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Designing a Sub which will use a Linkwitz Transform
Designing a Sub which will use a Linkwitz Transform
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Old 18th June 2019, 10:54 PM   #1
micmac1911 is offline micmac1911
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Default Designing a Sub which will use a Linkwitz Transform

Hello,
I have been reading conflicting info, and I would like to get a better idea on my design parameters before I purchase hardware. I am going to build dual(stereo) subs for my listening room. My plan is to use the Minidsp 2x4HD as a crossover and DSP, sending highs to my main speakers and equalizing the bass response. The Minidsp will also act as my DAC. My question is about designing the box and choosing the drivers for the sub. Should I just look at excursion and power handling, and then rely on DSP/Linkwitz transform to get the bass extension/f3 I want? Or is a sub/enclosure combo that gives a 10hz lower f3 advantageous?

Thanks
Michael
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Old 19th June 2019, 10:32 AM   #2
jimbro is offline jimbro  United States
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Have you seen this? Pluto + subwoofer
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Old 19th June 2019, 11:45 AM   #3
Greg32 is offline Greg32  Australia
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Hi have a look at Esp project 48 its good read on what you want to do
Sub-Woofer Controller
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Old 19th June 2019, 11:52 AM   #4
TBTL is offline TBTL  Germany
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Originally Posted by micmac1911 View Post
Should I just look at excursion and power handling, and then rely on DSP/Linkwitz transform to get the bass extension/f3 I want?
If the DSP can handle the required boost then I would say yes. Also look at the harmonic distortion performance. Assuming you want to have small boxes and have set a limit on the size, efficiency is relevant as well.

Subwoofers with small closed boxes and DSP operate largely below their resonance frequency. There, efficiency primarily is determined by the motor strength (BL^2 / Re) and suspension stiffness (incl. air volume, which is fixed due to the enclosure size). So their motor strengths must be high for an acceptable efficiency. Woofers designed for such small boxes can be recognized by their large magnet structures. They also tend to have heavy cones, as cone mass is not that relevant at frequencies below the resonance frequency, while cone stiffness is.

If large boxes and woofers are acceptable, these offer better performance at lower costs than smaller ones. Vented boxes also offer more output (or a lower cost for a given output) as compared to sealed boxes. You can still tune a vented box to a frequency as low as you want and then make the frequency response flat with the DSP.

Last edited by TBTL; 19th June 2019 at 12:11 PM.
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Old 19th June 2019, 02:08 PM   #5
kipman725 is offline kipman725  United Kingdom
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I have been finding that small, low tuned vented boxes with higher motor force drivers are the way to go for maximum LF output in minimum size. They can be made even smaller if you use passive radiators as the radiators do not have the pipe resonance issues long ports have and occupy less box space. However two high spec passive radiators are expensive. This is a good example of a compact vented:
dB v2
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Old 19th June 2019, 05:44 PM   #6
jimmyjazz is offline jimmyjazz  United States
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Originally Posted by kipman725 View Post
I have been finding that small, low tuned vented boxes with higher motor force drivers are the way to go for maximum LF output in minimum size. They can be made even smaller if you use passive radiators as the radiators do not have the pipe resonance issues long ports have and occupy less box space. However two high spec passive radiators are expensive. This is a good example of a compact vented:
dB v2
I'm finding somewhat the opposite: the higher cutoff and steeper rolloff of a PR design seem to dominate over the slight reduction in internal component volume. I'd love to be proven wrong, though!
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Old 19th June 2019, 06:22 PM   #7
TBTL is offline TBTL  Germany
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It depends on the passive radiator how much you lose, compared to a port. I found the Dayton SD215-PR to be quite poor, losing a few decibels at the tuning frequency. Other passive radiators perform better though.

Sometimes with long stroke woofers in small enclosures, ports are no option. They do not fit or the air velocity is excessive, resulting in port misbehaviour as well.

Last edited by TBTL; 19th June 2019 at 06:38 PM.
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Old 19th June 2019, 07:51 PM   #8
kipman725 is offline kipman725  United Kingdom
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I'm tuning low with a small box so the ports are quite big and limit the bandwidth of the box. After a certain point your port gets too long and its output is no longer I. Phase with the driver as well. Despite this due to cost for me ports are a better option.
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Old 20th June 2019, 08:10 AM   #9
chris661 is offline chris661  United Kingdom
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Quote:
Originally Posted by jimmyjazz View Post
I'm finding somewhat the opposite: the higher cutoff and steeper rolloff of a PR design seem to dominate over the slight reduction in internal component volume. I'd love to be proven wrong, though!
It's fairly common for a low-tuned compact box to have over 1/4 of the cabinet volume just as port.

Imagine what you could do with that extra cabinet volume if you used PRs instead.

Chris
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Old 20th June 2019, 05:44 PM   #10
micmac1911 is offline micmac1911
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Originally Posted by jimbro View Post
Have you seen this? Pluto + subwoofer
Jimbo,
Yes thanks. This is where I got the idea years ago. I have had the closed box spreadsheet from Linkwitz on my computer for a long time. It goes contrary to conventional wisdom the driving a subwoofer in a small sealed box to excursion limits takes relatively little wattage. Higher frequency is the difficulty for a large heavy moving mass. I have been told recently as I plan the system that these systems actually don't work well, and I'll never get a sub with an f3 of say 60hz to eq to 30 Hz. I just wanted to get feedback from people who have some practical experience with these things. Buying more watts is cheaper than buying more square feet in my house to place large subs.
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