Experimental Sub setup

[ysidfa]

I was gonna post on my old thread but its 4 months old and I know its frownd upon so heres a new update thread..

I recently came across an awesome deal on ebay,
Bose Accoustimass 3 Series 2 Active subwoofer (full system is worth upwards of £100)

Winning bid £2.20 +£10 next day delivery.

Being an active sub, the amplifier runs 240v - 12v @350w max then thats split to 2 "satalites" and the 2 drivers in the subwoofer. After doing some poking around on the bose forums I found that each driver in the enclosure are 100w RMS.


I know the sub is designed and built for a small and basic home cinema set up but as the box is digitally designed to give optimum bass response and ported perfectly, it really puts out some decent bass (tested on a friends home amplifier.)

What I plan to do:
With the help and advice from a knowledgeable friend,
- Find a amplifier capable of giving me 2 x 100w @ 2ohms
- Wire it up using a 8AWG wiring kit (doesnt need to go any thicker than that due to it only pulling 200wMAX).
- Take the RCA out from my HU and merge the Left and Right channels, effectively producing a Mono signal, then seperate them into the amp. (Doing this to stop production of standing waves and prevent dull and 'out-of-phase' bass)
- Wire the 2 seperate channels from the amp to each driver in the enclosure

Any critisim welcome, Should all be set up by the Peterborough meet so anyone is welcome to come and have a look

Tom

 

[volxstu]

Does you head unit not output mono on the sub output anyway?
I don't know where you have been reading up on the RCA but its not an issue and you would still be sending the same signal just merged together.
I'm using 2 sperate mono output RCAs (sub and Center) to my sub amp. This just gives me a higher voltage input allowing the gain to be lower so less distortion.

Also you will then have a problem with having to run 2 channels in mono. If you are sure both subs are 2 ohms each (unusual for home speakers) then connect them together to show 4ohms. Then use one single channel.

Don't restrict yourself to 200w RMS. A 240v amp will be more efficient than a car amp which is susceptible to voltage drop, higher current fluctuations etc etc. If you had an average car monoblock say 300-400w RMS and set with a scope you will be fine.
Sorry to keep using mine as an example but my midbass are rated at 200w and they are on an amp that is rated at 400.

One question that has to be asked though is how are the subs and original amp configured? Is it an isobaric bandpass? Is the enclosure designed to work with the woofers out of phase?

 

[ysidfa]

I believe its an 8th order bandpass enclosure,
http://hosting.superhighoutput.com/yamahasho/Sub%20Build/bose%20clear.jpg

After testing the sub on a range of different amps last night, I found that it ran best on a 250w max single channel amp. It gave a bit of distortion at heavy volume but ran well and gave a nice crisp bass throughout the range. (being 26 years old the enclosure isnt 100% structually sturdy anymore as the MDF has split a tiny bit on one side)

Pics will be up later

Tom

 

[Eklipze3k]

... set with a scope ... isobaric bandpass ... out of phase

... 8th order bandpass enclosure ...

I wish I understood more of the technical side of this stuff, most of it is Chinese to me

 

[volxstu]

I'm not an expert on Bandpass, but a team member is currently doing an 8th order for SPL comps.
It's not really designed for music, will have a couple of peaks and be very in efficient at any other frequency other than its tuned ones. Also I think there is some complexity in the phasing so make sure they both push and pull at the right time. Also make sure you have a sub sonic filter on the amp otherwise it will eat it's self.

 

[ysidfa]

Cheers Stu,
Ill dig up some pics today so you can see the layout.
Its not gonna be an award winning bank breaker of a set up but just something simple and not too room consuming.

Tom