Thank you freddi
I admit I have never heard before of the ‘frequency doubling and tripling effect’ that a bass reflex loading imposes on the frequencies which are below the system resonance Fc.
I wonder why BBC’s paper didn’t address that important claim of the inventors found in the paper of the Radio Club of America (which preceded the BBC paper by three years).
And I have reservations on the inventors relevant test setup (Fig.7).
The two speakers are IMO too close together, making the measurement results dubious:
As per Fig.7, when the one speaker is energized with an electrical signal, the sound it emits will acoustically excite the Helmholz resonator of the second speaker, which in turn will emit sound too.
Thus the microphone picks-up the composite output sum of the two speaker systems, not only the output of the electrically energized speaker.
The tricky point is that the passively excited speaker will emit sound with a variable delay (in respect to it’s acoustic excitation) and amplitude as the excitation frequency is varied around and below Fc.
Is this acoustic coupling enough to generate the 2xf and 3xf effect I read on the oscilloscope screenshots?
George
I admit I have never heard before of the ‘frequency doubling and tripling effect’ that a bass reflex loading imposes on the frequencies which are below the system resonance Fc.
I wonder why BBC’s paper didn’t address that important claim of the inventors found in the paper of the Radio Club of America (which preceded the BBC paper by three years).
And I have reservations on the inventors relevant test setup (Fig.7).
The two speakers are IMO too close together, making the measurement results dubious:
As per Fig.7, when the one speaker is energized with an electrical signal, the sound it emits will acoustically excite the Helmholz resonator of the second speaker, which in turn will emit sound too.
Thus the microphone picks-up the composite output sum of the two speaker systems, not only the output of the electrically energized speaker.
The tricky point is that the passively excited speaker will emit sound with a variable delay (in respect to it’s acoustic excitation) and amplitude as the excitation frequency is varied around and below Fc.
Is this acoustic coupling enough to generate the 2xf and 3xf effect I read on the oscilloscope screenshots?
George
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I'll have to look at those papers - I have 1-regular RJ15 and 1-RJ12 slimline enclosure.
there are two sets of RJ Eight enclosures on US Ebay
re:acoustic coupling - I've had the original Karlson K15 not connected play very strongly ! (and over a pretty wide range)
Vintage Pair of Vintage RJ Wharfedale HiFi Speakers RJ8 Al Authentic | eBay
Wharfedale RJ Speakers with Super 8 FS Al Super RARE 1954 1955 | eBay
RJ - style path 18" woofer of mine
vintage RJ 15 cabinet of mine with EV SP15 measured in a very small room
my RJ15's aperture
my slim RJ12 - very rare
there are two sets of RJ Eight enclosures on US Ebay
re:acoustic coupling - I've had the original Karlson K15 not connected play very strongly ! (and over a pretty wide range)
Vintage Pair of Vintage RJ Wharfedale HiFi Speakers RJ8 Al Authentic | eBay
Wharfedale RJ Speakers with Super 8 FS Al Super RARE 1954 1955 | eBay
RJ - style path 18" woofer of mine
An externally hosted image should be here but it was not working when we last tested it.
vintage RJ 15 cabinet of mine with EV SP15 measured in a very small room
An externally hosted image should be here but it was not working when we last tested it.
my RJ15's aperture
An externally hosted image should be here but it was not working when we last tested it.
my slim RJ12 - very rare
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I wonder how mirrored K slots would work with this design? The R-J is closer in appearance to a 6th order box than a Karlson, but may be a whole 'nother thing.
Its just harmonic distortion from increasing excursion.
Play a 50Hz tone through a woofer, then gradually increase the level. Note that the sound of the tone changes - this is entirely distortion, but doesn't sound too ugly...
Chris
A bit hard to read but a jpg image I picked up from Lafayette Hi Fi - AudioKarma.org Home Audio Stereo Discussion Forums
Seems to me like those 8" RJ's would have some ML-TL effect, despite the coincidental port and driver. Has anyone tried to sim them in hornresp, akabak, or MJK's old "sections" sheets?
I don't see how since no dimension is long enough to generate a low enough 1/4 WL pipe action.
No, but it's a 6th order alignment, so it can be in HR AFAIK or similar TL/horn software, but not MJK's.
GM
No, but it's a 6th order alignment, so it can be in HR AFAIK or similar TL/horn software, but not MJK's.
GM
It wouldn't appear that there is enough front chamber to be a 6th order box, it would seemingly react more like a restrictive duct.
The dims for the wharfedale loaded RJ linked to above claim that they are 24 x 10 x 11". Seems like that would do something? http://www.ebay.com/itm/Vintage-Pai...ge_Electronics_R2&hash=item4d214a90d8&afsrc=1
Anyhow, this sort of enclosure might be a optimized as a relatively compact alternative to building backhorns for various bright over-damped drivers, i.e. the FE126EN. I think we discussed this a long time ago, but IME choking down this sort of driver into a throat can really improve the sound subjectively, even if there is no actual horn attached.
Anyhow, this sort of enclosure might be a optimized as a relatively compact alternative to building backhorns for various bright over-damped drivers, i.e. the FE126EN. I think we discussed this a long time ago, but IME choking down this sort of driver into a throat can really improve the sound subjectively, even if there is no actual horn attached.
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It's still technically a 6th order alignment due to the air mass 'plug' in the diaphragm's cavity out the end of its 'duct', though with such a high tuning it's well damped enough to just help control the driver a bit more than a reflex and < a MLTL.
GM
OK, ~13560"_sec/2/24" = ~282.5 Hz, so considering that acoustic power changes exponentially [1/f], I don't see how it can have any impact on vent tuning many octaves below it.
Then there's the high aspect issue, i.e. one dim must be much > than the sum of the others, otherwise its modal structure will be much more diffuse to the point of becoming a ~ uniform particle density once the ratio becomes one of the 'golden' or lower order acoustic ratios.
Agreed, some form of it has been used to roll off excess HF BW on some prosound and at least a few consumer/studio monitor products over the decades.
FWIW, I used it to good effect to flatten the RS 40-1354 by making a polyfil 'grill' with the center cut out enough to allow free movement of its whizzer. combined with a MLTL, it was ~ +/- 3 dB from 40-12.5 kHz with the peaks/dips being low Q enough and in the generally right places in the BW to receive a 'toe-tapping' review/thumbs up at the first DIY Meet I went to.
GM
Freddi,
This has piqued my curiosity. Can you get me some dimensions of your RJ box? I need rear chamber volume and depth, slot vent dimensions of gap, width, length. I also need approximate dimensions of the aperture lens. For first cut I can guess it is about 60% of Sd? Also need dimension of outer ring where vents inject into the aperture I can guess it is 150% of Sd. Also model of driver or TS params. I think this is an easy to model speaker that probably has a slight resemblance to another patent for a reflex loaded horn where the reflex vents come out of the wall of the short horn.
Thanks,
X
This has piqued my curiosity. Can you get me some dimensions of your RJ box? I need rear chamber volume and depth, slot vent dimensions of gap, width, length. I also need approximate dimensions of the aperture lens. For first cut I can guess it is about 60% of Sd? Also need dimension of outer ring where vents inject into the aperture I can guess it is 150% of Sd. Also model of driver or TS params. I think this is an easy to model speaker that probably has a slight resemblance to another patent for a reflex loaded horn where the reflex vents come out of the wall of the short horn.
Thanks,
X
FWIW, I've found that on horns a 2:1 CR seems to be 'sweet spot' for a wide BW app and apparently, prosound designers have found 3:1 a good limit on [mid]bass ones.
GM
GM
Well then obviously you don't consider this pipe open on one end then? 🙂
With a situation like that driver/port on one end of a 24" column, I suppose it becomes impossible to say that it is purely a 1/2 or 1/4w resonator. This is likely the case for pretty much all ML-TL really. That's where computer sims will help.
hey X - if I can get to these things - the ~cubical RJ with the 15 is on the floor in a very cramped space and the slimline with 12 up high where I might not be able to handle it without a shoulder dislocating. Which one do you want me to examine? I also have Eliptoflex which had no aperture constriction. The little RJ bookshelf model probably had 3/4" cleat spacing between the port plate and lemon aperture - had one briefly 30-some years ago but didn't have any 8" to load nor make a drawing.
the standard RJ ~cube with SP15 sounds pretty good. My RJ 12 is loaded with a Diffusicone 12 - too small a box for that weaker motor - both would be better if made of thicker material or braced better.
the standard RJ ~cube with SP15 sounds pretty good. My RJ 12 is loaded with a Diffusicone 12 - too small a box for that weaker motor - both would be better if made of thicker material or braced better.
Freddi,
Whatever is easiest for you - don't hurt yourself getting dimensions. It would be helpful if you can get me dimensions from the box that you have measurements for.
X
Whatever is easiest for you - don't hurt yourself getting dimensions. It would be helpful if you can get me dimensions from the box that you have measurements for.
X
I don't consider it a pipe at all, ergo full of just a bunch of room modes same as any true reflex. 😉
GM
My initial model in AkAbak does indeed show the RJ to behave like a 6th order band pass. I am just using a Delta 10A and messing with dimensions of box, slot vent, keeping aperture at 0.5x Sd. Vent using 0.719 in thick ply as spacer about 14 in long x 12 in tall x qnty 2 is producing bass extension down to about 40 Hz. Bass efficiency is not matching 99dB driver efficiency though. Interesting to play with and supremely simple to build - very compact. Should probably be a sub?
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