Which sub(s) to fill my space? - Page 3 - AVS Forum
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post #61 of 68 Old 11-30-2013, 07:40 AM
 
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In my opinion, built in subs are an expensive add that only muddies the sonic waters. In this day and age of ID subwoofers and freeware measuring software, locking a subwoofer into a speaker cabinet is only going cause trouble due to not being able to properly place and manage the bass produced by the speaker system.

Today, with ID subwoofers and bass management capable AVRs equipped with EQ capabilities such as Audyssey, one is better buying a decent 5.0 surround speaker system, crossing over the content to 80Hz and let a subwoofer system, comprising of two or three subwoofers, including the LFE channel, do the job of producing all the bass.
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post #62 of 68 Old 11-30-2013, 07:52 AM - Thread Starter
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Thanks, BeeMan; that makes sense.

I'm really struggling with my speaker purchase. I am in no way an audiophile, but I do want to have good quality sound. I've never had a higher-end system, so I for know what I'm missing.

The Emp Tek's are a great deal, but perhaps for a reason. I like the Klipsch RF-82 setup, but don't want to pay that much more if I won't notice a difference. I need to decide today if I want the Emp Tek's, as the sale ends today.

Any thoughts?
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post #63 of 68 Old 11-30-2013, 08:24 AM
 
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Originally Posted by germ79 View Post

Thanks, BeeMan; that makes sense.

...biggrin.gif

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I'm really struggling with my speaker purchase. I am in no way an audiophile, but I do want to have good quality sound. I've never had a higher-end system, so I for know what I'm missing.

If it helps, this day and age, anything under ten grand, is a budget minded system. tongue.gif

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The Emp Tek's are a great deal, but perhaps for a reason. I like the Klipsch RF-82 setup, but don't want to pay that much more if I won't notice a difference. I need to decide today if I want the Emp Tek's, as the sale ends today.

Any thoughts?

Do a quick spin (search function) through the speaker forum. Those guys are a wealth of quick information. My preference is the Klipsch Reference series. In the end, it's all about the Benjamins and how many of them one has to spend.
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post #64 of 68 Old 11-30-2013, 08:43 AM
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Originally Posted by derrickdj1 View Post

This is the way the cabin gain works:
C/2*L
1130/2* 20=28.5 Hz so you will start gain 12 db/octave starting at 28.5.. This mean at 14Hz you will be up 12 db. Room gain is not boundary gain.
1130 is the speed of sound,C is cabinet gain and L is length of the room. A good amp and a PEQ will help a sealed sub in a large room. The low end can be brought up at the expense of headroom.
Is this how you calculate at what frequency cabin gain starts? Is this the same thing as PVG?

What are the units of measure for the above calc? Thx.
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post #65 of 68 Old 11-30-2013, 11:02 AM
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Originally Posted by dominguez1 View Post

Is this how you calculate at what frequency cabin gain starts?.
Where the longest room dimension is 1/2 wavelength. In feet that would be 1130 (feet per second speed of sound) divided by the room dimension divided by 2. For example, with a 15 foot longest dimension 1130/15/2= 37.6Hz. If the room is very well sealed you would have 12dB of cabin gain one octave down at 18.8Hz, though in an average room 6-9dB would be more likely. If you're not going to get cabin gain adequate to fill in the low end to your desired low frequency cutoff with a sealed sub you should go ported. 6dB of EQ boost in the lows doubles cone excursion and quadruples the power draw from the amp.

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post #66 of 68 Old 11-30-2013, 12:24 PM
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Originally Posted by Bill Fitzmaurice View Post

Where the longest room dimension is 1/2 wavelength. In feet that would be 1130 (feet per second speed of sound) divided by the room dimension divided by 2. For example, with a 15 foot longest dimension 1130/15/2= 37.6Hz. If the room is very well sealed you would have 12dB of cabin gain one octave down at 18.8Hz, though in an average room 6-9dB would be more likely. If you're not going to get cabin gain adequate to fill in the low end to your desired low frequency cutoff with a sealed sub you should go ported. 6dB of EQ boost in the lows doubles cone excursion and quadruples the power draw from the amp.
Thanks Bill.

So does this also mean that at 9.4hz you could potentially have up to 24db of gain? Also is what we're talking about also called pressure vessel gain?

How would you determine boundary gain typically?
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post #67 of 68 Old 11-30-2013, 02:06 PM
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Originally Posted by dominguez1 View Post

So does this also mean that at 9.4hz you could potentially have up to 24db of gain?
In a very tight room with substantial walls, yes, it's possible. That's how auto sound competitions get such silly high numbers, because the 'room' is so small. They even fill the doors with concrete and weld the doors tight just so they can see 162dB on a meter. rolleyes.gif
Boundary gain is pretty simple, less than 1/4 wavelength from a wall gets you up to 6dB, less than 1/4 wavelength from a corner gets you up to 12dB, compared to anechoic, ie., outdoors. But you generally don't get extra low end extension from boundary loading, as the gain is pretty linear below 200Hz or so. The exception is with folded horns, which tend to get more boundary gain down low than at the upper end of their pass band.

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post #68 of 68 Old 11-30-2013, 09:02 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Where the longest room dimension is 1/2 wavelength. In feet that would be 1130 (feet per second speed of sound) divided by the room dimension divided by 2. For example, with a 15 foot longest dimension 1130/15/2= 37.6Hz. If the room is very well sealed you would have 12dB of cabin gain one octave down at 18.8Hz, though in an average room 6-9dB would be more likely. If you're not going to get cabin gain adequate to fill in the low end to your desired low frequency cutoff with a sealed sub you should go ported. 6dB of EQ boost in the lows doubles cone excursion and quadruples the power draw from the amp.

Thanks Bill for answering his questions. I am away for the weekend and the internet is horrible, lol. Headroom should always be kept in mind if one does not want to exceed the systems capabilities. Good base will always sound better than a system under strain. Bill is corrected about going to a ported sub if there is little boundary gain the room or one needs more subs: it is all about trade offs.

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