Compact 10-12" DIY Sub

[Swizzy]

Hi everyone, I've been reading a ton about subs lately and have the increasing urge to finally build an active one. At the moment I have some Mackie CR3 speakers on my desk and a Jamo Sub210 8" under my desk hooked up to my PC. The subwoofer really fills the sound out but it doesn't really go far below ~50hz or so.

The room I'm in isn't large at all, 2.2mx3.2m roughly (plus a wardrobe, desk, a couple of PCs etc) which made me think about Hoffmans iron law. I dont need loud plus the room is small, I just need small and low! The Mackies max out at 97dB per pair, I rarely have them over halfway.

I have some experience using WINISD however I'm unsure of what I'm aiming for in terms of response. On the Transfer function mangitude graph, am I supposed to be making the longest flattest line possible with a steeper rolloff or a nice even curve?

I've been looking at the SB Acoustics SB29SWNRX-S75-6. If I go for a 1.75ft^3 (50L) box with a 24hz (4x30 inch port) tuning I get this

An externally hosted image should be here but it was not working when we last tested it.

80W signal results ~103dB output -3dB being at ~23hz, port air velocity just under 16m/s.

I know it's almost pointless asking but how would this compare to the Jamo I already have? It's roughly a ported 12" Cube, 8" driver and boasts -3dB 38-200hz but there is already noticeably lower SPL below 50hz.

Also I keep reading that we don't perceive lower frequency waves as well so how would I work out how many dB I need to keep up with the 97dB Mackies?

I know it's a lot of questions at once so feel free to take a stab at any/all of them and I'm fully open to suggestions.

I'm also aware that this will most likely be an awful return on investment, especially as a first timer. I wouldn't mind spending up to £300ish if it will get me decent results.

EDIT: Not sure why the picture isn't loading up. Uploaded to imgur and inserted using the forum.

 

[SpeakerBob]

Have you considered a small sealed box with a pair of 10's, or a pair of 12's using a Linkwitz transform ?

I think it could work well for your application.

Also maybe consider some of the better car audio brands as they can work out to be excellent value compared to more 'hifi' orientated drivers.

Rob.

Edit: Try uploading your image directly using the attatchment function when you post.

 

[Swizzy]

Thanks for the reply.

I'd be more than happy to consider a sealed but I've never used DSP for a sub before, I've done some minor correction to the Mackies though.

I had a quick look for a driver for a sealed box for cars and came across the Focal 30A4 12" for £90. Manufacturer suggests between 20-30L which seems perfect.



I tried to apply a linkwitz transform in winisd but it drove cone excursion off the charts. I'm guessing having to reduce input power to stop cone overexcursion is the price I pay for extended lowend?

Thanks for the attachment tip, it's been a while since I've used forums.

 

[SpeakerBob]

Yep the trade off for small and deep is low output at deep frequencies. If you think over excursion may be a problem at the lowest frequencies you could always apply a high pass filter to limit excursion. Don't forget you may get some room gain in the small room which will help real world results.

Cheers,
Rob.

 

[Kdent]

Also I keep reading that we don't perceive lower frequency waves as well so how would I work out how many dB I need to keep up with the 97dB Mackies?

Not sure what music you listen to, but most modern music wont go below 30-35hz unless your going for a home theater approach. If your planning on installing a powered plate amp on your subwoofer then you can adjust the gain via a knob to keep up with your speakers. A good rule of thumb is that your base shouldn't be overpowering by that you shouldn't be able to even realize a subwoofer is even in your room.



If you want the extension of a ported enclosure, and the tightness of a sealed enclosure, I would personally go with a passive radiator system.



When using DSP it important to know that the speaker pulls a lot more power as lower frequencies do. Also make sure when using DSP that the xmax of the speaker doesn't exceed its amount on the datasheet.


Let me know if you have any other questions.

 

[Swizzy]

Thanks for the info Kdent.

I guess what I mean is is that I'm worried I will build something that isn't loud enough. I'd rather build something too loud and turn it down than run something at 99% capacity. Is it also fair to say having headroom in terms of SPL, lowend extension and cone excursion should help with DSP corrections, in case something needs boosting?

You are right about passive radiator systems, I've heard a few sealed bass guitar cabinets and some cheaper home entertainment subs and was surprised however I have zero idea where to start. I've seen a nice 14" cube build with an 8" driver and passive radiator but the frequency range probably isnt much better than what I have already. The couple of 12" PR designs I've seen are rather expensive, with the PR + driver already going towards £250. Do drivers work similar in passive radiator systems as in a vented design because I'm not sure what to look for in terms of T/S parameters.

I know the questions seem endless but theres so damn many drivers in this world!

 

[kipman725]

Get a high excursion 12" and put it in a small box, add as DSP amplifier and EQ to taste. I wouldn't worry about the freqeuncy response too much as long as you can drive the cone to xmax with the power you have available. You will also want a measurement microphone as adjusting the crossover and level by ear is challenging.

 

[bjorno]

Thanks for the reply.

I'd be more than happy to consider a sealed but I've never used DSP for a sub before, I've done some minor correction to the Mackies though.

I had a quick look for a driver for a sealed box for cars and came across the Focal 30A4 12" for £90. Manufacturer suggests between 20-30L which seems perfect.

View attachment 817571

I tried to apply a linkwitz transform in winisd but it drove cone excursion off the charts. I'm guessing having to reduce input power to stop cone overexcursion is the price I pay for extended lowend?

Thanks for the attachment tip, it's been a while since I've used forums.

Hi Swizzy,All

FYI, Proof of Your suggested 2.1 System is in the Pudding(IMO OK) as can be seen in the submitted Pictures:

b

 

[waxx]

I would take a different approach, a 75L sealed sub with a 12" SB-ACOUSTICS SB34NRX75-6 get you there, even without linkwitz transform with an F3 of 35Hz and more important for a sealed sub, an F10 of just above 20Hz. You can make that box fit under your table, it's not that much bigger than what you had in mind, but it will sound better. Add a plate amp with low pass filter or dsp (like a Hypex F251, but cheaper will also work) of0 your choice and you're set. A very basic modelling gives me a cabinet of 45x45x55cm of 18mm plywood, and that is with some space calculated for the plate amp and bracing.