AudioKinesis Cabs Part VI...

[Dee-man]

Hey Duke. Thanks for clarifying and resolving (for practical purposes, at least) the unbalanced plugged port scenario. Hope you're doing well otherwise. DM

 

[DukeLeJeune]

Duke, with regard to stacking a 1203 and a 1553 (both 8 Ohms?)...

Well, if things go as planned, the 1553 can change from a "4 ohm cab" to an "8 ohm cab" and back again. You see, the woofer's equivalent resistance is 3.9 ohms, which makes it a "high 4 ohm" cab. If you look up the equivalent resistance ("Re") of several 8-ohm woofers on Eminence's website, you'll see Re figures down in the 5.1 ohm range, sometimes even a bit less. Hmmm. The difference between 3.9 ohms (which would be a "4 ohm cab") and 5.1 ohms (which would be an "8 ohm cab") isn't very much, is it??

Back before starting this project, I asked Jerry McNutt (the woofer designer) whether anyone had ever complained that two of his Re = 5.1 ohm woofers in parallel (for Re = 2.55 ohms) had EVER complained that the load was too difficult for ANY 4-ohm rated amp. He said no, never. Window of opportunity??

So for this woofer, I asked Jerry to give me that high 4-ohms impedance, and of course he did. I plan to put a high-power-handling set of resistors totalling about 1.2 ohms in series the drivers, with an external switch so that the resistors can be bypassed. Switch up, it's a 4-ohm cab. Switch down, it's an 8-ohm cab, and can safely be run in parallel with other 8 ohm cabs. We would lose about 1.1 dB of efficiency, relative to a 1-watt input (which translates to 1.4 dB loss relative to a 2.83 volt input) in 8-ohm mode. To give a point of reference, we start out with slightly higher efficiency than the Kappalite 15 (non-LF), and go to slightly lower efficiency in 8-ohm mode, so that's the ballpark.

The bottom end also warms up a little bit from the effective change in woofer parameters (an increase in effective Qes) in 8-ohm mode.

... and the conventional wisdom regarding mixing cabs - well, whaddya think? .... I don't anything about phase response beyond the little bit I can surmise from the term itself. I do know what in/out of phase signals are.

I wouldn't know diddly about phase relationships at low frequencies either if I didn't have a modeling program that predicts them. I'm going to go into geek mode a bit, and then try to sum up in English.

Okay, if two woofers are exactly in phase, and exactly the same loudness (like in a 210 cab), then their combined output is 6 dB louder than either one alone (in the bass region anyway - we'll leave the top part of the spectrum for another day). If they are 180 degrees out-of-phase, then they cancel one another out pretty much completely.

Halfway in between, at 90 degrees (one woofer's output is 1/4 wavelength behind the other's), we have a situation called "phase quadrature". Here the combination of the two is not as efficient as when they were in phase, so we get +3 dB instead of +6 dB.

In my opinion, we want to have a lot less than 90 degrees of phase shift between the two cabs, because +3dB down low is still weaker than the +6 dB we'll be getting higher up, where we're above the phase shift region. I'd like to stay within 30 degrees, which should give us about +5 db.

Now one characteristic of a ported cab is, more phase shift at low frequencies than you get with a sealed cab. So the worst case scenario would be sealed-mode 1203 + all-ports-open-mode 1553. They would be 41 degrees apart at 62 Hz (first overtone of low-B), and 82 degrees apart at 31 Hz (fundamental of low-B). Imo this is too much. So, let's unplug the port on the 1203, and plug one of the ports on the 1553 (lowering its tuning frequency to more closely approximate that of the 1203). Now we're only 16 degrees apart at 62 Hz, and 28 degrees apart at 31 Hz. That should work quite well. I'm not sure the phase relationship down at 31 Hz matters all that much, but up at 62 Hz it definitely does.

Okay, in English: If both cabs are sealed, no problem combining them, as far as low-frequency phase goes. If both cabs are vented, it's best if they have tuning frequencies close to one another, and if not, you might have a little bit less low end than you were hoping for. If one cab is ported and the other is sealed, you're probably not going to have as much low end as you expected, but there may be times when that's a good thing!

How about power handling? The sonic result vs. stacking two of either cab?

Power handling of the 1553 will be 500 watts. Its excursion is about like the 3015 (non-LF). In this size box (kinda small) and with the tunings available (50 Hz is the highest), that should be plenty of excursion to not get into fartout , which in turn means you gotta pay closer attention to how the cab sounds. If it starts to sound compressed or distorted, that means you're pushing it too hard, back off a bit. That's the disadvantage about these uberwoofers that don't fartout - they also don't give you as much warning before they've been pushed past their thermal limits. My solution is, I make my cabs so darn expensive that people make sure they don't cook them.

Since the 1553 will be the louder cab (about 3 db up relative to the 1203), it's probably going to dominate the tone, but they will be from the same camp tonally so I don't think that would be a problem. For situations where the 1553 is paired with a different cab, it'll have the midrange smoother switch and a top-end rolloff switch to tame its native voicing if desired.

 

[DukeLeJeune]

Both my TC112 and TC115 are the AF versions, and I just love the rear-firing tweeters and I have never once found myself wanting to turn them off. It's really just more of a sense of added "air" and "space," which I would not want to take away.

Thank you Tom, that's more or less what I expect from the Hathor 1553. Yes I could do a simpler 15 + mid cab, but other builders are already doing that and doing it quite well, so in the interest of widening the choices that bass players have, I'd prefer to do something that's not really being done yet (as far as I know).

Hey Duke. Thanks for clarifying and resolving (for practical purposes, at least) the unbalanced plugged port scenario. Hope you're doing well otherwise. DM

To go into a bit more detail, the cone-rocking problem in the Thunderchild 112 prototype arose from a combination of factors. First, the ports were way off to one side of the woofer cone, resulting in a severely asymmetrical air load on the back of the cone at some frequencies (it only happened on some notes, probably related to the suspension system's behavior as well)). Second, the long voice coil of a Kappalite-class woofer doesn't need to be rocked at much of an angle before it taps against the side of the magnetic gap (which is the cylindrical hole through the middle of the magnet where the voice coil resides). Third, the Thunderchild 112 was a smallish box for that woofer, which can handle a LOT of watts, so the result is that it's a very high-internal-pressure box. Those higher pressures exaggerate the effect of the asymmetrical airload.

So after tearing my hair out for several days I called Jerry McNutt and told him about the clicking. He asked me to describe the box configuration, diagnosed the problem, and suggested moving the two ports down so they were symmetrically positioned behind the cone. He suggested placing one port above the other, so that we'd get a little bit of "chimney effect" cooling, as hot air would tend to move out of the upper port, drawing cooler air into the lower port. Fortunately there was just barely enough cabinet depth for the ports + woofer magnet, but the unbraced area of my back panel (there's a horizontal window-pane brace in between woofer and horn) was too small for me to stack the ports vertically (they're flared ports with large diameter outer flanges). So Jerry said to put them on a diagonal, and they fit that way, so that's what I did!

That cone rocking/clicking thing was really traumatic for me because, until I had it solved, my super-cool first bass cab (which was pretty much my only hope to save my company from the Great Recession) had a totally mysterious and totally fatal flaw. So I probably over-reacted to it.

Speaking of ports, I read a paper about the effect of ports on woofer motor temperature. The paper did not consider the possibility of one port high and one port low to provide some chimney effect, but it found that ports do indeed help, and that turbulence (chuffing) helps even more... but I'm not planning on taking advantage of that just yet! They also looked at a sealed box, and as expected, it was definitely worse than any of the ported configurations from a temperature management standpoint. Something to be aware of for that really loud gig where you're going to be pushing it hard.

Actually the best thing for that really loud gig is, bring another cab. If a cab is pushed hard what can happen is, by the end of a loud set, the magnet has heated up so much that it has lost a lot of its strength. It's not getting louder when you crank the volume (severe thermal compression), and the low end is sloppy (loss of magnetic strength). The natural tendency is to blame the amp because it doesn't seem to be doing its job (making the cab louder when you goose the volume control), but the amp is not to blame - it's a speaker issue. You may even think you need a new amp. But then the next set starts, and whadda ya know, it sounds fine again! Unfortunately damage from overheating tends to cumulative, so you don't want to overheat your cab unnecessarily even if it "survives". If you don't have the option of being in the PA, you need to bring more cab next time, which may require investing in a folding handcart, but it's usually a solvable problem. Even if you don't play any louder, spreading the same amount of heat between two cabs will make a very worthwhile difference, because power compression shoots up rapidly when the motor gets really hot but is pretty much negligible up until then.

Back to ports for a moment, I've gotten a lot less paranoid about cone rocking because nobody has reported it since I made that change, so the 1553 will have three ports in a clover-leaf pattern centered behind the woofer cone. Plug one, two, or all three... but when you just plug one, maintain the vertical separation. You'd think chuffing would set in as we severely reduce the port cross-sectional area below optimum, but remember we're dropping the tuning frequency at the same time, down into a region where there's not as much energy so we can get away with the reduced port area on a bass cab.

 

[svtb15]

I have some house cleaning to do with other gear..
I like my bass in a studio setting.. So that is why teh TC118 has appeal to me. But I never played studio cabs in a live gig setting in TX where guitars will get loud and obnoxious at times.
So im leaning towards the 1855. I guess it has a full pillow down low but still have a good mid growl and just enough aire ontop to be present but not mask and get involved with other high freak sources?

 

[Logo]

If a cab is pushed hard what can happen is, by the end of a loud set, the magnet has heated up so much that it has lost a lot of its strength. It's not getting louder when you crank the volume (severe thermal compression), and the low end is sloppy (loss of magnetic strength). The natural tendency is to blame the amp because it doesn't seem to be doing its job (making the cab louder when you goose the volume control), but the amp is not to blame - it's a speaker issue. You may even think you need a new amp. But then the next set starts, and whadda ya know, it sounds fine again! Unfortunately damage from overheating tends to cumulative, so you don't want to overheat your cab unnecessarily even if it "survives"

Does that mean when i hear my cab loosing its strength at the end of a loud set that it is already getting damaged in this situation, may be just a little bit, by overheating ?

 

[Dee-man]

Dang, Duke, that's quite a response! Glad to hear it for both of our sakes.

 

[DukeLeJeune]

I have some house cleaning to do with other gear..
I like my bass in a studio setting.. So that is why teh TC118 has appeal to me. But I never played studio cabs in a live gig setting in TX where guitars will get loud and obnoxious at times.
So im leaning towards the 1855. I guess it has a full pillow down low but still have a good mid growl and just enough aire ontop to be present but not mask and get involved with other high freak sources?

The woofer in the Thunderchild 118 is, to the best of my knowledge, unique in that it combines better displacement than the Kappalite 3015LF (that 3" larger cone diameter doesn't hurt) with a smooth top end. But that means the cab's a one-trick pony; it doesn't do growly.

The Hathor 1855 is also pretty much a one-trick pony. Its woofer is more of a brute, with a big 4" voice coil (rare among bass cabs), powerful neo motor, and very long excursion, things that translate into solid impact rather than the "full pillow" of yesteryear's 18's. But smooth is not its thing.

The Thunderchild 212 is in the same general output class as these two cabs, and comes a bit closer to being a dual-voiced cab, but it's still more on the studio side.

A true dual-voiced (studio smooth/Texas growly) cab is something I'd really like to do one day, and that day may be about to get closer: A sample of what might be an important little puzzle piece will be shipped to me in the coming week or so.

 

[DukeLeJeune]

Does that mean when i hear my cab loosing its strength at the end of a loud set that it is already getting damaged in this situation, may be just a little bit, by overheating ?

Thermal compression (along with thermal modulation, its faster-acting little brother) is a dirty little secret. It means speaker systems don't get as loud as a quick calculation says they can.

As a ballpark rule of thumb, a woofer has about 1 dB of thermal compression after operating for a while at 1/10th its rated power; about 2.5 dB of compression after running at 1/2 its rated power; and about 4 dB of compression after running at its full rated power. Note that when going from half power to full power we'd expect a 3 dB increase, but we only get 1.5 dB, so fully half of our additional power is lost to compression!

My guess is, we're not in danger at 1 dB of thermal compression, but somewhere between there and 2.5 dB, we ought to be concerned.

(I don't know as much about fast-onset thermal modulation, but can try to go there if anyone is interested.)

Now the good news is, the ear is more sensitive to level changes in the bass region than in the midrange, so I think there's a pretty good chance you'll notice the onset of thermal compression before you get up into the danger zone (but I don't really know where the danger zone starts).

If you look at a set of equal-loudness curves, you'll see that they bunch up closer together in the bass region, which means that a small change in level is more perceptible. It takes a 10 dB increase in SPL to produce a subjective doubling of volume in the midrange region, but you can get that same subjective doubling of volume for only 6 or 7 dB increase in the bass region! So that 1 dB loss in the bass region (due to thermal compression) almost sounds like as big a change as 2 dB in the midrange. This is also why dialing in the settings on your amp often takes more finesse than on the guitarist's amp - small changes are more audible!

I run into this phenomenon all the time in the home audio world, where dialing in the exact setting on a subwoofer amp takes fine adjustments that are hard to get right - the difference between "just right" and "too much" or "too little" is just a whisker on the crappy little knobs we have. It's like you grab the knob and just think about turning it, and that's often the right amount.

 

[tombowlus]

The Thunderchild 212 is in the same general output class as these two cabs, and comes a bit closer to being a dual-voiced cab, but it's still more on the studio side.

Dangit, Duke! Now you have me intrigued by the TC212! How does it compare to the TC115?

And if I might, may I also suggest a pair of 1203's as a potential alternative to either a TC118 or an 1855. Two of those 1203's can cover a lot of ground, including "reasonably smooth" and "reasonably growly," IME/IMHO.

 

[Marial]

The TC212 absolutely slams. There are two reasons I'm selling mine: 1. I simply don't need that much cab, 2. the lightly mid-forward character of the Bergantino CN112 meets my tonal goals ever so slightly.

In my experience, you can get something different from Duke's cabs but you can't get something better.

 

[svtb15]

Thank you for your time and fantastic answers...
PS Im from brooklyn and stranded in TX Ive learned to do what they like here... In NYC i was all about clear, clean, hifi.. I still like hifi but like to dull it down just a tad..

The woofer in the Thunderchild 118 is, to the best of my knowledge, unique in that it combines better displacement than the Kappalite 3015LF (that 3" larger cone diameter doesn't hurt) with a smooth top end. But that means the cab's a one-trick pony; it doesn't do growly.

The Hathor 1855 is also pretty much a one-trick pony. Its woofer is more of a brute, with a big 4" voice coil (rare among bass cabs), powerful neo motor, and very long excursion, things that translate into solid impact rather than the "full pillow" of yesteryear's 18's. But smooth is not its thing.

The Thunderchild 212 is in the same general output class as these two cabs, and comes a bit closer to being a dual-voiced cab, but it's still more on the studio side.

A true dual-voiced (studio smooth/Texas growly) cab is something I'd really like to do one day, and that day may be about to get closer: A sample of what might be an important little puzzle piece will be shipped to me in the coming week or so.

 

[svtb15]

Is it possible that the TC212 would be equal VOL to two CN112s? or more...?
I have heard the TC115 that my friend adores.. It sounded like a pro rig...or a Meyer. .Ill bet Anthony Jackson would play one in a heartbeat... .I guess the TC212 is similar...
I want to find a GREAT cab that has fullness is not mid peaky YET has smooth clear mids of a P bass or J bass.. Sometime Active J5 but mostly passive. And be loud as or louder than a pair of other 112 cabs.. Im searching

The TC212 absolutely slams. There are two reasons I'm selling mine: 1. I simply don't need that much cab, 2. the lightly mid-forward character of the Bergantino CN112 meets my tonal goals ever so slightly.

In my experience, you can get something different from Duke's cabs but you can't get something better.

 

[MarkA]

Duke, many thanks for your superlatively detailed replies. I am glad that a classy operation like yours survived the Great Recession. Live long and prosper.

Oh, it's Back to the Future Day!

 

[Marial]

Is it possible that the TC212 would be equal VOL to two CN112s? or more...?
I have heard the TC115 that my friend adores.. It sounded like a pro rig...or a Meyer. .Ill bet Anthony Jackson would play one in a heartbeat... .I guess the TC212 is similar...
I want to find a GREAT cab that has fullness is not mid peaky YET has smooth clear mids of a P bass or J bass.. Sometime Active J5 but mostly passive. And be loud as or louder than a pair of other 112 cabs.. Im searching

I'm confident in saying the TC212 could meet your needs. I'm certain it would be loud enough for you.

 

[Freddels]

Is it possible that the TC212 would be equal VOL to two CN112s? or more...?
I have heard the TC115 that my friend adores.. It sounded like a pro rig...or a Meyer. .Ill bet Anthony Jackson would play one in a heartbeat... .I guess the TC212 is similar...
I want to find a GREAT cab that has fullness is not mid peaky YET has smooth clear mids of a P bass or J bass.. Sometime Active J5 but mostly passive. And be loud as or louder than a pair of other 112 cabs.. Im searching

I would say my TC115-8 does all that.

 

[tombowlus]

I would say my TC115-8 does all that.

+1 Yeah, that does sound like what the TC115 has to offer. I'm curious as to how the TC212, TC115 and TC118 compare/contrast.

 

[Chef]

For what it's worth; I was beating the holy heck out of that cab when it did that.
It's likely most scenarios would never cause that.
Cool that the "issue" got solved though!

Thank you Tom, that's more or less what I expect from the Hathor 1553. Yes I could do a simpler 15 + mid cab, but other builders are already doing that and doing it quite well, so in the interest of widening the choices that bass players have, I'd prefer to do something that's not really being done yet (as far as I know).



To go into a bit more detail, the cone-rocking problem in the Thunderchild 112 prototype arose from a combination of factors. First, the ports were way off to one side of the woofer cone, resulting in a severely asymmetrical air load on the back of the cone at some frequencies (it only happened on some notes, probably related to the suspension system's behavior as well)). Second, the long voice coil of a Kappalite-class woofer doesn't need to be rocked at much of an angle before it taps against the side of the magnetic gap (which is the cylindrical hole through the middle of the magnet where the voice coil resides). Third, the Thunderchild 112 was a smallish box for that woofer, which can handle a LOT of watts, so the result is that it's a very high-internal-pressure box. Those higher pressures exaggerate the effect of the asymmetrical airload.

So after tearing my hair out for several days I called Jerry McNutt and told him about the clicking. He asked me to describe the box configuration, diagnosed the problem, and suggested moving the two ports down so they were symmetrically positioned behind the cone. He suggested placing one port above the other, so that we'd get a little bit of "chimney effect" cooling, as hot air would tend to move out of the upper port, drawing cooler air into the lower port. Fortunately there was just barely enough cabinet depth for the ports + woofer magnet, but the unbraced area of my back panel (there's a horizontal window-pane brace in between woofer and horn) was too small for me to stack the ports vertically (they're flared ports with large diameter outer flanges). So Jerry said to put them on a diagonal, and they fit that way, so that's what I did!

That cone rocking/clicking thing was really traumatic for me because, until I had it solved, my super-cool first bass cab (which was pretty much my only hope to save my company from the Great Recession) had a totally mysterious and totally fatal flaw. So I probably over-reacted to it.

Speaking of ports, I read a paper about the effect of ports on woofer motor temperature. The paper did not consider the possibility of one port high and one port low to provide some chimney effect, but it found that ports do indeed help, and that turbulence (chuffing) helps even more... but I'm not planning on taking advantage of that just yet! They also looked at a sealed box, and as expected, it was definitely worse than any of the ported configurations from a temperature management standpoint. Something to be aware of for that really loud gig where you're going to be pushing it hard.

Actually the best thing for that really loud gig is, bring another cab. If a cab is pushed hard what can happen is, by the end of a loud set, the magnet has heated up so much that it has lost a lot of its strength. It's not getting louder when you crank the volume (severe thermal compression), and the low end is sloppy (loss of magnetic strength). The natural tendency is to blame the amp because it doesn't seem to be doing its job (making the cab louder when you goose the volume control), but the amp is not to blame - it's a speaker issue. You may even think you need a new amp. But then the next set starts, and whadda ya know, it sounds fine again! Unfortunately damage from overheating tends to cumulative, so you don't want to overheat your cab unnecessarily even if it "survives". If you don't have the option of being in the PA, you need to bring more cab next time, which may require investing in a folding handcart, but it's usually a solvable problem. Even if you don't play any louder, spreading the same amount of heat between two cabs will make a very worthwhile difference, because power compression shoots up rapidly when the motor gets really hot but is pretty much negligible up until then.

Back to ports for a moment, I've gotten a lot less paranoid about cone rocking because nobody has reported it since I made that change, so the 1553 will have three ports in a clover-leaf pattern centered behind the woofer cone. Plug one, two, or all three... but when you just plug one, maintain the vertical separation. You'd think chuffing would set in as we severely reduce the port cross-sectional area below optimum, but remember we're dropping the tuning frequency at the same time, down into a region where there's not as much energy so we can get away with the reduced port area on a bass cab.

 

[Dee-man]

I'm curious as to how the TC212, TC115 and TC118 compare/contrast.

Well, I'm just a weekend hack with an insatiable taste for the latest and greatest, but I'll do my best, having owned/still own all three (TC115AF (4 ohms in composite), TC118AF, and TC212):

First, they will all do what svtb15 is looking for, IMHO, with slight differences, of course, all of which I attribute to speaker size.

They are very similar in mids/highs to my ears. The TC212 sounds like it has the lowest extension (only by a hair), and is the punchiest. The TC118 has great low end too and is just huge in sound and dispersion. Reminded me of a Berg NV215 cab in how it envelopes the room. In comparison to these two, the TC115 is just an ordinary awesome 15 (!). Not as big as the TC118, not as punchy as the TC212, but is smooth and articulate from top to bottom and gets plenty loud. It is bigger and perhaps a touch darker than the TC112. It does not get as boomy as the TC118 or TC212 can (esp. when ports are unplugged).

If anyone has specific questions, I can try to answer them. In short, all different flavors of excellent. Thanks Duke!

 

[tombowlus]

Well, I'm just a weekend hack with an insatiable taste for the latest and greatest, but I'll do my best, having owned/still own all three (TC115AF (4 ohms in composite), TC118AF, and TC212):

First, they will all do what svtb15 is looking for, IMHO, with slight differences, of course, all of which I attribute to speaker size.

They are very similar in mids/highs to my ears. The TC212 sounds like it has the lowest extension (only by a hair), and is the punchiest. The TC118 has great low end too and is just huge in sound and dispersion. Reminded me of a Berg NV215 cab in how it envelopes the room. In comparison to these two, the TC115 is just an ordinary awesome 15 (!). Not as big as the TC118, not as punchy as the TC212, but is smooth and articulate from top to bottom and gets plenty loud. It is bigger and perhaps a touch darker than the TC112. It does not get as boomy as the TC118 or TC212 can (esp. when ports are unplugged).

If anyone has specific questions, I can try to answer them. In short, all different flavors of excellent. Thanks Duke!

Thanks! That makes sense. I am a huge fan of the TC115AF. It can cover any gig that I do, and I love it with clean tones, overdriven tones, and heavy effects. The pair of 1203's can also cover the same ground, but in a slightly different fashion.

 

[Type-55]

I have a question for the collective on adjusting the tone of the TC-112V.1 thru a change in pickups.
Looking for a little more cut in a mix but nothing harsh. Currently I have a jazz bass with Nordy NJ-4's running passive,
with LaBella light gauge flats and a TH 500. Great tone but a little too smooth. The guitarist say's he has a hard time hearing me sometimes.
Where have we heard that before. So rather than sell the cab and go thru all the work to find a new cab that has the sonic merits of this cab,
I thought a set of EMG's might solve the issue. Any thoughts on this are appreciated.