).
My take on that is that an 'audiophile' may look at the negative aspects of the problem and the cure and then claim that two wrongs don't make a right.Eva said:
What do you think about, or how do you explain the transient nature of room gain? i.e. the way a person could claim that a standing wave may not be excited by too small a portion of a wave. Can it be considered an echo or a reverberation? Is it something else?
RobWells said:
I concur and IIRC the 'resonance' of the human body cavity is ~80hz. Well within the realm of a decent midbass section. Excitation of around there should give you the chest feeling, as well as correct coupling/decoupling of human to chair to room... depending on taste and situation.
As usual, Siegfried Linkwitz has a very nice page on this, showing that maximum power may be required at ca. 120 Hz and that lower frequencies require rather low power. With discussion of voltage vs current vs power vs SPL limitation, for both closed box subs and dipoles.
Linkwitz on power requirements
Linkwitz on power requirements
If you go one page further Linkwitz describes similar relationships for dipoles, which don't rely on resonance but to the contrary, have to be boosted actively, and significantly.
Also, in a minimum phase system, what matters is the Q and slope of rolloff. How it is achieved - through box resonance, active EQ, or driver characteristics, does (in-principle) not matter. What speaks against using box resonances has more to do with radiation from the box, and especially, re-radiation through thr driver cone (the weakest link).
Also, in a minimum phase system, what matters is the Q and slope of rolloff. How it is achieved - through box resonance, active EQ, or driver characteristics, does (in-principle) not matter. What speaks against using box resonances has more to do with radiation from the box, and especially, re-radiation through thr driver cone (the weakest link).
Ohhhh - yes it does of course. You might misunderstand what is meant by "minimum phase".
A system is minimum phase if the Hilbert transform applies. Or simpler: If the phase-response can be derived from the amplitude response.
A reflex box is a fourth-order system as opposed to a closed box which is representing a 2nd order system.
And therefore the reflex box has more phase-shift than the closed one. I think this is what you are refering to, aren't you ?
Regards
Charles
I was meaning that a 'minimum phase' network is one where the phase response can be completely determined from the amplitude response. That is, the phase shift produced by the network is the minimum amount that is to be expected given the amplitude response. (such as you would get from a textbook 4th-order high-pass filter). If you measure the phase shift of a bass-reflex loudspeaker, it does not meet this condition, in spite of people assuming that it does!
Ahhh, I see that we basically agree ! so have you got a measured example ? Not out of distrust but out of curiosity.
There are many such papers discussing the spectral distribution of power. One was by George Augspurger and some of his students (JAES). Only one example had really high power demand below 60 Hz (the infamous "Ouverture 1812").
So for the average program material good low-frequency extension comes at lower cost than usually expected (at least for closed-box systems).
Regards
Charles
MBK said:
Notwithstanding the obvious, it indeed doesn't matter how you reach your Q, box or not, but what that Q actually is.
But Q does mean resonance.
Resonance, though, does not necessarily mean cones flapping out of control. A resonance can lose energy more easily than it stores it. Demonstrating this, why is it that people don't talk about creating closed systems with a Q of less than 0.5?
Anyways, a resonance means an impedance hump in a practical speaker. This means reduced power to the driver at those frequencies. The only other criteria to meet is that the program material in the upper bass is comparable to the mid/lower bass. I think this is usually true.
Because it might sound too lean to most people !
OTOH with a correctly chosen pole-frequency it might combine to a very accurate response in combination with room-gain.
I once made a small closed box with LTF having an f0 of 30 Hz and a system Q of 0.5 and I must say that it souned astonishing - but it might not be to everyone's likening.
Regards
Charles
You raise an intersting point there. I think the reason why I dislike bass-reflex loudspeakers in a domestic room environment is because the 24db/octave bass roll-off of the speaker is a poor match for the typical room gain enhancement. Having the correct speaker bass Q to match the bass increase due to room gain can give a very realistic bass response.
(I am happy with reflex speakers used in very large rooms, or outside, because the effects of room gain aren't relevant then)
(I am happy with reflex speakers used in very large rooms, or outside, because the effects of room gain aren't relevant then)
One of the big advantages to DIY IMO is the way we can design a system (room, speaker, amp) that were meant for each other. An attempt to see them as separate will likely be an uphill battle.
Whats more, we can relax the rules when we know they will be picked up elsewhere. Like the Q of 0.5 fitted to the room. I've done that too, and it is most pleasing.
OTOH, a bass reflex enclosure pleases me most when limited to rock music.
Whats more, we can relax the rules when we know they will be picked up elsewhere. Like the Q of 0.5 fitted to the room. I've done that too, and it is most pleasing.
OTOH, a bass reflex enclosure pleases me most when limited to rock music.
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