Help! Modifying the Dayton RS1200K kit

whbuchan

Member
2010-11-19 3:40 pm
Just purchased the Dayton Reference RS1200K kit from Parts Express. Never build a sub before, wanted this to be my trial run, since it's a pre-designed kit.

Simply put, it is HORRIBLE. Tons of droning midbass, ZERO deep response.

But I'd like to take an engineering approach to fix this terribly designed kit, rather than return it right off the bat.

I took some stuffing from my old subwoofer and placed it in this Dayton kit - that cleaned things up somewhat (not totally) but also reduced the gross output, and did not help to lower the frequency response.

I also experimented with room placement - no help.

In reading up, it appears that the general rule is that a ported box will provide deeper response. This kit is a sealed box. My old sub had an 8" paper woofer, but the box had two ports, and stuffing, and its performance DESTROYS this 12 inch kit. So, I am wondering:

- First, if the port is done properly, is the difference between a sealed box very substantial, or just incremental? Based on my experience (above), it would seem that a port is extremely important for deep response, and will make a big difference, not a small difference.
- If it is substantial, I would like to modify the enclosure to add a port. Considering I'm very new to speaker design, can someone point me to an easy source of info on port tuning...or better yet, post your recommended solution right here in this thread?

Here's the kit I bought (the new negative review was me, obviously):

Dayton RS1200K 12" Reference Series Subwoofer Kit | Parts-Express.com

My Goal: home theater application. I want serious visceral low frequency response, even if it comes at the cost of some accuracy. This kit advertises 25 Hz low end. It is CERTAINLY not achieving anywhere close to that right now. It also has NO accuracy right now anyways...standing over the enclosure I can actually hear the walls of the box singing...though the stuffing did help that somewhat.

Thanks everyone.
 

tb46

Member
2006-01-09 7:04 pm
Texas
H whbuchan,

Something does not sound right (pun intended). Have you contacted Partsexpress and talked to them about your experience? They are quite helpful, and support a nice forum.

This type of subwoofer has some form of low frequency response shaping to increase the output in the range where a sealed box would be falling off, and it almost always has a high pass filter to protect the speaker from excess excursion below its useful range. So there could be all kinds of things wrong here, the amp, the driver, wiring, the cross-over, the box (leaking, inadequate bracing).

Basically, you should have a working product with this particular driver in a sealed box. I'll attach a quick Hornresp SPL output comparing this driver in a seal v. a ported box (internal volume = 3ft^3).

Regards,
 

Attachments

  • whbuchan_RSS315HF_SEA_BR_SPL.jpg
    whbuchan_RSS315HF_SEA_BR_SPL.jpg
    29 KB · Views: 87
Last edited:

whbuchan

Member
2010-11-19 3:40 pm
Thanks for the reply.

I called Parts Express. They were able to address the hum: use a 3 prong to 2 prong adapter (ground isolator). I did that, and the hum is gone. First small victory.

Now, as for performance - I removed half of the stuffing I had placed into it, and used the amp's equalizer to boost 25 Hz with a very narrow bandwidth. This has helped some more. It is now the point where I could see with a few further tweaks, this thing might finally be up to snuff.

As I look at the woofer excursion, I know this thing has got the brute strength. It just seems like the sealed enclosure is really restricting its movement. One of the other reviews posted on Parts Express said the same thing. This is why I'm interested in porting the enclosure.

And so, back to the original questions:
Does a port really have a significant impact on low frequency response?
If so, who can give me some guidance on the diameter and length of the pipe I'll need?

Thanks!
 

tb46

Member
2006-01-09 7:04 pm
Texas
Hi whbuchan,

Good to hear you got some help from Partsexpress. This should be a nice subwoofer when you're done with it. If you make any changes keep in mind that the electronics are tuned to the present physical design: a small, sealed enclosure.

As to your original question: If you look back at my previous posts you can see the SPL comparison between 3ft^3 sealed and ported boxes in Hornresp. The difference between the respective SPL lines indicates the unequalized difference between the sealed and the ported alignment. There is also a quick run at the response of a tapped horn, but it's quite big. I did this real quickly as examples, all of these boxes would be workable, provided that the T/S parameters from the manufacturers spec sheet have something to do with the driver you have. As to port size: I took a quick look at the Partsexpress forum, and found another set of T/S parameters posted by "Jethro". For a ported box with factory T/S I end up with 4.5ft^3, and with Jethro's T/S with 2ft^3. Naturally, the port size changes too. I recommend you measure your own driver to have a starting point. For a shot in the dark you could try a duct 4"Dia.x 20"long.

A really important thing to check is that the box is free of leaks, including any build-in amplifier box. After that, one of the easiest modifications would be bracing the middle of all the nice square sides that make up the box (and where possible from brace to brace accross the box). A little more involved, but maybe more promising would be a shelf port under the existing box. Something similar to a toekick board on a kitchen cabinet can be made to work very nicely to provide added volume, or the room for a decent size port, or both. Another way to play with a port and the present box: you cut a hole in the bottom (back corner) and attach an external PVC ell and pipe, e.g.: 4"Dia.x 15" long. Then play with the tuning by changing the length of the pipe. (I prefer a 1.5"(2x4) high shelf port, and sticking pieces of 2x4 into it until the tuning is where I want it.)

I try to just make one change at a time, and take notes. That makes it easier to get back to a point where things were still working when I mess it up :).

Regards,