"Arny Krueger"
"Phil Allison"

There is no significant "lobing and comb-filter effects" with a
driver array that is **NOT** facing the listener - compared with
one that is.

In most cases the back drivers on a 901 are facing a smooth wall.
Lobes bounced off a wall are still lobes.


** The lobes are spread way out by the off angle reflection and
lost to the listener. A listener seated in the usual central position
could not detect
them.

Furthermore, there are those oddities where the array has a critical
distance,

** Define your terms, please.

I've cited this paper once already, and it's clear that there aren't a lot
of people on this thread who have actually even glanced at it:

** Being pompous and quoting absent documents does you no credit.



Author(s): Keele, Jr., D. B. Publication: JAES Volume 38 Number 10 pp.
723·748; October 1990.

Well, not everybody has the kind of library I have at my disposal. Sadly,
I
can't find any online references with enough detail. The "critical
distance"
w/r/t to an array of speakers is the point where the sound from the array
drivers starts to fuse into a single pattern.

** Which makes your original "oddities" remark even more mysterious.



This affects 89% of the sound coming out of a 901, if Bose is to be
believed.

** The "Hass" effect plus the extra proximity and brighter sound of
the forward facing driver normally makes it the apparent source for a
centrally positioned listener.

Already considered. Since I've been doing SR quite a bit I've learned to
love the Haas effect and figuratively take it to the bank every
opportunity.
However, Haas Effect fusion is not perfect - there is some perception of
added fullness or fuzziness, depending on the individual perceptions.

The other rear facing ones will produce a delayed and duller sound
- depending on the nature of the walls, distance away and their
coefficient of absorption at various frequencies. If the walls are
far away and acoustically dead then the forward facing driver
dominates strongly.

Agreed that if the back wall is dead than much of what the back speakers
do
is moot. However, most architectural features are not good absorbers below
1
KHz, less below 500 Hz, and very few below 200 Hz. Since all drivers in
the
901 are supposedly full-range...


** You say there is significant lobing going on at or below 500 Hz from an
array of 4 inch drivers ??

Below 500 Hz 901s pretty soon become non directional - providing there is
actually a wall behind them.




The "lobing ... effects" are only going to be audible if the
listener moves their head in the direct field where the lobes exist
- ie behind the 901.

Or as I've said once and feel somewhat put-upon to have to repeat - the
lobes will exist in front of the 901s if the walls are good reflectors.


** Keep repeating the dubious claim - it gets more convincing every time
you know. You need to show these alleged lobes are actually audible to a
listener seated in the central position on *music* programme.



The "...comb-filter effects" are audible where rear wall proximity
and reflection of sound creates them - it is not due to the way the
drivers are arrayed.

I've cited this paper once already, and it's clear that there aren't a lot
of people on this thread who have actually even glanced at it:


** Quoting the absent expert is a debating cheat - Arny.

You have seen my 10 cheats list.



IME both the 901 and 802 suffer from *gross* IM and Doppler
distortion at high SPL levels - nauseatingly so to my ears.


Well, that too. I think we're now agreeing about one of my earlier points
about how many small drivers it takes to equal a larger one.


** The comparison fails since the Bose 901 has falling output below 300Hz
without its equaliser. Early 901s ( there are at least 12 distinct
versions) used a sealed box with the drivers operating below resonance. The
equaliser added up to 15 dB boost ( 31 times power) at low frequencies to
compensate. The excursion limit of those drivers was *very soon* exceeded
if an amp of any size ( PL700s were popular !) were being used.

A good 10 inch driver has about the same cone area as the 9 used in the
Bose 901. Mounted in a tuned box somewhat bigger than a 901 it could equal
the 901's SPL at low frequencies with 31 times LESS power input and hence
massively reduced THD. Allow that 10 inch to be accompanied by a mid and
treble drivers and IM is reduced to nil as well.

I well remember a demo session with 901s and a PL700 in 1977 - every time
the bass drum thumped there was a distinct crack from the 901s and the mids
and tops went on a short holiday. The only surprising thing was that the
owner thought this sounded great and pushed the PL700 right up to clipping.

I left the room suffering from nausea after 10 minutes - just the sight of
a 901 induces that feeling now.




............. Phil