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Discussion Starter · #1 ·
I'm in the process of designing a nice pair of diy planar tweeter/6 1/2" mid speakers powered by some LM3886 gainclones and active crossovers (I've been working on this on and off for a while, but am really close to ordering parts finally!!!). I'm eventually going to add a sub to this design. In the process of doing research, I found out about servo subs and would love to get one for the system (I'd love super taught, accurate bass). However, I am a college kid after all, and my budget is really tight. I guess I'm asking - can I get a servo sub for a few hundred $? I'd be 100% to DIY something. Right now, I can't find much under $1K
 

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Also check out GR Research. Danny sells a couple versions of the Rhythmic sub kits using paper cone drivers. The main advantage is the ability to use a higher crossover without getting into cone ringing. You can do a single 12" for under $500 and a dual for just a touch more. The GR versions of the drivers and amps are also available for open baffle or sealed designs.


Rhythmic sells complete servo subs including a GR cone version at reasnable prices, all in sealed cabinets.
 

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If he is pairing them with a 6.5" midrange, I think they will limit output before the sub. I am also reading in to his post a desire for quality music reproduction over all out HT extension and output. For a music system my choice would be a sealed dual 12" GR version with opposed drivers, or two single driver GR versions, with the two separate subs being a good bit more expensive, and outside his price range. For a smaller room like a student is likely to live in, a single sealed 12" will be plenty and while not a few hundred, $500 is not a lot of money for the type of sub you are getting.
 

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Quote:
Originally Posted by m-fine416 /forum/post/17048572


If he is pairing them with a 6.5" midrange, I think they will limit output before the sub. I am also reading in to his post a desire for quality music reproduction over all out HT extension and output. For a music system my choice would be a sealed dual 12" GR version with opposed drivers, or two single driver GR versions, with the two separate subs being a good bit more expensive, and outside his price range. For a smaller room like a student is likely to live in, a single sealed 12" will be plenty and while not a few hundred, $500 is not a lot of money for the type of sub you are getting.

I understand what you are saying. Up to moderate levels, the need for higher crossover, and music only, the GR version is the way to go, especially if you do not need the lower extension. Agreed, $500 for the sound quality can not be beat....heck, I don't think it can be beat at under $1500.


As for the speaker hitting its limits before the the sub, I am not so sure, especially if you are taking bass duties away from the 6.5" driver. In a smaller room, you are right, the point is moot.
 

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I am pretty sure with the cone area and excursion of the gr 12", it will have more output at 40 hz than most 6.5" woofers can manage at 100. Not only does the 12" have four times the cone area, few 6.5" drivers can manage anywhere near 1.4" of linear excursion.
 

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Quote:
Originally Posted by m-fine416 /forum/post/17048941


I am pretty sure with the cone area and excursion of the gr 12", it will have more output at 40 hz than most 6.5" woofers can manage at 100. Not only does the 12" have four times the cone area, few 6.5" drivers can manage anywhere near 1.4" of linear excursion.

1.4" of excursion?

For 100hz, 100dB at 1m, I believe a 6.5" driver needs between 3.5 and 4 millimeters of excursion.


For a 12" driver, 100dB at 40hz, 1m, needs less than 7mm of excursion.
 

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Discussion Starter · #9 ·
I just wanted to clarify my intentions a little bit. Most of the time, the system resides in my room, which is about ordinary bedroom size. However, mine is the system of choice at parties and stuff (We listen at moderate levels). I would like something with really taught and articulate bass. A servo fits the bill, but I need something that costs a few hundred. Otherwise, I'll design a nice normal model.
 

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Quote:
Originally Posted by cschang /forum/post/17049786


1.4" of excursion?

For 100hz, 100dB at 1m, I believe a 6.5" driver needs between 3.5 and 4 millimeters of excursion.


For a 12" driver, 100dB at 40hz, 1m, needs less than 7mm of excursion.

That was my point, I think the rhythmic driver has way more than it needs to keep up with a pair of 6.5" drivers.
 

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Quote:
Originally Posted by mattdp /forum/post/17049926


A servo fits the bill, but I need something that costs a few hundred. Otherwise, I'll design a nice normal model.

The GR 12" driver is $149 and there is a 300 watt servo amp for $249. That will get you a darn good sub for $400 if you can scrounge up MDF to build it out of.


If you have to shave off another $100, and you do not already have an amp or driver you can use, it will be real hard to maintain quality levels.
 

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Quote:
Originally Posted by m-fine416 /forum/post/17050187


That was my point, I think the rhythmic driver has way more than it needs to keep up with a pair of 6.5" drivers.

Oh....got it. No question, your are right, but at that SPL, I believe the standard Rythmik driver may have the edge over the GR version.


In any case, the point is moot because the OP only needs moderate output.


mattdp, I agree with m-fine, if you can swing the $400 and build your own box, you will be VERY happy.
 

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Servo Subs are real hard to design at the corporate level (ask Bob Carver). For a DIY'er you may think that you got all the issues solved, but if tested by a skilled tester it will probably do poorly. For less time and money you can build a better sub using standard methods.
 

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Quote:
Originally Posted by Speedskater /forum/post/17051106


Servo Subs are real hard to design at the corporate level (ask Bob Carver). For a DIY'er you may think that you got all the issues solved, but if tested by a skilled tester it will probably do poorly. For less time and money you can build a better sub using standard methods.

Hmmm... You could just use the plans on the Rythmik page for the design they're discussing. From what I've read the servo subs are much more forgiving regarding variances in box size, etc as the amp will keep everything under control based on the feedback. Perhaps you're thinking of the difficulty getting the amp -> driver integration setup? That's not an issue as the amp and driver would come all ready, just pop them in the box and go.
 

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The problem with servo subs is getting the motion sensor, the logic circuit and the woofer cone to all work together all the time! Some well known sub-woofer system manufactures have solved the problems (probably with countless engineering man-hours) and make good units.


I spend a short time at the Rythmik site and they seem to say that servos are a design problem but they solved it. Their solution has been done many times before and it always took lots of man-hours to solve. They go on to say that their system works with almost any style sub-woofer. I for one don't believe all this.
 
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