My Sub-Low Reflex Project

I am still debating to use either 18 mm or 38 mm for the rear wall based on the amount of abuse it will endure once the drives excursion begins

If weight is not an restriction and you're doubting between two different constructions, there is only one rule of thumb imho; Use the strongest.

What are you gonna call the cab ?

^ not massively, ever had a look at th response plot of a scoop, aside from the hog theyre only really useful down to 40Hz or their abouts, elliot thanks for the very in depth laying out of your selection process, if you have in mind that level of bracing/construction, unless you have some verry well paid roadies i would definatley suggest singles, i wouldnt be happy lifting one of those up stairs with any amount of people to help personaly. too damn heavy bulky and aquard just my 2p, looking forward to some pics of this 

christ! 54mm baffle.  id rather do the whole cab in 24mm and brace accordingly. in a dropping situation those 21's are gonna buckle/break before any damage is done to a 24mm baffle board imo. 

Edited by rich_gale - 15 September 2008 at 7:24pm

i would not advise the use of drywall screws - they are made from a very hard but britle steel which is SPAX screws are available in the US try them - they are the best available this side of the pond

Thanks for the input.

I’ve been visiting sound system forums for around 10 years and within that time period I’ve rarely if any I’ve talked about my sound system.

I own two systems. The larger one consists of Twelve Double Eighteens having two cabinets sitting on one Crown MA 5000. The Dual Twenty-One or Single Twenty-One will be added to this system and, get another 5000. If they perform as expected I will build more and buy more Crown 5000s.

I have no use for Scoops, which I got rid of in the summer of 1995 due to having one Double Fifteen cabinet out shine two Scoops (out of a quantity of 10) from 50 Hertz – Down. My Double Eighteens go much lower than my Double Fifteens (Which I own 8 boxes and provides bass for my smaller system). The whole concept of this design is to exceed the Double Eighteens low-end response and maintain the same SPL or 1 dB less during the process.

The last thing I need is bass. This is evident by having five 18-inch drivers sitting in cartons for over five years and, four W bins sitting in the basement (Loaded with 18 inch drivers) that haven’t been used since 2004.

I am in no way gloating on what I have. I am merely letting everyone know where I stand with subs at the moment.

I’ve used drywall screws, silicone and, glue (very little if any) to build all my subs. The only boxes I’ve encountered losing their strength throughout the years are the ones I never put together myself (Purchased from a store). Please keep in mind that the box will be completely (Skeleton) framed with 2 (inch thick) by 4 (inch thick) bracing. So all the panels are attached to the brace. This is the concept behind my Double Eighteens and, with 13 years of moving them about with no signs of weakening it’s proven reliability that I cannot overlook.

The thickness of the baffle board will either be 36 mm or 58 mm pending if I go for a single 21 or two 21’s in one cabinet. I prefer having 58 mm wood holding 80 pounds (Two Beyma 21 L50s) of speaker than, 24 mm.

I know my method to many may look as overkill but, that is the whole idea of building it your self. You design the box to meet your requirements.


rich gale
The only way I can see drywalls failing in real wood is if you are counter sinking and making pilot holes. If you just drill the drywall in real wood it will remain in place until you use the drill to pull it out.


H…. & biotec
I will more than likely go for one 21 in it’s own cabinet so, the baffle board will be 36 mm. No name necessary for this design. It’s just a basic reflex box designed to low. Save the fancy names for the horns.

mobiele eenheid
strength is definitely the concept behind all my subs so, I might as well go for a 36 mm rear wall.

csg

I can’t say I’ve ever cut off my boxes at 36 Hertz. I’ve used 27 Hertz for a few years until last week when I reduced them down to 25 Hertz (12 dB octave). The driver’s unload (in the cabinet) at 14 Hertz. Yes, I measured them. When I noticed sound was still emitting through the boxes at 20 Hertz (SPL was low of course) I decided to find out how low will they go before the driver unloads.

wafflesomd

Having boxes offering frequencies below 30 Hz, usually means you are relatively flat @ 30 Hertz. For those tracks that sweep into 30 Hertz, a box offering a – 3dB in the upper twenties will do a far better job producing 30 Hertz than, a box offering a – 3dB point in the mid 30’s.

There is a shop in NYC that sells Beyma's so, that will be the next step.

Best Regards,


Edited by Elliot Thompson - 16 September 2008 at 12:56am