Hi,
My understanding is a sealed cabinet with a Qtc equal or above to 0.8 can lowish its -F3 by increasing the sealed volume. I assume so it's increasing the Qtc, the stifness of the curve below the -F3 and of course the timing factor towards less ideal behavior as less flat low end... anyway the room also adds is own gain.
Assuming it's about tunning an already made sealed box that has already no stuffing but the minimum felt on the walls, can we assume than foaming or stuffing with wool the enclosure will increase the virtual volume seen by the driver and so lowish the -F3 and increase the Qtc ?
What if about the front open load of an aperiodic design : can we also tune the port load chamber in front of the speaker(s) this time to acheive maybe a similar result with less : one can increase the volume up to 20% theorically with full stuffing on a given sealed enclosure volume but we can also play to decrease the volume by putting in it another volume like a brick, bag of sand, sealed bottle...
I surmise it may also move the electrical resonance frequency and the resonance mechanical frequency of the box as well.
How will you process wanting to redue the -F3 by -5 dB for instance with this aperiodic sealed bass cabinet scenario please ? Does such tunning move the band pass widthness of the spl curve and also moves the +F3 according to you ?
My understanding is a sealed cabinet with a Qtc equal or above to 0.8 can lowish its -F3 by increasing the sealed volume. I assume so it's increasing the Qtc, the stifness of the curve below the -F3 and of course the timing factor towards less ideal behavior as less flat low end... anyway the room also adds is own gain.
Assuming it's about tunning an already made sealed box that has already no stuffing but the minimum felt on the walls, can we assume than foaming or stuffing with wool the enclosure will increase the virtual volume seen by the driver and so lowish the -F3 and increase the Qtc ?
What if about the front open load of an aperiodic design : can we also tune the port load chamber in front of the speaker(s) this time to acheive maybe a similar result with less : one can increase the volume up to 20% theorically with full stuffing on a given sealed enclosure volume but we can also play to decrease the volume by putting in it another volume like a brick, bag of sand, sealed bottle...
I surmise it may also move the electrical resonance frequency and the resonance mechanical frequency of the box as well.
How will you process wanting to redue the -F3 by -5 dB for instance with this aperiodic sealed bass cabinet scenario please ? Does such tunning move the band pass widthness of the spl curve and also moves the +F3 according to you ?
You can lower the system Q of any sealed box design by increasing the enclosure volume, the lowest limit being the effective Qts' of the driver (where Qts' = Qts + any series R in circuit from wires, connections, amplifier output impedance &c.).
Depends what you call 'ideal'. Setting the room effects aside, 0.707 is maximally flat (lowest possible F3), not 0.8. Whether you actually want maximally flat is a different question; 0.5 for example is critically damped (transient perfect), 0.577 lowest group delay etc. all of which have their different balances of advantages and disadvantages.
It will have the effect of increasing the box volume, so the other way around: F3 will rise and Qtc drop.
Depends where the vent is, it doesn't have to be on the front
It doesn't matter according to whom. Resistive vent (aka 'aperiodic') boxes are essentially just a means of achieving a lower effective Q in a given box volume than is possible if it were sealed. Eventually it will unload 24dB/octave, although usually that is at a very low level and very low frequency, so the rough analogy holds. If you want the lowest F3, which is a questionable metric, then as far as sealed or its resistive vent approximations go, a system Q of 0.707 is as low as you can get. Other, partially resistive vented alignments exist which may allow a lower tuning to be achieved, but they are basically vented boxes with a bit of vent damping, so some way removed from what you appear to be looking at.
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Thank you ScottMoose for the complete answer 🙂
Ideal in my words was indeed 0.5 Qtc... and subjectivly still ideal up to 0.707: first Qtc at 0.5 always asking ridiculous very low Fs drivers to have a little bass in a sealed design I assume but infinity bass?
Did you mean +F3 in your quoted phrase please or -F3.... I assume it's -F3 if the stuffing is lowishing the Qtc in the scenario.
Let's please putt aside the aperiodic design and take a simplier sealed design or a band-pass design scenario with its "open" port for the band pass in front of the driver.
If the Qtc of the cabinet is more than 0.707 before increasing the stuffing and the virtual volume (if I understood V Dicckason meanings) and the driver in it more than 0.4 Qts will we have the opposite by increasing he volume : decreasing the -F3 towards the bottom but increase the Qtc (so no maximal flat but a lowish -F3) ?
I don't understand what you are meaning with a sealed and the lowish -F3 a Qtc can give. On the same Dickason coock Book illustration 2.1 from my old edition in the sealed design pages, Qtc of 1 seems to gives near - 4 dB lower frequency range at - F3 ? Did I missunderstood the illustration ? 🙁
... let's finally putt aside the tunning of the front chamber of a band pass design as I don't understand the basic sealed yet. (I drop the idea of an aperiodic bandpass idea... never seen btw, so bad idea)
increasing the stuffing reduces the Q only for the vented load or the lowest Q sealed designs (below 0.707 Q) is what I understood from the book... but indeed I doubt I understood it accuratly !
I really looking for lowering the -F3 but at the cost of the Q with stuffing to the max. But indeed some like Harbeth ful stuff to lowish their vented desiggn or Dunlavy I read on Stereophile also did with his sealed designs ???
That's what I'm lost in the Coocking book reading and asked 🙂
Ideal in my words was indeed 0.5 Qtc... and subjectivly still ideal up to 0.707: first Qtc at 0.5 always asking ridiculous very low Fs drivers to have a little bass in a sealed design I assume but infinity bass?
Did you mean +F3 in your quoted phrase please or -F3.... I assume it's -F3 if the stuffing is lowishing the Qtc in the scenario.
Let's please putt aside the aperiodic design and take a simplier sealed design or a band-pass design scenario with its "open" port for the band pass in front of the driver.
If the Qtc of the cabinet is more than 0.707 before increasing the stuffing and the virtual volume (if I understood V Dicckason meanings) and the driver in it more than 0.4 Qts will we have the opposite by increasing he volume : decreasing the -F3 towards the bottom but increase the Qtc (so no maximal flat but a lowish -F3) ?
I don't understand what you are meaning with a sealed and the lowish -F3 a Qtc can give. On the same Dickason coock Book illustration 2.1 from my old edition in the sealed design pages, Qtc of 1 seems to gives near - 4 dB lower frequency range at - F3 ? Did I missunderstood the illustration ? 🙁
... let's finally putt aside the tunning of the front chamber of a band pass design as I don't understand the basic sealed yet. (I drop the idea of an aperiodic bandpass idea... never seen btw, so bad idea)
increasing the stuffing reduces the Q only for the vented load or the lowest Q sealed designs (below 0.707 Q) is what I understood from the book... but indeed I doubt I understood it accuratly !
I really looking for lowering the -F3 but at the cost of the Q with stuffing to the max. But indeed some like Harbeth ful stuff to lowish their vented desiggn or Dunlavy I read on Stereophile also did with his sealed designs ???
That's what I'm lost in the Coocking book reading and asked 🙂
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I got it 🙂 now ! window 2.17 on V.D. Coocking book points towards ScottMose 0.707 Qtc answer 🙂 :
assuming the driver has for instance a fs=27 hz & a Qts=0.45
2.60 ft cube box gives a 0.8 Qtc for a 44hz f3
- reducing the volume increases the Qtc 0.9 ; 1 ; etc and increase the f3
- increasing the volume to 4.10 ft cube for the ideal 0.707 regarding the lower f3 gives a 43 hz f3... 1 db lower (but better transcient than 0.8 db)
Now to reach a 0.5 Qtc the volume box should increase up to a 24.8 ft3 box , the f3 will raise till 54 hz 🙁 ... but the fc aka box frequency resonance will drop from 43 hz to 35 hz... but we don't care for the lowest -3 db possible one want to targett !🙂
Ok maximum stuffing of an empty box only permits a virtual +20% Vb. If I had the 0.8 Qtc of the illustration with an empty box, the max I could acheive with stuffing is 2.6 x 2% = 3.1 ft3 ! maybe just a -0.5 hz f3 winned if the 1 db is at 4.10 ft for the best 0.707 Qtc one can acheive with the driver !
And I assume the maximum stuffing perhaps is giving less clarity ?
So not well done in the first post scenario !
Now if the sealed box had a Qtc=1 with this same particular driver (Qts 0.45 & Fs=27 hz) cause the volume = 1.47 ft3 for a 48 hz -F3 then a full stuffing increasing the Vb till 20% will give an almost better -2 hz f3 and reducing the Qtc till 0.9 !
Marginal tunning at best, but maybe for the box modes, fc is the most changing parameter. In the last illustration fc is 5 hz lower, does it change life according the room importance in the low frequencies... certainly not
The V.D. Coocking book windows 2.1 about Qtc curves is messy at first approximation : one has really the feeling than the 1 Qtc has its -f3 5 hz lower than the 0.7(07) Qtc looking at it!!!!😱
ok I will not waste my time with it in an enthusiast 2 cents tunning...
assuming the driver has for instance a fs=27 hz & a Qts=0.45
2.60 ft cube box gives a 0.8 Qtc for a 44hz f3
- reducing the volume increases the Qtc 0.9 ; 1 ; etc and increase the f3
- increasing the volume to 4.10 ft cube for the ideal 0.707 regarding the lower f3 gives a 43 hz f3... 1 db lower (but better transcient than 0.8 db)
Now to reach a 0.5 Qtc the volume box should increase up to a 24.8 ft3 box , the f3 will raise till 54 hz 🙁 ... but the fc aka box frequency resonance will drop from 43 hz to 35 hz... but we don't care for the lowest -3 db possible one want to targett !🙂
Ok maximum stuffing of an empty box only permits a virtual +20% Vb. If I had the 0.8 Qtc of the illustration with an empty box, the max I could acheive with stuffing is 2.6 x 2% = 3.1 ft3 ! maybe just a -0.5 hz f3 winned if the 1 db is at 4.10 ft for the best 0.707 Qtc one can acheive with the driver !
And I assume the maximum stuffing perhaps is giving less clarity ?
So not well done in the first post scenario !
Now if the sealed box had a Qtc=1 with this same particular driver (Qts 0.45 & Fs=27 hz) cause the volume = 1.47 ft3 for a 48 hz -F3 then a full stuffing increasing the Vb till 20% will give an almost better -2 hz f3 and reducing the Qtc till 0.9 !
Marginal tunning at best, but maybe for the box modes, fc is the most changing parameter. In the last illustration fc is 5 hz lower, does it change life according the room importance in the low frequencies... certainly not
The V.D. Coocking book windows 2.1 about Qtc curves is messy at first approximation : one has really the feeling than the 1 Qtc has its -f3 5 hz lower than the 0.7(07) Qtc looking at it!!!!😱
ok I will not waste my time with it in an enthusiast 2 cents tunning...
works : POLYFIL-Are there definitive rules on when/how to use it? | DiyMobileAudio.com Car Stereo Forum
thanks for this pdf
thanks for this pdf
I am starting a new woofer project (my thread is 3 1/2 way...). The CLOSED box size calculated comes to 33 liters and should give a Qtc of .707. I have ordered some Scan Speak "Flow Resistors" (similar to the Dynaduio "VariVents") for aperiodic if needed. I will test the completed system without the flow resistors at first. If I decide for some reason the Q is on the high side; I would then install the flow resistors and re-test. Here is my main question; would it be better to install the flow resistors DIRECTLY behind the woofer on the back panel or is it better to have them some distance away from the woofer centerline? My box will be a tower about 34 inches high and I am going to mount the woofer near the top of the box. If necessary; I could place the flow resistor anywhere on the rear panel; near the top, middle or bottom. Would I even be to tell any differences where these are located?
All interior walls will have a blended poly'/felt pad and also I will start out with about 75% poly' fill stuffing.
Thanks for any insights, info or experiences here; I have never used a "VarioVent" before.
Your sim will appear to have better bass with a higher Q. But that's because the driver has a spring. Low Q and bass boost makes more sense to me for SQ and low bass.
"Critical damping" is just false advertising.
B.
"Critical damping" is just false advertising.
B.
Unlikely with that design & stuffing. All you are in effect doing is introducing a damped leak-path to the box, bleeding off a small ammount of pressure to lower the effective Q. Since with 75% fibre fill the longitudinal eigenmode should be reasonably suppressed, the location of a variovent isn't likely to make a significant difference.
Thanks guys! If you read in my thread, I have a room mode around 40 Hz or so. I don't mind a Q lower than .707 if it helps smooth and tame the total in- room response. I am listening room size limited so designing a 10/11 inch size (closed) woofer box for a Qtc of 0.5 just would not fit as easily into the existing space (limited height, width and depth all for the intended location). By going with a larger diameter woofer and going from vented to closed box; I should have much more wiggle room (pun intended) or flexibility in minimizing "boominess". As I mention in my 3 1/2 way thread; my sub has good bass management adjustments. The goal is for a stronger bass but also more realism and higher "accuracy" all in the decade from about 40 to 400 Hz. So an "f3" anywhere in the 40's and even low 50's will do nicely. I have read that the variovent (aperiodic) causes an "alignment" roll off of 18 dB (3rd order) where as a closed box is 12 dB and a vented box is 24 dB. This could actually be to my advantage here in this particular room!
Thanks again!