Tumult 15" or 2 Stryke AV 15" ? (response curves) (1 Viewer)

[Michael R Price]

Dan, you're right that a flat response will have a room rise under the lowest node (25-40Hz usually). But we were assuming Seth would have an equalizer to fix something like that.

So Seth, which is more important, depth or output? I would lean towards the Tumult given its output is frankly absurd anyway.

 

[Jack Gilvey]

Dan, you're right that a flat response will have a room rise under the lowest node (25-40Hz usually). But we were assuming Seth would have an equalizer to fix something like that.

If it happens at all. Most folk's in-room posted measurements don't seem to reflect this. A slight rise below 30Hz wouldn't be in the "boom" region, anyway, and would likely lead to a more pleasing perceived balance if listening at less than reference levels.
If attenuation were in fact needed down low, this would lead to gains in headroom and distortion, of course.

 

[Dan Wesnor]

If it happens at all. Most folk's in-room posted measurements don't seem to reflect this.

http://www.knology.net/~wesnor/sb10page.html
Scroll to the bottom. This sub has an anechoic F3 of about 34Hz, and appears (and sounds) to be flat to 20Hz. There is no EQ, and no filtering/boost of any kind in the amp (it's a Marantz monoblock, not a sub amp). The room is about 8,0000 cu. ft., which is very large. The two humps and one dip below 80Hz correspond exactly to the room modes.
By having a big hump at the low end of the response, you are also adding group delay. When you EQ it out, you will add more group delay. Although it end up flat on the meter, it will end up 1/4 second late in the time domain and probably have severe ringing. So why build it in at all? Makes no sense to me.

 

[Seth_L]

So Seth, which is more important, depth or output? I would lean towards the Tumult given its output is frankly absurd anyway.

I want depth and output. What I'm trying to establish is does the average room have enough room gain to flatten the dual AV15 design or not. I've also looked at a LT of a quad AV15 design. But I don't know how to take the LT into account in Unibox.

Also, if I have a BFD, do I need a LT or can I just use the BFD to flatten the sub?

Seth

 

[Seth_L]

This should further complicate the issue.
Look at the "nice" step response of the dual AV15 (original design). Now, look at the step response of the Tumult (original design). Kinda makes you wonder...
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Seth

 

[Seth_L]

Oh, and for comparison here's the step response of a sealed .707 alignment 4 AV15.
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Seth

 

[Michael R Price]

Does low frequency extension affect the step response? I've always wondered that. It seems as if a deeper extending woofer would "sustain" the signal longer.

Seth, the peak at tuning creates group delay but do you really care if it's 50ms at 15Hz? What matters is the delay higher up in the 35+Hz "musical" region. Both the Tumult and AV15 will be fine in that regard. I think.

Anyway, Jack has a good point about room lift. The huge gain predicted by LspCAD just didn't show up (even in a fairly small, well sealed room) to help my way overdamped Kit281s and I have some pretty serious room response issues because of it. If your room has a lot of windows, doorways, or whatever, you might find you only have say 4db of gain at 20Hz.

Extra bass can't hurt, right? Whether you want it below or above, maybe, 25Hz is up to you.

 

[Seth_L]

Does low frequency extension affect the step response? I've always wondered that. It seems as if a deeper extending woofer would "sustain" the signal longer.

I'm not entirely sure to be honest. I was able to determine that the step response of the Tumult got worse as you lower Fb.

Seth

 

[Mark Seaton]

Hi guys,

I see a lot being discussed here, so I'll just throw out some comment for digestion.

First, I would submit that both models express the nature of the comparison. The Tumult lends itself to a smaller box with low tuning and high power. The dual AV15s would be more optimal in a larger enclosure requiring less power. The peak at Fb of the Tumult indicates an underdamped system. I would use a smaller box. Check the Tumult thread for some suggestions I had made. From what I've seen and heard both with EQ and real boxes, I believe there is a percieved difference with the peak down low vs. a smoother, more extended roll-off.

Now for the whole room gain issue. Yes, it is certainly a real phenomena, but it varies from room to room, and you need to consider the dimensions of the room. In most homes, you will see the frequency where you get into a pressure mode range from ~14-25Hz from the larger to the smaller rooms. I can tell you from experience, a ContraBass does sound overblown in a room with a >20Hz corner frequency without careful EQ. At the same time, a ContraBass sounds great in that room with a

 

[Mark Seaton]

OH... as for the impulse response, it is tied directly to the frequency response. Make the box size smaller on the Tumult and maintain or lower the tuning frequency and you will see a smoother impulse response. Making the box for the AV15s bigger would yield similar responses.

 

[Seth_L]

OH... as for the impulse response, it is tied directly to the frequency response. Make the box size smaller on the Tumult and maintain or lower the tuning frequency and you will see a smoother impulse response. Making the box for the AV15s bigger would yield similar responses.

Does this mean that the impulse response is somewhat useless? I guess I should ask if it means that the box with the lower tuning point will sound worse (sloppier)? Or are we simply seeing the resonance of the box after the impulse and I shouldn't worry about it?

Seth

 

[Seth_L]

The peak at Fb of the Tumult indicates an underdamped system. I would use a smaller box. Check the Tumult thread for some suggestions I had made.

Here's what Dan suggested:

Vented/PR: One good alignment is 6 cubic feet, tuned to 17 Hz. Goosed with 1400W, it's completely linear up to stupid levels. Boxes between 4 and 10 cubic feet look good for this guy.

You mentioned making the box even bigger and lowering the tuning point. My box is a little bigger at 7 cu-ft, but is tuned 1Hz higher.

Seth

 

[Mark Seaton]

When I mentioned making the box bigger, I was referring to the dual AV15 design. The Tumult would likely work out better in the 6 cu.ft./17Hz tune that Dan suggested.

I guess this gets down to what I would call simulation exercises. When looking at a simulated response, it is important to understand what it is telling you, and why you would change a parameter given what you see. Take a given driver, and start playing with one parameter while holding the other constant. Once you change one parameter, play with the others again while holding that one constant. Doubling and halving of any parameter usually gives results which help with understanding of the concepts. Once you get done changing box size and tuning frequency all over the map, then compare some of the same box sizes and tunings with another driver and notice the differences and similarities. Then try and get a similar response shape to the first one and see what that takes. This correllation is what will greatly help you reach alignments you are looking for.

 

[Jack Gilvey]

Anyway, Jack has a good point about room lift. The huge gain predicted by LspCAD just didn't show up (even in a fairly small, well sealed room) to help my way overdamped Kit281s and I have some pretty serious room response issues because of it. If your room has a lot of windows, doorways, or whatever, you might find you only have say 4db of gain at 20Hz.

That appears to be typical, although some have much more, as you see. I've had best results from designing for flat and not relying on the room. The group delay will be determined by the final in-room response shape, not really what it started out as before eq.

 

[Greg Monfort]

>Isn't that hump at the end of the Tumult graph indicative of an enclosure that is too large for the driver?
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Yes, though you can tune it lower or damp the vent Q.
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>The second graph in the first post will sound best of all that have been posted. It's the only one that works with the room to produce flat response. All the others will produce a large hump below 30Hz.
and later:
>By having a big hump at the low end of the response, you are also adding group delay.
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True, but not everyone has a room with this much gain, I know I don't, but then I have a 46ft pathlength though my room proper is only ~16ft x 21.5ft x 8ft. Size isn't the only criteria, construction matters just as much below ~30Hz. Since mine is stick built with lapboard siding, LF goes through it almost like it's not there below ~25Hz, and the in-wall fiberglass insulation sure isn't going to have any audible effect down low. With subs stuck in the corners I only get ~ +4dB of gain down low Vs the theoretical +9dB. Your remarks/measured performance implies that you have a much more solidly constructed house than I do, as do many folks, but not so many as for you to conclude that "All the others will produce a large hump below 30Hz."
Anyway, our hearing acuity WRT phase goes away down low so as long as the group delay has ~decayed away by 30-35Hz (either low Fb or 'critically' damping the vent required to achieve this), better IMO to design aneochoic and EQ down as desired to get the desired room response, whether by measuring, or what sounds pleasing to you.
Another reason to do it this way is that they're finally starting to offer low cost RTAs with the ability to store more than one EQ curve, so you can have a nice rolled off one for CD music, one for vinyl, and a more extended/boomy one for HT movies with lots of LF special effects.
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>When you EQ it out, you will add more group delay.
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You can't have it both ways. If increasing the Q of the response increases GD with increasing slope, then the opposite is true when you decrease it, and why as system Q goes down, so goes GD.
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>Although it end up flat on the meter, it will end up 1/4 second late in the time domain and probably have severe ringing.
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Severe ringing is an amount you can perceive, though not necessarily hear, and per my hearing remark above, even having 250ms (1/4sec) isn't a big deal if it decays away over time, in time. I do question the 1/4sec delay though. Since 250ms = 4hz, something doesn't jive.
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>So why build it in at all? Makes no sense to me.
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It doesn't have to make sense to you or anyone else here except whoever wants to build it. That said, it would have to be tuned too low for 250ms to decay away enough, so we agree that this alignment isn't one either of us would recommend.
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>I want depth and output. What I'm trying to establish is does the average room have enough room gain to flatten the dual AV15 design or not.
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Define average? Best to plan for none, you can always adjust it in some manner that provides superior audible performance.
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>Look at the "nice" step response of the dual AV15 (original design). Now, look at the step response of the Tumult (original design). Kinda makes you wonder...
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Hmm, 1ms = 0.06sec, and it probably settles by 2ms, this down where you can't hear the LF, only feel it, so much ado about nothing IMO since you'll be hearing things rattling in the room/house at a much higher SPL. FWIW, my 16Hz tuned cabs sim a 'sloppier' step response than this one since they are just simple reflexes, but no one has ever called then anything but incredibly 'tight'.
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>Here's what Dan suggested:
Vented/PR: One good alignment is 6 cubic feet, tuned to 17 Hz. Goosed with 1400W, it's completely linear up to stupid levels. Boxes between 4 and 10 cubic feet look good for this guy.
You mentioned making the box even bigger and lowering the tuning point. My box is a little bigger at 7 cu-ft, but is tuned 1Hz higher.
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Well, we're a product of our environment, and I guess the homes up in the NW are well built/insulated (seems reasonable), so the room gain dictates lower Vbs. If I were building one for max "depth and output", it would be 350L/13Hz Fb, and tailored to suit. After all, you may want to move it someday and the extra volume may be needed, even if you don't now.
Two modestly weighted 15" PRs drops vent mach to 0.01, so no real loss of output due to vent compression. Really, due to the extreme Vd and super low Fb, the PRs are just there to prop up the driver a bit above Fb, so vent mach isn't an issue in this case.
GM

 

[Chris Tsutsui]

May I ask why you would pay $400 for passive radiators when you could buy some PVC ports instead?

Do the passive radiators give the subwoofer a more dipole effect where bass radiates from all surfaces? If not, what advantages are there of PRs over just standard flared ports.

 

[Chris Tsutsui]

NM, I just read up on passive radiators and I forgot about port noise and sizes of ports.

Boy do things sure get expensive when you start asking for high and low spls, my oh my.

 

[Greg Monfort]

>Boy do things sure get expensive when you start asking for high and low spls, my oh my.
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Performance costs, so he who has the deepest pockets and most/best innovations wins.
GM

 

[Anthony_Gomez]

Chris....do worries, you don't need to buy PR's...just go sealed and buy yourself a Crown K2 ..oh wait, that doesn't help

 

[John E Janowitz]

Hi guys,

First off, can someone post the link the the latest Tumult parameters? I'd like to do a few comparsions but want to have accurate information before I do so. After I get the parameters I'll do up a couple models and then post my thoughts.

John