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Raise that Sub!


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So you're supposed to move Klipschorns off the floor?

 

Klipsch Lapel BS Button.jpg

 

The only time decoupling is needed is for suspended floors, and that's only for floor framing resonant frequencies. 

 

 

Chris

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His advice is very suspect.

 

When you generate the sound in a corner (or nearby) there will be the greatest number of pressure nodes being stimulated. This is good. An alternative way to conceptualize is that each boundary (floor, wall, adjacent wall) provides loading for the low frequencies. This is also good.

 

There is a nice discussion of this (and why multiple subs make sense) in Toole's book 

 

Good luck,

-Tom

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On 2/4/2021 at 2:20 PM, Chris A said:

So you're supposed to move Klipschorns off the floor?

 

Klipsch Lapel BS Button.jpg

 

The only time decoupling is needed is for suspended floors, and that's only for floor framing resonant frequencies. 

 

 

Chris

 

Wouldn’t you think that raising a subwoofer (not a main speaker) off the floor would reduce early reflections (“floor bounce”), which should be a good thing?  Getting it closer to the centreline of the room, or even closer to ear level, should make for a more even soundfield.  All four subs in my home (2 in the living room, 2 in the bedroom) are on tables, record boxes, etc., with heights of 13” and 14” in the living room (the main system) and 8” and 20” in the bedroom.

 

The raised positions were at first in order to reduce any vibrations going through the floor to the neighbours below, with the subs sitting on thick neoprene pads as well.  However, seeing them more than halfway to ear level (I like to listen with the sofa fully reclined) seems to make so much sense that I’d recommend it to anyone.  I initially had one of the living room subs behind the sofa, on a 27” high barstool.

 

That seemed fine, except that the higher resistance of the 16 metre cable I used meant that after the first sub turned on, the volume had to be rolled up an extra 6 dB before the second one would turn on.  That didn’t work well, especially when listening at low volume would often cause the rear sub to turn off and stay off.  Moving it to the front of the room and installing a 2 metre cable to match the one on the first sub cured that, and it sounded and looked better.  I just had to find something to put it on, and a record box was perfect.

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29 minutes ago, Islander said:

 

Wouldn’t you think that raising a subwoofer (not a main speaker) off the floor would reduce early reflections (“floor bounce”), which should be a good thing?  Getting it closer to the centreline of the room, or even closer to ear level, should make for a more even soundfield.  All four subs in my home (2 in the living room, 2 in the bedroom) are on tables, record boxes, etc., with heights of 13” and 14” in the living room (the main system) and 8” and 20” in the bedroom.

 

The raised positions were at first in order to reduce any vibrations going through the floor to the neighbours below, with the subs sitting on thick neoprene pads as well.  However, seeing them more than halfway to ear level (I like to listen with the sofa fully reclined) seems to make so much sense that I’d recommend it to anyone.  I initially had one of the living room subs behind the sofa, on a 27” high barstool.

 

That seemed fine, except that the higher resistance of the 16 metre cable I used meant that after the first sub turned on, the volume had to be rolled up an extra 6 dB before the second one would turn on.  That didn’t work well, especially when listening at low volume would often cause the rear sub to turn off and stay off.  Moving it to the front of the room and installing a 2 metre cable to match the one on the first sub cured that, and it sounded and looked better.  I just had to find something to put it on, and a record box was perfect.


This makes sense. Steve Guttenburg gave a presentation that having the sub closer to the seating position would also improve your listening pleasure. Like he stated, a sub should not be heard, as it needs to blend in seamlessly with the main speakers.

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The "diaphramatic absorption" referred to in the video is the same as the "subwoofer isolation system" feet I purchased for my SVS subwoofer. I bought these so less vibration would travel to the floor, and be heard/felt by my condo neighbors. But that vibration is part of what subwoofers add to sound; that tactile sense in electronic music and movie explosions. Other than consideration for neighbors, why get rid of it?

 

As for placing the sub off the floor, and at various heights, it does mitigate floor bounce but will reduce sub output level. And it's somewhat impractical for most of us aesthetically. It would be an interesting experiment nonetheless.

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3 hours ago, Peter P. said:

The "diaphramatic absorption" referred to in the video is the same as the "subwoofer isolation system" feet I purchased for my SVS subwoofer. I bought these so less vibration would travel to the floor, and be heard/felt by my condo neighbors. But that vibration is part of what subwoofers add to sound; that tactile sense in electronic music and movie explosions. Other than consideration for neighbors, why get rid of it?

 

As for placing the sub off the floor, and at various heights, it does mitigate floor bounce but will reduce sub output level. And it's somewhat impractical for most of us aesthetically. It would be an interesting experiment nonetheless.


The other consideration is the floor surface. Is it tile, hard wood, concrete, or carpet? 

My theater seating is a series of 3 riser platforms. The rear most two subs are elevated as a result, being nearer the center rows ear level. The front subs are in corners, at floor level, but near ear level for those seated front row center.

 

1612632821164-png.174863

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3 hours ago, Frzninvt said:

That is not a sub that is a very large midbass cabinet with not much output below 30Hz even eq'd and placed properly.  It will have midbass output 40 - 80Hz in spades though.

I beg to differ.  We got 20hz- 0db & 18.9 -3db with +13db @ 20hz PEQ on Xilica

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12 minutes ago, rigma said:

I beg to differ.  We got 20hz- 0db & 18.9 -3db with +13db @ 20hz PEQ on Xilica


Please put the 20 Hz PEQ settings in this thread as I am interested in trying them.

 

Also agree, that is not a mid-bass cabinet. 

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On 2/7/2021 at 5:34 AM, Islander said:

Wouldn’t you think that raising a subwoofer (not a main speaker) off the floor would reduce early reflections (“floor bounce”),

How long is a wavelength of sound at 40 Hz (room temperature)? 

Spoiler

340 inches...or 28 1/3 feet

Floor bounce has no meaning below the room's Schroeder frequency.  In a room as small as you have described elsewhere, that's probably around 200 Hz.  So the only thing you're attenuating from the other floors (above and/or below) is harmonic distortion from the subs.  If you are running clean output subwoofers, these harmonics should be at least 30 dB down from the fundamental frequencies at 100 dB (1 m) from the sub.

 

On 2/7/2021 at 5:34 AM, Islander said:

...Getting it closer to the centreline of the room, or even closer to ear level, should make for a more even soundfield...

If you think that you can hear the sub better in an elevated position, what you are probably listening to...is the sub's harmonic distortion at higher frequencies.  This indicates that the quality of the subs that are in use could be better to avoid being able to locate them via their harmonic distortion levels. 

 

For instance, the TH subs that I run cannot be localized in-room when operating (the crossover frequency to the other loudspeakers in-room is nominally 40 Hz).  I have to run separate REW sweeps to hear if a sub is working properly or not, because of the lack of higher harmonic distortion.  You actually want to hide your subwoofers (the type that make a lot of harmonic distortion) behind as many acoustically absorptive objects as you can to attenuate the higher frequency subwoofer harmonics that are not in your recordings.  Mine are located behind the Jubilee bass bins in the room corners:

 

1812476897_MeasuredDIYTH-SPUDHarmonicDistortionatLP.thumb.jpg.440f60df8d647b81dc87e7f48774bfd8.jpg

 

On 2/7/2021 at 5:34 AM, Islander said:

The raised positions were at first in order to reduce any vibrations going through the floor to the neighbours below, with the subs sitting on thick neoprene pads as well.

Then you have a suspended floor...and structure-borne vibrations to the floor and other portions of the building that you live in becomes a problem. 

 

But note: for very low frequencies, it doesn't really matter if you elevate the sub above floor level.  It will still be within 1/4 wavelength at the frequencies that it is producing, and will couple to the walls, ceiling and floor. The only attenuation is drywall or plaster-and-lathe flexing.  All you will be doing by elevating the subs is to break any mechanical noises in the woofers from being transmitted--and the sub's harmonic distortion.  If you are within 1/4 wavelength of the room boundary, it doesn't matter very much where you put the mouth of the horn or the cone of the direct radiating woofer.  It will couple to the room's boundaries within this radius.  The question is: how well will it couple?  How much EQ is needed to flatten its response when pulled away from a room boundary, such as the floor?  A 1/4 wavelength at 80 Hz is 42.5 inches, at 40 Hz (the crossover frequency of my subwoofers to the other loudspeakers in my array) it's 85 inches.  At 20 Hz, it's 170 inches.  Anything within that radius will couple to the subwoofers' output.

 

Chris

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5 hours ago, Frzninvt said:

That is not a sub that is a very large midbass cabinet with not much output below 30Hz even eq'd and placed properly.  It will have midbass output 40 - 80Hz in spades though.

 

1 hour ago, rigma said:

I beg to differ.  We got 20hz- 0db & 18.9 -3db with +13db @ 20hz PEQ on Xilica

I can concur with Marion's statement (KPT-1802-HLS) in a home hi-fi sized room via measurements.  But note, you do have to pay attention to the harmonic distortion down low.  This subwoofer really wants to make a lot of output at 40-80 Hz (a LOT of output), so dialing them in using something like a Xilica or similar DSP crossover is really required to get flattened SPL response throughout its passband.

 

I'm sure the 1802 sounds impressive in-room --the question that I ask: " is it clean output and is it well integrated with the fronts (L, C, R) in terms of its SPL response?".  Because it is such a large device, it will play extremely loudly at all frequencies mentioned above.

 

I will also say that a lot of the problem of getting good infrasonic bass response in-room in home hi-fi listening rooms is a matter of "filling up the room modes" at the room corners and at the room's mid-points between the corners, etc.  That's where the 1802 comes in--in Marion's (rigma's) room. 

 

Chris

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1 hour ago, Ole Dollar said:

Please put the 20 Hz PEQ settings in this thread as I am interested in trying them...

Here is one installation of an 1802 in-room (mid-wall front) crossing over (effectively at 40 Hz) in a medium-small listening room:

 

1402962737_KPT-1802-HLSin-roomPEQscrossoverfilter.thumb.GIF.e2398a5c2b1b70f7f2a06e312452fabe.GIF

 

The little numbers on the field of the plot tell you where each PEQ is located. Note the PEQs above 70 Hz (PEQs 3, 4, 6) to further attenuate output.  The 1802 really wants to put out a lot above even 80 Hz.

 

Note that these settings are probably not transferable between rooms and installations because there are so many in-room variables that control what you see above.  I posted this because it was requested, not because I think it will be useful without using some form of in-room acoustic measurements to dial in.

 

Chris

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2 hours ago, Ole Dollar said:


Please put the 20 Hz PEQ settings in this thread as I am interested in trying them.

 

Also agree, that is not a mid-bass cabinet. 

These are my settings and are based on MY ROOM measurements. Yours may vary.

PEQ            PEQ            PEQ           PEQ           Low Pass

+13 db       -18db         -15db         -15db         Linwintz

21hz            72hz          80hz         150hz         50hz   

.18oct        .12oct        .33hz         .25oct         24db/oct

Q=8.009    Q=12.018  Q=4.362    Q=5.763

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That's fairly similar to the one I posted, with the extra 29 and 32 Hz "shelf" added to the one I posted, which was probably related to the room modes encountered.

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