[MattSelinger]

Greetings fellow audio enthusiasts,

I am planning to build a sealed 12" Rythmik sub and was reviewing information on the Rythmik website where there is a recommendation to use a high pass (low cut) filter on the main speakers (in my case NX Studios) to limit or reduce distortion resulting from frequencies 80ish Hz and down on the main speakers.  My current system:

D90 Topping DAC --> RCA cables --> Emotive BasX 2channel amp --> NX Studios (full signal is sent to the NX Studios)
        (also from the D90) --> 2 XLR --> DIY sealed 10" sub

While I upgrade my sub I want to get the best out of the system so I am pondering if and how I high pass the NX Studios.  Is a high pass recommended?  If so, what are the suggested methods (products) that will give good results?  I am thinking DSP crossover (like miniDSP) but I am concerned I would be adding noise or latency into the system - causing as much harm as good maybe??

Thank you in advance for the responses and Merry Christmas!!

[mlundy57]

I use an in-line filter with a by-pass leg between my preamp and power amp. For this purpose, an in-line filter is just a capacitor. The value of the cap depends on the input impedance of the power amp and the frequency of the desired 3dB down point.

The preamp connects a full range signal to the in-line filter. The output of the filtered leg is connected to the power amp while the output of the by-pass leg is connected to the subwoofer plate amp. This method requires the use of a separate preamp and power amp. There are some integrated amps that will allow this type of filter to work.

Some of the older NAD stereo amps like my C372 have one or two preamp outputs and a power amp input. Normally one preamp output is jumpered to the power amp input. This jumper can be removed and the filter inserted between the preamp out and power amp in.

Another option is Raven Audio's Avian series integrated amps. These have a selectable 80Hz by-pass for the amp input and a full range subwoofer output.

[DannyBadorine]

I would suggest integrating the subwoofer without high passing the NX Studios.  Those are a sealed design and have a natural low end roll off.  Adding a high pass to them could potentially cause phase problems with the crossover point between them and the subwoofer if you're not careful in how you implement it.  I think it would be smoother sounding to just leave them how they are unless you like to listen really loud.
If you do want to experiment with a high pass then having an amplifier or preamp with one built in could be your best approach.  I like the miniDSP stuff, but then you will be adding an analog to Digital and Digital to analog conversion, which will affect the sound to some extent.  I wouldn't use DSP for only a high pass.  And, as the above comment mentions, adding a high pass before the amplifier is probably the best solution but you have to know the input impedance of your amplifier to get the capacitor value correct to do this.

You could add something like the Parasound New Classic 200 pre.  Send your DAC to that then use the high pass option on the back to go to the NX Studios and then use the full range sub output to your sub amplifiers that have their own low pass capabilities.  The high pass filter on this preamp is variable and could be helpful.
https://parasound.com/200_Pre.php

[Early B.]

I would suggest integrating the subwoofer without high passing the NX Studios. 

Ditto.

Since high pass filters may or may not improve the sound, I'm sure you can find several other upgrades that would be equally or more beneficial to you. For instance, there are lots of ways to build a helluva sealed sub including sand-filled, thicker/better MDF, No Rez, extra bracing, high-end finish, A370 amp, etc.   

[Chewbacca]

I agree to try them without a filter first. You need to see how your room responds to the bass output of the speaker first, IMO. Every room is going to be completely different. For example, I expected my NX-Oticas based on others experience to only play flat to about 70-80hz, but in my room they play flat down to 50hz, then drop like a rock. With the outrageously amazing bass they produce, I'd hate to cut any of it out and load it onto the sub - mainly because I'm currently using a Rythmik boxed sub, which definitely doesn't play as clean as the OB woofers on the Oticas. So I can set the sub to 35hz on the plate amp, they cross around 42hz and sum near perfectly. My case is a little different because I'm talking OB woofers, compared to yours being in a box. But regardless, I'd suggest you get them in your room and measure your response before you do anything regarding a filter. Also - As Lundy said, if you do a filter, a single cap between preamp and amp. In your case, between the DAC and amp - since it appears you're using it as such. Get the highest quality cap you can, since it's the whole signal going through it, a cheap cap will make everything sound like mud.

[mick wolfe]

I'm running the NX Studio's full range with a pair of REL subs. As Chewbacca has mentioned and I have to agree, the NX's Studio's sound very robust and certainly seem to dig deeper than 70 hz. In my small room, I don't feel to need for any sort of filter and prefer to keep things simple. To my ear they sound totally at ease running full range even at higher volumes. But every situation and room is different, so once again, YMMV.

[rockadanny]

I am planning to build a sealed 12" Rythmik sub ...

Hi. I am curious ... approx how much will this cost you to build?

[Tyson]

I've tried it both ways with my Super 7's (which only go down to 125hz) and ended up going with no cap.  Just sounds better to me run 'full range' and then just bringing the sub in underneath to fill in.

[Carl V]

Doesn't Vandersteen Speakers/ Subwoofers use this High Pass idea?

I know there have been a few variations to his Outboard Passive Box.
The thought process was to spare your amps from trying to reproduce a FULL RANGE signal
and Your speakers from trying to reproduce that FULL RANGE signal. Tube amps can at times have
Transformer saturation issues with Loud Deep Bass.

Ymmv

[DannyBadorine]

A high pass on the mains can definitely reduce some stress on the amplifier and can possibly clean up the mid range of the mid/woofer since it won't be trying to reproduce those low frequencies.  The problem is that you are inducing phase on the low end of that speaker so getting the sub to be in phase with it will be more difficult.  Essentially, you could be creating more problems than solutions.  With Mose decent solid state amps (and probably most tube amps) you can drive the NX Studios just fine without a high pass.  I would think that you would only clean up the mid range on them with a high pass filter if you are driving them really hard.  Those mid/woofers have an FS of 52Hz so they go pretty low.  The cabinet is sealed and designed around these parameters so adding a high pass could also effect that in ways that you don't want.  It's possible to get a good result with it, but I would definitely start without it because your low end is going to blend together much better.

[MattSelinger]

Hi. I am curious ... approx how much will this cost you to build?

I am planning to build the single sealed sub GR Research offers as DIY.  [https://www.gr-research.com/store/p19/Servo_Sub_Kit_1.html]

Current price is $661.  Need to purchase a sheet of 3/4" MDF ($60), glue, and finish materials. 

[MattSelinger]

Thanks for all the great comments and responses.  My system is in a small room so I am not driving the NX Studios at super high levels.  I will take the approach several mentioned - try blending the new sub without inserting a high pass and see how it goes.  My guess is it will work just fine.

Much appreciation.

[Chewbacca]

I think one of the best reasons to add a low pass filter (besides for unloading the frequencies from your amp/s) is you can potentially eliminate some room excitement the speakers could create. For instance, you may have a 40/50/60/70hz (whatever) bass bump in your frequency - without the sub/s. For instance, you have a bump at 50hz, you can potentially high pass them at 80hz or so, bring the frequency way down at 50hz, where there may still be a bump, but given it's at a much lower SPL with the filter, so it shouldn't excite the room as much. BUT your sub may also (depending on placement) create the same bump in frequency - but with this you have the ability to use the PEQ on the Rythmik plate amp to bring this level down to flat - something that you can't do with your speakers, unless you use a digital EQ...

Regardless, I believe you're on the right path, given you don't know exactly how your room will respond before investing in filters.

Best of luck!