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I've heard so many outstanding reviews of the Avatar 2x12 cabs that I thought I'd try one out. I decided to go with a pair of Greenbacks in a closed back cab for a "vintage" classic rock sound.
The results so far have been a little disappointing, as I've run into two problems: 1) excessive boominess, and 2) harsh clipping at louder volumes on the higher notes on the high E-string.
I guess I'll start off by saying that my reference standard for "balanced" sound in a speaker is an EVM-15L in an EV TL-606 Thiele-Small enclosure built of marine grade baltic birch plywood. I use that cab for both guitar and 4-string bass, and its response is essentially flat, with no peakiness at the high end, and essentially flat at the low end with an f3 in stepped-down mode at about 40 Hz. The bass response of that cab is so good that when I play any of my amps through that cab, regardless of whether I'm playing clean or distorted, I often have the Bass control turned down to a minimal setting -- not necessarily at 0, but typically not over 3 or 4.
Problem 1: The Avatar 2x12 closed-back cab with new Greenbacks is HORRIBLY BOOMY.
The bass response of this speaker/cab combo is abnormal. I mean, it goes BOOM! BOOM! and it sounds like a Ghetto Blaster. Something is definitely not right. Even when I dial the Bass down to Zero, there's still too much bass. The only way that I can stand to play the cab is to provide some EQ cut. When using my Mesa Mk IV, for example, I have to use a lot of cut on the 80 Hz slider to make things tolerable. That isn't a particularly appealing opiton, as not all of my amps have EQ. Something definitely needs to be done to tame the bass in this beast. It sounds as if there's a resonant peak in both the amp and the cab that's abnormally magnifying the bass response. More on that later.
Problem 2: Metallic harshness on high notes instead of "compression"
There's also another problem with the cab -- the Greenbacks develop a pretty harsh metallic sound when they're fed power that comes anywhere near their power rating. Now I understand that Greenbacks will break up early and that this is part of their charm. Even in a closed back cab, its impossible to get any sort of BIG, loud and clear bass notes out of them at any appreciable volume. I can accept that, as these speakers will never compare to the EV for that sort of thing.
But some of their breakup is damned ugly -- especially on the high E string above the 14th fret. Long singing blues notes don't compress -- I hear a harsh and metallic sort of rubbing sound, as if there's some serious cone-cry or ghost noting going on.
I've swapped amps and cabs to eliminate the ghost noting hypothesis -- that's not the problem. So its definitely cone cry or just very harsh breakup. I'm getting a new 2x12 shipped in from Avatar to confirm that defective speakers isn't the problem.
Is this something that might go away with break-in, or are these Greenbacks always going to sound this ugly on the high notes whenever they're fed a reasonable amount of power?
Getting back to the BOOMINESS problem, here's what I've been thinking might be the culprits:
1. Box Construction The Avatar cab is made out of voidless 13-ply baltic birch, so it won't be as damped as an MDF cab would be. From a theoretical standpoint, I think that this should help to augment the cab's bass response, and might be contributing to the excessive bass problem.
2. Speaker Resonance. Celestion lists the Fs (speaker resonance frequency) of the Greenback as 75 Hz, which seems kind of high -- that is to say, one might expect that it would cause boominess in the lower octave of a guitar.
I've thought about crunching the numbers for a sealed box enclosure using this driver, but unfortunately Celestion doesn't disclose the necessary T-S parameters for their speakers. Notably, they provide Fs of 75 Hz in their speaker data, but they fail to report other TS parameters, such as Qts. This, of course, makes it difficult if not impossible to approach the problem from an engineering standpoint. So it looks like I'm stuck with emperical approaches.
So I guess I'd like to ask a couple of questions before I take any further action.
a. Does anyone know the T-S parameters for the Celestion Greenback? I have read on the Celestion web site that they don't like to report T-S parameters because they don't think they're meaningful. Celestion has gone so far as to say that their speakers perform well in any closed back enclosure. I would have to disagree with them.
I've sent Celestion an email requesting this data, but I doubt that it will be forthcoming. I guess my only other option would be to calculate the T-S parameters myself, but that seems like an awful waste of time: http://www.bcae1.com/spboxad3.htm
b. Is this boominess here to stay, or will it go away after break in?
c. What's the best way to break-in the speaker without placing it at risk? I've considered the 60 Hz AC variac option, the option of playing music through the cabinet, and driving the speakers with a sweep function generator. I've also thought about a more novel approach -- placing the speakers in free air and driving them at their resonant frequency while not exceeding Xmax. Theoretically, this should be safer for the voice coils, but unfortunately, Celestion doesn't tell us the value of Xmax.
d. Will stuffing the box help? IIRC stuffing a box with fiberglass or synthetic fabric batting will help to decrease the resonant frequency of the box. I'm wondering if anyone could report their observations in this regard.
TIA.
The results so far have been a little disappointing, as I've run into two problems: 1) excessive boominess, and 2) harsh clipping at louder volumes on the higher notes on the high E-string.
I guess I'll start off by saying that my reference standard for "balanced" sound in a speaker is an EVM-15L in an EV TL-606 Thiele-Small enclosure built of marine grade baltic birch plywood. I use that cab for both guitar and 4-string bass, and its response is essentially flat, with no peakiness at the high end, and essentially flat at the low end with an f3 in stepped-down mode at about 40 Hz. The bass response of that cab is so good that when I play any of my amps through that cab, regardless of whether I'm playing clean or distorted, I often have the Bass control turned down to a minimal setting -- not necessarily at 0, but typically not over 3 or 4.
Problem 1: The Avatar 2x12 closed-back cab with new Greenbacks is HORRIBLY BOOMY.
The bass response of this speaker/cab combo is abnormal. I mean, it goes BOOM! BOOM! and it sounds like a Ghetto Blaster. Something is definitely not right. Even when I dial the Bass down to Zero, there's still too much bass. The only way that I can stand to play the cab is to provide some EQ cut. When using my Mesa Mk IV, for example, I have to use a lot of cut on the 80 Hz slider to make things tolerable. That isn't a particularly appealing opiton, as not all of my amps have EQ. Something definitely needs to be done to tame the bass in this beast. It sounds as if there's a resonant peak in both the amp and the cab that's abnormally magnifying the bass response. More on that later.
Problem 2: Metallic harshness on high notes instead of "compression"
There's also another problem with the cab -- the Greenbacks develop a pretty harsh metallic sound when they're fed power that comes anywhere near their power rating. Now I understand that Greenbacks will break up early and that this is part of their charm. Even in a closed back cab, its impossible to get any sort of BIG, loud and clear bass notes out of them at any appreciable volume. I can accept that, as these speakers will never compare to the EV for that sort of thing.
But some of their breakup is damned ugly -- especially on the high E string above the 14th fret. Long singing blues notes don't compress -- I hear a harsh and metallic sort of rubbing sound, as if there's some serious cone-cry or ghost noting going on.
I've swapped amps and cabs to eliminate the ghost noting hypothesis -- that's not the problem. So its definitely cone cry or just very harsh breakup. I'm getting a new 2x12 shipped in from Avatar to confirm that defective speakers isn't the problem.
Is this something that might go away with break-in, or are these Greenbacks always going to sound this ugly on the high notes whenever they're fed a reasonable amount of power?
Getting back to the BOOMINESS problem, here's what I've been thinking might be the culprits:
1. Box Construction The Avatar cab is made out of voidless 13-ply baltic birch, so it won't be as damped as an MDF cab would be. From a theoretical standpoint, I think that this should help to augment the cab's bass response, and might be contributing to the excessive bass problem.
2. Speaker Resonance. Celestion lists the Fs (speaker resonance frequency) of the Greenback as 75 Hz, which seems kind of high -- that is to say, one might expect that it would cause boominess in the lower octave of a guitar.
I've thought about crunching the numbers for a sealed box enclosure using this driver, but unfortunately Celestion doesn't disclose the necessary T-S parameters for their speakers. Notably, they provide Fs of 75 Hz in their speaker data, but they fail to report other TS parameters, such as Qts. This, of course, makes it difficult if not impossible to approach the problem from an engineering standpoint. So it looks like I'm stuck with emperical approaches.
So I guess I'd like to ask a couple of questions before I take any further action.
a. Does anyone know the T-S parameters for the Celestion Greenback? I have read on the Celestion web site that they don't like to report T-S parameters because they don't think they're meaningful. Celestion has gone so far as to say that their speakers perform well in any closed back enclosure. I would have to disagree with them.
I've sent Celestion an email requesting this data, but I doubt that it will be forthcoming. I guess my only other option would be to calculate the T-S parameters myself, but that seems like an awful waste of time: http://www.bcae1.com/spboxad3.htm
b. Is this boominess here to stay, or will it go away after break in?
c. What's the best way to break-in the speaker without placing it at risk? I've considered the 60 Hz AC variac option, the option of playing music through the cabinet, and driving the speakers with a sweep function generator. I've also thought about a more novel approach -- placing the speakers in free air and driving them at their resonant frequency while not exceeding Xmax. Theoretically, this should be safer for the voice coils, but unfortunately, Celestion doesn't tell us the value of Xmax.
d. Will stuffing the box help? IIRC stuffing a box with fiberglass or synthetic fabric batting will help to decrease the resonant frequency of the box. I'm wondering if anyone could report their observations in this regard.
TIA.
Hopefully that will loosen them up a bit. Maybe I'll get lucky and find out that driver compliance is the problem and the problem will improve with time.
but it was still about the nicest-sounding thing I ever heard.
The math for proper Thiele-Small design can be daunting, but I don't see anything wrong with just messing around and tuning it by ear.
ceramic magnet. 
Since EV was acquired by a conglomerate a few years ago, I wouldn't be surprised if some MBA thought of that as a cost-cutting idea, an the marketing people just decided to use the 200-watt label. As I mentioned previously, I really don't think that the 300-watt kit would be at all bad. I'd be happy with either one.
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