Sound WoodHow to read a sonic decay map
A decay map is easy to glance at and easy to misread. A big red blob looks alarming, a mostly green map looks reassuring, and both reactions can be wrong if you don't know what the colors are based on. This guide walks through a sonic decay map piece by piece, using the way Sound Wood draws it, so you can read it with confidence and explain it plainly.
Start with the setup: sensor positions and paths
Before looking at any color, look at the layout. The circle is the trunk cross-section at the height you tested. The sensor positions are labeled S1, S2, S3 and so on, numbered clockwise from the zero mark. With a two-sensor detector like the Tree Check, these are the spots you moved the sensors between. If you recorded which way S1 faced, the map shows a north arrow so you can match the map to the tree.
Each line between two positions is a path you took a reading on. Count them and look at where they go. A map with many paths crossing the center tells you a lot about the center. A map where most paths run near the bark on one side tells you less about the other side. The colors can only be as good as the coverage.
Green paths: sound wood
A green path was faster than the cutoff for that species. Sound got across without meeting anything that slowed it down much. Green paths do two jobs on the map. They show sound wood along their own line, and where a green path crosses a slow path, they tell you the crossing point is likely solid. That pushes the slow wood on that slow path somewhere else.
Red: confirmed decay
Red is where the evidence agrees. It's drawn where slow paths cross each other with no sound path between them. Two independent readings, from different directions, both say the wood there is slow. That's as close to "confirmed" as a sonic test gets.
The pocket map turns those red areas into shapes on a grid, filling the gaps between nearby red areas so one cavity reads as one pocket instead of scattered dots. That's usually the view to show a client, because it looks like what you'd expect to find if you cut the tree.
Decay reaching the bark
Sometimes several slow paths meet at one sensor and none of the paths through that sensor are sound. Unless a pocket in the center explains all of them, that pattern points to decay running out to the bark at that sensor. It's common at basal cavities, old pruning wounds and lawnmower damage. On the map the pocket reaches the edge of the circle at that sensor.
Yellow: possible decay
Yellow is where the readings say "maybe." It's used in two situations:
- A slow path that no other slow path crosses. You know there's slow wood somewhere along it, but nothing tells you where.
- A slow stretch of path that sits between two green crossings. The decay could be in that stretch, but no second slow path confirms it.
Yellow is not a softer shade of red. It's a gap in the evidence. More sensor positions, or paths that cross the yellow area from another angle, would turn it into either red or green.
The decay range: minimum and up to
The results show two numbers, not one:
- Decay (minimum X%) is the share of the cross-section that's confirmed red.
- Possible decay (up to Y%) adds the yellow areas, in case they turn out to be decay too.
The real figure is somewhere in that range. The verdict uses the confirmed minimum, but you should read both. A result of "minimum 8%, up to 10%" is a tight, confident picture. "Minimum 8%, up to 35%" says the test found decay but couldn't pin down how much, and it's a reason to add paths or test again before making a big call.
Rule of thumb: when you write up a result, give the range, not just the low number. A client who hears only the minimum hears the best case.
Check the numbers before trusting the picture
A map is built entirely from what you typed in. Before you read meaning into it, do a quick sanity pass:
- One position slow on every path? That's often poor contact, such as a loose nail or one set in loose bark, not decay radiating from one point. Reset it and re-test the paths from that position.
- One reading wildly different from its neighbors? Check for a typo, such as a dropped or doubled digit.
- Circumference and sensor positions right? An error there changes every distance and every speed.
Sound Wood's reading checks flag the common ones, but you know the tree and the day you had. Use the numbers tab to see each path's speed against the cutoff.
What the map can't tell you
A sonic map shows where sound is slow. It doesn't tell you the cause. Decay, a cavity, a crack, an included bark seam and a ring shake can all slow sound, and the map can't tell them apart. It also shows one height. Decay often changes shape up and down the trunk, so a map at 12 inches doesn't describe the trunk at 4 feet.
It also doesn't tell you how strong the tree is. How much the remaining sound wood can carry depends on where it is (a sound shell all around is very different from decay open to one side), on the species, the crown, the lean, the wind exposure and the target. That's your assessment, not the map's.
Putting it into words for a client
Clients don't need the method. They need what you found, how sure you are, and what you recommend. Something like this works:
- What you tested: species, where on the trunk, how many sensor positions.
- What you found: "Confirmed decay in about X% of the cross-section, possibly up to Y%," plus where it is ("toward the street side, reaching the bark at the old wound").
- What it means: in your words, with your judgment of the tree as a whole.
- What you recommend, and when to re-test if you're monitoring.
Sound Wood's field report puts the map, the range and your notes on one page with your name and business details, and Write it up can draft the observations from your readings for you to edit. The numbers and the verdict always come from your readings; the draft never changes them.
The short version
Green is sound. Red is where two directions agree the wood is slow. Yellow is a question the readings couldn't answer. Read the range, not just the minimum, check your inputs, and remember the map shows one slice of the tree. Read that way, a decay map is one of the clearest pieces of evidence you can hand a client.