[BigPines]

My first post here.

I am thinking about building one of the dual servo kits (specifically using the SW-12-08). The DS1200 and DS1500 can't be used in dual configurations anyway can they? The reason I am thinking about dual 12" drivers instead of a single 15" is based simply on air displacement and usable excursion. Two SW-12-08s move more air than one DS1500. The combined Sd of two SW-12-08s is 981 sq.cm vs. approximately 809 sq.cm for the DS1500. Based on my calculations, a dual SW-12-08 displaces more air in it's recommended cabinet size at both 20Hz and 30Hz while maintaining more available excursion for headroom.

What is the mounting depth of the SW-12-08 driver? I could not find that information anywhere.

I already happen to have a cabinet with approximately 3.6 sq.ft of internal volume and I'd like to use it if possible. I know this is a bit larger than the recommended 3.2 sq.ft for this kit but will it work? I was originally thinking of using a H600PEQ amp but given the extra internal cabinet volume, is that advised? Should I use either the A370PEQ or even the A300 due to the larger internal volume? I would prefer to go with the most amount of power but I don't want to bottom the woofers either. I know I could just throw some 2x4s in the cabinet and call it bracing to take up the extra volume but I'd rather not if I don't need to.

One more thing...If I wanted to get REALLY crazy and use 4 woofers in a HUGE cabinet, could I wire four SW-12-04s in parallel and then wire those two pairs in series to present the amp with a 4 ohm load? If this is possible, I would like to use the H600PEQ. What would the sensor coil wiring look like? 

That is is for now.

Thanks in advance.

Mike

[dvenardos]

Sounds like you are building the same sub as stereodude. This thread might be helpful:
http://www.audiocircle.com/index.php?topic=64259.0

[BigPines]

Thanks. I saw that thread but it didn't answer some of my questions. I wonder where he is at in his build? I should ask him.

Mike

[Danny Richie]

The DS1200 and DS1500 can't be used in dual configurations anyway can they?

No.

What is the mounting depth of the SW-12-08 driver?

About 6.5" from the mounting surface.

I already happen to have a cabinet with approximately 3.6 sq.ft of internal volume and I'd like to use it if possible. I know this is a bit larger than the recommended 3.2 sq.ft for this kit but will it work?

That will work just fine. The servo control system takes control of the driver. More air space means slightly less gain is needed to maintain linearity so the amp will actually have a little more head room.

The A370PEQ will work fine for you on the pair of woofers.

One more thing...If I wanted to get REALLY crazy and use 4 woofers in a HUGE cabinet, could I wire four SW-12-04s in parallel and then wire those two pairs in series to present the amp with a 4 ohm load?

With this control system you can't series/parallel these things.

[Stereodude]

Thanks. I saw that thread but it didn't answer some of my questions. I wonder where he is at in his build? I should ask him.

Mike

I haven't started cutting wood yet, but the design is basically done and I have all the raw materials.  The total lack of CAD drawings of the parts makes the design side much more difficult.

[BigPines]

I already happen to have a cabinet with approximately 3.6 sq.ft of internal volume and I'd like to use it if possible. I know this is a bit larger than the recommended 3.2 sq.ft for this kit but will it work?

That will work just fine. The servo control system takes control of the driver. More air space means slightly less gain is needed to maintain linearity so the amp will actually have a little more head room.

The A370PEQ will work fine for you on the pair of woofers.

Thanks for the answers. Can you give me a bit more information on what happens if I use a larger/smaller cabinet with these servo subs? My understanding is the servo basically tries to keep the FR flat to 14Hz. If the cabinet is smaller, is the F3 higher or the amp just has to work harder to keep the sub flat? If the cabinet is larger (as in my case) will the F3 be lower or the amp just has to work less? The main thing I am concerned about is available excursion. The larger the cabinet, the more excursion will be taken up but the same amount of power right or does the servo kick in and stop the excursion at a certain point? I am mainly concerned about damaging the drivers. If the cabinet is too large and I put too much power to the drivers I think I could bottom them. I have bass box pro. Are the servo virtual T/S parameters available so I can simulate the excursion? I'd like to use the 600 watt amp but I have a feeling there is not enough throw in these two drivers in this cabinet. For that reason, I'd like to at least use three 8 ohm drivers in parallel for a 2.7 ohm load but I guess the amps can't handle that. Do they just get hotter with lower impedance loads? Could I just add a larger heat sink?

Sorry for all the questions.

One more thing...If I wanted to get REALLY crazy and use 4 woofers in a HUGE cabinet, could I wire four SW-12-04s in parallel and then wire those two pairs in series to present the amp with a 4 ohm load?

With this control system you can't series/parallel these things.

Thanks. That is what I figured but I thought I'd ask anyway. Too bad the amp isn't rated to 1 ohm.

Mike

[BigPines]

I haven't started cutting wood yet, but the design is basically done and I have all the raw materials.  The total lack of CAD drawings of the parts makes the design side much more difficult.

You are doing a sealed sub right? That shouldn't be that difficult. Bass Box Pro will give you a parts list for a particular design.

-EDIT- Never mind. I just looked at the second page of your thread. You are planning some *SERIOUS* bracing there.

Please keep us update. I'd love to see pictures and hear what you have to say about sound quality.

Mike

[Danny Richie]

My understanding is the servo basically tries to keep the FR flat to 14Hz.

It is advertised to be flat to 20Hz. It certainly can reach -3db points down in that range though. It also depends on the amp settings.

If the cabinet is smaller, is the F3 higher or the amp just has to work harder to keep the sub flat?

The F3 is the same. The amp just has to work a little harder.

If the cabinet is larger (as in my case) will the F3 be lower or the amp just has to work less?

The F3 is the same and the amp has to work less.

The larger the cabinet, the more excursion will be taken up but the same amount of power right or does the servo kick in and stop the excursion at a certain point?

The servo senses and maintains a linear output then electrically stops the woofer after the signal has ended.

Are the servo virtual T/S parameters available so I can simulate the excursion?

I don't have any way of measuring the new virtual T/S parameters after the servo takes over. The standard T/S parameters are listed on our site but are really of little value once the servo system is connected.

I'd like to use the 600 watt amp but I have a feeling there is not enough throw in these two drivers in this cabinet.

One of the applications that Brian designed the 600 watt amp for was to drive a pair of the SW-12-08's. If you think about it, each woofer only sees 300 watts each. The single SW-12-04 sees more power than that from the A370PEQ amp. So even in the slightly larger box I don't think you'll have any problems with the 600 watt amp on them.

Strictly for sound quality, I would however recommend the use of additional woofers if you are pushing a pair of these or even a single woofer to its limits during play.

Do they just get hotter with lower impedance loads?

The amp is not rated to handle less than 3 ohms.

[BigPines]

Thanks Danny.

I meant the F3 was 14Hz.

Yeah, it's too bad we don't have the virtual T/S params. That would be educational.

I think I will try the 600 watt amp then. Yeah, it makes sense that since each woofer is only seeing 300 watts I should be OK. Yeah, I currently have two dual 12" subs. I would like to build one of these Rhythmiks to see how I like it. If I like it (and I expect I will). I will certainly build a twin for it. My room is not that large but I like lots of headroom as you can see.

Too bad the amp can't handle 2.7 ohms. A triple header would be REALLY cool. Maybe even two of them.

Mike

[BigPines]

I haven't seen this mentioned anywhere either. Should poly fill/fiberglass be used in these servo cabinets? Does this effectively do the same thing as using a larger cabinet and allow the amp to work less hard? I assume it is good for a little internal vibration damping as well.

[Stereodude]

As I understand it...  Basically think of the Servo system as a feedback based EQ.  The closer your design is to the desired response the less "EQ correction" it applies.

Ultimately you are power and excursion limited.  Design your sub to stay within the excursion limits of the drivers using the power on tap from the amp and the Servo will do the rest.

[BigPines]

As I understand it...  Basically think of the Servo system as a feedback based EQ.  The closer your design is to the desired response the less "EQ correction" it applies.

Ultimately you are power and excursion limited.  Design your sub to stay within the excursion limits of the drivers using the power on tap from the amp and the Servo will do the rest.

Yeah, I think this is exactly the right way to think about it. The problem is, it is really hard to know when you are reaching your excursion limits when you can't simulate the driver because you don't have accurate T/S params due to the servo interaction. 

Mike

[Stereodude]

The problem is, it is really hard to know when you are reaching your excursion limits when you can't simulate the driver because you don't have accurate T/S params due to the servo interaction. 

Mike

Sure you can.  The servo can't add excursion to the woofer and it can't make the amplifier put out more power.  So the two key design constraints in the limits of a sealed sub are set regardless of there being servo based feedback.  You can still determine the max output of the sub at any given frequency.

So if a pair of drivers in say 3.5 cu-ft can take 370W all the way down to 10Hz and below without bottoming then you're fine.  You want to make the box bigger you can, just make sure the available power doesn't push the drivers past their excursion limits.  The same goes for polyfill, or fiberglass...  Just watch the excursion.

[BigPines]

The problem is, it is really hard to know when you are reaching your excursion limits when you can't simulate the driver because you don't have accurate T/S params due to the servo interaction. 

Mike

Sure you can.  The servo can't add excursion to the woofer and it can't make the amplifier put out more power.  So the two key design constraints in the limits of a sealed sub are set regardless of there being servo based feedback.  You can still determine the max output of the sub at any given frequency.

So if a pair of drivers in say 3.5 cu-ft can take 370W all the way down to 10Hz and below without bottoming then you're fine.  You want to make the box bigger you can, just make sure the available power doesn't push the drivers past their excursion limits.  The same goes for polyfill, or fiberglass...  Just watch the excursion.

No but the servo *DOES* add effective EQ by changing the T/S parameters which *DOES* change the excursion at the effected frequencies with a given amount of power or am I thinking about this all wrong?

Mike

[rythmik]

No but the servo *DOES* add effective EQ by changing the T/S parameters which *DOES* change the excursion at the effected frequencies with a given amount of power or am I thinking about this all wrong?

Mike

Mike,

Servo does not increase the efficiency of the system. So we can still do simulation. However, the simulation results show the max excursion in a particular power and enclosure combination. The trick is to select a combination that would make best use of the driver without bottom-out. Also we can design the Q value of the driver so that we can take advantage of fact that physical max output and actual frequency response are now separated.  Actually, if we bring in the equivalent circuit Q value, there are 3 Q values in the system (not be confused with the 3 Q value our plate amp offers), the physical Q value after loaded in the enclosure, the equivalent Q value with servo (normally 0.3 or lower), and the Q value of the roll-off that determines the time domain ringing behavior.

If one uses H600, it is very comfortable for two drivers to share an enclosure size of 1.5*2=3 cu ft. If one still uses 370WRMS to drive two drivers, I would increase the enclosure volume to something like 2.2*2=4.4 to compensate for the power difference. This clearly demonstrate the trade-off between enclosure volume and required power at the bottom end. Of course one may contend the midbass output is not affected by enclosure volume. My explanation would be we have plenty of headroom in mid-bass range with our subwoofers we don't need high power amp to squeeze out output in that frequency range. We do need power to get us sufficient low end output and enclosure volume does help that.  

-Brian