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Old 29th July 2004, 02:07 AM   #1
wingman is offline wingman  Denmark
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Default what is underdamped and overdamped ?

Hi
Some body who can clear it up for me ?

From adire :
3.3 Adire Alignment Design
The Adire alignment design for Tempest is an overdamped vented alignment. This alignment matches a second order roll-off with a Q of 0.577 and an Fc of 20
Hz to within 0.5 dB down to 11 Hz. This overdamped alignment provides a very tight and accurate sound (with the group delay near 17 ms at 20 Hz), while
providing the potential for high SPL output. Overall, it provides the same effortless sonics of the EBS alignment, while yielding higher potential SPL output in
the midbass range. As a result, this alignment is well suited for both home theater and music-only applications.
The Adire alignment design is a net 214L cabinet, tuned to 15.4 Hz. It is stuffed with 64 ounces of polyfill. It’s external dimensions are 37. 5” tall, 22” wide,
and 22” deep. This includes the height from 4” tall legs. It is vented with a pair of FP3 three inch flared port kits, with 11” long center tubes. The Tempest and
vents are mounted on the bottom, downfiring. Three internal braces are used to stiffen the cabinet, and keep the widest panel span to a very good 9.75” or less.
Recommended building materials are void free plywood (such as marine ply, apple ply, or baltic birch), MDF, and particleboard, in that order.


Overdamped sounds nice !

Can some body help me make a Overdamped cabinet for this woofer : Monacor sph-380tc t/s

It is for HT and music

look here and help me : my thread

Thanks
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Old 29th July 2004, 05:55 AM   #2
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simply
an overdamped response has less ringing and more control
=better sound (and less output)





just take note that these real low tuned subs(eg20hz) dont handle nearly as much power as higher tuned ones!
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Old 29th July 2004, 08:42 AM   #3
AuroraB is offline AuroraB  Norway
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A maximally flat respons is one following a 1. 0rder Butterworth response giving a system Q of 0.707. Any system Q higher than this is defined as underdamped, and system Q lower than .7 is so called overdamped. A Chebychef response is defined as having a system Q of 0.57. 0.5 will be what is called Sub-Chebychef. It all relates to the classical filter theory, where a cabinet mounted LS unit acts as a HP filter circuit,- 2.order HP for closed box and 4.th order for reflex.
The most popular reflex alignment is called QB3, quasi 3.order Butterworth, - where the parameters are tweaked so that the upper part of the acoustical system follows a 3.order slope, to end in 4.th order way down on the slope.

Yes- overdamped circuits give you a much tighter bass,- i.e transient response. I have been using SC4 reflex alignments of Q=0.5 several times, and it indeed gives very goos bass compared to the traditional QB3 alignments. Some say that the nick "boom box" for reflex enclosures is a product of the commercially often used QB3 alignment, (Q= 0.9-1.2,) as this gives a smaller box than C4 or SC4 alignments. QB3 often feels like having having lots of bass, due to the overshoot of the reponse curve before dropping off. And yes,- it often sounds "boomy", as ringing will occur as you increase system Q above appx. 0.9!
That is the price to pay--- an SC4 alignment gives a box size 20-40% larger that QB3 !
In rough terms,- if you tune the vent lower than the LS unit Fs, you will be overdamped. Closed box can be overdamped by increasing the cab volume ,- unless you have a formulae that calculates volume on the basis of system Q.

Formulaes for calculating thevarious alignments are given sevral places, e.g. in Dickasons cookbook. Do you know it??

Have looked briefly at the Monacor param's.. don't have any means forcalcculating here, but this will be huge!! 200 liters???
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Old 29th July 2004, 09:19 AM   #4
AuroraB is offline AuroraB  Norway
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Seems like I need to get rid of my "QB-3 keyboard"... too much ringing!
An SC-4 "hackbrett" would be a lot better!!!
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Old 29th July 2004, 10:11 AM   #5
Doug is offline Doug  Canada
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The goal of the optimum vented box design is to select a vented box volume that will achieve the smoothest or flattest amplitude response in combination with a tuning frequency for the vent which will yield good bass response. Many consider the B4 or 4th-order Butterworth alignment originally described by A.N. Thiele to be the ideal maximally flat design. It has a 24 dB per octave roll-off and a system Q of 0.7 but it is possible only when the Qts of the loudspeaker equals 0.4 (assuming a box leakage loss or QL of 7). As Qts sinks below this value, the optimum vented alignment shifts toward a QB3 (quasi third-order Butterworth) alignment. As Qts rises above the B4 value, the optimum vented alignment shifts toward a C4 (fourth-order Chebychev) alignment.

Doug
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Old 29th July 2004, 05:15 PM   #6
GM is offline GM  United States
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>A maximally flat respons is one following a 1. 0rder Butterworth response giving a system Q of 0.707. Any system Q higher than this is defined as underdamped, and system Q lower than .7 is so called overdamped.

====

I know this is the common definition, but FWIW it's technically incorrect. Q = 0.5 (aka 'critically' damped) is the point between under/over damped, so the theoretically ideal in-room alignment is a 1st order roll off with an inverse response so they sum flat.

GM
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Old 29th July 2004, 05:31 PM   #7
wingman is offline wingman  Denmark
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Quote:
Originally posted by AuroraB
A maximally flat respons is one following a 1. 0rder Butterworth response giving a system Q of 0.707. Any system Q higher than this is defined as underdamped, and system Q lower than .7 is so called overdamped. A Chebychef response is defined as having a system Q of 0.57. 0.5 will be what is called Sub-Chebychef. It all relates to the classical filter theory, where a cabinet mounted LS unit acts as a HP filter circuit,- 2.order HP for closed box and 4.th order for reflex.
The most popular reflex alignment is called QB3, quasi 3.order Butterworth, - where the parameters are tweaked so that the upper part of the acoustical system follows a 3.order slope, to end in 4.th order way down on the slope.

Yes- overdamped circuits give you a much tighter bass,- i.e transient response. I have been using SC4 reflex alignments of Q=0.5 several times, and it indeed gives very goos bass compared to the traditional QB3 alignments. Some say that the nick "boom box" for reflex enclosures is a product of the commercially often used QB3 alignment, (Q= 0.9-1.2,) as this gives a smaller box than C4 or SC4 alignments. QB3 often feels like having having lots of bass, due to the overshoot of the reponse curve before dropping off. And yes,- it often sounds "boomy", as ringing will occur as you increase system Q above appx. 0.9!
That is the price to pay--- an SC4 alignment gives a box size 20-40% larger that QB3 !
In rough terms,- if you tune the vent lower than the LS unit Fs, you will be overdamped. Closed box can be overdamped by increasing the cab volume ,- unless you have a formulae that calculates volume on the basis of system Q.

Formulaes for calculating thevarious alignments are given sevral places, e.g. in Dickasons cookbook. Do you know it??

Have looked briefly at the Monacor param's.. don't have any means forcalcculating here, but this will be huge!! 200 liters???

i΄ll use 175L@18hz i think it will be ok.

Thanks for your help
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Old 29th July 2004, 08:42 PM   #8
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Quote:
Originally posted by GM
>A maximally flat respons is one following a 1. 0rder Butterworth response giving a system Q of 0.707. Any system Q higher than this is defined as underdamped, and system Q lower than .7 is so called overdamped.

====

I know this is the common definition, but FWIW it's technically incorrect. Q = 0.5 (aka 'critically' damped) is the point between under/over damped, so the theoretically ideal in-room alignment is a 1st order roll off with an inverse response so they sum flat.

GM

That is correct.

Someone correct me if I'm wrong about what follows:

One of the many equivalent definitions of Q is the ratio of energy stored to energy dissipated.

If the ratio of stored energy to dissipated energy is .5, and the energy source is removed, then the resonator will come to rest in one half of a cycle, in the quickest possible time, without ringing or overshoot. For loudspeakers, note that this means cone displacement (not SPL) does not overshoot.

Q's higher than .5 are called "under-damped," lower are called "over-damped," and .5 exactly is called "critically damped." There is nothing particularly remarkable about a Q of 1.0.
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