High pass filter need

If you are running your system balanced this works well:
Ashly XR-1001
https://www.amazon.com/Ashly-XR-1001-Crossover-Connection-Chassis/dp/B001UIQ1CM
I used one for a while before upgrading to the JL CR1 which has a slightly better feature set but at more than 10X the cost.

BTW, the Ashly has a jumper that you can remove to bypass the 20Hz hi pass (rumble) filter.

To block highs from your main amp, at a specific chosen frequency, you have to know the amp’s input impedance, and choose the correct value of capacitor, to install in series with the input signal. The old Dahlquist DQ-LP1 passive/active crossovers used this method, in their high-pass section. In the Dahlquist manual(I’m providing the link), you’ll find a table(and formulas) that will help you determine what value of cap(and perhaps, resistor) is necessary, to meet your desired crossover point. Dahlquist used a 6dB/Oct slope, because higher orders cause phase shifts. These typically very small value/size components, can be easily installed either inside your preamp(at the outputs) or inside the amp(at the inputs). https://sites.google.com/site/mpbarney/home/dahlquist-dq-lp1 

You should check out this HSU high pass filter!
http://www.hsuresearch.com/products/high-pass-filter.html

Thanks for the suggestions. The JL sub doesn’t have high pass outs so not an option. The Harrison labs FMOD look easy enough to try. Heck, I work in Dayton. (Location of Parts Express)

i am more worried about over driving the C1 woofers than the DNA-2. Its a beast. 600 w per ch into 4ohms. So the port stuffing is also worth trying. 

I’m selling a couple of passive high pass filters. Marchand manufactured. 

@bundy  

I'd suggest the Harrison Labs FMOD inline high pass RCA filters. 

I've used them, and they are quite transparent, and do the job just fine.  They filter at 12db/octave, so whatever value you get, take half of that value, and that becomes your -12db point.  For example, I have a pair of the 50Hz high pass filters, so the freq response is -12db (attenuation) at 25Hz.

They are around $25 ea at Amazon, Parts Express, etc.

You are going to laugh. 

Seal the port with a t-shirt or old socks. 

This will raise the -f3 point, as well as reduce excursion below the port tuning frequency. This will not however reduce the amplifier load. 

To reduce the amplifier load you need a line level crossover. What I suggest is you actually listen to the filter in the JL sub first and see if you hear any negative effects (besides less bass). 

I still recommend you seal the C-1s though. That will make integration better and give you more dynamic range. 

Best,

E