or Connect
AVS › AVS Forum › Audio › DIY Speakers and Subs › My multi location subwoofer thread inspired by Welti,Devantier,Geddes !!!
New Posts  All Forums:Forum Nav:

My multi location subwoofer thread inspired by Welti,Devantier,Geddes !!!

post #1 of 191
Thread Starter 
This is my thread about multi sub position to cancel room modes at the listening position (LP).

After experimenting with some BIC subs i had on hand i discovered the Welti/Devantier nailed it to the wall !!!!

I ended up building two subs using Dayton drivers and amps to help "Tune" the LP.

The subs are built, just waiting for the MiniDSP to arrive....

****** Warning ******* If you use a modified multisub system like I did, make sure the AUX subs match the main subs output ability, if not they will limit the systems total output capabilities, like my originals did, I'm now working on the upgraded versions......
post #2 of 191
I like the Geddes approach. Here is a nice walkthrough: http://mehlau.net/audio/multisub_geddes/

This is for 3 subs, but you can do the same with 4. Just treat every sub beyond your first two like the 3rd. The key is that the subs in the rear of the room produce only a fraction of the total output.

I don't know what drivers you presently have, but you might be best served to keep the four you have up front and simply add 1-2 smaller cheaper subs in the back. Using larger drivers designed for significant low frequency output is a waste on those rear subs.

I don't think that using a single Bassis would be advisable. At a minimum you need level and phase control for each sub location (not per woofer, but per woofer group that is colocated). This is part of the "blending" process that is described in the link above. Using something like the DCX or MiniDSP is ideal IMO, but the phase and level control on some plate amps would be fine.

There might be other approaches, but I think this is a good practical and feasible route.
post #3 of 191
I just run mine as a total unit. If the 4 subs are identical I would just treat them as one giant sub and process all of them at the same time as a unit. IMHO.

Since mine are all within 2ft of the same distance from the main listening position and identical to each other I don't adjust their distance differently, I also run them all at the same output (gain) level so as to maintain maximum headroom. I also run them all over the same bandwidth. I EQ and level them all as a unit. This works for me and the response and power distribution over a large area of the room is pretty good. Even when I am sitting significantly closer to one over the other or at some other non optimum position I don't notice anything being off as far as a smearing in the time domain or whatever, this is probably helped by the fact that as you get closer to a sub it's response will dominate more and also that even in the worst position in my room the maximum difference in distance to any one sub of the 4 is only 6 or 7 ft probably. If you get into delaying subwoofers to match the time arrival at one position, and you move from that position to another the difference in time arrival can be more exaggerated due to the delay introduced to align at the main position. Keep that in mind if you have multiple listening positions spread over a decent sized area and want to get the best sound over a wide area. Also consider that even if you have one subwoofer 10 feet further away than another that is 10ms, or less than 1 cycle of delay in the arrival at 100Hz to the listening position not counting all of the many delayed reflections from the room boundaries. At even lower frequencies a few ms difference in arrival is probably completely inaudible. If you or you and a partner are the only ones listening and you only care about the response at those one or 2 positions by all means time align since those are the only spots that matter. Either way with identical subs there is no need to limit range or output level of rear or side placed subs which would handicap the system somewhat from a standpoint of headroom and dynamics, again IMHO, YMMV, FWIW ,etc. Being surrounded on 4 sides by subwoofers the bass is about as omnidirectional as it gets. I'm sure plenty will disagree with what I am saying here. I'm just throwing out a different viewpoint from someone who has 4 identical subs on 4 different walls and how I run them.


If you do have disimiliar subs then yes you will need to go much further into tweaking each individual sub to play the best together with the others as a total system. I prefer identical subs for that reason.
post #4 of 191
Thread Starter 
I guess i should start with software and a mic... What do you suggest ?

I have'nt had measuring software since TruRta.. I have a new HP laptop
post #5 of 191
I like Room EQ Wizard (REW) because it works well and it is free.

For a mic, Dayton EMM-6 ($40) with a preamp like the Behringer Xenyx 802 (~$50). You connect the mic to the preamp and the preamp to the line-in of your computer's sound card. From there your software, such as REW will do the rest.

Another option is the Dayton OmniMic which is $250. It is a complete solution including mic, preamp and software.

Like Ricci points out, people have different approaches. Which you want to try is up to you.
post #6 of 191
Thread Starter 
Quote:
Originally Posted by coctostan View Post

I like Room EQ Wizard (REW) because it works well and it is free.

For a mic, Dayton EMM-6 ($40) with a preamp like the Behringer Xenyx 802 (~$50). You connect the mic to the preamp and the preamp to the line-in of your computer's sound card. From there your software, such as REW will do the rest.

Another option is the Dayton OmniMic which is $250. It is a complete solution including mic, preamp and software.

Like Ricci points out, people have different approaches. Which you want to try is up to you.

Wonder if Santa is up to it..... 250.00 is well worth the software and hardware...hmmmmm

How big is the box hahahahaha
post #7 of 191
Quote:
Originally Posted by coctostan View Post

I like Room EQ Wizard (REW) because it works well and it is free.

For a mic, Dayton EMM-6 ($40) with a preamp like the Behringer Xenyx 802 (~$50). You connect the mic to the preamp and the preamp to the line-in of your computer's sound card. From there your software, such as REW will do the rest....

+1, but....

With a laptop, you don't normally have a true sound card with a line input. Mic inputs are equalized. You may need an external DAC; I use a Behringer UFO202.
http://www.parts-express.com/pe/show...inger%20preamp

I've got a nice pair of 3 cu ft boxes if you'd like to test different locations....

HAve fun,
Frank
post #8 of 191
Another vote for the OmniMic system. I think it's still $50 off, even. I got mine and it's pretty damn cool but I haven't used it much... yet. Seems pretty easy to use and got mine set up in minutes. No soundcard hoopla to worry about either.

I'm of the mind of treating subs as Ricci mentioned but I know that's not the best approach for every person, every room or subwoofer 'system'. In your case, KG, I'd keep the quad Tumult's up front and then maybe try out a Geddes style multi-sub system as Coctostan mentions with two more lesser subs. That's what I'd do. Keeps your Bassis in-line doing it's thing on the proper subs and then you could use a couple smaller subs to smooth out the bass if you need to.
post #9 of 191
Thread Starter 
So, i can use my quad 15's, as one system as it is. Then the idea is to augment the mains with subs on the side and back wall. Wait, more subs and more amps..hahahahahaha. More days in the garage with my table saw...with mobile casters to aid in mobility....There is a Santa Claus.

Will the new subs need to be sealed like my mains to blend better, and is it neccesary to extend their response, like my mains...

More subs Bahahahah.....
post #10 of 191
Yeah, pretty much but you don't need uber subs for the Geddes treatment. Seriously, just pick up two 250w plate amps, make two 15" cubes, put a single 10" Dayton RSS HF in each one and try that. Hell... you could just buy a couple of cheap-ass whatever subs from PE and try with those first. No fuss, no muss. Or however that goes.
post #11 of 191
Thread Starter 
Not to put the cart before the horse, but dont we need to measure to see if there is a problem. I think the first step is to choose a measure device, seems for me the ease of the Omni system from PE....

Your thoughts.. Like i said a have a new laptop
post #12 of 191
Quote:
Originally Posted by fbov View Post

+1, but....

With a laptop, you don't normally have a true sound card with a line input. Mic inputs are equalized. You may need an external DAC; I use a Behringer UFO202.
http://www.parts-express.com/pe/show...inger%20preamp

I've got a nice pair of 3 cu ft boxes if you'd like to test different locations....

HAve fun,
Frank

I forget about that. I have a Creative USB something or other that is a soundcard and mic preamp. I think it was about $100 but I've had it for a while.

The OmniMic doesn't look like it is on sale right now. I think it is a significant premium to pay, but others obviously think the simplicity is worth the extra cost.

Quote:
Originally Posted by Scott Simonian View Post

Yeah, pretty much but you don't need uber subs for the Geddes treatment. Seriously, just pick up two 250w plate amps, make two 15" cubes, put a single 10" Dayton RSS HF in each one and try that. Hell... you could just buy a couple of cheap-ass whatever subs from PE and try with those first. No fuss, no muss. Or however that goes.

In fact, a single sub in the rear might be all that is needed. Ideally, two of the Tumults would be in the corners and two would be somewhere across the front of the room. The rear sub would be best placed higher than half the wall height.

Those are just generic ideals in my experience. They won't be ideal for all rooms and even if they are optimal for a specific room, compromises for practical reasons aren't drastic compromises.

To start, I'd just leave the Tumults as is across the front and add something like the single RSS HF sealed for the back. Just build something that fits your space.
post #13 of 191
Thread Starter 
^^^ i borrowd a friends mic and preamp and never really felt like i was doing things right, the Omni Mic is quite the package for me. I mull it over and probably pick one up by next week. I'm really curious to see how they measure. I guess i'll pick up a mic stand at my local pro audio store. Nice and solid with a steel base.

My wife got me a nice caster mobile base for my tablesaw, cool winter project.

How many measurements do i take. The laptop will feed the signal to the amps when doing sweeps
post #14 of 191
post #15 of 191
Quote:
Originally Posted by kgveteran View Post

The laptop will feed the signal to the amps when doing sweeps

With OM you play the CD in your AV system disk player.
post #16 of 191
Thread Starter 
Quote:
Originally Posted by noah katz View Post

With OM you play the CD in your AV system disk player.

What is the disc of choice.... I kinda liked the sweep my TruRta use to do. There are discs with sweeps..... Or is it just tones
post #17 of 191
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

back up to post #3.

http://www.harman.com/EN-US/OurCompa...s/multsubs.pdf

Ok, i'll try to digest this, whow 30 pages.......
post #18 of 191
"Ok, i'll try to digest this, whow 30 pages......."

you asked a very complicated question. if you just want the answer...
LL
post #19 of 191
I'm using #3 in the picture above. Unfortunately the listening position is close to the center of the room for me so that causes some big response variations but it's what I (and many others) have to work with.
post #20 of 191
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

"Ok, i'll try to digest this, whow 30 pages......."

you asked a very complicated question. if you just want the answer...

Lol, thank you !
post #21 of 191
Thread Starter 
The OM comes with a test disc, where do i begin when the OM system arrives. I will have to measure the subs to see that they are doing. Since my sofa has three seating positions will i measure from all three....

I have to work on my bass traps for the back wall corners also in the mean time, decay measurements will also aid in seeing that the before and after were worth the effort..
post #22 of 191
Thread Starter 
Just pulled the trigger...248.00. Is it really 350.00 regular price ?
post #23 of 191
Nah. That's the price no one pays. It's always been $300.
post #24 of 191
Thread Starter 
Fed ex should be delivering my OM tomorrow. Some measurements should let me know where i stand FR wise... Graphs to come..
post #25 of 191
Quote:
Originally Posted by kgveteran View Post

The OM comes with a test disc, where do i begin when the OM system arrives. I will have to measure the subs to see that they are doing. Since my sofa has three seating positions will i measure from all three....

I have to work on my bass traps for the back wall corners also in the mean time, decay measurements will also aid in seeing that the before and after were worth the effort..

As an OmniMic owner for over a year, I'd be glad to chime in. I'd measure close mic each enclosure prior to proceeding with anything else. Pot down everyone but the DUT, and then begin one sub at a time. Just a good practice to possibly flesh out potential issues you may need to address.

Then, proceed with LP measurements.


Good luck
post #26 of 191
Quote:
Originally Posted by kgveteran View Post

So, i can use my quad 15's, as one system as it is. Then the idea is to augment the mains with subs on the side and back wall. Wait, more subs and more amps..hahahahahaha. More days in the garage with my table saw...with mobile casters to aid in mobility....There is a Santa Claus.

Will the new subs need to be sealed like my mains to blend better, and is it neccesary to extend their response, like my mains...

More subs Bahahahah.....

I flank my mains with the dual subs I have now, have measured the results and the improvements made are significant, especially with respect to dealing with the main's floor bounce nulls. I plan to add two more following the Geddes or Romeyn method while retaining the flanks.

A good discussion describing the positive effects of flanking and multiple subs. http://www.diyaudio.com/forums/subwo...ubwoofers.html
post #27 of 191
Thread Starter 
Quote:
Originally Posted by foh View Post

as an omnimic owner for over a year, i'd be glad to chime in. I'd measure close mic each enclosure prior to proceeding with anything else. Pot down everyone but the dut, and then begin one sub at a time. Just a good practice to possibly flesh out potential issues you may need to address.

Then, proceed with lp measurements.


Good luck

dut ?
post #28 of 191
Device Under Test

I think that all 3 approaches discussed in the diyaudio thread are valid. The end result is the important part. Reducing the seat to seat variance WITH as little EQ use as possible is the goal.

With the Welti approach (symmetrically placed subs), it is done using standing wave theory that assumes a rectangular room with essentially identical walls. The drawback is that rooms rarely fit this category, but the approach works quite well in many instances. The drawback is that although the response is nearly identical at each seat, lots of EQ must be used for a flat response, and the overall LF contribution of multiple subs is not always realized, especially with 4 subs at wall midpoints.

The Geddes approach is more experimental, and also provides for cancellation of some floor/ceiling modes. By experimentation and measurement, a solution can be had with less subs.

The Parham approach is between the two, with an overall increase in LF radiators.

All three approaches are valid. The endpoint is of course measurement. Although none of the approaches breaches the subject at length, absorption on front and rear walls can significantly affect 1/4 wave suckouts in the 100-300Hz region. To a certain extent, absorption can also help with <100Hz content, but not nearly as much as mode cancellation with multiple LF sources. A combination of the two + DSP control (absorption + multiple sources + DSP control) can yield a very flat freq response and little seat to seat variation, as Toole experienced in his own living room (Room 3 at the end of the paper):

http://www.aes.org/tmpFiles/elib/20111227/13680.pdf

Start at section 6 of the paper, and this is the basic algorithm used by the JBL BassQ unit. It allows for optimized use of delays, levels and a single band of EQ per sub to reach a solution that allows for the least variance seat to seat plus as flat a freq response as possible using minimum EQ. A disadvantage to the BassQ system is that it only allows for four measurement locations (you use four mics simultaneously during setup). It also does nothing below 20Hz, a problem for the ULF-loving people here.

Since there is no established algorithm on how to do a BassQ type optimization with a laptop and single mic, experimentation and measurement are key.


JSS
post #29 of 191
Quote:
Originally Posted by maxmercy View Post

The Geddes approach is more experimental, and also provides for cancellation of some floor/ceiling modes.

As far as I can tell, the Welti paper discussion is confined to two dimensions.

The height mode might be addressed the same way by placing the opposite subs at floor/ceiling.
post #30 of 191
Quote:
Originally Posted by noah katz View Post

The height mode might be addressed the same way by placing the opposite subs at floor/ceiling.

Or half way up the wall, as that would then fail to excite the first floor/ceiling mode.
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: DIY Speakers and Subs
AVS › AVS Forum › Audio › DIY Speakers and Subs › My multi location subwoofer thread inspired by Welti,Devantier,Geddes !!!