Twin Avalanche 18", Sealed or PRs? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 23 Old 12-29-09, 12:55 PM Thread Starter
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Twin Avalanche 18", Sealed or PRs?

After MONTHS of kicking around ideas, I finally have started a build.

Im looking to build new subs because I want to get better low bass output then my present sub offers. So after shopping around and doing countless drawings and plots, I made a deal to purchase 2 Ascendant Audio Avalanche 18 drivers. Price along with performance played the major roll in picking this driver. Its funny, I started out looking at multiple 12s, then moved on to multiple 15s and somehow I ended up with dual 18s. The wife knows Im getting new subs, she just doesnt know I went with 18s, I think shes going to be shocked at the size of these monsters.

I plan on building a 260L cabinet for each driver, 22 wide x 21 deep and 45 high. I like the narrow tall style cabinet because it fits my space well and matches the style of my existing speakers (they are very narrow and vertical). I all my speakers are crossed over at 45 Hz and they sound very good, so all I need to do is fill in the bottom. I really dont need max SPL, just flat output down 15 Hz (lower if possible) with good SQ. But it is always nice to be able to crank it up to reference levels on the better movies or crank a good tune.

The room size (once the HT is built) will be 4500 cu ft and pretty well sealed off from the rest of the house. Each sub will be driven off one channel of my Yamaha P7000S and receive 950 watts, I could pick up another amp if needed down the line.

The first question is whether to build sealed or with PRs? I like the idea of sealed subs, Im just not sure they will get me down low enough with authority. The model of a single sub looks good but from what I hear, once you go dual subs, all bets are off and it becomes trial and error with placement and cancelation. Using a design with two Exodus Audio 18 PRs increases the output but also changes the sound. The problem is, I have never heard either configuration, only ported subs. This is tempting also because Kevin is having a clearance sale on his PRs and the prices are very appealing.

Building the subs as sealed with the idea of adding PRs later if needed has two major drawbacks. The first is driver placement. In a sealed design, ideally I would mount the driver in the middle of the vertical face for appearance reasons. In the PR layout I would have the driver and one PR mounted on the face, with the second PR mounted on the back side. Mounting the PRs on the sides of the cabinet doesnt work well for me. The second drawback to adding them later, is by the time my build is finished, Im afraid Kevin will be sold out and at that point, it would cost me almost double to add the PRs.

I guess I am looking for reassurance that dual sealed 18s will get me the output I need down low. Any advice would be helpful. I have a couple of weeks before the drivers are delivered, but I want to start on the cabinets as soon as possible.
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post #2 of 23 Old 12-29-09, 01:59 PM
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Re: Twin Avalanche 18", Sealed or PRs?

2 sealed subs will have the same output as one ported sub so that should tell you what you're giving up by going sealed. Have you modeled the subs to compare the differences between sealed and ported?




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post #3 of 23 Old 12-29-09, 04:42 PM Thread Starter
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Re: Twin Avalanche 18", Sealed or PRs?

It looks like a 3 db difference at 20 Hz and below. From my understanding adding a second sub will add 3 db. So, running 2 sealed subs I should be right at 109 db @ 15 Hz compared to 113 db @ 15 Hz for the dual PR subs. Does the graph look right to you?

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post #4 of 23 Old 12-29-09, 04:48 PM
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Re: Twin Avalanche 18", Sealed or PRs?

Post the parameters of the sub so I can model it. Thanks.




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post #5 of 23 Old 12-29-09, 05:47 PM
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Re: Twin Avalanche 18", Sealed or PRs?

As an owner of three Avalanche 18 drivers, I can tell you first off that unless you have speakers with amazingly capable woofer sections (like a 15" driver for bass), you would want to set your crossover higher than 45hz. I won't harp on that, but using dual Avalanche 18s and crossing them at 45hz seems like a big waste of capability.

Second, if you want to go after the low end and you don't want a very large enclosure, you'll probably want to go sealed with a LT to exponentially boost the low end. I'm not a fan of this method as it is very inefficient, but unless you're willing to increase enclosure size a few hundred more liters, it's really your only choice.


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post #6 of 23 Old 12-29-09, 06:04 PM Thread Starter
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Re: Twin Avalanche 18", Sealed or PRs?

I have VMPS RM40's for fronts, an LRC for center and a set of RM2s as surround. The system sounds fantastic with the crossover set to 45 Hz, but I'll play around with it once the subs are built.

I really don't want to go too much larger. The foot print needs to stay the same, I'd have to go taller.

These are the T/S specs for the Avalanche 18"...

Qts - .400
Qms - 6.00
Qes - .429
Vas - 550 Liters
Fs - 16 Hz
Re - 3.2 ohm
Vd - 6.53 L
Znom - 4 ohms (dual 2 Ohm coils in series)
Le - 2.4 mH
Mms 369 g
Xmax - 27 mm
Sd: 1210 cm^2
Voice Coil - Dual 4 Ohm
Pnom -800 Watts Rms

Cutout - 16.75"
Diameter - 18.5"
Mounting depth:
Gasket on - 9 7/16" (9.4375")
Gasket off - 9 9/16" (9.5625")
Weight - 42 Lbs
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post #7 of 23 Old 12-29-09, 06:52 PM
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Re: Twin Avalanche 18", Sealed or PRs?

Your graph in post #3 looks correct. The sealed with 950 watts input will need a Hi-Pass filter at 10 hz.




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post #8 of 23 Old 12-29-09, 07:48 PM Thread Starter
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Re: Twin Avalanche 18", Sealed or PRs?

Thanks Mike.

Now the only question is whether 3 db is worth adding PRs.

If I add another amp, feed them 1500 watts gets the sealed much closer to the output of the PR sub.

Steve, can these drivers handle 1500 watts?
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post #9 of 23 Old 12-29-09, 08:07 PM
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Re: Twin Avalanche 18", Sealed or PRs?

Those speakers each have a single 9.8" driver dedicated to bass duties, but I can't tell from their website at what frequency that woofer takes over. Two 10"s vs two 18"s....I'd take the two 18s" up to 80hz, but again, to each his own.

These drivers can handle peaks of 1500 watts, but the Avalanches aren't meant for really high continuous power handling. They use XBL^2 and therefore the coil isn't particularly large. That said, since these are 18" drivers and you'll be using two, they will be coasting along most of the time on no more than 2-3 watts each 90% of the time.

For your size enclosure, I just don't see much benefit being gained from the cost of passive radaitors - plus the radiators are going to give you a 6th order rolloff below tuning. I'd go sealed and hope that your room gain can keep these things going down into the low teens. If not, you'll want to look into a LT circuit or a Bassis.

Out of curiosity, did you acquire the older version with the four spoke basket or the later version with the 12-14 spoke basket.


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post #10 of 23 Old 12-29-09, 08:26 PM Thread Starter
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Re: Twin Avalanche 18", Sealed or PRs?

Steve,

These are the 12 spoke version with 2 ohm DVCs.

I know what you mean with 10" drivers, my old Infinitys had 15s but the RM 40 really pound out the bass. There are actually two 10" drivers and a 10" PR to handle the bass duties. VMPS claims 24 Hz at 115 db/1 m but I think they sound better crossed higher when playing at high volume.
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