Polk L800 speakers - SPL below 100 Hz dropped about 6db.

Jarod888
Jarod888 Posts: 61
edited October 2022 in Customer Service
Yesterday while I listening to my Polk L800, the bass suddenly became lighter. Today I spent whole day to find out what’s wrong.

After replacing the DAC and amplifier, I guess the problem is from the L800 speakers.

I tested the speakers, found out the SPL below 100 Hz dropped about 6db.

Screenshot attached, the purple SPL is the test conducted on Oct 25 before the bass problem. The green SPL is the test conducted today after the bass problem. SDA cable is disconnected.

The conditions of two tests are almost same.
Anyone can help? Thank you very much.

9j5ud3shl0jt.jpg

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Comments

  • mhardy6647
    mhardy6647 Posts: 33,785
    edited October 2022
    ... and the "before" trace?

    Anything change in the room/environment?
    LF is, of course, going to be very environmentally dependent.

    Did you test just one loudspeaker (vs. 2)?
    If both show the same effect "before" vs. "after", it's kind of hard to imagine its the loudspeaker(s).
    ... although with the complication of SDA, I guess anything's possible. SDA's only applied to the midrange/treble, though, isn't it?

    Mostly, it looks like you have a big suckout (null) centered on 100 Hz, as opposed to an overall drop in level. Was that suckout there before?
    Move any furniture (or a speaker)? Close the drapes? Get a large dog? ;)

    EDIT: Are you using any DSP/EQ? If so, what happens to the LF response if you turn it off?
    Post edited by mhardy6647 on
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  • msg
    msg Posts: 10,010
    What software is that, btw?
    I disabled signatures.
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  • Gardenstater
    Gardenstater Posts: 4,459
    Since you appear to have the equipment, could you isolate each speaker and do traces for L only and R only? Hard to believe that a speaker problem could suddenly occur in both speakers simultaneously. If one speaker has less bass than the other, try reversing the speaker cables and see if it follows the wire.

    Something to try anyway.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • Emlyn
    Emlyn Posts: 4,484
    Got a photo of the room layout showing where the speakers are located?

    Are the woofers in both speakers moving freely? Any scratching if they're pushed in gently?
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  • TroyD
    TroyD Posts: 13,077
    As been alluded to, there may be something room dependent / set up going on.....
    I plan for the future. - F1Nut
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  • Jarod888
    Jarod888 Posts: 61
    edited October 2022
    Hi Everyone, Thank you for all the replies.

    1. The room is not changed, the bass drop happened while I listening music, that's how I noticed this issue.

    2. All the tests I've done is in the same room, same enviromment.

    3. The testing software is REW (Room EQ Wizard), REW running from a Dell laptop computer, the Dell laptop computer connect to Rotel RA-1592 MK2 via USB calbe. All tests conducted with RA-1592 MK2 (brand new) and Dell computer.

    4. I've two brand new amplifiers, Rotel RA-1592 MK2 and Yamaha A-S2200, I also have a pair of new Focal Aria 936, so I have done many tests to confirm that all my amplifiers and UMIK-1 Calibrated Measurement Microphone is working properly.

    5. The tests have been conducted without SDA

    6. Both left and right speakers got this "bass drop" issue. The right one is even worse.

    7. My Polk L800 are not brand-new, they are ex-demo, I bought them from Polk New Zealand with full warranty. Maybe my L800 been abused in the store?
    Post edited by Jarod888 on
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  • Jarod888
    Jarod888 Posts: 61
    edited October 2022
    This morning (New zealand time), I've done another test.

    Here is the test result this morning, you can see the SPL of bass dropped further after played 20 minutes bass heavy music. (The bass crossover of L800 is 370Hz, is it possible that the crossover got hot so SPL dropping further?)

    Attached screenshot is showing test result of left speaker (Right speaker is even worse).

    The top SPL is before the issue (Oct 25), the mid SPL is from the test yesterday (Oct 31). The bottom SPL is from test this morning (1st November 2022). Please note nothing changed in the room.

    I wouldn't believe this if it wasn't happening in my room. Polk New Zealand distributor has no idea what's wrong.

    9snliifqy6y7.jpg
    Post edited by Jarod888 on
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  • VR3
    VR3 Posts: 28,631
    What makes this really strange is that both speakers are doing it and you still have bass coming from them in any capacity.

    Have you tried testing your gear to factory defaults and running all the calibration
    - Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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  • Jarod888
    Jarod888 Posts: 61
    edited October 2022
    VR3 wrote: »
    What makes this really strange is that both speakers are doing it and you still have bass coming from them in any capacity.

    Have you tried testing your gear to factory defaults and running all the calibration


    Yes.

    1. I've set the Rotel RA-1592 MK2 to factory default.
    2. Tested L800 speakers with Yamaha A-S2200, the L800 speakers still got this bass issue.
    3. The crossover of L800 is 370Hz, to be honest it looks like the crossover is not working properly?
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  • VR3
    VR3 Posts: 28,631
    The bass network in both speakers went out at the same time? Would be very strange.

    How loud was the volume
    - Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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  • nooshinjohn
    nooshinjohn Posts: 25,403
    I wonder if there might be something to listening without SDA causing this...
    The Gear... Carver "Statement" Mono-blocks, Mcintosh C2300 Arcam AVR20, Oppo UDP-203 4K Blu-ray player, Sony XBR70x850B 4k, Polk Audio Legend L800 with height modules, L400 Center Channel Polk audio AB800 "in-wall" surrounds. Marantz MM7025 stereo amp. Simaudio Moon 680d DSD

    “When once a Republic is corrupted, there is no possibility of remedying any of the growing evils but by removing the corruption and restoring its lost principles; every other correction is either useless or a new evil.”— Thomas Jefferson
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  • Jarod888
    Jarod888 Posts: 61
    nooshinjohn wrote: »
    I wonder if there might be something to listening without SDA causing this...

    Thanks, SDA doesn't affect the bass. And the "SPL before this issue" in the screenshot also tested without SDA.
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  • Jarod888
    Jarod888 Posts: 61
    VR3 wrote: »
    The bass network in both speakers went out at the same time? Would be very strange.

    How loud was the volume


    80db at my listening position. My room is 6 meter x 6 meter. Thanks.
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  • Jarod888
    Jarod888 Posts: 61
    edited October 2022
    I also tested at about 1 meter in front of the L800 speaker, the bass still not right.
    I've done all I can do, just wish Polk New Zealand or Polk US can help me out. Thanks.
    joyce2h0bafe.jpg
    mb8hyjdt5dlm.jpg
    1be0sofbdtnz.jpg


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  • Jarod888
    Jarod888 Posts: 61
    Emlyn wrote: »
    Got a photo of the room layout showing where the speakers are located?

    Are the woofers in both speakers moving freely? Any scratching if they're pushed in gently?

    The woofers in both speakers moving freely. no any damage.
    At the moment I suspect it's the crossover not working properly.
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  • Gardenstater
    Gardenstater Posts: 4,459
    edited October 2022
    Have you tried listening to, and testing, just the L and just the R? The whole fact that the bass suddenly went away while you were listening is just so bizarre. Your original pre-problem frequency trace doesn't look so hot either but that could be your room acoustics. I'm sure if I could test those low frequencies in my room I would detect similar situation, which I have been lately curing with very large bass traps in the corners of the room by the ceiling.

    It is almost as if the phase of the two speakers suddenly went out of phase in the low frequency zone. Equally bizarre.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • skipshot12
    skipshot12 Posts: 1,158
    This is a strange one.
    And no dropout with the other speakers?

    Any way something could have shorted damaging the speakers/crossovers?
    Does the L800 have the possibility of bi-amping?
    No loose connections including inside of the speakers?
    Spiders damaged on the woofers from over-excursion?
    Have you checked the Ohms on the the woofers?
    Damage to the voice coils?

    If everything checks out it may be time to look inside the speakers...
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  • Jarod888
    Jarod888 Posts: 61
    edited October 2022
    Gardenstater wrote: »
    Have you tried listening to, and testing, just the L and just the R? The whole fact that the bass suddenly went away while you were listening is just so bizarre. Your original pre-problem frequency trace doesn't look so hot either but that could be your room acoustics. I'm sure if I could test those low frequencies in my room I would detect similar situation, which I have been lately curing with very large bass traps in the corners of the room by the ceiling.

    It is almost as if the phase of the two speakers suddenly went out of phase in the low frequency zone. Equally bizarre.

    Thanks. I have tested just the L and Just the R.
    I'm also writing to the microphone manufacture, need to make sure it's not a microphone issue although the microphone works well with my Focal Aria 936.
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  • Jarod888
    Jarod888 Posts: 61
    skipshot12 wrote: »
    This is a strange one.
    And no dropout with the other speakers?

    Any way something could have shorted damaging the speakers/crossovers?
    Does the L800 have the possibility of bi-amping?
    No loose connections including inside of the speakers?
    Spiders damaged on the woofers from over-excursion?
    Have you checked the Ohms on the the woofers?
    Damage to the voice coils?

    If everything checks out it may be time to look inside the speakers...

    Thank you. the L800 was ex-demo, but with full warranty. I wish Polk New Zealand will help me out. At the moment they told me they have no idea.
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  • SeleniumFalcon
    SeleniumFalcon Posts: 3,774
    I'll refer this issue to some friends at Polk.
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  • Emlyn
    Emlyn Posts: 4,484
    edited October 2022
    It could be something going on inside the speakers. Maybe the dealer had them hooked up to an AV receiver and damaged them. The L800s need a lot of power. Both your integrated amps should have more enough though.

    The Rotel integrated amp has bass and treble tone controls at, I believe, 100 Hz for bass. Suggest accessing that menu to turn the controls on and see if it has any effect on the speakers by gradually lowering and increasing the levels from the -10dB to +10dB levels. If it does you'll know the drivers are working. Rotel doesn't suggest using the tone controls for best sound but they can be useful in some situations and they don't recommend cranking them all the way up because of the excessive demands they can put on the output devices.

    Only other thing I can think of is something in the signal chain may be out of phase. The big dip in bass output looks suspicious/bizarre on the graphs. If it were me and the tone control adjustments weren't doing anything I'd disconnect every cable and reconnect just the integrated to the speakers using a single simple source component like a CD player then see how it sounds. I'd also remove the granite(?) slabs from beneath the speakers and take those rubber feet off.
    Post edited by Emlyn on
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  • Jarod888
    Jarod888 Posts: 61
    SeleniumFalcon wrote: »
    I'll refer this issue to some friends at Polk.

    Thank you very much!
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  • Jarod888
    Jarod888 Posts: 61
    This afternoon I tested at 30cm from bass driver. here is the result:

    Green is left speaker, Red is right speaker, is the SPL looks all right?

    vx56wpoyc5om.jpg
    6pmr64i9puwt.jpg
    t8jqrletqjhq.jpg


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  • VR3
    VR3 Posts: 28,631
    It really looks like they are crossed over or adjusted upstream. Speakers don't break like you are describing
    - Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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  • Gardenstater
    Gardenstater Posts: 4,459
    It certainly looks a lot better than the previous graphs and you don't have that precipitous trough at 100 Hz anymore. The question is why? When you are isolating L and R you are not just placing the mic close to one of the speakers with the other one still playing, correct? When L is tested R not playing and vice versa?

    You have ruled out the upstream equipment as the cause by testing just fine in the same room with different speakers.

    I think you should try taking resistance measurements across the binding posts when the speakers are cold and also when you have been playing bass heavy music for a while, and compare the readings.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
    · Share on FacebookShare on Twitter
  • mhardy6647
    mhardy6647 Posts: 33,785
    VR3 wrote: »
    It really looks like they are crossed over or adjusted upstream. Speakers don't break like you are describing

    Yup.
    Were it me -- I'd turn off any and all EQ and/or reset any processors (i.e., if there are any) to factory default and test again.
    If all seems normal, add back the frosting on the cake one layer at a time. Uh-oh, I am getting stuck in this metaphor...



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  • Jarod888
    Jarod888 Posts: 61
    Gardenstater wrote: »
    It certainly looks a lot better than the previous graphs and you don't have that precipitous trough at 100 Hz anymore. The question is why? When you are isolating L and R you are not just placing the mic close to one of the speakers with the other one still playing, correct? When L is tested R not playing and vice versa?

    You have ruled out the upstream equipment as the cause by testing just fine in the same room with different speakers.

    I think you should try taking resistance measurements across the binding posts when the speakers are cold and also when you have been playing bass heavy music for a while, and compare the readings.

    Thanks for the reply.

    All tests I've done are isolating L and R, that means when I test L, R is not playing, when I test R, L is not playing.
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  • skipshot12
    skipshot12 Posts: 1,158
    Will be staying tuned to hear what this turns out to be.
    I’m at a loss….
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  • SeleniumFalcon
    SeleniumFalcon Posts: 3,774
    Polk's head speaker designer, Scott Orth, is aware of what's going on and is making suggestions on how to troubleshoot the speaker with the folks in New Zealand.
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  • Jarod888
    Jarod888 Posts: 61
    edited November 2022
    Tested again this morning (Nov 2) after playing bass heavy music. The mic is at 30cm from woofer. Test result below. The testing volume is 85db, from the result we can see, the bass response not even meet the L800 products specs: 32Hz (-3dB limits)

    Please compare today's result with the test result of yesterday (in previous post) , you can see the bass response changed a lot.

    I've spent two days and done so manys tests, I'm sure the bass of my L800 speakers is getting weaker.

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    zt3x1nxrq8m1.jpg
    mimmuiye9pl3.jpg




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