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Old 27th February 2006, 05:10 PM   #1
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Default New Here. Will you check me design?

I have started a sub project. It's a 126 l ported design. I'm using a Dayton 12 HiFi driver, a 300 Watt Bash amp, and I purchased a 17" dual flared port. So far I have the box half done but I'm a little worried about port speed. In WinISD I'm getting up to about 39 m/s at the lowest range at 16 inches. I suspect it will be ok but I don't want to mess up. I'm having trouble finding the best way to get a bigger port in there without any bends in it. Any advise for the port or the project in whole will be appreciated.

Also does WinISD compensate for the speaker volume in the box? The box is 126 l without the bracing, speaker, and amp so it's a little less air space with all that if WinISD doesn't.

Thanks a lot.

Ryan

Dayton 12 HiFi

Specifications: *Power handling: 400 watts RMS/700 watts max *VCdia: 2-1/2" *Le: .95 mH *Impedance: 4 ohms *Re: 3.3 ohms *Frequency range: 23 - 1,000 Hz *Fs: 23 Hz *SPL: 89 dB 2.83 V/1m *Vas: 3.00 cu. ft. *Qms: 3.00 *Qes: .52 *Qts: .44 *Xmax: 14mm *Dimensions: A: 12-3/8", B: 11-1/8", C: 5-3/8".

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Old 27th February 2006, 05:42 PM   #2
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Sorry that was a 4" port 17" long.
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Old 27th February 2006, 07:21 PM   #3
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Sightseeker1,

WinISD does not compensate for the volume of the speaker or bracing or the vent which need to be subtracted from the internal box volume. Generally you can forget about the speaker and the bracing because a little stuffing will have the effect of increasing the box size.

However when you have a large port you will need to subtract the vent external volume from the box volume to make the box the right size.

IF you have a port larger than 4 inches it will be even longer unless you raise the tuning frequency of the box.

Unless you can live with a really big box this is not practical so stick with the four inch vent. It will be OK.

Otherwize things look OK, but if you are going for a high end sound quality the bracing needs to be improved.
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Old 27th February 2006, 09:01 PM   #4
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Ok I didn't even think of the port since it was hollow. I guess the volume belongs to the port not the box then. I dropped the box volume and it actually helped my port speed some so that is a good thing.

As far as bracing I have done a lot of searching and have seen all different kinds of ways. I just started with what I have and will keep going if that is what you guys think. The thing is that it is very strong now. I stood on the box and it didn't move. Should I double up on what I have? Maybe add some more columns?

I wasn't planning on using any stuffing. Should I or it doesn’t matter.

Thanks
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Old 27th February 2006, 09:51 PM   #5
simon5 is offline simon5  Canada
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Stuffing will virtually increase the box size if it was made a bit too small. It's also help to kill higher frequency stuff.

The best bracing is windowed bracing.
There's several examples on the web, like this one :
Attached Images
File Type: jpg bracing.jpg (87.7 KB, 483 views)
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Old 28th February 2006, 12:37 AM   #6
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Good picture Simon5,

It often takes a lot of searching to find how the really good bracing schemes are done.

Sightseeker1,

I would put a small amount of convoluted foam around the entire inside of the enclosure. And glue it down with silicone glue. This mostly helps to damp internal vibration and improves the sound somewhat in the higher frequencies. Make sure it is glued across it's entire surface or it doesn't work to dampen many vibrations.

To really kill the internal standing waves in the box it has to be completely stuffed with dacron or acoustic fibers. This is how to get the best sound but it is not recommended for a first time builder because it is hard to adjust to get it right. And the more it is stuffed (to a point) the more it will have the effect as to make the system behave as if the box had increased in size(to a point). So it changes the whole tuning of the system.

You can experiment with some stuffing as it is cheap (dacron) but make sure the area around the inner vent opening is unrestricted and there is no stuffing right around the vent opening. One thing you can do is stuff only the top or bottom half of the speaker where the vent isn't. IT's best to stuff the area right behind the driver as long as it's not too much stuffing.

For instance if you have a good quality shelf brace in the middle of the enclosure and the driver is on the top half and the vent is on the bottom half you can stuff only the top half behind the driver with a loose fill and the shelf brace will help to keep the stuffing in place so it doesn't fall down and impead the vent operation.

Make sure that the stuffing is not touching or getting into the driver.

Also if you are going after a really high quality sound the subwoofer cabinet needs a lot of internal bracing and if there is a lot of bracing it is a good idea to subtract it from the needed internal volume. So you will have to add more total internal volume to compensate.

For the minimal amount of bracing that you have in your project it is not enough to worry about because it is so little in relation to the size of the box. But if the bracing is extensive it is a good idea to subtract it.

Good luck
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Old 28th February 2006, 03:41 PM   #7
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Quote:
Originally Posted by Hezz
I would put a small amount of convoluted foam around the entire inside of the enclosure. And glue it down with silicone glue. This mostly helps to damp internal vibration and improves the sound somewhat in the higher frequencies. Make sure it is glued across it's entire surface or it doesn't work to dampen many vibrations."
Thanks. What is that stuff exactly and where would I get it? Can I use a can of spray adhesive instead to secure it? Does this process get rid of boomyness?

Also can anyone tell me about the bass boost of the BASH 300 watt amp I ordered? It says there are connectors you can remove and re-solder. Should I just leave it alone? The way my graph looks it doesn't really start to drop off below 21 - 22 Hz so I don't know if I should use it.
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Old 28th February 2006, 07:14 PM   #8
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You want an adheasive that forms a lossy barrier between the acoustic convoluted foam and the enclosure wall. The vibration of the foam will turn into heat at the lossy adheasive boundry. Otherwise the effect will be minimal. Most spray adheasives won't go on thick enough but it dosn't need to be very thick.

Parts express has the acoustic foam for cheap. Use the two inch kind as much as you can as it works better at lower frequencies.

Boominess is usually caused by poorly designed box which is too small and poor cabinet construction which vibrated too much. Also the foam will help a little to be less boxy sounding.

Also most subs are square. This is a good shape for small strong box but poor for acoustics because it reinforces a one frequency bass standing wave inside the box. If you can a rectanular box is better and a pyramid variation is better still. For best sound all walls should be non parallel. But spherical shapes are also poor in fact the worst.

After the box and cabinet are designed properly stuffing helps the most to reduce boominess. But if you get the box and construction right will already have won 70 percent of the battle.
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Old 1st March 2006, 08:22 AM   #9
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Quote:
Originally posted by Hezz
For best sound all walls should be non parallel. But spherical shapes are also poor in fact the worst.


iiieek!

do you mean that??
I asked a question on this forum some time ago about a spherical enclosure, nobody sait anything about being worse than any onther enclsure..

to be hones, I found some other resources saying that a sphere does not produce standing waves.

Sorry to hijack this thread.. but I've been working on a spherical enclosure for a few months now.. and You scared me with the above statement..
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Old 1st March 2006, 09:07 AM   #10
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In theory, spherical internal shape is the worst because it has only one standing wave mode but every single direction has it. For outside reflections it is the best as there is no sharp change of plane.

For a subwoofer shape is irrelevant as any modes will be way above normal operating frequencies. Unless you make a monster American sub...
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