Low distortion drivers for sub-bass in shallow sealed cabinets

[sigbergaudio]

@sigbergaudio thank you for continuing to discuss this. I think the phrase "knows just enough to be dangerous" applies to me. The way I was thinking about the issue and using the published measurements does indeed lead to absurd results. My approach is overcomplicated, and this is compounded by the difficulties in comparing measurements between reviewers.

Reframing the problem based on your feedback, my question becomes "What is the excursion for driver X for 10% THD?". SPL can be calculated from that and Sd. I'd also forgotten about James Larsen's excellent page on the topic at https://www.audioholics.com/loudspeaker-design/audibility-of-distortion-at-bass, which goes some way toward justifying my wish for 10% THD, and mostly 2nd if possible

Upon closer reading of the Vance Dickason's measurements at AudioXpress, he is consistently using the Klippel default measure of 20% distortion to define linear Xmax for subwoofer drivers where he has Klippel analysis. The SB driver hits 20% at 8mm limited by surround stiffness, not Bl, so we can guess that it might be 10% at 5-6mm, which is way below the published Xmax of 12mm.

I still think there is a valid question here, but answering it seems very hard.

It is perhaps a case of decision paralysis. When presented with a number of good choices, it easy to overcomplicate things.

My main reason for pointing out your error with regards to the Purifi driver isn't because it is a good choice in your situation (I don't think it is, because it is too expensive), but because someone else may come along in the future, reading your table and wrongfully assume that the Purifi is a poor driver (which it is not).

Shallow mount drivers are usually less capable than traditional drivers and in general reproducing 20hz at high SPLs is difficult in a small sealed enclosure. So you have a starting premise that is difficult to achieve. Cheap, small, loud. Pick two.

Given your constraints, the SB Acoustics driver is a good choice. But you are likely to require more drivers than you think to achieve what you claim you need. On the other hand you may realize that you don't require as loud SPLs at 20hz as you think.

 

[mcdn]

5mm excursion at 10% THD for the SB driver is OK, the bigger problem is finding equivalent measurements for other drivers.

 

[sigbergaudio]

5mm excursion at 10% THD for the SB driver is OK, the bigger problem is finding equivalent measurements for other drivers.

You will not find perfect and directly comparable information for all drivers you are interested in, so you will have to make a decision based on incomplete data, unless you have the competence to analyze the Thiele-Small parameters.

 

[mcdn]

Competence isn’t a factor here. The T/S parameters simply can’t be used to derive the distortion limited excursion for a driver.

 

[sigbergaudio]

Competence isn’t a factor here. The T/S parameters simply can’t be used to derive the distortion limited excursion for a driver.

Not directly, but they can be used as an indication of the performance of the driver.

 

[sigbergaudio]

If you are looking for / insisting on a shallow mount driver, I'm reasonably confident you won't find anything that is significantly better than the SB Acoustics driver.