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PostPosted: December 6th, 2016, 8:34 pm 
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Joined: July 24th, 2015, 4:17 pm
Posts: 1701
Location: Parkville, Maryland
The live event. What else would one compare to?

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Walt


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PostPosted: December 6th, 2016, 9:50 pm 
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Joined: August 16th, 2013, 8:52 pm
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Location: Pikesville
Normal room size and acoustic is much different from a room where a live concert commonly occur.
I'm not 100% sure yet about the seal enclosure, however, about 15 years ago, I was playing with Altec woofer in a TL and I thought that the Altec travel way too much in this type of enclosure.

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PostPosted: December 6th, 2016, 9:58 pm 
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Joined: July 25th, 2015, 12:47 pm
Posts: 60
In general,

1) Transients are best with a sealed box with Qtc=0.5 or less. I like it when its 0.5 but you dont get that stomach massaging bass unless its closeer to 0.707.
2) Transmission lines are very good. Those I have heard were big and I would say it sounds different, not better than a sealed box. I was under the impression that its hard to get it right. So, my thinking was that in theory, its better than a sealed box and the tuning is hard. If Walt got it with a half-ass box... you may have nailed it.
3) Ported box, if you just want loud bass, not much to it.
4) Band pass always sounded excellent for movies as the ambient retrieval appears to be better than other.
5) The TQWP may give the best of everything but has a few challenges. Biggest is getting it right. Next, a sharp cut off at a frequency before it bounces back up and dampening the subsequent oscillation. Critically damping is needed and I thought I would fix it with an adjustable port.

Did I sort of get this right?


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PostPosted: December 6th, 2016, 10:33 pm 
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Transient response is not really affected by the Qb. That primarily affects the frequency response around resonance. The reason some people think that a low Qb gives better transient response is that they mistake a roll off in low frequency response for tighter, "faster" response. In like fashion, a high QB leads to a bump at resonance that provides more bass and reduces the effect of the higher frequencies, subjectively making the sound "slower". In reality the transient response is affected by the suspension damping or lossiness and the amplifier damping. Don't be fooled by extraordinarily high amplifier damping factors because you have to also take into account the Re or DC resistance of the coil which is in series with the amp output plus the crossover DC resistance if a passive crossover is used. My Crown Macro Reference has a damping factor of 20,000 which represents and output impedance of less than 1 millohm, but it would not provide significantly higher control of the woofer than an amplifier with a damping factor of 100 because of the DC resistance of the coil. A typical 4 ohm driver will have an Re of around 3 to 3.5 ohms. The limiting factor of how much current the amp can sink when the driver goes into generator mode is limited by far by the Re unless your amplifier has an output impedance approaching Re which some single ended tube amplifiers do have.

To improve the electrical damping you have to go to servo control where the amp can actually put out a reverse voltage to allow more current to be sunk from the driver even across the DC resistance of the coil. That could increase the ability of the amp to stop the driver faster. In reality, music can start quickly with an instrument that is struck like a drum kit but the sound usually decays at a slower rate making the damping factor less important.

With ported or other assisted alignments, you not only have the conditions mentioned above for the driver itself but you also have the resonating mass of the air in the port or transmission line or the mass/compliance of the passive radiator that not only start later but also have no connection to the amplifier to absorb the stored energy. That can and does significantly affect the transient response.

Also comparing the sound of a vented system to a live performance may or may not be the best way to compare different configurations. When at a live performance, you will certainly have room nodes and delays that can affect the sound. The best way to compare is to have both systems in the same location and then compare them where all the other factors are the same. I believe you will then hear the difference.

There is no doubt that vented systems can produce more bass but they fall off below port resonance faster than a sealed box. In addition, ported systems unload the driver below port resonance resulting in excessive excursion and at least increased distortion if not actual bottoming of the voice coil support or over extension of the suspension, leading to damage.

Tom


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PostPosted: December 16th, 2016, 8:22 pm 
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Joined: July 25th, 2015, 12:47 pm
Posts: 60
An online calculator claims to be only ad-hoc, it gives an enclosure volume of 11.5 cu.ft. for TQWT. Anyone think its too small or too big?


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