DIY Home Theatre Subwoofer

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ShinyChrome

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#255763 28-Aug-2019 10:28

After spending a bit of time being teased by the promise of strong, low HT subwoofer performance for pennies compared to off-the-shelf offerings, I've been thinking about ordering in a single 15" driver, building my own ported MDF box from the multitude of designs available online, and buying an amp locally. And if that turns out ok, get a second one in future. From what I have seen of other builds online, that should be enough to get strong performance into the teens of Hz for a bit less than the cost of a PB2000. If WAF wasn't a factor, I think the choice would be clear.

I tried looking for drivers locally since after the currency conversion + shipping + maybe import fees it starts to lose its budget appeal, but its either car subwoofers, which seem to more about getting loud than low, or weaker PA ones.

Part of the fun for me would be in the DIY project itself, but if it was a wash with a locally supplied, performance comparable product with a warranty, well that's a no-brainer. Anyone here had any similar experience with DIYing your own subwoofer here, either locally sourced or overseas?

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#2307180 28-Aug-2019 10:56

Ive DIYed a few speakers

I made Transmission Line sub , with a Vifa 10", TL cabinet was too big , so I cut it down to a ported.
Powered it with a DIY AMP and active crossover .

1ST thing, decide if you want ported, sealed, transmission line etc etc
THAT will decide on the speaker you buy, specs have to match the type of box : eg low Q, high Xmax, efficiency vs freq response
Ideally , you need to make a rig to test the speakers specs , because quoted specs may not be accurate, especially on cheaper speakers
If you cant get the full specs (eg many car sub drivers) , dont buy it.
Do you want good audio bass, or bass that shakes the cupbaord. Pick one

Think about the size and shape of the room. That makes huuuuge difference . Some rooms will never have great low bass sound (like my lounge)

The hardest thing with DIY , is making it look Professional rather than garage built :-)

1101

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#2307183 28-Aug-2019 11:05

axent audio in Ak used to sell quality speaker drivers , not sure if they still do. They may have something .

Jaycar sell budget speaker drivers that are quite popular for DIY. They also sell amp kits , and used to sell active sub xover kits.

Also , a large bass speaker in a comparatively small box will be 100% compromise . As with most store bought sub boxes.
Theres a reason serious DIY subs used to be 7ft++ tall .
No one wants that size cabinet in their lounge though.
:-)

ShinyChrome

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#2307223 28-Aug-2019 12:03

Transmission line subs look awesome, but the space and I'm not sure my DIY-fu will be good enough to build one sadly.

I would think going ported or vented, as low (<20hz) bass for HT is my primary goal. From what I have seen online from others modelling, the Ultimax (15" specs here) lineup seems to work well for either, but that is without running the numbers myself. Also, the amp I was looking at includes a DSP section, so I've heard that can help work with the response a bit to smooth it out.

The room now isn't great, effectively ~3500ft3 to pressurize in a two-different-sized-rectangles-stacked shape, but it won't be in there forever. And with the amp above, I could easily power two of them.

Yeah, aesthetics is one of the things that gives me pause. If I do go down this route, I definitely plan to take my time with making the box pretty to pass inspection haha.

ShinyChrome

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#2307319 28-Aug-2019 14:28

Haha yeah, having seen some of the crazy big ones in dedicated home theater rooms or even infinite baffle systems, I'd be inclined to agree.

Although now that I look at the actual size of some of the ported designs, I think I would have to sacrifice a bit of low-end extension for a bit more WAF friendly sizing and go sealed with a similar design to this if going for bigger drivers than 12".

I had a look at the Jaycar options, but like most places that sell components here they seem to be slanted towards loudspeaker designs/replacements. I'd also be happier to spend more money for better quality and bigger drivers. Axent don't seem to have much of a web presence unfortunately.

1101

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#2307665 29-Aug-2019 11:01

Yeah, looks like Jaycar have stopped selling good speaker drivers. Just cheap junk now.

12" or 15" into a small sealed box will be really inefficient at low freq, so may require eq to flatten out low bass response. You'd need to get a equiliser designed for low sub use .
But in a 'normal' size lounge , all that may not even matter . Just build it & Im sure you'll be happy enough .

Ive seen photos of DIY's where they built the sub cabinet under the floor , as they were so damn big . :-)

Dunnersfella

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#2307770 29-Aug-2019 12:28

Ring Axent and ask for Kelly, he should be able to talk to you about something.

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ShinyChrome

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#2308379 30-Aug-2019 11:17

Dunnersfella:

Ring Axent and ask for Kelly, he should be able to talk to you about something.

Top man, I'll give them a buzz.

1101:

Yeah, looks like Jaycar have stopped selling good speaker drivers. Just cheap junk now.

12" or 15" into a small sealed box will be really inefficient at low freq, so may require eq to flatten out low bass response. You'd need to get a equiliser designed for low sub use .
But in a 'normal' size lounge , all that may not even matter . Just build it & Im sure you'll be happy enough .

Ive seen photos of DIY's where they built the sub cabinet under the floor , as they were so damn big . :-)

That's a shame, but I guess that's the market.

Yeah, that's I what I figured; if I have the driver and amp, I can always refactor the box design in future. I have heard people get some good results with that amp and the built-in DSP or using a Mini-DSP. But as you said, any dedicated sub is gonna be 80% better than none haha.

Senecio

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#2308384 30-Aug-2019 11:32

Just be cautious. Buying a subwoofer and slapping it in a box without understanding the physics of it just won't work. Particularly with ported enclosures. The sizing of the enclosure according to the Thiele-Small parameters of the driver is critical for performance. Especially if you want it to go low, be responsive and handle the power.

When I was into car audio in a past life this book was my bible. Over 300 pages of incredible detail to make the most of the driver you select.

http://www.zilesystems.com/wp-content/uploads/2014/12/Loudspeaker-Design-Cookbook.pdf

Fred99

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#2308979 1-Sep-2019 11:13

I read good things about Dayton Audio.

I don't know about shipping options. The drivers come with full specs and ported or sealed enclosure design guides etc. They also sell plate amps with active x-over, 110/230v switchable.

I suspect 2 large subs may be a logistical nightmare with practical placement and room acoustics. Certainly would be for music, but for HT infrasonic FX, flat response etc probably doesn't matter much.

For home HT use that got down to 20Hz and below, then even if a large 15 or 18" driver was ideally needed, then there may be no need to go for a very large power rating despite obvious temptation - if cost is going to be a limitation.

Dunnersfella

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#2308982 1-Sep-2019 11:21

How big is your current space?

I'd have thought that aiming for a sub that can go sub-20Hz is largely foolish unless you have a BIG room so the sound waves can propagate.
I say, aim smaller.

Fred99

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#2309114 1-Sep-2019 19:01

Dunnersfella:

How big is your current space?

I'd have thought that aiming for a sub that can go sub-20Hz is largely foolish unless you have a BIG room so the sound waves can propagate.
I say, aim smaller.

That's not quite correct, for example extremely deep bass extension can be achieved in car interiors, despite the space being extremely small (ie a 43Hz bass note wavelength is about 7 metres - and I've heard car systems capable of very much deeper than that).

A car interior is pretty dead. In a room which won't be so dead unless you've put traps all over the place, sub placement on a floor and near a wall or corner acts as a waveguide and accentuates deep bass, reflections further accentuate when they're in-phase, attenuate when they're out of phase, and you end up with a complete mess. You more than double the problem of sorting the mess by using two subs - not one. But yeah, I think a pair of 15" subs would be overkill in any domestic music listening situation, unless your listening space is absolutely massive.

I think one active sub and two two-way bi-amped mains with active x-over (24dB/octave) are the business these days, better to achieve clean bass and subsonics than two large full range speakers, and you can within reason put the mains where you want for best dispersion / stereo imaging, without being stuck with a compromise on where the deep bass driver/box needs to be to suit room acoustics, and the room doesn't need to be dominated with ostentatious expensive gear. Consider me a huge fan of subs, it would take a hell to convince me I'm wrong.

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1101

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#2309283 2-Sep-2019 10:29

Senecio:

the Thiele-Small parameters of the driver is critical for performance.

The quoted T-S parameters on most cheap ish drivers will be way off what they actually are anyway.
You'd need to setup a test rig & determine ACTUAL T-S parameters

A 12" or 15" sub in a small sealed box will never be the optimum regardless. It'll be boomy & need alot Eq to fix the low freq .
Many guys who build these dont have test gear to actually measure what they've built . If you build it yourself you will allways thinks its better
than it actually is.

Add to that, the speakers literally wont be able to cope with full power of the amp and very low freq, they'll top out .
A 200W sub wont be able use to 200W at 30hz or below

Look for well established designs , tested & measured, and built by alot of guys .

Anyway, the size & shape of the room will have just as much effect as design of the sub. My lounge has alot of boom & cancellation issues .
Subs sound boomy (yuk) , bass from front speakers tended to cancell out. I cant win :-)

ShinyChrome

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#2309555 2-Sep-2019 15:37

1101:

Look for well established designs , tested & measured, and built by alot of guys .

Exactly, I must admit my working knowledge is based on bits and pieces that I have picked up from AVSforums, Reddit etc from other peoples builds. That is why my first instinct was to build something like this using a sub from the Dayton Audio Ultimax line and replicate the MDF box myself from measurements, since it seems to be quite a popular bang-for-budget design in the US. The box design is supplied by Denovo aka DIY Sound group, a well known DIY kit builder in the US. Alternatively, there seem to be quite a few similar designs online to match with that line-up as well.

So I was thinking replicating someone else's design first, rather than re-invent the wheel. I realize that I am not going to get comparable performance to say an SB-16 or something like that, but I was keen to give it a go to see if I can get 80% of the way for 20% of the money haha. I also realise I am not gonna get it perfect the first time either. But I am also working from no having sub as well, so starting off with this, and then once I learn more, refining it, maybe design my own box etc.

I estimate room size is roughly around 3500ft. From my understanding, the primary concern is to match the size of the subwoofer to room size to effectively pressurise the room. Then figure out any acoustic room issues with positioning, room correction, and for that last 20%, bass traps etc. And then, once you have figured that out add a second one to mess it all up haha. Although I have seen people say that a second sub properly positioned and with room correction can fill out the bass a lot more than just a single.

I guess this is less about clean-sheeting my own design, and more of a quick check before I go down this route to see if anyone had done something similar/any better ideas for the money.

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#2309605 2-Sep-2019 17:23

Have you had a look at MartySubs? They have very good documentations and parts are common albeit having to source them outside NZ.

There are sleeper subs in car audios, but staying with Dayton, or Infinity Ref. is much better. I've built L ported subs (yeah car subs) for home theatre before, using a couple of JBL 12, it was crap, at 22Hz tuning, I was asking too much low on a crappy sub design and I wasn't using MDF.

Last year I redesigned another L ported enclosure at 30Hz, MDF, it came out miles better, and surprisingly delivered a low that were much cleaner than the 22Hz tuned box.

I'd personally go for a dual 12 rather than a single 15, it will sound much better, but YMMV. You've already done your research, just go for it. DIY sub is very rewarding for thus who wants to tinker a lot, and DIY sub + room analysis(EQ) would still be cheaper than a single SVS of the same size.

If you are interested, I can help you with box design in my free time. Though I forgot some steps now, I still have Bassbox Pro installed.😁

1101

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#2310011 3-Sep-2019 16:11

If you have the $ , perhaps an Isobaric design . You can then use a box 1/2 the size .
You have to buy 2 drivers though :-)
http://audiojudgement.com/isobaric-subwoofer-box-design/

I'd tend to go 12 rather than 15 as well. 12" should be plenty. Bigger doesnt allways mean better .
My 10" DIY was better than my 12" DIY . The 10" did cost considerably more at the time though.

Resale will be a bugger . It'll be worth beggar all when you sell it , upgrading or down scaling . Just something to factor in.
What does it cost to have a heavy sub driver sent to NZ? . I cant image that being cheap .

The box would be an easy build if you are going to paint it black. I would just build a box from particle board rather than import a flat pack.
Plenty of free software to design & optimize the enclosure. Thats the easy part .

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