Separate subs for music and HT/surround

 Hello DB,

     It seems like you positioned your subs symmetrically in your room to make your system as visually appealing as possible.  However, I strongly suspect this positioning fails to optimize the audio bass response performance quality attainable in your room utilizing your four high quality subs. 
      I believe you'll obtain significantly improved bass performance, primarily noticed as improved seamless integration with your KEF main speakers, improved bass impact, dynamics, smoothness and naturalness, by positioning all four subs along the perimeter of your room in a distributed bass array configuration.  
     This is accomplished by sequentially utilizing the 'crawl method' beginning the search for the ideal positioning of the first sub at the front right corner of your room and proceeding counter-clockwise around the perimeter of your room.  
     Just continue positioning each sub optimally and sequentially until all four are located.  It's really up to you to decide whether you prefer to locate the larger 15" subs first, last or alternate between a 15" and 10" sub.  No matter the distribution pattern you choose, the ultimate audible result will be excellent bass response quality throughout your entire room.

     The bass results will be similarly smooth, natural and well integrated with your main speakers whether you deploy your current pair of 15" and 10" subs or if you deploy four 10" subs.  Including the larger pair of 15" subs will provide overall bass response that extends a bit deeper, has a bit greater impact and slightly better dynamics.

Tim

   I was unable to get two of my subs in the perfect crawl tested locations but they were close. The Auto EQ did take up the slack in my room.
   I ran my Earthquake, the DD-18 and two DD-12 Plus mastered from one of the 12s. I was able to closely match the equalization of the 18 to the others with the calibration mic at the listening position, individually running Auto EQ followed by a few minor Manual EQ adjustments on the Velodyne's. 
   Your listening space may not need all four units. What sounds good to you is key. There are no absolutes. 

Tim,

I'm willing to sacrifice a bit of acoustic perfection for visual appeal.  And acoustic room correction can help with the residual problems.  I strive for good organ pedal response without bass boom from jazz recordings.  A setup with a HGS-10 aside each KEF Ref 1 results in satisfying full range sound free of obvious sub involvement with the HGS-15s turned off.  An HGS-10 on either side of the Ref 1s, i.e., four of HGS-10s, might sound even better while remaining visually appealing.  The HGS-15s provide the slam for movie special effects, and may ultimately fit in for music.

db

Hello DB,

     Okay, I understand. 
     If you like the looks and sound of a HGS-10 aside each KEF Ref 1, I'd suggest you try positioning your two HGS-15s in the following manner:

     Leave both of your 10s exactly where they are aside each main speaker.  You already know these sub positions result in very good integration with your main speakers which is virtually the same as utilizing the crawl method to locate them.  I suggest you just consider their current positions are the optimum positions for your sub#1 and sub#2 in the 4-sub distributed bass array (DBA) system you're creating and just proceed to optimally locate your two 15s, as sub#3 and sub#4, in your room. 
     To do this, just do the following:

1.  Hook up one of your 15s and place it at your listening position.
2.  Play some of your jazz with good repetitive bass through the 15 and your two 10s.
3.  Use the crawl method, starting at the left side of sub#2 (located aside your left channel main speaker) and continue walking counter-clockwise around the perimeter of your room until you determine the exact spot that the bass sounds best to you (best integrated and the most natural). 
4.  Position sub#3 at this exact spot.
5.  Hook up your other 15,place it at your listening position and repeat steps #2-4 to optimally locate it.
6.  Once completed, sit at your listening position, play the same music with all four subs playing and verify that the bass sounds seamlessly integrated and natural.  Note: You will likely need to precisely adjust the Volume and Cutoff Frequency controls on both 15 subs until you determine the overall bass performance has been optimized at your listening position.  It's best if you recruit a volunteer for assistance on this step.

     If you follow this procedure precisely in relocating your pair of HGS-15s, I believe you'll notice a few things. 
     First, you may be surprised at the locations that the two 15 subs actually wind up positioned at in your room when optimized for bass sound quality.  However, I can't predict even generally where they'll each be positioned in your room since it depends on the subs used, your ears/brain and your room qualities (dimensions, wall/ceiling/floor materials, furnishings and any room treatments present).  I just suggest you follow the procedures strictly and make sure you pay close attention to bass quality when locating them.
     Secondly,  I'm almost certain you'll prefer the overall sound quality using all four of your subs when compared to using just the pair of HGS-10 subs.   Remember, I'm speaking from experience using not only a pair of subs but a 4-sub DBA as well.  You'll notice the bass is even smoother, more detailed and with the realistic bass power, impact and dynamics that are usually only heard and felt when you're present listening to music played live. 
     But don't worry, the high quality bass is always there but the volume control still allows you to choose the overall volume level for playback.

Enjoy,
 Tim

Okay listen first off its not gonna sound like it but I totally get it. People with HT setups love their HT setups in spite of the horrid sound. Or maybe even because of the horrid sound. I get that. Do not understand why anyone would want to waste their money on horrid sound but they do and so I totally get that.

I was watching Over Lord last night, if anyone wants a demo scene on their Horrid sounding HT :0) , this is the ticket,the first 15min is a roller coaster.
 
And that was the 5.1 version on PrimeVideo upmix to DolbyD+DDS, I immediately ordered the 4K Atmos disc