Subwoofer design plan .. Is this O.K? - diyAudio
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Old 15th September 2003, 08:10 AM   #1
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Default Subwoofer design plan .. Is this O.K?

Through the advice and help of the members of this forum and the invaluable 'winisd' i have finally come up with this design for my 2x10inch Response XL subwoofers.

Im not sure how aesthetic this design will turn out to be (using 3/4inch mdf) and how the use of 2 ports will affect the sound (the mach level was O.K according to winisd).

If you can see any indiscrepancies in this design PLEASE don't hesitate to tell

thanks,
lach
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Old 15th September 2003, 11:12 AM   #2
Vikash is offline Vikash  United Kingdom
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Hi,

It looks good to me. For looks, I would mount the drivers flush with the baffle (use a double thick baffle).

5.8cm is an acceptable size for the ports. But it seems you have space on both the baffle for a wider port, and internally for the resulting length increase - so I would also do that.

The only real concern is the lack of bracing in your diagram. Consider a brace fixed length ways parallel to the baffle, with many large circles cut out.
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Old 15th September 2003, 12:43 PM   #3
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Lach,

Generally it looks like a well laid out sub. I think the proportions and symmetry work nicely. I do have some further suggestions:

*port size
I don't know if you investigated the vent velocity at max output, but if you have this capability, you want to aim for less than 17m/s if you haven't already. Even if these ports are fine in terms of no "chuffing" or turbulence, to my eyes they look too small. I think 90mm vents would look better, even if not necessary ... having 2 vents looks good

*bracing & lining
If you are using 18mm MDF you will definately need some bracing. You want the sound to come from the drivers and not the enclosure - keep in mind that 50% of the sound enters the room directly and the other 50% less what goes through the port needs to be converted to heat in the box when absorbed in the box. If the box is not rigid enough and lacks damping (lining) it will vibrate the enclosure and colour the sound. I would have a look at some different examples of bracing - look at matrix bracing used by B&W, and you could also look at the papers on Adire's website - eg. download some Shiva vented applications.

You might consider making the front baffle double thickness. Also are you going to do a grille?

I have just built a prototype 70L enclosure 18mm thick, no bracing or lining. It sounds very hollow and probably not even good enough for a test box! The size is similar to yours and if used as a final enclosure like that it would work better as a drum than a subwoofer!!!

Of course, you may have already thought of this and not shown it in your drawing.

Are you happy with the look of your design? ... I could suggest some alternatives but what you have with some bracing added should work just fine.
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Old 15th September 2003, 09:39 PM   #4
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Firstly, please excuse me for this somewhat shortened response as this computer decided to refuse me Login status and returned me with a page full of >>>xYr-Uڳ<<< jibberish instead of my somewhat large response.


Basically, thanks a heap for your responses guys I havent added any bracing to the cad drawing as i dont know what material ill have left from my wood cutout that im yet to buy.

If i change the port size to something larger (say 88mm or so?) will it drastically alter the sound dynamics of the box?

Also any suggestions for any improvements would be really appreaciated PLEASE dont hold back any critisicms of this box as it is my first vented box. :P (about a year ago i made a WickedOne but for some reason the left size of the box was offset by 1 inch which totally screwed the design!! i KNEW there was something wrong with it but everyone told me i was a fool eheeheh)

Wow, there goes my excuse of not writing a decent response (not NEARLY as big as the other but im pretty sure i got my message across to you

Thanks heaps,
Lach
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Old 16th September 2003, 01:39 AM   #5
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Increase the diameter and you increase the length to keep the tuning the same - this will reduce the air speed in the port which is an advantage - the airspeed in the port should not exceed 17m/s. The problem with vents that are too small is turbulence. This is reduced by having ports large enough so that the velocity won't exceed 17m/s and by flaring both ends. If you can't flare the ends then you might make the vents bigger.

To see if they are too small, use a simulation package that will model air speed in the port when the driver is operating at xmax. I have done this for my current project, but haven't had a chance to make sure that the results are right (I dont' think they are, but that's another thing.)

I don't know if you will have a problem with yours, not knowing the drivers. However, to me they look a little small from an aesthetic point of view (if you disagree, then just check the airspeed and if it's okay then disregard).

Keep in mind that as you increase the diameter of the vents, they get a lot longer as well - the relationship between diameter and length is not linear. As you get bigger vents, it gets harder to fit 2.

Bracing - I'd suggest you don't just use left over bits. In fact, a brace that touches all walls inside is more like it. Here are a few examples to consider:

http://www.coincidentspeaker.com/eclipse.htm
B&W
http://www.bwspeakers.com/index.cfm/...7F00D0B7473B37
a DIY project ...
http://www.acc.umu.se/~sagge/audio/supreme/
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