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Re: Richard...,might I ask a question?

Posted by Richard BassNut Greene on November 17, 2004 at 08:58:41

In Reply to: Richard...,might I ask a question? posted by Tony on November 17, 2004 at 07:10:32:

You mention that you have a fireplace on a side wall. I have a similar setup. How does something like a fireplace effect bass.
RG:
My fireplace is on the right side wall and had no measureable effect on bass vs. being covered with plywood.

There was a small echo that affected the midrange and interfered with the soundstage so I use Sonex to cover the opening while listening to music and the problem disappears.
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My room seem to suffer from nulls rather than peaks.
RG
Under 80 Hz. standing wave bass peaks are the most common complaint, but every standing wave has both peaks and nulls.

Parametric EQ can address the peaks at one listening position and that often benefits nearby seats too.

The nulls are best addressed by moving your ears, assuming you have the flexibility to move your ears a few feet in any directions, you can almost always avoid the deepest portion of standing wave nulls (can be -15dB to -30dB) which are physically narrow.

But even after finding the best seating location, you will almost always hear at least one null under 80Hz., and often two nulls, but hopefully no worse than -6dB .

For subwoofer bass frequencies -6dB is subjectively "half as loud", so even -6dB is a significant null ---(for midrange frequencies -10dB is subjectively "half as loud", as many audiophiles already know).

The best subwoofer/listener location I have found in my own room has a null at 58Hz. about -4 to -6dB deep. It took me since 1987 and hundreds of measurements, to find those optimum positions.

Above 80Hz. the most common complaint are nulls caused by 1/4 wavelength cancellations (aka comb filter cancellations).

These are best addressed with bass traps as EQ has no effect on nulls.

Without bass traps you can move the speakers nd your ears but all that does is change the frequencies of the cancellations.

However it's a good idea to place speakers so they are not the same distances (or multiples) from more than one room surface.

A worst case might be a woofer 3 feet off the floor, 3 feet from the side wall and 3 feet from the back wall (measured around the front baffle) and the two speakers 6 feet apart.

Those dimensions would cause stacked 1/4 wavelength cancellations (multiple cancellations at the same frequency that are additive).
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"I am unable to eliminate a bass suckout from around 125hz-400hz or so. Looking around the room,"
RG:
I stop using the term bass at about 150Hz. -- you seem to have lower mid-range problems.

However I've never measured, or even heard of, weak output that covered such a broad range of frequencies (almost two octaves) in that range.

Is that what you hear, or just what you measure?

Do the speakers measure properly from one foot away?

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