Hi guys I'm looking for a subwoofer that pairs well with the mackie hr824 that goes down to about 15-20hz

I was originally buying yamaha hs80m but someone recommended the mackies. I need a sub because in working on my short film and I produce music and need to hear and feel the bass my current m audio a suck lol.

I'm looking online and the mackies are really cheap now

Unless you want to spend big bux for a matched sub..... do what I did.  I looked around online and found a home audio sub made by Polk Audio. It was on sale for somewhere around $200 IIRC and bought it.
 
10" driver with 100w continuous 200w peak. It adds that bottom end to the Mackie MR-5's nicely. I have it turned down because it will deliver much more bottom than I would ever need.
 
http://www.polkaudio.com/products/psw110
 
I got mine in basic black.

This is for music production or sound effects? If the former, it's unlikely you'll need a sub with the Mackies at all. With few exceptions (contrabass, concert bass drum, pipe organ) musical instruments generally do not produce useful content below around 40Hz. And nothing goes down to 15Hz except shock waves from earthquakes and large bombs.

I have these speakers (HR824's) and they do have a very smooth and extended low end. My speakers are on concrete stands well out from the walls too and I have a useable output at 35 Hz still so that gives you an idea about how low they can go under the right conditions.
 
I would not be pairing any old sub up with these speakers either. I would only consider the Mackie sub woofer to go with the HR824's. It is a lot more about how low any old sub can go. It is also about tightness and transient bass response from the sub that is going to match the speakers etc..
 
http://www.mackie.com/products/hrs120/
 
Although I think this sub might not be available anymore. They do make a 10" version to go with their MR series here but not sure how well it would pair with the HR824.
 
http://www.mackie.com/products/mrmk3-studio-monitors/
 
Click on the MR10S Mk3 over at the right but this sub is deisgned for their MR mk3 series of speakers. You still might find a HRS120 around for sale perhaps in a shop or ebay otherwise it is back to finding another brand of sub that is going to pair well with the HR824's.