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Discussion Starter · #1 ·
First time poster, long time reader.


Setting up a budget system for my girlfriend that requires me to use a 2.1 setup due to space limitations. Small bookshelf speakers and a sub linked to an old Onkyo TX-2500 I have that she thinks looks pretty (it is.) I'm a bit confused when it comes to connecting the sub and using the in-built LPF. I know there are many posts about this but I haven't found a specific answer to my questions. We'll use a polk psw10 as an example for now since that's what I'll likely get her.


1: Is the low pass filter included regardless of speaker level input vs line level? Hoping it doesn't matter.


2: Does the filter cut the lower frequencies from being sent to the mains, cut the higher from the sub, or both? I am assuming it sends the full range to the mains and merely attenuates the highs from the sub?


The sub must be connected via speaker level as those are the only outputs on the old receiver. I'd prefer a sub that cuts the low frequencies from whatever small mains I decide on, or an equally simple/cheap solution. Seems as if this would be beneficial to keep those little drivers from stressing about the low stuff. I know the drivers will have their own natural roll-off frequency and the LPF on the sub can be tuned near this. However, I wouldn't mind a little more control to take a little more low-end load off the small mains, and giving a little more to the sub despite the roll-off frequency of the mains.


I've searched high and low for an answer to this and haven't quite found the right info or perhaps haven't wrapped my head around it in the proper way. I'm more accustomed to vintage 2.0 set ups, and have rarely used a sub in my life. Thank you all in advance.
 

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Discussion Starter · #2 ·
In line high pass filter to each channel after sub output? I've never used one or heard much about using them in home audio, but is this a passable solution?
 

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Quote:
Originally Posted by jakaston  /t/1525365/simple-subwoofer-lpf-question/0_100#post_24556548


First time poster, long time reader.


Setting up a budget system for my girlfriend that requires me to use a 2.1 setup due to space limitations. Small bookshelf speakers and a sub linked to an old Onkyo TX-2500 I have that she thinks looks pretty (it is.) I'm a bit confused when it comes to connecting the sub and using the in-built LPF. I know there are many posts about this but I haven't found a specific answer to my questions. We'll use a polk psw10 as an example for now since that's what I'll likely get her.


1: Is the low pass filter included regardless of speaker level input vs line level? Hoping it doesn't matter.


Generally, yes. The way it works is that the speaker level inputs use high value resistors to reduce the signal to a line level signal and then it is fed into the amplifier, the same as if it were a line level input that you were using. The filter will be in that part after the resistors, so it will not matter whether it is a line level or speaker level input.

Quote:
Originally Posted by jakaston  /t/1525365/simple-subwoofer-lpf-question/0_100#post_24556548


2: Does the filter cut the lower frequencies from being sent to the mains, cut the higher from the sub, or both? I am assuming it sends the full range to the mains and merely attenuates the highs from the sub?


It depends on the particular model of subwoofer. You should download the manual for whatever you are considering, before you buy it, so you know what you are getting. Most seem to do nothing to the speaker level output to which the main speakers are connected, but some have a high pass filter to get rid of the deep bass.


If the manual is unclear, contact the manufacturer, but you should pretty much figure that it will probably be sending a full range signal out the speaker outputs if it does not mention a filter in the manual.

Quote:
Originally Posted by jakaston  /t/1525365/simple-subwoofer-lpf-question/0_100#post_24556548


The sub must be connected via speaker level as those are the only outputs on the old receiver. I'd prefer a sub that cuts the low frequencies from whatever small mains I decide on, or an equally simple/cheap solution. Seems as if this would be beneficial to keep those little drivers from stressing about the low stuff. I know the drivers will have their own natural roll-off frequency and the LPF on the sub can be tuned near this. However, I wouldn't mind a little more control to take a little more low-end load off the small mains, and giving a little more to the sub despite the roll-off frequency of the mains.


I've searched high and low for an answer to this and haven't quite found the right info or perhaps haven't wrapped my head around it in the proper way. I'm more accustomed to vintage 2.0 set ups, and have rarely used a sub in my life. Thank you all in advance.


I agree that it would be desirable to have a filter for the deep bass for the main speakers, particularly if the main speakers are very bass deficient (as they must be, if you are considering adding such a wimpy subwoofer as the Polk PSW10). In the absence of such a filter, you will want to adjust the filter on the subwoofer to filter out the frequencies that the main speakers cannot do.


Before you buy a subwoofer for her, you may wish to consider the possibility of simply replacing the main speakers with something that has better bass than whatever her main speakers are. Whether that will be a better option or not depends on exactly what the speakers are that she has and what you can get to replace them and what the system goals are (i.e., what she wants from it).
 

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Quote:
Originally Posted by jakaston  /t/1525365/simple-subwoofer-lpf-question/0_100#post_24556570


In line high pass filter to each channel after sub output? I've never used one or heard much about using them in home audio, but is this a passable solution?

You could make one. Essentially, you would follow the directions for making a crossover. A very simple way would be to put a capacitor in series with the speakers. Here you can see a formula and a chart:

http://www.carstereo.com/help/Articles.cfm?id=1



See also:

http://www.parts-express.com/resources-crossover-component-selection-guide



You would want to make sure that it can handle all of the power that will ever go through it, which will be approximately the total power output from the receiver. And the value you would want would depend on the desired filter frequency, which would depend on the speakers that will be used.


However, I would try it without that first and see if it worked okay without filtering the deep bass from the main speakers.
 

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Subs with speaker level inputs do have a high pass filter on the speaker level outputs to the mains. It's almost always a simple 1st order filter using an NPE capacitor, so the slope isn't steep and the corner frequency depends on the impedance of the mains. It's not a great arrangement, but it's better than no filter at all. The low pass filter in the sub amp works the same whether the speaker level or line level inputs are used. Be sure that a sub you're considering has speaker level inputs and outputs, as that option is rapidly disappearing.
 
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