With same woofer,
the larger the cabinet volume, the higher the damping,
and vise versa, as you know well.
In my experience,
it was not always good when choosing the optimal volume which was calculated by softwares with Qts and VAS.
Commonly, in my case, high damped type feels better in bass which is more clean, deep, tight and massive.
This is in case that a 6.5 inch woofer which is recommended for bookshelf type is applied to the floor standing cabinet of which volume is 30 liters or something.
I would like to have your experiences.
the larger the cabinet volume, the higher the damping,
and vise versa, as you know well.
In my experience,
it was not always good when choosing the optimal volume which was calculated by softwares with Qts and VAS.
Commonly, in my case, high damped type feels better in bass which is more clean, deep, tight and massive.
This is in case that a 6.5 inch woofer which is recommended for bookshelf type is applied to the floor standing cabinet of which volume is 30 liters or something.
I would like to have your experiences.
A 30 liter box is rather small, even for most 6.5 inch woofers, and isn't a floor standing cabinet.
For a given woofer, as you increase box volume making the system Q or Qtc less than 0.71, there is some improvement of transient response, but at the same time the bass cut-off frequency becomes higher. So you have to compromise between improved transient response versus less lower bass response.
A woofer larger than 6.5 inch generally will make it easier to have both good lower bass and transient response.
For a given woofer, as you increase box volume making the system Q or Qtc less than 0.71, there is some improvement of transient response, but at the same time the bass cut-off frequency becomes higher. So you have to compromise between improved transient response versus less lower bass response.
A woofer larger than 6.5 inch generally will make it easier to have both good lower bass and transient response.
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Most of 6.5 inch midwoofers requires around 15 liters for vented box with system Q 0.71.
Because they mostly (Seas, Scanspeak, SB, Morel and etc) have Ots 0.3~0.4 and VAS 15~30 liters.
Then, do you mean, the calculated optimal volume is too small in practically ?
As increasing box volume, transient response improvement is right, but the bass cut-off frequency becomes not higher but lower.
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That is according to my experiences including below drivers :
Morel TiCW638Nd
Audiotechnology C-Quenze 18H
Scanspeak 18W/8545K
Eton Symphony 7-200
My statement about 30 liters being a small volume for a 6.5 inch woofer is very likely incorrect. I haven't worked very much at all with that size of woofer.
If you were to increase the volume of a system with Qtc = 0.7 to lower Qtc to 0.5 or transient perfect, the bass cut-off frequency F3 becomes only slightly higher than previously. The box resonant frequency Fc is lowered by the factor 0.7 while the ratio of F3 to Fc is increased from 1.0 to 1.55. Factor 0.7 times 1.55 equals 1.09.
In lowering Qtc from 0.7 to 0.5, the loss of bass response comes from the fact that bass roll-off starts earlier. Comparing the frequency response curves of my example of increasing volume, there isn't much of a change, but it would seem that it is audible to a lot of people.
F3 moves higher, but that is the nominal -3dB point of the high pass filter. Toole has shown that F3 has nomeaning to our ear/brain and we should be looking at F6 or F10.
From the arbitrary sealed sim attachec, lower Q actually goes lower by this criteria.
dave
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Okay, well that's interesting. In the past I've seen posts referring to F6 and F10 and didn't understand what that was all about. I thought that F3 was the most important roll-off frequency.
Possibly I could argue that bass roll-off with respect to Qtc = 0.5 starting at a higher frequency than where Qtc= 0.7 is more influential than the lower F10 of Qtc = 0.5. The earlier starting roll-off of the frequency response for Qtc = 0.5, relative to that of Qtc = 0.7 looks to be not more than -1 dB, but it does extend over a fairly wide frequency bandwidth.
Ray Alden in his book Advanced Speaker Systems attributes less bass response from choosing Qtc = 0.5 to bass roll-off (for frequency above F3) starting at a higher frequency, compared to a Qtc > 0.5.
Initially it was in my head that choosing Qtc = 0.5 resulted in a loss of bass response, but as I discovered I really didn't understand what that might derive from.
-Pete
I wanted to ask about a different aspect of overdamped sealed enclosures. Do some woofers generate distorted sound ("grainy" bass) if they are in oversized overdamped enclosures. I did one enclosure with Q somewhere between 0.5 and 0.6, and I am hearing a kind of graininess in the lower-mids and bass which surprises me. The woofer is the 6.5" Vifa PL18 (I believe now called the Scanspeak Discovery 18W/8434).
Is there any such connection? Does one need to do a "right-size" enclosure and not go overboard in overdamped enclosures?
Is there any such connection? Does one need to do a "right-size" enclosure and not go overboard in overdamped enclosures?
The graininess has is no connection with the enclosure (as long as it is properly built).
One should keep the enclosure size such that the end Qts is between 0.5 and say 1.0 (i don't like taking it that high). Do consider that damping will increase the apparant size of the box (say as high as 20%). That is quite a range of box size.
dave
One should keep the enclosure size such that the end Qts is between 0.5 and say 1.0 (i don't like taking it that high). Do consider that damping will increase the apparant size of the box (say as high as 20%). That is quite a range of box size.
dave
I would think so too. I've built over-damped enclosures for all my speakers (the Asawari, the Asawari 2, later the Darbari), but I've never faced this problem. Only with the Asawari 3, which used these Vifa PL18 drivers, did I face this strange bass. I think I'll need to play with the enclosure, tune the port, etc, and get to the bottom of it.
Thanks.
Oops. I was under the impression that overdamped means Q < 0.707
What's the term for 0.5 < Q < 0.707?And thanks for the kudos.
For a sealed enclosure loudspeaker:
Q < 0.5........Over damped...........No overshoot to rest position after a step input, extended settling time, tapered low frequency response
Q = 0.5........Critically damped......No overshoot to rest position after a step input, minimum settling time without overshoot
Q > 0.5........Under damped..........Overshoot to rest position after a step input
Q = 0.577.....Bessel Function.........Very slight overshoot to rest position after a step input, minimum settling time
Q = 0.71......Butterworth Function..Slight overshoot to rest position after a step input, lowest flat frequency response
Q < 0.5........Over damped...........No overshoot to rest position after a step input, extended settling time, tapered low frequency response
Q = 0.5........Critically damped......No overshoot to rest position after a step input, minimum settling time without overshoot
Q > 0.5........Under damped..........Overshoot to rest position after a step input
Q = 0.577.....Bessel Function.........Very slight overshoot to rest position after a step input, minimum settling time
Q = 0.71......Butterworth Function..Slight overshoot to rest position after a step input, lowest flat frequency response
Now I'm seriously confused. I used to believe that my Q = 0.6 was overdamped. Now I am hearing that it's underdamped.
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