Is it possible to apply the "Linkwitz transform" to a midrange speaker? The main idea being to use a smaller enclosure and achieve a flat response at the cost of an increased power requirement?
Would this make any sense at all?... Also would this shift the cone breakup point or just the resonant frequency of the driver?
Would this make any sense at all?... Also would this shift the cone breakup point or just the resonant frequency of the driver?
You could, Linkwitz himself uses it in his open baffled speakers =)
In practice it's just a fancy word for a low end boost, so it won't impact the top end. Keep in mind that power requirement might not be the biggest issue but rather excursion, most pure mids don't have that much xmax and even if they have they don't always behave well when pushed to xmax.
In practice it's just a fancy word for a low end boost, so it won't impact the top end. Keep in mind that power requirement might not be the biggest issue but rather excursion, most pure mids don't have that much xmax and even if they have they don't always behave well when pushed to xmax.
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Neither; you're not changing the driver parameters, you're just shaping the drive signal EQ.
Midrange speakers are usually not used below 2x their fs. Do you have a driver in mind, which you want to run this low?
When using a midrange below its designed lower limit, the distortion will usually rise. Also, the power sent to the driver increases, especially when using Linkwitz transform. And the volume reduction is small, compared to the volume the woofer requires.
When using a midrange below its designed lower limit, the distortion will usually rise. Also, the power sent to the driver increases, especially when using Linkwitz transform. And the volume reduction is small, compared to the volume the woofer requires.
Specifically what driver and what application are we talking about here? Without that nobody can very well tell you what you'll get out of it. In general it's a bad plan, but in a sealed enclosure, Xmax is the same for a given frequency and output no matter what you do behind the driver. If the volume is too small it will just take more power, and some drivers would be okay with that depending on how much output you require, though at somewhat increased distortion. The main problem you run into is that if you're that pressed for space, you're probably not considering very high power capability drivers anyway. There is also the issue of power dissipation in small sealed volumes.
ltx can be used with tweeters/mids/bass to modify the lower rolloff resp.
to use it well, it is nessasery to accuretly measure the existing Q/Fres (software).
If your current box/driver has Q1.2 Fres 150 this could be changed to Q0.7 100 give a acoustical output of butterworth at 100hz.
a Qof0.499 would yeild an LR12 acoustical output etc...
above all accuretly measuring the existing Q/Fres is needed to cancel the existing Q/Fres.
to use it well, it is nessasery to accuretly measure the existing Q/Fres (software).
If your current box/driver has Q1.2 Fres 150 this could be changed to Q0.7 100 give a acoustical output of butterworth at 100hz.
a Qof0.499 would yeild an LR12 acoustical output etc...
above all accuretly measuring the existing Q/Fres is needed to cancel the existing Q/Fres.
The Linkwitz transform is most known as way to extend the low frequency range of drivers. However its real aim is to obtain a new transfer function from the drivers, changing their resonance frequency fs and Qts to new apparent frequency and Qts, either lower or higher.
That was made very clear and used in the first Linwktiz's articles in1978.
For example,
the response of a tweeter having a resonance at 1000 Hz with a Qts equal to 1.0 can be transformed to that of an apparent resonance at 2000 Hz with and a Qts of 0.707.
Adding another electronic hi-pass filter at 2000 Hz and Q = 0.707,
the final result, driver + filter, will be the response indentical to a perfect LR fourth order high-pass filter at 2000 Hz.
There are free Excel sheets which can do all the calculations for you.
Almost the same behavior can be obtained with digital processors.
That was made very clear and used in the first Linwktiz's articles in1978.
For example,
the response of a tweeter having a resonance at 1000 Hz with a Qts equal to 1.0 can be transformed to that of an apparent resonance at 2000 Hz with and a Qts of 0.707.
Adding another electronic hi-pass filter at 2000 Hz and Q = 0.707,
the final result, driver + filter, will be the response indentical to a perfect LR fourth order high-pass filter at 2000 Hz.
There are free Excel sheets which can do all the calculations for you.
Almost the same behavior can be obtained with digital processors.
The LT is a specific case applied to an OVERSIZE sealed box; one of very low Q. This is not what you are talking about. You are just talking about active eq. Do not confuse that with the specific case of the LT. You may use the same circuit as there is nothing magic about that. Siegfried also recognized the advantages of low Q boxes for their sonic charistics and low distortion.
It is the same thing I have done to shape the LF response of a DX25TG09 tweeter, taking its 0.42/631Hz Q/fs parameters to 0.7/1550Hz, and then adding a 2nd order HP Butterwoth filter at 1550Hz. It works really fine and it avoids changing the FT slope from 24dB/oct to 36dB/oct at the original fs
I do not understand what you mean.
LT is a (clever) equalization and is not restricted to specific cases.
It can be applied to small closed box to lower the apparent resonance frequency, setting Q to a desired value, - within some limits, of course -
Or to increase the resonance frequency.
Linkwitz has done it in both ways in his 1798 paper.
forr
How you do it is a simple eq as you say, but to be a LT, it is the specific case about raising the Q of a sealed box allowing it to be used well below fs. The resonant frequency of the driver is not modified by eq.
Of course the circuit, and his correct methods of finding the poles and zeros to determine the proper filter, can be applied to any eq problem, the LT concept is about flattening a low Q box correctly by looking at the overall transfer function with respect to Q.
Active Filters
Siegfried is not a kid any more, but I don't believe he published in 1798.
How you do it is a simple eq as you say, but to be a LT, it is the specific case about raising the Q of a sealed box allowing it to be used well below fs. The resonant frequency of the driver is not modified by eq.
Of course the circuit, and his correct methods of finding the poles and zeros to determine the proper filter, can be applied to any eq problem, the LT concept is about flattening a low Q box correctly by looking at the overall transfer function with respect to Q.
Active Filters
Siegfried is not a kid any more, but I don't believe he published in 1798.
It is the same thing I have done to shape the LF response of a DX25TG09 tweeter, taking its 0.42/631Hz Q/fs parameters to 0.7/1550Hz, and then adding a 2nd order HP Butterwoth filter at 1550Hz. It works really fine and it avoids changing the FT slope from 24dB/oct to 36dB/oct at the original fs
If you even THINK about using tweeters that low you have a lot to learn about distortion. Read what Siegfried says about DISPLACEMENT. I have used that tweeter and would NEVER use it below 2500 second order electrical.
Hi,
An LT is used in an UNDERSIZED box, Not an OVERSIZED box.
For midranges its not likely to be needed. Typical midranges
that need an enclosure usually have a low Fs, but if its quite
high the rear vollume needed is very low anyway.
DIY'ers often oversize the midrange enclosure, going for a
Q of 0.7, when in reality you could easily use an enclosure
often about half the size to get a Q in the range 0.9 to 1.0.
The mild 1dB bump is easily accomodated in the design.
rgds, sreten.
An LT is used in an UNDERSIZED box, Not an OVERSIZED box.
For midranges its not likely to be needed. Typical midranges
that need an enclosure usually have a low Fs, but if its quite
high the rear vollume needed is very low anyway.
DIY'ers often oversize the midrange enclosure, going for a
Q of 0.7, when in reality you could easily use an enclosure
often about half the size to get a Q in the range 0.9 to 1.0.
The mild 1dB bump is easily accomodated in the design.
rgds, sreten.
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I HAVE measured the tweeter distortion from 500Hz to almost 15kHz at about 2.83V (92dB SPL as per datasheet) using ARTA, and there is almost no change in distortion from about 1kHz to the end of the test range. As the resulting filter is a 4th order LR (not a second order one), you get about 1/4 of the applied power at that xover frequency, so it isn't that critical anyway
.The "LT" is the circuit, and doesn't have anything to do with box size or driver type (woofer, midrange, tweeter).
Siegfried uses this on a tweeter to change the effective low end rolloff behavior. He does this by INCREASING Fs (the opposite of what you usually do with a subwoofer+LT). What is convenient for the tweeter is that you can make its response into whatever 2nd order electro-acoustic function you want, e.g. you are free to choose the Q and corner frequency of the LT-transformed driver. You can then add on another 2nd order electrical filter of appropriate Q and Fc to get an overall 4th order (LR4 for instance) response out of the driver+LT+filter combo. This is what Siegfried has illustrated somewhere on his web site I believe (for a tweeter).
Siegfried uses this on a tweeter to change the effective low end rolloff behavior. He does this by INCREASING Fs (the opposite of what you usually do with a subwoofer+LT). What is convenient for the tweeter is that you can make its response into whatever 2nd order electro-acoustic function you want, e.g. you are free to choose the Q and corner frequency of the LT-transformed driver. You can then add on another 2nd order electrical filter of appropriate Q and Fc to get an overall 4th order (LR4 for instance) response out of the driver+LT+filter combo. This is what Siegfried has illustrated somewhere on his web site I believe (for a tweeter).
No. Box size is irrelevant. The LT is a circuit. It doesn't care about the ratio between Vas and Vb.
I think that your assertion is based simply on the observation that many people use the LT to extend the response of their subwoofer which, in an effort to make it visually as small as possible, is put in a relatively small (in terms of Vas) box for the driver. The LT circuit in that case is then used to flatten and extend the response by shaping and boosting the applied power. This is just one application of the LT, by no means the only one or the only valid one.
I believe you are incorrect. It is used in a low Q box. Oversize. The LT then provides a BOOST to match the early gentle roll-off. An undersized box generates a hump before roll-off. I don't doubt some bright person has tried to eq their way out of too small a box, but that is not what Linkwitz is saying to do.
Mid-range enclosures are frequently undersized because the crossover is substantially HIGHER than the natural roll-off. If it rolls off at 100, and your crossover is 500, why have evened out. This is why midranges are usually sealed.
Good grief, there seems to be a lot confusion and misinformation here about the LT. I've been using it successfully in my designs for many years and I've gained some insite to it's strengths and weaknesses. Most important, it's not a panacea that can work miracles, and one needs to pay close attention to all the ramifications of implimenting it in thier designs. It can be used to transform an undersize box or an oversize box, a low Fs to a higher Fs or a high Fs to a lower one, and it can raise or lower system "Q." But, as they say, the devil's in the details. Trying to lower system Fs more than an octave or so gets problematic due to power requirements and driver limitations. Raising Fs more than an octave generally isn't necessary. There are also built-in mathematical limitations that simply won't allow some transfer functions. In my current system I'm using it to transform the woofers from 57Hz @ .57 to 40Hz @ .5, and the mids from 100Hz @ .88 to 100Hz @ .7, and it all works pretty well.
Mike
Mike
This is only true for SL's circuit. What has become known as the "Linkwitz Transform" is actually a "biqudratic filter", and there are several (many actually) realizations of this using analog circuits. You can also use DSP to implement the LT or any biquadratic filter - I created a whole set of tools for loudspeaker crossover design, including the driver responses, that can dial up whatever filter function you want (including the LT or any biquadratic response). I also have a spreadsheet for calculating the component values for a single op-amp biquadratic filter following Steffen's design, but it can not create boost, only cut - for boost you follow it with a gain stage.
Otherwise, everything else you mention is pretty much spot on.
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