Best way to handle 25hz & down 2 Tempests - diyAudio
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Old 21st June 2005, 07:22 AM   #1
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Default Best way to handle 25hz & down 2 Tempests

I have 2 of the original Tempests to use, a 200sq ft room (20 sq M), and space isn't an issue due to some dead space adjacent to my room. I need to handle only 25hz and down with this sub as 25hz and up is dipole. The room is well sealed, so I can count on room gain. I need that bottom end extension just for HT. What is the best way to accomplish this ?

Driver specs-
Fs 18.8
Qts .38
Vas 317
Sd 779
Xmax 16
Power max 750
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Old 21st June 2005, 04:38 PM   #2
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Dipoles down to 25 Hz?! Why so low?

Sounds like a job for a pair of big EBS subs designed to get down to 15 Hz. I have a RTA permanently in my system and I notice some movies have more output in the bottom octave than the rest - this occurs in quieter but tense moments, often in thrillers, horror movies, sci fi - movies like Blade, Resident Evil. This is where you will really appreciate the depth, as it gives a dark feel and a sense of weight and depth - dark and ominous. My RTA doesn't show below 20 Hz, but I suspect that quite often the SPL in these moments actually continues down well below 20 Hz, however you have to determine the point at which you just don't have enough displacement to get an impact.
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Old 21st June 2005, 04:53 PM   #3
zobsky is offline zobsky  India
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for that extra sense of "impact" and a free bass shaker effect , you could try positioning the subs nearfield.

for instance, i place a single shiva / ported EBS / 17Hz sonotube in the empty space behind my couch in a 150 sq. ft room and believe me, it does more than i need, even with only 100W.


your amplifier power requirements are also reduced to an extent, with the sub closer to the listener.
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Old 21st June 2005, 06:48 PM   #4
simon5 is offline simon5  Canada
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If you don't care about space taken, I would use something like two 15 cu.ft internal boxes, then you tune around 12 Hz. You would get around 123 dB from 11 Hz to 25 Hz or 129 dB corner loaded (but you will probably have some room loss at such a high SPL level... hehehe). You would need only a single 400W amplifier for both subwoofers, or dual 200W if you prefer.
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Old 21st June 2005, 07:03 PM   #5
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OK, how about getting crazy...

Do a 6th order bandpass box (drivers in the box, two chambers, each ported). Isobarically mount the two drivers, wire voice coils of each driver in series, then parallel the two drivers...

Make the rear chamber 340 liters (12 cubic feet), and tune to ~11.5 Hz with a 4" diameter by 17" long flared port.

Make the front chamber 56.6 liters (2 cubic feet) and tune to 28 Hz with a 4" diameter by 17" long flared port (same as the rear chamber).

All output will be via the two ports. Goosed with 200W into the 8 Ohm nominal load, you should have more than 110 dB SPL in-room, and a bandwidth that is +0/-3 dB from ~11 Hz to 40 Hz.

How's that strike ya?

Dan Wiggins
Adire Audio®
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Old 21st June 2005, 07:16 PM   #6
GM is online now GM  United States
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Greets!

'In for a penny, in for a pound', so I'll 'up the ante' :

For such a low, narrow BW, only a BP makes sense to me also, especially since you have a spare room available. With a ~IB rear Vb (preferably at least 224 ft^3), a ~20 ft^3 filter chamber and a ~10.125" dia. throat (to keep the CR reasonable) placed as close to the floor/wall corner junction as practical. Plug the info into Hornresp to fine tune/get an idea how much gain there will be, with the understanding that at some point the corner typically becomes increasingly transparent if not built like a bomb shelter, so will probably begin to roll off quicker than predicted.

GM
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Old 21st June 2005, 08:20 PM   #7
simon5 is offline simon5  Canada
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Hi, I want to know why you guys prefer bandpass since the group delay is worse and the output is lower?

Why not go even more crazy? Two dual chamber bass reflex boxes. 10 cu.ft main chamber with 5 cu.ft small chamber, using 6 four inches diameter ports 28 inches in length. One chamber will be tuned around 10.5 Hz and the other around 14.5 Hz. I guess this would beat bandpass IMHO.
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Old 21st June 2005, 08:30 PM   #8
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I like all those ideas, but Dan's will prove the easiest and very little work because I already have a sealed cube for a 15. I think it's 90L, so I'll need to shorten the port. I also have an EBS box for a Maelstrom which I think is 360 liters (why aren't those box designs on the Adire site any more?). I was wondering what to do with it anyway since my Maelstrom is part of my dipole bass. It already has dual 17" by 4" flared ports, so I can play with resistance in the port(s) to tune it however I want. I also already have the other flared port.

It won't look pretty, but will be hidden by a false stage. The only work to to is fix one baffle to fit a Tempest, add a port to the cube (the hardest part), and join the boxes.

I'm leaning toward making a sizeable airspace between the 2 drivers which really smooths out the response of the Decware Housewrecker, a 6th order BP design. It I do that, then I can add a removeable plexy window for viewing and driver access. It's a no pressure zone, so plexy is OK. Then just stand this monster up in the one unused corner which just happens to have concrete walls.

The big question is, should I go all the way and intentionally make it look like a cyclops robot? It will be such a monster that it deserves a name, maybe Iron Man, and initiate him with some Sabbath cranked up on the HT system.

This is going to be fun. I'll have to warn the neighbors so they don't think we're having an earthquake because no way 10hz is staying in the room.
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Old 21st June 2005, 08:42 PM   #9
simon5 is offline simon5  Canada
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Just checked your box volumes in WinISD Pro, you could leave the volumes like they are, if it's exactly 360 liters and 90 liters internal, it will work well at the frequency Dan recommended you to tune to.

You would need to use a 17 inches by 4 inches port for the 360 liters part and a 10.5 inches by 4 inches for the 90 liters part.
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Old 21st June 2005, 08:46 PM   #10
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Quote:
Originally posted by simon5
Hi, I want to know why you guys prefer bandpass since the group delay is worse and the output is lower?

Why not go even more crazy? Two dual chamber bass reflex boxes. 10 cu.ft main chamber with 5 cu.ft small chamber, using 6 four inches diameter ports 28 inches in length. One chamber will be tuned around 10.5 Hz and the other around 14.5 Hz. I guess this would beat bandpass IMHO.
If I understand group delay correctly, it won't be an issue because I have a variable distance setting for the sub on the receiver, so I can adjust timing that way, plus it is only going to be used for HT. Music will be 100% OB.
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