My dual Rythmik Servo sub is complete!

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This will just be a repeat for those who also peruse the AVS forums. But I got some good guidance here too, so I wanted show the results I'm getting with the Rythmik kits. To keep things easy, I put everything up on a web page: http://bass.consumes.us. I put it together in a rush, so I need to go back and fix some typos, and add some details I left out such as box dimensions, etc. But hopefully there's enough info there for anyone who may be considering the servo kits.

I also should add that Brian Ding with Rythmik Audio has been a big help, and has been very patient with my many questions, and even helped me tailor a couple of details for my specific application. He's been a great guy to do business with. :)
 
You did a nice job integrating the sub into your room. I agree with using servo subs as they can dramatically reduce distortion.

In hindsite, it probably would have been better to build two distinct subs, placing each of them in different parts of the room to prevent the creation of room nodes.

Retsel
 
rythmik, dayton, and polk

ah, bass-consumes-us,

very very nice completed project. seems like you have quality to spare.

i had a pair of sunfire subs, very impressive, a bit bloated (maybe that's unfair -- but it seemed accurate). i hadn't gotten a BFD, so i wonder if it would have corrected things. but anyway, i've been trying to decide on 1 of 3 alternatives:

1 - the rythmik: not sure whether to go the servo route or just implement the linkwitz transform portion
2 - dayton or peerless with the linkwitz transform
or,
3 - tune up an old polk 10A (pair of 6.5" woofers with a 10" passive radiator)

the BFD essentially is such a good tool, that i've wondered whether the sub choice is more or less important than the room eq. (of course, both are important; it's just a matter of where the money goes first).

my listening room is a bit longer, about 15' x 20', so i wonder as well if a single sub is sufficient, or it's necessary to go the route you took and have 2 subs. space is not an issue. and i probably should mention that my home theater is up in the ceiling:
2-front
2-side
2-rear
1-center channel
all parts express (the 6.5"woofer with 0.5"dome pole mounted). this was a wifely accommodation so that there were no cables showing anywhere.
surprisingly though, after talking to a lexicon engineer (who said they found balance - same amps and same speakers for all channels - was a key factor in good sound), i did what was suggested. the sound is in fact quite balanced and consistent. better stuff all around of course would simply be better (and when the budget exists, it'll be upgrade time).

so a question or two:
did you consider several other avenues before the rythmik?
ever try the passive radiator route?
i have several nelson pass diy-amps. i'm thinking of using those class-a designs instead of the plate amps. in talking to rythmik, is it possible to implement the servo design with an external amp instead of the plate amp?
i'm not sure you mentioned, but did you try the linkwitz transform? are you using it with the servo? or are you just using the servo?

thanks for the feedback.
and nice job.
an inspiration: it looks like exactly what i need to add some real dimension to my home theater. the few times i had a subwofer running, it changed the whole nature of the experience.

fermatsEnigma
 
Re: rythmik, dayton, and polk

fermatsEnigma said:
so a question or two:
did you consider several other avenues before the rythmik?
ever try the passive radiator route?
i have several nelson pass diy-amps. i'm thinking of using those class-a designs instead of the plate amps. in talking to rythmik, is it possible to implement the servo design with an external amp instead of the plate amp?
i'm not sure you mentioned, but did you try the linkwitz transform? are you using it with the servo? or are you just using the servo?
I briefly considered a commercial sub such as the SVS cylinders, which I also could have painted to look like a column. But I wanted to get away from the rapid roll-off of a ported system, a lower tuned (16-46) model would have been too tall, and I felt I could get more bang/buck DIY. I did also consider ports or PRs... I thought if they were tuned low enough that the "negative" points of a ported system would have been limited to the infrasonic range. But Port tuning that low would have required a big box and very long ports, which again was a space problem. And some playing with PRs in WinISD showed that there were some "ported characteristics" still present well above the tuning point. Plus, getting enough mass and volume for PRs would have cost just as much as a second driver. And ultimately, I've always been interested in the accuracy that a servo system can provide. With the Rythmik being the only DIY with that option, that narrowed the list pretty fast.

I never asked about external amps. Obviously it could be done, but it would have to be implemented in between the pre-amp section (gain, phase, x-over, etc.), and I can't say how willing Brian would be to invest the time in doing that, or what it would cost. I did talk to him about a 15" kit, which he has been trying to offer, though he's had some problems getting his hands on the drivers. I never really considered LT (it's either/or with the servo... the servo inherently provides the equalization that an LT does). Not a huge price difference between the two, and servo provides all the equalization benefits of an LT, but does it without needing to be tuned to the enclosure, and also has other benefits the LT can't provide (such as distortion reduction).
 
rythmik feedback

dscline,

thanks for the input.

i was going to take a shot at fiddling with the polk, as much as a learning experience as anything else (and i have one). but i have to take driver and passive radiator measurements before i can model it -- so maybe it's simply not worth the time.

and thanks for the LT and servo feedback. somehow i thought you could apply both.

so then just one last question:
since my ceiling speakers have no real low frequency output, i will try to take the sub all the way up to 120hz, where the lexicon dc-1 provides a crossover point (choices are 80hz or 120hz). do you think the rythmik will make it nicely to 120hz? the graphs you show suggest response might be still behaved there.

and thanks again.

fermatsEnigma
 
Well, you really have to take my measurements with a grain of salt, since they are all "in-room" measurements. What I'm seeing won't be the same for you. But in MY case, the in-room response seems to dip down above 100hz. It's hard to follow because of all the room peaks/nulls, but if you look at the following graph, the blue line is the sub on it's own:

An externally hosted image should be here but it was not working when we last tested it.


The blue line gets covered up by other lines in the upper frequencies, but in that range, it follows the green line. However, I've taken some full range frequency response measurements, and my mid-bass seems to be down even in the range where the mains should be covering it. So I don't know if the drop-off above 100hz is solely the sub, or if the room is causing at least part of it.
 
sub response

dscline,

interesting - i missed that (i read the printer output, and not the screen; so i lost the color).

i wonder if it's the woofer falling off, or the servo circuit has some sort of band-pass effect?
and i think the LT circuits might not behave that way -- but then you lose the potentially lower distortion of the servo.

for me, i need to get it up to at least 120hz before it starts to fall.

would it be okay if i post this thread to rythmik and see if he would comment?

fermatsEnigma
 
Re: sub response

fermatsEnigma said:
would it be okay if i post this thread to rythmik and see if he would comment?
Of course! But again, I think it's important to remember that my measurements are all in-room. The sub may indeed roll off above 100hz, or it may be my room. I have no way of distinguishing the two, since I never did any outdoor measurements. Another graph that my be pertinent that I don't have on my site is one I did to analyze my overall frequency response:

An externally hosted image should be here but it was not working when we last tested it.


As you can see, I'm low in the upper bass / lower midrange area, even well into the frequencies that are strictly into the realm of my mains. Perhaps the Rythmik rolls off at the high end early, AND my mains roll off in the low end early, or perhaps my room and speaker layout is causing this. Brian should be able to tell you what to expect from the Rythmik. :)
 
Dscline,

Its my opinion that if you want to discover if the dip in your response is due to your subwoofer or your room, a good idea would be to find a nice day where the wind is at a minimum and do your measurements outside. That way you can get as close to anechoic as possible and be able to tell what the true output of the subwoofer itself is.

Then compare the two graphs and then you will be able to determine exactly the performance of the only subwoofer itself. You wont have to waste a bunch of money trying to acoustically treat your lisening room to diagnose a problem that might actually be with the sub or enclosure itself.

My strong suspicion is that it does have to do with the room, but you never know. Measurements outside is a relatively easy thing to do rather than guessing ;)

Just my two cents.

Logonwheeler
 
logonwheeler said:
Its my opinion that if you want to discover if the dip in your response is due to your subwoofer or your room, a good idea would be to find a nice day where the wind is at a minimum and do your measurements outside.

While I can't disagree with you, I suspect that if YOU had been the one here trying to help me lift this 100lb+ topheavy best up onto a temporary scaffold I built just as a landing to be set on 6' in the air so it could be slid back onto it's mounting shelf without crussing the armoire, you'd probably have the same opinion as me: it is where it is, and it's staying there until an earthquake brings it down. :D
 
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