Background:
After months of debating about build vs buy I have decided to build a HT sub. It has not been easy with the great deals available lately from Hsu on there STF series and new Mk3 series I came very close to purchasing one. But I felt that their subs were limited by a "fixed" subsonic filter in STF series limiting the lower response and have limited power ( http://www.hsuresearch.com/forum/showthread.php?t=2392).

Since this sub will be used primarily for movies and HD programs I wanted one with lots of "impact" that can be felt and with good response below 20Hz.

I was also of concerned is the vinyl wrapped finish or sprayed texture paint on commerial subs in the lower price range. Since me and my wife prefer real wood that can be stained to match other furniture in the room. Also I do not like the "looks" of a oversized water heater in the room from a LLT design. :p

Environment:
The sub will be going into our newly constructed family room which is dedicated to home theater. It is located in a half basement with a size of about 13 x 20 x 7.5 (2000ft^3) with a opening to an open staircase. The walls and ceiling have been insulated. With the opening on one side of the room I am thinking that it might not be possible to pressurize the room.

Project:
I have selected one of Rythmik Audio newer 15" Servo kits (http://www.rythmikaudio.com/servo_product.htm) for the higher output from a smaller 3ft^3 enclosure. There are not a lot of example projects available so I want to document my project and experience with this kit here.

Since the kit is pretty straight forward with a sealed enclosure this is really only one option left. Should I built it to have the driver front firing towards the listeners or down firing design like the Hsu?

I have place my order and hope to start the project next week. :D

As long as it has sufficient clearance, I doubt you'd find any difference in down-firing/front firing. Brian recommends 3-4 cu ft... I'd try to go closer to 4 than 3. You're powering the 15" driver with the same power as the 12" kit, so the larger enclosure may make that power go a little further. If it turns out there's any benefit to going with a smaller enclosure, you can always add bricks or blocks inside to take up volume. Can't go the other direction.

And congrats! :)

That looks like a great kit,with a quality 15" in a reasonably compact sealed box with servo correction, whats not to like.
I'm looking forward to your documenting of the build.

You've made a great choice. I look forward to your build.

Finally, a Rythmik 15" project! :D

I definitely want to see what Brian's 15 is capable of. Remember that there are no limiters on the amp so you can bottom out the driver if you are not being safe. (I've bottomed out my Rythmik plenty of times, it's a loud clanking noise, it still runs just fine ;) )

Some recommendations:

-Get an SPL meter ~$40
-If you can, get REW for free and use it to measure the sub

As long as it has sufficient clearance, I doubt you'd find any difference in down-firing/front firing. Brian recommends 3-4 cu ft... I'd try to go closer to 4 than 3. You're powering the 15" driver with the same power as the 12" kit, so the larger enclosure may make that power go a little further. If it turns out there's any benefit to going with a smaller enclosure, you can always add bricks or blocks inside to take up volume. Can't go the other direction.

And congrats! :)

Good point, I should go with a larger enclosure. I will most likely go with a front firing design to show off the shiny 15" TC driver in action and for near field measurements.

Do you know if all the internal wiring is included or if the sensing coil requires anything special?

Do you know if all the internal wiring is included or if the sensing coil requires anything special?

Everything is included (except maybe screws for mounting) and is foolproof, you connect the 4-pin MOLEX connector from the amp to the driver (which can only connect one way) then fire it up.

I'm considering the 15" as well for my HT setup. I have talked to Brian a couple of times and he told me that 2 cu ft. for the 12" and 3 cubic feet for the 15" offered a good balance between efficiency and power handling. The larger you go the more you risk bottoming the driver. But as pointed out, you can always reduce the volume, but its difficult to increase it. He also said the driver could be used in a down firing configuration, and would need about 2-3" clearance from the adjacent surface. I look forward to seeing your design and results; you're ahead of me on the curve by about two weeks.

I am thinking about getting the 12" kit and using it with a PE 2 cubic foot enclosure and/or a 15" kit and using it with the 3 cubic foot PE box. The goal would be as near a turn-key kit as possible. I have limited woodworking equipment (a jig saw) and even less woodworking skill :p .

Remember that there are no limiters on the amp so you can bottom out the driver if you are not being safe. (I've bottomed out my Rythmik plenty of times, it's a loud clanking noise, it still runs just fine ;) )

Some recommendations:
-Get an SPL meter ~$40
-If you can, get REW for free and use it to measure the sub

Thanks for the warning. :p I am wondering is the 15" will bottom out with the same 370 watts amp before it start clipping. If so that is good thing since that means there is plenty of "headroom" in the amp. I already have a SPL meter, REW and a BFD. While I wait for the kit to arrive I am going to try and learn how to work with REW so that I can publish some results.

I'm considering the 15" as well for my HT setup. . . I am thinking about getting the 12" kit and using it with a PE 2 cubic foot enclosure and/or a 15" kit and using it with the 3 cubic foot PE box. The goal would be as near a turn-key kit as possible. I have limited woodworking equipment (a jig saw) and even less woodworking skill :p .

Glad to here it. If you are going the PE cabinet route you should order it soon while they still have free shipping. I have all the tools to build my own cabinet (table saw, router, etc) which is why I am going the DIY route more control over the quality and design of the cabinet.

I've bottomed out my Rythmik plenty of times
Just curious Chris... how big is your box? I built mine to be right around Brian's recommended size of 2ft³(actually a little less, since his numbers include amp/driver). I've never bottomed, but I HAVE clipped the amp using test tones. I've often wondered if I should have gone just a tiny bit larger (which is probably what prompted me to make the suggestion I did).

Just curious Chris... how big is your box? I built mine to be right around Brian's recommended size of 2ft³(actually a little less, since his numbers include amp/driver). I've never bottomed, but I HAVE clipped the amp using test tones. I've often wondered if I should have gone just a tiny bit larger (which is probably what prompted me to make the suggestion I did).

A bit smaller than his 2 cubic feet.

I've definitely bottomed it trying to calibrate it at 85db at Chucks theater.

Rythmik 15" kit finally...i've been waiting for this.
I've bottomed my Rythmik 12" a few times on WOTW.

FYI

The PE 2ft^3 cabinet after subtracting the brace, driver and amp comes to about 1.6ft^3. I would recommend going with the 3ft^3 cab and do some additional bracing,top to bottom,front to back. The brace included with the PE cab runs from side to side, not enough, IMHO, for 3/4" walls.

FYI

The PE 2ft^3 cabinet after subtracting the brace, driver and amp comes to about 1.6ft^3. I would recommend going with the 3ft^3 cab and do some additional bracing,top to bottom,front to back. The brace included with the PE cab runs from side to side, not enough, IMHO, for 3/4" walls.

Eh? The bracing, driver, and amp are taken into account with the 2ft^3 spec.

The 2ft^3 cab I have here measures out at 17x17x16.25, subtracting the 1.5 brings it down to 15.5x15.5x14.75, or 3543.6875in^3, for the internal measurements.This is 2.05ft^3 before any other displacment is accounted for.
At least I hope I have the math right. ;)

The 2ft^3 cab I have here measures out at 17x17x16.25, subtracting the 1.5 brings it down to 15.5x15.5x14.75, or 3543.6875in^3, for the internal measurements.This is 2.05ft^3 before any other displacment is accounted for.
At least I hope I have the math right. ;)

Yeah, my fault, I used the depth dimension which includes the grill.

I still think the bracing is already taken into account, and the driver won't take up more than .1ft^3.

Excellent, someone about to build a 15" version!!

I am seriously considering going with a 12 or 15 DS sub myself, in a sealed box.
I want it to sound clean with music, as well as pretty deep with HT.

I was seriously leaning towards the 12" due to Brians own discussions regarding music, as the sub I build will be 50/50.

Good Luck, and Have Fun!!

m

I received the Rythmik kit today. It arrived in two heavy well packed boxes. Overall both the amp and the driver have a high quality feel to them. They appear well built and a nice heavy feel like they are well made with quality components.

What is included:

Package of short wood screws to install Amp
Package of wood screws to install driver
One 15” foam gasket be installed under the driver
One DirectServo 350 watt amp (A370-SE)
One 15” DirectServo driver (DS15TC )
Driver hookup with Molex connector
Power cord



http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/Servo15Kit.jpg

The biggest surprise was a lack of instructions or a manual, not even a basic overview sheet how the “kit” should be assembled. Most consumer electronics manufactures desire to include a manual to provide warnings on how not to use their product along with instructions on how to properly setup it up. Rythmik may have manual I just did not find one in the boxes or on their site.

http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/A370-SEFront.jpg

The amp has many of the features you would except from a higher model like infinite phase control between 0 and 180 degrees instead of a fixed 0 or 180. This is important when trying to get the phase prefect in your room and to blend with the mains. Another nice feature in the power switch with an On-Auto-Off selection. I have seen many posts where someone can’t get their amp to stay on at very low volume or some just want it on all the time. The stereo RCA inputs/output would be great for creating a 2.1 setup with any preamp/amp or a stereo receiver with loopback connections.

Note that the amp has a built-in foam gasket under the mounting flange which makes it easy to install/reinstall.

I think the installation is pretty straightforward.

-Mount the amp
-Connect the two molex together
-Mount the driver

On his site he has the information to what each of the switches do (damping and extension)

Remember, ask us if you have any questions; many of us have probably asked them before with the 12" Rythmiks. ;)

I think the installation is pretty straightforward.

-Mount the amp
-Connect the two molex together
-Mount the driver

On his site he has the information to what each of the switches do (damping and extension)

Remember, ask us if you have any questions; many of us have probably asked them before with the 12" Rythmiks. ;)
Believe me I have no confusion here just trying to provide a review for others. I feel that solid documentation is very important probably because of years experience in the software engineering field. It would be nice to see a very well organized manual with all the information outlined clearly like the ones you see from Hsu, Velodyne and others. Then maybe everybody does not need to keep asking the same questions.

The 15” Servo driver is custom built by TC Sounds in the USA and has many the build qualities of the TC–1000 series drivers ( http://www.tcsounds.com/tc1000.htm). The voice coil is exclusive to the Rythmik patented DVC design with the second coil for sensing.

http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/DS15TCMotorView.jpg


Here are a few quotes from the TC-1000 that can be applied here based on what “I see”:

It is housed in a 12 spoke cast aluminum frame. Each one is powered coated with an elegant silver metallic paint. The coil is suspended to the frame by our exclusive poly-cotton spider with woven in coil leads to eliminate unwanted lead-slap distortion. The diaphragm on the TC-1000 gets the same treatment as our more expensive models, namely, a solid piece of brushed aluminum, elegantly finished with a clear coat to ensure it will last. The cone is attached to the frame with our standard 1", highly linear and durable, Nitrile Butadiene rubber surround. ( http://www.tcsounds.com/tc1000.htm#design)

http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/DS15TCSpiderView.jpg


From this view you can see the poly-cotton spider with DVC intergraded woven leads and the sparkly power coating. The outside flange is dressed in a thick rubber boot and gasket to protect the driver and screws. A very cool feature of the solid aluminum cone (beside it’s good looks :D) is that it works as a heat sink. This is very important for a sealed enclosure and something I did not think until reading it.


We have a number of high-end diaphragm (cone) materials we primarily develop with. Our most common type of material is aluminum. It poses an excellent strength to weight ratio and it is extremely ridged. It also acts as a giant heat sink to help cool the voice coil without the need to make the voice coil longer which only adds weights to the moving mass and inherently makes the speaker worse and compromises mouthing depth. (http://www.tcsounds.com/tctop.htm#cone)
I can’t wait to hear how this is going to sound. I should be able to pickup some MDF and start assembling the box tomorrow.

Believe me I have no confusion here just trying to provide a review for others. I feel that solid documentation is very important probably because of years experience in the software engineering field. It would be nice to see a very well organized manual with all the information outlined clearly like the ones you see from Hsu, Velodyne and others. Then maybe everybody does not need to keep asking the same questions.

I am working on a user manual. The assembly is pretty much plug-and-play. I found the break-in time of 15" kit to be about 1 week, a bit longer than the 12" kits. SPL measurement can start immediately, but the sound will get tighter and more coherent after a week.

Chris,

It is unfortunately that yours bottom out. Somehow your unit/enclosure combination is too "efficient". What you heard was the spider hitting the top plate, so the voice coil was not affected. But I would still recommend you not to do it too often. You can put a white dot to the cone and let me know what excursion you are seen when you hit the bottom because that should be something around 2" peak-to-peak.

Brian

Rythmik Audio

I am working on a user manual. The assembly is pretty much plug-and-play. I found the break-in time of 15" kit to be about 1 week, a bit longer than the 12" kits. SPL measurement can start immediately, but the sound will get tighter and more coherent after a week.

Chris,

It is unfortunately that yours bottom out. Somehow your unit/enclosure combination is too "efficient". What you heard was the spider hitting the top plate, so the voice coil was not affected. But I would still recommend you not to do it too often. You can put a white dot to the cone and let me know what excursion you are seen when you hit the bottom because that should be something around 2" peak-to-peak.

Brian

Rythmik Audio

Don't worry about it Brian, it only happened a few times when I was finding the limits of the sub. It is playing fine now with no bottoming.

BTW, excellent news on the user manual. ;)

BlueEnergy

Well, ya finished yet?

:p

I found the break-in time of 15" kit to be about 1 week, a bit longer than the 12" kits. SPL measurement can start immediately, but the sound will get tighter and more coherent after a week.


I have reached the prototype stage. :) I built the MDF box yesterday it is very solid and well braced. I let the glue set over night and have a chance today to assemble it. To try it out I grabbed the first DTS disc I found Jurassic Park, wow the bass hit very hard pretty scary at first. :eek: I was thinking do I really need a 15"? Oh yeah!

I will leave the sub in the prototype stage for the break-in period. Then next weekend add some caulk to seal it up and some damping material. I will try to run REW tomorrow to get some measurements.

I'm always following these Rythmik servo sub builds with fascination. Great DIY projects. keep the pictures and measurements coming, Blueenergy!

Today the Almighty Google led me to what appears to be a new Rythmik website in the making? The server is Australian, which has me a little confused.

CLICK HERE (http://www.webworks.3corners.com.au/index.html)

In case you read this Brian, any chance we'll see a dual driver 15 / single amp configuration? How about black cones on the 15?


Dr V

Today the Almighty Google led me to what appears to be a new Rythmik website in the making? The server is Australian, which has me a little confused.
Wow, good catch. I didn't have a chance to do anything beyond looking at the front page, but it looks very professional!

I'm always following these Rythmik servo sub builds with fascination. Great DIY projects. keep the pictures and measurements coming, Blueenergy!

Today the Almighty Google led me to what appears to be a new Rythmik website in the making? The server is Australian, which has me a little confused.

CLICK HERE (http://www.webworks.3corners.com.au/index.html)

In case you read this Brian, any chance we'll see a dual driver 15 / single amp configuration? How about black cones on the 15?


Dr V

Oh, that site looks much better! :eek:

I think Brian has said before that the dual driver 15 kit would take up a whole lot of volume for the box. I think you would be better off just buying dual kits and stacking them.

I'm always following these Rythmik servo sub builds with fascination. Great DIY projects. keep the pictures and measurements coming, Blueenergy!

Here are a few pictures. First the front baffle being glued together with one 3/4 MDF with a 15 3/4" cutout to flush mount the driver. Then another 3/4 MDF with a 14" cutout. Followed by 1/4 plywood to give the T-Nuts something to bit into. Also shown is the internal brace. The box has 3/4 sides, top and bottom.


http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/15FrontBaffle.jpg


I wanted to wait and see what screws to use for mounting the driver once I receive it. I would only recommend using #10-32 Socket Head Cap screws (http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-776) which were a snug fit through the rubber boot. Plus the Allen head has a good a mount of safety by locking the driver to the screw so that it does not skip out. I have punch a hole in the rubber surround before using a screw gun on Phillips screws in the past. :rolleyes:

http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/MountHardware.jpg


Here the current box in it's raw form. You will see that some of the boards are a bit long. I followed the recommendation from Boxnotes (http://www.users.bigpond.com/bcolliso/freesoft.htm) to over cut the top and bottom panels by a 3/16". I will flush trim those boards later with a router. This technique work well in allow me to square up all the sides to a perfect 90 and not have to be held to trying to cut a prefect 90 on all four corners on the top and bottom.
http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/15RawBox.jpg


I did some measurements with REW and the result looked unbelievable. There was +2-3db slope from 10Hz to 25Hz then flat all the way to 100Hz. I am not sure that I know what I am doing with REW. To validate the results a bit I going to measure my "free" sub that came with my HTIB to compare. If anyone has a recommendation on how to setup REW I would be glad to run the tests that way.

Your results do not sound too good to be true, if thats what you're worried about.
http://www.hometheatershack.com/forums/bfd-rew-forum/

check out the sticky threads at the top.

I'm always following these Rythmik servo sub builds with fascination. Great DIY projects. keep the pictures and measurements coming, Blueenergy!

Today the Almighty Google led me to what appears to be a new Rythmik website in the making? The server is Australian, which has me a little confused.

CLICK HERE (http://www.webworks.3corners.com.au/index.html)

In case you read this Brian, any chance we'll see a dual driver 15 / single amp configuration? How about black cones on the 15?


Dr V

Paul in Australia is helping me build the new website. What is why Google finds it from there.

Chris is correct that to use the same amplifier to drive two drivers, I need to design the enclosure size approaching infinite baffle. In that regard, I am looking for more powerful plate amps. I have successfully implemented servo circuitry in BASH amplifiers (which is essentially a BTL class G amp). I should be able to characterize the results soon. I am also thinking about porting the servo circuitry to PA amps like Behringer (which is class H amp). The efforts there is definitely higher. But the NL4 4 wire speaker connector and cable seems to be perfect for servo application. That is what motivates me this time.

Brian

Rythmik Audio

Paul in Australia is helping me build the new website. What is why Google finds it from there.

Chris is correct that to use the same amplifier to drive two drivers, I need to design the enclosure size approaching infinite baffle. In that regard, I am looking for more powerful plate amps. I have successfully implemented servo circuitry in BASH amplifiers (which is essentially a BTL class G amp). I should be able to characterize the results soon. I am also thinking about porting the servo circuitry to PA amps like Behringer (which is class H amp). The efforts there is definitely higher. But the NL4 4 wire speaker connector and cable seems to be perfect for servo application. That is what motivates me this time.

Brian

Rythmik Audio

Thanks for the updates Brian. You certainly have a lot of projects going on.
I'd love to see the servo applied to an amplifier with balanced inputs, such as the Behringer you speak of.

Can you explain how the dual 12" driver / single amp combo implements the servo feedback with only 1 amplifier? Specifically how does it work if one driver suffers an anomaly, will both drivers will be sent the correction signal? Are two discreet servo feedback & correction signals maintained?

I hope my questions cause no disrespect to the OP's thread topic, but i figure most of us keeping current in the thread would benefit.

Thanx,
Dr V

Everything I've seen suggests the dual kit uses the same amp as the other kits. Therefore, it can't be two discreet correction signals, since it's a single channel amp. It would take a two channel amp and two servo circuits to keep the correction discreet. I would imagine the feedback coils in the dual kits just get wired in parallel or series, and fed to the single servo input on the amp. Since the dual kit uses 8ohm drivers, I would GUESS that the impedance on the servo coil is also changed so that wiring two servo circuits together results in a similar signal as the feedback in a single driver kit. Otherwise, I would think he'd have to have a different servo board for the dual kit (although perhaps he does anyway).

I did some measurements with REW and the result looked unbelievable. There was +2-3db slope from 10Hz to 25Hz then flat all the way to 100Hz. I am not sure that I know what I am doing with REW. To validate the results a bit I going to measure my "free" sub that came with my HTIB to compare. If anyone has a recommendation on how to setup REW I would be glad to run the tests that way.

Nope, you measured it right, the Rythmiks have exceptionally flat FR. ;)

http://i2.photobucket.com/albums/y22/crackyflipside/ht/14hz-near-85db.jpg

Paul in Australia is helping me build the new website. What is why Google finds it from there.

It looks very cool so far. From a pure marketing standpoint IMHO your current site is too crowded with techno mumbo jumbo and the products for sale don't have a clear presentation. You have great products just need some flashy marketing to show them off. :) Then supplement the product pages with links to the more technical stuff. When you integrate a PayPal shopping cart for purchasing you will not be able to keep up with the orders flying in. :D

Everything I've seen suggests the dual kit uses the same amp as the other kits. Therefore, it can't be two discreet correction signals, since it's a single channel amp. It would take a two channel amp and two servo circuits to keep the correction discreet. I would imagine the feedback coils in the dual kits just get wired in parallel or series, and fed to the single servo input on the amp. Since the dual kit uses 8ohm drivers, I would GUESS that the impedance on the servo coil is also changed so that wiring two servo circuits together results in a similar signal as the feedback in a single driver kit. Otherwise, I would think he'd have to have a different servo board for the dual kit (although perhaps he does anyway).

Darin, I agree. However if that is the case, and ONE driver misbehaves it will be corrected by the servo and the other driver will be forced to produce distortion because it is not misbehaving and yet receives the same input, or an equal proportion of the same input. I can't see this as being acceptable. Jury is out until Brian chimes in again. Cracky may have the best solution, just build scalable multiple single units with the potential to add another on top, or back to back. I did like the idea of using less power and making them more IB like.

Dr V

Thanks for the updates Brian. You certainly have a lot of projects going on.
I'd love to see the servo applied to an amplifier with balanced inputs, such as the Behringer you speak of.

Can you explain how the dual 12" driver / single amp combo implements the servo feedback with only 1 amplifier? Specifically how does it work if one driver suffers an anomaly, will both drivers will be sent the correction signal? Are two discreet servo feedback & correction signals maintained?

I hope my questions cause no disrespect to the OP's thread topic, but i figure most of us keeping current in the thread would benefit.

Thanx,
Dr V

No problem going off the 15" kit topic anything Rythmik is welcome here. I was on the fence between a dual 8ohm kit and the 15" for a while. There is some information that I shared in this thread Rythmik dual 12 kit (http://www.avsforum.com/avs-vb/showthread.php?t=768484).

if that is the case, and ONE driver misbehaves it will be corrected by the servo and the other driver will be forced to produce distortion because it is not misbehaving and yet receives the same input, or an equal proportion of the same input.
True, it really does nothing to improve anomalies that would be unique to an individual driver of a pair. Essentially, the correction signal would result in "half" of a correction (sine the magnitude of the anomaly would only show up as 50% if the other driver wasn't exhibiting the same anomaly), and therefore the anomaly would only be half corrected in the driver with with the anomaly, and half induced in the driver without it. Therefore a wash, and being the same as not being corrected at all. So the big question is, when using two identical drivers in the same enclosure operating under the same conditions powered by the same amp, how many anomalies are random enough that they aren't the same in both drivers? I would certainly think some, but certainly not the majority. If true, then two drivers sharing a single servo correction circuit might be a little inferior to discreet circuits, but probably still much better than no servo at all.
Jury is out until Brian chimes in again.
Very true. I'm just throwing in my educated guesses. :)

There is some information that I shared in this thread Rythmik dual 12 kit (http://www.avsforum.com/avs-vb/showthread.php?t=768484).
And that's probably where our comments belong. It's so easy to get off track. :o


P.S... I noticed this morning he now has graphs up comparing output and excursion of the various configurations. Interesting stuff.

Darin, I agree. However if that is the case, and ONE driver misbehaves it will be corrected by the servo and the other driver will be forced to produce distortion because it is not misbehaving and yet receives the same input, or an equal proportion of the same input. I can't see this as being acceptable. Jury is out until Brian chimes in again. Cracky may have the best solution, just build scalable multiple single units with the potential to add another on top, or back to back. I did like the idea of using less power and making them more IB like.

Dr V

I apologize to be off-topic again.
Darin is correct that I do have a different servo circuit for the dual 8ohm version. The circuit topology should be applicable to future IB models, if I can make that happen. The concern about how one driver's anomaly affects the other driver(s) is valid. So my effort is to minimize the impact.

I choose to drive those 2 drivers in parallel instead of in series. It will minimize the thermal difference of the two drivers. A series connection will make the thermal imbalance more prominent. Let us say one of them is already at higher temperature, so the Re is already higher than the other. If I had used a series connection, this higher Re will receive more power and therefore continue to rise more than others. The parallel connection does not have this problem. Higher Re receives less power. So you can imagine on the driver coil side, it's parallel, and on the servo feedback side, it is in series. One advantage is that you can add more drivers later on without changing the servo board. Also one can think of parallel connection as voltage drive (or steering) method and series connection as current drive (or steering) method.

Given this circuit topology, anomaly in one driver is corrected by both drivers, each doing half of the work. If those 2 drivers are placed next to each other, this shouldn't make much difference. We can imagine the whole system depends on two feedback, one is sum of the sensing signals, and the other is the current passing through both drivers when they are driven in parallel. It should be pretty robust.

Brian

Rythmik Audio

Brian,

Thanks for the explanation. Simple ohms law and good engineering practice. I can see now while not quite as perfect as a single driver unit, it does very much minimize the problem mathmatically.

Dr V

In that regard, I am looking for more powerful plate amps. I have successfully implemented servo circuitry in BASH amplifiers (which is essentially a BTL class G amp). I should be able to characterize the results soon.

Brian

Rythmik AudioI've been following this thread with great interest from the outset. Great work by blueenergy and I look forwards to seeing and hearing more about it.

Brian - had you considered using digital amps? To my mind they can be good enough for full-range amplification, and for sub duty, they have particular advantages such as relatively low power dissipation, easier harmonic filtering and subjective sound quality at low frequencies.

And would be too daft to ask whether you have an 18" on the drawing board? You already seem to have very successful products, and that must be an irresistable natural extension. Sorry for seeming to be greedy, but what price a 1000W 18" Rythmik sealed-box Direct Servo Sub kit?

Best regards, Nick

I was able to run a test with REW a few days ago to measure in-room response. To test is out a bit I watched 3 to 4 DVDs, so about 6- 8 hours of break-in at the time of the test. Keep in mind that this is my first "serious" sub and it is still unfinished. :o I have a lot to learning about in-room response and REW and sometime soon even BFD. The sub settings are Minimum dampening, 14Hz for bass extension, 180 degrees phase and 160Hz crossover. I am using a external USB Audio box connected directly to the sub for the test. I ran an automatic measurement from 10 to 125 Hz at 1/6 octave.

http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/ra15firstgraph12-27-06.jpg

Before running the tests I used the suggested Important Setting from HT Shack. (http://www.hometheatershack.com/forums/bfd-rew-forum/37-rew-room-eq-wizard-quick-links-faq-tips.html#post121) The chart looks pretty much what I was hearing during the test with some drops in volume at different points.

I am hoping that once the sub is past the break-in period this weekend that I can take it a part seal up the cabinet and install some dampening foam. By then it will have over 24 hours of break-in complete. Then run the same test to see if there are any improvements. If anyone has suggests on how the test should be done please let me know.

Very interesting, please keep us updated

I was able to run a test with REW a few days ago to measure in-room response. To test is out a bit I watched 3 to 4 DVDs, so about 6- 8 hours of break-in at the time of the test. Keep in mind that this is my first "serious" sub and it is still unfinished. :o I have a lot to learning about in-room response and REW and sometime soon even BFD. The sub settings are Minimum dampening, 14Hz for bass extension, 180 degrees phase and 160Hz crossover. I am using a external USB Audio box connected directly to the sub for the test. I ran an automatic measurement from 10 to 125 Hz at 1/6 octave.

http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/ra15firstgraph12-27-06.jpg

Before running the tests I used the suggested Important Setting from HTGuide. (http://www.hometheatershack.com/forums/bfd-rew-forum/37-rew-room-eq-wizard-quick-links-faq-tips.html#post121) The chart looks pretty much what I was hearing during the test with some drops in volume at different points.

I am hoping that once the sub is past the break-in period this weekend that I can take it a part seal up the cabinet and install some dampening foam. By then it will have over 24 hours of break-in complete. Then run the same test to see if there are any improvements. If anyone has suggests on how the test should be done please let me know.

Ok, do a test where the mic is a few feet away from the sub so you get nearfield response because the in-room response looks crazy, lol.

I don't think there's really anything all that unusual about the in-room response... rooms do crazy things to response curves. It at least looks like he's getting decent in-room response down to 10hz... pretty much like the rest of us. :) Tweaks to positioning may help the peaks and valleys, and some EQ could help even further. blueenergy, since you can generate these curves fairly easily now, you may want to experiment with running sweeps with the mic in different listening, just to get an idea of how different the response can be just by moving a few feet here and there. Ultimately, if you've got the flexibility, you'll want to play with as many sub positions as possible and try and find a place that gives a good combination of output and smooth response.

I realize it's still not really finished yet, but do you have any initial subjective impressions yet?

I was able to finish sealing the box and installed 3 sheets of acoustic foam (http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-525) on all the walls. This should get rid of the standing waves and give me a very dead box. I also glued the T-Nut into place with Ultimate glue since half of them fell out when taking the driver out. Now the sub is completely finished (except for veneering) and ready for full testing and listening.

Ok, do a test where the mic is a few feet away from the sub so you get nearfield response because the in-room response looks crazy, lol.
To start with I setup a in-room nearfield test only about 6" away from the box.

http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/NearFieldTest.jpg

This resulted in a beautiful house curve. Climbing up from the 14Hz Base Extension setting to a +3db in the upper teens and running very flat down to 100Hz. Very impressive. :D

http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/ra15nearfield1-1-07.jpg

I don't think there's really anything all that unusual about the in-room response... rooms do crazy things to response curves. It at least looks like he's getting decent in-room response down to 10hz... pretty much like the rest of us. :) Tweaks to positioning may help the peaks and valleys, and some EQ could help even further. blueenergy, since you can generate these curves fairly easily now, you may want to experiment with running sweeps with the mic in different listening, just to get an idea of how different the response can be just by moving a few feet here and there. Ultimately, if you've got the flexibility, you'll want to play with as many sub positions as possible and try and find a place that gives a good combination of output and smooth response.
The in-room response has improved some. After moving the sub around to the different corners in the room (man is this thing heavy). I found that it had the best response closest to center up front near the entertainment cabinet.

http://i117.photobucket.com/albums/o74/blueenergy/Rythmik/ra15listeningposition1-1-07.jpg

I can live with this curve and adjust it some once I have the BFD hooked up.

I realize it's still not really finished yet, but do you have any initial subjective impressions yet?

So far the sub has a great amount of output and great quality of sound. I have been watching the Battlestar series on DVD and it has been giving the sub a great workout, you can really feel the action.

I have set the levels for all channels to blend with the Avid DVD and pink noise. The sub is a bit muted at times since the LFE varies by DVD or type content. So I find that the sub is missing and have to adjust its level at times. I also believe that the Main and Center channels are holding the whole system back. They are simple MTM that came with my HTIB and offer little midbass. The front speakers will be my next project and those should have higher output and more midbass then hopefully I can blend things better.

I have a few Superbit DVDs on the way which should provide alots of good sound quality. I will listen closely to those and ask the wife how she likes the sound.

The sub settings are Minimum dampening, 14Hz for bass extension
Is this still how you have it set? FWIW, the high damping setting will provide the flattest response, while the min damping will give a bit of bass boost, and a steeper rolloff below the boost. The following helps to compare the three settings (all at 14hz):

http://www.rythmikaudio.com/pic/servo/14hz.jpg

Of course, you may have already known that, just pointing it out in case. :)

Regardless, your final in-room response looks great, especially considering that's pre-EQ. A little bit of attenuation of that minor hump between 30-50hz, and you're about as flat as you could hope for for in-room response. If are ARE running at low damping, changing to high would probably also reduce that hump around 20hz, and simultaneously raise the output a little down in the teens.

Is this still how you have it set? FWIW, the high damping setting will provide the flattest response, while the min damping will give a bit of bass boost, and a steeper rolloff below the boost. . . Regardless, your final in-room response looks great, especially considering that's pre-EQ. A little bit of attenuation of that minor hump between 30-50hz, and you're about as flat as you could hope for for in-room response. If are ARE running at low damping, changing to high would probably also reduce that hump around 20hz, and simultaneously raise the output a little down in the teens.
Thanks for pointing that out Darin. After some testing I found that the Middle damping setting gave the best results (as in flattest response) for my room for both nearfield and from the listen position.

Yes, having the ability to change the filters with those switches is quite convenient. :)

Those graphs look great now!

I have a few Superbit DVDs on the way which should provide alots of good sound quality. I will listen closely to those and ask the wife how she likes the sound.

The phase lag of 15" kit at 80hz is about 30-45 degrees more than the 12" kit. I would recommend to set the delay time adjustment on the HT receiver menu to be about 2-3 ft farther than the actual physical distance. By doing this, we put a phase lead on the sub that will compensate the phase lag so that the phase alignment between the front speakers and sub is close to the ideal zero phase difference. Non-ideal phase alignment may cause a response dip at the mid bass. The ideal adjustment will certainly depend the front speakers and the xover frequency. I am looking forward to your wife's opinion ;)


Brian
Rythmik Audio

The phase lag of 15" kit at 80hz is about 30-45 degrees more than the 12" kit. I would recommend to set the delay time adjustment on the HT receiver menu to be about 2-3 ft farther than the actual physical distance. By doing this, we put a phase lead on the sub that will compensate the phase lag so that the phase alignment between the front speakers and sub is close to the ideal zero phase difference. Non-ideal phase alignment may cause a response dip at the mid bass. The ideal adjustment will certainly depend the front speakers and the xover frequency. I am looking forward to your wife's opinion ;)


Brian
Rythmik Audio

Thanks for the recommendation. That reminds me that I should do some measures with the receiver and the main to see if everything is blending together well. If there is an infinite 0 - 180 degree phase control on the RA amp why not use that? Is it simpler to just change the base management in the HT receiver?

My wife is slowly getting on broad and has agreed to adjust the seating area a bit so that the sub will fit better up front. :)

Thanks for the recommendation. That reminds me that I should do some measures with the receiver and the main to see if everything is blending together well. If there is an infinite 0 - 180 degree phase control on the RA amp why not use that? Is it simpler to just change the base management in the HT receiver?

The phase adjustment on the RA amp is only for phase lag adjustment. In other words, it cannot adjust from 0 backward to -180 degrees. On the other hand, the delay time adjustment can do both phase lead and phase lag.


Brian
Rythmik Audio

Great post! Newbie question to Brian from a potential soon to be Rythmik kit builder. I'm entertaining the idea of two 12" kits, to experiment with mono or stereo subs at a single or multiple location.

Just want to clarify, you are saying that all speakers in the system using bass management should be delayed, in relationship to the sub signal, on top of the delays needed to match any other speaker distances? (My receiver only allows delay of center and surrounds, guess I could use a digital EQ to delay the main L/Rs)

Great post! Newbie question to Brian from a potential soon to be Rythmik kit builder. I'm entertaining the idea of two 12" kits, to experiment with mono or stereo subs at a single or multiple location.

Just want to clarify, you are saying that all speakers in the system using bass management should be delayed, in relationship to the sub signal, on top of the delays needed to match any other speaker distances? (My receiver only allows delay of center and surrounds, guess I could use a digital EQ to delay the main L/Rs)

What you describe is correct (that is, it is the same thing). Keep in mind, if you want to "delay" the center channel, you need to set its distance to be shorter. If you want the opposite effect (phase lead), then set its distance to be farther. It is counter-intuitive. One can easily translate distance to phase. 80hz sound wave has a wavelength of 12ft. That means it is 30 degrees adjustment for each foot. Actual optimal adjustment depends on a lot of factors. So it definitely needs a couple of iterations.

-Brian

Blueenergy, how is the sub sounding at this point? I've got a 15" kit of my own on the way, and am jonesing for info/listening impressions!

Well I experience my first Superbit DVDs over the weekend. I was very impressed with the image quality on my 50" 1080p display and the DTS sound track.

The movie Vertical Limit (http://www.amazon.com/Vertical-Limit-Superbit-Collection-ODonnell/dp/B00005V5NW) gave the 15" sub quite a workout. It really come to life late in chapter 2 when some Pakistani guy says that it is 3'o clock and time to wake up the Indians and they start firing off heavy artillery guns. Holy Crap I think that I might have waked up the house across the street! :eek: Lots of subsonic action, definitely felt the guns firing in room. Later in the movie there of lots of avalanche screens and sub provided lot of rumbling noise as the snow was coming down the mountain.

Overall I am very happy with the new sub, it is giving me the "impact" that I was seeking for Home Theater. As I have stated before the sub is now over powering the wimpy speakers that remain from the HTIB the Rythmik has much more headroom than my mains do. Those will be the next project. I start with the servo kit for upgrading my HT because it was so simple to build and the old was hardly noticeable. I only have about 16 hours into the whole project from design to the semi-finish state now. The final steps will be integrating a BFD and veneering the cabinet in a few weeks or so.

blueenergy, great stuff! Seems like you're happy with the outcome.

What is your favorite damping setting? low, medium, or high?

Post #49

blueenergy said:

"After some testing I found that the Middle damping setting gave the best results (as in flattest response) for my room for both nearfield and from the listen position."

Thx.

If anyone finds this interesting, i've found the middle setting to be the sweet spot on the 12" sub as well.

After having a few sealed subs in this room i've decided that the decrease in transient response performance associated with medium Qtc's was definitely worth the trade-off in increased output @ the more audible frequencies.

So, for future sealed projects i'll aim towards a qtc of .707 and possibly work my way down with EQ/power...when necessary. fortunately it isn't necessary in my current living situation ;)

Thx.

If anyone finds this interesting, i've found the middle setting to be the sweet spot on the 12" sub as well.

After having a few sealed subs in this room i've decided that the decrease in transient response performance associated with medium Qtc's was definitely worth the trade-off in increased output @ the more audible frequencies.

So, for future sealed projects i'll aim towards a qtc of .707 and possibly work my way down with EQ/power...when necessary. fortunately it isn't necessary in my current living situation ;)

hello my friend...long time...now what's with this .707 bidness? :p

Martin! howdy.

Yeah I asked myself the same question...Then I took a few variables into consideration. The sound of the Rythmik driver alone is very clean and is almost impossible to sound boomy even at the low damping setting (subjectively). Q = 1.1 IIRC. My room is ~1040ft^3 so I wouldn't need that much improved output below 20hz with this type of room gain going on. So the happy medium for me is Q=.707.

So, for future sealed projects i'll aim towards a qtc of .707 and possibly work my way down with EQ/power...when necessary. fortunately it isn't necessary in my current living situation ;)

I'm somewhat new at all this, and still trying to learn, but I was under the impression that parametric EQ can only raise Qtc; i.e. it is impossible to lower Qtc with PEQ, and PEQ always raises Qtc. You can do interesting things with a LT circuit, but this is not used with the servo amp. Am I mistaken?

I'm just trying to verify my "knowledge" on this topic, and alter/expand it if necessary.

Thanks.

What Exocer is talking about isn't PEQ. He is referring to the damping factor setting on his Rythmik's amp.

Yes.
Also, work my way down as in use a behringer deq like device to emulate an LT circuit, for future projects that do not include the Rythmik amp.

Any updates blueenergy?

WOW! That sub rocks! I think I'm a soon to be Rhythmic owner! 15" here I come!!!

What was your total cost for your project? You have inspired me!

I'm somewhat new at all this, and still trying to learn, but I was under the impression that parametric EQ can only raise Qtc; i.e. it is impossible to lower Qtc with PEQ, and PEQ always raises Qtc. You can do interesting things with a LT circuit, but this is not used with the servo amp. Am I mistaken?

I'm just trying to verify my "knowledge" on this topic, and alter/expand it if necessary.

Thanks.

You are correct. The reason is the bandwidth for the PEQ needs to be very narrow and only high Q bandpass and bandstop filter can do that. Personally I think PEQ is complementary to LT or servo, not competing. BTW, LT is not used in servo as that is the whole purpose of servo.

Brian

Rythmik Audio

WOW! That sub rocks! I think I'm a soon to be Rhythmic owner! 15" here I come!!!

What was your total cost for your project? You have inspired me!

I would also be interested in the cost info, as well as any final pics if you have them! Did you end up using wood veneer?