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-   -   Use Linkwitz Transform to reduce size of Enclosure? (http://www.diyaudio.com/forums/subwoofers/179960-use-linkwitz-transform-reduce-size-enclosure.html)

Aucosticraft 28th December 2010 08:46 PM

Use Linkwitz Transform to reduce size of Enclosure?
 
I was simulating different closed enclosure for the same driver using WInIsd and adding Linkwitz Transform to extend its lower frequency response. While doing this I thought if it is possible to reduce the size of enclosure and extend lower frequency response of the system.
say for first design I get 50liters of enclosure with f3 of 50Hz and design Qtc = 0.7 and implement Linkwitz Transform to get F3 of 20Hz.

now next suppose I design smaller enclosure, 25liters, f3= 100Hz, Qtc = 1.5
and implement Linkwitz Transform to get F3 of 20Hz.

so can I say that with the help of LT we can reduce the size of enclosure keeping the lower frequency response same? what all things would be affected? which one of two will sound better?

chris661 28th December 2010 10:11 PM

What size driver are you using?
There's no point in using eq to get more bass, if you run out of linear displacement before it'll play 20hz loud enough. Having used it in the past, I wouldn't advise going lower than an octave below the uneq'd response, as the amount of gain required to go further makes an even bigger problem of excursion.
Next up, despite efforts to flatten the response, a resonant system (q=1.5) will still exhibit that resonance, so a large peak before rolloff would best be avoided.

Regards,
Chris

sreten 28th December 2010 10:46 PM

Hi.

You can create any frequency response you like actively, the real issue
is if the maximum SPL related to the volume displacement of the driver
is suitably matched by the driving amplifier power and the bass alignment.

Simply put if you model it the LT will need more amplifier power as long
as the driver can take it, noting the max SPL of any driver in terms of
excursion capability is completely independent of the box response.

More power essentially allows a smaller box to reach fixed SPL limits.

rgds, sreten.

An LT changes the box Q, its simply not true its still there.

Aucosticraft 30th December 2010 06:37 AM

Dear chris661 and sreten, thanks for the reply. Also wish you a happy new year in advance.

@chris661
I am using 8 Inch driver.
To handle excursion problem I have chosen the woofer with high excursion. also after simulation when I saw the its excursion at the f3 frequency, it was within the limit.

@sreten
I ll keep in mind the guidelines you provided. also i understand it don't change any of the box characteristic. I was trying to know that if two boxes designed with different f3. ( one lower and other higher) and then equilized system with LT to get same f3 of both, will sound same?

chris661 30th December 2010 08:31 AM

Here's some reading for you.
ESP - The Linkwitz Transform Circuit
Sounds like you've taken the displacement required into consideration. In that case, experiment with the circuit (try different Q of the response - some say Q=0.5 is better than Q=0.7).
Looking briefly at some sims, an 8" driver will need to move 9mm each way to reproduce 20Hz at 86dB. This wouldn't be audible, but will eat up a lot of headroom. I'd set a target for more like 30Hz, but that's just me...

Sreten, if you eq a response to be flat, does a resonance disappear? Then surely, a system with a resonance in it's frequency range could exhibit that resonance from time to time?

Chris

Aucosticraft 30th December 2010 08:42 AM

3 Attachment(s)
just few graph which i forgot to post.

@ Chris

I will read the link provided by you. thanks.

Don Hills 30th December 2010 09:01 PM

Quote:

Originally Posted by chris661 (Post 2415030)
...
Sreten, if you eq a response to be flat, does a resonance disappear? Then surely, a system with a resonance in it's frequency range could exhibit that resonance from time to time?
Chris

No, EQing a resonance to flat makes it disappear, both in the frequency and time domain.

For example, take a 6 dB resonance with a Q of 0.7.
Starting from no signal, excite it with a signal at its resonant frequency and plot the level over time. It will rise from the original level to a level 6 dB higher, over a time period determined by the Q. (High Q = longer rise time.)

Now take a 6dB notch with a Q of 0.7 and repeat the excitation. The level will drop to a level 6 dB lower, over a time period determined by the Q.

Now put them in series and repeat. The rise in level over time of the peak will be exactly countered by the drop in level of the notch.

AndrewT 30th December 2010 09:29 PM

LT works at low levels of LF gain.
By the time gain gets to 20dB the speaker will be incapable of playing bass that can keep up (SPL wise) with the mid and treble.
At 15dB of LT gain you will be struggling to get a speaker to play well with this much signal being sent to it.
Try to limit your LT gain to 10dB or certainly less than 12dB.

The further you push the F-3dB frequency down, the more LT gain your speaker will need.

If you need 50W to play your Mid and Treble drivers which are both rated at 88dB/W @ 1m then +12dB of LT gain requires 800W to get the same SPL from an 88dB/W @ 1m bass driver.
If the bass driver is 85dB/W @ 1m the bass driver will need 1600W to match the 50W driving the Mid and Treble. I see that as a big problem.
Now get your self a high efficiency PA bass driver that cannot go down low but has lots of Power capability and lots of Sd.
Lets say you find a 96dB/W @ 1m driver.
Adding on the 10dB of LT gain to get the extension you need is equivalent to 86dB/W @ 1m.
Now you need just 80W to the Bass driver to match the SPL of the 50W to Mid and Treble.

chris661 30th December 2010 10:37 PM

Quote:

Originally Posted by Don Hills (Post 2415779)
No, EQing a resonance to flat makes it disappear, both in the frequency and time domain.

For example, take a 6 dB resonance with a Q of 0.7.
Starting from no signal, excite it with a signal at its resonant frequency and plot the level over time. It will rise from the original level to a level 6 dB higher, over a time period determined by the Q. (High Q = longer rise time.)

Now take a 6dB notch with a Q of 0.7 and repeat the excitation. The level will drop to a level 6 dB lower, over a time period determined by the Q.

Now put them in series and repeat. The rise in level over time of the peak will be exactly countered by the drop in level of the notch.

According to winISD, you'll still get phase shift around resonance. Anyway, in terms of level, you're right, but won't the system tend to ring at that frequency? This would show up on things like impulse measurements. Isn't a too-small box the cause of boomy bass, with lots of "overhang"? Even when eq is applied, the problem doesn't disappear.

Chris

sreten 30th December 2010 10:55 PM

Quote:

Originally Posted by chris661 (Post 2415030)

Sreten, if you eq a response to be flat, does a resonance disappear? Then
surely, a system with a resonance in it's frequency range could exhibit
that resonance from time to time?

Chris

Hi,

One version of the LT has poles and zeros that entirely cancel
the real poles and zeros and then adds lower poles and zeros.

Though I do admit you have a point. The above is small signal, the
reality is large, and that fact might become apparent sometimes,
though the actual differences will still be relatively small to most.

It will be the real resonance affecting large signal behaviour, and that's
probably why some extreme active speakers never sounded that good.

rgds, sreten.


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