diff --git a/.gitignore b/.gitignore
index e1b18dfa..b379281b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,4 @@ build/
 dist/
 .eggs/
 sfs.egg-info/
+
diff --git a/sfs/util.py b/sfs/util.py
index ed3a3a8f..7a3e4314 100644
--- a/sfs/util.py
+++ b/sfs/util.py
@@ -362,7 +362,7 @@ def db(x, power=False):
 
     """
     with np.errstate(divide='ignore'):
-        return 10 if power else 20 * np.log10(np.abs(x))
+        return (10 if power else 20) * np.log10(np.abs(x))
 
 
 class XyzComponents(np.ndarray):
diff --git a/tests/test_util.py b/tests/test_util.py
index 89ff89d1..d391d996 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -1,17 +1,19 @@
 import numpy as np
 from numpy.testing import assert_allclose
+from numpy.testing import assert_array_equal
 import pytest
 import sfs
 
 cart_sph_data = [
-    ((1, 1, 1), (np.pi/4, np.arccos(1/np.sqrt(3)), np.sqrt(3))),
-    ((-1, 1, 1), (np.arctan2(1, -1), np.arccos(1/np.sqrt(3)), np.sqrt(3))),
-    ((1, -1, 1), (-np.pi/4, np.arccos(1/np.sqrt(3)), np.sqrt(3))),
-    ((-1, -1, 1), (np.arctan2(-1, -1), np.arccos(1/np.sqrt(3)), np.sqrt(3))),
-    ((1, 1, -1), (np.pi/4, np.arccos(-1/np.sqrt(3)), np.sqrt(3))),
-    ((-1, 1, -1), (np.arctan2(1, -1), np.arccos(-1/np.sqrt(3)), np.sqrt(3))),
-    ((1, -1, -1), (-np.pi/4, np.arccos(-1/np.sqrt(3)), np.sqrt(3))),
-    ((-1, -1, -1), (np.arctan2(-1, -1), np.arccos(-1/np.sqrt(3)), np.sqrt(3))),
+    ((1, 1, 1), (np.pi / 4, np.arccos(1 / np.sqrt(3)), np.sqrt(3))),
+    ((-1, 1, 1), (np.arctan2(1, -1), np.arccos(1 / np.sqrt(3)), np.sqrt(3))),
+    ((1, -1, 1), (-np.pi / 4, np.arccos(1 / np.sqrt(3)), np.sqrt(3))),
+    ((-1, -1, 1), (np.arctan2(-1, -1), np.arccos(1 / np.sqrt(3)), np.sqrt(3))),
+    ((1, 1, -1), (np.pi / 4, np.arccos(-1 / np.sqrt(3)), np.sqrt(3))),
+    ((-1, 1, -1), (np.arctan2(1, -1), np.arccos(-1 / np.sqrt(3)), np.sqrt(3))),
+    ((1, -1, -1), (-np.pi / 4, np.arccos(-1 / np.sqrt(3)), np.sqrt(3))),
+    ((-1, -1, -1), (np.arctan2(-1, -1),
+                    np.arccos(-1 / np.sqrt(3)), np.sqrt(3))),
 ]
 
 
@@ -27,3 +29,77 @@ def test_sph2cart(coord, polar):
     alpha, beta, r = polar
     b = sfs.util.sph2cart(alpha, beta, r)
     assert_allclose(b, coord)
+
+
+direction_vector_data = [
+    ((np.pi / 4, np.pi / 4), (0.5, 0.5, np.sqrt(2) / 2)),
+    ((3 * np.pi / 4, 3 * np.pi / 4), (-1 / 2, 1 / 2, -np.sqrt(2) / 2)),
+    ((3 * np.pi / 4, -3 * np.pi / 4), (1 / 2, -1 / 2, -np.sqrt(2) / 2)),
+    ((np.pi / 4, -np.pi / 4), (-1 / 2, -1 / 2, np.sqrt(2) / 2)),
+    ((-np.pi / 4, np.pi / 4), (1 / 2, -1 / 2, np.sqrt(2) / 2)),
+    ((-3 * np.pi / 4, 3 * np.pi / 4), (-1 / 2, -1 / 2, -np.sqrt(2) / 2)),
+    ((-3 * np.pi / 4, -3 * np.pi / 4), (1 / 2, 1 / 2, -np.sqrt(2) / 2)),
+    ((-np.pi / 4, -np.pi / 4), (-1 / 2, 1 / 2, np.sqrt(2) / 2)),
+]
+
+
+@pytest.mark.parametrize('input, vector', direction_vector_data)
+def test_direction_vector(input, vector):
+    alpha, beta = input
+    c = sfs.util.direction_vector(alpha, beta)
+    assert_allclose(c, vector)
+
+
+db_data = [
+    (0, -np.inf),
+    (1, 0),
+    (10, 10),
+    (10 * 2, (10 + 3.010299956639813)),
+    (10 * 10, (10 + 10)),
+    (10 * 3, (10 + 4.771212547196624)),
+    (10 * 4, (10 + 6.02059991327962)),
+    (10 * 0.5, (10 - 3.01029995663981198)),
+    (10 * 0.1, (10 - 10)),
+    (10 * 0.25, (10 - 6.02059991327962396))
+    ]
+
+
+@pytest.mark.parametrize('linear, decibel', db_data)
+def test_db_amplitude(linear, decibel):
+    d = sfs.util.db(linear, True)
+    assert_allclose(d, decibel)
+
+
+@pytest.mark.parametrize('linear, decibel', db_data)
+def test_db_power(linear, decibel):
+    d = sfs.util.db(linear)
+    assert_allclose(d, 2 * decibel)
+
+
+image_sources_for_box_data = [(
+    (([1, 1, 1], [5, 4, 3], 1)),
+    ((((1,  1, -1),
+       (1, -1,  1),
+       (-1,  1,  1),
+       (1,  1,  1),
+       (9,  1,  1),
+       (1,  7,  1),
+       (1,  1,  5)), ((0, 0, 0, 0, 1, 0),
+                      (0, 0, 1, 0, 0, 0),
+                      (1, 0, 0, 0, 0, 0),
+                      (0, 0, 0, 0, 0, 0),
+                      (0, 1, 0, 0, 0, 0),
+                      (0, 0, 0, 1, 0, 0),
+                      (0, 0, 0, 0, 0, 1)))),
+)]
+
+
+@pytest.mark.parametrize('in_image_source, out_image_source',
+                         image_sources_for_box_data)
+def test_image_sources_for_box(in_image_source, out_image_source):
+    X, L, N = in_image_source
+    Xs, wall = out_image_source
+    e = sfs.util.image_sources_for_box(X, L, N)
+    img, wall_count = e
+    assert_allclose(img, Xs)
+    assert_array_equal(wall_count, wall)