Bass issue - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 11 Old 12-16-2014, 05:00 AM - Thread Starter
Member
 
windshear's Avatar
 
Join Date: Jul 2001
Location: Jhb, South Africa
Posts: 160
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked: 11
Bass issue

I have a problem in my current system. Up until recently I was happily ignorant with my set up. My main subwoofers are a pair of B&W DB1's. The other day I managed to get my hands on the Dolby Atmos disc. While running the Amaze sample at the bass demo I find that both my subs bottom out. This has not happened on any other disc before, at least not that im aware of. The problem I have is that this is happening at 6dB volume setting below where I find my comfortable limit/ normal listening level. I have confirmed this happening with both my Onkyo and Marantz Processors running Audyssey. If I turn Dynamic EQ off, this no longer happens. I close measured my subwoofers at 1 foot individually and measured with and without DynEQ on and off. I found that DynEQ is boosting the below 20Hz by up to 15dB's. I temporarily put a low pass filter with my minidsp into the chain below 20Hz with the obvious removal of the issue.

I now feel my subs are inadequate with insufficient headroom. Their specs rate them with a F3 of 16Hz and I more or less measured this in room with a near field measurement. Room gain gives me a pretty good response measurement down to even 4Hz. Given that these subs are dual opposed 12" drivers with a xmax of 28mm, im considering the following.

I would like to build 2x dual opposed sealed box's with the TC Sounds LMS-R 15" in the smallest possible box. The question I have is what will I gain by doing this over what I currently have. Im not looking for max spl but for headroom to handle transients like happened on this sample disc. As far as I can tell WINISD does not take this configuration into consideration. Also would there be an issue by having the two magnets very close to each other in the back to back dual opposed configuration?

My dream would be to do this with the LMS Ultra 5400 but I don't have the space in that location as these subs are at mid wall down the longest walls. I also have 4 smaller subs in the respective 4 room corners to fill in various nulls and they don't go below 20Hz due to design as well as electronic limits (crown Xti 4002 has a sub 20Hz filter I think).

CA2300 CA5300 CA2100 2xRB1582
CP800 "2.6" AV7702 "7.6.4"
2x800Di HTM1D 4xSCMS 2xDS8S 4xCCM7.4
2xDB1 2xCTSW15 2xCTSW10
windshear is online now  
Sponsored Links
Advertisement
 
post #2 of 11 Old 12-16-2014, 05:22 AM
Member
 
swtfman's Avatar
 
Join Date: Jul 2007
Location: Arkansas
Posts: 120
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 25
Are you sure your room isn't causing the problem? 15dB of boost below 20Hz seems a bit excessive.

If you do go with the DO LMS-R you will be gaining cone area while losing a bit of xmax (25.4mm vs 28mm). The voice coil on the LMS-R is vented through the rear of the magnet so you do need some clearance for that. I don't know how close you can put them together, but I would feel comfortable with 2" between them.

My Stuff:
JVC DLA-RS45U projector - Seymour H115 screen - Samsung UN65EH6000 TV
Fusion 12 Tempest L/C/R - diy coaxial surrounds - SI HT18 subs x4,
Denon AVR-X4000 - EP4000 x2 - Minidsp
HTPC w/AMD R9 270X - Linux Mediaserver w/ 18TB storage - PS3
swtfman is offline  
post #3 of 11 Old 12-16-2014, 06:22 AM
Senior Member
 
rhodesj's Avatar
 
Join Date: Apr 2005
Posts: 306
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 106 Post(s)
Liked: 72
Headroom is basically the difference between max SPL and normal listening SPL. The LFE channel alone is up to 115dB at reference. And keep in mind, subs need enough output to handle the LFE channel plus all the content from your L/C/R/surrounds that's below the crossover point. I believe the worst case is that the subs need to be able to output up to 126dB to handle the LFE plus seven channels of bass-managed audio at reference volume.

So you really do need to identify your max SPL requirements, and see how much sub you need to meet that.
rhodesj is online now  
post #4 of 11 Old 12-16-2014, 07:37 AM
AVS Addicted Member
 
Bill Fitzmaurice's Avatar
 
Join Date: Nov 2009
Location: New Hampshire
Posts: 10,509
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 1771
Quote:
Originally Posted by swtfman View Post
Are you sure your room isn't causing the problem? 15dB of boost below 20Hz seems a bit excessive.
It's way beyond excessive. Every 6dB of EQ doubles excursion and quadruples amplifier power demand. Having to boost by more than 6dB anywhere within the passband indicates a problem, probably placement sourced.
Quote:
I would like to build 2x dual opposed sealed box's with the TC Sounds LMS-R 15" in the smallest possible box.
Getting the maximum LF extension and output in the smallest possible box is an engineering oxymoron.

Bill Fitzmaurice Loudspeaker Design

The Laws of Physics aren't swayed by opinion.
Bill Fitzmaurice is online now  
post #5 of 11 Old 12-16-2014, 07:45 AM
Advanced Member
 
dtsdig's Avatar
 
Join Date: Mar 2009
Location: Rochester NY
Posts: 976
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 196 Post(s)
Liked: 179
Quote:
Originally Posted by Bill Fitzmaurice View Post
Getting the maximum LF extension and output in the smallest possible box is an engineering oxymoron.
Well, with an MSRP of $4500 (each!) they must be truly magical. The more money you spend, the more the engineers can defy the laws of physics, I guess.
dtsdig is online now  
post #6 of 11 Old 12-16-2014, 08:24 AM - Thread Starter
Member
 
windshear's Avatar
 
Join Date: Jul 2001
Location: Jhb, South Africa
Posts: 160
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked: 11
The more I dig around with regard to whats going on, on this demo disc and coupled to bass management and Audyssey DynEQ the more interesting it gets. It seems like the sample disc has a lot of bass on every channel below 20Hz. I had all my loudspeakers set to small and the crossovers set between 40-80Hz based on REW smoothest measurement. Every pair of loudspeakers that I changed from small to full range(taking care to actually off each amplifier driving the pair) bought me between 2-3dB of extension, until I had every speaker set large. I had 10 dB of headroom over where the bottoming first occurred. Turning off the DynEQ bought me another 5-7dB. So yes as mentioned it seems the Max spl will be the limiting factor here. The demo disc seems to be a worst case scenario based on bass output on every channel coupled to bass management.

Would I be getting any meaningful benefit from going from the pair dual opposed 12" subs to a pair of 15" dual opposed subs or do I need to be looking at bigger?

CA2300 CA5300 CA2100 2xRB1582
CP800 "2.6" AV7702 "7.6.4"
2x800Di HTM1D 4xSCMS 2xDS8S 4xCCM7.4
2xDB1 2xCTSW15 2xCTSW10
windshear is online now  
post #7 of 11 Old 12-16-2014, 08:29 AM - Thread Starter
Member
 
windshear's Avatar
 
Join Date: Jul 2001
Location: Jhb, South Africa
Posts: 160
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked: 11
Quote:
Originally Posted by dtsdig View Post
Well, with an MSRP of $4500 (each!) they must be truly magical. The more money you spend, the more the engineers can defy the laws of physics, I guess.
I don't know of anyone that pays MSRP, so what I paid was a pretty good deal at the time. Honestly for what they do they aren't bad, but obviously not in the league of a decent home build, especially considering their diminutive size.

CA2300 CA5300 CA2100 2xRB1582
CP800 "2.6" AV7702 "7.6.4"
2x800Di HTM1D 4xSCMS 2xDS8S 4xCCM7.4
2xDB1 2xCTSW15 2xCTSW10
windshear is online now  
post #8 of 11 Old 12-16-2014, 09:19 AM
AVS Addicted Member
 
Bill Fitzmaurice's Avatar
 
Join Date: Nov 2009
Location: New Hampshire
Posts: 10,509
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 1771
Quote:
Originally Posted by windshear View Post
Would I be getting any meaningful benefit from going from the pair dual opposed 12" subs to a pair of 15" dual opposed subs or do I need to be looking at bigger?
What you need to be looking at is a speaker capable of delivering the response and output that you want. That has far more to do with the size of the enclosure than it does the size of the driver.

Bill Fitzmaurice Loudspeaker Design

The Laws of Physics aren't swayed by opinion.
Bill Fitzmaurice is online now  
post #9 of 11 Old 12-16-2014, 11:25 AM
AVS Special Member
 
BassThatHz's Avatar
 
Join Date: Apr 2008
Location: East side of NW Cascades
Posts: 3,475
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 468 Post(s)
Liked: 475
two 15's vs two 12, is a 55% increase in cone area. It might be 3db louder. Hard to say for sure...
BassThatHz is online now  
post #10 of 11 Old 12-16-2014, 01:49 PM
AVS Addicted Member
 
Bill Fitzmaurice's Avatar
 
Join Date: Nov 2009
Location: New Hampshire
Posts: 10,509
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 1771
Quote:
Originally Posted by BassThatHz View Post
two 15's vs two 12, is a 55% increase in cone area. It might be 3db louder. Hard to say for sure...
Cone area is moot, displacement is what matters. You can find some tens that have more displacement than some eighteens. But if the cab is too small to allow the driver to work with adequate sensitivity adequately low the displacement is secondary to the result.

Bill Fitzmaurice Loudspeaker Design

The Laws of Physics aren't swayed by opinion.
Bill Fitzmaurice is online now  
post #11 of 11 Old 12-17-2014, 08:18 AM
AVS Special Member
 
BassThatHz's Avatar
 
Join Date: Apr 2008
Location: East side of NW Cascades
Posts: 3,475
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 468 Post(s)
Liked: 475
Quote:
Originally Posted by windshear View Post
crown Xti 4002 has a sub 20Hz filter I think
With a shelf boost + room gain and sealed subs I get to 4hz with an XTI4k; so getting low won't be your problem, insufficient watts will be. Maybe 02 version is vastly different, but 00 wasn't an uber-strong amp, not even as strong as an EP4000.
BassThatHz is online now  
Reply DIY Speakers and Subs

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off