Acme B2 - "optimum" distance?

[pogipoints]

Acme cabs have insignificant port output above 80Hz, so as long as the rear ports are within 3'6" of the back wall the ports will only contribute positively to the bass out front.

...

The other issue affecting how you hear your cab is directionality. If you can stay within 30 degrees of on-axis then you'll get a more accurate picture of your sound.

The above reasons are why I tend to place my Acme cab as close to the corner of any room as possible, so I can stand a good distance away from it and thus be close to on-axis despite being much taller than the cab, and have in next to as many room boundaries as possible for maximum reinforcement and minimum cancellation.

Alex

Thanks for the massive amount of info. This will be very helpful on my next gig.

 

[KJung]

Most probably due to my lack of early afternoon coffee, I have no idea what the above has to do with my post.

I think my rambling response post probably had to do with me having too much morning coffee

 

[jokerjkny]

I think my rambling response post probably had to do with me having too much morning coffee

i think 43% of my posting is affected by that, characterized by my "exurberant" tone.

 

[tombowlus]

BUT,

if you hear a fluttering sound, pushing the speaker into overdrive mode, thats not a good thing, and all the more reason the Acmes might not be the right cab for your app.

That might be an issue with the SWPS Stewart, too. I've encountered some similar problems when using my Acmes with SMPS amps like QSC and Stewart. But when I use a toroidal power supply (like CA9, or iAMP 800 head), I have no such problems.

[Edit: the 50 Hz filter on the PLX series amps may help reduce this problem, though.]

Tom.

 

[Lowtonejoe]

That might be an issue with the SWPS Stewart, too. I've encountered some similar problems when using my Acmes with SMPS amps like QSC and Stewart. But when I use a toroidal power supply (like CA9, or iAMP 800 head), I have no such problems.

Tom.

Tom,

Assuming that SMPS is switch mode power supply,

I have heard that the problem with SMPS's is that when used for bass, they tend to lose their oomph.

Something about capacitors not being able to maintain output for the required time or something like that.

Is that correct?

Or am I, possibly, barking up the wrong tree?

Could you point out the differences between toroidal and switch mode ps's?



Joe.

 

[KJung]

Tom,

Assuming that SMPS is switch mode power supply,

I have heard that the problem with SMPS's is that when used for bass, they tend to lose their oomph.

Something about capacitors not being able to maintain output for the required time or something like that.

Is that correct?

Or am I, possibly, barking up the wrong tree?

Could you point out the differences between toroidal and switch mode ps's?



Joe.

Layman's definition.... switching power supplies are very lightweight and 'create the power as you need it'. Analog (toroidal) power supplies have a large, heavy 'storage' device that is tapped when the power is needed.

Many bassists (including me) feel that the standard power supply products are better designed to deliver those huge power peaks that are needed when aggressively playing a bass in the lower registers, where some switching power supplies seem to run out of juice.... i.e., deliver a somewhat compressed, weak sound in the lowest end of the sound spectrum.

Many EE types have posted that this doesn't have to be the case with a 'properly designed' switching power supply. However, many current models (Walter Woods, AI, and the Stewart stuff) seem to have this 'problem'. That's why I find my 500 watt Thunderfunk to outperform my 1200 watt Walter Woods in low end punch.

When you combine the 'limitation' of a switching power supply amp with the extreme inefficiency, low tuning and high power needs of the Acme... it's probably 'the worst of all worlds'.

There are a couple of companies (EA and Epifani) that are trying to get around this 'problem' but still keeping their amps small and light by using a standard analog power supply with a class D amplifier. That's a cool idea... small, cool running amps with that analog power reserve to deliver a wumping low end.

 

[alexclaber]

The SMPS vs 'linear' power supply issue is a complex one, that I'm only starting to get to grips with the reality of, rather than the hearsay.

What it appears to come down to is that the THD of any power amp inevitably increases with frequency, so if you quote 20-20,000Hz power @ 0.1% THD for a typical amp, it is the output power in the high frequencies before exceeding 0.1% THD that restricts your power rating. This means that an amp which is rated at 1000W 20-20,000Hz <0.1% THD @ 4 ohms may be able to put out more than 1000W @ <0.1% THD in the low frequencies. There's a bonus for us bassists that you weren't expecting!

However, if you're designing a lightweight power amp and you're speccing it at 1000W 20-20,000Hz <0.1% THD @ 4 ohms then in the interest of keeping the weight down you may design it so the LF output matches the spec but doesn't exceed it (usually by using a less hefty SMPS). So when the amp says it puts out 1000W @ <0.1% THD, that's what you're getting - not >1000W at low frequencies as a heavier power amp may provide.

I went from a Mackie M1400 to a QSC PLX3002 in my rig. The PLX definitely betters the Mackie - more headroom, smoother sound, deeper tighter fatter bass - which is to be expected because it has usefully more power, and which more than makes up for any extra power above the rated power that the Mackie had in the lows. Maybe a CA9 would put out even more power in the lows despite being rated at similar power - but then we come up against the limitations of the cab as I'm alreading working on a 900W:350W amp:cab power rating ratio.

So maybe what you're getting with a well designed linear power supply amp is extra headroom in the low frequencies which you don't realise you have - it just translates as fatter lows. And if you want that extra fatness from a lightweight SMPS amp you should compensate by choosing an amp with a higher power rating.

Alex

 

[KJung]

So maybe what you're getting with a well designed linear power supply amp is extra headroom in the low frequencies which you don't realise you have - it just translates as fatter lows. And if you want that extra fatness from a lightweight SMPS amp you should compensate by choosing an amp with a higher power rating.

Alex

+1 on that (and good morning... or I guess good afternoon where you are!).... that's the way I interpret it. I was hoping that the 1200 watts of the Walter Woods would equate to the equivalent punch of a 500 watt traditionally designed amp, but it just doesn't IME. Ditto with the Focus. However, it's difficult to determine if that is actually a switching power supply issue, or just the design of those specific amps.

Edit: By the way, both those amps (WW and Focus) sound great and are plenty loud... I'm only talking about low end punch at high volumes.

Edit2: And Tom and Andy....yes, I know, I know, Jim Bergantino has miraculously found a class D amp and switching power supply that totally eliminate all these issues and will actually improve your time and groove

 

[tombowlus]

However, it's difficult to determine if that is actually a switching power supply issue, or just the design of those specific amps.

I agree. I have heard conventional power supply power amps that did not sound as good as one would expect from their ratings, as well as SWPS amps that didn't sound as good as I'd expect. Conversely, I have heard some really good SWPS amps, too. My opinion of the WWU is a bit more positive than yours, Ken, but I do think that that particular amp responds better with certain cabs. There's also a certain 'other amp' which you seem much more jazzed over than am I (though I do find that particular amp to be a highly competent performer). It might be that our personal preferences come into play yet again, and the subtle differences in the sound of different power sections (and yes, I'm one of those freaks who does believe it's possible to hear such a difference, even with matched gains! ) leads one of us to prefer one cab over the other. And then again, there is the amp/cab interaction, which may lead one amp to sound much better/worse with a given cab than it does with other cabs which may play to a given amps strengths/weaknesses.

I guess I'm focusing on three points. One, there are better and worse implementations of any kind of technology (SWPS and conventional power supplies included), two, different amps work better or worse with different cabs, and three, personal preference still comes into play.

Tom.

P.S.

Oh, and yes, I do happen to believe that the SWPS amp in the Bergantino IP cabs is the best iteration of such technology that I have heard. It hasn't done squat for my technique (I'm happy enough with my timing), though I has certainly enhanced my own personal enjoyment of my groove.

 

[KJung]

I agree. I have heard conventional power supply power amps that did not sound as good as one would expect from their ratings, as well as SWPS amps that didn't sound as good as I'd expect. Conversely, I have heard some really good SWPS amps, too. My opinion of the WWU is a bit more positive than yours, Ken, but I do think that that particular amp responds better with certain cabs. There's also a certain 'other amp' which you seem much more jazzed over than am I (though I do find that particular amp to be a highly competent performer). It might be that our personal preferences come into play yet again, and the subtle differences in the sound of different power sections (and yes, I'm one of those freaks who does believe it's possible to hear such a difference, even with matched gains! ) leads one of us to prefer one cab over the other. And then again, there is the amp/cab interaction, which may lead one amp to sound much better/worse with a given cab than it does with other cabs which may play to a given amps strengths/weaknesses.

I guess I'm focusing on three points. One, there are better and worse implementations of any kind of technology (SWPS and conventional power supplies included), two, different amps work better or worse with different cabs, and three, personal preference still comes into play.

Tom.

P.S.

Oh, and yes, I do happen to believe that the SWPS amp in the Bergantino IP cabs is the best iteration of such technology that I have heard. It hasn't done squat for my technique (I'm happy enough with my timing), though I has certainly enhanced my own personal enjoyment of my groove.

You know I had to tweek you a little bit on the Bergy lovefest

And again, I love my Walter for most things... it just doesn't do the big bottom as well as other amps. Also, as always, my comments are strictly based on gigging situations and my own tone and playing style. We all know that different techniques and tones work better with some amps than with others, and also that some amps that sound not so good in a controlled listening environment really sing on a gig, and others that sound great alone get totally buried in a mix.

I guess that's why it's good to have all these different comments and views from lot's of different players. The 'truth' usually eventually emerges!

 

[tombowlus]

Tom,

Assuming that SMPS is switch mode power supply,

I have heard that the problem with SMPS's is that when used for bass, they tend to lose their oomph.

Well, I am definitely a layman on this topic, but I'll share my thoughts/experiences anyway. I believe that, as Ken has pointed out, SWPS do not store energy in (comparatively) larger capacitors (as linear power supplies do: thanks for the clarification, Alex!) but rather attempt to generate sufficient energy on their "rails" to recharge their (comparitively) smaller capacitors and handle any transient (or other) demands. But, in practice, it seems to me that some SWPS do sound like they don't have as much dynamics, force, and overall "heft" as some toroid-based amps I have used. Furthermore, I have experienced what sounded like speaker distortion on two occassions with my Acmes, and each time, I noticed that the clip lights were going crazy on the amps in question (both SWPS-based amps). Further inspection of the amps proved them to be in perfect working condition. The speakers seemed not to be the culprit (they functioned fine with another amp), though on one occassion, one of my Low B-2II's had both 10" drivers damaged by what I perceived to be amp clipping.

FWIW, I think that the relative inefficiency of the Acmes was at work here, too. I had used both of those amps in this same room at a similar volume with different cabs and did not have a problem. And I also think that the AC wiring of this room (and the total load that each circuit was carrying) may have had an impact. It makes sense to me that a SWPS amp might be more dependant upon receiving a good, steady AC current in order to maintain proper functionality (while a conventional amp has a bit of a "cushion" in this regard - again, these are the hypothetical ramblings of a layman, so take them for what they are worth!).

It's not too scientific, but that's my "Acme with SWPS amps" experience in some greater detail. And FWIW, I don't think that my WWU (SWPS) sounds as good with my Acmes as my iAMP 800 (toroid). But, on the flip side, I prefer the SWPS amp in the Berg IP series to both my WWU and iAMP 800 (driving two HT112's).

Tom.

 

[KJung]

Hey Tom ... you are starting to type as fast as I do... you typist

 

[tombowlus]

You know I had to tweek you a little bit on the Bergy lovefest

As I like to dig at your for a couple of your own (somewhat baffling, to me ) lovefests.

We all know that different techniques and tones work better with some amps than with others, and also that some amps that sound not so good in a controlled listening environment really sing on a gig, and others that sound great alone get totally buried in a mix.

Good point, though I will say that not since the days that I gigged with Peavey cabs have I ever felt "buried in a mix", though as you say, part of that is playing style. I may not play all that fast, but you tend to hear the notes that I do hit.

Tom.

P.S.
In case sarcasm and good humor isn't coming across as well as I would like, I'm really just busting your chops on the "baffling" lovefest thing. I know what you like and why you like it, and hearing you play, I can totally see where your gear works for your sound.

 

[tombowlus]

Hey Tom ... you are starting to type as fast as I do... you typist

LOL!!! I was just thinking about that private (and public) joke the other day when we were PM-ing.

 

[KJung]

As I like to dig at your for a couple of your own (somewhat baffling, to me ) lovefests.


P.S.
In case sarcasm and good humor isn't coming across as well as I would like, I'm really just busting your chops on the "baffling" lovefest thing. I know what you like and why you like it, and hearing you play, I can totally see where your gear works for your sound.

+1 I baffle myself sometimes

 

[alexclaber]

I'm not sure if anyone noticed my vaguely technical assessment of the situation but I'm pretty sure that in a linear power supply the only thing storing energy is the capacitors not the transformer, and they are recharged 50 times a second by the transformer from the mains.

In a SMPS the capacitors are storing a much smaller amount of energy but are recharged many thousands of times a second so should be able to keep the rails at just as high a voltage even when the current demands are high.

I'm guessing that the downside of this is the demands on the mains supply, which this:

http://en.wikipedia.org/wiki/Switched-mode_power_supply

appears to confirm. (Worthwhile reading btw). Which then leaves me pondering whether the European mains supply (at twice the US voltage) is better suited to driving bass amps than the US mains (just as it does a much better job with electric kettles!).

Alex

 

[KJung]

Thanks for posting that link. I'll look forward to learning more about this topic, since I seem keep buying amps with switching power supplies!

Interesting on the 220 thing also... never really thought about that!

K

 

[tombowlus]

I'm not sure if anyone noticed my vaguely technical assessment of the situation but I'm pretty sure that in a linear power supply the only thing storing energy is the capacitors not the transformer, and they are recharged 50 times a second by the transformer from the mains.

Thanks for pointing that out. Note to TBers: for technical accuracy, read what Alex writes, and not what I write!

Which then leaves me pondering whether the European mains supply (at twice the US voltage) is better suited to driving bass amps than the US mains (just as it does a much better job with electric kettles!).

Alex

That is an excellent question. I would tend to think that they would, but man, that commute makes it tough to do a quick A/B comparision!

 

[KJung]

Thanks for pointing that out. Note to TBers: for technical accuracy, read what Alex writes, and not what I write!

Ditto with regards to my 'poor man's EE' ramblings!

 

[jkdahlman]

Just thought I'd add my .02 here. Most class D and class T (tripath) amps are very load dependant. As speaker impedance changes, the freq. resp.
changes all over the place.When they say a given FR into a 8 or 4 ohm load, they mean it. Anything outside that and the FR is different.
Of course, the problem now is: no speaker has a constant impedance. That varies all over the place, too You get a peak at Fs and then it falls away above and below that. There's a pretty typical plot here of a well known woofer. Invalid Link Removed Just for illustration.
I learned about this researching the UcD amps (www.hypex.nl). They seem to have solved this. I've ordered one of the 400W units to try. I will be using a toroidal PS, as I haven't heard a SMPS based amp I like yet, or that sounds better than my Bryston 4B I will say that the UcD amps I've heard so far have been really impressive. I know that Hypex makes amp modules for Hevos, too.
Not trying to cloud the waters.