Question 20cm deep sub??

indus

Distinguished Member
First of all please take into account that I know nothing about subwoofer design. At the moment I have a huge XTZ 3X12 subwoofer and it's a bit of an eyesore as it has to sit under the screen. My room is only 5.5m by 3m and so there aren't any other options for placement for this or any other reasonably sized sub.

Due the small size of the room the 3x12 is probably far more than I need. What I'd really like is to have the sub/subs behind my AT screen. However space constraints are against me again,in terms of depth there is only about 20cm (perhaps 25cm at a push) behind the screen.

This is probably a really stupid question but is it possible to build a sub that is only 20cm deep that would approach the performance of my 3x12? It doesn't need to match it because as I said it's probably overkill for the size of my room anyway.

The screen is 150cm high and 260cm wide. So even if I were to upgrade my LCR to larger alternatives in the future I estimate that I could accommodate two subwoofers that were circa 100cm high, 40cm deep and 20cm deep each.

Is this a physical possibility?

Thanks for looking
 

indus

Distinguished Member
certainly possible, particularly if you stick to small(er) drivers.


Hi Matt
Any suggestions on the size of drivers and in what configuration? I don't know what the maths is behind this. Even though I don't need to match the 3x12 how do I calculate how many drivers and of what size I need in a 20cm deep enclosure to approach its performance?

Thanks
 

mattkhan

Distinguished Member
what's the budget?

do you run the current one sealed or ported?

what output levels do you actually want?
 

indus

Distinguished Member
what's the budget?

do you run the current one sealed or ported?

what output levels do you actually want?


Hi Matt
I run it sealed. Ported seems to overwhelm the room and doesn't sound great.
Budget is very flexible.

In terms of what output I need; I don't know how to answer that. I need enough to be able to provide more than enough output and extension for the space I have.
 

indus

Distinguished Member
it boils down to extension and output level (which is a function of house curve, if any, & master volume)


Hi Matt
I'm not sure how to respond. Do you want me specify an output and lower level for extension?
Thanks
 

mattkhan

Distinguished Member
This is how you work out how much sub you need to meet your needs. what level do you listen at? What sort of house curve, if any, do you use? How deep do you want to go?
 

indus

Distinguished Member
This is how you work out how much sub you need to meet your needs. what level do you listen at? What sort of house curve, if any, do you use? How deep do you want to go?


Hi Matt
I listen quite load. I would say reference level assuming 0 on the MV on my AVR refers to reference level.
I tend to use the standard dirac curve. If I ever try and increase the bass on the curve the sub seems like it is over powering the room.
In terms of low end extension I run my 3x12 in sealed mode which is rated to 22hz. I also run it in 'room mode' which means frequencies below 35hz are reduced. The review below says it's suitable for rooms of 5000ft3 or more....my room is about 1800 ft3!

So I would have thought that subs that could reach 50% of the output of the 3x12 would be more than enough for my room?

Thanks
 

mattkhan

Distinguished Member
well 50% of your sub is something like a single 15" or a pair of 12s (using some decent subwoofer driver)

fwiw your sub was measured, data is in Data-Bass though this is ported so you'd have to take some off for sealed mode.

this says 107dB ground plane long term at 20Hz, port seems small for the box so maybe take off 6dB for sealed, this is about 23dB short of peak level reference playback for a bass managed system with no house curve at all.

At 80Hz, it's about 6dB short so getting closer but still not a reference capable sub.

I don't think your expectation about your current sub is realistic in relation to the stated listening levels but if you're happy with it then that doesn't really matter. Simple solution is pick up a pair of 12s instead.
 

indus

Distinguished Member
well 50% of your sub is something like a single 15" or a pair of 12s (using some decent subwoofer driver)

fwiw your sub was measured, data is in Data-Bass though this is ported so you'd have to take some off for sealed mode.

this says 107dB ground plane long term at 20Hz, port seems small for the box so maybe take off 6dB for sealed, this is about 23dB short of peak level reference playback for a bass managed system with no house curve at all.

At 80Hz, it's about 6dB short so getting closer but still not a reference capable sub.

I don't think your expectation about your current sub is realistic in relation to the stated listening levels but if you're happy with it then that doesn't really matter. Simple solution is pick up a pair of 12s instead.


Thanks Matt.
However I can't just pick up a pair of 12s. Ready made 12 inch subs are always more than 20cm deep. I don't want to see the sub in the room anymore so it needs to go behind the AT screen where I only have circa 20cm. I see some in wall subs for sale but they are then only 10cm deep and I'm not sure about their performance.

So I'm trying to figure out what I could achieve in a box 20cm deep, up to a metre high and 40cm wide. I could potentially have two of these if needed.
40cm wide and a metre high would allow me to accommodate three 12 inch drivers.
However I have no idea how to figure out what sort of output or extension I would get when the depth is only 20cm.

I hope that makes sense?

Thanks
 

mattkhan

Distinguished Member
What I mean by pick up a pair of 12s is a pair of 12" drivers and make some appropriately sized boxes to fit the space :)

You have space to do this for sure
 

indus

Distinguished Member
What I mean by pick up a pair of 12s is a pair of 12" drivers and make some appropriately sized boxes to fit the space :)

You have space to do this for sure


Ah ok, sorry, understand now.
However before I spend the money and put all that work into I need some idea of what the end result will be.
Good quality subs are, on the whole, big and not 20cm deep. There must be a reason for that and so how do I figure out how three drivers in a 20cm box will actually perform?

Is there a formula or modelling software?

Thanks
 

mattkhan

Distinguished Member
Is there a formula or modelling software?
The total volume is what matters not the shape (except in extreme cases). One advantage of DIY is precisely this ability to use that volume in whatever shape you want rather than some mostly cubic box like a commercial sub.

For modelling, I use hornresp but for a simple sealed sub then winisd will do.
 

indus

Distinguished Member
The total volume is what matters not the shape (except in extreme cases). One advantage of DIY is precisely this ability to use that volume in whatever shape you want rather than some mostly cubic box like a commercial sub.

For modelling, I use hornresp but for a simple sealed sub then winisd will do.


Thanks, I'll download winisd later:thumbsup:
 

The Dreamer

Distinguished Member
Consideration of how you’re going to power these subs will be needed. A lot of people use inuke power amps or similar, and these are quite noisy - so really need to be out of the listening room (or use a different amp).

Just something to bare in mind.

I managed to squeeze UM18s into sealed cabinets just 14” in depth, so squeezing some 12’s into your space shouldn’t be a huge issue. Many manufacturers and even retailers, produce recommended cabinet volumes to use with their drivers - and for sealed subs certainly, these often prove to be more than adequate. I simply created boxes of the recommended size, as published on the Parts Express web-site for my drivers, and it’s worked just fine.
 

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