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JBL310s subwoofer polarity

ShiZo

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What is the purpose of the polarity (0, 180) button on my JBL310s subwoofer? I've done some research and I guess it changes if the speaker inverts or everts under some circumstances.

What would be the actual application of this and what setting should I have if I have my 2.1 setup pretty normal, subwoofer under my desk and in-between both speakers. Both are about a foot and a half away from the wall with the subwoofer slightly offset to the middle-left.
 

dadregga

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There's not actually a "right" answer - it depends on your setup/amp/speakers/etc.

Listen to the sub both ways - one of the phase settings won't sound very good, or will sound less loud/powerful. Pick the phase setting that sounds good.
 

TheWalkman

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I’ll take a shot at this.

The switch insures that when your other speakers are moving out (albeit in thousandths of a second) your woofer is moving out (in, “phase”) or in synch with the smaller speakers.

If the speakers aren’t in phase, they are working against each other, canceling out the sound of one another. Not good.

This is why you want to be certain the red and black leads on all speakers are properly connected to one another.

If the speakers are not in phase, (zero degrees), the switch reverses the movement of the woofer, or changing its signal by 180 degrees, (remember polar coordinates from high school trigonometry) so it is working together.

Does that make sense?
 
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ShiZo

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That does make sense. This is how my speakers are set up if that helps. The port of the sub is facing forward and speaker port is facing the opposite direction if that matters.

I feel like it does sound better with normal polarity, but cant be sure if it's placebo.
 

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AdamG247

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witwald

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What is the purpose of the polarity (0, 180) button on my JBL LSR310S subwoofer? I've done some research and I guess it changes if the speaker inverts or everts under some circumstances.
That's correct. When activated, the polarity switch simply inverts the polarity of the signal. This converts positive going waveforms into negative going ones, and vice versa. If the speaker is reproducing a positive pressure pulse, then inverting the polarity will turn it into a negative pressure pulse.
What would be the actual application of this and what setting should I have if I have my 2.1 setup pretty normal, subwoofer under my desk and in-between both speakers. Both are about a foot and a half away from the wall with the subwoofer slightly offset to the middle-left.
In your situation, there should be no need to activate the polarity button. Your subwoofer is placed very close to both main speakers, so any path length phase differences between the subwoofer and mains are very small at the 80 Hz crossover frequency. At this frequency, the wavelength of sound is 345/80 = 4.31 metres (14.1 feet). To cause 180° of phase shift between the woofer and subwoofer output, the subwoofer would need to be sited 4.31/2 = 2.16 metres.

Below is a VituixCAD simulation of the response of the JBL LSR310S subwoofer and the LSR308P MkII loudspeakers, with zero offset between the subwoofer driver and the 8" driver. 4th-order Linkwitz-Riley high-pass and low-pass filters have been assumed, with 80 Hz cut-off filters. This shows good blending of the responses.
1630720877748.png

1630721043164.png

In your situation, the subwoofer is placed quite close to the main speakers, so the phase difference between the separate outputs is quite small. It will likely affect the blending of the low frequencies to only a small extent. This can be compensated for simply by adjusting the level of the subwoofer relative to the main speakers.

For example, if we add in a 0.500 metre separation between the woofer and the subwoofer, we get the following response, which is only slightly changed from the previous one. The small sensitivity to such changes is due to the use of the Linkwitz-Riley filter topology, with 4th-order filters. I checked with JBL Tech Support, and was informed that, to the best of their knowledge, that 4th-order LR filters are used in high-pass and low-pass sections of the LSR310S.
1630723947117.png
 
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ShiZo

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That's correct. When activated, the polarity switch simply inverts the polarity of the signal. This converts positive going waveforms into negative going ones, and vice versa. If the speaker is reproducing a positive pressure pulse, then inverting the polarity will turn it into a negative pressure pulse.

In your situation, there should be no need to activate the polarity button. Your subwoofer is placed very close to both main speakers, so any path length phase differences between the subwoofer and mains are very small at the 80 Hz crossover frequency. At this frequency, the wavelength of sound is 345/80 = 4.31 metres (14.1 feet). To cause 180° of phase shift between the woofer and subwoofer output, the subwoofer would need to be sited 4.31/2 = 2.16 metres.

In your situation, the subwoofer is placed quite close to the main speakers, so the phase difference between the separate outputs is quite small. It will likely affect the blending of the low frequencies to only a small extent. This can be compensated for simply by adjusting the level of the subwoofer relative to the main speakers.
Thanks for the advice.

I do notice that too. Bass sounds a little more quiet. But on loud songs it's still loud so I thought it just wasn't overexaggerated.
 

soyabeaner

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This one is a tricky setting for me. I have also have the LSR310s and LSR305 (first gen). Mine are placed close to my bedroom wall and corner. They also situate very close to each other. Having tested many times with both polarity settings, I came to conclusion that the best audio setup is at the 180 degree reversal because it provides the smooth transition to blend sub & speakers. There are internet sources I've read along with the manual that recommend going with the one that provides the most bass, but I prefer to go with one with the smoothest blend, as if the crossover is as seamless as possible.

I don't have any measuring equipment to see the frequency response at my listening position, which is right up front (nearfield) to the speakers. Instead, I had to rely on pure listening to test tones and frequency sweep tones I downloaded from www.audiocheck.net years ago. Test files used:
audiocheck.net_headphonesweep20Hz-10kHz.wav
audiocheck.net_bandlimited_20Hz_80Hz.wav
audiocheck.net_bandlimited_120Hz_300Hz.wav
audiocheck.net_frequencychecklow.wav
and various frequencies from 20-70Hz to test the subwoofer response. Each polarity setting affected the loudness levels of frequency. It's a trade off, so unfortunately for me they're not even. I also picked some of my known songs where there's noticeable sub-bass to pick which is the better one. Most of the time it's not obvious.

I also don't EQ them, which I refuse to do unless I have from visual measurements of my room because I don't like to adjust by ear as I'll take forever and not be accurate.
 
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ShiZo

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That's correct. When activated, the polarity switch simply inverts the polarity of the signal. This converts positive going waveforms into negative going ones, and vice versa. If the speaker is reproducing a positive pressure pulse, then inverting the polarity will turn it into a negative pressure pulse.

In your situation, there should be no need to activate the polarity button. Your subwoofer is placed very close to both main speakers, so any path length phase differences between the subwoofer and mains are very small at the 80 Hz crossover frequency. At this frequency, the wavelength of sound is 345/80 = 4.31 metres (14.1 feet). To cause 180° of phase shift between the woofer and subwoofer output, the subwoofer would need to be sited 4.31/2 = 2.16 metres.

Below is a VituixCAD simulation of the response of the JBL LSR310S subwoofer and the LSR308P MkII loudspeakers, with zero offset between the subwoofer driver and the 8" driver. 4th-order Linkwitz-Riley high-pass and low-pass filters have been assumed, with 80 Hz cut-off filters. This shows good blending of the responses.
View attachment 151333
View attachment 151334
In your situation, the subwoofer is placed quite close to the main speakers, so the phase difference between the separate outputs is quite small. It will likely affect the blending of the low frequencies to only a small extent. This can be compensated for simply by adjusting the level of the subwoofer relative to the main speakers.

For example, if we add in a 0.500 metre separation between the woofer and the subwoofer, we get the following response, which is only slightly changed from the previous one. The small sensitivity to such changes is due to the use of the Linkwitz-Riley filter topology, with 4th-order filters. I checked with JBL Tech Support, and was informed that, to the best of their knowledge, that 4th-order LR filters are used in high-pass and low-pass sections of the LSR310S.
View attachment 151352

Would increasing the bass provide more bass in the dip?
 

witwald

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Yes, increasing the output level of the subwoofer would provide more bass in the dip. Keep in mind though, the dip is quite minor, being 0.3 dB deep. In the plot below, I've added an extra +0.3 dB to the subwoofer output level, and the dip at about 55 Hz or so is now essentially gone. However, we do have a +0.3 dB peak at about 39 Hz or so.
1630725985569.png
 
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witwald

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As an example, if we invert the polarity on the subwoofer, then we will get a response like the following. The dip is not a perfect null, which is due to other phase response effects related to the low-pass alignments of both the woofer in the mains as well as the subwoofer.
1630726195271.png
 
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ShiZo

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As an example, if we invert the polarity on the subwoofer, then we will get a response like the following. The dip is not a perfect null, which is due to other phase response effects related to the low-pass alignments of both the woofer in the mains as well as the subwoofer.
View attachment 151354
Seems like inverting the polarity and increasing sub db a little would be beneficial or am I missing something?
 

witwald

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Inverting the subwoofer's polarity introduces an 11 dB dip into the summed response. That's not a good thing to have happen. The bass response will be considerably inaccurate with the inverted polarity. Keep the polarity switch at 0° for the smoothest bass response. You will then just need to try different settings of the subwoofer volume control in order to determine a setting that works best for you.

Below I've included response examples with volume control settings that are +3 dB above and –3 dB below the reference volume setting that produces a flat response. That should give you an idea of how things might sound bass-wise.

+3 dB subwoofer volume re level for nominal flat response
1630730045092.png


–3 dB subwoofer volume re level for nominal flat response
1630730091614.png
 
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A Surfer

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Seems to run counter to my experience, but I will try again. I have my mains, Monitor Audio PL200s supported by two SVS SB2000 Pro subs. The subs are very close to the mains, in between them and essentially flush aligned so with what has been described here I should expect that a 0 degrees phase shift would be best, but it most certainly does not sound that way. At 0 degrees phase the bass output is measurably lower (using a pretty decent phone app) and subjectively I hear less bass as compared with doing 180 degrees phase shift. And my speakers are wired in phase from the amp. I have been using speakers since the 1980s and never once wired a speaker out of phase. Not sure why this is?
 

Pdxwayne

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Seems to run counter to my experience, but I will try again. I have my mains, Monitor Audio PL200s supported by two SVS SB2000 Pro subs. The subs are very close to the mains, in between them and essentially flush aligned so with what has been described here I should expect that a 0 degrees phase shift would be best, but it most certainly does not sound that way. At 0 degrees phase the bass output is measurably lower (using a pretty decent phone app) and subjectively I hear less bass as compared with doing 180 degrees phase shift. And my speakers are wired in phase from the amp. I have been using speakers since the 1980s and never once wired a speaker out of phase. Not sure why this is?
The amp of the sub also adds delay. My receiver always set my subs much further away than actual distance due to amp delay.
 

witwald

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The amp of the sub also adds delay. My receiver always set my subs much further away than actual distance due to amp delay.
The simulation below shows the summed response when there is 3.5 msec of delay added to the subwoofer and its output is polarity inverted. The result is quite smooth in this configuration.
1630735028997.png


If the polarity inversion is removed, the resulting response is shown below. It has a very significant dip through the crossover region, which would be very audible.
1630735062293.png
 

A Surfer

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The simulation below shows the summed response when there is 3.5 msec of delay added to the subwoofer and its output is polarity inverted. The result is quite smooth in this configuration.
View attachment 151367

If the polarity inversion is removed, the resulting response is shown below. It has a very significant dip through the crossover region, which would be very audible.
View attachment 151368
Sadly I am quite ignorant in this area. To achieve the type of phase inversion you are speaking about (3.5ms) if the subs are very close to the speakers, which mine are, in terms of degrees of shift, what might I begin experimenting with? As I mentioned, currently my subs are both shifted 180 degrees and crossed at 79Hz.
 
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ShiZo

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So should my sub volume be the same or a couple notches above speaker volume?

@witwald
 

witwald

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Firstly, the user manual states: "When the LSR310S is used in a system with LSR305 and LSR308, set the INPUT SENSITIVITY switch on the LSR305 or LSR308 to the –10dBV setting regardless of the LSR310S input sensitivity switch setting."

I would then proceed as follows. First, set the volume level on the LSR310S to –∞. Next, set an appropriate volume level for your main speakers, keeping in mind that they are being high-pass filtered at 80 Hz and so will be quite weak in the bass. Then you can increase the level of the LSR310S until you consider that you are getting the desired level of bass response from the complete system.

Whether you have the LSR310S volume set the same as the speakers or a little bit above them is for you to decide. If using the system for mixdowns, then I'd tend to aim for a more neutral, flatter response, where the LSR310S blends in smoothly with the output from the main speakers.

In your set up, I would try to determine the setting on the LSR310S that provides a correct theoretical blending of the low-pass filtered subwoofer output with that of the high-pass filtered output from the main speakers. This will require some measurements to be done. You will need to have access to an 80 Hz test tone, which your DAW may be able to create for you. First, set the volume level on the LSR310S to –∞. Play the 80 Hz test tone at a moderate level, say 70 dB or so. Use a microphone mounted on a stand to measure the response and take note of the signal level in your DAW. You should be able to get a reading that is stable to about ±0.5 dB or better. Then slowly increase the volume on the LSR310S until the measured signal level is 6.0 dB higher than the original reading. At that point, the subwoofer and main speaker output levels at 80 Hz are identical. Take note of the volume settings on both the LSR310S and main speakers for future reference.

Increasing the volume level on the LSR310S beyond that point will result in boosted bass response, as illustrated in an earlier post. You can decide what you want to hear and adjust accordingly, either above or below that reference level. I think that the approach that I've described should get you in the right ball park without more extensive measurements. Of course, it assumes that the response of subwoofer within its bandwidth is relatively flat. Even if it isn't entirely so, we have still achieved a reasonable degree of calibration of the monitoring set up.
 
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ShiZo

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Firstly, the user manual states: "When the LSR310S is used in a system with LSR305 and LSR308, set the INPUT SENSITIVITY switch on the LSR305 or LSR308 to the –10dBV setting regardless of the LSR310S input sensitivity switch setting."

I would then proceed as follows. First, set the volume level on the LSR310S to –∞. Next, set an appropriate volume level for your main speakers, keeping in mind that they are being high-pass filtered at 80 Hz and so will be quite weak in the bass. Then you can increase the level of the LSR310S until you consider that you are getting the desired level of bass response from the complete system.

Whether you have the LSR310S volume set the same as the speakers or a little bit above them is for you to decide. If using the system for mixdowns, then I'd tend to aim for a more neutral, flatter response, where the LSR310S blends in smoothly with the output from the main speakers.

In your set up, I would try to determine the setting on the LSR310S that provides a correct theoretical blending of the low-pass filtered subwoofer output with that of the high-pass filtered output from the main speakers. This will require some measurements to be done. You will need to have access to an 80 Hz test tone, which your DAW may be able to create for you. First, set the volume level on the LSR310S to –∞. Play the 80 Hz test tone at a moderate level, say 70 dB or so. Use a microphone mounted on a stand to measure the response and take note of the signal level in your DAW. You should be able to get a reading that is stable to about ±0.5 dB or better. Then slowly increase the volume on the LSR310S until the measured signal level is 6.0 dB higher than the original reading. At that point, the subwoofer and main speaker output levels at 80 Hz are identical. Take note of the volume settings on both the LSR310S and main speakers for future reference.

Increasing the volume level on the LSR310S beyond that point will result in boosted bass response, as illustrated in an earlier post. You can decide what you want to hear and adjust accordingly, either above or below that reference level. I think that the approach that I've described should get you in the right ball park without more extensive measurements. Of course, it assumes that the response of subwoofer within its bandwidth is relatively flat. Even if it isn't entirely so, we have still achieved a reasonable degree of calibration of the monitoring set up.
Thank you for the help, I will do that. I can tell you right now that when the volume is completely equal on both it sounds a little bass anemic. I've yet to determine if I need to change polarity but I'm pretty sure regular polarity has more bass. Last thing I'm wondering is how many db each step on the jbl310s is.
 
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