Polk PA4A Oscilloscope Testing

[Mainah]

Warning!!! Technical content contained within. Skip down to the Verdict section for the quick read.

Today I tested the stock Polk PA4a as a second step in tuning in my sound system. The first step was testing the outputs of the iPhone 7 I am using as the source. I did not grab shots from the iPhone but suffice it to say that that it put out a little less than 1 volt, has no clipping to the top end and is a very clean signal. This matches what labs have observed in their testing. The oscilloscope I am using is not lab grade but I did install custom firmware that I coded with a custom configuration for this purpose and then bench calibrated both the hardware and software. So again not lab quality but for this purpose already a bit overkill.

I tested the "front" RCA outputs with the speaker harness disconnected and everything set to flat except for the loudness which I had to turn on to get decent voltage out of the head unit. For all tests documented in this post the iPhone volume was turned up to max and I was using a professional calibrated signal generator app outputting a 1k sine wave test tone that yes I also tested and validated. My comments related to distortion are from observing the frequency and mvDC in real time (with a buffer). The more it fluctuates during the test the worse the signal and I did not turn on min/max/hold as I like to observe the change in more detail than the screen allows.

Bluetooth -
I have commented that my human ear observations had me believe that bluetooth in the headhunt was less than stellar and I was not wrong. The chipset is pre BT 4.1 so that is not very surprising. Even a clean 1k sine wave had distortion at the helm and got worse further away from the head unit. Clipping occurred above 95% head unit volume (1st screen shot is what clipping looks like, sawtooth pattern as opposed to wave). The max rms voltage with no clip was 2.32v.


USB-
I had commented that I thought USB to be best. I discovered there is slight distortion likely because the DAC chip the head unit employs causes it. The reason I may have thought this is because the headunit achieves 2.88v at 100% volume with no clipping.


Aux In-
Using the iPhone dongle (hate that it is even needed) I got a pure signal all the way up to 95% volume and 2.88v rms. Above 95% there was clipping.


Verdict-
2.88v was the max output voltage without clipping which is well shy of the perfect 3.7v rms with a 1k sine wave test tone. In other words not complete junk but not that good either. JL amps as as example will handle 4.0v rms without issue and since amp increase at a constant rate based on the gain a weaker input voltage means less output will be achieved. I am going to have to ponder what I am going to do about this wether that be getting a WS420, a completely different head unit or something else. In the mean time even though Aux In was proven best given slightly less distortion I am going to stick with USB as it is more convenient, will achieve the same max pre clip rms output voltage, and there is no clipping at 100% volume so can't go wrong by cranking it as long as the amps are tuned right. Bluetooth on the other hand will mean less volume without clipping and more distortion so while more convenient at times it is better not to play at high volumes with bluetooth on this unit.

Closing-
I am sure there are some experts that are going to poke holes in this. Keep in mind that there was more testing done but stopping and taking screen shots and then posting all of it takes time not to mention gets too deep in the weeds for most. Notice my other channels are set to off for these screen shots to keep things clean. I am not an engineer and just a guy with an electronics hobby. If I did make a major error please do let me know. Stay tuned for my JL amp tuning results with sound spectrum monitoring to fine tune and record db levels.

 

[Jaylex]

Kool info....I follow a lil more than half of the technical jargon, but follow the gist.

Interested to see the results of the JL amp for obvious reasons.

So usb will def be my new connection, charges too.

 

[swatski]

Warning!!! Technical content contained within. Skip down to the Verdict section for the quick read.

Today I tested the stock Polk PA4a as a second step in tuning in my sound system. The first step was testing the outputs of the iPhone 7 I am using as the source. I did not grab shots from the iPhone but suffice it to say that that it put out a little less than 1 volt, has no clipping to the top end and is a very clean signal. This matches what labs have observed in their testing. The oscilloscope I am using is not lab grade but I did install custom firmware that I coded with a custom configuration for this purpose and then bench calibrated both the hardware and software. So again not lab quality but for this purpose already a bit overkill.

I tested the "front" RCA outputs with the speaker harness disconnected and everything set to flat except for the loudness which I had to turn on to get decent voltage out of the head unit. For all tests documented in this post the iPhone volume was turned up to max and I was using a professional calibrated signal generator app outputting a 1k sine wave test tone that yes I also tested and validated. My comments related to distortion are from observing the frequency and mvDC in real time (with a buffer). The more it fluctuates during the test the worse the signal and I did not turn on min/max/hold as I like to observe the change in more detail than the screen allows.

Bluetooth -
I have commented that my human ear observations had me believe that bluetooth in the headhunt was less than stellar and I was not wrong. The chipset is pre BT 4.1 so that is not very surprising. Even a clean 1k sine wave had distortion at the helm and got worse further away from the head unit. Clipping occurred above 95% head unit volume (1st screen shot is what clipping looks like, sawtooth pattern as opposed to wave). The max rms voltage with no clip was 2.32v.
View attachment 70854 View attachment 70855

USB-
I had commented that I thought USB to be best. I discovered there is slight distortion likely because the DAC chip the head unit employs causes it. The reason I may have thought this is because the headunit achieves 2.88v at 100% volume with no clipping.
View attachment 70856

Aux In-
Using the iPhone dongle (hate that it is even needed) I got a pure signal all the way up to 95% volume and 2.88v rms. Above 95% there was clipping.
View attachment 70857

Verdict-
2.88v was the max output voltage without clipping which is well shy of the perfect 3.7v rms with a 1k sine wave test tone. In other words not complete junk but not that good either. JL amps as as example will handle 4.0v rms without issue and since amp increase at a constant rate based on the gain a weaker input voltage means less output will be achieved. I am going to have to ponder what I am going to do about this wether that be getting a WS420, a completely different head unit or something else. In the mean time even though Aux In was proven best given slightly less distortion I am going to stick with USB as it is more convenient, will achieve the same max pre clip rms output voltage, and there is no clipping at 100% volume so can't go wrong by cranking it as long as the amps are tuned right. Bluetooth on the other hand will mean less volume without clipping and more distortion so while more convenient at times it is better not to play at high volumes with bluetooth on this unit.

Closing-
I am sure there are some experts that are going to poke holes in this. Keep in mind that there was more testing done but stopping and taking screen shots and then posting all of it takes time not to mention gets too deep in the weeds for most. Notice my other channels are set to off for these screen shots to keep things clean. I am not an engineer and just a guy with an electronics hobby. If I did make a major error please do let me know. Stay tuned for my JL amp tuning results with sound spectrum monitoring to fine tune and record db levels.

Very informative - thank you for taking the time to run those tests and posting the results!

This is the kind of information that would make me switch to different system.

One aspect of this analysis is of particular interest to me. At the risk of sounding like a complete idiot, let me ask you this:
Does your testing tell us anything about the efficiency of generating clean sound in those systems?

For example, when comparing a system with amp A to a system with amp B (both class D) is there a difference between amps/output modes - say Polk vs JL amps, or USB vs BT outputs - in terms of efficiency of converting 12v current into Decibels of clean sounding music?

Your testing made me think that in addition to amplifier class and characteristic, the choice of output may also be important for energy efficiency of music reproduction.

Which can translate into less worries about battery power when hanging out and chilling on the water!

--

 

[bronze_10]

whoa!

 

[Mainah]

Very informative - thank you for taking the time to run those tests and posting the results!

This is the kind of information that would make me switch to different system.

One aspect of this analysis is of particular interest to me. At the risk of sounding like a complete idiot, let me ask you this:
Does your testing tell us anything about the efficiency of generating clean sound in those systems?

For example, when comparing a system with amp A to a system with amp B (both class D) is there a difference between amps/output modes - say Polk vs JL amps, or USB vs BT outputs - in terms of efficiency of converting 12v current into Decibels of clean sounding music?

Your testing made me think that in addition to amplifier class and characteristic, the choice of output may also be important for energy efficiency of music reproduction.

Which can translate into less worries about battery power when hanging out and chilling on the water!

--

Class D amps are not the best sounding but they are the most efficient. This is because of the how they amplify the music. Tuning for efficiency would require measuring current draw very accurately and is not something I plan to do as I don’t think there is much to be gained. Getting better, bigger, more batteries is the way to go if needed IMO.

For this season I had better not do anymore installs if I want to stay married but I am likely getting a WS 420 in the future.

 

[adrianp89]

Great info! I am shocked the radio is clean at that high of a level. What does 95% equate to on the volume knob? 42-43? I think that is important to note, as that is the most important factor here for tuning. It also shows, not much is to be gained by going another route, besides ease of use. The voltage is rather irrelevant if you have no noise in the system, and spending $500 to gain potentially one volt would not be worth it.

I just want to point out that wording can be a little tricky here. You can still obtain maximum output for your system on bluetooth, you should just tune below the clipping point. If that would be 43, than tune for your amps for 40 to account for poorly recorded music.

 

[Mainah]

Great info! I am shocked the radio is clean at that high of a level. What does 95% equate to on the volume knob? 42-43? I think that is important to note, as that is the most important factor here for tuning. It also shows, not much is to be gained by going another route, besides ease of use. The voltage is rather irrelevant if you have no noise in the system, and spending $500 to gain potentially one volt would not be worth it.

I just want to point out that wording can be a little tricky here. You can still obtain maximum output for your system on bluetooth, you should just tune below the clipping point. If that would be 43, than tune for your amps for 40 to account for poorly recorded music.

The Connext display shows gain as a percentage. I should correct the clean statement to include the the word relatively. The buffer setting I was using to observe the values and wave made it appear cleaner than it actually was but still relavant for comparing the different inputs. Also I was only testing the rca outs and I bet when I test the speaker level outs it is far from clean at high levels.

Voltage does matter when the amp inputs are analog. The amp is multiplying the voltage so a higher signal is better to a point. Class D amps are pwm so it is taking the sine wave converting it into a square wave amplifying the square wave and converting it back into a sine wave. With Bluetooth the max unclipped volatge was 2.32 and with USB and aux it was 2.88v. This is enough to make a difference.

One other thing I should mention is that the volume control is far from linear. Going from 80% to 95 % is almost double the voltage.

Most folks are not going to swap out their head unit especially given the connext intergration so more than anything I was trying to figure out the best source and at what point the clip occurs with each input. More to come testing the speaker outs as those with a bone stock system or powering some speakers from the headunit as I am currently will benefit from that.

 

[adrianp89]

Ah I have a cheap boat (so to say lol) so I control my volume through the Polk radio it's self, which just shows volume.

The voltage issue is age old debate. There was a very long and super informative thread over on DIYMA some time ago. I am not sure one conclusion was truley settled upon, but I firmly landed on the side that output voltage does not matter (as long as it's clean) because either way, the amplifier will work the same and efficiency is the same (when tuned accordingly). This was further enhanced with IASCA world champions using head units that only put out 2v. Great read if you have a few hours to burn one day. More importantly this data shows if you tune for BT, and you play USB or AUX, that you should be a hair more conservative on the volume. I think the BEST solution here is tune for USB, plug your phone in, and control your phone over BT through your watch for the flexibility.

 

[Mainah]

Ah I have a cheap boat (so to say lol) so I control my volume through the Polk radio it's self, which just shows volume.

The voltage issue is age old debate. There was a very long and super informative thread over on DIYMA some time ago. I am not sure one conclusion was truley settled upon, but I firmly landed on the side that output voltage does not matter (as long as it's clean) because either way, the amplifier will work the same and efficiency is the same (when tuned accordingly). This was further enhanced with IASCA world champions using head units that only put out 2v. Great read if you have a few hours to burn one day. More importantly this data shows if you tune for BT, and you play USB or AUX, that you should be a hair more conservative on the volume. I think the BEST solution here is tune for USB, plug your phone in, and control your phone over BT through your watch for the flexibility.

I certainly have more to learn when it comes to audio and I love learning. When it comes to an analog input being converted to PWM more resolution (voltage) is usually better when clean speaking form a pure circuity stand point. I certainly agree on plugging in the phone to usb and controlling from ones watch is the best case scenario for quality and human interface. The only downside is needing that phone to take photos.

 

[swatski]

Man, what an awesome discussion! I want to chew on that for a couple of days, but I think I can understand some of it, actually!

--

 

[Jgorm]

Cool info. I wonder what it does at 50 and 100hz where you really need some serious output power.

 

[jcyamaharider]

The Connext display shows gain as a percentage. I should correct the clean statement to include the the word relatively. The buffer setting I was using to observe the values and wave made it appear cleaner than it actually was but still relavant for comparing the different inputs. Also I was only testing the rca outs and I bet when I test the speaker level outs it is far from clean at high levels.

Voltage does matter when the amp inputs are analog. The amp is multiplying the voltage so a higher signal is better to a point. Class D amps are pwm so it is taking the sine wave converting it into a square wave amplifying the square wave and converting it back into a sine wave. With Bluetooth the max unclipped volatge was 2.32 and with USB and aux it was 2.88v. This is enough to make a difference.

One other thing I should mention is that the volume control is far from linear. Going from 80% to 95 % is almost double the voltage.

Most folks are not going to swap out their head unit especially given the connext intergration so more than anything I was trying to figure out the best source and at what point the clip occurs with each input. More to come testing the speaker outs as those with a bone stock system or powering some speakers from the headunit as I am currently will benefit from that.

This is the EXACT same result that I seen with my DD-1 tester ( although you went some steps beyond ) My entire system is tuned to 95% on the connext with no other adjustments from the head unit. EQ to flat and no loudness. I also tuned my system using bluetooth test tones and USB test tones to see the difference. 1k and 40hz tones. No distortion in my system. I don't adjust volume per my head unit ( unless I am in the water ) I use the Wetsounds 420.

 

[robert843]

Hmm that great info. I'm very surprised that the best quality came from the usb I had always been under the impression from other sources I had read the bluetooth was the best connection very interesting indeed.

 

[FloJet]

Warning!!! Technical content contained within. Skip down to the Verdict section for the quick read.

Today I tested the stock Polk PA4a as a second step in tuning in my sound system. The first step was testing the outputs of the iPhone 7 I am using as the source. I did not grab shots from the iPhone but suffice it to say that that it put out a little less than 1 volt, has no clipping to the top end and is a very clean signal. This matches what labs have observed in their testing. The oscilloscope I am using is not lab grade but I did install custom firmware that I coded with a custom configuration for this purpose and then bench calibrated both the hardware and software. So again not lab quality but for this purpose already a bit overkill.

I tested the "front" RCA outputs with the speaker harness disconnected and everything set to flat except for the loudness which I had to turn on to get decent voltage out of the head unit. For all tests documented in this post the iPhone volume was turned up to max and I was using a professional calibrated signal generator app outputting a 1k sine wave test tone that yes I also tested and validated. My comments related to distortion are from observing the frequency and mvDC in real time (with a buffer). The more it fluctuates during the test the worse the signal and I did not turn on min/max/hold as I like to observe the change in more detail than the screen allows.

Bluetooth -
I have commented that my human ear observations had me believe that bluetooth in the headhunt was less than stellar and I was not wrong. The chipset is pre BT 4.1 so that is not very surprising. Even a clean 1k sine wave had distortion at the helm and got worse further away from the head unit. Clipping occurred above 95% head unit volume (1st screen shot is what clipping looks like, sawtooth pattern as opposed to wave). The max rms voltage with no clip was 2.32v.
View attachment 70854 View attachment 70855

USB-
I had commented that I thought USB to be best. I discovered there is slight distortion likely because the DAC chip the head unit employs causes it. The reason I may have thought this is because the headunit achieves 2.88v at 100% volume with no clipping.
View attachment 70856

Aux In-
Using the iPhone dongle (hate that it is even needed) I got a pure signal all the way up to 95% volume and 2.88v rms. Above 95% there was clipping.
View attachment 70857

Verdict-
2.88v was the max output voltage without clipping which is well shy of the perfect 3.7v rms with a 1k sine wave test tone. In other words not complete junk but not that good either. JL amps as as example will handle 4.0v rms without issue and since amp increase at a constant rate based on the gain a weaker input voltage means less output will be achieved. I am going to have to ponder what I am going to do about this wether that be getting a WS420, a completely different head unit or something else. In the mean time even though Aux In was proven best given slightly less distortion I am going to stick with USB as it is more convenient, will achieve the same max pre clip rms output voltage, and there is no clipping at 100% volume so can't go wrong by cranking it as long as the amps are tuned right. Bluetooth on the other hand will mean less volume without clipping and more distortion so while more convenient at times it is better not to play at high volumes with bluetooth on this unit.

Closing-
I am sure there are some experts that are going to poke holes in this. Keep in mind that there was more testing done but stopping and taking screen shots and then posting all of it takes time not to mention gets too deep in the weeds for most. Notice my other channels are set to off for these screen shots to keep things clean. I am not an engineer and just a guy with an electronics hobby. If I did make a major error please do let me know. Stay tuned for my JL amp tuning results with sound spectrum monitoring to fine tune and record db levels.

@Mainah
Did you test both 1k and 40k tones? I believe you shouldn't get the same clipping rate with both tones. One would need to compensate for the 40k tone as that should clip before the 1k. Interested to see what you get when you add the WS420. I too keep my volume at 95% with absolutely no clipping using Bluetooth. Good post. I knew you would come up with technical stats soon. Lol

 

[FloJet]

I also forgot to mention that the results for Aux and USB will be differently on everyone's phones. Each phone brand or model has it's own Digital to Analog Conversion (DAC) system. So some are better than others obviously. So I think folks need to consider this when building their systems. But the results will be the same for Bluetooth as then, the DAC is being utilized by the connext system.

 

[swatski]

I don't adjust volume per my head unit ( unless I am in the water ) I use the Wetsounds 420.

That's the best part of the WS420 in Connext boats, IMO.

Good info! Interesting - and even I noticed you can crank up the Connext HU almost all the way without issues.

--

 

[FloJet]

That's the best part of the WS420 in Connext boats, IMO.

Good info! Interesting - and even I noticed you can crank up the Connext HU almost all the way without issues.

--

Yes sir. It can go up to 100% volume on 1k tones without clipping sometimes. Just depends on where the source is coming from. One reason I don't like using the electronics as the end all. There are deviations to take into considerations. Just because 1k doesn't clip at 95 or 100% volume does not mean music will not clip. It's just more safer bet than any other way I believe. At some point there is clipping of music but not significant enough to cause any damage to equipment as those are usually very short bursts.

When I blew my first Rev 410 and subs, I was introducing almost constant clipping into the equipment which is very bad for it as I didn't have the system tune correctly. And I was pushing 1200 watts to the speakers too!! LMAO.

 

[adrianp89]

A good rule of thumb is... if its rap music or edm... its probably clipping a little. Most party boat music is not going to be well recorded or produced. At the end of the day it's going to come down to your ears to make sure your system is playing safe.

 

[FloJet]

A good rule of thumb is... if its rap music or edm... its probably clipping a little. Most party boat music is not going to be well recorded or produced.

FALSE STATEMENT. There is no good rule of thumb for that. For your info most rap don't utilize high hertz like that. So if it's clipping it's due to incorrect tuning for the subs. Highs will not clip just because you are listening to rap music.

 

[adrianp89]

FALSE STATEMENT. There is no good rule of thumb for that. For your info most rap don't utilize high hertz like that. So if it's clipping it's due to incorrect tuning for the subs. Highs will not clip just because you are listening to rap music.

You always have to start something. Clipping is clipping regardless of frequency. A lot of rap music is extremely poorly recorded. This is well documented.