Questions about Tumlt/ADA-1200 combo (1 Viewer)

[David_P]

No one's asked, so I'll be first...

This seems like a match made in heaven, but does it really work out? I don't know of any software which allows adequate modelling of power/excursion, Lt'ing, boosting, etc.

1) I can simply up the size of the box to get q=.577, but does this gain anything? How much "oompf" does the Q change of the LT circuit use, as compared to the simple eq required? Or is this too simplistic a way to look at it.

2) Will the Tumult be overdriven by this combo/amp?

3) What will it be capable of in terms of extension and spl?

David

 

[Jack Gilvey]

http://hometheaterforum.com/htforum/...18#post2393218

Tough to say if it really works out, as I don't think the amps have shipped yet.



If you size the box for the Qtc you want, all you need is a simple shelving boost to lower F3. An LT will lower Qtc and F3 in a smaller-than-ideal box. The former is preferable as the power requirements and resultant compression can be considerably less.

 

[David_P]

That's an interesting piece of a spreadsheet at that link... thank you

I'm not sure if you, Jack< or anyone else has played around with it, but if so can i ask of the following assumptions are true?

1) firing the spreadsheet up gives you a tumult set at vb= 2 cu ft, target fsc=14hz, and it appears from looking at the power/excursion graphs that the ada-1200 would run out of power at about 15hz. The other information under amp/eq shows amp=200w (4 ohms) and eq=100w... I assume that this means applying 100 "watts" to the eq (which equates to 200w due to the 4 ohms load) will mean the eq is demanding 1200 watts at about 15 hz to attempt to "keep up"?

2) upping the size of the box to 4 cu ft (roughly a .577 box) and dropping the desire Q to 0.577 (actually upping the Q) means that 1200 watts runs out at about 11-12 hz instead?

3) And how exactly does the peak spl=106.40 fit into all this (from the information page)? Is this the db which the tumult will supposedly produce in a 0.5q box with 100w (200w) before rolloff starts? It's obviously different from the 118.44 db listed as max spl under the driver parameters section.

thanks in advance for any explanations

David

 

[dave alan]

I prefer to model the sub with no EQ.

Since you'll get the same F3 if you put the Tumult in a 2 cubic feet or a 4 cubic feet box and your amplifier power is already defined, it makes no sense to build a larger box if you plan to use an L/T circuit.

The peak SPL is defined in the driver parameters. The Tumult's sensitivity is 87.1, 1W/1M. The power handling is 1600 watts. Doing the math from there gives you a peak SPL of 118ish dB.

That number stays the same regardless of the L/T. If you model the sub with 1200 watts of input power, you'll see the max at 116ish dB.

When using an L/T circuit, if you choose to extend the F3 1 octave, it will require approx. 12 dB of boost. (F3 of 'X' with a 12 dB/octave roll off in a sealed sub. So, 1 octave lower than F3 is down 12 dB. If you want that to be your new F3, you'll need to boost the signal 12 dB).

12 dB of boost is 16 times the power of the original signal. If your amp has 1200 watts on tap, divide that by 16 and you get 75 watts. With 87.1 at 1W/1M, at 75 watts you'll get approx. 106 dB at your new F3.

I would put the Tumult in the smaller box and go for an F3 of 20 Hz. This will mean a max boost from the L/T of approx 10 dB, which is approx 10 times the power applied to the original signal.

That will yield a max SPL of close to 108 dB at 20 Hz, 1 meter, anechoic, using a 1200 watt amp.

Now, if, for example, you're playing music (which doesn't have much info below 30ish Hz), you can crank the sub to the amp's max and see 116 dB peaks because the L/T circuit doesn't kick in until you get below the original F3. But, if an 18 Hz note happens to hit all of a sudden at that level, the amp will give out because it doesn't have the juice to boost that signal 12 more dB.

The cool thing is that these numbers are all theoretical anechoic numbers and in the real world there is room gain and very little high level signal below 20 Hz.

The bottom line is (as you've seen in the spreadsheet) the amp will give out before the Tumult does.

If you model the sub in a sealed box of 2 cubes, just go down 10 dB from the modeled F3 and then straight across to the new F3. In the average room, you'll find that the real response will be pretty much flat to below 10 Hz at that SPL.

Hope this helps.

Dave

 

[David_P]

thanks Dave for an informative post...

A couple of points?

and what would happen with a different box size (e.g 4 cu ft). I can't wrap my head around how this works exactly :frowning:

David

 

[DanWiggins]

David,

You are correct. The larger the box, the less EQ needed for a given response, meaning more power left in reserve for headroom. Hoffman's Iron Law still reigns, even for Linkwitz Transforms...

Dan Wiggins
Adire Audio

 

[Jack Gilvey]

Yup...as I implied above, the less power you pour into a driver, the better. More headroom, less thermal compression, etc. A bigger box is worth it if you can fit it.

 

[Mark Seaton]

Just to keep the entire picture in mind... Remember there are two limits; power limited output as well as excursion limited output. At some point you have "enough" power to reach Xmax. That is not to say there is no reason for a bigger box. Adding more power is not exactly a free lunch. It works rather well in dynamic peaks, but you put 1000W into any driver for any length of time and you will see significant compression. You need to weigh the two factors. With a Linkwitz Transform design, consider your box volume to be your adjustment of how much power/boost it takes to reach Xmax. The Tumult is a rare case where a small box can make for a system you can't easily bottom even with 1200W. If you are one not to show as much self-restraint, or you expect less experienced users to crank it up, having a power limited low end is NOT a bad idea. Clacking/bottoming drivers are never a good thing.

Cheers,

 

[dave alan]

I agree with Mark. I call it a free built in compressor.

I think that over excursion is more of a concern than thermal compression when talking about short subsonic bursts.

There is also the final system Q to consider. I personally like the critically damped (.56) sound of the larger box, but experience and several studies conclude that most people prefer the .65-.71 range you'll get with the smaller box.

Trading those items for the couple of dB advantage at 20 Hz is the real question, IMO. I say advantage instead of headroom because, as Mark points out, headroom of a couple dB is in the restraint of the user.

Aside from those points, David may have answered his own question in the same sentence...

"So what exactly is the disadvantage (except for box size/SAF etc) of going with 4 cu ft, for example?"

There is Hoffman's Iron Law and then there is Husband's Iron Law.

More seriously, I've found that 2.5 cubes with 1600 available watts preceded by a 12 dB L/T is the near perfect combination in an average room using a single Tumult. YMMV.

 

[Jack Gilvey]

Good points, Dave A. One of the reasons people tend to use multiple drivers in IB is that there's no built-in compressor/HP filter in the form of a box...they can bottom drivers easily that survived without a problem in a small box due to the high sensitivity in the lowest bass. What Qtc and F3 did you use for that box?

 

[Brian Bunge]

As an experienced Tumult/LT user let me add in my own $.02. My Tumult is in a 2ft^3 enclosure and my LT gives me a resultant Q=.6 and a resultant Fb of 18Hz. Max EQ is right at 10dB at 10Hz but only 7dB at 20Hz. I'm using a Crown K2 for power. Initially I was using the K2 bridged for 2400W and fried a voice coil before I ever reached the driver's excursion limits. So I now only use one channel of the K2 for 800W and haven't had any more problems.

 

[David_P]

and Brian (re)posted this link to the in room response of his Tumult/LT combo in another thread... spooky low-end response

http://www.rutledgeaudiodesign.com/p..comparison.jpg

David

 

[Brian Bunge]

What's really scary is that it can do that while looking this good!

 

[Dave Milne]

Very nice Brian. I fear that this thread is pushing me over the edge to subwoofer "upgrade-itis".

Jack made an interesting statement at the beginning:


So it seems that the Tumult in 4 cubic feet doesn't need the LT option on the ADA amp. If I am looking at the Tumult spreadsheet correctly, 4 cubic feet gives Qtc of 0.559 - which seems a bit low to me. I've generally shot for something in the "classic" Butterworth 0.707 range. If I back the volume down to, say, 2.5 cubic feet, the spreadsheet says Qtc= 0.650. This "feels" right... so why would I want to LT it?

 

[Brian Bunge]

Dave,

If you can get the Qtc that you want in a box size that is acceptable to you then I guess there really is no reason for you to want to LT it. I wanted a lower Qtc in a smaller box and flat response to 20Hz or below. So that is why I LT'd mine.

 

[dave alan]

Jack,

I have a 3 position switch that allows selection of .5, .6 or .7 Qts in my circuit.

I usually (90% of the time) select .5 and each of the selections alters the F3 slightly, in-room and requires an approx. 2dB recalibration each step.

With the .7 Q selected, my anechoic F3 is approx 17 Hz, but in-room response with room gain is flat to around 7 Hz.

Brian,

That sure is a gorgeous sub! Very high quality sound, too. 2400 watts...hmmm...I just gained some insight into the maniac side of you I wasn't previously aware of.

 

[Brian Bunge]

Dave,

Thanks! Most people actually think that the top is real marble until the see it up close.

Yeah, a 2ft^3 enclosure must give the Tumult good protection from bottoming, because it sure didn't show any signs of distress all the way up until the VC fried. And even then only one of them actually fried.

I do like your idea of switchable Q. It would be interesting to hear the differences in sound with a flick of the switch.

 

[Mark Seaton]

Hi guys,

I get the sense that people have the notion that the Qtc of the driver in the box affects the sound of the final system after applying the transform. First, realize the Linkwitz transform is nothing more than an easy means to make the response of a known sealed box respond like a sealed box of the desired parameters via a precise EQ. What needs to be remembered is that the sound character of the system is due to just that... the system. This includes any EQ applied.

Translation... So long as the driver is displacing less than say 5% the box volume, and there is no additional power compression happening, there will be no difference in the sound produced by a sealed box with a Q of say 0.57 and fc of 20Hz and the same driver in a smaller box with a Linkwitz transform applied to result in the same Q of 0.57 and fc of 20Hz. The smaller box will require different power than that of the un-eq'd box. There are a few further compounding factors, but all are matters of non-linearities and cases of extreme electronic correction.

 

[dave alan]

Mark,

The amount of variation in Q seems to be related to the amount of boost from the L/T.

It appears that if you use the larger box to limit the amount of boost needed, you also limit Q options, from my experience. I don't know of a formula, just have observed the results.

The point being that, if you choose the smaller, excursion limiting box with larger reserve amp power, you have a wider window of options to alter the final Q, whereas, if you start with a lrger, low Q box to limit L/T boost and prefer a high Q sound, it may not be feasible.

Actually, I should have qualified the statement as I'm not an educated person...just have observed the in-room results and made the conclusion for myself.

 

[Mark Seaton]

Have you looked at any of the shareware Excel spreadsheets which calculate the circuits and resulting response for you. I'll have to look, but I seem to recall it being on TrueAudio's site and maybe a few others as well.

The idea is that one part of the circuit inverts the response of the sealed speaker and then creates the desired 2nd order low pass response.