Speaker positioning - bass prominence

[Bourney]

I've mucked about with speakers, many many speakers :D in various rooms for over 30 years, I've never moved speakers closer to a back wall and reduced bass quantity before. Except today, I did it by accident just shuffling stuff around.
I know I've got funny alcoves that do react with some speakers and not others but never experienced this in 16 years living here.
Any ideas?

[Lawrence001]

Can't explain it but it happened to me with Celestion A3s in my bay window. It was good for me as it meant I could keep them out of the way without any boom.

[Macca]

you found a speaker position where the bass waves at the listening spot are reduced in amplitude and it ameliorates any level increase from the boundary reinforcement.

Maybe. Speaker-room interaction is too complex to predict without computers and that. Shuffling stuff around until it works is what I do too.

Going to be different for every different speaker so might explain why you never encounter it before.

[Jimbo]

This is possible where the room nodes simply work different in relation to your listening position and the speakers regardless of the fact they are nearer the back wall and may well actually produce more bass as a result.

You don't perceive this extra bass because your listening position is now further away and as I say the sound waves are now acting differently in your room.

[Lawrence001]

The ports on the A3s were the biggest I've had, I assume they were tuned very low (which makes sense given there are 3 forward facing bass drivers which will go quite low directly) and thought this might be below the room node that other speakers excited. Still not sure why moving them closer to the wall reduced bass though. Cancellation?

[AJSki2fly]

The ports on the A3s were the biggest I've had, I assume they were tuned very low (which makes sense given there are 3 forward facing bass drivers which will go quite low directly) and thought this might be below the room node that other speakers excited. Still not sure why moving them closer to the wall reduced bass though. Cancellation?

Like you say it may be the bass output from the rear port is reflecting off the wall and is in opposition to the front drivers and thus causing some cancellation. I would think if you moved them out or back a little at a time you should here a change in sound.

[walpurgis]

Wavelengths at low frequencies are large and it would require in the region of 180 degrees of phase shift for significant cancellation to be obvious. Cancellation can occur at other divisions of the fundamental though and room effects can do weird things (that's why low fundamentals can be discerned in rooms that could be regarded as too small for this :)).

[Lawrence001]

Yes I had discounted the cancellation effect due to the long wavelengths

[struth]

might just be reflecting the bass to different parts of room. most bass that goes backwards promptly goes to opposite wall, so might just depend on angles and seating position etc. as martins
says, move things around til it sounds best.

[Barry]

Wavelengths at low frequencies are large and it would require in the region of 180 degrees of phase shift for significant cancellation to be obvious. Cancellation can occur at other divisions of the fundamental though and room effects can do weird things (that's why low fundamentals can be discerned in rooms that could be regarded as too small for this :)).

Which is why I don't understand why OB speakers work as well as they do - the 'baffle' doesn't seem to be large enough to provide adequate low-frequency cancellation. :scratch:

[walpurgis]

Which is why I don't understand why OB speakers work as well as they do - the 'baffle' doesn't seem to be large enough to provide adequate low-frequency cancellation. :scratch:

Apart from any bass equalisation that may be applied to counter the steep cancellation roll-off, I think out of phase bass notes from the rear of the driver may be reflected around the listening environment to long enough distances to reach the listener in phase or partly, maybe at 1/2 or 1/4 or even 1/8 wavelength, etc. Enough to reinforce the emissions from the front of the driver.

[Lawrence001]

And people tend to use 15-18" drivers in OB speakers.

[walpurgis]

Somebody once said, "the ultimate speaker is a point source with a baffle of infinite size" (I think :)).

[Macca]

open baffles never sound right in the bass, at least to me.

[walpurgis]

One of the most interesting speakers I've come upon, was ages ago at an indoor market record seller's booth.

He had a pair of elliptical vintage 'radiogram' type drivers operating full-range in large floorstanding homebuilt hardboard sealed boxes built with aluminium angle frame structures. The drive units were about 10" x 6" with doped pleated paper cone surrounds.

All 'wrong' I know and you'd think they'd be pretty dire, but they weren't. They sounded remarkable for some mysterious reason, maybe an inadvertent example of the low energy storage principle.

Now many years on, I've never forgotten being blown away by how good the things were.