finally building that sub

[johnkane]

I recently cleaned out the garage and found the following collecting dust.

13OV.2 elemental designs, a Behringer dsp1124p and a used hafler pro amp. So i think im going to finish this subwoofer right now. But i might need help with the tuning of the box. I started this years ago but i have no recollection on how to proceed. Below are the specs of the discontinued elemental designs driver.


Power: 600 Wrms
Qts: .28
Qes: .30
Qms: 3.3
Fs: 21 Hz
Re: 8.3
Vas: 176 L
Mms: 195 g
Bl: 21.7 T*m
SPL: 89.1 dB
Sd: 545 cm^2
Xmax: 18.3 mm
Voice Coil: 62.5 mm

thank you

[JonMarsh]

How big a box are you willing to handle? Do you want the most extended alignment possible, and minimal EQ? Or a small box and a fair amount of EQ? And less output.

[johnkane]

Well, Ive got some space so, 24*24*20 or something in that range. If the box is too big wont the driver look small?

[JonMarsh]

It's not about how it looks (to us, anyway) but how the physical parameters of the driver interact with the enclosure choice. This is governed by what are called the Theil/Small parameters- for example, some drivers have lower mass cones and are focused on efficiency, but to get a given tuning for bass extension, will then require a larger enclosure. Also, there's this thing called Hoffman's iron law, which basically relates to the fact that you can only go so deep in a certain size box at a certain efficiency level; you can trade LF extension for efficiency, but you can't really optimize both simulataneously.

If you have access to one of the free programs for box design, such as Unibox (runs in Excel) you could enter the parameters to create a model for your woofer and do some what if's. I should be able to find some time this weekend to do that, too, if you'd like. There's enough data in your provided spec to model the woofer.

[wkhanna]

@Johnkane....

LINK to a plethora of useful info regarding freeware & other reference material you will find helpful

[johnkane]

I dl unibox and tried some numbers, i dont know if what i did is right and i dont know what Le and Le2 is.

But unibox says with a box 24x24x20 inches with an internal volume of 5 Cuft or 170L, i would need a 9.65cm(4") port and 38.53cm long to get a frequency fb of 16 Hz.

Can anyone confirm this? If i didnt port this box does the frequency fb go up to 28 Hz?

what is absorption Qa and Leakage Ql? Are these standard?

Thanks ,

John

[johnkane]

Internal bracing: How much is necessary? Can i just brace the around the internal edges with 2x3s or is that too much volume? What kind of bracing is recommended?

Thanks,

John

[JonMarsh]

I dl unibox and tried some numbers, i dont know if what i did is right and i dont know what Le and Le2 is.

But unibox says with a box 24x24x20 inches with an internal volume of 5 Cuft or 170L, i would need a 9.65cm(4") port and 38.53cm long to get a frequency fb of 16 Hz.

Can anyone confirm this? If i didnt port this box does the frequency fb go up to 28 Hz?

what is absorption Qa and Leakage Ql? Are these standard?

Thanks ,

John

You could tune it that way, but if you look at the predicted response curve, it's what is called an EBS alignment, which trades tuning extension for output level- the response would be down 5-6 dB in the range of 16 Hz to 30Hz.

170L is actually six cubic feet, not five. Also, one has to be careful about very low frequency port tuning and the resulting port velocity- it calls for a larger diameter port tube, which in turn calls for a much longer port. A 4" port tube diameter is too small for 16 HZ- look at what happens on the ported report page with input power of 100 to 150W- at low frequencies the port air speed is too high.

A possible alternative design with flatter system response and more manageable box and port dimensions might be a net (not including woofer and port) volume of 120L (4.2 cu ft) with a port tuning of 20 Hz, diameter of 4" (smaller than ideal) and length of 16-1/2". The main issue would be making the enclosure deep enough for the port length- it's not ideal to have it too close to the enclosure wall. IDEALLY, that should be a 6" port, but then it practically becomes a stove pipe. This is why I usually prefer passive radiators to ports. But PR's cost more money, and matching their characteristic to a specific woofer can be hit or miss if they don't come with a complete set of tuning weights.

As to bracing, that depends on what you make the box out of- BB ply you might not even need much, but MDF certainly will, I'd suggest subdividing the box. Take a look at these Parts Express knockdown enclosures. you can get the idea for a good bracing plan.



This is a 4 cu ft subwoofer box available from Parts Express in knockdown kit form, either for an 18" UMC driver or a blank panel. It shows a good way to do bracing.




Checking online, your driver looks to have been originally developed for automotive applications, and optimized more for sensitivity, hence it needs a pretty big box to go low for a 12" driver.

[TEK]

Hmm, I have never got the point with that leakage Q. Why would I build a leaking box :roll:

[---k---]

Funny off topic story about leaks.
I had a speaker I demoed at DIY Chicago last year. It was my Ochocinco TM, with a ND140. The ND140 has a stamped frame. If you tighten the screws down too tightly, it is easy to twist the frame and created a leak. I didn't know this. Until I played the event demo disc with some deep bass. All of a sudden there was this weird horn sound coming from my speaker. Seriously, it sounded like a trombone or something. At first I thought maybe it was oddly part of the track, then I thought someone was punking me. I was able to easily recreate it at home. Kind of cool to see the audible impact that a leak can cause.

[jwanck11]

grab a freeware product called winisd

You can model your driver with different box parameters to find an optimal size for the tuning you desire.

[wkhanna]

i remember years ago here, one of our members made a sub from sonotube.
i guess everyone had told him to be sure he got it sealed up real good.

after he got built he posted pics (it was a good looking build, btw) of water condensation inside the unit.
turns out, it was sealed so good he needed to drill a small vent hole to allow the humidity inside the sub to escape!

[sdl2112]

Hmm, I have never got the point with that leakage Q. Why would I build a leaking box :roll:

Drivers with phase plugs inherently have leaks around the voice coil. Some fabric surrounds may be leaky?

Aperiodic enclosures intentionally have a resistive leak to damp the resonant peak somewhat.

Others just don't make a well sealed box

[johnkane]

Im a little confused. I dl WINisd but a little too technical for me. Lets say i use 3/4" plywood, then bracing goes down to a minimum. What do the dimensions look like for the vented box? If it gets too complicated, how about just a simple sealed box. I can try to make it as big as possible. Well within reason.

john

[JonMarsh]

Im a little confused. I dl WINisd but a little too technical for me. Lets say i use 3/4" plywood, then bracing goes down to a minimum. What do the dimensions look like for the vented box? If it gets too complicated, how about just a simple sealed box. I can try to make it as big as possible. Well within reason.

john

John, before the end of the week end I'll post my full recommendations and plots and build suggestions. Got a lot going on today...

[johnkane]

Thank you John, i really appreciate it.

[johnkane]

Ive been looking at the interior fill material and just want to use what i have on hand. I have some fiberglass pink or some old sonopan accoustic paneling. Opinions welcome.

[JonMarsh]

Pink fiberglass is fine.

Been on a 14 hour day scheduled for work lately, will be done the end of tomorrow...

[johnkane]

Hey Jon, I'm back from a small vacation. Do you think you could help me out with this design? I'd love to start work on it.
Thanks