Tempest X2 in an 8 cu. ft. sealed box - diyAudio
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Old 22nd September 2012, 08:35 AM   #1
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Default Tempest X2 in an 8 cu. ft. sealed box

I have 2 Tempest X2s and I want to put them in a sealed box like so...

Note - the HF driver will be at ear level, while the subs will be on the floor...

Click the image to open in full size.

I'm going to have 3Pi speakers mounted in-wall - as will be these subs. I had wanted to put each sub under a 3pi, simplifying my build by becoming a stand for the 3pi's, and providing about 6 cu. ft. volume for each sub. However, Wayne from Pi speakers suggests that the subs "flank" the mains, as this would help average out modal problems. With this in mind, I came up with the possibility you see in the pic above...

My questions:

I have just about 9" of usable depth (after 1" MDF boxes), but I have about 48" of width, and up to 40" height available, so I can easily meet the manufacturer's recommendation of 8 cu. ft. Is this extreme shallowness going to become an audible problem?

The manufacturers recommendation reads as follows:

Click the image to open in full size.

However, another forum member has modeled it as follows, and this one looks far less inspiring...

Given that I am a rank amateur, and that is one of the reasons why I am opting for a sealed sub, what should I believe?

Click the image to open in full size.


Another question... can I put discrete L and R subs, powered of course by discrete amps, in the same box? Almost all of the signals coming to each driver are going to be identical anyway. Or do I have to make it a dual driver mono sub? The former is easier for my to accomplish because I intend to buy two Behringer Inuke NU6000DSP amplifiers, one to power each side. It will take care of sub/mains crossover duties, as well as provide me with aboundant tone shaping possibilities

Thanks for any inputs...
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Old 22nd September 2012, 10:54 AM   #2
DrDyna is offline DrDyna  United States
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The chart you have for the second one is driver excursion, not frequency response.

Having two cabinets is a better arrangement, imo. It allows you to use placement as a tuning method with more effectiveness than a single cabinet allows.
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Old 22nd September 2012, 04:43 PM   #3
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Quote:
The chart you have for the second one is driver excursion, not frequency response.
I am aware of it... not sure if I'm interpreting it right, though... The excursion seems to be exceeding the driver's limitations below 30 Hz, and the f3 is @ 36 Hz, with 2000 watts of power...? I was hoping for an in-room f3 of around 20 Hz..., without equalization, as per the attached documentation from the manufacturer...
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Old 23rd September 2012, 01:07 AM   #4
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Altec used a 1.5x minimum driver depth, but never seen any write-up on it, probably because it dates from the extensive early Bell Labs/W.E. anechoic chamber testing.

If so, this was from using drivers with only a few mm excursion capability, so with a 26 mm Xmax it may be too little.

That said, your cab will have ˝ WL TL loading, so probably all you need is some room for the rear vent. Frankly, I’m surprised DIYCable doesn’t address this in their documentation.

The TL loading will add notches in the response since the drivers will be at one end, but assuming a typical < 80 Hz/4th order XO, these shouldn’t be audible.

The excursion plot is most likely a 2pi space one, i.e. if the speaker was sitting on the ground in a large flat field, so in room there will be some LF boost like one gets in a car, only not as much and since yours will theoretically begin in earnest around ~565 ft/16.67 ft = ~34 Hz, this sealed alignment should work well all the way down as far as you’re likely to need without exceeding Xmax unless your room is much more lossy than your drawing implies.

Matching drivers in a common space is fine if a sealed or TL type of alignment, though for reflex [vented] they need to be reasonably well matched spec wise, so I recommend putting them in their own vented space and the divider helps to brace the cab and raise the cab’s harmonic structure as bonus.

For the latter reason alone, I recommend a vertical divider in your cab to create two much narrower TLs; otherwise I would still recommend it due to wanting ‘stereo’ subs.

All that said, your subs are in a crappy location acoustically, especially with the listening position backed up against the opposing wall:

http://www.google.com/url?sa=t&rct=j...b-hLZ5Yr1MztIA

GM
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Old 23rd September 2012, 05:03 AM   #5
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Quote:
All that said, your subs are in a crappy location acoustically, especially with the listening position backed up against the opposing wall:
Thank you GM. I wish the world would be as candid. I guess this is what you wanted me to see...

Quote:
Putting subwoofers on either side of a null results in cancellation, due to the opposite polarity.
So I'm kind of back to where I started... the subs as stands for the speakers, as there is absolutely no real estate available in the room. (Not indicated in the layout pic are equipment and amenities that occupy all of the available space).

Click the image to open in full size.

I get just under 6 cu. ft. with this arrangement. Here is the manufacturer's spiel on a 5 cu. ft. box.

Click the image to open in full size.

Am I going in the right direction?
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Old 23rd September 2012, 06:57 AM   #6
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Where did you get that quote about nulls?
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Old 23rd September 2012, 08:40 AM   #7
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Where did you get that quote about nulls?
from the following document pointed to by GM, top of page 8.

this one.
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Old 24th September 2012, 12:07 PM   #8
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by audiothings View Post
from the following document pointed to by GM, top of page 8.

this one.
My favorite line from that document is this one:

"This simulation shows 5000 subwoofers randomly located in test room."

I almost had coffee coming out of my nose.
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Old 24th September 2012, 02:33 PM   #9
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Quote:
Originally Posted by DrDyna View Post
My favorite line from that document is this one:

"This simulation shows 5000 subwoofers randomly located in test room."

I almost had coffee coming out of my nose.
Yes, but they did also say:
Quote:
With 5000 subwoofers, modal variation is virtually
eliminated. The frequency response at all 16 seats is nearly
identical.
and
Quote:
Since putting even 50 subwoofers (randomly) in a room is not practical,
this approach is not practical.
You can now finish your coffee... safe in knowing the optimal practical number of subwoofers in a single room is probably > 0 and <= 50
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Old 24th September 2012, 02:44 PM   #10
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by J. L. View Post
Yes, but they did also say:

and


You can now finish your coffee... safe in knowing the optimal practical number of subwoofers in a single room is probably > 0 and <= 50
lol, I know, there was just something about the image that conjured up, something like Chevy Chase's Christmas lights and the electricity meter spinning so fast it starts to smoke.
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