Why are my BassBox 6 Volume Estimates so different from those on product pages?

[AllisterMcRae]

Hello,

I've googled a few things about how PE does the work of getting the BB6 volume estimates - but nothing seems to hammer home on this topic. Its mostly conversations around whether to trust software.

If I enter all the T/S parameters from the datasheet/specifications section of the page, I get a different box volume.

For example: The morel TiW 638FTgives us 0.41 cu ft. When I put the T/S into BB6, I get 0.23 cu ft.

What am I missing?

Thanks!

[DeZZar]

"getting" the volume from software depends on a desired alignment. The volumes will be quite different depending the chosen alignment (applies to both sealed and vented):
https://audiojudgement.com/bass-refl...nts-explained/

So it ultimately depends on what sits behind the "suggest" button in this software. Something like WinISD allows you to choose which aligned you would like a suggested volume for when you setup the project.

Also, there is no definitive "volume" required for every speaker - so the job of the modelling software is to give you the results for a chosen volume and for you the designer to decide on what you want to achieve. Suggested volumes are usually just a starting point - neither parts express or some software are necessarily "wrong".

[AllisterMcRae]

Thanks for the response, DeZZar.

I certainly wouldn't count any software or other people's finding as wrong.

Just for kicks, I put the information into WinISD. That returns 0.652 cu ft. That is another question, though. I'd like to stick with BassBox and I'll investigate this issue separately.

I'm attempting to emulate the system that Parts Express uses so that I can learn from their wealth of experience. I thought I had the alignment information to do so with the "determined using BassBox 6 Pro High Fidelity suggestion" part of things. I've followed their steps, as far as I can tell, exactly. But resulting in half the volume of space.

I also see that I can't suggest the "Desired F3" of 62Hz without getting an error "Bassbox unable to achieve desired F3 Because it is too low...please suggest higher F3." Seeming to show it as impossible to get the number prescribed on the page.

Could one of the PE testers also jump in on this and help me understand the process? I really want to understand this!

Thanks

[billfitzmaurice]

I've noticed that the product page listings for suggested box sizes are small, to the point that I ignore them entirely and do my own calcs.

[AllisterMcRae]

I've noticed that the product page listings for suggested box sizes are small, to the point that I ignore them entirely and do my own calcs.

Thanks Bill. Do you have your own formula you use for your own calculations? Or do you use software? If software, which?

So funny. I get 0.21 in BB6, PE says 0.41, WinISD says 0.65 - all about 0.2 cu ft apart.

Now if I could figure out how to get the volume in VituixCad or a non-excel version of Mr Bagby's sheets, hopefully we could at least have a comparable number to at least one of those

Thank you!

[billfitzmaurice]

I use WinISD 0.7 and HornResp. The differences you're seeing are probably because each program has a different idea of what's best for a given set of parameters. I don't care what the programs think is best, I care about what I think is best, so I tweak the box size and tuning to that end.

[AllisterMcRae]

... I don't care what the programs think is best, I care about what I think is best, so I tweak the box size and tuning to that end.

Thats what I've seen in lots of your responses over time - and why I think its important to learn some of your magic.. and then dive in and build/test to learn more.

Thanks!

PS. VituxCad Clocks in at 0.25 Cu Ft.

[a4eaudio]

I know in WinISD you have to go into settings to change Qa for stuffing, lining with foam, etc. Not sure what PE's default is, but they state that they estimate an optimal enclosure using Bass Box 6 Pro's High Fidelity suggestion.

To Bill and other's points, this may or may not be the "optimal" for your needs and is only as good as the T/S parameters used. I appreciate that PE provide this and take it much like a frequency response on an IEC baffle - you need standardization to make valid comparisons but need to understand the limitations. But a standard is better than have a random PE employee simulate the box that he likes for a given driver.

[billfitzmaurice]

And that begs the question 'what is High Fidelity'? WinISD defaults to the maximally flat alignment for a ported cab, but that isn't necessarily the best possible alignment for a given application. Neither is a specific Q value for a sealed cab. If I've seen a common thread in the PE recommended box sizes it's that they usually are as small as one can reasonably go. That's fine if the main criteria for choosing a driver and enclosure combination is WAF, but that's not my criteria.

[a4eaudio]

https://www.ht-audio.com/pages/support/BBxPTopic18.html

"Suggested" Vented Box
BassBox Pro/Lite provide a "Suggest" button for vented box designs. When this button is clicked, a "Design Priority" window will open so that you can control the way BassBox Pro/Lite make their suggestion. Choices include "high output", "high fidelity", "extended bass" and "desired F3". These options are described in BassBox Pro's on-screen and printed manuals and BassBox Lite's on-screen user manual.

The "high fidelity" option attempts to create a "maximally flat" alignment. The maximally flat response is most closely achieved with a B4 alignment. However, a true B4 alignment is only possible when the driver has a total Q (Qts) of approximately 0.4. What if the driver's Qts is lower or higher? Generally, a QB3 (quasi third-order Butterworth) alignment is used for lower Qts values and a C4 alignment is used for higher values. BassBox Pro/Lite's "high fidelity" option follows this QB3–B4–C4 progression. Depending on how extreme the driver Qts value is, BassBox Pro/Lite's "high fidelity" suggestion may or may not be truly maximally flat. If it is not, feel free to experiment with the box volume (Vb) and tuning frequency (Fb) until a desired response shape is achieved.

[billfitzmaurice]

And there's part of the problem. Alignments like BB and QB3 made sense back when I was using 'Bullock on Boxes' and a scientific calculator to come up with designs, as they simplified the process. The pertinent quote there is "feel free to experiment with the box volume (Vb) and tuning frequency (Fb) until a desired response shape is achieved". You don't have to choose between a few pre-configured alignments when there are thousands of possibilities available to you by changing the box size and, in the case of ported, tuning frequency.

[AllisterMcRae]

I seem to recall Soundeasy had some tools that would do those experiments for you, running X hundreds/thousands of attempts so you could choose the best one (but I lost the dongle for that program years ago).

A4eaudio, I appreciate the digging your doing! I still find it curious that my results are so different from the PE results since I am choosing that high fidelity option. But I'm learning lots here besides Definitely not just going with the suggestions.

Now here's a new part of the same riddle: I can choose Vented Box - High Fidelity in BB and I get 1.074 cu ft - or , very close to the PE number of 1.08. Something is amiss in PE, methinks.

[Chris_Perez]

Hello,

I've googled a few things about how PE does the work of getting the BB6 volume estimates - but nothing seems to hammer home on this topic. Its mostly conversations around whether to trust software.

If I enter all the T/S parameters from the datasheet/specifications section of the page, I get a different box volume.

For example: The morel TiW 638FTgives us 0.41 cu ft. When I put the T/S into BB6, I get 0.23 cu ft.

What am I missing?

Thanks!

Hello Allister,

The majority of the recommendations on the PE website do use the "Suggested - High Fidelity" enclosure volume from Bass Box.
There are some cases where we do vary from the recommendations, such as really low or high Q drivers just to make the enclosure volumes reasonable (or in some cases just to make them possible, for example a 0.2 cubic foot enclosure with an F3 of 100 Hz for a 21" driver just won't do).

From looking at your example with the Morel TiW-638Ft, we did stick with the "Suggested" volume. When we do the simulation we have the Fill set to Minimum on the "Damping" tab in the "Box Properties" window. With the Fill set to Heavy then BassBox will suggest a smaller enclosure to achieve the desired Qtc (0.707 in this case). If I remember right, BassBox defaults to Heavy for sealed enclosures, you can change this in the preferences.

Please check the "Damping" tab and adjust the Fill to Minimum and your model should match what we recommend on the website.

Hope this helps,
Chris P

[AllisterMcRae]

Hi Chris,

Thanks for pointing out about the filling. I wasn't getting it on the tests yesterday - but today (magically?) I am getting those numbers.

I appreciate you getting back to me - and everyone involved in the conversation.

Thank you.