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Sealed subs and room gain...

post #1 of 16
Thread Starter 
Can anyone help me understand this a little better? I'm under the impression that sealed subs do better in a small closed off room due to room gain. Don't all subs do better in smaller spaces? I've read that sealed subs are even preferred in smaller rooms due to this. Does this help them dig deeper or does it help in other frequencies?
post #2 of 16

This is mainly due to helping them improve output at low frequency, unlike a ported sub, which won't gain as much, since they roll off much more sharply below their port tuning.

 

Sealed subs typically start rolling off much earlier than an equivalent ported sub, say, around 30-40 Hz.  Room gain will flatten this out and cause low frequency output to remain much higher.  A ported sub will often still hold some advantage close to its port tune, down to which point they tend to be very flat, followed by a sharp drop off.  Room gain usually only adds a couple of Hz in extension to a ported sub.

 

A ported sub will be fairly flat down to port tune, say 18-22Hz(some lower) regardless of room size.  A sealed sub must have a small enough room to maintain a flat response.

post #3 of 16
Quote:
Originally Posted by Trace79 View Post

Don't all subs do better in smaller spaces?
They do.
Quote:
I've read that sealed subs are even preferred in smaller rooms due to this. Does this help them dig deeper or does it help in other frequencies?
The reason sealed subs are generally preferred in rooms small enough to use them is that sealed subs are smaller. The advantage to a small room is that you don't have to use larger ported subs in them to reach flat to 20Hz.. But you can.
Quote:
This is mainly due to helping them improve output at low frequency, unlike a ported sub, which won't gain as much, since they roll off much more sharply below their port tuning.
Ported and sealed subs will realize exactly the same cabin gain in the same room. The significance of the roll off slope between sealed and ported is vastly overstated; with well designed subs of both types a difference in the end result will only be seen below 15Hz, which is of little consequence to most users.
post #4 of 16
I don't want to take credit but this is from Bill Fitzmaurice: you take 565 divided by the room's longest dimenstion and that is the frequency where room gain will start. So for a room with a longest dimension of 18ft the room gain would start around 31.5hz. So if you had a room like that then you would want a sealed sub flat to about 30hz then room gain would help you from there down.
post #5 of 16
Quote:
Originally Posted by flickhtguru View Post

I don't want to take credit but this is from Bill Fitzmaurice: you take 565 divided by the room's longest dimenstion and that is the frequency where room gain will start. So for a room with a longest dimension of 18ft the room gain would start around 31.5hz. So if you had a room like that then you would want a sealed sub flat to about 30hz then room gain would help you from there down.

So how much extra room gain will you get, like flat for another 10 hz down to 20 for example?  

 

I have a sealed room with an 18 ft long wall as it so happens, and I've tossed around the idea on a sealed sub. Many of them roll off at or around 30. 

post #6 of 16
Quote:
Originally Posted by ClawAndTalon View Post

So how much extra room gain will you get, like flat for another 10 hz down to 20 for example?
 The theoretical maximum is 12dB/octave, though 8-10dB is more realistic in an average room.
Quote:
I've tossed around the idea on a sealed sub. Many of them roll off at or around 30. 
That would be on the low side, and I'd want to see measurements before I believed it.
post #7 of 16
Quote:
Originally Posted by Bill Fitzmaurice View Post


 The theoretical maximum is 12dB/octave, though 8-10dB is more realistic in an average room.
That would be on the low side, and I'd want to see measurements before I believed it.

Bill, it would appear that the new SVS SB2000 begins it's roll off at 30 hz according to their website. 

 

So I'd possibly be at 20 hz or close to it before a roll off on that sub?

 

Not to mention EASILY getting single digits with the gentle roll off... Unless I'm missing something 


Edited by ClawAndTalon - 2/18/14 at 9:44am
post #8 of 16
Thread Starter 
Quote:
Originally Posted by ClawAndTalon View Post

Bill, it would appear that the new SVS SB2000 begins it's roll off at 30 hz according to their website. 

So I'd possibly be at 20 hz or close to it before a roll off on that sub?

Not to mention EASILY getting single digits with the gentle roll off... Unless I'm missing something 

I too was looking at the SB-2000 for my room...well, duals actually. My room is very small at 14' x 9' x 8' and there is little room for a big ported sub. The only ported sub worth its salt I can have would be a SVS cylinder (was thinking the PC12+). The largest sealed sub I could get would be the SB13-Ultra. I know the Sb13 would be massive overkill in that room biggrin.gif and a pc12+ would probably be more than enough but I would lack the benefit of having duals. Two SB-2000's come to mind but I wonder if I would get that low-end from room gain that would match or come close to the pc12+? I also wonder if the SPL from 40hz and up would be more/less than a pc12+. Placement of duals SB2000 would be easy though.
Any thoughts?
post #9 of 16
Quote:
Originally Posted by Trace79 View Post

I too was looking at the SB-2000 for my room...well, duals actually. My room is very small at 14' x 9' x 8' and there is little room for a big ported sub. The only ported sub worth its salt I can have would be a SVS cylinder (was thinking the PC12+). The largest sealed sub I could get would be the SB13-Ultra. I know the Sb13 would be massive overkill in that room biggrin.gif and a pc12+ would probably be more than enough but I would lack the benefit of having duals. Two SB-2000's come to mind but I wonder if I would get that low-end from room gain that would match or come close to the pc12+? I also wonder if the SPL from 40hz and up would be more/less than a pc12+. Placement of duals SB2000 would be easy though.
Any thoughts?

There is no such thing as overkill, you can always turn the sub down and the less it has to work to achieve a desired output level, the better it will sound. That being said the sb13 and pc12+ would be similar in output above 30hz, the pc+ would have a bit more below 30hz.
post #10 of 16
Thread Starter 
Yes
Quote:
Originally Posted by basshead81 View Post

There is no such thing as overkill, you can always turn the sub down and the less it has to work to achieve a desired output level, the better it will sound. That being said the sb13 and pc12+ would be similar in output above 30hz, the pc+ would have a bit more below 30hz.

Yes, I know I can always turn the gain down. But knowing my friends and I when we get drunk would be like when a redneck says, "hey yall, check this out!" biggrin.gif

If I did get an SB13 it would go under the desk where the TV sits, facing the MLP and only about five feet away. Same if I got dual SB2000s, but one would go somewhere else.

The PC12+ would be tucked away in a corner.

If I could get below 20hz at decent SPL with a sealed sub, this would be preferred.
post #11 of 16
Even though sealed subs are great for smaller rooms, sealed subs can be used in a larger HT. I run Chase subs SS 18.2 and stacked SS 18.1 in a 5300 cu ft space and have excellent output/LFE. Four 18 in drivers move a lot of air for a good pressure effect. These passive subs are smaller than the Rythmik and HSU ported 15 in. subs.
Edited by derrickdj1 - 2/20/14 at 10:02pm
post #12 of 16
Quote:
Originally Posted by Trace79 View Post

I too was looking at the SB-2000 for my room...well, duals actually. My room is very small at 14' x 9' x 8' and there is little room for a big ported sub. The only ported sub worth its salt I can have would be a SVS cylinder (was thinking the PC12+). The largest sealed sub I could get would be the SB13-Ultra. I know the Sb13 would be massive overkill in that room biggrin.gif and a pc12+ would probably be more than enough but I would lack the benefit of having duals. Two SB-2000's come to mind but I wonder if I would get that low-end from room gain that would match or come close to the pc12+? I also wonder if the SPL from 40hz and up would be more/less than a pc12+. Placement of duals SB2000 would be easy though.
Any thoughts?

I use a SB Ultra 13 in a 3.5 m x 3m room. Sounds great, not overkill (tried SB 12" and needed more grunt for movies) the 12" didn't rumble the room like the 13.5" can.
post #13 of 16
Quote:
Originally Posted by Trace79 View Post

I too was looking at the SB-2000 for my room...well, duals actually. My room is very small at 14' x 9' x 8' and there is little room for a big ported sub. The only ported sub worth its salt I can have would be a SVS cylinder (was thinking the PC12+). The largest sealed sub I could get would be the SB13-Ultra. I know the Sb13 would be massive overkill in that room biggrin.gif and a pc12+ would probably be more than enough but I would lack the benefit of having duals. Two SB-2000's come to mind but I wonder if I would get that low-end from room gain that would match or come close to the pc12+? I also wonder if the SPL from 40hz and up would be more/less than a pc12+. Placement of duals SB2000 would be easy though.
Any thoughts?
Well I can tell you that with a 14' length...your room gain should start at about 40Hz. You will have a modal peak at about 40Hz, like my room (14x11x8), where I had to make a big cut from 35 - 45 Hz after the Linkwitz Transform was engaged. I don't think the SB-13 Ultra would be overkill at all. You are looking at an estimated 4 liters of displacement peak to peak [assuming 30 - 32mm xmax x 635 cm^2 Sd]. Bosso's formula says you need 10 liters peak to peak for the "real deal" (1008 cu. ft. x .01]. I say [one way displacement / cubic feet] should be higher than 40 for a "compelling" experience. With one SB13, you will be at 20, best case [32mm xmax]. I am not sure of the xmax capabilities of the Ultra driver, but I would guess around 30 mm or better. Overkill starts at two or more...wink.gif
post #14 of 16
Quote:
Originally Posted by kramskoi View Post

With one SB13, you will be at 20, best case [32mm xmax]. I am not sure of the xmax capabilities of the Ultra driver, but I would guess around 30 mm or better. Overkill starts at two or more...wink.gif

According to the review of its big brother the hometheaterhifi PB13 web, reads as follows:

The driver does not end just with an extra inch and a half in size. It is capable of 3" excursion, which means it can move a lot of air.
http://www.hometheaterhifi.com/volume_14_3/svs-pb13-ultra-subwoofer-9-2007-part-1.html

It's a really rough, not exact. But perhaps it can serve as a reference and I guess the tour between SB13 and PB13 will be similar.

I add:

3" tour seems excessive to me, I have no reason to doubt the data, but I think it's best to ask Ed Mullen to be sure.
post #15 of 16
I read the SB Ultra 13 driver has a bit more cone excursion compared to the PB/PC models..
post #16 of 16
Quote:
Originally Posted by Trace79 View Post


I too was looking at the SB-2000 for my room...well, duals actually. My room is very small at 14' x 9' x 8' and there is little room for a big ported sub. The only ported sub worth its salt I can have would be a SVS cylinder (was thinking the PC12+). The largest sealed sub I could get would be the SB13-Ultra. I know the Sb13 would be massive overkill in that room biggrin.gif and a pc12+ would probably be more than enough but I would lack the benefit of having duals. Two SB-2000's come to mind but I wonder if I would get that low-end from room gain that would match or come close to the pc12+? I also wonder if the SPL from 40hz and up would be more/less than a pc12+. Placement of duals SB2000 would be easy though.
Any thoughts?

To help you with due diligence, check and see if the PSA XS15, or the perhaps even the XS30 has dimensions which would be suitable for your room. PSA also has the XV 30f, which is a ported sub with two front firing 15"s stacked vertically (to save space). But, again check and see if the footprint and dimensions would work for you. YMMV and yade yade, but I personally don't think you'd get much gain from duals in that listening space as long as there are no audible nulls in your sitting area. That's just me though...

 

Room gain is always going to be tricky. The long wall formula, while being a decent first step, is a very general rule. Different subs, and more importantly different rooms, and their contents (bed, sofa etc) will skew the appropriate answer for your particular listening space. http://www.data-bass.com/data?page=content&id=80

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