Properties of auditory working memory for sounds that lack strong semantic associations and are not readily verbalized or sung are poorly understood. We investigated auditory working memory capacity for lists containing 2-6 easily discriminable abstract sounds synthesized within a constrained timbral space, at delays of 1-6 s (Experiment 1), and the effect of greater perceptual variability among list items on capacity estimates at delays of 1-6 s (Experiment 2). Working memory capacity estimates of 1-2 items were found in all conditions and increased significantly as the perceptual variability among the list items increased. Nonetheless, the capacity estimates were smaller than the commonly observed average working memory capacity limit of 3-5 items. Decay profiles in both experiments were comparable with those previously reported in the verbal and auditory working memory literature. The results help define boundary conditions on capacity estimates for nonverbalizable timbres that lack strong long-term memory associations. (Contains 2 tables, 4 figures and 1 footnote.)