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Line Level Low-pass filter.
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Old 12th January 2020, 03:32 PM   #1
Surtsey is offline Surtsey  United Kingdom
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Default Line Level Low-pass filter.

I know nothing about electronics but I do own a soldering iron. I'm playing with the concept of budget, compact, efficient active subwoofers.

I'm using a ported cabinet with a 6.5" driver. My amp delivers around 20w. I need a low-pass filter but my thinking is this: I don't want to use a post-amplification coil because amplifying a part of the signal only to resist it later seems inefficient. I do not want to to install an active filter as this would complicate power supply requirements.

What can I use the restrict the signal? I'm not too fussed . . . anywhere between 100 and 500Hhz is okay.

Last edited by Surtsey; 12th January 2020 at 03:59 PM.
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Old 12th January 2020, 03:49 PM   #2
troystg is offline troystg  United States
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EBay has them for way less then you could build one. But if you do want to build one it could be perf boarded easy.

Check rod Elliott's site.

Elliott Sound Products - The Audio Pages (Main Index)


More specifically:

Linkwitz-Riley Electronic Crossover
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Last edited by troystg; 12th January 2020 at 03:52 PM.
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Old 12th January 2020, 04:04 PM   #3
Surtsey is offline Surtsey  United Kingdom
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Quote:
Originally Posted by troystg View Post
EBay has them for way less then you could build one. But if you do want to build one it could be perf boarded easy.

Check rod Elliott's site.

Elliott Sound Products - The Audio Pages (Main Index)


More specifically:

Linkwitz-Riley Electronic Crossover

Even more specifically . . . Which part of the 'passive' specification was complicated? By definition, an electronic Crossover requires a power supply.

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Old 14th January 2020, 07:26 AM   #4
Chompy is offline Chompy  United States
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You just need to know your amp's input impedance. Here is a circuit: TLS.org | Passive Line-Level Crossover

I don't know how this commercial product gets around not knowing the input impedance, but these Harrison Labs inline RCA filters are $25 a pair, for comparison. FMOD - Parts Express

Search this forum & google for 'PLLXO' for more.

(I've never done one of these but I'd love to find out how to measure an amps input impedance if no specs are available. For all I know, you might be able to read it directly with a multimeter in resistance mode. But if so, should the amp be on or off?)

Last edited by Chompy; 14th January 2020 at 07:40 AM. Reason: clarify
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Old 14th January 2020, 11:53 AM   #5
troystg is offline troystg  United States
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Quote:
Originally Posted by Surtsey View Post
Even more specifically . . . Which part of the 'passive' specification was complicated? By definition, an electronic Crossover requires a power supply.

You're not helping.
You failed to mention PASSIVE line level XO.
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Old 14th January 2020, 01:00 PM   #6
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by Surtsey View Post
I do not want to to install an active filter as this would complicate power supply requirements.
Passive Line Level Crossovers
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Old 15th January 2020, 07:02 PM   #7
TBTL is offline TBTL  Germany
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Quote:
Originally Posted by Surtsey View Post
compact, efficient ... subwoofers
Unfortunately that is not possible. Compactness, efficiency and bass extension cannot be combined.
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Old 16th January 2020, 01:06 PM   #8
Surtsey is offline Surtsey  United Kingdom
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Originally Posted by TBTL View Post
Unfortunately that is not possible. Compactness, efficiency and bass extension cannot be combined.
Of course they can. Efficiency is the pinnacle of the art. A Wharfedale E90 can produce a higher SPL from 1 watt than. Eminence bass drivers are particularly efficient.
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Old 17th January 2020, 09:33 PM   #9
Think is offline Think  Netherlands
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Line Level Low-pass filter.
Single Power Supply Heavy Subwoofer Preamp Low Pass Filter Pre-circuit Board | eBay
or with a master volume to control sub and main/top speakers:
2.1 Channel Subwoofer Preamp Board Low Pass Filter Pre-Amp Amplifier Board L4A7 194452411078 | eBay


There is also a version with a high pass for the tops at 120hz (if I remember correctly) but can't find it atm.

Last edited by Think; 17th January 2020 at 09:40 PM.
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