Let  $\mu _{M,D}$ be the self-similar measure generated by
$\mu _{M,D}$ be the self-similar measure generated by  $M=RN^q$ and the product-form digit set
$M=RN^q$ and the product-form digit set  $D=\{0,1,\ldots ,N-1\}\oplus N^{p_1}\{0,1,\ldots ,N-1\}\oplus \cdots \oplus N^{p_s}\{0,1,\ldots ,N-1\}$, where
$D=\{0,1,\ldots ,N-1\}\oplus N^{p_1}\{0,1,\ldots ,N-1\}\oplus \cdots \oplus N^{p_s}\{0,1,\ldots ,N-1\}$, where  $R\geq 2$,
$R\geq 2$,  $N\geq 2$, q,
$N\geq 2$, q,  $p_i(1\leq i\leq s)$ are integers with
$p_i(1\leq i\leq s)$ are integers with  $\gcd (R,N)=1$ and
$\gcd (R,N)=1$ and  $1\leq p_1<p_2<\cdots <p_s<q$. In this paper, we first show that
$1\leq p_1<p_2<\cdots <p_s<q$. In this paper, we first show that  $\mu _{M,D}$ is a spectral measure with a model spectrum
$\mu _{M,D}$ is a spectral measure with a model spectrum  $\Lambda $. Then, we completely settle two types of spectral eigenvalue problems for
$\Lambda $. Then, we completely settle two types of spectral eigenvalue problems for  $\mu _{M,D}$. In the first case, for a real t, we give a necessary and sufficient condition under which
$\mu _{M,D}$. In the first case, for a real t, we give a necessary and sufficient condition under which  $t\Lambda $ is also a spectrum of
$t\Lambda $ is also a spectrum of  $\mu _{M,D}$. In the second case, we characterize all possible real numbers t such that
$\mu _{M,D}$. In the second case, we characterize all possible real numbers t such that  $\Lambda '\subset \mathbb {R}$ and
$\Lambda '\subset \mathbb {R}$ and  $t\Lambda '$ are both spectra of
$t\Lambda '$ are both spectra of  $\mu _{M,D}$.
$\mu _{M,D}$.