Home Theater Forum and Systems banner

1 - 20 of 23 Posts

·
Registered
Joined
·
41 Posts
Discussion Starter #1
After MONTHS of kicking around ideas, I finally have started a build.

I’m 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. It’s funny, I started out looking at multiple 12”s, then moved on to multiple 15”s and somehow I ended up with dual 18”s. The wife knows I’m getting new subs, she just doesn’t know I went with 18”s, I think she’s 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 don’t 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, I’m 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 doesn’t work well for me. The second drawback to adding them later, is by the time my build is finished, I’m 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 18”s 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.
 

·
Registered
Joined
·
41 Posts
Discussion Starter #3
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?

 

·
Registered
Joined
·
2,398 Posts
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.
 

·
Registered
Joined
·
41 Posts
Discussion Starter #6
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
 

·
Registered
Joined
·
41 Posts
Discussion Starter #8
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?
 

·
Registered
Joined
·
2,398 Posts
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.
 

·
Registered
Joined
·
41 Posts
Discussion Starter #10
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.
 

·
Registered
Joined
·
41 Posts
Discussion Starter #12
So it looks like I will be building 2 sealed cabinets. WndISD calculates the cabinet volume at 280L for a Qtc of .703. This design has an -3db of 29 Hz and an output of 105 db @ 13 Hz. All of these calculations are for one sub so there should be another 3-4 db gain by adding a second sub.

These calculations do not include any fill in the cabinet. Is there any disadvantage in building a smaller box, then adding fill to bring the Qtc back to .7?
 

·
Registered
Joined
·
41 Posts
Discussion Starter #14
As the design stands, I have only 3/8” clearance between a brace and the hole on the back of the magnet structure. Do I need to increase this clearance to ensure adequate cooling to the driver’s motor?
 

·
Registered
Joined
·
272 Posts
Brax, i dont want to dispute opinions of others but I have concerns with the limits of the enclosure type. I just simulated a good performer with a sealed enclosure, cause the parameters you gave are uncomplete, (theRSS390HF with Fs 18Hz, Qts 0,42, 87db SPL…) and that one with a ported enclosure simulates down to 18,8Hz F3 with a 264liters box. And guess, with a sealed one it is impossible to tune the thing below 39Hz ! I know the majority uses WinISD but I have done subs with BasBoxPro and the results are very close to what the program says. Just wanted to make mark here,

Regards,Veltinorian

(Also BassBoxPro seems to consider more driver parameters doing its math)
 

·
Registered
Joined
·
41 Posts
Discussion Starter #16
Veltinorian,

I welcome any advice since I am not a seasoned a sub designer like many on this board.

First are you saying, the T/S parameters for the Avalanche are not complete enough to model in BassBox? If so what is missing?

I filled out what I could in WinIsd and those were the plots I got, I did the same on Unibox and came up with identical plots. I did find it strange that the model with 2 passive radiators did not have a huge output advantage over the sealed design.

I am building two subwoofers, so I thought I could handle the drop in out put and still meet my needs with sealed designs. Do you think I would be better off going with the passive radiator design?
 

·
Registered
Joined
·
272 Posts
Bl, 1-W SPL and Cms are missing and they are important. (Cms can be calculated as there are Fs and Mms provided but there are still the Bl and 1-W SPL missing.)

Here is the answer to the question: Sealed give nothing over ported as long as the Xmax is not a concern, i.e. at for example at 300Watts to the driver you get the equal ouput from both as long Xmax is not reached, what is more the ported one extends even deeper to the lows, here is what i mean (done this with daytons RSS390HF):



The green one is sealed F3 is 40Hz box 58liters and orange one is ported F3 18Hz 260Liters. Even though i force the sealed enclosure above 58 liters, 158, 285, 585 it cannot go lower than 39Hz, thats it.

But here is one big but, if you choose to force the sub with more power the ported will reach its Xmax earlier and will not continue to produce an increase in power f.ex. when power is >300W with the volume going up, but but the sealed will increase its output, cause Xmax isnt reached yet and the outpuut from it will increase. And going on and on and on till it reaches say 400Watts. The power to the ported is also 400W but as SPL level it will be as there were only 300W to it. So for a SPL competition sealed wins (only if power > 300Watts), for low extension ported wins. Passive are not far than ported(drop a bit sooner 1 to 2 Hz) but have more flexibility to play tune the box, resolve problems with port noise and port displacement..but costs more for a passive to buy 50..80$
 

·
Registered
Joined
·
2,398 Posts
You guys are going to make me plug in my other computer to grab the original Avalanche 18 parameters :R

I will say that I'm 99% sure you can't get a flat response to tuning with this driver if you want a 15hz tune in only 260 liters. This driver likes large enclosures. I'll fire up the old computer sometime over the weekend and get the right parameters to test.
 

·
Registered
Joined
·
41 Posts
Discussion Starter #19
Steve,

In my modeling, I don't see a huge gain in low end output with a larger cabinet. I modeled all the way up to a 500L cabinet, and it didn't increase the low end out enough to justify the extra size or cost of the cabinet.

Unless there is something wrong with my models..............
 
1 - 20 of 23 Posts
Top