Re: Subwoofer testing standards
- The issue was whether one should measure anechoically
or use Keele's close miked woofer response method.
The latter is a poor substitute for the former.
It is quite true that if one places speakers very
close to the wall, then there are loading effects
which are not part of the omni character, eg
if a driver is up against a wall.
The discussion in question was about a speaker
which is intended for free space mounting
where close-boundary loading effects are not part
of the situation--though of course Allison effects
--- In firstname.lastname@example.org, "HM" <hmartinburm@...> wrote:
> Measuring close to woofers still clearly indicate room resonances, measuring at the seat shows Allison effects at listening position too.
> The sonic differences of corner woofers that are pushed snugly to the adjacent walls or pulled away few centimeters is clearly audible, I mean 1-5 cm (1"-2").
> Any other woofer placement further apartfrom room boundaries than 1/4 crossover frequencies wavelength will affect frequency response.
> Cancellations come with severe phase shifts, I believe, these degrade the soundstage imaging.
> How much subwoofers depend on minor distance from room boundaries can be easily tested by turning the woofer chassis to the wall and allow it to fire under an angle of 30°-45° against the wall into a short conical horn.
> Extras like better damping will affect resonant frequency positively, it will be lowered. Its transient response (tonebursts) will become better. This is not only so in physics, it happens with woofers audibly.
> I dont see how the anechoic response can tell anything about aforementioned reasonable aspects of setting up woofers. It covers only one of the many aspects that matter audibly.
> Flushmounting inwall speakers may solve some problems but the seat position in the room remains with all related (Allison + room reflections) problems. One has to find a good wellbalanced sweet spot in the room modes and compensate the remaining problems with speaker placement in the room. This will keep timing /phase problems at minimum too. Any frequency response issue can be addressed by fine EQ or digital room correction systems.
> BR HM
> > Robert,
> > how to properly measure corner woofers?
> > As a corner is a part of the woofer design I wonder how an anechoic
> > measurement gives reasonable results to predict the woofer behaviour in a
> > corner.
> > It seems that just a measurement in free field with but with a corner is
> > the only solution. What do you think about?
> > Uli
> > On Tue, Jun 12, 2012 at 6:59 PM, Robert <regtas43@> wrote:
> > > **
> > >
> > >
> > >
> > > Of course they do not, but the anechoic environment
> > > gives uniform and transferrable information.
> > > It is entirely normal in science and engineering to
> > > measure things in isolation
> > > and then transfer the information suitably to their
> > > actual environment.
> > >