Double 21'' Subwoofer project

[mattmcl]

FWIW, you can mount two of them in an isobaric configuration (push/pull). Basically you put the drivers facing each other, hook one up positive to positive, and the other positive to negative. You half the volume required for the box and increase sensitivity.

[theAnonymous1]

Fs = 37 Hz
Qms = 9.56
Vas = 666.9 liters
Cms = 0.0421 in/lb
Mms = 2.716 oz
Rms = 4.129 lb/s
Xmax = 4.7 mm
Xmech = 0.278 in
P-Dia = 16.61 in
Sd = 1398 sq.cm
P-Vd = 0.0232 cu.ft
Qes = 0.3
Re = 8 ohms
Le = 1.93 mH
Z = 9.6 ohms
BL = 4.912 lb/A
Qts = 0.29
no = 10.86 %
1-W SPL = 102.5 dB
2.83-V SPL = 102.5 dB

A few of the specs might be slightly off because I'm sure Re isn't exactly 8R.

[Shrewm]

Hey
Sorry for taking so long to reply; Iv'e been away for quite a while and haven't had the opportunity to get involved in this again.. Anyways I' here now and if you guys still wan't to help I'm super thankful and i promise i'll spend an adequate amount of time here

However, I've decided to make the box for two 18'' subs instead, since i figured that's enough.. Also i want to be able to move the thing when it's done :P

So, yesterday i went to the shop where ill buy the speakerelements, and they have a box made out of the same 18'' i want. They let me take some measurements on it, and by peeking through the fence and carefully measuring the thing, here's what i made of it..





This is from behind with the back of the box taken off.
What makes me confused is the grid thing going on in the middle of the two speakers, instead of isolating them entirely from each other. I was hoping someone here might make more sense out of it, because the one in the shop sounds really good, and it's their best and most expensive sub..

Hugs
/Leon

[Shrewm]

Wow, thanks everyone for sorting out those parameters and for coming with tips! I'm afraid i can't make much of it though, not yet. I'm still at square zero with this so i don't really understand what you all are saying. I'm sure it will come of use soon though, i really want to learn

to "wakeup":
Well neither really.. It's for concerts, parties and such, and i don't like renting equipment, and i want to know how everything works

And yeah, i dunno if i screwed up trying to insert the images of my attempt on making prints for the sub, so here are the direct links:

http://img513.imageshack.us/i/bassbox3.jpg/

http://img513.imageshack.us/i/bassbox2.jpg/

Bye for now

[chris661]

The grid thing going through the middle is bracing, to stop the cabinet vibrating along with the drivers. If it was left to vibrate, the sound wouldn't be as good (words like smudgy and colouration tend to apply).

Chris

[Shrewm]

I see, thanks. So the drivers playing into the same chamber wont mess up the sound? Would it be better to make this bracing into a plane; separating the chamber into two?

Leon

[technofreak]

IMO, double designs are pointless if you don't use push-pull configuration like this (which I recommend to do since it reduces distortion significally). Singles give you exactly the same extension and SPL but are more portable - imagine lifting that double-18" upstairs and downstairs after gig, not fun.

[Rademakers]

The alpha version is Extremely sensitive when you put in the data for a new driver, if it's not spot it won't work.

True,

There are two generally accepted ways around this. Either put in the T/S-parameters in a specific order or ...turn it off (auto-calculation at the bottom of the input tab ).

Best regards

[AndrewT]

Originally posted by technofreak
Singles give you exactly the same extension and SPL but are more portable - imagine lifting that double-18" upstairs and downstairs after gig, not fun.

I have a double 18 (300Litres) and I use it lying on it's side doubling up as a table/support for the TV.
It has four grab handles built in by Tannoy.
I cannot lift it by myself.
It is not intended to be portable, even if I fitted castors to it.