Arcsabre

1 hour ago, kipman725 said:

I have made subs that are long like this and yes you need a lot of stuffing to combat standing waves, the higher you can push the first standing wave up in frequency the more effective the stuffing will be:

Another thing to consider is your driver placement is a worst case scenario for standing wave generation (mid pipe).  If you consider possible standing waves in the pipe you can have a maximum at the driver and two minima at either end at 86Hz (fundamental modes.  You would be better off putting the driver at one end.

Make sense to me actually my speakers Dynaudio C5 is designed in the way you described. Instead of using the conventional design which is the woofer in the middle of the cabinet, they had the woofer on top end of front baffle and they have one of the tightest and most accurate bass for that price. (although not much, as they are sealed and I put them away from the corner. they sound so bad when you put them in the corner)

Perhaps I would put one driver on each end of the long box haha...

5 hours ago, SME said:

@kipman725: I'm pretty sure he's not talking about a DBA.

Hi @arcsabre, I think I know what paper you are referring to.  It's also covered here: https://www.audioholics.com/room-acoustics/optimum-locations-for-subwoofers-in-rectangular-rooms

The study is a theoretical investigation of standing wave room resonance behavior, and the opposing mid-wall placement recommendation arises as the optimal placement for two subs (run together as one, with no differential delay in the signal going to each) that minimizes seat-to-seat variation of frequency response in the room interior  I want to highlight a number of problems with taking that conclusion from the study and running with it.

First, the study is theoretical and does not consider absorption and losses in the walls, floor, and ceiling.  Unless you're inside a bunker, those losses are not trivial .  The lack of symmetry due to different kinds of construction on different walls is one thing.  If your walls aren't particularly rigid, you may not have much of a problem with standing waves anyway.  That's because standing waves require multiple successive reflections to build up.

Second, mid-wall placements typically have poor output efficiency and suffer more from boundary interference effects from the adjacent walls.  My own experience is that these problems can be severe.  Depending on your room, such interference problems may predominate over standing waves for much of the response.  In general, subs are most efficient in a corner because the corner allows more pressure to build near the cone, which improves energy transfer.  This efficiency boost is very important because it reduces the amount of equipment and cost required to reach a particular output goal.  Also because the sound energy spreads through a smaller section of the unit sphere ("pi/8 space" vs "pi/4 space", the directivity is effectively higher, meaning you get high SPL for the same power output too.  Even the paper notes that mid-wall placements tend to have poor output vs. corner placements, but they are focused on minimizing seat-to-seat variation regardless of cost or compromise.

Third, the study treats the subwoofer system completely independently of the mains speakers.  The trouble here is that the subs do eventually cross over with the mains, and that crossover region is quite broad even with fairly steep high order.  For an 80 Hz crossover 4th order LR, it might be 60-110 Hz, which is nearly an octave, and covers frequencies that are crucial for enjoying all bass content.  IMO, a good crossover with the mains is likely to be *more important* than avoiding standing waves at lower frequencies, especially if your focus is music.

My suggestion if you are building two subs is to put one in each front corner of the room.  This puts them relatively close to the mains, so they will be more likely to combine  with the front channels at multiple room locations.  These placements will also cancel out some of the standing waves along the width of the room, if that's a problem for you.  It will not cancel out standing waves across the length of the room.  This is most likely to be a problem for in the very middle of the room (length-wise) or a little further back, and if it's possible to move those seats even a couple feet, it might make a big difference.  If you can build 4 subs, then you can put one in each corner.  Though this might make integrating with the front mains channels a bit trickier---or not.  A lot depends on specifics.

Thanks mate, there's so much useful knowledge in your response...I need to spend more time considering every point you made. And my view is somehow similar to yours, only that the room does not allow me for such setup. Please see the attached picture. Meaning of different color: Yellow-Lights, irrelevant here. Blue-Absorption Purple-Diffusion DarkBlue-Bass Trap. the bottom of this plan is the french doors and that opens up throughout the whole wall (left wall to right wall all the way) thus subwoofers cannot be put there...

After reading your response I do agree with you on the priority of bass design - room mode shouldn't be a major concern, especially when using dual or 4 subs with DSP. However throughout years of using subwoofers from big brands - SVS and Rel especially - I do find putting subs close to the corner do sound muddy and boomy and I had no luck fixing that using DSP in the past. If room modes and phase problems emerging from reflections adding onto/cancelling each other are not that important, how can we make subs sounds good in the corner? (like how they should perform on paper)I mean putting a reasonably sized merchandise subwoofer right in the corner shouldn't blur the bass on paper - but it does in reality. I'm not 100% sure what the issue is.

In my case I have 4 units of Dayton UM15-22 subwoofer driver. The amp I've prepared are not subwoofer's plate amp but Hypex NC500 monoblocks. I'm using one for each subwoofer and these amps can output 700W clean power stably, for each channel. I've got really inefficient floorstanders Dynaudio C5 (sensitivity=83db) and these monoblocks drive them easily ------ only need -30db from preamp for really loud symphonies I compared with my friend's Dynaco and Krell, and they cannot get much bass out from the C5. so with the Hypex amps power isn't really an issue here.

After reading your inspiring response I think there are three ways I could use the drivers in this room and they are:

1. 2 sealed subs, with one driver on each enclosure. Both subs on the floor, one located at mid-backwall, one located at mid-frontwall. But as there's a french door in front the front sub can only get so close to it (there will be a gap at least) and my impression is this is a kinda embarrassing distance from the wall, not far enough to avoid reflection issues but also not close enough to solve them in another way.

2. 2 sealed subs, with one driver on each enclosure. Both subs on the floor, located below the 2 bass traps (see the floorplan). fit snugly against both walls of the corner.

3. 4 subs mount directly onto very thick MDF - such as a 3" thick one made of 3 sheets of 1" with green glue between them. 4 MDF board mount onto the midpoint of each wall, for side walls ------ 1 meter from the floor and 1 meter from the ceiling. For backwall ------ floor. For front ------ Above french doors. Use pure amp power to push them hard enough so they work to desired SPL without enclosure.Kinda like IB subs but I don't have that much space in the wall.

Which way would you recommend? Much appreciated (go back to read your response again🏋️‍♂️)

47 minutes ago, kipman725 said:

I have run between one and 4 subs at home and much prefer 4 subs, they are mostly corner placement.  I take a frequency response measurement at each seat of my sofa and vector average the results.  After I have dialed in the sub crossover I fit the response to a target curve below 500Hz as my main speakers are close in to the corners and designed to be flat in free space  so this has to be compensated for and there are some large peaks in the lower bass that need to be cut to avoid the whole thing been boomy.  Works well but I wish there was a more scientific method.  SME when you say flattest possible response do you mean an actually flat response? as from my understanding a constant directivity speaker in a domestic room which has a flat free space response should have a tilted downwards response in room (and will sound natural in this condition) so equalizing to flat in room will make a speaker sound overly bright.

What you said about the flat response is correct. If a speaker's in-room response is EQ'ed to be flat (or downward-flat) that literally means Direct Sound + all Reflection = fixed number across all frequencies, and since almost all speakers has non-linear off-axis SPL, trying to get flat in-room response like this would mean wobbly output across all frequencies. Of course this wouldn't sound good.

In my layman's understanding the flat response and downward-flat in-room response thing simply means that's people's average preference, if there's a pair of speakers that performs consistently on-axis and off-axis. Statistics averages out different speakers' frequency response (both on-axis and off-axis) so what we are seeing from those study tells us something about all tested speakers as a whole, and simply applying it without careful tweaking would almost guarantee generating weird sound, for any particular pair of speakers.

So if we have a pair of speaker which measures flat in an Anechoic chamber, both on-axis and off-axis, and output narrows linearly as frequency goes up - would measure flat downwards in a normal room, and sound excellent to most people. Of course no speakers are this good yet.

Sounds like we're in the same situation but I guess I'm just asking in advance before going out to the workshop and start cutting MDFs 🤤

Like this - although ultimately I'm looking at building one with sloped front baffle. More like a trapezium or triangle, viewed from left and right side.

indicative only - would need to develop internal bracing , stuffing .etc in the official design

Hi I am just wondering if a sealed subwoofer box with a size of, say, 30cm x 30cm x 2 meters, is going to work out? this gives us around 6.35 ft³ of box size, which is ideal for some 15" drivers to have a Qtc of around 0.7, which seems to work out on paper.

I am trying to build something that stays as close to the back wall as possible without having to knock a hole on the wall. With such proximity to the wall (thinking of it as a wedge against the backwall) the phase cancellation would not occur until goes up to above 200hz. way above the crossover point.

This design would allow it to stay close to the wall and have decent box size without standing out like a sore thumb in the room (and got Mrs as "excited" as you could imagine)

But seem to be a weird design aside from on the paper. (Anyone seen such thing before?) Do you think it's going to work similarly to a traditional shaped subwoofer of the same internal size?(like 1.8' x 1.8' x 1.8')

I suppose with a sealed box it is less concerned about the internal structure? (compared to a ported one, which may require complicated air path internally)

Anyone could shed some light? Much appreciated

If someone has tried this setup and found issue I might just go for a single 21" DIY sub in the middle of the backwall like something Ricci designed...

16 hours ago, peniku8 said:

I think he is planning to run a double bass array, which works best if everything is perfectly symmetric. I'm not sure how well this particular arrangement would work, but I guess it wouldn't hurt to try.

That's right and I'm just more concerned about whether this setup is going to work similarly as the "front-wall-midpoint" and "back-wall-midpoint" dual sub method which has been proven to work well. I will run test with measurement mic and REW after installation but I probably have to fix them to their position once installed (especially the ceiling one). I am able to adjust the phase and EQ afterwards but not relocate them so just wanna see if there's any obvious issue that can only be solved by moving them to a different place.

Hi all, I am currently designing a DIY subwoofer for a rectangular theatre room which is to be built and fixed to the floor and against the back wall. It will be located the midpoint on the virtual floorplan view.

I've done some research and Floyd Toole's paper inspired me of a symmetric dual-sub setup, with Sub1 placed at the midpoint of the front wall, and Sub2 at the midpoint of the backwall. Both are sealed.

However as the front wall of my theatre room is actually french doors I can't have Sub1 built the same way as Sub2. I have to tweak the idea slightly.

I am now considering to build Sub1 at the midpoint of the front wall but just below the ceiling instead of on the floor. so the 2 subs will still be symmetric but the symcenter is in the middle of the room in 3D, instead of the center of the floor.

Is there going to be some issue if I have Sub 1 firing towards the audience's face but tilted downwards (like 25° or so) while Sub 2 firing towards the back of the audience but tilted upwards?

I've never seen such design that's why I'm just a bit concerned.

I'm aware of bass being omnidirectional and I'm not really worried about that part. Just what do you guys think about this idea in terms of any potential phase cancellation/wall reflection? I'm going to have my subs fixed to the walls and possibly the ceiling and floor.

In this case I should be able to get relatively clean bass due to non-existence of reflected bass from the back wall right? I see Floyd Toole's paper in which he tested subs against the walls and some dual setup (and quad sub setups) could actually provide excellent result, contrary to the common understanding that "subs should be as far from the corner & walls as possible".

The size of the sub in the picture 1 below is only indicative and I am planning to build relatively wide enclosures so the size of the boxes isn't going to be too small. the size I'm currently thinking about is h330 d270 w600 (height and depth are shown in the picture) a relatively wide shape. I can certainly go wider (not taller or deeper) but I'm slightly worried about matching the damping factor of the enclosure to the driver. Currently I yield a Qtc of 0.4688 using a 15" subwoofer driver from Lavoce (see picture 2). A lot people recommended a Qtc of 0.707. If I go wider the Qtc of this DIY sub would drop below 0.4688 and getting even lower. So I don't know if this is something that's limiting me from going any wider.

Would be great if any one knowledgeable could shed some light 🐸 thanks all ba(by)ss

Pic1

Pic2