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Old 24th January 2004, 05:18 AM   #1
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Default Need these sub plans reviewed before I start the build

I have an SAE 1204 and Apex Sr amp that I bought from ApexJr.com. I am almost ready to build my powered sub and need some help reviewing my specs and plans before I actually start any cutting. Here is the plot from WinISD.

I am planning on using some plans from Adire Audio's Shiva ported enclosure plans. Instead of the one port they use I was planning on using two like in the next picture. Will this cause me any problems? Should I position them differently? If everything looks ok, I would like the go ahead so I could start the build ASAP. Please let me know. Thanks.
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Old 24th January 2004, 05:19 AM   #2
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Sub plans bottom view
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Old 24th January 2004, 07:20 AM   #3
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I see that your sub has both the cone and the ports facing downward.

Are you certain that it is a good idea for your subwoofer to be facing down? These long excursion subs like the SAE 1204 might be a good deal more subject to sag than other woofers.

One member called up the company for a subwoofer he had, (I don't know if it is SAE or not), and asked if it was all right to have the cone downfiring. He was assured it was.

Two years later, the cone was sagging.

Peerless specifically recommends against downward or upward firing subs, and their drivers do not have the excursion of the SAE even. So I hope you get away with a downward firing, long excursion woofer.

Nothing wrong with having the ports downfiring, however.


I see the two ports are 4" diameter. That is good. You might try ading flares for even smoother operation, but it might not be necessary.
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Old 24th January 2004, 08:38 AM   #4
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Quote:
Originally posted by kelticwizard

I see the two ports are 4" diameter. That is good. You might try ading flares for even smoother operation, but it might not be necessary.
First off, my bad about the ports. They are actually 2" diameter. WinISD says that I can use (2) 2" ports that are each 8.99" long to give a Vent mach of 11.1 Here is the new pic. I can't edit the other one so here is the new one.

And about the downfiring sub. Maybe this isn't a good idea. I wasn't sure, I just saw that the plans looked good. Does anyone know if this is bad for sure? I will change my plans definitely if this is not a good idea. I am open to all suggestions as this is my first powered sub/speaker build. I built some BR1's but that was cake because the cabinets were already made. Please let me know about the downfiring sub. Thanks all.

-Ed
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Old 24th January 2004, 08:39 AM   #5
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Nice to see that the bracing doesn't run down the centre of the box.... i'd mount the driver on the side for the same reasons KW states... i'd also tune it for more droop on the bottom. With the response you've modeled it is going to have a big peak as room gain kicks in.

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Old 24th January 2004, 08:45 AM   #6
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Quote:
Originally posted by planet10
Nice to see that the bracing doesn't run down the centre of the box.... i'd mount the driver on the side for the same reasons KW states... i'd also tune it for more droop on the bottom. With the response you've modeled it is going to have a big peak as room gain kicks in.

dave

Could you explain a little more. Do you mean I should make the tuning frequency lower? Should I drop it to something like 18 or 20Hz? I would like to keep the volume at 85L. Please let me know. I will definitely be changing my plans now to be a forward firing sub. Can I just make the bottom the front as it is a cube? Does having the ports and driver on the same side matter? Thanks for everyone's help so far.
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Old 24th January 2004, 08:55 AM   #7
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I'm not much into vented boxes... what does an 85 litre sealed box look like...

dave
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Old 24th January 2004, 08:59 AM   #8
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85L sealed enclosure
I would like some good low end. I listen to Home Theatre and music, but more Home Theatre than music. Right now I'm using BR1's and I need some low end. I do not mind building a sealed or ported. I just would like something that sounds good. I'm open for any suggestions. Also, if it would be better to make a smaller enclosure than that's fine too. I just would like a max of 85-95 liters. Thanks again.
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Old 24th January 2004, 09:16 AM   #9
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Let's see, 85l BR or an 85l sealed box? Sounds like the best of both worlds to me. Build the box with the ports. Listen with the ports plug or not depending on how you're feeling at the time.

Although I'm partial to BR designs, your sealed curve looks pretty good. BTW, my vote is to mount the driver on the side as KW indicated.

Anyone up for some M&M

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Old 24th January 2004, 02:25 PM   #10
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Quote:
Originally posted by AudioIsFun

Can I just make the bottom the front as it is a cube?
Well, the legs might look a little funny sticking out the front. I'd put them on the bottom. Otherwise, go ahead.



Quote:
Originally posted by AudioIsFun
Does having the ports and driver on the same side matter?
No. However, although I have not built a sub with downfiring ports yet, I have communicated with people who say that mounting the ports downward is a truly great way to build a ported box, especially a sub. The output gets coupled to the room and comes out very smoothly and powerfully.

Now for some bad news. I do not think two 2 inch diameter ports are adequate. Added together, they have the same cross-sectional area as one 3" port. A 3" port is adequate for a 10" woofer perhaps, but not a super long throw 12 inch. Use at least two 3" ports, and put flares on the ends, (available Madisound or Parts Express), because a port flared on both ends is supposed to be the equivalent of a port with twice the cross-sectional area. Not twice the diameter-twice the cross-sectional area. So a flared 3" dia port is equivalent to an unflared 4" diameter port.

Your SAE 1204 moves a lot of air, and requires a lot of space to accommodate that large bass output rushing out the port.

I would tune the box to at least 20 Hz or below, to account for room gain.
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