Low level body/weight presence wanted: Can 12" full range deliver?

[rjbond3rd]

So it is reproducing 31.5Hz... The sound, though, and its not the "port noise" I suspected... it seems higher pitch/frequency than what it is supposed to be.

Hi udailey, the fundamental is "missing" but the overtones are still there. So you're hearing only the harmonics of the (missing) fundamental. Sometimes this is done intentionally.

If it's really high, maybe it could be bell resonance (where anything circular resonates at a tone where the wavelength = the circumference). That seems like a longshot though.

 

[Scottmoose]

Hmm, maybe I need to read up on what Fs is. My definition may be different than reality. I wonder if the BR enclosure is helping it get lower than its Fs. Guess it depends on how they tested it.

Fs is just the free-air resonance of the driver. Depending on the design, you can go lower.

Maybe this information you're reporting can mean something to GM and Scottmoose.

Nothing that hasn't been known for the best part of 9 decades or so.

Yes, CSA made a point of having their BR's go to 40 with authority. However it's supposed to be the nature of a BR to enable that. The question then becomes: at what cost to quality? Apparently, not much in this case - you're quite happy with all the frequencies.

True, I believe they usually tune their larger boxes to ~40Hz, although not everyone would necessarily agree with the way they go about it, or the advisibility of this with all their drivers. I certainly don't.

As for the quality question, depends who you ask, the design, circumstances & a myriad of other factors. Like any vented, back-loaded box, a BR cabinet reverses the phase of the output from the rear of the driver cone (that's why they're called phase inverting cabinets) & use that to provide more gain in the lower registers. There is a delay involved naturally, which can be audible or inaudible depending on the design.

I was wondering, though, what would happen if you put damping in your vent?

You'll reduce cabinet output & lower the first impedance peak.

...I have to reveal that my sig other has claimed the right that if there is none she be allowed to have the smaller of the choices. So far that's GM's 1.8 cu.ft. TL.

Only recently, after much reading, have I come to appreciate the value of relieving the driver, as GM describes it, of the majority of the high excursion BW when crossing closer to 80Hz. I feel I have no choice but to give up being able to cross my sub any lower than that. I was too idealistic about FR drivers... Or maybe "ignorant" would be the word.

No. Many users of FR units are quite happy with them run full range, with no support. Fine for some types of acoustic music for e.g., especially if you don't crank the volume up, but not ideal for your use.

Before I place myself at the mercy of my spouse, may I ask about this possibility? Or whether it would be bad form to ask if, relieved of the requirement for a lower extension than 80Hz altogether, you would have originally preferred a different approach?

I'd build GM's TL, if I wished for this sort of system & couldn't go bigger. However, since you ask about a smaller / higher tuned aperiodic box, for interest's sake, you could use the standard 2.8ft^3 CSA cab., with a 6in diameter x 2.25in long vent. Stuff a la a TL with ~0.8lbs ft^3 of material & stuff the vent too (same density), with a grill of some sort at each end to keep the damping in. See attached.

Kofi, it seems we will have to wait for someone to design nice horns for these things some day... I'm not sure 40Hz is going to do it for me, and I'm reasonably sure I do not want the adultaration, complexity and added cost of subs...yet.

GM's BIB not nice enough for you?

 

[Scottmoose]

I wouldn't make too much of the comparisons if you're comparing a 4 1/2in FE127E to a 12in AN.

 

[udailey]

Hi udailey, the fundamental is "missing" but the overtones are still there. So you're hearing only the harmonics of the (missing) fundamental. Sometimes this is done intentionally.

If it's really high, maybe it could be bell resonance (where anything circular resonates at a tone where the wavelength = the circumference). That seems like a longshot though.

Thanks RJ I appreciate the explanation. No its not really high just higher than, for instance, the 31.5Hz which is clearly audible so I knew something was amiss with the others below that.
Uriah

That tone/circumferance/wavelength is interesting. Audio waves do some weird things.

 

[udailey]

I wouldn't make too much of the comparisons if you're comparing a 4 1/2in FE127E to a 12in AN.

Much less a comparison and much more just "I have this nifty disc now lets see what the speakers I own will do."
Uriah

 

[VanJerry]

I'd build GM's TL, if I wished for this sort of system & couldn't go bigger. However, since you ask about a smaller / higher tuned aperiodic box, for interest's sake, you could use the standard 2.8ft^3 CSA cab., with a 6in diameter x 2.25in long vent. Stuff a la a TL with ~0.8lbs ft^3 of material & stuff the vent too (same density), with a grill of some sort at each end to keep the damping in. See attached.

Thank you kindly, Scottmoose.

Last, about stuffing:

I know for BR you actually line the sides with varying thickness between say, an inch or two. By a la TL stuffing do you mean where stuffing is fluffed out and evenly dispersed and it's dense enough to stay where it is - perhaps in a larger cab with the help of bracing? Would this density of stuffing make Matrix bracing unnecessary?


jerry

 

[Scottmoose]

Yes. Stuff the thing as per the density mentioned. Which will damp down almost the entire BW. This assumes hollow-fibre stuffing like dacron BTW.

As for bracing, bracing is to help control panel resonances, rather than internal, so they go hand in hand.

 

[VanJerry]

I forgot Scottmoose, before I leave you alone for a while,

Will these need a baffle step correction? Or is that standard these days as long as not a bipole, regardless of cab?



Jerry

 

[Scottmoose]

Depends where you put them, and the amp used.

In free space, expect a -3db frequency through step-loss at 314Hz, which is about right to ~start blending into room gain, especially if near a rear wall. TBH, I doubt you'd need any.

 

[VanJerry]

Great.
Thank you.

 

[Kofi Annan]

Anyway, using the AN12's published specs and assuming a zobel is added, a max flat impedance TL that except for size meets all the criteria of reasonably extended LF BW to allow a low acoustic subwoofer XO point, ~critically damped roll off slope for excellent impulse response, benign impedance if using a high output impedance amp and when properly located in-room may not even need a sub system for the majority of movie soundtracks:

L = 85.468"
CSA = 335.121"^2
zdriver = 32.197"

All dims approximate and sim assumes 1.091 lbs/ft^3 of polyfil. Compared to a sealed version it has a much lower Q Fs impedance, ergo flatter phase and slightly better impulse response, faster roll off below Fs and slightly more gain BW above it. If SS driven I doubt you can hear these subtle differences in-room though since it dominates down low, but you can always seal up the terminus (port) to test it.

Note that if you end load the driver its impulse response further improves a bit with the trade-off of its response mirroring the sealed's down to Fs.

GM

I see... so this is really a BIB, right?

I'd need to fold this mother as I have 8' foot ceilings and a 7' BIB with an open terminus at the top would likely cause acoustic / aesthetic / marriage issues.

I've managed to find this, courtesy of Godzilla, so I'm assuming this would be the way to get the 24" x 14" x 42.75" dimensioned model.

I'll need to figure out how to dimension the folds to keep the 85.468" L, so any shove in theright direction would be appreciated.

Lagging behind as usual...

Kofi

 

[GM]

GM's BIB...........

As in 'BIB' TL, the full size 16 ft^3 one. The 'BIB' pipe horn checks in at a Godzilla proportioned ~80.66 ft^3: http://www.diyaudio.com/forums/showthread.php?postid=1576770#post1576770

GM

 

[VanJerry]

Scottmoose or Anyone?

I've been thinking about 3.5 ft^2 giving a more relaxed realistic sound. It's been suggested to me I be better off with the larger BR than the 2.8.

using standard 3/4 in. material, the Commonsense's regular 2.8 ft^2 box is 39in. Tall x 14.5in. Wide x 12in. Deep

For WAV's sake I would have wanted to keep the Width the same and increase height and depth to accommodate any larger volume. Height would also help bring the AN 12's center closer to ear height - as Udailey did with his pedestals.

I'd rather not go above 42in tall, but at 42T x 14.5W x 13D (which gives 3.5 ft^2) the depth is approaching the width.

Question: I recall reading that equal dimensions is a no-no. Is 14.5 x 13 approaching a square enough to be a problem? If so I can make it 15 x 13 or kick the height up some more.


Jerry

 

[Scottmoose]

Methinks you're having a problem making your mind up.

When we say reflex, are we talking reflex or aperiodic?

Square dimensions are not ideal, but it depends how much damping is in the enclosure. Both of the examples I did assumed a fairly reasonable quantity of damping / stuffing so it's not going to be much of an issue. Undamped or more lightly damped, it starts getting to be a problem.

 

[VanJerry]

Hi Scottmoose,

I wasn't clear.

No, I was referring in both cases to your very own damped vent semi-aperiodic BR. The original as suggested being 3.5 ft^2 and the more recent smaller version being 2.8 ft^2. The thing is that someone who's advice I hold in esteem emailed me that the original 3.5 ft^2 would appear hardly any larger than the 2.8 ft^2 but be worth the sound quality.

I started to mess around with some dimensions. I felt I could go as visually tall as 42in. which would also improve the driver center ear height. (44in. would be better but too visually imposing as seen from the front.)

For WAV the dimension I could play with the most was depth but I was concerned about approaching a square section - hence my question.


Actually, I would like to take this opportunity to ask if significant sound comes out of these semi-aperiodic damped vents? I'm asking on behalf of the Center.

I've attached 2 possible configurations for a 12in. center based on the 2.8 ft^2 volume with one 6in. aperiodic damped vent. I'd like to be able to use "Center A" which is much deeper than it is wide allowing a smaller front face.


Jerry

 

[GM]

I'd rather not go above 42in tall, but at 42T x 14.5W x 13D (which gives 3.5 ft^2) the depth is approaching the width.

'Circling the drain' of indecision are we?

Rearranging the larger of my two TQWTs (~4.066 ft^3) yields a 14.875" depth and enough bottom end 'bloom' to probably not need any BSC:

GM

 

[Scottmoose]

Bingo.

Re output from an aperiodic cabinet of any description, by nature, it's extremely minimal.

 

[Nordic]

No man Scott, we look up to you for clever designs.
Any chance of a metronome with these drivers?

Or is there a specific quality to these drivers that only make them suitable for those sqaure coffins?

 

[VanJerry]

'Circling the drain' of indecision are we?

GM

Originally posted by Scottmoose
Bingo.

Not sure quite how to take that.

 

[VanJerry]

Rearranging the larger of my two TQWTs (~4.066 ft^3) yields a 14.875" depth and enough bottom end 'bloom' to probably not need any BSC:

GM

Thank you GM,

I appreciate that tweak. But I've had a few thoughts on my way around - or down - the drain.

Scottmoose doesn't believe BSC will be an issue in his design, especially with wall reinforcement - which I would expect to have in (over) abundance due to the small room:

In free space, expect a -3db frequency through step-loss at 314Hz, which is about right to ~start blending into room gain, especially if near a rear wall. TBH, I doubt you'd need any.

When I was considering the helper woofer direction for HT earlier I grappled with the fact that I might underestimate the room gain for my small 11x15 basement room. I must say, I've simply never purposely sought to own anything but flat response speakers in the past. And then most recently, I learn from Udailey that the AN 12 inch class have ample - if not alarming - authority in the LF.

So, while an even elevation across the whole bottom end could be desirable for HT I find myself both tempted and timid at the prospect of a more concentrated and isolated bump below 200Hz. One that I fear may actually accentuate the slight dip I see between the critical 200-300Hz in this case - which itself may be accentuated by any step-loss from 314Hz not improved by room gain. I would feel safer at a broader bump that spanned closer to 300Hz, but I gather that's not how TL's work.

I've begun to appreciate the role lack of experience has in this decision making process. I am certainly guilty of having proposed some wild schemes over the course of this thread. The fact is all but the bold operate from knowns. In my case what I know has never included a bump. And I will have 3 x 12in drivers in the small room, with another 2 x 8in, so I think I prefer not to add any further complexity than what I will face with room gain. In the worst case scenario what I planned to use is appropriately sized hinged baffle extensions on either side of the towers that would be folded away when not in use. And if that's not enough, the addition of bipolar with cast 8's augmenting each 12. Because by then I will have already begun to look like Nordic's avatar.

The other aspect that appeals to my inexperienced self is that the 3.5 ft^2 aperiodic damped vent BR provides some flexibility to go lower. Scottmoose has told me that the issue of running these drivers FR may not be so terrible except for HT (I presume at higher volumes.) So this design would allow me to better experiment with what kind of sub crossover I might like for music and lower volume HT and basically help me define the envelope of these AN cast 12's.


Jerry