Frequency & SPL - Home Theater Forum and Systems - HomeTheaterShack.com

Old 01-03-13, 08:57 PM Thread Starter
Senior Shackster

Mike

Join Date: Jan 2009
Location: OKC
Posts: 338
Frequency & SPL

I would like to pose a couple of scenarios.

Suppose that I have 16 cu ft ported enclosure, with 2 drivers tuned to 15 hz. It is 70hz at 121 db.
At 15hz it is at 114db

I have two 8 cu ft enclosures one driver each also tuned to 15hz. At 70hz it is at 115db and at 15 hz it is at 107.5db.

On either of these will I or anyone be able to tell a huge difference? If so would it be better to go with an enclosure that is 7 cu ft tuned to 20 hz, that may be a little more linear ( if that term is correct)?

At 70 hz it is 117 db and 20hz at 112db and around 15hz at 101db ( at a little less than half of max power)

Hope to learn something new, and know how to use it.
Mike
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Old 01-03-13, 10:10 PM
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Stereodude

Join Date: Feb 2010
Posts: 261
Re: Frequency & SPL

Something isn't quite right with your numbers. Two 8ft^3 boxes with one driver each can give the same SPL as a single 16ft^3 box with 2 drivers assuming the power per driver is the same. So at 70Hz you should get 121dB either way.
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Old 01-03-13, 10:20 PM Thread Starter
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Mike

Join Date: Jan 2009
Location: OKC
Posts: 338
Re: Frequency & SPL

I have two drivers. I modeled the box for one driver. That is what one box one driver does. I would of course have two enclosures. There may be something I don't get, but it is my assumption that having two enclosures is going to keep me from having any dead spots( or whatever the correct terminology is)

Hope to learn something new, and know how to use it.
Mike
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Old 01-03-13, 10:52 PM Thread Starter
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Mike

Join Date: Jan 2009
Location: OKC
Posts: 338
Am I to understand that if I have any two identical subs, that my frequency response will be the same as it is for one but my overall SPL will be higher with two subs versus one?

Hope to learn something new, and know how to use it.
Mike
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Old 01-04-13, 06:08 AM
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Mike

Join Date: Apr 2007
Posts: 19,397
Re: Frequency & SPL

Two single cabinets will have the same SPL as one single caninet with 2 drivers.
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Old 01-04-13, 07:04 AM Thread Starter
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Mike

Join Date: Jan 2009
Location: OKC
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Things are clearer, just all too new to me. Trying to wrap my head.

Either way two cabinets are better than one, if your current config., doesn't work then you will be ready to something different.

Now with this view if I go back to o. p. then
a 7 ft cab to 20 hz or an 8 ft can to 15?
Both will make it to 15, just one a little louder.

Both make it to 20 one is flat pretty much to that point the other is dropping slightly.

Is this something that will be real noticeable?

Or do I just build it one for the experience and see what happens, even though I would have know way knowing without side by side??..

Hope to learn something new, and know how to use it.
Mike
Audiodreamer is offline
Old 01-04-13, 07:36 AM Thread Starter
Senior Shackster

Mike

Join Date: Jan 2009
Location: OKC
Posts: 338
Re: Frequency & SPL

Okay this is what I modeled. Keeping in mind that I want to tune around 15 hz.
I know in room response will be better with two. Will I get what I am wanting from the 8 ft cabinet(s)?

Or do I build the 16 ft cabinet with two drivers ( which is very large IMO)?

My issue seems to be with port velocity on the 8ft cabinet.

shake the foundation.wpr

aa.wpr

Hope to learn something new, and know how to use it.
Mike
Audiodreamer is offline
Old 01-04-13, 08:17 AM
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monomer

Join Date: Dec 2006
Posts: 169
Re: Frequency & SPL

Quote:
Stereodude wrote: View Post
Something isn't quite right with your numbers. Two 8ft^3 boxes with one driver each can give the same SPL as a single 16ft^3 box with 2 drivers assuming the power per driver is the same. So at 70Hz you should get 121dB either way.
Actually... by stacking the two singles, he should get a theoretical increase of 6dB, 115dB + 6dB = 121dB... which means his numbers do work. Its just that with two singles he will have more options in placement, especially if he finds he needs to separate them to smooth out the in-room response, albeit with a reduced total output response. (To OP: If the two subs are moved apart the dB increase will be something less than the theoretical max.) Also the reduced weight factor of two singles vs one humongous dual will make moving the thing around easier... OP: have you even estimated the final weight of dual drivers in a 16 cu ft MDF box? Were you planning on using casters?

Last edited by monomer; 01-04-13 at 08:27 AM.
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Old 01-04-13, 08:37 AM Thread Starter
Senior Shackster

Mike

Join Date: Jan 2009
Location: OKC
Posts: 338
I'm the type that will beat this thing to death before I start cutting!

After moving around 4x8 sheets of mdf. I think 16 cu would be as heavy as my fridge and it has casters.

And all in all with all the info and research two cabinets are better than one which means that I'm opting for the two 8cubes. Which to get port velocity down is actually 8.75 net.

And if the total output is quite what I want then maybe I will wish I had the 18's. but I am going from no bass at all so I am hoping that these will be tremendous

Hope to learn something new, and know how to use it.
Mike
Audiodreamer is offline
Old 01-04-13, 08:55 AM
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monomer

Join Date: Dec 2006
Posts: 169
Re: Frequency & SPL

Quote:
Audiodreamer wrote: View Post
...I am going from no bass at all so I am hoping that these will be tremendous
Just for point of reference... 120dB is generally considered the threshold of pain at which permanent hearing damage can begin to occur so... if you do listen at max volume for too long you'll be back to "no bass". Seriously, I have no idea of the space you are going to be trying to pressurize nor how much power you'll be using to drives these subs nor how you like to setup your listening levels but I'm thinking you'll more than likely have enough bass with just the 15"s. Good luck there.
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