Linkwitz correction for TL and vented subs? - diyAudio
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Old 8th February 2004, 08:59 AM   #1
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Cool Linkwitz correction for TL and vented subs?

Hi,

Can Linkwitz correction be used for vented and Transmission lines as well? If yes how?

Thanks and Regards,
Goldy
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Old 8th February 2004, 12:20 PM   #2
Did it Himself
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It can't be used for a TL, but can for a vented, However, not just any standard vented box. I have spent over a year researching and building one of these systems and it's not trivial. I wrote software to work stuff out for me it was that bad.

Basically you need to make the box many times smaller than the Vas of the drive unit such that the roll-off changes to an approximate 2nd-order response. That's the easy bit. The hard bit is then to determine an equivalent true 2nd-order response to make your LW Transform.

You lose a fair bit of efficiency over a standard vented box.

Unless you really know what you are doing and have kit to measure speakers I would look for a simpler project
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Old 8th February 2004, 01:00 PM   #3
sreten is offline sreten  United Kingdom
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Simply put you cannot use a LT type circuit below the port
resonance of a reflex or the cutoff point of a TL, as this will
overload the driver.

You can add a port to sealed LT type alignment, where it will
barely register on the frequency response, but will give extra
power handling, but at these enclosure volumes a passive
radiator will probably be required.

sreten.
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Old 8th February 2004, 02:42 PM   #4
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Correct sreten. I usually set my Fb at or just a little above my desired F3, but even then as you point out it's hard to practically implement the port due to the small box/long port undesireable combination.
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Old 8th February 2004, 04:50 PM   #5
Ron E is offline Ron E  United States
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It's pointless to use a 2nd order pole shifting circuit (Linkwitz Transform) on a vented box. These circuits will apply boost below Fb and cause overexcursion if driven at all hard. Vented boxes often have excursion-limited powerhandling on the order of 10Watts or so below Fb... Modifying a vented box to make it respond like a sealed box is really silly, why not just make a sealed box?.

For vented boxes, it makes more sense to tune a bit low and use a 2nd order highpass filter to boost response at Fb and cut response below Fb. This is a 6th order Bass reflex, and seemingly incredible results can be obtained in terms of sensitivity and F3 for a given box size. The boost is applied at Fb where it causes little increase in cone excursion, and the 2nd order rolloff below Fb actually protects the driver from overexcursion due to low frequency information in the signal...

The best free software out there for this is Bullock's old DOS Boxmodel.
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Old 8th February 2004, 04:53 PM   #6
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This has been discussed in Wireless-World a few years ago and was called Microflex by the author.

Another type of EQ-ing a reflex enclosure is a 6th order tuning.
Or use a shelving filter on a QB5 or similar (would be called an EBS I think).

Edit: I started writing just befor RonE posted. So my statements refer to the posts before.
Regarding Ron's statement about not making sense to tune a BR in a way that it behaves like a closed-box: You will gain a bit regarding excursion limit (according to "perfect-box" about 6 dB, which will be about double lodness at the lower end).

Regards

Charles
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Old 24th February 2004, 02:27 PM   #7
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Cool Put it the other way

What is 6th order tuning. Are there any free tools to model this alignment.
I think my question was misunderstood. I am putting it the other way now.
Let us have two drivers, A tunes to say 25 Hz and B tunes to 35Hz. Is it possible to equalise B so that it behaves like A.
In no way I am saying that the driver should be operated below the tuning frequencey. I am saying tune it lower than suggested and equalise the no linearity in some way.
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Old 24th February 2004, 07:30 PM   #8
sreten is offline sreten  United Kingdom
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simply put six order tuning is :

A combination of an overdamped reflex alignment and an active
2nd order high pass circuit that has a Q (1 to 3) that allows it to
peak at the port tuniing frequency.

Compared to a standard reflex alignment you lower the port
tuning (x 0.7 to x 0.5) to give an overdamped response.

High pass filters Q's of around 2 for x 0.7 and 3 for x0.5 will
restore flat response but due to room gain usually result in
overblown bass. Making Q adjustable is a very good idea.

Depending on the driver sometimes an overdamped bass
response gives a flat response in room due to room gain
and the active boost is not required, for the x 0.7 case.
Boost will be required for the x0.5 case.

sreten.
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