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Discussion Starter · #1 ·
I'm going to copy the notes I took the day that I tested my DCM KX speaker series' infrasonic frequency capabilities (date of the test: 11/1/19), edit them, and paste them here. (See my signature for the details of my setup).
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Today, I opened Spotify on my Xbox One S (which is connected via HDMI to my Onkyo TX-NR787 AVR), removed the grille from my left KX-12 Series 2 speaker, and played a frequency sweep track that sweeps from 20 Hz to 1 Hz. [...] The volume level on my AVR was at around -20 or -18 dB; in addition, Spotify on Xbox One seems to add volume to bass frequencies. There was significant excursion from both the 12" driver and the 6" driver, even at 1 Hz. Then, I switched to the Spotify app that is built-in to my AVR, and played the same track. It is worth repeating that the Spotify app that is built-in to this AVR produces music with less bass than the Spotify app on Xbox One. That same driver excursion happened, but the AVR's volume level had to be louder--I had to set it to around -10 dB. Next, I played the same track on my AVR's Spotify app while watching the front-right KX-12 Series Two, and both the 12" and the 6" drivers showed visible excursion all the way down to 1 Hz.

My KX-12 Series Two speakers are rated to go down to 25 Hz, but can go lower, apparently, when the volume of those lower frequencies is increased, though I worry about the damage that doing so could cause to those speakers, short-term and/or long-term.

Why would the 6" driver move at those low frequencies? Shouldn't there be an internal crossover that would stop ultra-low frequencies from reaching the 6" driver? The 6" drivers in my KX-6 Series Two speakers (which serve as my side-surround speakers) and in my KX-Center center speaker barely moved at all, and I could only tell that they were moving when I touched their rubber surrounds; visually, they appeared to be not moving, or barely moving.
 

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Discussion Starter · #2 · (Edited)
I didn't measure the amount of excursion that I was seeing from my left KX-12 Series Two's 12" and 6" drivers, but I'd say it was less than an inch. Perhaps it was half an inch.

After that test, I switched my AVR's input source back to my Xbox, and opened the Netflix app on my Xbox. When the Netflix logo animation and sound played, I heard--or at least I thought I heard--a tiny bit more 'wobble' for a split second, twice during the logo sequence; two very quick moments, and not throughout the whole logo sequence.)

It also seems like the bass is louder now, though that could be because I did this test not long after moving my speakers from one room to another, and the acoustics of this room are better, so maybe that is the reason for the louder bass.
 

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You can determine your speaker woofer cone's maximum inward excursion (probably best done while not connected to your amp) by placing your fingers in a circle around the central dust cap and pushing in gently until it stops, because it hits the back plate. Of course it also moves forward by about the same amount. Add the front distance to the rear distance and try to never hit that point with music or test tones. If you do it will make a rattling/buzz noise my co-workers called "stamping". It probably won't harm anything if only done briefly on rare occassion but you are fundamentally "overdoing it" at that point and asking for trouble.

Speakers can also "break up" and distort before that point. I suspect that was the wobble sound you heard. The woofer cone stops moving in and out pistonicly like a rigid/stiff cone and starts to twist/warp and shake. You can sometimes see this more clearly with the help of a stroboscope freezing the image such as a variable flash rate from a cell phone LED using the right strobe app and frequency of flash. Again probably not so dangerous if only briefly and on rare occasion, but back down on your volume knob immediately if/when you hear serious distortion in general. Distortion means either the amp is clipping or the speakers are being overloaded. Both are potentially dangerous and they sound bad too.

I use my vid which on a really deep bass capable system also demonstrates that not only do speakers plummet in bass at a certain frequency, so does hearing due to Fletcher Munson curves. It is a very important concept in audio.

 

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Discussion Starter · #4 ·
I'm currently reading your post and I just wanted to mention that I edited my post that is immediately above yours. I added a bit of information.
 
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at 1m34s he hits heavy distortion and should immediately back down but he doesn't.
 

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Discussion Starter · #6 ·
You can determine your speaker woofer cone's maximum inward excursion (probably best done while not connected to your amp)
Is it necessary for me to disconnect the speaker from my amplifier, or is putting my amplifier into standby mode sufficient?

by placing your fingers in a circle around the central dust cap and pushing in gently until it stops, because it hits the back plate.
I put my receiver into standby mode and followed the rest of your instructions on my front-left speaker's 12" woofer, and as I gently pushed I didn't feel the driver "hit" anything, but there is a point at which it cannot be pushed further. Again, I don't feel it "hit" anything, but the resistance increases so that I cannot push it further without worrying that I'll damage the driver. It's hard for me to eyeball the distance I can push it back, but I guess that it's maybe 1/4"-1/3". I could be wrong.

In case you didn't see my previous message, I edited the message that appears immediately above yours, in order to add information.
 

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Why would the 6" driver move at those low frequencies? Shouldn't there be an internal crossover that would stop ultra-low frequencies from reaching the 6" driver? The 6" drivers in my KX-6 Series Two speakers (which serve as my side-surround speakers) and in my KX-Center center speaker barely moved at all, and I could only tell that they were moving when I touched their rubber surrounds; visually, they appeared to be not moving, or barely moving.
Speakers move in and out not only because the electrical signal going to them says to, but also because the air in the cabinet, perhaps from other drivers, is moving them. Keep in mind woofer cones make just as much sound into the cabinet as they do outwardly. This is why if you place your hand on the top of the cabinet you can feel it shake at high volumes.

Just because you can see a woofer move in and out at a certain frequency does not prove it is filling the room with that sound at any meaningful volume level.
 

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Is it necessary for me to disconnect the speaker from my amplifier, or is putting my amplifier into standby mode sufficient?
Best to disconnect at least one lead to the speaker, at whichever end is easier to get to. Leaving the speaker connected but the amp in standby may hinder the free movement of the cone for the test.
 

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Discussion Starter · #9 ·
Speakers move in and out not only because the electrical signal going to them says to, but also because the air in the cabinet, perhaps from other drivers, is moving them. Keep in mind woofer cones make just as much sound into the cabinet as they do outwardly. This is why if you place your hand on the top of the cabinet you can feel it shake at high volumes.

Just because you can see a woofer move in and out at a certain frequency does not prove it is filling the room with that sound at any meaningful volume level.
If the midrange drivers were moving simply because the air inside of the cabinet was being moved by the woofers, then wouldn't the 6" drivers be pushing out as the 12" drivers are pushing in, and vice-versa?

I should add that each of these KX-12 Series Two towers has two large ports on the bottom of their backsides, behind the woofer. I'd guess that each port is maybe 6" or 7".
 

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Again, I don't feel it "hit" anything, but the resistance increases so that I cannot push it further without worrying that I'll damage the driver. .
OK then that is your limit of motion. Do not exceed that. Listen to my last posted video to hear what exceeding it sounds like with a test tone. (acually the sound he has is breakup. speaker excursion limits being exceeded is similar though but sometimes sounds like a rapping or repetitive whacking sound.

It's hard for me to eyeball the distance I can push it back, but I guess that it's maybe 1/4"-1/3". I could be wrong.
Most in your price range are around that. Expensive speakers would be more, perhaps double that, and can therefor play music more loudly and with more bass. Big bad subwoofers often can move even an inch or more.
It can be easier to see when in motion by first placing a white dot of paint on the cone, or a small dot of easy to see tape (I use fluorescent orange duct tape for this). When the test tone comes on the white/orange dot visibly blurs and turns into a line. The length of the line is the full excursion at the moment. Fun. Try it.
 

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If the midrange drivers were moving simply because the air inside of the cabinet was being moved by the woofers, then wouldn't the 6" drivers be pushing out as the 12" drivers are pushing in, and vice-versa?
No, not necessarily. It might be that they are "sympathetically vibrating". Since your speakers have ports this means the air inside is not fixed anyways.
 

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Discussion Starter · #12 ·
Best to disconnect at least one lead to the speaker, at whichever end is easier to get to. Leaving the speaker connected but the amp in standby may hinder the free movement of the cone for the test.
What about unplugging the amp from the wall?
 

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Best to disconnect at least one lead to the speaker, at whichever end is easier to get to. Leaving the speaker connected but the amp in standby may hinder the free movement of the cone for the test.
What about unplugging the amp from the wall?
WTF? If the amp is in standby, it's essentially off and doing nothing. What's the logic that you'd want to remove a wire from one of the legs?
 

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Discussion Starter · #14 ·
After that test, I switched my AVR's input source back to my Xbox, and opened the Netflix app on my Xbox. When the Netflix logo animation and sound played, I heard--or at least I thought I heard--a tiny bit more 'wobble' for a split second, twice during the logo sequence; two very quick moments, and not throughout the whole logo sequence.)

It also seems like the bass is louder now, though that could be because I did this test not long after moving my speakers from one room to another, and the acoustics of this room are better, so maybe that is the reason for the louder bass.
So while the bass might be louder because the speakers are in a better room, I wonder if playing the frequency sweep that included infrasonic frequencies, with my AVR set to the volumes that I mentioned loosened my drivers by stretching their excursions, and damaging the drivers by leaving them slightly looser, able to push more but slightly more wobbly. And maybe that's why the bass seems louder now. I don't know. I hope that I didn't damage them. I'll have to look at the videos that m. zillch posted tomorrow, because it's 11:56 PM now and I better not run speaker tests now because I don't live alone.
 

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WTF? If the amp is in standby, it's essentially off and doing nothing. What's the logic that you'd want to remove a wire from one of the legs?
A speaker's woofer cone's motion when playing around with it by gently pushing it inward with your fingers, or say tapping it gently to try to deduce (by ear) the frequency of resonance will behave somewhat differently depending on if its + and - terminals are connected to an amp or not.

No need to bother disconnecting both leads which is why I suggested disconnecting only one.
 

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Discussion Starter · #16 ·
https://www.youtube.com/watch?v=kGSJC46oHD4
at 1m34s he hits heavy distortion and should immediately back down but he doesn't.
OK then that is your limit of motion. Do not exceed that. Listen to my last posted video to hear what exceeding it sounds like with a test tone. (acually the sound he has is breakup. speaker excursion limits being exceeded is similar though but sometimes sounds like a rapping or repetitive whacking sound.
So while the bass might be louder because the speakers are in a better room, I wonder if playing the frequency sweep that included infrasonic frequencies, with my AVR set to the volumes that I mentioned loosened my drivers by stretching their excursions, and damaging the drivers by leaving them slightly looser, able to push more but slightly more wobbly. And maybe that's why the bass seems louder now. I don't know. I hope that I didn't damage them. I'll have to look at the videos that m. zillch posted tomorrow, because it's 11:56 PM now and I better not run speaker tests now because I don't live alone.
I watched the video on my tablet instead of on my TV in order to not bother anyone else. Based only on what I heard from that video out of my tablet's speakers, I do not hear the 'buzz' from my speakers that can be heard in the video. It's just that twice-momentary wobble at low frequencies during the Netflix app loading logo. And it's possibly all in my head.

Ideally, I'd have a pink noise sound from 1 Hz-20 kHz and a good mic for REW so that I can test my speakers' frequency response curves to see if there are spikes in the low frequency areas of their responses.
 

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If the midrange drivers were moving simply because the air inside of the cabinet was being moved by the woofers, then wouldn't the 6" drivers be pushing out as the 12" drivers are pushing in, and vice-versa?
The mids will have their own sealed section in the cab and tweeters are sealed at the back. Pressure from the woofer will not affect them internally.
 

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His speakers are "modified transmission line" cabinets. There are three driver, plus ports, but I suspect the reason they don't list two crossover frequencies is because they are not 3-way designs: they are 2.5 way designs. Although his transmission line ports are on the back, not the front, I think his internal cabinet is akin to this:



The fact that he says the mid driver motion and bass driver interact suggests the same cavity of air.

P.S. At first I was thinking it was another port but then I realized the round hole on the back here is for a round speaker wire terminal cup. Like this.
 

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His speakers are "modified transmission line" cabinets. There are three driver, plus ports, but I suspect the reason they don't list two crossover frequencies is because they are not 3-way designs: they are 2.5 way designs. Although his transmission line ports are on the back, not the front, I think his internal cabinet is akin to this:



The fact that he says the mid driver motion and bass driver interact suggests the same cavity of air.

P.S. At first I was thinking it was another port but then I realized the round hole on the back here is for a round speaker wire terminal cup. Like this.
ok... wow... very strange design. The back pressure from the woofer would be constantly interfering with the mid cone movement. Could the mid driver in this design possibly have a sealed back ?

here is one https://www.parts-express.com/grs-5sbm-8-5-sealed-back-midrange--292-432
 

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It is strange, yes. Hard to say anything for sure. Without him unscrewing and removing the bass driver to take a look inside we may never know for sure. . .

I guess one test would be to stuff plugs into the ports, like small throw pillows or a wadded up bath towel to temporarily make it a sealed box. If then pushing in one driver makes the other push out we'd know for sure they share the same air space.

How they normally interact at high speed with music playing however gets more complex and can't be analyzed properly by this test.
 
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