Questions for Sub DIY'ers

[phoneisbusy]

Hi,

I'd appreciate any thoughts from all the DIY'er out there. I picked up a Dayton Titanic 1200 from the flea market and so now what? ;)
Based on what I've read, the driver is best suited for a sealed system. The T/S parameters seem indicate it would be a poor candidate for a vented system.

PE recommends a 2-2.5 Cu ft box stuffed with an F3 of 35 Hz, with effective F3 as low as 20Hz with room gain (is this optimistic?).
Their dayton kit favoured a 3 Cu ft box.

I'm earmarked this as a project for the 2 ch. rig so I was favouring sealed already. It will see most of it's duty for classical music and some jazz and rock oldies. It would be nice if it could pull HT duties but I'm not sure how realistic this is.

I've done some preliminary calculations using the sealed XLS from diysubwoofers.org and have the following results:

Driver Specifications
Driver Dayton Titanic 1200 Original
Vas 280.280 litres Equivalent air compliance
Qts 0.407 Total driver Q at resonance
Qes 0.420 Driver electrical Q at resonance
fs 16.0 Hz Driver resonance frequency
Xmax 14.20 mm Maximum linear excursion
Dia. 30.48 cm Effective diameter
PEMax 350 watts Thermal power rating


Qtc 0.71 Total system Q at resonance
Qr 1.74
Vr 2.02
Vb 4.90 Cu Ft Net box size
Fb 27.8 Hz System resonance frequency
F3 27.8 Hz Cutoff frequency (-3dB)


Qtc 0.85 Total system Q at resonance
Qr 2.09
Vr 3.36
Vb 2.94 Cu Ft Net box size
Fb 33.42 Hz System resonance frequency
F3 28.71 Hz Cutoff frequency (-3dB)



Qtc 0.90 Total system Q at resonance
Qr 2.21
Vr 3.89
Vb 2.50 Cu Ft Net box size
Fb 35.4 Hz System resonance frequency
F3 29.3 Hz Cutoff frequency (-3dB)


Qtc 0.95 Total system Q at resonance
Qr 2.33
Vr 4.45
Vb 2.22 Cu Ft Net box size
Fb 37.3 Hz System resonance frequency
F3 30.1 Hz Cutoff frequency (-3dB)


Qtc 1.10 Total system Q at resonance
Qr 2.70
Vr 6.30
Vb 1.57 Cu Ft Net box size
Fb 43.2 Hz System resonance frequency
F3 32.7 Hz Cutoff frequency (-3dB)


My observations/assumptions so far being that I'm a newbie and know nothing about speaker design/building.

a) Qtc of 0.707 is the flatest and ideal according to what I've read.
b) I can get a smaller box (I like that idea) without giving up much on the F3 area. I'm favouring Qtc of .9
which apparently emphasizes the bass a bit.
c) Shape of the box is not as seceptible to standing waves and a cube is not the only acceptable shape for a sub box.

Anyways, if I'm total off on my numbers or assumptions, I'd like to hear it.

Anyone have experience with choosing an Fb, F3 for a sealed system? Any gottchas?

Finally, have I overlooked any other configurations ? e.g. TL, Bandpass, PR?

Thanks

Dave

[gatemplin]

Having made a few DIY subs I'll try to help,

That driver would seem to me to be well suited for either sealed or vented with a mid Qts. But I know you want a sealed sub anyway.

You're right, 0.707 is maximally flat for the longest but starts to roll of more steeply than a lower Q design.

Also, even though you can build a smaller box and not change F3 by much, you are changing the character (Q) and the efficiency of the design. A larger box will be more efficient.

Dont be too worried about standing waves, you're box is too small I think. Just slap some polyfil on the walls.

Dont bother with TLs, Bandpasses etc. For a first sub try sealed or vented, they are already hard enough.

[gatemplin]

What materials are you planning to use and what are you using to power it?

[phoneisbusy]

Planning on using MDF for the box. Covered either with veneer or cabinet grade plywood. Will probably pick up the PE 250 W plate amp.

So larger is more efficient and a Qtc closer to the .707 will be more flat and accurate?

I'm trying to avoid a 19 - 20" cube. I think I could get away with something like a 16" x 16" x 34" cabinet/obelisk in terms of waf.

Thanks

Dave

[gatemplin]

I think you should take a look at the SUB250 amp from www.creativesound.ca in BC, it is 360W into 4.

3/4" MDF works well. What kind of veneer? I used some oak veneer from HD and it turned out really well. I let some wood glue dry on both the veneer and the MDF then ironed it on.

Yep, larger is more efficient. 0.707 is the flattest but maybe not in room.

A 16X16X34" box stuffed with 360W would be awesome.

[phoneisbusy]

I've seen them on the site in passing but never looked closely at the specs. I always assumed they were more or less like the PE amps. PE amps are cheaper but a bit of a hassle with customs and duty. They might warrant some serious consideration.

Haven't decided with veneers yet. It'll depend on what sort of box design I come up with. One thought was to build it to resemble an end table type but the most intriguing idea is to build the box so that it resembles a vintage Philco radio console. I'm more of a wood wreker at heart you see... :D

Thanks for the suggestions. I'll probably check some other sites of insights and advice. The design and building of the box will probably take a while though.

regards

Dave

[gatemplin]

There are some very knowledgeable DIY sub experts over at HTF. They can give you some great advice on box design and construction.