Big sub sealed

Hello diyers,
I've been playing sub-less for few months but with time I realised I was really missing a clean first octave.
My boxes are not able to go very low, it's 2x 15OB350 per side in around 200 L.
They can go low with EQ of course, but they just sound better crossed around 35/30hz, lower is just noise.
Don't know if it's the drivers high fs/qts, the "still" too small boxes or maybe not strong enough, or the room placement, probably all combined.
I see them more as big mid-bass in fact.

I had in mind to upgrade the drivers at one point, for the nero-15sw800 that should better fit the needs, but even if they're not that expensive it's still four of them that I'd need. And more important I'm not 100% convinced it will be a big improvement due to the mains placement.

So before going there I have to try spread bass again, within following constrains:
1 - nice look and integration with furnitures
2 - high sensitivity
3 - critical damping if possible

#2 means big drivers, I still have my four 18sw450 from my previous dipole, why not using them?
#2 and 3 kind of go together, but against #1 for the size implied.
#3 is a way to finally decide for myself if an L/T box can really sound the same as a big natural one (and I believe not, but lets' test).

I started with what I had around and within the new room layout constrains, with a sealed um12-22 in maybe 100-120 liters (much bigger in real but with sand walls) right behind me.
Not bad at all but not enough juice, plus it's not easy to nicely integrate with the furnitures.
I couldn't try my old concrete ported one as I got rid of it few months ago (and for that I had to destroy it in place, too heavy to get out 😛). I don't regret, it stayed for years unused in the same spot, it was fun to build, but also just too bulky, and too hard to move around to test different spots.

So, I had to find a way for 2-3 subs, placed behind me, light enough to move around a bit, but big enough to not require an L/T, easy?
Thought about it few months ans was about to buy woods when… again my favorite/hated shop just launched a new serie: the rådmansö.
Beautiful pieces in my mind, I would have loved to start with these when I've built my mains, a lot of cool stuff could be built around them.
Went to see them in real, and realised even the big one could do it, this one, 159x64x46cm, 468L. :

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Got one, some mdf, some valchromat and let's go.
Like previous stuff I've just built a box within a box, 18mm glued all around inside, 24mm for the back, half the baffle doubled in valchromat, bracing with scraps, kind of light. The good surprise is that the radmanso is full particle boards, no honeycomb core on this like on many others, so nearly 4cm thick particles + mdf at the end.
The baffle is removable so I could add more bracing later if needed (I already found a spot that may need it).
And I could try 1 or 2 drivers, even clamshell isobaric if the box is still not big enough 😛
It's around 330-350 L. I'm guessing. Yes I did some sims but, they're just sims…

I of course did few mistakes again, my very first move was one! While sanding the inside of each panels for better glueing, I messed up and sanded the wrong spot of the panels, the edge that would have been visible outside. So I couldn't get the recessed baffle like I initially wanted.
Damn' what an idiot. So the baffle is now flushed, I'm sure it would have looked much better with the recess (like the mains).
Maybe I'll add a fabric grill, I'll see, it's fun to see the big driver too.
Then the valchromat was finished with tung oil, for a nice dark contrast.
Some details are left for later like the right cable, neutrik connector, better driver screws, replace temp wheels once in place to decouple a bit etc.
Not sure I’ll use the original steel stand that comes with it, it’s sturdy but will add 20cm in height.

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I quickly plugged one little fosi on it yesterday and it seems promising, efficient for sure.
I hope I can move it in the right place soon to measure it.
Meaning right below the diffusors behind me, where I now have a bunch of besta used for storage.

In all this I kind of try to find the same effect I had in my car years ago. I might repeat myself but it was so fun with 2x15'' at few cm right behind the head. Breathtaking was the right word, literally, and I'm not talking SPL, just air movement in your lungs even at low levels, like someone with a pump trying to empty your lungs at every beat!

Of course home environment is a total animal but if I can get 10% of this I'd be happy 😛
Will come back with measurements soon, if a success I will build another one, and maybe even 3 in total.
Cheers!
 
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Hi!

I'm just curious to understand your goals.

If you speakers are for indoor use and not for super high SPL, why do you limit your plans to have a high sensitivity speaker?
In general, they don't have a good bass extension.

According to your description, your first box had 200 liters with 2x15OB350.
In this configuration F3=44Hz and F6=41Hz. Too much space and material for not a good result.
For a pleasent bass response, F3 must be at least 30Hz.

With your new size, 350 liters sealed and just one 15OB350 speaker, things will get just a bit better: F3=43Hz and F6=33Hz.
Still, a lot of volume for just F3=43Hz

The option with your speakers would be a ported box which can be easily implemented in your project (just a round hole and a duct).
With 350 liters tuned at 25Hz and 1 x 15OB350, you can have F3=25Hz and F6=21Hz - This is really good!!

On the other hand, if you use a lower sensitive subwoofer SB26SFCL38-8 (10" / 88 dB SPL), less than EU100.00, for example, in a 350-liter box tuned at 19Hz you get F3=16.5Hz and F6=15Hz. This box would be something really special and with amazing listenting experience.
 
Hi Ron68!
I do like pro drivers yes, but I also enjoyed more typical sub when size was a constrain.
About the low extension they can often do just the same, their efficiency largely compensating their slope.
Plus they’re really happy to go higher if needed.

But I see that I wasn’t clear.
The 15OB350s are used in my actual main speakers (check the link at the beginning), I picked these at the time for their price and because I wanted to stay sealed.
Their response goes down to 30Hz naturally where they're placed, a bit lower with EQ but then don't sound right so low imho.
I also want to use multiple subs to manage some room modes.

One of the goal was also to re-use what I already have (that's 3xUM 12 and 4x18SW).
I could have used the 12s in small boxes like in a previous setup, but wanted to test the big ones.
So the new boxes are for sub only, will be placed in the back where I don't have size constrains, kind of nearfield (around 1m.).
And I don't want ported right now, I just prefer sealed, for the ease of integration with extension and delays, and sound preference, so far.
Now it's not a guarantee that it will work, all will depends of the integration, will have to keep the xo low, or play with a bit of overlap with the mains I'll see.

One last thing, I really enjoy for some reasons lowering the power needs, simpler and smaller amps, or even tubes.
Got down to 2w for mids and high, 100w for the woofers with low boost but much less without.
Based on the quick test yesterday I imagine the new subs to be happy with less than 100w too.
 
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Started the integration yesterday.
Bit of a pain to remove all diffusors to place the sub, centered for now.
With two I will spread them apart a bit, symmetrically or not from MLP.

Capture d’écran 2025-04-29 à 08.55.49.png

Capture d’écran 2025-04-29 à 08.55.54.png


Anyway, nearfield and MLP sweeps:

Capture d’écran 2025-04-28 à 13.11.01.png
Capture d’écran 2025-04-28 à 13.09.04.png


I'm guessing the large dip between 50-70HZ comes from a mix of ceiling and front wall cancellation (2.7 and 5m.)
Should be manageable with 2 subs and a bit of EQ.
And I could try to add a bass trap on the ceiling right above me, already have a bunch of diffusors up there but really thin, mostly for the highs and the look.

I can only show these screenshots because for some reasons I can't save my REW files since few days!
So strange, the soft won't let me, not such a big deal because I don't really save anything anymore, just too many files and I usually don't reopen them anyway if I can finish in one session.
But now I need more time for these subs, I should try to reinstall it maybe.
Or maybe it's due to my recent mac update.


Also some DATS measurements, out and in the box:

18sw450 out.png
18sw450 rad 8c.png


I selected the driver with the lowest FS of the four, 28HZ when all 3 others were around 32Hz, similar Q for all, at 0.35.
The in-box sweeps shows a little messy impedance.
8 polyester cushions inside, it's a bit of a pain too to remove the baffle especially now in vertical position so I won't adjust that soon.
Only when the second box will be ready once I displace everything again.
Box Q is very low so I wonder if I could just add another driver in there, after all I have four, and then use the smaller box/dresser for the others…


Then started the XO work, ended up with 50Hz at 24db LR, acoustic.
Tried some overlap and it was not bad but I would need more time.
The sub has severe eq cut and I tried to minimise EQ use on the main woofers.
In fact I now don't EQ them at all and it sounds good.
Took the following screenshot during the process, these are not MLP sweeps, but nearfield to track the targets.
MLP sweeps were of course a lot messier:
Capture d’écran 2025-04-28 à 13.29.56.png



I struggle a bit to define the time delay, I have to favor one side of the main, both can't sum perfectly at the same time.
it could be good for 90% of the tracks and then suddenly something will sound off or the sub will start to call attention on a few new tracks.
But it's on the right path I think, there's definitely some breath/chest effect.

Funny thing is that I seem to play everything at a lower level, maybe around -5db for a similar feeling.
Sub energy is so dense that the mains use now even less power (and of course for the woofers).
This is the honeymoon period, revisiting tracks is fun but I need to find the sweet spot between thump for electro and not distracting for jazz.
And I'm surprised that it doesn't rattle more, it’s only on 4 little wheels and on a concrete floor, but maybe the diffusors weight tames that.
But all this will be more clear once I can share measurements again!
 
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