F20 which direction

[Lbk]

Going to put an f 20 sub up front  centered on an 11ft wall, room is 11 by 17 by 8 ft. Which direction should I point the mouth opening, towards the near wall or into the room. If pointed towards near wall I could give it up to a 6 inch clearance, thanks.

[CECAA850]

Try it both ways.  There may not be much of a difference.  You'll get more output though if you get it out of the center of the wall and put it in a corner.

[Lbk]

8 hours ago, CECAA850 said:

Try it both ways.  There may not be much of a difference.  You'll get more output though if you get it out of the center of the wall and put it in a corner.

Thought about that but would have to build a speaker stand for one speaker. Do you think the output would be significantly better? May be worth the extra work.

 

Maybe this winter I build a second one.(maybe)

 

 

[Pete H]

IMO, put it where it best fits in the room and with your layout, and it will provide plenty of output.  I've built a few, have one in my HT that is centered up and supports all of my gear and plasma T.V. and no complaints.  There's always some trade offs, there's always better, but if you place it and get it dialed in with the room treated properly, you will spend more time enjoying it and less time moving it around.  My .02 worth.  

[Lbk]

6 hours ago, Pete H said:

IMO, put it where it best fits in the room and with your layout, and it will provide plenty of output.  I've built a few, have one in my HT that is centered up and supports all of my gear and plasma T.V. and no complaints.  There's always some trade offs, there's always better, but if you place it and get it dialed in with the room treated properly, you will spend more time enjoying it and less time moving it around.  My .02 worth.  

That was my idea, f 20 centered and use  it for equipment and tv. My equipment is racked on the long wall so it's hard to do any room treatment on that side. Been wanting to do room treatment for a while.

 

Have a revel b15 I can use for rear fill if needed. Pete does your f 20 fill room or do you run another sub. This will be mostly for music.

 

 

 

 

[Pete H]

I'm 90% music, but full HT setup and my room is really open, living room/kitchen/dining/office, not huge, but about 1200 sq.' (11,000 cu') and don't need anymore for music or HT, IMO.  I replaced 2 RSW15's with the F20 and fits my needs well.  I put casters on it and there's a skirt board so you don't see them and it's simple to move it with everything on it, even for my wife.  I'll try and find the picture, I think I posted in the build thread.

 

[Pete H]

Things have changed a bit and there's a lot more gear stacked on it, but still shows you what I did 5 years ago, and it's still in the rig, so I'd say I'm happy.

[Lbk]

11 hours ago, Pete H said:

Things have changed a bit and there's a lot more gear stacked on it, but still shows you what I did 5 years ago, and it's still in the rig, so I'd say I'm happy.

Wow I love it, my f 20 is painted black. Casters and pics are giving my some idea's! ( I can steal) Is your build in the tech/mod section I would like to look at it, nice work!

 

[Pete H]

1 hour ago, Lbk said:

Wow I love it, my f 20 is painted black. Casters and pics are giving my some idea's! ( I can steal) Is your build in the tech/mod section I would like to look at it, nice work!

 

Let me try and find it.  Should be on the Subwoofer section.

[Lbk]

12 hours ago, Pete H said:

Let me try and find it.  Should be on the Subwoofer section.

If you find it great but the pic alone helps alot, thanks!

[Pete H]

1 hour ago, Lbk said:

If you find it great but the pic alone helps alot, thanks!

Found it.

[Lbk]

9 hours ago, Pete H said:

Found it.

 

[Lbk]

1 hour ago, Lbk said:

 

Very nice, interesting read and picked up a few new tricks. I PL'ed everything and had to use sandpaper to clean up joints, not fun. Thanks for posting it will help now and on my next build.

 

[Pete H]

10 hours ago, Lbk said:

Very nice, interesting read and picked up a few new tricks. I PL'ed everything and had to use sandpaper to clean up joints, not fun. Thanks for posting it will help now and on my next build.

 

Great!  That's why we're all here.  Great community and many have helped me along the way and continue to.  What are you powering the F20 with?  It doesn't take much.

[ClaudeJ1]

On 10/6/2020 at 9:19 PM, Lbk said:

Going to put an f 20 sub up front  centered on an 11ft wall, room is 11 by 17 by 8 ft. Which direction should I point the mouth opening, towards the near wall or into the room. If pointed towards near wall I could give it up to a 6 inch clearance, thanks.

After reading Todd Welti's paper for JBL all about subwoofer placement, #1 (the best for even distribution) is 4 subs in each center wall, which no one I know has ever done. However, even better than #3, which is 4 in corners, is #2 (which is truly second best) where you put one in the front center wall, and one in the rear center wall (standing up vertical if you need). Also, if you model your room, like I did, you will find that your sweet spot will be smack in the center of the room, which means 8.5 feet from the front wall for you. Have the F20's mouth firing directly outward, since your room loading (cabin gain) will give you a natural INCREASE of bass below 30 Hz.. But yeah, build 2 of those puppies and you will never have to upgrade your sub woofers for the rest of your life!

[Chris A]

On 10/6/2020 at 8:19 PM, Lbk said:

Going to put an f 20 sub up front centered on an 11ft wall, room is 11 by 17 by 8 ft. Which direction should I point the mouth opening, towards the near wall or into the room. If pointed towards near wall I could give it up to a 6 inch clearance, thanks.

You didn't really describe the crossover frequency to your fronts, which is a fairly important factor in your question, above.  I'll assume 80 Hz, but a lower crossover frequency is preferred if your fronts can go lower in bass response than ~40-60 Hz.

 

What I've found is bass bins (even horn-loaded ones) tend to produce a lot of harmonic distortion at the high SPLs that they're typically used at.  I've also found that these are not desired to hear in my listening preferences.  Other people seem to revel in "hearing the subwoofer" (i.e., listening to that distortion at higher frequencies) as part of their preferred listening experience.  Why am I talking about this?  I've found that a lot of people really aren't trying to achieve hi-fi reproduction especially at low frequencies.  I'm not one of those people, however. 

 

So realizing that frequencies above ~70 Hz tend to be attenuated via use of bass traps in room (and if you don't have bass traps, you're probably not very serious about sound quality at bass frequencies in your listening room), these harmonics can be partially absorbed in the listening room by careful positioning of the horn-loaded subwoofer mouth.  The lowest frequencies that are produced are not directional, but higher frequency harmonics are directional above about 80 Hz--so you can use this property to attenuate the harmonics without affecting the desired low bass output.

 

It's the length of the Owens-Corning 703 acoustic panels that's often used for bass traps (nominally 4 feet in length) that determine the lowest frequency (1/4 wavelength) of the bass traps effectiveness.  For a 4-foot panel across a room corner with one end against the floor or ceiling to form a closed-end cavity (like a Helmholtz resonator), that frequency for single-length bass traps is about 70 Hz.  [If you place two bass traps end-to-end across two room boundaries and one open end against a third room boundary to form an enclosed cavity, it will drop the frequencies that are absorbed by one octave (i.e., to 35 Hz), etc.]  I use single-length bass traps (double thickness 703 panels) which control down to 70 Hz, and then rely on the wall/ceiling drywall to absorb below that frequency. 

 

So to address your question:  I'd aim the mouth of the horn-loaded subwoofer away from the listening position, and in fact, add acoustic absorption material around the mouth of the subwoofer to absorb the higher frequency harmonic distortion.  I even use the backs of my Jubilee bass bins to extend the effective path length of each horn subwoofer behind each Jubilee by an additional ~3 feet, thus lowering the cutoff frequency of the subwoofers even more. 

 

Six inches of clearance from the wall to the subwoofer horn mouth is probably enough, but you can experiment with the standoff distance while listening at various places across the listening room for deep extended bass response.

 

Chris

[ClaudeJ1]

13 minutes ago, Chris A said:

Six inches of clearance from the wall to the subwoofer horn mouth is probably enough, but you can experiment with the standoff distance while listening at various places across the listening room for deep extended bass response.

 

Chris

You didn't mention that he should actually use a High Pass Filter at 20 Hz. to keep all the distortions down. Based on statistical observation of modern movies with lots of "boom" in them, there are very FEW of them with content below 20 Hz. anyhow. Unless one listens to big pipe organs, or dub step synthesizer music, there's no practical need for the F-20 to ever see a signal in the teens.

[Chris A]

33 minutes ago, ClaudeJ1 said:

You didn't mention that he should actually use a High Pass Filter at 20 Hz. to keep all the distortions down.

I don't use [extra] high pass filters in the LF circuit.  I've found that the phase shifts associated with them can take away almost 50% of the deep bass perception.

 

33 minutes ago, ClaudeJ1 said:

Based on statistical observation of modern movies with lots of "boom" in them

"Boom"" is actually in the 100-200 Hz region, and is the reason why bass traps are necessary.

 

33 minutes ago, ClaudeJ1 said:

Unless one listens to big pipe organs, or dub step synthesizer music, there's no practical need for the F-20 to ever see a signal in the teens.

I think this is a sweeping generalization.  The only type of program material that typically doesn't have much below 20 Hz is stereo music discs (especially phonograph records...but also CDs in practice).  Everything else (multichannel music, demastered stereo music tracks with deep bass response in the instrumentation--including bass drums and pipe organs, etc., and cinema/home theater movies, etc.) all have significant SPL content below 20 Hz in my experience, and this adds greatly to the listening/tactile experience, in my opinion.

 

Chris

[ClaudeJ1]

1 hour ago, Chris A said:

I don't use high pass filters in the LF circuit.  I've found that the phase shifts associated with them can take away almost 50% of the deep bass perception.

 

"Boom"" is actually in the 100-200 Hz region, and is the reason why bass traps are necessary.

 

I think this is a sweeping generalization.  The only type of program material that typically doesn't have much below 20 Hz is stereo music discs (especially phonograph records...but also CDs in practice).  Everything else (multichannel music and cinema/home theater movies, etc.) all have significant SPL content below 20 Hz in my experience, and this adds greatly to the listening/tactile experience, in my opinion.

 

Chris

It's a GOOD sweeping generalization, because it's true. Design for the majority and not the minority. I'm right about the MAJORITY spectral content of Blue Rays below 20 Hz. not being there. Keeping in mind that even IMAX specs out at 23 Hz. at the low end....................Also, the phase shift you speak of is an acceptable trade-off for the majority of people to lower other forms of distortion and save the driver from over-excursion or voice coil burnouts, since most people tend to overpower their subs as another general rule.

 

This is not right vs. wrong, it's still a choice involving physics, measurements, and sound perceptions. I happen to think it's a good trade. I accomplished my original goal by getting your to mention what you didn't mention before. FYI, I don't use high pass filtering either so I practice what you preach.

 

That being said, I looked up the bandwidth and distortion curves of the F20 from LilMike (the designer) and found that things get pretty nasty below 20 Hz. with that sub. Hence the recommendation in the trade off.

 

Obviously I don't totally disagree with you by practice, but the OP's circumstances are different from yours and mine, so it was just food for thought if nothing else. Like you, I'm just trying to help. I recommend a 60 Hz. Xover point to the subs for similar reasons you do, but I actually use a 40 Hz. crossover for my own subs with no high pass because I use only 200 watt amplifiers for my subs because the drivers can handle 1 and 4 Kilowatts respectively without damage. Such is not the case for the F-20 driver. Safety first, with or without Covid. My room dimensions are similar to his, FYI and my subs couple together as one below the 40 Hz. crossover.

 

[Lbk]

Down the road sub amp with subsonic filter for freg. below 20k. Play with cutoff freq. at 40 - 60 hz. Been wanting to to do room conditioning for awhile, moving equipment onto centered f20 will allow this. 

 

Chris how would I go about installing acoustic material around  horn mouth. Material on sides of horn mouth ( an acoustic channel around mouth ) or directly over mouth?

 

Till I decide to build if I want to another f20 I could try my revel b15 centered on rear wall.