New bass loading technique ?

[ashok]

Have you guys seen this
http://magazine-audio.com/actualite/reportages/142

So is this 'new'?

[poynton]

http://www.affordableaudio.org/AtelierFirstHorn.pdf



The article in the first post indicates a rigid construction but the link above seems to imply flexible panels.


Andy

[phase_accurate]

If something is said to defy the laws of physics then usually my alarmbells ring !

Regards

Charles

[kelticwizard]

Poynton:

The link no longer works.


GM has been referring to something called the transflex enclosure for some time now-wonder if that is the "V flex" enclosure they keep referring to here.

[kelticwizard]

These folks can talk all they want about a small driver "reaching down" to 20 Hz, and being only 6 dB down at 20 Hz, but the fact remains that a certain amount of air must be moved to produce Sound Pressure Level that can be heard in those ranges.

The article mentions something about 100 dB SPL. Personally, I think that is rather low for a 20 Hz tone, I don't think 20 Hz would be heard or experienced particularly at 100 dB SPL. But just for the heck of it, let's use that.

The unit uses a 16.5 cm, (6.5 in) driver. Cone area is likely to be 20 sq inches, give or take a little, (too lazy to look up the Fostex website, lol).

According to Small's chart here, in a sealed system that cone would have move 40 cubic inches of air to produce that 100 dB SPL at 20 Hz. At 20 sq inches of cone area, that means it would have to move 2 inches back and forth!



Metric chart and discussion located in this other thread.

Fortunately, there are ways to use the enclosure to severely reduce necessary cone excursions to produce the same SPL. If the speaker in question is put into a well made ported box tuned to 20 Hz, it would need to move only 1/4 as much back and forth to produce the same SPL, (75% excursion reduction). If put into a Mass Loaded Translmission Line, it would have to move only 1/6 as much back and forth, (83% excursion reduction).

But even if the cone only must move 1/6 as much as it does in a sealed box, then at 20 Hz the cone must move 0.33 inches back and forth. The Fostex can only move about 1 mm or so-0.05 inches.

That leaves us with two possibilites.

A) Either this V Flex loading technique has an excursion saving similar to an ported box or even Mass Loaded Transmission Line, in which case it can only output about 85 dB SPL at 20 Hz before the Fostex runs out of excursion, or

B) This V Flex loading technique only requires the driver to move about one fortieth as much back and forth that it would in a sealed system. This would be as opposed to a 1/4 as much in a ported box or 1/6 as much in a MLTL. Which seems very unlikely, but theoretically it might be possible.

It should also be pointed out that for this enclosure to be useful, the frequencies near it must experience roughly proportionate excursion reductions. For instance, if the enclosure is tuned to 20 Hz and receives a 97.5% reduction in it's excursion requirement, (which is what would be necessary for it to produce 100 dB at 20 Hz), at 28 Hz it should also receive a 95% reduction in it's requirement, at 40 Hz it should receive a 90% reduction in it's requirement, etc. up the line. If these other reductions do not occur, then the speaker could produce a high SPL at 20 Hz only, but get blown to bits if required to play any other frequencies in the deep bass.

[kelticwizard]

What the heck, here's the same chart in Metric, (which was actually Small's original chart, I just changed the numbers over to inches in the other chart).



Linkwitz also has a calculator on his site. The numbers are slightly different using that, but still in the same ballpark.

[geoffstgermaine]

Looks interesting, but I really dislike it when people say that a product "defies the laws of physics". I guess that's just the physicist in me.

[Netlist]

Originally posted by kelticwizard
The link no longer works.

One needs to copy and paste the link in a new browser.

/Hugo

[SY]

I don't see a claim regarding large-signal performance in any of their puff stuff.

I'd love to have an Augspurger one liner here.

[soongsc]

Originally posted by geoffstgermaine
Looks interesting, but I really dislike it when people say that a product "defies the laws of physics". I guess that's just the physicist in me.

I'm with you.

However, I've found that the speakers and room need to have a good match which is really important.

I couldn't find where it talked about the bass loading. Maybe I didn't look hard enough or it's being too vague about the loading technique.