use cpufreq-set according to the help output below and observe the effect on the frequency of the CPU/s until you get it as you want it.
In your case I would be inclined to use the governor and select 'ondemand' ...... which will keep the freq low unless required.
If that is not sufficient you could try 'conservative' or 'powersave'.
[user@XPS ~]$ cpufreq-set --help
cpufrequtils 008: cpufreq-set (C) Dominik Brodowski 2004-2009
Report errors and bugs to firstname.lastname@example.org, please.
Usage: cpufreq-set [options]
-c CPU, --cpu CPU number of CPU where cpufreq settings shall be modified
-d FREQ, --min FREQ new minimum CPU frequency the governor may select
-u FREQ, --max FREQ new maximum CPU frequency the governor may select
-g GOV, --governor GOV new cpufreq governor
-f FREQ, --freq FREQ specific frequency to be set. Requires userspace
governor to be available and loaded
-r, --related Switches all hardware-related CPUs
-h, --help Prints out this screen
1. Omitting the -c or --cpu argument is equivalent to setting it to zero
2. The -f FREQ, --freq FREQ parameter cannot be combined with any other parameter
except the -c CPU, --cpu CPU parameter
3. FREQuencies can be passed in Hz, kHz (default), MHz, GHz, or THz
by postfixing the value with the wanted unit name, without any space
(FREQuency in kHz =^ Hz * 0.001 =^ MHz * 1000 =^ GHz * 1000000).