Space after tabular environement

I want to add a space after a tabular environement. I tried to use the \vspace comand but it does not work, it adds the space between the first and the second line before the table instead of between the first line and the table itself. Any suggestions?

Here is the code:

\begin{tabular}{||m{0.3\textwidth} | m{0.7\textwidth} ||}
\hline \hline
Instruments and measure set up &
\begin{itemize}
\item Power supply
\item Waveform generator ($f=1\mathrm{kHz}, V_{pp}=0.8943\mathrm{V}$)
\item Oscilloscope
\end{itemize}
\\
\hline
Measured data &
\begin{itemize}
\item Output voltage: $V_o$
\end{itemize}
\\
\hline
Involved  variables, measured values and procedure &
Using \textit{Math Mode}, measure the voltage drop amplitude across the $8\mathrm\Omega$ resistor taking into account the $\frac{1}{\sqrt{2}}$ factor of the RMS.\newline
Applying the following formula:
$$P_o = I\cdot V_{o_{RMS}} = \frac{V_{o_{RMS}}^{2}}{R_L} = \frac{V_o^{2}}{2\cdot8\mathrm{\Omega}}$$
we obtain the power delivered by the amplifier to the speaker.
\\
\hline \hline
\end{tabular}
\vspace{1cm}
\noindent
Specification: $1\mathrm{W} \le P_o \le 3\mathrm{W}$\\ \\
Measurements:
\begin{itemize}
\item $V_o=\frac{V_{pp}}{2}=\frac{7.68\mathrm V}{2}=3.84$V
\end{itemize}
\noindent
\\
{\Large \textbf{Result:} $P_o=0.92$W}
• Put an empty line before the vspace. Jan 15 '17 at 11:08
• Now it generates the space between the second and third line... Jan 15 '17 at 11:10
• please always post a complete document so people can see the problem. But tabular has no special spacing rules it is just like a big letter X any space you add with vspace or hspace are unrelated to the tabular you would get the same space if you replaced the tabular by X or \rule{2cm}{3cm} or any other tex box. Jan 15 '17 at 11:16
• the \\ you have in that fragment outside the table are completely wrong and you should start by removing them (they surely make warnings in the log file? then add blank lines where you want to start a paragraph, and then vspace will work as you expect/ Jan 15 '17 at 11:18

A little bit more compact. Units and values done with siunitx to ensure they are properly typeset. Changed the width of the second column of the tabular, to account the little space that LaTeX adds at both sides of a column. Removed the vertical lines to make it a bit more smooth. Added package parskip because that seems to be what you actually want here. If this is a homework assignment, no one will argue about it, if this is within a thesis or report, i would reconsider the whole presentation. \documentclass{article}
\usepackage{array}
\usepackage{geometry}
\usepackage{ragged2e}
\newcommand{\tabitem}{\par\RaggedRight\textbullet~}
\usepackage{siunitx}
\usepackage{booktabs}
\usepackage{parskip}
\begin{document}
\begin{tabular}{m{0.3\textwidth}  m{0.64\textwidth} }
\toprule
Instruments and measure set up &
\tabitem Power supply
\tabitem Waveform generator ($f=\SI{1}{\kilo\hertz}, V_{pp}=\SI{0.8943}{\volt}$)
\tabitem Oscilloscope
\\
\midrule
Measured data &
\tabitem Output voltage: $V_o$
\\
\midrule
Involved  variables, measured values and procedure &
Using \textit{Math Mode}, measure the voltage drop amplitude across the \SI{8}{\ohm} resistor taking into account the $\sqrt{2}^{-1}$ factor of the RMS.\newline
Applying the following formula:\par
$\displaystyle P_o = I\cdot V_{o_\mathrm{{RMS}}} = \frac{V_{o_{\text{RMS}}}^{2}}{R_L} = \frac{V_o^{2}}{2\cdot\SI{8}{\ohm}}$\par
we obtain the power delivered by the amplifier to the speaker.
\\
\bottomrule
\end{tabular}

\medbreak
Specification: $\SI{1}{\watt} \le P_o \le \SI{2}{\watt}$

Measurements:
\tabitem $V_o=\frac{V_{pp}}{2}=\frac{\SI{7.68}{\volt}}{2}=\SI{3.84}{\volt}$

{\Large \textbf{Result:} $P_o=\SI{0.92}{\watt}$
\end{document}
• regarding table width: try with \begin{tabular}{>{\raggedright}m{\dimexpr0.3\textwidth-2\tabcolsep} >{\raggedright\arraybackslash}m{\dimexpr0.7\textwidth-2\tabcolsep} } Jan 15 '17 at 11:53
• @zarko Nah. It doesn't ned to be perfect :-) Jan 15 '17 at 11:55
• Thanks @Johannes_B, this was a homework. Also thanks for the \siunitx package recommendation it works grerat. Jan 15 '17 at 19:16

I propose to use tabularx to have the exact columnwidths ratio, and a description environment for the vertical spacing after the table, and some other improvements:

\documentclass{article}
\usepackage{array}
\usepackage[showframe]{geometry}
\usepackage{ragged2e}
\newcommand{\tabitem}{\par\RaggedRight\textbullet~}
\usepackage{siunitx}
\usepackage{booktabs, tabularx}
\usepackage{enumitem, nccmath}%
\renewcommand{\tabularxcolumn}{>{\abovedisplayskip=2pt\belowdisplayskip=5pt\arraybackslash}m{#1}}
\newcolumntype{Y}{>{\hsize=0.6\hsize}X}
\newcolumntype{Z}{>{\hsize=1.4\hsize}X}

\begin{document}

{\centering%}
\begin{tabularx}{\linewidth}{YZ }
\toprule
Instruments and measure set up &
\tabitem Power supply
\tabitem Waveform generator ($f=\SI{1}{\kilo\hertz}, V_{pp}=\SI{0.8943}{\volt}$)
\tabitem Oscilloscope
\\
\midrule
Measured data &
\tabitem Output voltage: $V_o$
\\
\midrule
Involved variables, measured values and procedure &
Using \textit{Math Mode}, measure the voltage drop amplitude across the \SI{8}{\ohm} resistor taking into account the $\sqrt{2}^{-1}$ factor of the RMS.\newline
Applying the following formula:
$P_o = I\cdot V_{o_\mathrm{{RMS}}} = \frac{V_{o_{\text{RMS}}}^{2}}{R_L} = \frac{V_o^{2}}{2\cdot\SI{8}{\ohm}}$
we obtain the power delivered by the amplifier to the speaker.
\\
\bottomrule
\end{tabularx}
}

\begin{description}[font=\normalfont, leftmargin=0pt]
\item[Specification:] $\SI{1}{\watt} \le P_o \le \SI{2}{\watt}$.
\item[Measurements:]\leavevmode\vspace{-1.5ex}
\begin{fleqn}
\begin{equation*}
\bullet\enspace V_o=\frac{V_{pp}}{2}=\frac{\SI{7.68}{\volt}}{2}=\SI{3.84}{\volt}
\end{equation*}
\end{fleqn}
\end{description}
\vspace*{\topsep}

{\Large \textbf{Result:} $P_o=\SI{0.92}{\watt}$

\end{document} 