[Tyson]

Yes, earlier in the thread Danny said I'd need a separate amp for the second sub.  I think the issue is running servo cables more than a few feet won't work.

Yep, servo amps need to be as close to the woofers as possible.  The shorter the better. 

[Captainhemo]

and.... yes,  Tyson  has the  win with the slam   

And aside from not being  stereo without the  2nd amp,   yes you  need the  2nd amp  to keep the   run lengths as short  as possible,  you  can't split   2  drivers/one amp from one side of the room to the  other

jay

[Early B.]

yes you  need the  2nd amp  to keep the   run lengths as short  as possible,  you  can't split   2  drivers/one amp from one side of the room to the  other

I've heard that many times, but there's never an explanation for the short run lengths. I've combed through the Rythmik Audio website and the instructions for my 370 amp, and unless I missed it, there's no mention of a requirement or suggestion for shorter wire length. Over the years, I've seen a few images of guys who used long runs, so it appears to work for them. In what way do long runs affect the servo circuit?

[Hobbsmeerkat]

I can see it being an issue for the servo circuit, but I'm guessing it could also be a power droop or time delay issue?
But without a kit on hand to test, I'm not exactly certain what the reason is..

[Sonicjoy]

I'm sure it is the time delay that is the issue. Servo control works on sensing the movement of the voice coil and correcting any deviations from the input signal thus the times we are talking about are very short and and the longer the cables the longer it takes for the signal to travel back and forth causing delays in response times.
 

[Early B.]

Are these time delays theoretical??  We're only talking about an extra few feet of wire. At what point does the length of wire become problematic or audible? Fifty feet? One hundred feet? Probably not 5 or 6 feet.

 

[Hobbsmeerkat]

I'm guessing it has more to do with the servo circuit, which im guessing is more likely to use a much lower voltage than the driver circuit, so I imagine its going go be more sensitive to distance than the primary circuit.

[Sonicjoy]

Yes we are talking about the feedback circuit not the audio.

[Early B.]

Sort of my point -- we're all guessing.

It would be great if Brian at Rythmik Audio could provide us with a definitive response since he designed the circuit. Alternatively, Danny has mentioned the short wire approach more than once, so maybe he knows the "why."

Another option is for someone who is techno savvy is to add several additional feet of wire from their servo amps to the woofers and measure the differences (not sure how or what you'd be measuring which is why I can't do it) and also determine if you can hear any differences. That would be a quick and cool experiment.

I'm interested in the outcome primarily for aesthetic purposes. I'd like the option of positioning my amps further away from the drivers.

 

[Larpy]

Thanks for all the replies.  The consensus seems to be in favor of a second sub for "stereo bass."  But I'm not exactly sure what you all mean by that.  If my crossover is set to 80Hz, how can I possibly hear frequencies below that in "stereo"?

[Early B.]

Thanks for all the replies.  The consensus seems to be in favor of a second sub for "stereo bass."  But I'm not exactly sure what you all mean by that.  If my crossover is set to 80Hz, how can I possibly hear frequencies below that in "stereo"?

You're right -- most recorded music doesn't separate the bass tones for stereo output. However, some recordings have stereo bass and you definitely want to hear it.
One more thing -- if you're using servo subs, you'll want to set the crossover to something like 150Hz. One of the main benefits of servo subs is their ability to play higher.   

[sruffle]

I thought about posting a new thread but my situation is pretty similar to Lampy's so I thought I would keep it here.  Like Larpy, I have very recently taken the plunge to open baffle.  Right now I have the LiiAudio Crystal 10s in a baffle running full range powered by my Decware 2 watt amp.  My subwoofer is an Omega Deep 8 (sealed 8 inch downward firing woofer) which is high-passed and crossed over at 110 hz. 

After making adjustments to the subwoofer, it feels like it is integrated well and I am pretty happy with the sound.  All that said, the idea of open baffle bass with a servo amp(s) is very appealing.  However, space limitations are a problem.  The only way I may be able to accommodate dual subs is to emulate the setup shown in the picture above where one woofer is used in a separate box underneath the main full range driver.

I have lots of questions on the viability of this scheme but will ask a few basic ones:

1) How high can an OB sub play without sounding localized?  The small Omega sub does very well in that it is cut over at a fairly high frequency but still blends well.

2) Where actually can the servo amp(s) be placed (I don't see it in the cabinet design plans)

3) Can the SW-12-08 woofer be placed on the front of the baffle underneath the full range driver or does it need to be recessed into a cabinet?  If it is placed on the front of the baffle I would build a partial cabinet behind it.

4)  Am I making things too difficult?  Is it just more practical to keep what I have or buy a Servo Sub kit 2 and stick with a sealed subwoofer?

Any thoughts or comments are greatly appreciated.

[guf]

great update! good job for following through. I'm excited to see how it tuns out in the end.

[Larpy]

Well, I've got a second 370PEQ and SW-12-08 driver on the way.  I don't know that I "need" a second sub, but I like the idea of symmetry, and the second H-frame is already built. . . .

Sruffle, I can answer at least one of your questions:  the amp comes with around 32" of hard-wired speaker cables.  I decided I wanted a bit more length, so I cut the stock wire and built a wood enclosure with two sets of binding posts (one for the driver coil and one for the servo coil).  I have 4 feet of cable going between the amp and the subwoofer.  Here's a photo:



In previous threads, Danny has insisted that the sub needs to be close to the amp.  That's why I'm not using my one amp to power two subs.  In my situation, the cable would be too long.  But I don't hear any issues with my 4' cable length.

[Early B.]

1) How high can an OB sub play without sounding localized?  The small Omega sub does very well in that it is cut over at a fairly high frequency but still blends well.

2) Where actually can the servo amp(s) be placed (I don't see it in the cabinet design plans)

I'll take a stab at these two questions...

1. It's an audio myth that bass below 80Hz can't be localized. Don't believe me? Take any sub and move it around your room. There's a 99% chance you'll be able to tell where the sound is coming from. OB subs aren't any different.

2. Servo amps are typically placed directly behind the sub. 

[sruffle]

I'll take a stab at these two questions...

1. It's an audio myth that bass below 80Hz can't be localized. Don't believe me? Take any sub and move it around your room. There's a 99% chance you'll be able to tell where the sound is coming from. OB subs aren't any different.

2. Servo amps are typically placed directly behind the sub.

thanks for the reply.  I don’t have much flexibility with where I can put my sub but I believe you.  I have that thought in the back of my mind when considering the idea of two subs or low frequency woofers.

[sruffle]

Well, I've got a second 370PEQ and SW-12-08 driver on the way.  I don't know that I "need" a second sub, but I like the idea of symmetry, and the second H-frame is already built. . . .

Sruffle, I can answer at least one of your questions:  the amp comes with around 32" of hard-wired speaker cables.  I decided I wanted a bit more length, so I cut the stock wire and built a wood enclosure with two sets of binding posts (one for the driver coil and one for the servo coil).  I have 4 feet of cable going between the amp and the subwoofer.  Here's a photo:



In previous threads, Danny has insisted that the sub needs to be close to the amp.  That's why I'm not using my one amp to power two subs.  In my situation, the cable would be too long.  But I don't hear any issues with my 4' cable length.

Larpy- thanks for the picture.  It is very helpful.  This question will expose what a novice I am.  How are you getting the signal from your source to the two Servo amps?

[Danny Richie]

1) How high can an OB sub play without sounding localized?  The small Omega sub does very well in that it is cut over at a fairly high frequency but still blends well.

Anything over about 80Hz starts getting pretty directional, and that is with any sub.

2) Where actually can the servo amp(s) be placed (I don't see it in the cabinet design plans)

Anywhere you want so long as the leads to the woofer are kept short.

3) Can the SW-12-08 woofer be placed on the front of the baffle underneath the full range driver or does it need to be recessed into a cabinet?  If it is placed on the front of the baffle I would build a partial cabinet behind it.

For the best performance it should be placed into an H frame design. And it isn't used as a single. They are designed to be used in pairs with one amp.

4)  Am I making things too difficult?  Is it just more practical to keep what I have or buy a Servo Sub kit 2 and stick with a sealed subwoofer?

I'd say that if you go open baffle servo subs then you'll never go back to anything else.

[Danny Richie]

In previous threads, Danny has insisted that the sub needs to be close to the amp.  That's why I'm not using my one amp to power two subs.  In my situation, the cable would be too long.  But I don't hear any issues with my 4' cable length.

Your 4' length could be causing some loss of control. You may notice some improvement by shorting that up.

[sruffle]

Anything over about 80Hz starts getting pretty directional, and that is with any sub.

Anywhere you want so long as the leads to the woofer are kept short.

For the best performance it should be placed into an H frame design. And it isn't used as a single. They are designed to be used in pairs with one amp.

I'd say that if you go open baffle servo subs then you'll never go back to anything else.

Many thanks for your comments.  I may be able to rearrange my layout to make room for one H frame or W frame sub.   Before making any decisions, the next step is to get a decent microphone and do some measurements to better understand what is going on.

Even with the limited amount of mid bass that the Crystal 10s are putting out, I am getting a very small flavor of what open baffle bass is like.  I can uNderstand the comments that once you hear it, you never go back.