Mark Seaton's Terraform XL Discussion/Owner's Thread - Page 3

Mark, so the 2 15" drivers are mounted inside the box?
I don't quite understand why you use the PRs and a slot port?



front chamber and large ported rear enclosure?

It might be helpful to show both the front and back of the XL.

Mark,
Given its size, I was wondering if it could be used as a stand (horizontal orientation)for my 60" plasma.

Does it vibrate when in use... or does this sound like a really bad idea and could damage the display?

It's called a bandpass sub.

A 6th order bandpass sub to be more specific.

Yep, and port or PR can be used in either chamber.

thanks

Hi Jim,

The only thing on the back of the Terraform is the amplifier. We'll have more pictures after I have them here and together (the shots above are from the cabinet shop constructing them for me).

I wouldn't have any reservations in placing a plasma on top of the Terraform, although if there was a wall behind the plasma, I'd likely prefer a wall mount if it's an option for a variety of reasons. The cabinet won't be quite as dead still as the SubMersive, but being as massive as it will be (85-90 lbs of drivers, amplifier and PRs get added to the already heavy box you see) and a good deal of bracing, I expect box motion to be minimal. If there was any concern, you can always place a slab of wood or other solid panel with a few rubber feet or sorbothane patches and have nothing to worry about in vibration. The bigger concern will be vibration of other items in the house if not in a heavily build, dedicated room.

Mark,

Can you enlighten us about what improvements we can expect from Submersive 2 and Terraform XL from their predecessors?

I know Submersive was designed to be superior at high frequencies and Terraform at low-end. Is this still the case for Submersive 2 and Terraform XL? Are they still meant to complement each other at an ultimate room?

Thanks Mark. I wasn't confused with the SM2, just the actual design. I thought the internal 15" drivers were opposed and the 18" PR's were the same. My fault. Will you have any internal pics? That's what I'm really curious about.

With so many preconceptions about design types out there based on experience with poor executions, I much prefer to focus on the results and the reasons for the approach than the specific means and execution. I've posted it many times already, but to confirm both the SM2 design and Terraform XL are more expensive and larger than the SubMersive with greater output. They are not replacements for the SubMersive.

I'm not going to be posting full section views, but I did already posted this on my own forum in Johnsteph's thread, "New Convert to Seaton Sound!" You can see the smaller round mounting hole directly behind each 18" PR:



The rear of the 15" drivers loads the large rear enclosure and slot port, just as in the case of a typical ported box. The best way to conceptualize this design is to view this similar to the behavior of a dual 18" ported design, but replacing the directly driven 18" driver with the 18" PR which is acoustically coupled to, and driven by the 15" driver behind it. This makes for a very efficient way to leverage and drive the 18" radiator with air pressure across every square inch rather than just a round voice coil, while also providing an acoustic decoupling above ~100Hz which effectively filters out the most audible components of any distortion produced by the driver.

Hi hd',

The only good reason to use SubMersives with the Terraform XL would be for the placement advantage the smaller size has for the upper bass range (~40-100Hz). If you can fit multiple Terraform XLs in the desired locations, multiple Terraform XLs would be even better than Terraform XL + SubMersives.

This is my first time hearing of this. I was like "Why would someone do this?" It dawned on me what you are trying to achieve with the PR's (as far as filtering out the highs from the active driver) when I was looking at the pic, then confirmed when I read further. That is a brilliant idea, Mark, damned impressive. Did this idea originate from you?

Thanks Mark.

I believe this was not the case with original Terraforms. Correct me if I am misquoting you, but I believe you were recommending Submersives for the upper bass to Terraforms. Should I take it that this is no longer the case with Terraform XL's and they can handle mid and upper bass as proficiently as Submersives now?

How about pairing one of these babies with some PB13s? Was thinking about replacing my 12/2 Ultra with something in the future to use along with my PB13s...........this looks to be an "upgrade" over that sub (12/2)

How much delay is added because of the PR?

It doesn't matter because any good Receiver / Pre-Pro has distance settings for all the speakers and the sub which would allow you to dial out any delay the PR might add.

Does anyone know/speculate about answers for Lion's questions:

http://www.seaton-sound-forum.com/post?id=3974721

Actually the delay and phase response EXACTLY matches a reflex system of the same frequency response with a 2nd order low pass added. The PR helps hold this front chamber/low pass behavior much better than a port does which allows higher harmonics to incrementally sneak through.

As Stereodude indicates, the added order low pass to the system is really a non-issue with any modern system where distance/delay adjustments are available. The addition of a 2nd order low pass to a 4th order is not really that big a change in the scheme of things, and results in much less latency than horns or other designs with inherent propagation delay.

i know i do (speculate)

That I know. Sorry, I should've asked for a number specifically. I was just curious.

Thanks for the reply Mark.

Hey you are here. Did you get any of those questions answered? I am looking for the same answers.

So long as the intent is to use them in different locations, I expect the additional subwoofers, in this case PB13s, could be used to your benefit. I wouldn't bother without having some measurement capability, or you could roll the dice and hope Audyssey/SVS's 2ch sub EQ can sort things out, but to have confidence in complimentary placement a few measurements will tell a lot. I would probably plug one port on the PB13 and use the "room gain" knob to shelf down the low end some to give a bit more headroom in the system.

Thanks Mark. I am running one port plugged right now, so that should be fine. The subs would be in different locations.

I am also considering replacing the 12/2 with a submersive possibly since I am curious about how a sealed sub would do in my room and trying that out with the PB13s maybe (plus these would fit in my room better than the XL). How would I adjust phase though since there is no variable phase on a submersive or terraformXL (right?)? I have found that 180 degree phase is best for my front subs and to get the rear sub in phase requires just a hair over 90 degrees. How could I get the submersive or terraform at 180 degrees phase wise? I do have an SMS-1, but I can only set 1 global phase setting on it and considering I need 180 for the fronts and ~90 for the rear I just leave the SMS phase at 0 and do the phase adjustments at the subs. I would like to keep the SMS, but I am a little confused how I can get the seaton subs to do what I need phase wise.

Not quite yet. Mark (for obvious reasons) is tight lipped about technical details and questions regarding "different sound signatures" - especially if you consider that these are unfinished designs (Submersive 2)

But not getting an answer sometimes is a strong indication that you asked the right questions...(the critical ones)


So I did some reading. I am especially interested in the 4th order bandpass design of the Submersive 2. Drivers/PRs are identical to Terraform XL, but instead of a vented it uses a sealed rear chamber.

To put it simple I expect the Submersive 2 to have much better transient response than the 6th order bandpass Terraform design - at the expense of (very) low frequency response and distortion.

For me transient response (as I understand it) is one of the most important metrics but in the grand scheme of things just one of many factors that influences subjective sound quality. Any design approach compromises on some of them. It is important to choose a design which provides the best combination of design compromises for your given application (room, personal sound preference, source material, placement,...).

How about the mid-bass? Submersive 1 had the upper hand in terms of mid-bass compared to Terraform. Mark hinted this no longer would be the case with Submersive 2 and Terraform XL.

I am surprised you feel Submersive 2 will have superior transient response than Terraform XL. Doesn't Terraform XL have a bigger cabinet size? From what I know the bigger the box is, the better the transient response should be. Mark can always correct me of course

What's the peak output on a Terraform XL?

Here is a post that where Mark was talking about the basic Terraform sub. So the XL should be more then what is stated here.
"A good comparison would be that it takes 2 Terraforms to compare with the headroom of a single SubMersive in the bulk of the subwoofer range. Below ~30Hz on down to 10Hz is where the Terraform really comes into its own. While those 2 Terraforms are similar to the single SubMersive in the upper octave or so, the pair are lower in distortion and have the power of 3-4 SubMersives in the 10-16Hz range with the same total power.

In larger rooms where there is less LF gain and/or more real estate available for subwoofers, the Terraform really shines. It can work very well in moderate size rooms as well, with more maximum power in the lowest octave (10-20Hz)." Now enough people have posted SPL numbers on Marks site so we can guesstimate what it might do. But, if I am not mistaken there should be some Terraform and or Terraform XL subs in their owners hands petty soon. So then we can get some more real world numbers for them.

Great, thanks Mike. My room is a similar size to your room and my SubM is pretty much turned all the way down with my subwoofer channel at -8 (-10 is the lowest), so I'm using a fraction of what it offers (meaning I have no clue how loud it can get!!!!).

I don't remember what mine is at but I am pretty sure that I have plenty left in the tank. As Mark likes to say, headroom is your friend . Having more is a good thing. That way you never have to worry about it.

He recently delineated further. Here: