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
The article in the first post indicates a rigid construction but the link above seems to imply flexible panels.
Andy
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.
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.
SY:
I think I recall 100 dB SPL being mentioned in some pdf they link to about acoustics. I don't think the pdf ever said this speaker can produce 100 dB at 20 Hz. I just think that number might be implied by the use of that pdf.
But yes, in the body of the discussion of the website, they scrupulously avoid telling you what SPL at 20 Hz you can expect.
I believe Bose claimed an excursion saving of 15/16ths, (94%) with their acoustic cannon. I never tested it. But even there, if there isn't a similar excursion saving an eighth of an octave above the tuning frequency, or a quarter of an octave above it, etc, you really don't have anything useful.
I think I recall 100 dB SPL being mentioned in some pdf they link to about acoustics. I don't think the pdf ever said this speaker can produce 100 dB at 20 Hz. I just think that number might be implied by the use of that pdf.
But yes, in the body of the discussion of the website, they scrupulously avoid telling you what SPL at 20 Hz you can expect.
I believe Bose claimed an excursion saving of 15/16ths, (94%) with their acoustic cannon. I never tested it. But even there, if there isn't a similar excursion saving an eighth of an octave above the tuning frequency, or a quarter of an octave above it, etc, you really don't have anything useful.
Oops, it wasn't a pdf.
It was discussion on their horn loudspeaker where they made the reference to 100 dB SPL.
It was discussion on their horn loudspeaker where they made the reference to 100 dB SPL.
soongsc said:
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.
Back-loaded horn with flexible plates = v-flex?
Cut and paste my earlier link.
Andy
Looking through some of the previous posted links, I see back loaded horns similar to a Japanese site, but nothing talks about flexible plates. I must be missing something?poynton said:
But anyway, it does refresh some thinking. If the length of the horn is close to the desired quarter wave length and the cross section is chosen to provide good friction for damping, the low frequency is possible, but you still need the cone area to have good punch though. Hmm, wonder how this would simulate in Martins worksheets.
The way they describe the V shaped interior might not be flexible, but could reduce certain horn resonance frequencies.
There are at least statements talking of rattling windows or the like and some (subjectively) felt low end authority at a listening session.
But they do indeed avoid the combination of undistorted SPL and low-end extension on their webpages.
Are you talking about his comments on the patent-review pages in JAES ? If yes, they are indeed cool. But some of the patents are even more entertaining by themseves than any comment about them could ever be !
Regards
Charles
I have reversed engineered a couple of designs from this company in the past year, as well as a few others where geometry and measurements were available, and what I concluded was that their claims were not completely false but showed a lot of marketing imagination and stretching of the results in the best possible light. For example, one of the designs I analyzed also claimed some very low bass output from a small Fostex full range driver. My results showed that there was bass produced at the frequency stated but it was so far down in SPL from the output above 100 Hz I was skeptical of the claimed in room performance for the speaker design. I like what these guys write as goals for their speakers but I take the performance claims with a grain of salt. If I were considering buying from them I would want to hear the speakers before I ordered it off the Internet based on some reviewer's comments.
soongsc said:
Extract from the link.............
It became quite apparent that this speaker had a significant boost in the mid bass region..
...................... The sidewalls of the horns are allowed to resonate, and reinforce the bass in the 80 to 100 hertz range.
The output of the rear horn was allowed to extend into the midrange area in order to give the speaker a spacious presentation....................... However, the installation of the bass augmentation plates transforms the First Horn into a very sweet sounding speaker. Since the bass augmentation plates changed the performance of this speaker in a dramatic way
............................. What is impressive about the First Horn is the quantity of bass that is this cabinet design is able to extract from the 4-inch Fostex driver. .............................A 4-inch driver is just not physically capable of moving enough air, ..
Andy
The little speaker in my avatar is also 3", I would claim that 40Hz is "audible", but needs a smallish room no larger than 6M by 4M. Just last week we ran it in a 3M by 3M room, and almost all the instruments played well except the very low end of organs and punchy type music. They were placed back close to walls.MJK said:
Many manufacturers don't use the standard -3db point as the frequency range now-a-days (some qoute -10db). So we need to take care when looking at the specifications and use some knowledgeable judgement.
Thanks for the extract.
Allowing the side walls to resonate means there is going to be multiple modes. Normall with this kind of resonance method, the sound continuity would not be do good if you listen closely to how the recorded timbre and studio/hall reflection change throughout the program material, for example, if you listen to people stomping the stage floor, the initial stomp may be at a correct location with depth, but the floor resonance may sound like it's in front of the speaker and cannot be located where the actual stage floor should be in the recording.
poynton said:
Allowing the side walls to resonate means there is going to be multiple modes. Normall with this kind of resonance method, the sound continuity would not be do good if you listen closely to how the recorded timbre and studio/hall reflection change throughout the program material, for example, if you listen to people stomping the stage floor, the initial stomp may be at a correct location with depth, but the floor resonance may sound like it's in front of the speaker and cannot be located where the actual stage floor should be in the recording.
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