Low group delay active woofer - what TS parameters am I seeking?
So, I have been pondering for while over a new SW (SubWoofer) project and I know so far I want to build a low group delay SW and am now looking for what kind of TS parameters the element should have, but here's the thing... I am going to skip passive filters and the reliance on natural frequency behavior, (such as if I would go for passive BR then the element Qts would optimally be roughly around 0,38 etc etc...), but instead of passive, I am going to use an analog active EQ'ing with no reliance on some of those "natural laws" as the aforementioned BR example inside parenthesis, therefore I guess other types of TS parameters are to be sought!?
For the choice of element I am imagining a very low Qts and VAS, on the other hand Fs not necessary needed to be very low because that is relying on passive parameters such as a relatively heavy cone to get a low Fs in a passive system, but that's not what I want because I am going to use active EQ'ing.
What I have loosely in mind is a 15" woofer in a, let say 80 liters box, and with a rather heavy dampening filling which would get the effective box volume up to perhaps as much as 95 liters, eventually I could stretch the volume up to 100 liters before filling (w. filling ~120 L.).
My question is now, what kind of element TS parameters am I looking for in order to get a low group delay with a relatively "medium-smallish" box volume when active EQ'ing is to be used without a too much suffering group delay and yet retaining a low frequency response??
Also element suggestions are welcome.
Oh, almost forget to mention what type of box I have in mind, so far I have understood naturally low Q box types are sealed, but also BR could be ok depending on tuning, so I think these are the ones to go with.
So, I have been pondering for while over a new SW (SubWoofer) project and I know so far I want to build a low group delay SW and am now looking for what kind of TS parameters the element should have, but here's the thing... I am going to skip passive filters and the reliance on natural frequency behavior, (such as if I would go for passive BR then the element Qts would optimally be roughly around 0,38 etc etc...), but instead of passive, I am going to use an analog active EQ'ing with no reliance on some of those "natural laws" as the aforementioned BR example inside parenthesis, therefore I guess other types of TS parameters are to be sought!?
For the choice of element I am imagining a very low Qts and VAS, on the other hand Fs not necessary needed to be very low because that is relying on passive parameters such as a relatively heavy cone to get a low Fs in a passive system, but that's not what I want because I am going to use active EQ'ing.
What I have loosely in mind is a 15" woofer in a, let say 80 liters box, and with a rather heavy dampening filling which would get the effective box volume up to perhaps as much as 95 liters, eventually I could stretch the volume up to 100 liters before filling (w. filling ~120 L.).
My question is now, what kind of element TS parameters am I looking for in order to get a low group delay with a relatively "medium-smallish" box volume when active EQ'ing is to be used without a too much suffering group delay and yet retaining a low frequency response??
Also element suggestions are welcome.
Oh, almost forget to mention what type of box I have in mind, so far I have understood naturally low Q box types are sealed, but also BR could be ok depending on tuning, so I think these are the ones to go with.
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In general group delay becomes important around the rolloff frequency and lower. But lower SPL is falling so mostly the concern is in the region of Fb. Keeping Q low minimizes group delay peaking around Fb. Low means less than 0.7. There are slight differences above Fb, but the peaking around Fb is the main "problem area".
With that in mind, you can't have it all. You want low group delay in a smallish box AND frequency extension. Look up Hoffman's Iron Law. You can't have extension, small size, and lower input power requirement for a given SPL. Using a multi-kiloWatt amp and trying to actively correct the alignment is NOT a good solution because TS parameters are moving all over the place with high driver excursion.
If you want good quality low bass and high SPL from a sealed system you just need to put a large driver in a large box, large enough to keep Qts between 0.5 and 0.7. Then live with whatever Fs you get without using active EQ like an LT. Use your favorite box modeler to run some sims to see if how this scenario will play out for the driver you are thinking about using.
Also, don't overstuff in an effort to make the box "bigger". Too much stuffing is not helpful. The "right" amount can be beneficial, but I would make the box physically larger instead of overstuffing.
Finally, if group delay is a concern I would use a closed box system, not a PR, BP or vented since all have worse time domain properties compared to CB.
With that in mind, you can't have it all. You want low group delay in a smallish box AND frequency extension. Look up Hoffman's Iron Law. You can't have extension, small size, and lower input power requirement for a given SPL. Using a multi-kiloWatt amp and trying to actively correct the alignment is NOT a good solution because TS parameters are moving all over the place with high driver excursion.
If you want good quality low bass and high SPL from a sealed system you just need to put a large driver in a large box, large enough to keep Qts between 0.5 and 0.7. Then live with whatever Fs you get without using active EQ like an LT. Use your favorite box modeler to run some sims to see if how this scenario will play out for the driver you are thinking about using.
Also, don't overstuff in an effort to make the box "bigger". Too much stuffing is not helpful. The "right" amount can be beneficial, but I would make the box physically larger instead of overstuffing.
Finally, if group delay is a concern I would use a closed box system, not a PR, BP or vented since all have worse time domain properties compared to CB.
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For closed box woofers, group delay is entirely determined by system Q and low frequency cutoff. Both can be adjusted using EQ. Linkwitz Transform is available for analog filters.
I assume you pursue tight bass. If the woofer will be used indoors, bass thightness will be dominated by room acoustics, so making the woofer faster does not help too much. Fix the room acoustics instead, or the way the woofers interact with it by using multiple subwoofers. EQ'ing room resonances also helps but requires DSP for convenience.
I assume you pursue tight bass. If the woofer will be used indoors, bass thightness will be dominated by room acoustics, so making the woofer faster does not help too much. Fix the room acoustics instead, or the way the woofers interact with it by using multiple subwoofers. EQ'ing room resonances also helps but requires DSP for convenience.
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Doing this with my new studio subs. 15" driver, 130 liter sealed box, little or no stuffing (20-80Hz only) in a wall/floor junction QTs 0.7. Then a MiniDSP to EQ for xMax at 103dB at 22 Hz. Hope the reality equals the sims
OP neglects to mention the basic issue: why do they want low group delay. If the poster is keen on purist acoustical recordings and sound quality, that leads in one direction and other motivations lead in other directions*.
Without fussing over many other sound things CharlieLaub says... but a low Q approaches zero. Everybody see the difference between making music and reproducing music? Long ago, that difference was called "east coast sound" and "west coast sound".
And then that silly "Iron Law". As I once posted about motorcycle mufflers, there are lots of trade-offs people have to make, not just three. See post #10
http://www.diyaudio.com/forums/subwoofers/312696-build.html#post5195008
B.
*one problem with the sub forum is that some threads are really about sounds in cars and trucks (esp the 10th order bandpass threads) and other threads about quality home sound and not always obvious which is which
I've told you before and I'll say it again, Ben, a system q approaching zero = zero bass. That's just the way it is. You definitely don't want a system q anywhere near zero.
Please do some minimum amount of research on these things before posting the same nonsense over and over and claiming I'm stalking you with my bad attitude.
The system q describes the frequency response curve near the low knee. It can't be zero if you want bass.
Your recommendation is always a large leaky sealed box (or oddly enough a Khorn) so what does it matter what the end use is? Anything that produces any resonances is out as far as you are concerned, although oddly enough even a sealed box produces a resonance and a Khorn is riddled with resonances that are not well controlled. The Khorn is the epitome of everything you say you hate yet you loved yours. The issue isn't resonances or group delay. Furthermore, the average domestic room has resonance and ringing issues MUCH worse than the average car. That's what you get when you have 3 pairs of massive undamped boundaries for a listening enclosure.
What about EAS (Electronically-Aided Sealed) subwoofer type?
Basically, all the nonlinearities comes around the roll-off point of the system response IMHO. Below that is just a -6dB/oct slope, and above that is just (semi) linear response. In the EAS method, what you're doing is instead of taking your roll-off point as low as you can, you take it well above the Maximum frequency you need from your sub. So Instead of making the sub box larger, you're lowering its size. Then all you're left with is an innocent -6dB/oct slope which can be compensated by a simple integrator circuit at the input.
NOTE 1: The mentioned approach is too expensive for average use. You'll need thousands of watts and a beefy, hard driver. as the gentlemen told before if you're willing to go that way, first invest on room treatment/subwoofer placement.
NOTE 2: As you're equalizing the lower end, the group delay will go up as well. If you test it with your ears, you'll notice that the on-time, punchy bass gradually changes to a dead and lazy one; though still much better and more natural than most higher-order bass reflex approaches.
Here's a good link for more info:
Sub-Woofer Controller
PS: Feel free to correct me whenever I'm wrong. I'm happily willing to hear more.
PPS: I've actually done a small project like that. A couple of 6" high-excursion woofers (each powered at 30W) paired with two tiny, 2.5" midrange-tweeter satellites (each powered at 2W). The sub goes down to 35Hz at low levels of use aka listening to music alone in my room. At higher levels I have to limit the subwoofer or it will bottom out! while The satellites still playing
Cheers, Ali
Basically, all the nonlinearities comes around the roll-off point of the system response IMHO. Below that is just a -6dB/oct slope, and above that is just (semi) linear response. In the EAS method, what you're doing is instead of taking your roll-off point as low as you can, you take it well above the Maximum frequency you need from your sub. So Instead of making the sub box larger, you're lowering its size. Then all you're left with is an innocent -6dB/oct slope which can be compensated by a simple integrator circuit at the input.
NOTE 1: The mentioned approach is too expensive for average use. You'll need thousands of watts and a beefy, hard driver. as the gentlemen told before if you're willing to go that way, first invest on room treatment/subwoofer placement.
NOTE 2: As you're equalizing the lower end, the group delay will go up as well. If you test it with your ears, you'll notice that the on-time, punchy bass gradually changes to a dead and lazy one; though still much better and more natural than most higher-order bass reflex approaches.
Here's a good link for more info:
Sub-Woofer Controller
PS: Feel free to correct me whenever I'm wrong. I'm happily willing to hear more.
PPS: I've actually done a small project like that. A couple of 6" high-excursion woofers (each powered at 30W) paired with two tiny, 2.5" midrange-tweeter satellites (each powered at 2W). The sub goes down to 35Hz at low levels of use aka listening to music alone in my room. At higher levels I have to limit the subwoofer or it will bottom out! while The satellites still playing
Cheers, Ali
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Elliot's ideas are always compelling.
But for almost the same effort and parts count as his (or similar) circuits, you could make a "bridge" motional feedback board and have bass like you never heard before.
B.
Here is a circuit providing the same job as a Linkwitz transform but all parameters (fo, Q0, fp, Qp in Linkwitz nomenclature) can be set independantly. It is based on two State Variable Filters :
https://jipihorn.files.wordpress.com/2013/06/linkwitz-variable-state.pdf
The first SVF is set to make the frequency response of the driver linear "removing" its main resonance.
The second SVF sets the parameters (fp, Qp) of a new second order high pass filter.
However, it can be entirely removed or replaced by a first order (6 dB/o) high pass filter. Group delay is then low.
Of course, a frequency dependant signal limiter, has to be inserted in the circuit to avoid damage of excessive cone movements.
As extreme bass signals are usually not of great amplitude, the woofer can reproduce them, preserving time fidelity.
This scheme is used in S250 and S500 Atohm amplifiers :
S250 - ATOHM
https://jipihorn.files.wordpress.com/2013/06/linkwitz-variable-state.pdf
The first SVF is set to make the frequency response of the driver linear "removing" its main resonance.
The second SVF sets the parameters (fp, Qp) of a new second order high pass filter.
However, it can be entirely removed or replaced by a first order (6 dB/o) high pass filter. Group delay is then low.
Of course, a frequency dependant signal limiter, has to be inserted in the circuit to avoid damage of excessive cone movements.
As extreme bass signals are usually not of great amplitude, the woofer can reproduce them, preserving time fidelity.
This scheme is used in S250 and S500 Atohm amplifiers :
S250 - ATOHM
Could you please explain the circuit a bit more. Too big for me to digest without your additional capable help.
I don't understand how what appears to my simple grasp as a familiar filter topology can bring about the changes to Q, etc. that you mention.
B.
Don't you know Active Filters ?
Jipihorn's circuit does the same thing as Linkwitz's circuit but is more flexible.
There are two other ways to modify the second order, high pass filter behavior of a driver in a closed box : by motional feedback as said by Bentoronto or by a special output impedance of the amplifier as shown by Erik Stahl.
The upper section of Jipihorn's circuit is set by P1 (fo) and P2 (Qo) such as having the inverse response of the closed driver to be "transformed".
The lower section is intended to set the new parameters by P4 (fp) and P3 (Qp).
If you prefer an overall first order high pass response or a flat response, the lower section can be simplified, but a limiter must included.
Right, but shouldn't we consider "special output impedance" to be a variant of motional feedback?
With the driver wired to the amp and with current flow being the feedback characteristic*, the driver's Back EMF is cooked along with the amp feedback*.
That is another way of solving what the OP was asking about.
I bet the eyes of many sub forum members are glazing over when we talk about electronics on this thread. Pity there are "two solitudes" dividing the electronics geeks and the carpentry geeks.
B.
*in contrast to the familiar voltage amps that have totally captured the business of driving the ancient Rice-Kellogg cone mechanisms
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Inventor of this technique Karl Erik Stahl says it is different from motional feedback. I think it is only a detail if it is or not. Anyway, studying it is extremely instructive. By the way
http://www.diyaudio.com/forums/subw...anical-parameters-electrical-means-print.html
Thanks for link.
"Inventors" always say their gizmo is different so they can fool the patent office. Motional feedback is re-patented every few years.
As best as I can tell, ACE bass is just current feedback, a simple way to do it. I think it is the case that motional feedback amps act as if they had a negative output impedance - otherwise they wouldn't zig when the speaker zags.
B.
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