Bass Decay in the Small HT

[derrickdj1]

Bass decay in the small home theater is a problem that all of us face.  Trying to get the bass right in the system is the hardest part of setting up the HT in my opinion.  A lot of times you can walk into an impressive HT only to be disappointed after your hear it.  Some people go out and even buy new subwoofers.  Room can sound boomy, dead, reverberant or live.  These things are not easily seen and diagnosed by a FR graph.  The FR graph does not tell you how the room sounds.  The boomy, dead, live or reverberant descriptions are referring to bass decay times.

 

Most of us have seen water fall graphs used to help us with bass decay.  Bass decay is a time domain problem. Below is a water fall graphs  with Frequency on the X axis,  and spl as the left Y axis and time in ms as the right Y axis.

 

What the heck do you look for to interpret the graph?  Way in the back of the graph is quick bass decay and the stuff coming out to the front of the graph is the slow decay or ringing.  For example a bass note that has a decay time of 200 ms is faster than one with a time of 500 ms.

 

Next what time frame are we talking about?  Most bass measurement are are 20 Hz-200 or 300 Hz.  The critical time is 350 ms or less down to 35 Hz and 450 ms for under 35 Hz.  When taking measurement with REW or Omnimic, the spl needs to be around 40 db over the ambient room noise or about 90 db for measurements.

 

Lastly, I will comment on a couple of graphs from my room.  There are a few DIY sound panels, no big thick bass traps, or diffusers, ect.  Most of the treatment have been done with furniture that I already have in the house.  The HT has eight large subwoofers spread around the room.  These are not identical subs  with the largest one 17 cu. ft and the smallest one only 4 cu. ft.  The graphs were done using my aggressive house curve and at a high spl(MV-10 on the avr).

 

Omnimic uses a two dimensional graph for bass decay.  The peak in the graph are the same as the bass decay frequencies that protrude to the front in a waterfall graphs.  Also note the shallow drop of of the tail of the FR graph.  Right now the system is being ran as vented with no port plug with an 18 db Butterworth slope since the  system is tuned to 15 Hz.  You want the graph breaking before you hit the systems tuning point to protect the driver.  As seen in the FR graph, the break starts around 20 Hz.

[RX8]

To be honest, you lost me immediately after Bass Decay....  

[derrickdj1]

2 hours ago, RX8 said:

To be honest, you lost me immediately after Bass Decay....  

This is one of the reason I started this topic.  We talk a lot about which sub to buy or build but, proper setup and some room measurements are more critical to the quality of the bass in the room.  There are no bad question and feel free to ask.  

 

I underlined a couple of the main points in the opening post.

 

In the small HT, the room is 50% of what we hear as bass.  Bass will bounce off wall and objects in the room.  Autocalibration helps a lot but, for those looking for a great 2 ch or HT sound system thing like bass decay, reverb, distortion and room treatment need to be looked at also.

 

I have consider posting a subwoofer setup guide to help newcomers.  Klipsch or the moderators could make it a sticky so that it does not get lost after the nex 50 topics posted.  If there is interest it can be done.   This way people don't have to get bits and piece of info searching thru a ton of threads.

[MikeFord]

Sometimes I think the primary aspect of the audiophile hobby is paranoia about the system/room sounding right.