Help with deciding subwoofer design.

[ppataki]

Forgot to mention it, but yeah, I was planning on filling all volume with rock wool.

Why skip the divider?

What's a Sealed DOS

both baffle was done with a flush cut bit for the opening. so they're are as symmetric as I could make them. Reading your comment I think I get what you mean. Id have to make sur the opening are positioned exactly at the same distance from the back and the front for example.

Also made me realize I forgot to put a picture of my "folded acrylic grille" concept.




I really dont know how to answer to this. I dont know.


thanks for you reply!

DOS stands for Dual Opposed Subwoofer - when there are 2 or 4, etc. bass drivers in one single sealed cabinet on the opposing sides (like 1-1, 2-2, etc.)

You can check some of my designs:

Dual Opposed Subwoofer project (2x RSS210HO8)

This is yet another project that we will start relatively soon. It is linked to another in-process project: https://www.audiosciencereview.com/forum/index.php?threads/home-theater-project-using-markaudio-chn110.26019/ that we are doing for my neighbor (who is the carpenter :)) The above project...

www.audiosciencereview.com

DOS subwoofer with 4x 6.5" woofers

I am posting this on behalf and with the permission of one of my friends who has built this project Concept: Dual opposed subwoofer (DOS) using 4 pieces of 6.5" Tang Band W6-1139SIF subwoofers, 2 in the front, 2 in the rear Closed cabinet with the below properties: Made with 22mm thick...

www.audiosciencereview.com

and there is a fresh one too but the internals are not done yet:

Another Markaudio CHN110 based project with a Beyma DOS sub

Just sharing yet another project I designed for my brother-in-law this time Basically it is about building two sealed cabinets (baltic birch plywood) with Markaudio CHN110 drivers and accompany them with a sealed DOS (dual opposed subwoofer) sub using 2x Beyma 8BR40/N drivers. Here is how the...

www.audiosciencereview.com

I have never seen a DOS with a divider - that would make it into two separate subs.

Your UM15 drivers are DVC subs; DVC stands for Dual Voice Coil, meaning that each driver has two voice coils (having a resistance of 2 ohm each) hence two sets of speaker terminals
If you want to drive them with a 1-channel amp you will need to wire them properly. You can wire them in three ways:
1. Total resistance will be 0.5 ohm
2. Total resistance will be 2 ohm
3. Total resistance will be 8 ohm

I guess you would want to go for the 8 ohm solution which requires the voice coils to be connected in series (so 2+2 ohms = 4 ohms) and then wire the drivers in series too (4+4 ohms = 8 ohm)
If you will be driving them with a 2-channel amp then you will only need to wire the voice coils in each driver, again in series to have 4 ohms each

 

[fineMen]

Forgot to mention it, but yeah, I was planning on filling all volume with rock wool.

The drivers are of modern design, much venting on the back? Better not use rockwool because it will decompose not quickly but surely and even tiny amount of the drebris can easily ruin the drivers.
DOS still needs bracing. But bracing doesn't need to be that massive or precise.
A port needs to be of sufficient size, really. Otherwise the chuffing from rapid air movement will limit clean output. The chuffing is way more distracting than harmonic distortion. In consequence a sealed box may deliver more subjectively clean sound for a given volume.
The sub is greatly oversized given the room as depicted.
A sealed box is easily tuned to a desired f-3 by equalization, don't worry about the raw roll-off. (I use 450cm^2 of cone area in just 18 liters of internal volume. F-3 is 85Hz and still after e/q have massive output at 20Hz. )
In subs there are no substantial standing waves to be considered. 3 foot => 330Hz => 150Hz first resonance outside of the targeted bandwith, in this case anyway canceled by opposing drivers. (Don't believe, do the math considering the phase.)
Driver differences, if at all significant, affect very low frequencies only, say 5Hz or so, don't worry.
Avoid, as already decided, 'down/up/firing' because especially subwoofer drivers tend to develop a sag. The cone slowly creeps under the influence of gravity which cannot be undone. (Like shelf boards under heavy load, its permanent after time.)
The design with the slot might will show some chuffing if the corners are not rounded at say 1" of a radius. Same might apply to the grille.
A 'devider' won't cancel the DOS functionality.

Not mentioned yet in this thread: if sealed, don't over-seal ;-) You know weather, so you know air pressure and that it changes. Better to leave a tiny leakage path to provide equalization. A bore of 1mm width suffices but may need a felt pad to dampen too rapid air flow preventing whisteling.

 

[Wolf]

I watched the other thread over there, but kinda stayed out of it.

Honestly, if you do the slot loaded, open BOTH sides, not just one, to avoid the cavity resonance between the drivers and the slot volume. I think this would be fine. No grilles to rattle. Space as far as you can in between.

The rockwool needs to be loosely confined to keep the drivers safe. If you use it, place between the brace walls and glue poly batting in a circle over the top. This will reduce the fiberglass fibers moving through the cab and motors. You can also mount the drivers into a poly batting envelope for double security. Honestly, I find the blue denim insulation to be just as effective, and no problems with fibers.

Having built many, brace and loosely fill the volume if sealed. You don't want sound from inside getting outside. Stiffen wit braces, damp with stuffing, and mass load with ceramic tiles or rubber mats. You will thank me later...

The Inuke has 2 channels, run each sub in series per channel for 4 ohms per amplifier channel. Use a Neutrik 4 pole Speakon for connection.

 

[Sebr023]

DOS stands for Dual Opposed Subwoofer - when there are 2 or 4, etc. bass drivers in one single sealed cabinet on the opposing sides (like 1-1, 2-2, etc.)

Gotcha! learned something today

I have never seen a DOS with a divider - that would make it into two separate subs.

Somebody with more knowledge than me could chime in On that.

Your UM15 drivers are DVC subs; DVC stands for Dual Voice Coil, meaning that each driver has two voice coils (having a resistance of 2 ohm each) hence two sets of speaker terminals
If you want to drive them with a 1-channel amp you will need to wire them properly. You can wire them in three ways:
1. Total resistance will be 0.5 ohm
2. Total resistance will be 2 ohm
3. Total resistance will be 8 ohm

I guess you would want to go for the 8 ohm solution which requires the voice coils to be connected in series (so 2+2 ohms = 4 ohms) and then wire the drivers in series too (4+4 ohms = 8 ohm)
If you will be driving them with a 2-channel amp then you will only need to wire the voice coils in each driver, again in series to have 4 ohms each

i recall briefly thinking of how I would connect them back in last december when I designed the subwoofer. But honestlyt i dont remeber anymore.
I think I have a pair of speak on which has 4 terminal on them.
but if I recall correctly, I only have 1 terminal for the subwoofer.

Is 8 ohm better than 4 ohm ?

I'm more of a wood worker than an electrical guy, that part makes me dizzy XD

 

[Sebr023]

The drivers are of modern design, much venting on the back? Better not use rockwool because it will decompose not quickly but surely and even tiny amount of the drebris can easily ruin the drivers.

Rockwool is not firbergalss wool. Dont think it ever decompose nor come loose. but I would make some sort of fabric wall to keep fiber not on the driver side

DOS still needs bracing. But bracing doesn't need to be that massive or precise.

So I should remove some to get back the internal volume? Filling the space with rockwool give you back 15-20% IIRC.

A port needs to be of sufficient size, really. Otherwise the chuffing from rapid air movement will limit clean output. The chuffing is way more distracting than harmonic distortion.

Thats why I went with sealed. Didnt really have the space to put a port in there.

The sub is greatly oversized given the room as depicted.

What you mean?

In subs there are no substantial standing waves to be considered. 3 foot => 330Hz => 150Hz first resonance outside of the targeted bandwith, in this case anyway canceled by opposing drivers. (Don't believe, do the math considering the phase.)

I dont know what the math is for that.

Driver differences, if at all significant, affect very low frequencies only, say 5Hz or so, don't worry.

Ok. thank you.

Avoid, as already decided, 'down/up/firing' because especially subwoofer drivers tend to develop a sag. The cone slowly creeps under the influence of gravity which cannot be undone. (Like shelf boards under heavy load, its permanent after time.)

I know theres a math for this too, but I dont remeber it. anyway, the intent was to cancel vibration since it would be a table.

The design with the slot might will show some chuffing if the corners are not rounded at say 1" of a radius. Same might apply to the grille.

Mmmm.. I prefer the look with not a round over, but I understand the issue. Can it be a chamber instead of a round over?

A 'devider' won't cancel the DOS functionality.

thats what I beleive, but its my first subwoofer. but I dont see why it would.

 

[Sebr023]

Honestly, if you do the slot loaded, open BOTH sides, not just one, to avoid the cavity resonance between the drivers and the slot volume. I think this would be fine. No grilles to rattle. Space as far as you can in between.

Yes of course, both side would be open, like the screen shot.

The rockwool needs to be loosely confined to keep the drivers safe. If you use it, place between the brace walls and glue poly batting in a circle over the top. This will reduce the fiberglass fibers moving through the cab and motors. You can also mount the drivers into a poly batting envelope for double security. Honestly, I find the blue denim insulation to be just as effective, and no problems with fibers.

Yes! didnt think of using fabric what ever poly batting is. but thats a good idea.

Having built many, brace and loosely fill the volume if sealed. You don't want sound from inside getting outside. Stiffen wit braces, damp with stuffing, and mass load with ceramic tiles or rubber mats. You will thank me later...

Subwoofer will already be like 100-150 pounds with both driver and woods.

The Inuke has 2 channels, run each sub in series per channel for 4 ohms per amplifier channel. Use a Neutrik 4 pole Speakon for connection.

That the type of speakon I purchased IIRC. But for the connection, I'm a bit lost hahaha.

 

[Wolf]

If going opposed on both ends, using a divider is common and a good idea. If you have a driver failure, the loss of air spring on its side will not interfere with the other driver's air spring and not allow it to fail as well. Without the divider, both are subject to issues with the other.

Poly batting is just that. Quilts are made with batting, that is what gives them the loft or pillowing look. It is polyfill in sheet form as opposed to stuffing or wadding.

As to the Speakon, one pair to one driver (1+,1-), and the other pair to the other driver (2+,2-).
At the other end, where the amp is, and depending on the Behringer's connections, you'll have options. If they are posts, terminate with spades, bare wire, or bananas. If they are dual Speakons, then it could be done 2ways. Some pro amplifiers have both channels in a single Speakon, and the second channel in a Speakon. This way you can use a single 4 pole Speakon to connect both channels to one jack, or use 2 Speakons as one for each channel. Refer to your amplifier manual for clarity on this matter.

 

[Sebr023]

If going opposed on both ends, using a divider is common and a good idea. If you have a driver failure, the loss of air spring on its side will not interfere with the other driver's air spring and not allow it to fail as well. Without the divider, both are subject to issues with the other.

Poly batting is just that. Quilts are made with batting, that is what gives them the loft or pillowing look. It is polyfill in sheet form as opposed to stuffing or wadding.

I'm french canadian, so poly batting didnt ring a bell at all! but I googled it and i see what your talking about. Thing is I already have the rock wool from previous reno in my house. I'll use this not to throw it away.its a good point for the divider in dans not screwing with air pressur if one goes bad.

i kinda have the same problem for slot desing. if one goes bad, how do I get the drivers out ?!

It should probably be screwed instead of glued, but I was thinking this may be a bad idea cause of "sealed" part. Feel like it would be less air tight.

 

[Wolf]

I was not saying to not use the rock wool, but encapsulate it in the cab with the poly batting.

That didn't even occur to me, you are correct some measures would be needed. I would either:
A- make the woofer boxes swivel within the top and bottom panels. A clever locking pin or removable bolts would not be that difficult.
B- make the top and bottom removable from the woofer boxes.
C- mount with the drivers on the ends as a single box. =)

 

[fineMen]

Rockwool is not firbergalss wool. Dont think it ever decompose nor come loose. but I would make some sort of fabric wall to keep fiber not on the driver side

Rockwool, or better to say the fibers are quite brittle. They'll break. Ikea has cheap raw cushions that consist of polyfill. You don't need to mute resonances, so poly will do perfectly, maybe even better for increasing the compliance of the air.

Admittedly I looked into this thread for entertainment and was astounded by how far several propositions departed from what I (feel to) know. It's your first subwoofer. I only tried to help.

 

[Sebr023]

Rockwool, or better to say the fibers are quite brittle. They'll break. Ikea has cheap raw chushions that consist of polyfill. You don't need to mute resonances, so poly will do perfectly, maybe even better for increasing the compliance of the air.

Admittedly I looked into this thread for entertainment and was astounded by how far several propositions departed from what I (feel to) know. It's your first subwoofer. I only tried to help.

Haha and that’s fine and I’m glad you chimed in!

I have the rockwool, that’s why I would want to use this. If not, I’d have to throw away the rock wool and give it on marketplace cause now one will buy a single bundle of rockwool

 

[fineMen]

I have the rockwool, that’s why...

Maybe it would be feasible to stuff the rockwool into lady's nylons. But would you do that practically? The fine dust of common consruction rockwool is the pest. Gardening grade, still better not. I dismissed it, despite its excellent action against resonances, when those modern 'open' drivers came up.

Have fun with your project!

 

[Salt]

I use sheep wool for house damping without any issues.

 

[Sebr023]

Don’t know where you live, but a quick google search found a r-20 bag for 325$ that’s a bit too much for me. Haha.

 

[Salt]

Don’t know where you live

Germany.
And this it what I use:

https://www.bausep.de/daemwool-dws-wlg-044-schafwoll-daemm-matte.html

 

[dasdoing]

Picture 6-7 : LCR with laser cut grille, 3d printed grille stand off, and corian baffle (backed with 3/4 birch ply)

as others, I would be interested in seeing measurements with these panels on/off. it will most certainly also affect dispersion? also, it probably resonates.

 

[Sebr023]

as others, I would be interested in seeing measurements with these panels on/off. it will most certainly also affect dispersion? also, it probably resonates.

Yes. Probably all of this.

Like I said, I didn’t do it for sound quality. I did it to protect the driver and because I didn’t feel like having a regular cloth grille.

When I can, I’ll get measurement.

 

[Sebr023]

So I had a bit of time to play around.
And re-re install winisd.

Here’s the update design of the subwoofer.
Gives an internal volume, per driver, of 55liters. Qtc of 1.1

Blue line is if drivers are facing outward and have a 150 litres total. Qtc of 1 or 0.9.

Green mine is with a box of 450liters.

Legs are tbd. Cause I don’t know how I feel about those legs.

And Speakon connector / wire connection is also tbd.

 

[Sebr023]

Here is the graph with a linkwitz applied and a high pass.

The green mine is in 460l box. I applied a high pass because the excursion was off the chart too.

 

[fineMen]

Another recommendation. Today we don't deal with vinyl warble anymore. You may get away with just setting a nice clean 20Hz / Q=0,5 equalization target and done. All will be controlled by room acoustics, especially pressurization anyway.

I'm happy to experience like 9dB of a bass lift due to huge window panes that resonate cleanly (!!) at 30Hz. I'm living in a drum ...