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Old 16th May 2013, 01:11 AM   #21
opcom is offline opcom  United States
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Quote:
Originally Posted by opcom View Post
Thank you for correcting that misconception.
Here's the room. At "A" the 30-40Hz bass was not as loud or effective as at "B". What causes this?

The room is only a little smaller than the OP's room. Seems relevant.
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Old 16th May 2013, 02:42 AM   #22
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Quote:
Originally Posted by opcom View Post
Here's the room. At "A" the 30-40Hz bass was not as loud or effective as at "B". What causes this?
Usually uneven coverage at low frequency is due to modal activity. There are room mode calculators online but they are very simple. For precise answers you would need to provide info about construction materials (rigidity), leakage (doorways, cracks, HVAC holes) and a precise layout (taking into account the overall dimensions of the group of rooms and the boundaries and doorways between them) and absorbtion (furniture, carpeting, etc), among other things. In other words, it's currently impossible to map out response accurately at any given spot in a room but if the room booms it's probably caused by standing waves.

Last edited by just a guy; 16th May 2013 at 02:47 AM.
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Old 16th May 2013, 12:52 PM   #23
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(--^) For small-room acoustics use LISA. Free/Affordable Finite Element Analysis Software.
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Old 16th May 2013, 01:14 PM   #24
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Alex, it helps to know your flag/country for future resources.
The driver posted by just a guy on post #18 will need (each) an enclosure of 300/350L and amp of 2000/2200W@4Ohms. Have you decided your project directions?
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Old 16th May 2013, 01:49 PM   #25
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Originally Posted by Inductor View Post
The driver posted by just a guy on post #18 will need (each) an enclosure of 300/350L and amp of 2000/2200W@4Ohms.
No, the SI 18 doesn't need anywhere near that much space and can't handle even close to that amount of power.

If used in IB you can fit 5 drivers on an 18 inch cube manifold. You can increase the depth of the manifold and fit more drivers per manifold if you don't mind keeping the low pass crossover relatively low. Or just use more manifolds. Even in a sealed box you can go as low as 4 cubic feet, lots of people do it.

As for power, these are rated at 600 watts rms and I wouldn't push it too far past that. They have a tiny 2.5 inch voice coil and they will burn if you get too aggressive. (They are fairly new and I've seen reports of burned voice coils from experienced users.)
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Old 16th May 2013, 04:30 PM   #26
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Dear all ,

thanks for all your comments... forgive me if i am going a little too ahead.... But I have a doubt... if iam going to use conventional 18" drivers ... what type of enclosure will help me to achieve the best result in reaching the mark of 10Hz. or below ? taking the room to be a rectangle with (18' x 10'x 10') , with plain concrete walls and one door which may not be perfectly airtight......

regards,

Alex
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Old 16th May 2013, 04:39 PM   #27
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IB or sealed will yield the smallest enclosures. Any type of box that uses resonance (ported, tl, any type of horn) will have to be large to get to 10 hz or below.

If the room is concrete IB may not be possible.
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Old 16th May 2013, 04:44 PM   #28
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Here's an idea for sealed boxes for the SI 18 woofer.
4 cu ft Subwoofer box - Subwoofer Flat Packs DIY Sound Group

Shipping costs would be prohibitive to India but you can make your own.

Your room is fairly small and quite rigid if it's concrete, and probably airtight enough, so 2 or maybe 4 of the SI 18 woofers should be enough, depending on how low you want to go and how loud you want it to be.
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Old 16th May 2013, 05:40 PM   #29
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Originally Posted by just a guy View Post
If used in IB you can fit 5 drivers on an 18 inch cube manifold.
Back in the late 1970's Anicom Sound in Minneapolis used to use a large sealed cabinet called the "Futz" which had 4 drivers on a triangular manifold, three on the sides, one in the back.

The rear driver consistently was ruptured while the other three never had any problems.

There are tougher cones now (the Futz used JBL 15" woofers) but I still would not put a single cone in the back space of a manifold, even if it would not tear up the cone, it would probably add distortion.
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Old 16th May 2013, 05:53 PM   #30
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Originally Posted by weltersys View Post
Back in the late 1970's Anicom Sound in Minneapolis used to use a large sealed cabinet called the "Futz" which had 4 drivers on a triangular manifold, three on the sides, one in the back.

The rear driver consistently was ruptured while the other three never had any problems.
I'm having trouble imagining this layout. A quick search didn't lead to any pics of this creation. Are you saying the manifold exit was at the peak of the triangle (like a pyramid)? If so that's an extremely odd layout and I'm not sure why the manifold exit would be made smaller than the cross sectional area where the woofers mount.

Maybe I'm not imagining it right, but any type of triangular manifold sounds very odd and a very bad idea.

Anyway, afaik only pressure can rupture cones and there shouldn't be any pressure worth noting in a 5 driver IB manifold with a consistent cross sectional area and an exit equal to the cross sectional area. Using a smaller sealed box would be different, that could generate extreme pressures.

Quote:
There are tougher cones now (the Futz used JBL 15" woofers) but I still would not put a single cone in the back space of a manifold, even if it would not tear up the cone, it would probably add distortion.
I can't imagine why the 5th driver would add distortion. It wouldn't have the benefit of opposed forces that the other 4 drivers have but that's not adding distortion, it's just not benefiting from reduced opposed forces distortion.

Last edited by just a guy; 16th May 2013 at 06:00 PM.
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