Normally if the low frequenciy rolls off slower, it gives the impression of lower and accurate bass.
Does anyone know where to get a copy of Small's resistive enclosure explanation?
Does anyone know where to get a copy of Small's resistive enclosure explanation?
This is one attempt to flatten out impedance using the enclosure.
An externally hosted image should be here but it was not working when we last tested it.
The room modes in combination with the different box resonances and roll offs. See where th BR gains, the Res loses and vice versa. Acoustic interactions and their phase in a few words. You will not get such anechoically or in different positions.
Gee...these are old files, can't be totally sure, but for the rest of the spectrum and for their SPL they almost superimpose, so they must have been taken with same standards. The resolution must be a bit different. I don't swear that I recall clearly the measurement session sequence that I did then, though. None the less, the trends matter. The resistive rolls easier and room gains deeper, also the lower impedance peak of the BR is eradicated when resisted. That BR is a tall narrow and deep slot, physically. For the other measurement (green) that slot got stuffed with dimple foam. I still use it like that.
“The resistive rolls easier and room gains deeper”
That’s consistent with Small . .
If a PDF of Small's chapter could be put on the web . .
As I live in the same country as Richard Small was when his thesis was published, if I had an exact reference I may be able to track it . .
According to http://www.audioxpress.com/magsdirx/voxcoil/addenda/media/mowry-small-int.pdf he got his Ph.D. at the University of Sydney (in New South Wales, not the University of 😉 ) in 1972. Will that be enough; they'll probabaly be a cost?
That’s consistent with Small . .
If a PDF of Small's chapter could be put on the web . .
As I live in the same country as Richard Small was when his thesis was published, if I had an exact reference I may be able to track it . .
According to http://www.audioxpress.com/magsdirx/voxcoil/addenda/media/mowry-small-int.pdf he got his Ph.D. at the University of Sydney (in New South Wales, not the University of 😉 ) in 1972. Will that be enough; they'll probabaly be a cost?
Worked for me up to a point, but couldn't find his thesis in the various e-libraries: http://opac.library.usyd.edu.au/record=b1734824
GM
GM
That's "Thesis (Ph. D.)--University of Sydney, 1973" -
not the one we're after?
What title are we after?
not the one we're after?
What title are we after?
Lynn Olson said:
Hi,
It is 3rd order highpass in the same way a driver on an open baffle is
a 3rd order high pass function. Whilst 3rd order is obviously between
2nd order and 4th order, one could argue the alignment is not between
sealed and vented.
My guess is what the AES did not like is the inelegance of the
approach. Basically the resistive vent output cancels with the
driver output and this can be regarded as a "bodge" to fix an
incorrectly chosen box size / driver in the first place.
Whilst resistive vents are a good idea for some drivers there
is nothing special about the approach or the quality of bass
it provides, in fact IMO it works best for drivers that if put
into a similar sized sealed box would be a little "boomy".
FWIW regarding the "SAFE" measurements :
a) driver Fs is way off Jordan specs of 45Hz free air.
b) to drop free air Fs requires significant mass loading,
therefore if the results are correct the principle is not,
i.e. the added loading to the driver is not purely resistive.
🙂/sreten.
Don't know how many have owned Jordan drivers here. But my experience is that left sitting there for a few months or so, the Fs will rise. I did not do any breaking in before measurements. I've even measured Fs of 200Hz on my JX53.sreten said:
Well, I certainly don't know how lowered Fs will sound, but I am not using SAFE as the means to do so. I've just based the study on the model Ted Jordan presented in an WW article about aperiodic loading, and came up with similar results. Right now I have not seen any enclosure that gives a purly resistive load and sound good. Mainly because it effects the transient dynamics of the driver. However, if a variable load is created, things might be different. I still have my fingers crossed.
Shouldn't resistive enclosures have a flat impedance? The green line looks like a normal base reflex enclosure.salas said:
soongsc said:
Black is bass reflex, twin peaks and a saddle, green is with the added acoustic resistance in the slot port. It kills the lower peak and is looking like a typical closed box one peak impedance trace. Only not so broad because its faster rolling in the frequency domain than a normal closed box. Something like a big Variovent.
Salas brought up some interesting points about how the pressure from room modes could effect driver output in a resistive vent design.
This is something I had not considered, but could the resistive vent not act as a kind of damped feedback system on the driver at frequencies where room modes are high.
Would this have a tendency to be self regulating so as to create a smoother total in room response?
Steten,
I have to disagree about the "nothing special about the bass" argument. This might be so when cramming a high Q speaker in a small box and using a resistive vent to get passable sound.
But the best sounding bass I ever got was from a good quality driver of about qts .35 in a cabinet size that would have been about a Q of .6 in a sealed alignment and then used a resistive vent. Bass was amazing in quality. Almost as transient perfect as a good TL but with better weight and amazing pitch definition. My brother in law is now using them as mixing monitors.
This is something I had not considered, but could the resistive vent not act as a kind of damped feedback system on the driver at frequencies where room modes are high.
Would this have a tendency to be self regulating so as to create a smoother total in room response?
Steten,
I have to disagree about the "nothing special about the bass" argument. This might be so when cramming a high Q speaker in a small box and using a resistive vent to get passable sound.
But the best sounding bass I ever got was from a good quality driver of about qts .35 in a cabinet size that would have been about a Q of .6 in a sealed alignment and then used a resistive vent. Bass was amazing in quality. Almost as transient perfect as a good TL but with better weight and amazing pitch definition. My brother in law is now using them as mixing monitors.
Hezz said:
Hi,
Its still the same point. What about a simple sealed box with the
same ~ Q as the "aperoidic" q=0.6 box. One would expect this Q
to be near 0.5 i.e. critically damped. Whatever fans of sealed Q=0.5
boxes say, the engineering department say you are chucking away
a shedload of bass extension, bass efficiency and power handling
capability by not going vented for Qbox = 0.5.
Q=0.6 is marginal for going vented but lowish vent frequency
damped vented (not aperoidic) is workable, your description
does not exclude the possibility the alignment is damped
vented rather than aperoidic.
🙂/sreten.
I have read that the back-radiation from the acoustical resistance unit is delayed more than mere geometry suggests because of the RC-circuit formed by the resistance unit and the compliance of the air in the box, so one may view the design of an aperiodic enclosure as the search for an optimal combination of: a) delay of rear radiation to lower the cancellation, b) box size, and c) the efficiency of the resistance unit (the ratio of reflected wave to that which comes through), e.g. too dense a material will create a long delay but will reflect most of the sound back into the box.
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Here is a working link.
Notice that according to Jordan the aperiodic enclosure is a technical breakthrough, because it excels the bass-reflex in all aspects: a) is half as large, b) works from a lower frequency (Jordan's worked from 20 cycles up), and c) has better impulse response.
Jordan managed almost completely to suppress the higher impedance peak of the bass-reflex design without seriously affecting the lower one. The resulting loudspeaker worked not from the saddle point between the peaks as bass-reflex does, but from the apex of the lower one.
I have never been able to reproduce these wonderful results, nor have seen others do it.
It is possible for Jordan drivers. I have accomplished such, and currently trying to find a way to control the characteristics for different drivers.
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My congratulations! Can you share your design procedure and the requirements for the driver?
Am I right that in Jordan's design both the depth and the area of the resistance unit must be accurately calculated a) to contain a specific mass of air, and b) to provide a specific box tuning? I don't see how this is possible with the resistance unit in the form of a shallow panel.
I used a Symmetric Air Friction Enclosure design originally published in Popular Mechanics back in the 80s and discovered it worked quite nicely for the JX92s. I kind of wonder whether Ted's discovery led to the Jordan Watts driver or not. But I haven't checked. In any way, it is still necessary to control the back side wave which is why I looked into the SAFE concept.
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