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- - Slam (https://www.audiobanter.co.uk/uk-rec-audio-general-audio/533-slam.html)

On Sat, 4 Oct 2003 08:33:02 +0100, Chris Morriss
wrote:

In message , Stewart Pinkerton
writes
On 03 Oct 2003 07:08:40 GMT, John Phillips
wrote:

"Slam" is an effect I have never actually felt in the concert hall even
with big bass percussion so it may only be an artificial effect which
occurs in "small" listening rooms. It happens in mine on all kinds
of music. Perhaps it is an effect which gets created at large rock
concerts but I only listen to rock at home.

It is certainly used as reviewer jargon and as a marketing term. The
differences of opinion here belie statements to the effect that it is
a well understood term.

It's commonly associated with a noticeable hump in the bass response
around 60-80 Hz. Check out any dance club, you'll find a fair bit of
EQ in this band, probably combined with speakers which drop off fast
below 50Hz. This gives bass which is commonly described as 'tight' and
'fast', with plenty of 'slam'.

Since a hump in that part of the bass spectrum and a fast roll-off below
that is exactly what I hate (I like well-damped bass that continues
slowly dropping off as the frequency drops. One of the reasons I still
can't agree with you about reflex boxes) then I'll avoid any speakers
that people say have 'Slam'.

It should be noted that whether a speaker is a sealed box or a reflex
design says *nothing* about how well-damped is its bass response.
That's purely a function of system 'Q'. Listen to the bigger ATC
designs for top-class examples of well-damped reflex sytstems which
will thump your chest cavity with ease on loud kick-drum (now that's
what *I* call 'slam'!), but have no lumpiness or 'one note' quality
about their bass response. Since they're flat down to 20-25Hz, how
fast they drop off *below* that frequency is hardly relevant to music
listening.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

In article , Andy Evans
wrote:
Your description seemed to be equivalent to saying "a koala bear is not
a kangeroo".

More like saying "why should I define what a flying pig is"

You've reminded me of an old Pink Floyd LP. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article , Stewart Pinkerton
wrote:
On Fri, 03 Oct 2003 16:09:47 +0100, Jim Lesurf
wrote:

In article , Stewart Pinkerton
wrote:
On Thu, 02 Oct 2003 19:56:27 +0100, Laurence Payne
wrote:

Any really good amplifier will be able to handle full power
more-or-less continuously - certainly for several minutes - without
a problem.

And wouldn't object to being asked to deliver considerably more if
momentarily demanded? You seem to be arguing against transient
headroom :-)

Anyone who knows anything about amps *does* argue against 'transient
headroom', which is just another word for a cheap power supply.

In that case, I'm afraid I don't know much about amplifiers. :-)

Oh, come now, that can't be true! :-)

Well, I know a damn sight less that I used to, and far less than might be
useful. :-) If nothing else, my knowledge of many modern designs is quite
limited.

My own view/experience is that it can be quite useful in the context of
reproducing musical signals to arrange for the amp/PSU to have a
short-term power ability that is well above the sustained power
ability. The reasons for this in my view are;

1) Most music tends to include relatively brief musical transient
events which reach short-term levels well above the mean level.

Fair comment, *but* 'relatively brief' is generally (a lot) more than 20
milliseconds, so that it's still necessary for the power supply to be
fully recharged by the mains.

Yes, I agree that we need to be careful with 'brief' here as some transient
peaks may last for somewhat longer than a single spike, so we need to take
this into account. The rails have to stay up for long enough to cope with
any reasonable length/power transients that tend to come along.

2) Allowing the rail voltages to fall under sustained demand helps
reduce the power dissipation in the output devices compared with what
you get if you try to maintain the same rail levels as existed for
short-term high power bursts. This keeps the device tempeatures down,
etc, which can be useful.

That's true, but also leads to bias changes in many amps, meaning that
the sound can have a different character after loud passages.

Yes, that's the kind of reason why I would include the qualification about
ensuring the amp design isn't bothered much if the rails waggle around a
bit.

Note that I'm referring to pretty poor amps here - but then you've
pretty much confined the field to such amps, with your pre-qualification
of extremely saggy power supplies. I take it that we're not dealing with
Class G multi-rail amps here?

No. I'm really meaning the deliberate choice of designing the PSU so the
rails do fall under sustained demand, but hold up for musical transients.

The main disadvantages are in my view:

1) The sustained mean power levels measured in a review tend to be
under-reading the actual ability (e.g. the 700 I designed only rated at
200Wpcs 'rms' sic both channels sinewave driven, but could actually
deliver around 300Wpc mean per channel for a tenth of a second or so.
(This is not the peak 'instananeous' transient value, which I'd agree
is misleading.) Thus in terms of actual use the 200Wpc perhaps didn't
really indicate how much the amp could provide with music.

2) You have to ensure the amp does not produce distortion or become
upset in some way when the rails fluctuate. This seems sensible,
anyway, to me, as it avoids things like distortion crosstalk between
channels.

I'm interested in the logistics of an amp with such a disparity between
its 'toneburst' and continuous ratings. Was this a PSU problem, or just
thermal dissipation in the output stage?

In the case of the specific amp I was referring to it was not a 'problem'
as such, but a deliberate design choice. I could have gone for a 'stiffer'
supply, or made it stabilised, but felt it was better not to.

My view tended/tends to be that allowing the rails to fall under sustained
(high) current demand tends to help keep down the output device
temperatures when high continuous powers are required into low loads in
particular. This can be useful for various thermal and SOA reasons.

This is in the context, though, of struggling get high powers and
reliability on the one hand, but avoid either fans (noise) or a whopping
great box/heatsinks. Also in the context of the days of IHFA-202 which
required powers to be rated on a pretty nasty basis that was designed to
cause poor-spec amps to burst into flames, but with other rules about the
max temperature any external (touchable) heatsink could reach.

Hence I tended prefer to focus on ensuring the performance with real music
means you can get high powers and currents, well beyond what the sinewave
ratings might imply. In effect, for a given cost, etc, it tended to come
out as a choice between

A) about 220W short or long term, with 'clamped' rails

B) about 300W or more short term, but 200W long term, with soggy rails.

'B' seemed a better deal to me for use with music. Snag was, it meant we
could only say it was a 200Wpc amp... :-)

I should say that for myself, I much prefer a 'stiff' power supply, with
all that means in terms of coping with tough loudspeaker loads. This may
be overkill for many systems, but it gives me confidence that thew sound
of the amp won't change under any conditions of load or musical dynamics.

I'd agree that you need plenty of current available. For a 200Wpc I'd go
for well over 30Arms continuous, and bigger short-term available. However
soggy rails don't have to preclude this.

I used to be wary of stabilised rails, as this can lead to problems with
getting the stabilisers to work well. In effect, they end up becoming part
of the amp itself. My own preference was to spend the time and money on the
amp itself, working from a more basic PSU (old fashioned transformer,
bridge, and big caps with low ESR.)

I tend to also regard it as important that the amp should not be affected
by rail waggle for other performance reasons, so soggy rails should not be
a problem if the design was one I was happy with. Of course, rails could be
*too* soft and soggy, and then the power rating becomes a joke. So this is
a matter of getting things about right.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

On Sat, 04 Oct 2003 11:48:43 GMT, Stewart Pinkerton
wrote:

It should be noted that whether a speaker is a sealed box or a reflex
design says *nothing* about how well-damped is its bass response.
That's purely a function of system 'Q'. Listen to the bigger ATC
designs for top-class examples of well-damped reflex sytstems which
will thump your chest cavity with ease on loud kick-drum (now that's
what *I* call 'slam'!), but have no lumpiness or 'one note' quality
about their bass response. Since they're flat down to 20-25Hz, how
fast they drop off *below* that frequency is hardly relevant to music
listening.

The ATC SCM 300A system is perhaps the best example of this, and *the*
best loudspeaker system that I have ever heard. I am personally
looking forward to getting my ATC Active 10s and CA2 pre-amplifier
which should be ready in the next few days!

--
Anthony Edwards

In message , Jim Lesurf
writes
I'd agree that you need plenty of current available. For a 200Wpc I'd go
for well over 30Arms continuous, and bigger short-term available. However
soggy rails don't have to preclude this.

I used to be wary of stabilised rails, as this can lead to problems with
getting the stabilisers to work well. In effect, they end up becoming part
of the amp itself. My own preference was to spend the time and money on the
amp itself, working from a more basic PSU (old fashioned transformer,
bridge, and big caps with low ESR.)

The problem with the use of really big caps (22,000uF or so) is that the
current taken from the mains is in very short, high-amplitude pulses. My
new 200W mains SMPSU I've just designed at work needs a power-factor
correction stage converting the 90 to 260V rms into 400V dc before this
feeds the main islolating stage, to make the PSU look resistive to the
mains.

The law is now that any PSU over 85W needs PF correction. Does this
apply to amplifiers for domestic use?

It's easier to get a reasonable PF by using low value capacitors
(2,200uF or so) and tolerate the dc ripple by regulating down to a
stabilised output.
--
Chris Morriss

On Sun, 5 Oct 2003 09:01:08 +0100, Chris Morriss
wrote:

In message , Jim Lesurf
writes
I'd agree that you need plenty of current available. For a 200Wpc I'd go
for well over 30Arms continuous, and bigger short-term available. However
soggy rails don't have to preclude this.

I used to be wary of stabilised rails, as this can lead to problems with
getting the stabilisers to work well. In effect, they end up becoming part
of the amp itself. My own preference was to spend the time and money on the
amp itself, working from a more basic PSU (old fashioned transformer,
bridge, and big caps with low ESR.)

The problem with the use of really big caps (22,000uF or so) is that the
current taken from the mains is in very short, high-amplitude pulses. My
new 200W mains SMPSU I've just designed at work needs a power-factor
correction stage converting the 90 to 260V rms into 400V dc before this
feeds the main islolating stage, to make the PSU look resistive to the
mains.

The law is now that any PSU over 85W needs PF correction. Does this
apply to amplifiers for domestic use?

It's easier to get a reasonable PF by using low value capacitors
(2,200uF or so) and tolerate the dc ripple by regulating down to a
stabilised output.

Or, if you have the money for it, you can use a choke-filtered supply
to maintain the rail voltage without active regulation. Musical
Fidelity use this in their better amps, as do most valve amps. It's
definitely the best electrical solution, since it gives a very quiet
power rail, but those big chokes are *seriously* expensive!
--

Stewart Pinkerton | Music is Art - Audio is Engineering