If the 7B is rated at 500 wpc at both 8 & 4 ohms, that was the amp / Stereophile review that i was referencing. When i saw that spec, i laughed out loud and immediately thought that Bryston was a fan of SS Mac designs.
As far as being dynamically limited, this has to do with many different factors, impedance being one of them.
In terms of "doubling down" and rated power, most all of that is BS. Very few amps come close to doubling down in reality, even if they are factory rated to do so. If you doubt this, forget the "rated power" and start looking at the actual power as measured at clipping vs impedance. Manufacturers can fudge a rating however they want to make a product look good on paper, but what it actually does "balls out" is what really counts.
Once you start looking at the power at clipping vs impedance, you'll soon see that most amps are quite lacking in power supply, quite lacking in output capacity and / or a combination of the two. Things really get hairy when you start seeing what some of these supposed "big" amps do when called upon to deliver steady state power into very low impedances.
There are some highly reviewed SS amps that actually do less power at 2 ohms than they do at 8 ohms. Needless to say, these amps will behave like "sonic chameleons" depending on the speaker / cable load that they are connected to. Just as the impedance dips and the amp needs to step up to the plate, it lays down and "bogs out".
Needless to say, this doesn't sound good, although it may be difficult to understand why a certain amp / cable / speaker combo just doesn't sound "right". That is, unless one knows how to interpret test results and can put 2 + 2 together.
This is one of the reasons why some speaker cables seem to work better with some amp / speaker combo's. That is, by changing the nominal impedance ( along with some other factors of the cable ), the cable itself can act as a "buffer" to what the amp sees. Obviously, if the amp is having a hard time driving lower impedance loads, using a higher impedance cable can help stabilize the system.
On the other hand, if the amp is truly up to driving the speakers, and the amp and speakers are both reasonably accurate performers, something along the lines of the flat Goertz cabling / Electro-Fluidics ( British made Goertz clones ) / Magnan Reference and possibly the Ridge Street speaker cables should sound best. I can't say for sure about the RSA's as they don't have any worthwhile info posted about them on their website. From what i can see, they would appear to be a low impedance design utilizing flat solid core conductors for minimal skin effect. This description should not be confused with the design of Nordost speaker cabling, as it is anything but a low impedance design.
Selecting an amp that exhibits unstable performance into low impedances can tend to have you juggling tons of variables, especially cabling, in order to get decent performance out of it. In the long run, many find that it is both cheaper and easier to just buy another amp that is both more stable and more robust in design.
In this regard, the Bryston 14 that you referenced wasn't quite this bad, but it only went up 30 watts going from 8 ohms to 2 ohms at clipping. You have to admit, this is pretty pathetic in terms of percentages vs what one would / should expect according to theory. On top of that, and if you REALLY look at the chart, the amp is actually going into clipping just prior to the rated 900 wpc rating @ 4 ohms. You can see this as the distortion by-products start to climb through the roof on what looks almost like a straight vertical climb at this point. This is usually a sign of high negative feedback, which tends to make the amp sound "sterile" and lifeless. High frequency performance of such a design is sometimes described as sounding cold, hard or bright, especially when being pushed.
While some would say that this power level is so high that nobody would ever hear it / experience this under normal conditions, those are the same people that have never really measured dynamic power demands of low efficiency, low impedance speakers at higher volumes. Obviously, some of this can be avoided through careful system matching, but once again, unless one knows how to properly interpret test results, this can be a long and frustrating path.
Obviously, everything that i've discussed here pertains to SS designs ( and not just Bryston's ), as tubes work in a VERY different manner. Tube amps really are very different creatures in most cases. Sean
>
As far as being dynamically limited, this has to do with many different factors, impedance being one of them.
In terms of "doubling down" and rated power, most all of that is BS. Very few amps come close to doubling down in reality, even if they are factory rated to do so. If you doubt this, forget the "rated power" and start looking at the actual power as measured at clipping vs impedance. Manufacturers can fudge a rating however they want to make a product look good on paper, but what it actually does "balls out" is what really counts.
Once you start looking at the power at clipping vs impedance, you'll soon see that most amps are quite lacking in power supply, quite lacking in output capacity and / or a combination of the two. Things really get hairy when you start seeing what some of these supposed "big" amps do when called upon to deliver steady state power into very low impedances.
There are some highly reviewed SS amps that actually do less power at 2 ohms than they do at 8 ohms. Needless to say, these amps will behave like "sonic chameleons" depending on the speaker / cable load that they are connected to. Just as the impedance dips and the amp needs to step up to the plate, it lays down and "bogs out".
Needless to say, this doesn't sound good, although it may be difficult to understand why a certain amp / cable / speaker combo just doesn't sound "right". That is, unless one knows how to interpret test results and can put 2 + 2 together.
This is one of the reasons why some speaker cables seem to work better with some amp / speaker combo's. That is, by changing the nominal impedance ( along with some other factors of the cable ), the cable itself can act as a "buffer" to what the amp sees. Obviously, if the amp is having a hard time driving lower impedance loads, using a higher impedance cable can help stabilize the system.
On the other hand, if the amp is truly up to driving the speakers, and the amp and speakers are both reasonably accurate performers, something along the lines of the flat Goertz cabling / Electro-Fluidics ( British made Goertz clones ) / Magnan Reference and possibly the Ridge Street speaker cables should sound best. I can't say for sure about the RSA's as they don't have any worthwhile info posted about them on their website. From what i can see, they would appear to be a low impedance design utilizing flat solid core conductors for minimal skin effect. This description should not be confused with the design of Nordost speaker cabling, as it is anything but a low impedance design.
Selecting an amp that exhibits unstable performance into low impedances can tend to have you juggling tons of variables, especially cabling, in order to get decent performance out of it. In the long run, many find that it is both cheaper and easier to just buy another amp that is both more stable and more robust in design.
In this regard, the Bryston 14 that you referenced wasn't quite this bad, but it only went up 30 watts going from 8 ohms to 2 ohms at clipping. You have to admit, this is pretty pathetic in terms of percentages vs what one would / should expect according to theory. On top of that, and if you REALLY look at the chart, the amp is actually going into clipping just prior to the rated 900 wpc rating @ 4 ohms. You can see this as the distortion by-products start to climb through the roof on what looks almost like a straight vertical climb at this point. This is usually a sign of high negative feedback, which tends to make the amp sound "sterile" and lifeless. High frequency performance of such a design is sometimes described as sounding cold, hard or bright, especially when being pushed.
While some would say that this power level is so high that nobody would ever hear it / experience this under normal conditions, those are the same people that have never really measured dynamic power demands of low efficiency, low impedance speakers at higher volumes. Obviously, some of this can be avoided through careful system matching, but once again, unless one knows how to properly interpret test results, this can be a long and frustrating path.
Obviously, everything that i've discussed here pertains to SS designs ( and not just Bryston's ), as tubes work in a VERY different manner. Tube amps really are very different creatures in most cases. Sean
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