Ask an Acoustic Engineer (me)

[Justin Zazzi]

I don't see any problems. To get a QTC of 0.707, the DVC version wants a bigger box ~0.9cuft and the SVC version wants a smaller box ~0.35cuft. I think you both did good simulations. Maybe you're confusing which sim is which?

For fun, I ran some sims with my tool at 600w below. The displacement scales are not the same, but you get the idea.



edit: fixed left/right oops

[Grinder]

It's a bit confusing...

In JC's post #55, I was under the impression that his modeling results were based on the correct driver (the "44" DVC) ...thus my response in post #57. It seemed quite odd to me that his results for the DVC were so close to those I've gotten when modeling the SVC version.

Now jump to JC's posts #65 and #68, where he has indicated that there was initially a mix-up between the SVC and DVC versions, but that the original model he posted was actually the DVC, though by coincidence; and that he has checked his numbers (TS parameters) against mine (for the DVC) and found them to be nearly identical.

Thus it appears that JC's results for the DVC version are roughly what I get for the SVC version.

Fun, huh?


<edit> Wait... your models appear to be labeled backward. The one on the right is actually the SVC, and the one on the left is the DVC. Other than that, they appear to roughly confirm my results for both drivers.

[Justin Zazzi]

Well, I'm going to push the believe button on that one *boop*

And you're right I got my labels backwards. Thanks for seeing it. Fixed.

One day I'll do something cool with the simulator. It only took years to make it lol.

[Grinder]

I thought that might have been a test to see if I'm paying attention.

[Grinder]

Thank you for clearing this up for me, Justin. I now consider the issue settled.

[JCsAudio]

So, I took the Dayton RSS265HO-44 parameters and did a basic fresh clean new model instead of loading the parameters from BassBox Pro files, again for the Dayton RSS 265HO-44 DVC subwoofer. Letting the program pick the sealed box size I now get a sealed box size recommendation of .506 cu ft net and a qtc of .654, which is more in line with Parts Express recommendation of .55 cubic feet using the same program on their end. Attached is the PDF file for that model so you guys can check me. I do not know why you guys keep coming up with such a large sealed box for a 10" subwoofer. For a 10" subwoofer designed for a small box, and for car audio, a nearly 1 cu ft box is I think not typical. If you start modeling a lot of 10” subwoofers in sealed box’s you should find that most model well in about ½ cu foot boxes. There are exceptions of course, especially for home audio applications, but for car audio .5-.6 cu ft is the norm.

Maybe when I have some time later on I will try one of these other programs and try and figure out why these numbers are different. See below PDF of model.

Dayton RSS265HO-44 new model.pdf

Also note what Dayton recommends:

http://www.daytonaudio.com/product/1...ubwoofer-2-ohm

[Grinder]

"SVC" and "DVC" modeling results via:
WinISD 0.7.0.950
http://www.linearteam.org/


RSS265HO-4 10" (SVC)
SVC: .506 ft^3 = .638 Qtc - 55.74 Hz F3
SVC: .366 ft^3 = .707 Qtc - 55.45 Hz F3
SVC: .300 ft^3 = .756 Qtc - 55.73 Hz F3
Dayton/PE recommended: .3 ft^3 for 60 Hz F3
https://www.parts-express.com/dayton...4-ohm--295-462


RSS265HO-44 10" (DVC)
DVC: .506 ft^3 = .851 Qtc - 45.71 Hz F3
DVC: .970 ft^3 = .707 Qtc - 43.34 Hz F3
DVC: .550 ft^3 = .829 Qtc - 45.22 Hz F3
Dayton/PE recommended: .55 ft^3 for 46 Hz F3
https://www.parts-express.com/dayton...oofer--295-463

[Justin Zazzi]

JC, I think the difference is BassBox can model stuffing and you have it turned up to max, and there are also additional box leakage/losses in the BassBox model.
I haven't added those features to my tool yet and I doubt WinISD does them.
That might explain why you get smaller boxes than we do. It's entirely possible that Parts Express assumes some box stuffing too.

This is a really good example of how textbook-perfect equations can give one answer, but when you add things like polyfill or friction losses or any number of real-world things then your results can change dramatically!

[Grinder]

Ha! I bet that explains it.

Here is an interesting article by Harris Tech on precisely those features:
https://www.ht-audio.com/pages/support/BBxPTopic11.html

[DirtyBumOAK510]

I have a qtc question. AudioFrog recommends their GB subwoofers in specific sized enclosures, and the qtc ends up being ~0.9 (0.927 for the 12" and 0.893 for the 10"). I noticed somewhat similar qtc's with some of the JL subwoofers I've modeled too. I asked Andy about why it isn't the magical .707 and he replied:
"The boxes I suggest aren’t based on this standard Qts of 0.707 thing. I start with an in-car target that’s based on a whole bunch of transfer function measurements. Then, I decide on a box volume that makes sense for sealed and vented boxes, and then we design a woofer to hit the target."

So my question ...
When modeling boxes and subs in programs like WinISD should we be shooting for closer to 0.9? Should we be shooting for a different number depending on if we have a hatchback, SUV, or a Sedan with a trunk?

When you are designing a box, what specifically are you taking into consideration when you model it? qtc? fsc? etc.