If you add weights to a cone supported by only a soft surround it'll sag. Buy 2 surrounds without cones, and mount them on either side of a disc of something maybe half an inch thick or so. If it's the same thickness as the cabinet walls then you can just build it straight in.
Basically make a passive radiator in the style of the Tang Band RBM drivers. You do not need a spider, but a single surround isn't a good idea.
Basically make a passive radiator in the style of the Tang Band RBM drivers. You do not need a spider, but a single surround isn't a good idea.
Far and away the best idea in this whole thread! I did that once years ago, when experimenting with LEAP and LMS. It worked like a charm! If I remember, and I may not correctly, capacitance made a difference for the tuning frequency. (?) All I know is, I wound up with about five different responses for one box, without messing around with added mass like bolts or goop etc.
Try it! You can also do that with one coil of a dual VC sub, but obviously the trade-offs are many. Less power etc.
Also you can go to ebay and search, "passive radiator." There are dozens of them from 4" to 15" and many are cheap. 🙂
Could you go into more detail about the process of that? I'd be a very happy man if I can adjust tuning without removing the magnet and adding mass.
How does this even work? The driver is not connected to anything, so how does wiring resistors help?
Trust me, if I could buy a passive radiator with the amount of excursion I needed I would not try something as complicated as making my own passive radiator!
How does this even work? The driver is not connected to anything, so how does wiring resistors help?
Trust me, if I could buy a passive radiator with the amount of excursion I needed I would not try something as complicated as making my own passive radiator!
Looking into it. I'll try to find more info, but very hard. I thought of that idea, then Sonus Faber patented it for their flagship Extrema loudspeaker. He used a Kef B-139 in the rear. Link below:
Sonus Faber Extrema loudspeaker | Stereophile.com
Sonus Faber Extrema loudspeaker | Stereophile.com
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I am SURE that I added a ton of capacitance to change the tuning frequency. I’m talking 500-1000 uF, but hard nto remember. I was experimenting with two 12” woofers. – One was the electrical passive. I THINK in T/S paramaters, capacitance = mass. Two links below to Parts Express conversations.
Using intact speaker as passive radiator?? - Techtalk Speaker Building, Audio, Video Discussion Forum
Here’s another P.E conversation about it. If you have a way of measuring response, try it!
Subwoofer driver as passive radiator? - Techtalk Speaker Building, Audio, Video Discussion Forum
Using intact speaker as passive radiator?? - Techtalk Speaker Building, Audio, Video Discussion Forum
Here’s another P.E conversation about it. If you have a way of measuring response, try it!
Subwoofer driver as passive radiator? - Techtalk Speaker Building, Audio, Video Discussion Forum
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For the resistors, I am using 5 values, starting from 0Ohm (total shunt) up to four times the value of the Impedance of the driver. 0, 2, 4, 8, 16, 32 Ohm. I just guessed the values!!
.........
http://www.diyaudio.com/forums/multi-way/88063-sonus-faber-extrema-5.html
For the resistors, I am using 5 values, starting from 0Ohm (total shunt) up to four times the value of the Impedance of the driver. 0, 2, 4, 8, 16, 32 Ohm. I just guessed the values!!
.........
http://www.diyaudio.com/forums/multi-way/88063-sonus-faber-extrema-5.html
COOL! Let us know what happens, and show us some graphs if you have that type of gear to measure it with.
Some speculations:
Add a resistor to the passive radiator? To bring resistance up from a short or down from an open?
For sure, if anybody said, "Add a resistor in series to your driver in order to reduce damping.." you'd call the person nuts because any impairment of damping (which means enhancement of looseness and resonances). A high damping factor is keenly sought by all audio enthusiasts.
So why should it make any kind of sense to have some kind of box that could ever get to sound better with less damping?
Is something is wrong with that concept?
Just asking.
Ben
Add a resistor to the passive radiator? To bring resistance up from a short or down from an open?
For sure, if anybody said, "Add a resistor in series to your driver in order to reduce damping.." you'd call the person nuts because any impairment of damping (which means enhancement of looseness and resonances). A high damping factor is keenly sought by all audio enthusiasts.
So why should it make any kind of sense to have some kind of box that could ever get to sound better with less damping?
Is something is wrong with that concept?
Just asking.
Ben
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Are you aware that we are talking about a separate, passive driver that is used as a P.R.? This is NOT the driver connected to the amp that we are talking about.
Yes, of course.
My question-note compares the inconceivable action of adding a series resistor to a (powered) driver versus the proposed action of adding a series (sort of) resistor (or subtracting the resistance from an open) on a passive radiator.
No question in my mind that the resistor on the passive radiator would have the effect of changing the damping (up from an open but down from a short). But it seems odd to me, at first glance, nobody would ever want to traffic in damping by reducing any available damping.
Fussing with damping will delight sim advocates and might produce a freq response curve that looks just swell. But you want damping for reasons that may never be apparent from eyeballing your sim's FR. Easy to fix FR with EQ, but not possible to "correct" boom with EQ.
And just to add a further two-cents, if you are going to proceed with a resonant bass box, better to go for an "aperiodic" vent or a vent controlled in any way possible (such as with a passive radiator).
For sure, best would be a vent covered by a block of wood.
B.
My question-note compares the inconceivable action of adding a series resistor to a (powered) driver versus the proposed action of adding a series (sort of) resistor (or subtracting the resistance from an open) on a passive radiator.
No question in my mind that the resistor on the passive radiator would have the effect of changing the damping (up from an open but down from a short). But it seems odd to me, at first glance, nobody would ever want to traffic in damping by reducing any available damping.
Fussing with damping will delight sim advocates and might produce a freq response curve that looks just swell. But you want damping for reasons that may never be apparent from eyeballing your sim's FR. Easy to fix FR with EQ, but not possible to "correct" boom with EQ.
And just to add a further two-cents, if you are going to proceed with a resonant bass box, better to go for an "aperiodic" vent or a vent controlled in any way possible (such as with a passive radiator).
For sure, best would be a vent covered by a block of wood.
B.
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Good point about an aperiodic! That might be eaiser. NOW that I read the review of the Extrema's I see that the B-139 is used as damping, and not as a passive. I STILL think that a bunch of caps will get it to act like a tunable P.R. though. Years ago, I lost all my tests with a computer crash, and gave up on the idea. I know it sounds lame, but I just can't remember! 🙁
So I've been doing some reading on tuning passive radiators with resistors, but one thing I can't confirm is if the change in damping is simply reducing the passive radiator's output, or is it actually changing the tuning frequency of the box. Any thoughts?
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Man... IDK for sure. Here is the test of it fig. 3.
Sonus Faber Extrema loudspeaker Measurements | Stereophile.com
Sonus Faber Extrema loudspeaker Measurements | Stereophile.com
I am now thinking it acts as a sealed box and the ABR just changes the Q or bass tightness. Not what the O.P. was looking for at the start of this. I also thing this must be what Legacy uses when Bill talks about one bass driver used as a brake.
From the measurements it seems like it just reduces the passive radiator's output. Increasing the damping actually slightly increased the tuning frequency.
In purist form, the BR box is a resonator that counter-acts the driver's behaviour and pumps sound out the port; the port sound is in phase above resonance (where you don't want the boost), neutralized at resonance (where you'd like it) and is anti-phase below resonance (where you'd dearly like to have some boost but instead get cancellation).
A sim lets you finagle the box construction (given a specific driver that you just bought) in order to get the freq response, as scrambled by the weird behaviour described in the preceding paragraph, until it looks flat to your eyeball looking at the sim pictures (which is not the same as right to your ear).
Controlling box resonant behaviour by controlling port flow is what we're talking about in this thread. It can improve the box in several ways.
Linear damping equals resistance. Strictly speaking, it has nothing directly to do with tuning.
Ben
A sim lets you finagle the box construction (given a specific driver that you just bought) in order to get the freq response, as scrambled by the weird behaviour described in the preceding paragraph, until it looks flat to your eyeball looking at the sim pictures (which is not the same as right to your ear).
Controlling box resonant behaviour by controlling port flow is what we're talking about in this thread. It can improve the box in several ways.
Linear damping equals resistance. Strictly speaking, it has nothing directly to do with tuning.
Ben
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Ben,
Your above interpretation has several errors:
I don't know whether you meant to write "purist", rather than "purest", but in any form of BR (bass-reflex) enclosure, the Helmholtz resonation of the box around Fb (box tuning frequency) does not counter-act the driver's behavior, it complements it, providing additional output SPL (sound pressure level) compared to a sealed box.
The port output is out of phase with the sound waves emanating from the front of the driver's cone above Fb, but fortunately, if properly designed, that upper output is so minimal that it is of no sonic importance.
Passive radiators work identically to BR, but do offer the advantage of nearly completely blocking the out of phase sound waves above Fb, as well as not using up the valuable volume occupied by a port that is large enough to not be "blown out" at high drive levels. More expensive than a plywood or cardboard duct, but "you get what you pay for".
Around Fb (also known as the box resonant frequency) the port (or passive radiator) output is in phase (not "neutralized") with the sound waves emanating from the front of the driver's cone, but lags behind the front radiation by one cycle, which is why BR designs are also known as "Phase Inversion" designs. The phase inversion is the reason that the port output doubles (+3dB) the BR cabinet's LF (low frequency) compared to a sealed enclosure. In addition to the +3dB gain, at Fb the port is "doing all the work", the cone excursion drops to a minimum, hardly moving at all, allowing far more power to be used in that region compared to a sealed enclosure, without exceeding the driver's Xmax (maximum linear operating range). Because of the reduction of driver excursion, and the 3 dB gain afforded by the phase inversion, it is not uncommon for a BR design to have 6 dB (or more) LF output potential than the same driver in a sealed box of the same size- distortion, driver, cabinet and amp count reduced by 2 (or more) for the same SPL.
Below Fb, the port output rapidly deviates (but is not typically "anti-phase") from being in phase with the speaker's front output, and SPL drops rapidly. Below Fb, the driver "unloads", excursion rises rapidly as if there were no box at all, output being the same as if the driver were operated "naked".
Cheers,
Art
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Hi all,
Instead of a lots of text, using a series resistor in order to achieve a desirable Qts, is a proven method and with respect to damping ;-)
Cheers,
Djim
Instead of a lots of text, using a series resistor in order to achieve a desirable Qts, is a proven method and with respect to damping ;-)
Cheers,
Djim
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Unfortunately this DIY PR attempt is a failure.
I did not realize that Sd and Mms are not the only things that affect PR tuning. I thought Sd was the equivalent of the port diameter and Mms is the equivalent of the port length. However, in PR's Cms can dramatically affect PR tuning because it is the Fs of the PR that determines tuning. The Tang Band woofer's suspension is extremely stiff, so it requires much more mass to hit the tuning I want than anticipated (around 4x the original Mms). There is no way the suspension can support this kind of weight.
Now I'm back to square one. Most likely I'm forced to just use the Peerless 5.25'' PR's. I'm trying to find another woofer with good excursion with a very soft suspension, but this is tough, and can get expensive.
I did not realize that Sd and Mms are not the only things that affect PR tuning. I thought Sd was the equivalent of the port diameter and Mms is the equivalent of the port length. However, in PR's Cms can dramatically affect PR tuning because it is the Fs of the PR that determines tuning. The Tang Band woofer's suspension is extremely stiff, so it requires much more mass to hit the tuning I want than anticipated (around 4x the original Mms). There is no way the suspension can support this kind of weight.
Now I'm back to square one. Most likely I'm forced to just use the Peerless 5.25'' PR's. I'm trying to find another woofer with good excursion with a very soft suspension, but this is tough, and can get expensive.
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