Tumult response with LT (1 Viewer)

[Brian Bunge]

I thought I'd share some response curves of my Tumult subwoofer. I've got the Tumult in a 53L enclosure (18" cube, 1.5" thick walls) with an LT circuit and a single channel of a Crown K2 amp. These measurements were taken using my Stryke Bass Zone test disk and the Radio Shack analog SPL meter. I know it's not the most accurate form of testing, but I did use a correction spreadsheet. I do have a nice mic and preamp and both JustMLS and TrueRTA but with my laptop's soundcard I don't totally trust those measurements either. I'm still trying to work those out and we'll see if I can get better measurements soon.

Also, these measurements were taken just to show the curve; not for max SPL. The sub is approx. 6' away to the left of my seating position along the back wall and about 2' from the corner. The sub pulls double duty as an end table so that's where it will have to stay. There's a pretty big hump that obviously needs to be handled, but I'll eventually install my BFD to deal with that.

Anyway, here are the graphs:

 

[Gary Griffiths]

Brian

Thanks for your diagram. As an experienced speaker designer could you offer me some advice please?

I'm debating swapping a pair of Tempests for Tumults so that I can use a smaller cabinet and locate them in the same plane as my main speakers. Currently my Tempests are in a 16^3 cabinet/plinth beneath my sofa at the back of the room driven via a Marchand Bassis and a Paradigm x30. Despite matching phase I'm not happy with the speakers not being in-line with the mains.

Do you think a pair of 98l Tumults (.577?, critically damped) would work well with a Bassis and give me an improvement in sound quality over the Tempests. Ideally, I'd like to get rid of my KEF Reference 4's and use the Tumults as the bass section of a Seas Tweeter/mid range 2 way design to give improved treble response and imaging. Your thoughts would be most welcome

 

[Brian Bunge]

Gary,

I'd first try the Tempests in smaller boxes with the Bassis unit. The whole point of the Bassis (or any LT) is to adjust both the Qtc and Fb of the system. I'd only think you'd need to step up to Tumults if you wanted super small enclosures and the Tempests couldn't handle the power you were feeding them along with the Bassis.

 

[Greg Yeatts]

Brian

Did you try flipping the phase of the woofer. That may help a bit of the hole you have around 70 hertz. I had a big hump at 45 hertz on my Tumult. Sounded much better once I used the BFD to equalize it.

Also, once I got rid of the hump, I needed to recalibrate my sub. The result was much more balanced. I think my calibration tones were centered around the hump (or at least influenced by them).

 

[RichardHOS]

.5 is critically damped, not .577

IIRC, .577 is the ratio of tensile and shear yield strength for an isotropic elastic material.

 

[DanWiggins]

0.577 is often called a Bessel alignment; it provides as flat a group delay as possible. Not necessarily the lowest group delay, but the most constant.

As far as your results go, Brian, it looks downright spooky! Relatively flat response to below 10 Hz, in-room, is just crazy...

Dan Wiggins
Adire Audio

 

[RichardHOS]

0.577 is often called a Bessel alignment; it provides as flat a group delay as possible. Not necessarily the lowest group delay, but the most constant.

Temporarily stored in a few unused brain cells... soon to be wiped out by a Corona or two.

 

[Scott Simonian]

Brian, Ive been waiting a long time to finally see someone post some response graphs with the Tumult. This is awesome. Goddamn! Look at the extension.

Curious, what Qts and Fb did your LT change?

 

[Jack Gilvey]

Brian, Ive been waiting a long time to finally see someone post some response graphs with the Tumult. This is awesome. Goddamn! Look at the extension

Actually, this response is achievable with much less capable a driver than Tumult. It's the LT that's doing the work. What's great about a Tumult-based LT is the fact that you can have extension and usable SPL.

 

[Brian Bunge]

Greg,

I haven't tried that yet. I'll try to work it in sometime soon.

Dan,

I still think you need to send me a T-Shirt saying "I blew Dan's big woofer!"

 

[Patrick Sun]

I did not need that visual!

 

[Nat Ward]

It's amazing to see the sub hold its own on the bottom end, but I've got a question about overall response. Since I'm still new and trying to gather all the info I can, if you were able to tame that mid frequency hump, would the still ~10dB variation across the curve sound good? Would using a BFD or any other type of EQ be able to dial that in to a flatter response--after taking out the ~45Hz bump? I don't know how flat you want your overall response to be (+/- 10dB, +/-5dB, or other). I'm pretty sure I want to go with a Tumult when I go DIY in a month, but I'm having a hard time deciding on an alignment. Thanks for the info.
Nat Ward

 

[DanWiggins]

Brian,

Only if you promise to walk around CES wearing it... Cover up when you pass by Patrick, though!

Dan Wiggins
Adire Audio

 

[Brian Bunge]

Nat,

I don't think it sounds bad now, but I would like to get rid of the big peak. If I could get to within +5dB I'd be happy. Looking at the response, if I could take out the majority of the peak between 36-56Hz I'd probably leave well enough alone.

Dan,

I'm sure Pat's seen much worse at some of those DragonCon freak shows!

 

[Gary Griffiths]

Brian

Thanks for the advice. Small boxes is certainly what I was looking for, although my main interest was sound quality. I was wondering if the Tumult offered an improvement in sound quality over the Tempest. At present I use Krell monoblocs on my main speakers and slightly lower quality monoblocs on my Tempests, however, if there's nothing to be gained in SQ by going for the Tumult I'll stick with the Tempest and try it in a smaller cabinet and see what it sounds like.

 

[Brian Bunge]

Gary,

The only improvement you might get will be when you're pushing your Tempests to their limits the Tumults would be coasting along. If you'll be using the Tempests well within their excursion and power limits I'd stick with them. If you'll be pushing them pretty damn hard then upgrading to the Tumult might be a good idea. That's also assuming you've got a good 500W or more into a 4 ohm load that you can use on the Tumults.

 

[Rich X]

Brian,
Looks pretty good even un-eq'd. I plan on taking some measurments on my tumult rig this weekend and seeing if I can dial in my BFD.

I have not had time to throw anything too heavy at the Tumults yet, but so far the best way I can describe them is effortless. I have only used them for music (DTS and DVD-Audio) thus far, but in the listening that I've done they provide a weight and presence that is fantastic.

 

[Brian Bunge]

Rich,

Your subs should look pretty similar down low (unless you have any big nulls or peaks) considering you the exact same subs and LT circuit as mine.

Glad you like them.

 

[Greg Yeatts]

Brian

The large 45 hertz hump my sub has is a room mode. It has plagued every sub I have had in that room (3 subs actually). Equalized response sounds much better unless you are one of those guys who like to ride down the street thumping bass like mad. Not that there's anything wrong with that.

Once I got my sub to about +-4 db I stopped tweaking the eq. I would have stopped sooner, but for some twisted reason I find the eq process fun. I had a song with a nice wandering bassline (all over the place). The bassline evened out (to my ear anyway) once I had it about +-5 db. With more tweaking, I could do better but I'm having too much fun listening.

I was very worried about group delay on my enclosure. My enclosure is tuned to about 19.5 hertz. I did some research and found out that group delay really only gets bad around Fb. I beleive this nugget of knowledge came from the True Audio website. The music I listen to rarely goes below about 45 hertz. Therefore I have no group delay problem. With HT material with extreme LFE around 20 hertz and below I am not too sure how much difference it makes that exlplosions are boomy due to group delay. It is doubtful most people would notice this. Sorry for rambling.
:b

 

[Tom Rosback]

Hey Brian,
Just send that bad boy up here and I'll run it on my MLSSA system with a Calibrated AKG CK-63ULS mic! Don't know if the capsule can take it....

Was the response you ran at the diaphram, or at 1m? or something else?

Hard to beleive it's been a year since CEDIA in Minneapolis.

I'm finally getting around to building a sub. I've settled on a Tumult driver, and now have to decide if I'll use it sealed with an LT circuit, or with a couple of 18" PR's.

Do you know what the difference between the LT method and the Greiner-Schessow pole-zero cancellation methods? I've got the AES pre-print on the Greiner-Schessow method.