's load is only less than 10 watt, fluctuating from 2-8 watts, then can I assume it's safe as i use it now even with 2 ohm ? even if your measurement is halfed, my listening volume is still below it so it should be safe, right ?

Yea, I only run 2 ohm for the sub, and the sub is pbtl, I think, coz the wattage is doubled from 50, pbtl becomes 100watt

Thanks , it's safe then, because the pbtl even can go to 1.6 ohm minimum from your image

 

[wwenze]

Just use a 0dBFS sine wave of your preferred frequency and measure it at your preferred volume knob position. Any music will mathematically have to use less power than that.

With PBTL the "preferred" impedance of the amp is the value of the single amp divided by how many amps get paralleled. For the specific case of TPA3116D, 4ohm is the preferred impedance for lower THD at higher power. And if you're PBTL-ing it the preferred impedance drops to 2ohm. It's all good.