proac 2.5 building questions

[xs0]

Hi all!

I tried hard to find this information, but wasn't succesful, so I'll ask a few questions:

- I'm having trouble finding the bitumised felt; is it the same, if I just use thicker MDF (say, 30mm instead of 25 and 25 instead of 18)?

- what's the best "base" for the crossover? wood, or plastic, or ? how do you fix the elements on it?

- I can only find 70mm reflex port. I guess it should be a different length to be tuned to the same frequency; any ideas what that length should be?

- what is Dacron (i.e., what is its generic name)?


Any help appreciated.


xs0

[Bose(o)]

- There have been posts as to where the crossover should be located but, not what should it be located on. I believe that it doesn't matter and that if you are worried about magnetic fields disrupting your crossover, that you keep it external and away from the speakers or another noise source.

- Depending on the type of box, bandpass, TL, Horn or bassreflex, the port requirements will change. Same goes with drivers. So, What drivers are you using? In what type of box do you prefer to use them in?

If you want to tune, you may be able to use theory on the resonance in an open air column. Remember the universal wave equation? Use that, and make sure to use a length of half the wavelength (that's when resonance occurs). The diameter of the port changes the pressure in the tube, thus changing velocity; minus many other factors.

- Dacron is a type of fill to 'absorb' sound and reduce resonances that are caused by boxes. I have not used it personally, but have used other materials in the past. Someone else may be able to expand on this.

[pinkmouse]

Originally posted by xs0
- I'm having trouble finding the bitumised felt

Any good DIY outlet should have it, it is sold as roof covering for sheds and outhouses. I believe it is also made into shingles on your side of the pond as well.

what is Dacron (i.e., what is its generic name)?

Dacron is all I have ever known it as, but it is sold in craft shops as stuffing for pillows, upholstery, and soft toys. It is a spun polyester material. A similar material is sold at a higher price as BAF, Bonded Accoustic Fibre, and that should be available from most diy speaker dealers.

[xs0]

Originally posted by Bose(o)
- Depending on the type of box, bandpass, TL, Horn or bassreflex, the port requirements will change. Same goes with drivers. So, What drivers are you using? In what type of box do you prefer to use them in?

I guess the subject wasn't obvious enough I'm building the ProAc 2.5 clone from
http://www.geocities.com/diyproac25/

So, the driver is Scan-Speak 18W/8535-00, the box is bass-reflex. The port should have diameter 75mm and be 140mm long, but I can only get 70mm diameter, and am wondering what length it should be...


Thanks,
xs0

[Alain]

Hi,

Dacron is also known as polyester stuffing or padding in places where they sell tissue.

Bitumen felt can be replaced by rolls of roofing felt or lead or barium impregnated rubber or vinyl sheeting found at car repair suppliers (this is the material used to sound proof cars). Using thicker MDF will not haave the same effect.

As for port, I have used the 3 inch flared ports sold by Madisound (http://www.madisound.com) and cut to obtain a total length of 180mm. Madisound ship anywhere in the world. The advantage of using the Madisound port is that you can remove it to access the cross over if you place it at the bottom of the speakers.

I mounted my crossover of 0.5 inch MDF board. I glued the components with a silicone glue.

[Matt]

Hi

You can mount your crossover on anything so long as it is an insulator.

Suitable porting can be obtained at www.wilmslow –audio.co.uk (I know it is uk but best I can do) but to be honest it is only heavy duty plastic drain piping. They do the correct internal diameter and cut it to your required length.

The bitumous felt can be obtained from Wilmslow also but car spares supply it as well but at a price! Never tried the roofing felt but it is similar and will probably do at a cheaper price.

Dracon is a damping material like cotton wadding I’m sure you can get similar from a fabric shop but if you want the real thing Wilmslow and falcon do it. The deadening material is only the same as you find around dishwashers and the like to quieten the machines. Nothing too scientific or specialised.

www.falcon-acoustics.co.uk also supply speaker parts.

I’m in the middle of my clones so can’t say if they are good or not. There are great sites about. Use a search engine to find them. Lots of advice. Best of luck.

Matt