[Wisewood]

OK, so as hinted at HERE one of my current projects is a sub-woofer to be sited front and center to beef up my bottom end. (sorry, been watching too much Bakeoff)
For anyone interested the 'round the houses' back story to the current design, it can be seen on DIYaudio.com
I'll be building it out of 19mm MDF with a 25mm birch ply front panel (just 'cos I've got some offcuts handy) The driver is a Kenwood KFC W2509 10" jobbie (just 'cos I had it) but most 10" drivers would work OK
I'll be posting all info I have including measurements and maybe templates in case anyone else wants to do similar.
Any questions please ask, makes me question myself and might turn up things I've not thought of.
:ILU:

 

[Wullie P]

This is the one in my bus..

Mines is bonded onto the floor and the dash board to seal up the unit, I also found that fitting the speaker onto rubber tap washers with the screws helps cut down on vibrations. T:

 

[jt-design]

Thanks for starting this WW.

Wullie, is there a solid panel at the bottom and the top, or are you letting the moved air hit the floor and the dash?

Can't see any sound holes. Is it pretty much sealed like you described?

Cheers

JT

 

[jt-design]

Just read the thread in your link WW.

Sorry for being such a dime bar on this, but what the hell does: "hit Xmax @ 32 Hz requires a ~4" diameter vent according to Small's math and HR says it only needs ~140 W" mean?

I'm technical director of a web software company, have been coding and talking jargon for 30+ years, but this is dark magic. I get frequencies, power ratings etc. and I can tell the difference between a Turbo rig and a Martin rig from outside a venue. But...

Xmax? (I know I could google it and look clever, but I'd rather hold my hand up and look stupid.)

Why 32Hz when 60Hz is a good thump point? (Forgive me, I'm also a rock drummer, and I like thump)


Cheers

JT

 

[jt-design]

Found this link about car audio tech

My head hurts.

My plan of: Make a screwed and glued ply box, cut a 3" hole in the side and 10" in the front, carpet it, mount the amp inside and the speaker to the front, is now scrapped. I now have to learn about the dynamics properly or I'll go mental from always wondering whether my sub sounds "right" or not.

In for a penny, in for many pounds and many hours research.


Cheers

JT

 

[jt-design]

Acronyms explained here

 

[Wisewood]

This is the one in my bus..
Mines is bonded onto the floor and the dash board to seal up the unit, I also found that fitting the speaker onto rubber tap washers with the screws helps cut down on vibrations. T:

Very nice Wullie, am I right in thinking that this is three sided- sides boded to dash with the back being the dash itself?

...but what the hell does: "hit Xmax @ 32 Hz requires a ~4" diameter vent according to Small's math and HR says it only needs ~140 W" mean?

Yeah, quite a lot of jargon in there, it's reasonably simple when you translate it... kind of:
Xmax is the limit of linear excursion, i.e. the loudest the sub will go before distortion
Small is (was?) a seminal protagonist in the field of loudspeaker design and together with another - Thiele - published a paper that became the basis of modern loudspeaker development including setting out the driver parameters that when measured should be able to tell you how a driver will perform in a given situation (enclosure/frequency/power...) These are commonly known as T/S parameters (as described in your link that scrambled your brain) and any drivers worth their salt have them available.
HR is HornResponse, an amazing freeware simulation program that I took the response plot from above. Takes a while to get your head round it but it's incredibly powerful. Originally developed to sim horn loaded full range drivers but now seems to sim just about anything.

...
Why 32Hz when 60Hz is a good thump point? (Forgive me, I'm also a rock drummer, and I like thump)
JT

Good question. It really depends on what you're after. If you only listen to Rock / pop type stuff heading for a 60Hz hump would be a much easier target and give some punch to the drums.
I come from more of an audiophile ultra-fidelity home stereo background and, while squeezing that into a noisy van stereo system is a nearly pointless, I do listen to a very wide range of music, some with detailed bass lines that drop below 60Hz. Without a flat response certain notes can be lost or boomy or just normal. Sounds bad...

As a purist I'd say your system should produce a flat well extended response but this becomes far more difficult.

I like a challenge.

 

[Wisewood]

Incidentally-

...My plan of: Make a screwed and glued ply box, cut a 3" hole in the side and 10" in the front, carpet it, mount the amp inside and the speaker to the front...

You may spend many hours research + design and then end up doing exactly that. (maybe with a tube in the 3" hole)
But then you'll know you got it right!

 

[jt-design]

Just came back to this thread and realised my last post didn't get posted for some reason. Probably got distracted by my daughters and just shut down.

Agreed, getting something achieved to the best of your ability/budget and knowing that it's as good as you can do, is worth it's weight in gold.

Just had a look at the door speakers, the dash speakers and the rear speakers (Caravelle). They are all standard, tired and in 2 cases, not working So phase one may have to be getting those replaced before I can make my nice thumpy toy.


Cheers

JT

 

[Wisewood]

OK!
I've been really busy lately, in a good way and a bad way, and I'm starting to wonder which is which...
I have made some progress though:ILU: so here's a little update:

scrap ply template for a decent fit.

Rationalizing the shape into MDF panels.

Cutting the template for the side panels.

25mm birch ply front panel and a check to see how it looks.

Checking in the van... 'tis big...

Trace templates onto MDF and rough cut on bandsaw.

and then use the template with a guided router bit for perfection.

Another check to see how it looks.

Putting the results into CAD to get the angles for cutting the rest of the panels.

I now realize the stepped bottom section could have been done in one continuous piece with very little loss of volume but hey:*
When I get time I'll post the template properly in case anyone wants it. DXF or PDF?
I've actually now cut the cross panels too, and cut the hole for the driver but didn't get any more pics.
More soon T:

 

[jt-design]

Wow! That is looking stunning. If you have a pdf version you could share, that would brilliant. What kind of volume is in there? Are you going vented or fully sealed? Carpeting it?

 

[jt-design]

Have you thought about selling the cut wood as a flat pack? Folks could screw and glue themselves. I imagine most of us haven't got a nice table saw etc.

The other thing I wondered is, from the height of the front, how far off squeezing in a 12" was?

 

[Turbo Nick]

I'd also be interested to know the internal volume and how deep it is?

I've currently got a JL 8w7 behind my drivers seat in a slot ported 32hz box and although it drops real low it's far from ideal for the everyday rock/metal I listen to.

I'd much prefer to have it upfront in a nice sealed box.

 

[Wisewood]

...What kind of volume is in there? Are you going vented or fully sealed? Carpeting it?

I'd also be interested to know the internal volume and how deep it is?...

At some point I'll find time to make a proper post of my progress. Maybe over the weekend.
Until then:
Internal volume is coming out at a smidge over 24l (0.85 cuft)
It's currently going as a sealed box as I'm finding conflicting info on port design and until I get to the bottom of it the sealed should sound OK with some equalization.
I can always go back and drill holes for ports after.
Currently toying with the idea of a long port coming externally round the gearstick and past the handbrake.

Nick, that JL driver is a very nice piece of kit and this would be an almost ideal sealed enclosure for it.

Have you thought about selling the cut wood as a flat pack? Folks could screw and glue themselves. I imagine most of us haven't got a nice table saw etc.

The other thing I wondered is, from the height of the front, how far off squeezing in a 12" was?

A 12" driver should fit fine, the only problem is the internal volume being too small for most that I know of.

A flatpack is not out of the question... but the table saw is not entirely necessary either.T:

 

[brm1286]

I've a 12" fusion in the same place, not as graceful a design as i reused the original sub box but for under £40 for sub, amp, custom box & all cables... I'm happy

 

[Wisewood]

One word update:...

... THUNDEROUS! ...

More soon I promise I:

 

[Kevr124]

Hi, I used to do a lot of big car installs back in my days at Road Radio, including one for Carl Cox (DJ) when he had his Cherokee Jeep, it was in a mag called Fast Forward T:
A couple of cheat tips that were used in the game for getting a better sound from a custom sub box were,

1, Don't port a box unless the exact volume and requirements were worked out, its an absolute mine field and brain meltdown on that subject

2, The Rockwool or recycled Plastic bottle insulation as we have these days was fluffed up and put loosely in the sealed sub box to give a deep bass sound, this was mainly used to stop the direct air pressure rebound that would stop the sub cone moving fully in a small or shallow box (it quite simply acts as a kind of baffle and), it completely transformed the sound on many installs T:

3, Dynamat was sometimes put inside some boxes to stop a lot of bass resonance and annoying rattles, also bass is non directional so it wont matter where you fit your sub T:

These are just a few tricks of the trade that were used to good effect in sound offs back in the day T:

Good job on your sub mate it looks very good, its not as easy as it looks to make a sub enclosure T:

 

[Wullie P]

Sorry guys for not getting back on this thread, I can get lost sometimes on the threads that I`ve responded to. My sub is basically a three sided box that is bonded onto the floor and all the way up the dashboard, So the floor and dash act as the back side. The box is then carpeted and the speaker hole cut out, there are no other holes on the unit. The speaker is a 10" one and is mounted on rubber tap washers behind the screws, but it is a fairly sealed unit. I do get a bit of buzzing through the dash if I have loose thing sitting around like change in the ash tray but it isn`t to bad. If I cut a couple of vent holes in the sides this might help with the displaced air, I might need to give it a try.

 

[Wisewood]

Hi Kevr,
Thanks for the tips, I was considering the rockwool inside anyway and have just insulated my workshop roof so I went for it. Having listened before and after I'm convincedT:
I looked at Horace's build thread expecting some fantastic four 15" sub install after your post but I guess you went a far more sensible route and just got a sony box. Much easier if you have the room.
Some great stuff in your thread though, will be revisiting that on a few occasions. A:
Wullie, thanks for getting back. I do like that shape. The tapering looks good, and fits much better with the under dash shape. I might go this route myself if I make another How does it sound by the way? Any idea how low she goes?

My Progress, continuing from where I left off:

...Well kind of, I didn't get any pics of fitting the panels round the back but it was pretty straight forward.
Cut a strip of mdf 340mm wide and then cut each piece to the required dimensions and angles (I will get that template soon people I
I then used plenty of glue and a brad nailer, always making sure everything is flush and square.

Cut the mounting hole and chamfer inside edge:

Ready to fit front panel to box:

The MDF is not great for screwing into so requires long screws with deep thread and must be well tapped and tightened gingerly.
Again, plenty of glue. MDF edges soak it up.

installing the driver:

PE foam tape should give a nice seal:

Test fitting:

The banana plugs and binding posts were, again, something I had lying around.
The fit is good!

A little on amp installation:
I though it best to cut the end of the power lead at an angle to aid its passage

I cut a slit in the black grommet and fed the wire through:

Which popped it out under the middle of the glove box...

...and the fed it under the carpet, round the wheel arch and along the top of the step to under the passenger seat

The amp is mounted on slats running crosswise, fixed to slats drilled to fit the seat bolts. the ground is taken to a ring terminal on a seat bolt.

Phono cables (currently far too long) and speaker wire runs from seat corner to under gear stick trim

In the engine bay again- the fused feed ready for connection:

BTW- Connect this to the POSITIVE terminal of your battery! What kind of idiot would connect it to the negative eh?

...I:

Back to sub:
Carpeting-

a flat surface, a lot of weight and some patience help.

And it's done!

Yeah I know my van needs cleaning...Rasp:

Initial test tone fiddling reveal that it's pretty strong down to around 37Hz, if a little lumpy. There's some cabin resonance around 100hz and I need to tweak my EQ a little.
My stupid head unit (KDX50BT) allows you to set sub crossover frequency up to 120Hz and then a separate high pass on the normal speakers. But the HPF seems to be around 300Hz and fixed! Which means everything in between is a bit muted and needs boosting by EQ. Not ideal. If I turn the HPF off, the mid-bass gets too overblown and needs EQing down with the door speakers and sub competing for phase around a crossover point..:*
Half my reason for wanting a sub was to alleviate the door speakers from from the bass so they could produce cleaner mids.

But for now though my set up does that and sounds pretty good. Listening to music in my van is a whole new experience

Apologies for such a long and pic heavy post but I hope it might be of use to some people.
Any questions and I'll do my best to help.

 

[Wisewood]

P.S.
Forgot to mention:
In the last pic the sub is secured to the dash with three 6x100mm screws horizontally through the top piece of the sub, front to back, with four more smaller screw going through the rearmost bottom piece into the plastic trim below.
Feels rock solid, I'm not worried about it flying around, and I'm sure it sounds better.
T: