I have some vented speakers with an F3 of about 40 Hz in an EBS
alignment. I have severe room interaction problems, clearly audible
and confirmed by LSPCad: a VERY deep valley around 60 Hz. I can't
solve it without really inconvenient furniture rearrangements, so I'm
going to add a subwoofer (closed, Q=0.7, F3=37Hz) actively crossed
over to the main speakers with a 4th order LR filter. I will have to
use a xover frequency of about 100 Hz, above which the main speakers
behave reasonably well where they are placed. Luckily I have found a
very convenient spot for the sub where its response will be very flat
and it's at exactly the same distance from the listening position as
the main speakers.

Just for fun I checked what would happened if I closed the vents in
the main speakers and what I get is a Q of about 0.5, although the
rolloff starts slightly above 100 Hz so there would be a small dip
(less than 1 dB anyway) in the overall frequency response.

I understand the closed main speakers would have a much better
transient response than if I leave them vented, but I'm not sure about
their contribution to the overall system transient response. Since in
any case I'm filtering them electrically with a 4th order slope, does
it really matter how they are aligned below the xover frequency? In
other words, will the overall transient response depend on the box
alignment of the main speakers, or only on the overall system
response, crossover and sub included?

Many thanks in advance,

Carlos

Carlos,

I have severe room interaction problems

No matter what speakers you use and in what room you put them, there will
always be problems unless the room is properly treated. However, large rooms
generally have fewer low frequency problems than small rooms. How large is
your room?

--Ethan

"Ethan Winer" ethanw at ethanwiner dot com wrote in message ...
Carlos,

I have severe room interaction problems

No matter what speakers you use and in what room you put them, there will
always be problems unless the room is properly treated. However, large rooms
generally have fewer low frequency problems than small rooms. How large is
your room?

--Ethan

It's large but squareish (4.6 x 5.5 x 2.5 m), maybe that's the
problem. I have physically tried two possible arrangements and then
simulated in LspCAD all the other "reasonable" ones (i.e. the ones
that will allow me to keep all my furniture), and there's always a big
valley at the listening position, so I think the best solution is the
sub. At its intended spot it will blend very well with the room gain
and will give me a very flat and extended response. Besides, I love
building stuff, so I've got the perfect excuse.

Carlos

Carlos,

It's large but squareish (4.6 x 5.5 x 2.5 m)

As far as room acoustics is concerned that's a small room, and so it suffers
from the same problems of skewed low frequency response that are common to
all small rooms.

there's always a big valley at the listening position, so I think the best
solution is the sub.

A big dip in the bass range in a room that size is ALWAYS caused by acoutic
interference due to reflections off the walls, floor, and ceiling. It might
be fun to build a sub, but it's the wrong approach. (Unless your main
loudspeakers really are deficient in the bass range.) Not only will a
subwoofer not solve the real problem, it will likely make things even worse.
However, it will give you more "thump and boom" if that's all you care
about.

Have a look at my Acoustics FAQ, second in the list on my Articles page:

www.ethanwiner.com/articles.html

It's not what you asked for, but I believe it's what you need.

--Ethan

"Ethan Winer" ethanw at ethanwiner dot com wrote in message ...
Carlos,

It's large but squareish (4.6 x 5.5 x 2.5 m)

As far as room acoustics is concerned that's a small room, and so it suffers
from the same problems of skewed low frequency response that are common to
all small rooms.

Well, I didn't make myself clear: it's largER than the one I had
before, where I didn't have problems like this. I know, I was just
lucky then.

there's always a big valley at the listening position, so I think the best
solution is the sub.

A big dip in the bass range in a room that size is ALWAYS caused by acoutic
interference due to reflections off the walls, floor, and ceiling.

Of course. That's exactly what LspCAD models and, from the looks of
it, quite accurately. But those reflections depend also on where the
loudspeaker is and where the listening position is, so a possible
solution is to move the source of the frequency band that gives
problems to a different location, provided you can't locate spatially
sounds in that band. I have made experiments in the past and, below
100 Hz, I can't.

It might
be fun to build a sub, but it's the wrong approach. (Unless your main
loudspeakers really are deficient in the bass range.) Not only will a
subwoofer not solve the real problem, it will likely make things even worse.
However, it will give you more "thump and boom" if that's all you care
about.

Well, my main speakers are actually really good in the bass range, but
their bass range gets seriously screwed up by the room acoustics below
100 Hz, and, as I said, I can't move them and/or the listening
position around to improve that; however, the subwoofer, placed in a
certain spot, results in a very flat response (no "thump and boom")
below 100 Hz at the current listening position, so if I design and
build it properly, which I know how to do, and also design and build
properly a crossover that removes the problem band from the main
speakers and feeds it to the sub, which I also know how to do, I will
solve the problem.

I'm not saying other approaches, like changing the room acoustics,
won't work (though I doubt a very deep valley in the frequency
response like the one I have can be solved without very seriously and
disruptively altering the room), I'm just saying there's no reason why
the sub must be "the wrong approach" and "make things worse".

Just to clarify: I'm not adding a boom-box to my system to get more
"thump". I'm adding a very fine Scan-Speak 25W/8565 bass driver in a
closed box with maximally flat alignment adequately crossed over
(Active 4th-order Linkwitz-Riley) to the main speakers and with its
location carefully chosen to have the flattest possible FR. Frankly I
don't see what could be wrong with that.

Carlos

Carlos,

it's largER than the one I had before, where I didn't have problems like
this.

What's much more likely is you had many peaks and nulls at the listening
position, but they were merely at more pleasing / flattering frequencies.

those reflections depend also on where the loudspeaker is and where the
listening position is

Absolutely. But in a small room there are NO locations that have a flat
response. Again, some places may sound better than others, but NONE of them
are accurate.

my main speakers are actually really good in the bass range, but their
bass range gets seriously screwed up by the room acoustics below 100 Hz,
and, as I said, I can't move them and/or the listening position

If you understand that it's a room problem, why do you resist the idea of
fixing the room?

You are welcome to keep trying to fix an acoustic problem with gear, but in
my opinion it really is the wrong approach.

--Ethan

Carlos,

it's largER than the one I had before, where I didn't have problems like
this.

What's much more likely is you had many peaks and nulls at the listening
position, but they were merely at more pleasing / flattering frequencies.

those reflections depend also on where the loudspeaker is and where the
listening position is

Absolutely. But in a small room there are NO locations that have a flat
response. Again, some places may sound better than others, but NONE of them
are accurate.

my main speakers are actually really good in the bass range, but their
bass range gets seriously screwed up by the room acoustics below 100 Hz,
and, as I said, I can't move them and/or the listening position

If you understand that it's a room problem, why do you resist the idea of
fixing the room?

You are welcome to keep trying to fix an acoustic problem with gear, but in
my opinion it really is the wrong approach.

--Ethan

"Ethan Winer" ethanw at ethanwiner dot com wrote in message ...
Carlos,

It's large but squareish (4.6 x 5.5 x 2.5 m)

As far as room acoustics is concerned that's a small room, and so it suffers
from the same problems of skewed low frequency response that are common to
all small rooms.

Well, I didn't make myself clear: it's largER than the one I had
before, where I didn't have problems like this. I know, I was just
lucky then.

there's always a big valley at the listening position, so I think the best
solution is the sub.

A big dip in the bass range in a room that size is ALWAYS caused by acoutic
interference due to reflections off the walls, floor, and ceiling.

Of course. That's exactly what LspCAD models and, from the looks of
it, quite accurately. But those reflections depend also on where the
loudspeaker is and where the listening position is, so a possible
solution is to move the source of the frequency band that gives
problems to a different location, provided you can't locate spatially
sounds in that band. I have made experiments in the past and, below
100 Hz, I can't.

It might
be fun to build a sub, but it's the wrong approach. (Unless your main
loudspeakers really are deficient in the bass range.) Not only will a
subwoofer not solve the real problem, it will likely make things even worse.
However, it will give you more "thump and boom" if that's all you care
about.

Well, my main speakers are actually really good in the bass range, but
their bass range gets seriously screwed up by the room acoustics below
100 Hz, and, as I said, I can't move them and/or the listening
position around to improve that; however, the subwoofer, placed in a
certain spot, results in a very flat response (no "thump and boom")
below 100 Hz at the current listening position, so if I design and
build it properly, which I know how to do, and also design and build
properly a crossover that removes the problem band from the main
speakers and feeds it to the sub, which I also know how to do, I will
solve the problem.

I'm not saying other approaches, like changing the room acoustics,
won't work (though I doubt a very deep valley in the frequency
response like the one I have can be solved without very seriously and
disruptively altering the room), I'm just saying there's no reason why
the sub must be "the wrong approach" and "make things worse".

Just to clarify: I'm not adding a boom-box to my system to get more
"thump". I'm adding a very fine Scan-Speak 25W/8565 bass driver in a
closed box with maximally flat alignment adequately crossed over
(Active 4th-order Linkwitz-Riley) to the main speakers and with its
location carefully chosen to have the flattest possible FR. Frankly I
don't see what could be wrong with that.

Carlos

Carlos,

It's large but squareish (4.6 x 5.5 x 2.5 m)

As far as room acoustics is concerned that's a small room, and so it suffers
from the same problems of skewed low frequency response that are common to
all small rooms.

there's always a big valley at the listening position, so I think the best
solution is the sub.

A big dip in the bass range in a room that size is ALWAYS caused by acoutic
interference due to reflections off the walls, floor, and ceiling. It might
be fun to build a sub, but it's the wrong approach. (Unless your main
loudspeakers really are deficient in the bass range.) Not only will a
subwoofer not solve the real problem, it will likely make things even worse.
However, it will give you more "thump and boom" if that's all you care
about.

Have a look at my Acoustics FAQ, second in the list on my Articles page:

www.ethanwiner.com/articles.html

It's not what you asked for, but I believe it's what you need.

--Ethan

"Ethan Winer" ethanw at ethanwiner dot com wrote in message ...
Carlos,

I have severe room interaction problems

No matter what speakers you use and in what room you put them, there will
always be problems unless the room is properly treated. However, large rooms
generally have fewer low frequency problems than small rooms. How large is
your room?

--Ethan

It's large but squareish (4.6 x 5.5 x 2.5 m), maybe that's the
problem. I have physically tried two possible arrangements and then
simulated in LspCAD all the other "reasonable" ones (i.e. the ones
that will allow me to keep all my furniture), and there's always a big
valley at the listening position, so I think the best solution is the
sub. At its intended spot it will blend very well with the room gain
and will give me a very flat and extended response. Besides, I love
building stuff, so I've got the perfect excuse.

Carlos

Carlos,

I have severe room interaction problems

No matter what speakers you use and in what room you put them, there will
always be problems unless the room is properly treated. However, large rooms
generally have fewer low frequency problems than small rooms. How large is
your room?

--Ethan