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Aiming for SQ in a sub ...
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Old 21st September 2005, 11:38 PM   #31
Retsel is offline Retsel  United States
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I agree that removing the woofer from the box will cause a roll off in frequency response at the lower frequencies which does affect the sound of the bass being produced. But what I am noticing is the abiliity of the driver to reproduce the midbass (not the frequency response. Even though the deepest frequencies are not being heard (they are not anyways, they are felt) the woofer is still trying to reproduce them. However, what I am comparing when the woofer is in the box or not is the upper frequency bass because that is what was so poor when the woofer was mounted in the box without the servo hooked up to it (it could not "keep up" with the mains). When removed from the box the woofer suddenly had a dramatically improved ability to reproduce the midbass and improved ability to match the mains.

The driver is likely being affected in other ways when it is mounted in the box. For example, the pressure or vacumn created by the woofer as it moves forward or backwards in the box will cause the driver to distort (become more concave or convex). But again, the problem that I am hearing with the woofer in the box is not that the midbass is slightly distorted by these cone movement artifacts, it just cannot track the signal being given to it. Now in this case the woofer is likely a fairly high Q driver mounted in a fairly small box thus raising the Q to very high levels. So it is an extreme example of what happens when a woofer is placed in a box. But this does not matter in this application as designed because the engineers at Genesis designed the woofer to be used with a servo device thus lowering (dramatically so) the Q of the system.

So what is Q. I have read that it is the ability of a speaker reproduce versus dampen (store) the input energy provided to it. Placing a woofer into a box decreases the damping (increases the Q). As I understand it, a desired Q would result in a flat frequency response to provide deep bass without the need to have to roll off the higher frequencies. So if a driver is underdamped (high Q) it will produce deeper bass at a higher output than the higher frequencies. If a driver is a lower Q, it will produce the higher frequencies at a higher output than the lower frequencies.

However, isn't it also logical that damping also affect the ability for the driver to follow the input signal? A well damped driver will reproduce the input signal particularly well while a poorly damped driver (heavy cone/small magnet) will flop around at the same frequencies. These drivers can reproduce lower frequencies OK because the response needed is "slow" (i.e., 20 to 40 cycles). But as the frequency needing to be reproduced increases (100 to 200 hz), the lack of damping takes its toll.

Another issue may be at play for woofers in general. I know that Adire has stated that the high inductance of a woofer can contribute to a poorer frequency response by woofers at higher frequencies. However, in my case, removing a woofer from a box should not affect the inductance of the woofer. So I doubt that inductance is the cause of this effect. However, it perhaps could be a combination of inductance and lack of damping which causes woofers to be "slow" at the higher frequencies.

Well, this is more musing on my part....

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Old 25th September 2005, 09:41 AM   #32
paulspencer is offline paulspencer  Australia
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I just re-calibrated my system for use without the subwoofer with eq to get it flat down to 25 Hz in room. Then I played the Dianna Krall live in Paris music DVD which is an excellent bass test DVD as it has a lot of acoustic double bass. When the double bass plays low, most of its deep output seems to be 50 - 100 Hz, and I noticed that when just my TL speakers, the sound is noticeably more articulate than with my subs supplementing the bottom end, even when crossed low!

The sound is fantastic with just the TLs, but now dynamics are gone
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