Lambda driver-based sub build.

[Brett a]

As many of you may know, I recently moved from a lifetime with floor-standing speakers to a pair of stand-mounts (Focal 807Ws). I just fell in love with their imaging and transparency. So much so that i was willing to give up that bottom octave.

But I'm nothing if not restless and I don't think it took 2 weeks before my mind went to getting a sub. The sub that matches my speakers is too expensive for me to buy any time in the near future. ($1,500) and I've been told that it's really nothing too special anyway.

So after considering buying an SVS and looking at DIY, I finally decided to learn about DIYing a sub and build not just one, but a pair of sealed units myself.
That whole precess played out in this thread: Subwoofer: Buy or Build?

Long story short, after a lot of reading and planning, I decided I wanted to build a pair of sealed passives and run them with a single plate amp. So this meant looking at 8 ohm drivers to share one 4 ohm amp.

After looking at all the offerings at Parts Express, I was intrigued by a set of Lambda 12" 8 ohm drivers off eBay.

I somewhat hastily pulled the trigger w/o really grokking the implications of these drivers needing a lot of cubic feet to flatten out in. More on that a few posts down.

Anyway, here are the drivers:
Lambda SB12-8:

The Lambda SB12 driver is designed for sealed enclosure.
It has a high Xmax, stiff poly cone with stiff poly dustcap, coated and sealed foam surround,
12 spoke aluminum basket, dual stack 120oz magnet, gold binding post, military spec coatings and
glues. It is a high excursion, very low distortion, super tight bass driver.
Recommended maximum crossover point is 500Hz, rated power handling is 500W. 2.83VSPL = 88.6dB

Specs
Size: 12"
Motor : PL (overhung)
Magnet : 3.4Kg Ceramic 5
VC diameter : 51mm
VC Former: Black Anodized Aluminum
VC Wire: 2 Layer Copper Roundwire
Basket : Cast Aluminum 12 Spoke
Cone : Mineral Filled Hard Poly
Surround : Doped Foam, 2 layer treatment
Dustcap : Hard Poly
Spider : Hard stiffness Nomex
Faraday : Copper
Terminals: Gold Plated Binding Posts
Weight : 10 Kgs
Fs : 20.9 Hz
Qms : 4.23
Qes : 0.64
Qts : 0.56
Vas : 160 Liters
Cms : 0.4 mm/N
Mms : 145 grams
Sd : 531 cm2
Rms : 4.5 Kg/S
Pe (nom) : 300 Watts
Pe (max) : 500 Watts
Pe (transient) : 1000 Watts
Air Gap : 14 mm
VC Length : 38 mm
Linear Xmax : 14 mm (peak)
Mech Xmax : 20 mm (peak)

 

[Brett a]

I'm going to jump ahead a bit and show you the most recent pics of it/them finished and in action:

So far (April 2nd), I'm finding best results with one sub. Which I am still tuning mostly by ear.

 

[Brett a]

It will be a sealed box 18x18x22. (3.23 cubic feet before subtracting driver and bracing displacements)

Here's how it plots:

I'm going to power both drivers with a single Yung SD500 500W Class D Subwoofer Amp Module (No Boost)

Parts Express link:
http://www.parts-express.com/pe/showdetl.cfm?partnumber=301-512

From the listing:

Overview

For applications that demand extreme levels of continuous, high-quality power, the Yung SD500 Class D subwoofer amplifier module produces 500 watts RMS at 4 ohms.
Highlights

Class D amplifier circuit with switching power supply provides excellent efficiency
Capable of sustained, continuous output without thermal shutdown
Built-in limiter circuit protection prevents peak overloads
Low-level, high-level, and LFE inputs for flexible interconnection
Manual and automatic on/off mode options
Fully adjustable phase, gain, and crossover points ensure system optimization
Switchable 115/230V input voltage


Specifications:
• Measured power output: 500 watts RMS into 4 ohms @ < 1.0% THD
• Signal to noise ratio (at rated power): >90 dB
• Input sensitivity (@ low level): 210 mV/50 Hz
• Input sensitivity (@ high level): 3.0V/50 Hz
• Low pass adjustment: 40 Hz to 200 Hz
• Phase adjustment: Continuously variable from 0º (normal) to 180º (reverse)
• Power requirements: Switchable, 115/230 VAC, 50/60 Hz
• Dimensions: 9-7/8" W x 10-5/8" H x 3" D; Cutout dimensions: 8-7/8" W x 9-3/4" H.

 

[Brett a]

I started the box build last night

 

[Brett a]

I'll be filling the above posts in with more details as I have time. So please check back.

 

[Brett a]

Running total:

Pair of Lambda drivers (used) with shipping. $253.76

Parts Epress order:
3x Acousta-Stuf Polyfill 1 lb. Bag $32.40
8x Penn-Elcom F1687 Rubber Cabinet Foot 1-1/2" Dia. x 3/8" H $7.52
4x Round 4-1/2" Speaker Terminal with Insulated Binding Posts ($2.90ea) $11.60
1x Yung SD500 500W Class D Subwoofer Amp Module No Boost $199.58

Total PE order with shipping $256.05

Home Depot MDF, router bit, glue, etc. $80.00

Total as of 3/27 $589.81

 

[audiozaz]

Nice project, glad you decided to go DIY, it's really rewarding IMO. Sealed bass that plays that low with what visually appears as Qtc=0.7 will sound waaay tight! :thmbsp:

I'd probably go for something similar if I had a larger room.

az

 

[dumptruck]

Q would be 0.9+, but with heavy fill (which seems to be included automatically by Brett's sim program) it should get close to 0.7. You gonna put the amp in one of the sub boxes or its own box?

 

[Brett a]

Q would be 0.9+, but with heavy fill (which seems to be included automatically by Brett's sim program) it should get close to 0.7. You gonna put the amp in one of the sub boxes or its own box?

I'm going to put the amp in its own box and initially hook it up with cables long enough so I can adjust it from the listening position. Once I get it dialed in, I figure it can sit on the floor behind the rest of the setup or maybe hang on the back or the LP crate the Shanling sits on.

I only bought 3lbs of filling so far. I was going by PE's guideline of 1/2 lb per cubic foot. I may order another pound or two to have the adjustability.

 

[dumptruck]

You could pick up a small bag of insulation to throw in the mix also/instead.

 

[Brett a]

You could pick up a small bag of insulation to throw in the mix also/instead.

It looks like I can get poly fill at the local dept store pretty cheap. And with a bit more reading, it seems the internet says 1lb/cubic ft.

This is a good read.
http://web.archive.org/web/20021007....cyberglobe.net/caraudio/resources/fiberfill/

 

[donprice]

Total as of 3/27 $589.81

Not bad for a $300 DIY budget

 

[audiozaz]

Not bad for a $300 DIY budget

200% budget is still within norms and DIY tolerances I believe...

az

 

[Brett a]

But I'm getting 2 for that price. So really I'm running under budget!

 

[Brett a]

I'm just taking a little break. And while I do that, please enjoy some photos from earlier this evening:

I've never used a router before. I watched a few videos on how to cut a circle with one. They all said to make a jig to attach to the foot then screw it to the work and spin it.

I went one more step and made a cradle to hold the work so the center wouldn't drop out when I completed the cut.



It took me four test cuts to master the set-up and get the size of the whole dialed in. But one I did, the woofer fits it perfectly with no slop.



Right now, one of them has its face glued and clamped. I'm going to go back downstairs and do the other one now.

I'll check back later.
--brett

(BTW, instead of marking any pieces to go with cabinet 1 or cabinet 2; I have named them Mingus and Garrison for two of my favorite bass players.)

 

[Jeffery]

I like running the amp separate, that way you can always add another with little trouble

 

[Brett a]

I just pretty much finished one. I'll get pics up later.

But tell me if I'm figuring the displacement of my braces correctly.
I made braces out of some of the extra MDF that have a "T" cross section. It's a 1 x 3/4" strip glued to a 2 x 3/4" strip to make a "T".

So the 2" x 3/4" section has a footprint of 6 square inches (8/4 x 3/4 = 24/4)

add to that the 1" x 3/4" section which has a foot print of 3 square inches (4/4 x 3/4 = 12/4)

So the braces have a cross-section that totals 9 square inches (36/4).
I have three braces, one in each dimension, totaling 53.5 linear inches.

I assume I simply multiply the area of the cross section by the number of linear inches to arrive at the total cubic inches that the braces displace, yes?

So, a brace with a 9 in sq. cross section x 53.5 linear inches = 481.5 cubic inches which is 0.28 cubic feet.

That's quite a loss of volume.

Well, I'll see how they do. I can always cut these braces out and try something that takes up less room.

:scratch2:

 

[budgetaudio6]

coming along nicely...if i may say something, when i see the word lambda or even hear it i think of the nerds. Hey i grew up watching tehm Very nice subs by the way.

 

[nexus]

you are going to want to add a moderate bass boost depending on your room and desire for low bass (after all they are SUB woofers). subwoofers used to be actual SUB woofers before Bose and everybody started calling 35hz 'subwoofing' (sic).

old OLA Advent speakers could easily do 30hz back in the day.

you probably should hunt about for a decent used parametric EQ, maybe a Behringer unit. pro audio is the best deal for that.

i don't have first-hand experience with PE's amps but the one with the built-in adjustable eq and 55hz notch is ideal for eq'ing a sealed sub.

you could get the unit from Marchand and do a linkwitz transform.

looks good so far. good luck!

 

[donprice]

Your cross-section calculations are off by a factor of 4.