Rythmik 15 sealed sub build - two of them - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #21 of 24 Old 06-17-09, 11:19 AM
Join Date: Jun 2009
Location: Colfax, CA
Posts: 12
Re: Rythmik 15 sealed sub build - two of them


Thanks for the detailed account of your project. I think this will be quite helpful as I begin planning out a sub project, myself.

I will be using a Rythmik DS1200 and probably the 300 amp. That is what is in my F12 (stock build from Rythmik).

Will also go front firing.
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post #22 of 24 Old 06-19-09, 10:55 AM
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Join Date: Jun 2007
Posts: 227
Re: Rythmik 15 sealed sub build - two of them

Very fine work!

Nice spike feet btw.
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post #23 of 24 Old 10-10-09, 01:51 PM Thread Starter
Join Date: Jun 2008
Location: Denver, CO
Posts: 38
Re: Rythmik 15 sealed sub build - two of them

The REW results are in!

The following results were collected using a new Galaxy CM-140. I followed all the recommendations from this forum as to how to calibrate the sound card, graph mins and max's etc. So I believe all the data below to be as accurate as possible. There is no smoothing on any of the charts.

So here is the update to my build of two 15 inch sealed Rythmik subwoofers.

Location had an enormous affect on the output of both my old and new speakers. I used to move them around and find an ideal placement using my ears, but now with REW I have a more precise way to find the best location. So the following is my journey into trying dozens of speaker locations and settings in order to get the best sound possible. In the end I believe I have done that. But you be the judge, the charts below are the most meaningful ones that I recorded.

For this charting exercise, I started out with my original home made subs of 15 years ago. I charted them for comparison purposes and to see exactly what I had been listening to for the last 15 years! They are 12 inch down firing ported Rockford Fosgates (car subs) tuned to 45 Hz. It looks like they are tuned to 200 Hz though!
It's amazing how much bass I thought they were able to create throughout the years.
Here I try two locations to see how they performed and to use these charts as my baseline.
Old subs directly in front of the screen
Rythmik 15 sealed sub build - two of them-old-subs-near-screen.jpg
Old subs in the front corners of the room. This produced a noticeable dip around 77 Hz.
Rythmik 15 sealed sub build - two of them-old-subs-front-corners.jpg
For the new Rythmiks 15 inch sealed speakers, I played around with many a location. Behind the couch, other end of the basement (about 45 feet from the screen). Near the water heater (or about 10 feet behind the couch), etc. These extreme locations produced severe drops in certain frequencies. Below are the locations that seemed to work fairly well. My final location and orientation is at the bottom. Orientation seemed to have a pretty large affect on frequency dips, not so much output. So my goal was to find the location with the least amount of 'dips' or 'peaks'.
My basement is unfinished with black felt hanging from the ceiling along with a photographers muslin behind the front screen. I placed a carpet remnant on the floor to get rid of the cold concrete. The entire basement is unfinished. Here is a drawing of my basement layout. The area with the couch and screen is 16 foot by 21 foot, but opens up to the remainder of the basement. There are no walls. The entire basement has 9 foot ceilings.
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Here I placed the Rythmiks on each side of the couch, and a little forward (in other words, center of room on each side), facing down. Notice the wretched drop at 32 Hz and the overall lack of bass being produced.
Rythmik 15 sealed sub build - two of them-sides-room-just-behind-columns.jpg
Another location tried is with the speakers in the extreme front two corners of the room. Orientation made a big difference here. So the first shot is with them both facing away from the screen. Dips and peaks everyhere! Run!!
Rythmik 15 sealed sub build - two of them-front-corners-again-both-side-facing-out.jpg
Here they are both facing in the same direction (east). Definately better, but noticeable drop off above 60 Hz is introduced.
Rythmik 15 sealed sub build - two of them-front-corners-again-each-facing-east.jpg
Here they are both facing the sky. 28 Hz to 38 Hz frequencies are lost with this configuration.
Rythmik 15 sealed sub build - two of them-both-extreme-front-corner-sitting-up.jpg
Next I tried both speakers directly in front of the screen.
I tried them each 'facing' each other in a 45 degree pattern as shown below in picture:
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Why did I try a 45 degree angle? Because when I had them both face me directly or to the sky, down or any other way in any other direction the dips became extreme. I must have tried over 2 dozen variations of placing them in front of the screen. In the end this 45 degree angle produced the best results. So here is the chart from the above picture.
As you can see, I get bad drops at 32, 48 and 64 Hz.
Rythmik 15 sealed sub build - two of them-both-45-deg-laying-down-pic-taken-.jpg
Same orientation, I just pointed them to the sky. Oops, there goes Mr. 65 Hz!
Rythmik 15 sealed sub build - two of them-both-standing-up-45-deg-pic-taken-.jpg
So in the end, here is my final location (Old subs not hooked up for picture or REW testing). Best results I could find is with the speakers located one in a corner facing east (perpendicular to screen) and on in front of the screen dead center facing me as shown. This final configuration took three 4 hour sessions of testing on several different evenings in dozens of locations to come up with which seems to produce the best sound possible.
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Here is the chart. No crossover or rumble filter.
Rythmik 15 sealed sub build - two of them-final-dead-center-me-corner-center-speaker.jpg
Here is the speaker location but the rumble filter is turned on and the crossover on the speaker and the receiver are set to 80 Hz, but fall off does not happen until around 150 Hz. Don't know why. I also have the PEQ set to plus 3db at 25 Hz. This causes both ends to fall off and the hump between 35 and 40 Hz to be more pronounced. Can't really hear the difference during a movie scene, but the rumble filter is supposed to help prevent damage to the speaker during loud scenes.
Rythmik 15 sealed sub build - two of them-final-rumble-filter-plus-3-db-25-hz.jpg
Here is the final shot with my mains included. The reciever and subs are set at 80 Hz crossover. I purposefully have the high end turned down, but the rather noticeable drops in volume around 48 Hz and 150 Hz and 500 Hz I could not get rid of using my cheesy 12 band $10 equalizer that is about 15 years old. Also, my mains are hanging from the ceiling, so I cannot move them around to see what affect that may have.
Does anyone know how I can improve the 48 and 150 Hz drop? It does not exist with the Subs alone, as shown above. It only occurs when I combine the subs with the mains. 150 Hz is lower end of voices, so I would like to level that out.
Final location, orientation and settings:
Rythmik 15 sealed sub build - two of them-subs-fronts-together.jpg
Here are the main speakers with no subs, so you can see that the 48 Hz drop is only from when I combine the fronts with the subs. Is there a way to manage this negative harmonic interaction?
Rythmik 15 sealed sub build - two of them-main-spkrs-no-eq.jpg
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post #24 of 24 Old 01-13-10, 05:21 PM
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Join Date: May 2007
Location: Melbourne Australia
Posts: 167
Re: Rythmik 15 sealed sub build - two of them


Thanks for sharing your journey! Some very interesting results.

I'm not sure if you're still after suggestions but I have a few. It looks like you have tried options with the subs placed together, and you have measured by moving them. Here's an alternative. Place one sub in the listening position, then move your mic. Measure all over the room, including different heights. Even if you can't use the locations, it's educational!

Instead of just a few measurements, it's easy to take 50 then you get more data and can come closer to the ideal. It will get you there quicker.

Then I suggest you place them differently, choosing locations that give you synergy. Where one sub has a dip, the other should be placed so that it doesn't. The combined response will ignore the dip, so you aim as a minimum to overcome the dips acoustically and try to minimise the peaks, but the ones you can't remove can be tamed with EQ. Once you have your data you can narrow it down, then start measuring with the subs in those places. From here you can also experiment with phase settings. You might also try some downfiring options again. When I measured the corners in my room, the best response was right down at floor level and ceiling level.

You might also consider building some bass traps.

Writer for Hifi Zine & Red Spade Audio blog
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