OB servo subs - output and EQ

sfdoddsy · « **Reply #20 on:** 8 Oct 2009, 02:07 am »

Thanks Brian. That does clarify things. The 4:1 OB to sealed ratio is about what I expecting, and I guess 101dB would be possible with 6dB or so of room gain.

Unfortunately my room is very big so I don't get that much room gain, so it sounds like I would need to cross to monopole subs for the deep and loud stuff, and of course for HT.

I was planning on trying out a pair of the 12" GR servo subs in a sealed so I might start there, if they ever respond to my email.

Just as a matter of interest, if I wanted to get some idea of the OB 12s capability, could I use the regular SW12s and pre-EQ them using my DCX? Would the servo still work in this scenario?

rythmik · « **Reply #21 on:** 8 Oct 2009, 01:50 pm »

Quote from: TomS on 7 Oct 2009, 12:20 pm

Quote from: rythmik on 7 Oct 2009, 12:07 pm
...
BTW, one single A370 can drive up to 4 SW12-16. I haven't seen anyone going to that extreme.

Brian
Brian,

So are there already 4 sets of connections for servo loops and drivers if using a single 370PEQ with 4 OB drivers? That is, if for some crazy reason someone might want 4 OB drivers per side and only 2 amps

Tom

You bet. I have those connector assembly, available for anyone who wants to go with 4 drivers and one amp.

Brian

rythmik · « **Reply #22 on:** 8 Oct 2009, 02:01 pm »

Quote from: sfdoddsy on 8 Oct 2009, 02:07 am

I was planning on trying out a pair of the 12" GR servo subs in a sealed so I might start there, if they ever respond to my email.

Just as a matter of interest, if I wanted to get some idea of the OB 12s capability, could I use the regular SW12s and pre-EQ them using my DCX? Would the servo still work in this scenario?

The servo network for SW12-16 is different from SW12-4. So we cannot mix the two. Also OB version has a shelving function built-in. But most importantly is SW12-4 has a Qts value of 0.4 and SW12-16 has a Qts value of 0.9. This factor of 2x difference is what makes SW12-16 to have 1.4x (the formula is square-root of Qts ratio) of the excursion at Fs point (or around it). In other words, SW12-16 is really made for OB and SW12-4 isn't. You can still use it, but you won't be able to use its full excursion potential in OB. When I looked at Siegfried's website, he listed a 10" Peerless driver with Qts of 0.17 as a potential candidate driver. That is plainly wrong. I understand some see him as an icon. But sometimes, you cannot be right on everything. And that includes me.

Brian

jtwrace · « **Reply #23 on:** 8 Oct 2009, 02:11 pm »

Quote from: rythmik on 8 Oct 2009, 02:01 pm

Quote from: sfdoddsy on 8 Oct 2009, 02:07 am
I was planning on trying out a pair of the 12" GR servo subs in a sealed so I might start there, if they ever respond to my email.

Just as a matter of interest, if I wanted to get some idea of the OB 12s capability, could I use the regular SW12s and pre-EQ them using my DCX? Would the servo still work in this scenario?

you cannot be right on everything. And that includes me.

Brian

You should TM that!

sl_1800 · « **Reply #24 on:** 8 Oct 2009, 05:53 pm »

Brian,

I have two of the GR OB drivers mounted in a Hframe driven by the 370 amp. If I were to add two more drivers would you recommend a separate Hframe for those or would some other OB design be better which would incorporate all 4 drivers in one sub unit? I have seen a design on the Linkwitz web site, http://www.linkwitzlab.com/woofer.htm, the claim is to reduce vibration compared to other designs. Have you ever built one of those.

drphoto · « **Reply #25 on:** 8 Oct 2009, 08:13 pm »

Hey wait a minute, I thought Danny said in another post that 3 drivers per amp was the limit. I'm running 4 and the amp gets very hot, unless I keep the level low, or put a pancake fan on the fins. (that works, but the one I have currently is noisy) I was prepared to shell out for a second amp, but now you're saying it's ok to run 4?

As I've said many times, I love these things, but it takes a lot of fiddling to get them dialed in.....all part of the fun, I suppose.

Davey · « **Reply #26 on:** 8 Oct 2009, 09:02 pm »

Brian,

Just in case you missed it, and for what it's worth, Siegfried explains his wrong-headed thinking here:

http://www.linkwitzlab.com/faq.htm#Q34

In my experience, which is pretty limited, I tend to agree with this approach. However, I've heard other systems with high-ish Qts drivers that sounded fine to my ear also.

Cheers,

Dave.

Danny Richie · « **Reply #27 on:** 8 Oct 2009, 09:05 pm »

Personally I like a little cushion rather than being right at the limits of the amp. 4 woofers pushes the resistance to just under 3.5 ohms while 3 woofers only pushes it to 4.6 ohms. So three is a reasonable load still.

Steve, If you thought the side panels on your Orion were flexing and resonating then just think how bad it would be on the large unbraced panels of the box that you posted a link to.

sfdoddsy · « **Reply #28 on:** 9 Oct 2009, 12:21 am »

Quote from: rythmik on 8 Oct 2009, 02:01 pm

Quote from: sfdoddsy on 8 Oct 2009, 02:07 am
I was planning on trying out a pair of the 12" GR servo subs in a sealed so I might start there, if they ever respond to my email.

Just as a matter of interest, if I wanted to get some idea of the OB 12s capability, could I use the regular SW12s and pre-EQ them using my DCX? Would the servo still work in this scenario?

The servo network for SW12-16 is different from SW12-4. So we cannot mix the two. Also OB version has a shelving function built-in. But most importantly is SW12-4 has a Qts value of 0.4 and SW12-16 has a Qts value of 0.9. This factor of 2x difference is what makes SW12-16 to have 1.4x (the formula is square-root of Qts ratio) of the excursion at Fs point (or around it). In other words, SW12-16 is really made for OB and SW12-4 isn't. You can still use it, but you won't be able to use its full excursion potential in OB. When I looked at Siegfried's website, he listed a 10" Peerless driver with Qts of 0.17 as a potential candidate driver. That is plainly wrong. I understand some see him as an icon. But sometimes, you cannot be right on everything. And that includes me.

Brian

Thanks again Brian,

I wasn't planning to use the SW-12-08 permanently as an OB driver, but temporarily swap them from a sealed application. I would use the shelving filters in my DCX2496 to give the required boost, but if it will muck up the servo action there is no point.

I'll have to decide whether the full Servo OB bass route is worth the expense in my application. Four new drivers plus two amps starts to add up when they'll only be used between 40 and 100Hz.

rythmik · « **Reply #29 on:** 9 Oct 2009, 12:40 am »

Quote from: drphoto on 8 Oct 2009, 08:13 pm

Hey wait a minute, I thought Danny said in another post that 3 drivers per amp was the limit. I'm running 4 and the amp gets very hot, unless I keep the level low, or put a pancake fan on the fins. (that works, but the one I have currently is noisy) I was prepared to shell out for a second amp, but now you're saying it's ok to run 4?

As I've said many times, I love these things, but it takes a lot of fiddling to get them dialed in.....all part of the fun, I suppose.

The reason for me to say four is the limit was based on:
1) DCR compatible with sealed version. SW12-4 has 3.2ohm DCR. SW12-16 has 14ohm. So four of them is 3.5ohms.
2) The impedance curve. The impedance hump is around 25hz. High impedance load is easier for amplifier. So the amp should have handled with ease.

The two combined is my rationale. However, if you and Danny find the amplifier gets too hot, there is other factors I haven't considered and I will stand corrected.

drphoto · « **Reply #30 on:** 9 Oct 2009, 12:56 am »

sfdoddsy. all things audio are subjective, but I've been really happy w/ my four OB servos run off a single amp (w/ the caveat that either low levels or cooling is required for the amp) The cool thing, is no expensive enclosure required. I'm just running them in 2'x3'x1.5" flat piece of MDF w/ shelf brackets for feet. $50 or so and a few hours work. I'm using the shipping box, sans lid for the plate amp. Sure it's all a bit tacky looking, but I don't know where you'd get this sort of sub performance for ~$1K. Eventually, I'll do a sand filled baffle w/ properly rounded edges and a painted finish to match my monitors. I can actually live w/ the cardboard box, but one could always fab up something nicer.(I could claim, it's an environmentally friendly solution)

I honestly don't know whether the W box sounds better, or is just a more compact/visually pleasing solution. Maybe someone will comment on that.

I'd say give it a shot. If not your cup of tea, I'm sure you could unload everything for a minimal loss. Hell, I'll buy an amp and maybe another pair or drivers from you! Now 3 per side would rock!

cheers,

joe

sfdoddsy · « **Reply #31 on:** 9 Oct 2009, 02:17 am »

Thanks Joe,

I'd be using the subs in a similar application to the GR V1, as stereo bass units in an H-Frame underneath a mid panel, and so would definitely need two amps.

And since I'm in Australia, shipping adds another few hundred.

As for giving it a go, I've been using dipole subs for about eight years, so I know how good they sound.

The question is whether the servo version would sound appreciably better than my already excellent subs in my application.

drphoto · « **Reply #32 on:** 9 Oct 2009, 03:43 am »

Ah....didn't realize you were from 'down under'. I guess that would negate me buying them from you if you tried and didn't like.

I actually don't think of these speakers as 'subs' in the traditional sense, but more as woofers, as I run the crossover quite high. (around 85hz, although I'm still playing around with it)

I'd consider my system w/ monitors as more a 3 way than a 2.1.

I should qualify my comments by saying I never had a quality conventional sub, say an ACI, VMPS, or REL, in my system to compare. I had a crappy Mirage bipolar unit, but all it did was make some muddy, thuddy noise.

BTW: when I get out of pharmacy school and work a few years to pay off the debt, I hope to become your (sort of) neighbor by immigrating to NZ.

sfdoddsy · « **Reply #33 on:** 9 Oct 2009, 02:36 pm »

I'm actually from New Zealand. Small world.

TRADERXFAN · « **Reply #34 on:** 9 Oct 2009, 05:26 pm »

Quote from: drphoto on 9 Oct 2009, 03:43 am

I actually don't think of these speakers as 'subs' in the traditional sense, but more as woofers, as I run the crossover quite high. (around 85hz, although I'm still playing around with it)

I see this ability to play higher, into the 150 hz range, a major benefit of this ob "sub" design. If you look at it from the perspective of room modes adding another source that plays up to this range can help better smooth the spatial average of room modes. Since, from what I read, a typical size home will have a schroeder frequency 100-150 hz.

-This isn't necessarily the crossover point you set on your amp, this may be in the form of reduced output from the sub ABOVE the crossover point that is set on the amp maybe using the 12db slope.

-Tony

Milehighguy · « **Reply #35 on:** 10 Oct 2009, 03:52 am »

Hey Joe,
Have you ever tried disconnecting one of the 4 woofers and going with 3? I'd be interested to know if you still get too much heat from the amp that way when you crank it up a bit.

TRADERXFAN · « **Reply #36 on:** 20 Jan 2011, 06:21 pm »

In the discussion above, talking about loading 3 or 4 of the 16ohm drivers on an ob enclosure. My question would be, what would happen if one wanted to put 4 of the 4 ohm drivers onto one servo amp, sealed enclosure? Series parallel to give the original impedance?

Would you gain a lot of output, or is that too much for the amp?

I already have a single sealed 4 ohm servo, and I would like to get more out of it, at the low end for HT. Thought about buying 3 more drivers and rebuild it into a 4 driver sealed enclosure.
-Tony

Danny Richie · « **Reply #37 on:** 20 Jan 2011, 06:25 pm »

Quote

In the discussion above, talking about loading 3 or 4 of the 16ohm drivers on an ob enclosure. My question would be, what would happen if one wanted to put 4 of the 4 ohm drivers onto one servo amp, sealed enclosure? Series parallel to give the original impedance?

You can't series/parallel the coils with these or the servo sensing system will not work properly.

Quote

I already have a single sealed 4 ohm servo, and I would like to get more out of it, at the low end for HT.

It is already flat to 20Hz. If you need more output then you'll need to add more woofers and more amps.

TRADERXFAN · « **Reply #38 on:** 20 Jan 2011, 06:26 pm »

Thanks. Thought it wasn't as simple as it seemed.

TRADERXFAN · « **Reply #39 on:** 28 Jan 2011, 03:33 am »

If one wanted to go for a semi-ob application, how big of an enclosure volume would each 16ohm driver require? I read somewhere that 1.5x the Vas was good rule of thumb for an IB effect. I would still pair them up to an amp, and keep the drivers very close together.

Would this give me the very low end output (~20hz area for HT) with 1 16ohm driver equivalent to a 4 ohm sealed version?
-Tony