Question about how toCalculate Box Volume - Home Theater Forum and Systems - HomeTheaterShack.com

Old 02-28-12, 03:22 PM Thread Starter
Shackster
Dan

Join Date: Feb 2012
Posts: 37
My System
Question about how toCalculate Box Volume

I have found a few formulas on the intenet to calculate Vb ( Net box volume litress) based on QTC,Qts and Vas.

Qr=Qtc/Qts
Vr = Qr^2-1
Vb = Vas/Vr

When I model the volume in WinIsd there is a 5 litre descrepancy when compared to the formulas provided.
I assume WinIsd is more accurate. Are these formulas basic or are there more advanced ones that would provide the same accuracy that WinISD does. Any help appreciated.

Dan
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Old 02-28-12, 07:57 PM Thread Starter
Shackster
Dan

Join Date: Feb 2012
Posts: 37
My System
Re: Question about how toCalculate Box Volume

I think I may have just found my own answer.
I got this from another post on this site.

QTC is just a number and its effect on sound relates to other details about the driver.

Now generally I like to shoot for a qtc around .57 to .62. I think this gives a good balance of bottom end effeciency without totally nerfing power handling. A higher qtc near .7 to .8 will improve the amount of power you can throw at the driver (because the box will reduce driver efficiency at low frequencies) for more peak output. The problem is, most drivers have too high an fs for a higher qtc as above, so what you can often get is a midbass emphasis with no bottom end - an overly punchy sound. Now a qtc = .8 is acceptable enough with enough internal fibrefill but if you're not getting any bottom end, the sound will lack depth and subjective "smoothness". This is because the fundamental frequency is less emphasized than it's supposed to be. A qtc = .45 to .55 will give you the optimal extension that you can squeeze out of the driver, but may have too early a corner on its shallow rolloff, which without EQ may sound dead and lifeless - but again it depends on the driver parameters.

And that's what it boils down to,

- EQ via box (qtc)
- EQ via room gain (very low frequencies)
- EQ via electronics (to compensate for room gain or lack thereof)
- EQ via placement (mid bass frequencies).
- EQ via multiple subwoofers (midbass frequencies)

All within the physical limits of your system.

At the end of the day, we need to know about

- Your goals (output? extension? whatever you can get?)

to figure out where to go from there.

Now given that your driver is the RSS265HF, I at least know rated xmax = 12.3mm

Is your driver the 4 ohm version or 8 ohm version? What is your amp? How large is your room?

My personal opinion is that this driver is likely too inadequate to be using sealed at all. Simply put, you're getting no bass extension which is especially problematic for HT. I simply don't consider anything less than a long throw 15 incher to work sealed.

I'll say this though, a qtc = .60 is by no means too small. I consider it to be just the right balance although with a 10" driver you'll find yourself overdriving the woofer much too easily.

Read more: What is a good QTC for HT? - Home Theater Forum and Systems - HomeTheaterShack.com

There is so much info on this site. I sure takes time to find it
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Old 02-28-12, 08:02 PM
Shackster
BigJBK

Join Date: Jan 2012
Location: Fairfield, CA
Posts: 33
Re: Question about how toCalculate Box Volume

That's great info I will save it for my next build, Thanks Dan.
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Old 02-29-12, 12:29 PM
Senior Shackster

Join Date: Nov 2011
Location: St. Louis, MO
Posts: 147
Re: Question about how toCalculate Box Volume

Thanks for giving me lots to think about!

Tom
tshifrin is offline
Old 03-02-12, 02:02 PM Thread Starter
Shackster
Dan

Join Date: Feb 2012
Posts: 37
My System
Re: Question about how toCalculate Box Volume

I was looking for answers but if that helped you guys, your very welcome
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Old 03-03-12, 11:55 AM
Senior Shackster

Join Date: Nov 2011
Location: St. Louis, MO
Posts: 147
Re: Question about how toCalculate Box Volume

Qtc is a preference, and you have found yours, so plugging in the values in the formulas seems pretty straightforward. By my calcs, both those drivers work well sealed, but there's only so much bass to be had from their Xmax and size. Home theater requires more bass, and generally lower extension, so at your preferred Qs, I'd suggest you look at other drivers. (Just my .02 cents worth.) You have a handle on all the trade-offs, so you're well on the right path.

Tom
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