Ultra-X12 Subwoofer Floor Loading

I have had an Ultra-X12 subwoofer (used in the maximum extension mode) since its introduction, to use with my RR2150 receiver. Overall, I am very pleased with the sound quality when paired with my small KEF LS50 speakers, though it took a while to adjust the levels and X-Over frequencies ('Pink Noise' + a 1/3rd octave analyzer). However, I still have the feeling that the bass is not as 'tight' as it could be, possibly due to a driver/port 'loading' problem. As I have hardwood flooring, I do use the supplied 'discs', PLUS (at my wife's 'request') I added under each disc an 'Easy Glide' padded disc to make the subs easily movable for floor care/cleaning. Thus, the overall height from the floor to the subwoofer bottom is 2-inches, probably twice the distance than just using the spikes on deep, plush carpeting. Too high? My listening room size is about 26'L X 18'W X 10'H (and is connected directly to a 12' X 8' Foyer and side corridors). It would be easy to add a layer of carpet or (properly damped) wood under the sub driver and/or the one open port to correct the 'loading' (and prevent driver damage). Any thoughts or suggestions that might provide some guidance?

Check out this solution. I use it for both my subs and it definitely isolates the sub from the floor.

http://www.sweetwater.com/store/detail/GRAMMAII

Thanks for the info. Not sure, however, how this would affect 'loading'.

As an added reply, I should have noted that the Ultra-X12 being a downward firing sub with a downward firing ports, caused my concern. The question of 'loading' really applies to both the driver AND the ports.
My KEF LS50 main speakers are vented, with the port being on the enclosure rear surface. KEF makes a great fuss about placement of the speakers with respect to the enclosure to wall distance, and includes 2 port 'tuning' plug sizes to compensate for placement distances less than 500mm (about 20-inches). With that in mind, I am as concerned about BOTH the driver and port distance from the floor.
Thanks again for your interest.

I doubt that any lack of "tightness" is due to issues with how the sub is interacting with the floor. Even a very lightly built home has literally thousands of pounds of flooring, furniture and "stuff" weighing down the joists. If the home is on a slab there is even less chance of the sub really "moving" the floor. There is a higher probability that whatever "easy glide" pads the sub is sitting on are allowing the sub to "float". You can try putting a bag or two of sand http://www.amazon.com/Quikrete-1113-51-50Lb-Play-Sand/dp/B00005C6E3/ref=sr_1_2 on top of the sub to increase its mass in an effort to keep it from skittering around. If the sandbag(s) are slipped into a fancy pillow-case http://www.westelm.com/products/cloudy-abstract-pillow-cover-shockwave-t2609/?pkey=cpillow-covers you can even convince yourself / your spouse it is a "designer decorator enhancement"

Without knowing the total volume of the listening space and adjacent foyer (two story??) it is likely that there is simply a whole lot of space being excited by the single sub. It is not going out on a limb to suggest that there is some nasty mode coupling muddying the sound...

How best to fix this???

There is really weird relationship between how much POWER is necessary to get acceptable levels of bass and HOW MANY subs are used. Yep, MORE drivers == LESS power "leaked". Even harder to believe, using MORE subs will actually result in both a TIGHTER sound AND less need for "soundproofing" as there is less "mode coupling".

This might sound like some hocus-pocus dreamed up by the firms that make & sell subs, but the FACT is that even firms that make their money selling bass control / sound absorption products can confirm that ADDING SUBS IS BETTER than trying to increase "soundproofing" -- http://www.acousticsciences.com/art-noxon/buy-subwoofers-instead-soundproofing

In re-reading your original post I assumed you wanted to ensure that the sub did not move around and did not cause bass loading to your flooring. Once I re-read it I came away with the idea that you have an issue with the way the driver is loading the ports inside the sub. If you are having what some refer to as "port chuffing" due to air movement through the port, increasing the distance from the floor may affect your ability to hear it somewhat. The GRAMMAll is designed to both elevate and isolate from the floor. It is carpeted to ensure the chuffing is somewhat absorbed also.

Even if your house sits on a slab the sub has the capability to transmit significant energy to the floor and around the house at high volumes and low frequencies. If you want to do an experiment, play a 20-25 hz test signal through your sub and walk around your house to listen for items vibrating. I do this anytime I set up a new room to make sure everything is going to stay where I put it.

Sorry, but I have away for a while. I have tried changing the 'loading' of the Ultra-X12 driver and/or vent. The changes were definitely audible, but never sounded as 'tight' as the bass of my ancient Transtatic I (KEF B309 in a TL + KEF mid-bass in TL + ESL mid-treble , , the best overall sound of any loudspeaker I have ever owned). 'Chuffing' or other strange sounds not a problem, just the quality of the bass. I am beginning to think that realistic, really 'taut' bass can not be produced by a downward firing subwooferdue to the necessity of the driver to 'squeeze' the air out from under the sub + the vent tuning is effected by the sub-floor space.

Sub woofer placement is a key to getting good bass response. Have you ever done the sub crawl. Place your sub in your prime seat and slowly crawl around the room while playing a test signal of around 25 hz. The position where you get the best bass is where the ideal spot is for your sub.

Well, first do you know what this sub weighs? Hard to place on my 'listening chair'. Second, if I worry about floor loading, what would a plush cushioned chair smaller than the sub result in? Third, my 50+ years of audio has taught me that the sub needs to be near (preferably between) the main speakers; otherwise a multi-miked viola would have the bowing on the left, the finger work on the right and the bass (maybe) behind me. Most unrealistic.

Most sounds from a sub a low enough that humans can't determine direction very well. And yes, I do know what it weighs, since I have the LFM1-EX which was its predecessor and weighs 1 pound more at 67 pounds. I placed mine on a piece of plywood directly on my theater seating to do the sub crawl. My 50+ years of experience tells me that the sub needs to be placed in the room in the right location OR you will get muddy bass due to the room nodes interfering with the response. If you can't put it on your listening chair then substitute something that will hold it while you do the crawl. 4 cement blocks and a couple of two by fours will do nicely to support the sub. There is no way that the sub is challenging the floor loading in your house. It weighs significantly less than you do, unless you are a 12 year old girl, so it isn't a problem. I weigh 5 times what that sub weighs and I don't have a floor loading issue in my stick frame home.

Well, I believe that we have digressed entirely from my original ‘post’.

In my 75+ years, starting in the 60’s, I have built Heath and Dynaco kits, both audio and analyzers; I have also built and/or modified a number of loudspeakers and cross-overs (with the help of LEAP). I currently have a number of audio systems (all stereophonic) including my old Dynaco ST70 Amp/PAS3 Preamp/FM tuner, plus Phase Linear Amp and Preamp, Adcom, Hafler, etc.; I also possess Duntech PCL 3 speakers (excellent), Magnepans, ESS Transtatic I’s (old,1972, but still produces one of the finest sounds around . . will empty your cupboard and rattles your doors at 15 Hz, and the ultrasonics will drive your cat insane), and KEF LS50’s (for background music).

My original ‘posting’ was to determine the optimum height of this downward firing subwoofer above a wood floor. My experience indicates that with such an arrangement the floor actually becomes part of the speaker, with respect to both driver/vent loading and vent length/action. I have a 65” SONY Bravia TV with built-in, front mounted 3-way speakers, supplemented with the SONY wireless sub. This 8” sub produces better, cleaner (if not as deep) bass than the Ultra X-12: a bass drum has ‘impact’ and is taut, versus X-12’s ‘muddy’ sound (as if was under a blanket!).

My wife likes the appearance of the X-12 so if I cannot obtain better, cleaner bass from it I will probably gut it, invert it, Drylok it and make it into a planter. I have already spent too much time and effort on this subwoofer.

Thanks for your replies, though.

I guess I read your post right the first time. The GRAMMA isolation pad is designed to eliminate the floor from becoming part of the speaker. It uses some heavy duty high density pads that are about 3 inches thick and is mounted to a carpeted piece of MDF for the sub to sit on. It raises the sub off the floor about 3-4 inches and lets the sub breath a little better. I have the first version which is as described. The newer version doesn't appear to give the same rise.

I have an Ultra-X12 that has replaced my LFM-1 Plus. I love it and I'm quite happy with my decision to replace the Plus. The bass response, I find, is very tight and precise. I also have it on hardwood flooring using the spikes/discs, but haven't experienced any "loading" or undesirable muddiness.

Since introducing it into my system several months ago, I've enjoyed an improved listening experience from what I had with my previous sub.

One example...
Playing "Edge of Tomorrow's" opening scene, which contains some extremely low bass, demonstrates to me the X-12 can reproduce accurate, precise bass at these low levels and every desired frequency above those.
Just my 0.2¢.

1.25" to 1.5" is the proper height to make sure you do not have an issue with cabinet/vent loading. This is the required amount of space to allow the driver to displace enough air that it can properly go through compression and rarefaction. If using the Outlaw feet, you are fine. The Ultra is a very tight sub, as the internal bracing eliminates most cabinet resonances and the Class LH amp tracks the audio signal - if you are experiencing 'muddy' sound, I would also recommend an isolation pad to decouple the sub from the floor.

Voila!!

But, if the loudspeaker design intends the floor to be part of the speaker (similar to a more complex multi-cavity enclosure), then raising the subwoofer will defeat the original design intent
Anyway, I have been sending out 'feelers' to find a vintage ACOUSTICAL MFG, Ltd (later "QUAD") 50's full-range corner ribbon speaker in good, working condition. Exquisite design and cabinet. Virtually extinct.

The GRAMMA doesn't just raise the sub off the floor. It provides a raised, isolated platform for the sub to sit on. Subs don't intentionally try to make the floor part of the speaker although sometimes they can. Otherwise designers would have to give different specs for different floor stiffness and design.

RE my previous post, yes, my sources have all indicated that the "QUAD" loudspeaker I mentioned does appear to be extinct; a carcass or two might be found in an English attic.
I found a review of this "Corner Ribbon Loudspeaker" in "Wireless World", December 1950 issue, page 29. From the article I have concluded that all of these (I believe) magnificent loudspeakers have been 'incinerated' by the advent of more powerful, double digit Watt amplifiers.
Short of a human sacrifice, I do not believe I will get my wish for a pair, much less one, of these beauties. Amazingly priced at £83, including installation! Of course 1950 £83 translates, based on the 1950 £ to $ conversion rate and the inflation factor, to only a mere $1,100. Nothing of this caliber could be produced today for anything close to 10X this price, considering stunning finish (even the hidden sides) and complex interior bass acoustic filter structure.
Thanks for everyone's advice on my X-12 question; I appreciate the replies. Will try the absorption pad . . . a cheap option.

The Quad ESL is still being made in an updated form by the same company, Quad-hifi. Google quad esl and you will find it. There is also someone rebuilding the originals but that is very expensive. I have a pair of Magnepan 1.6 which although different in form, operate on the same principle and are awesome for music. They are also reasonably priced. Check out http://www.magnepan.com/index

While listening to my Ultra X-12 and thinking about subwoofer sound, another thought popped into my head: listening room construction. When I lived in NYC, Manhattan all of my apartments had thick plastered interior/exterior brick walls, rather than the sheet rock over 2X4 wood studs construction of my house here in Texas (which my English friends referred to as ‘stick and wattle’). I remember having to use a rotary impact drill with a long carbide drill bit, and a lot of force, to drill holes to run wire from room to room. My first experience here with that drill here resulted in a drill chuck size hole, with the drill bit protruding into the next room as soon as I started the drill!
Thinking that over, I am fairly certain that the flimsy, thin wallboard vibrates with low bass frequencies, absorbing then releasing energy which may make low bass sound ‘muddy’. I do not have a laser interferometer to measure wall ‘bending’ modes, so my thoughts are not confirmable. Could wrong, but there may be some truth in this as I have read about loudspeaker manufacturers using interferometry to measure and control cabinet resonances. And, loudspeaker cabinets are a lot smaller than my large listening room walls and, especially, the much less braced ceiling. Thoughts?

Many people add a second layer of drywall glued to the first layer with some glue that is said to isolate the resonance from being transmitted. This is usually done to prevent transmitting sound beyond the listening area. Other than the room nodes generated by the sub itself and reflected by the walls I would think using some sort of bass management feature to adjust the sub and its position in the room. It may also be useful to set up a second sub in the room.

Unfortunately, this could be occurring. This really is what occurs with standing waves, as they store and release energy that will greatly impact the sound. Room construction and layout definitely impacts this.

This is actually a real concern. I volunteer on my church's buildings and grounds committee and when we hired a firm to tune the new DPS sound system I tagged along with the folks that did the work. One of the things that they liked about our building was the relatively high amount of exposed brick that is generally among the more acoustically consistent surfaces. Surfaces that measure out with similar reverb / dampening can actually have things called "coincident dips" that require more carefully designed narrow spectrum / phase-based tuning... (this is also why I recommend folks spring for the highest resolution room correction, typically homes are harder to tune than commercial construction -- http://www.audyssey.com/technologies/multeq/flavors)

More details on these topics --
http://web.mit.edu/parmstr/Public/NRCan/CanBldgDigests/cbd239_e.html

http://www.acousticalsurfaces.com/acoustic_IOI/101_22.htm

http://wiki.naturalfrequency.com/wiki/Sound_Transmission

I would try to re-position the sub to another area first and check to make all the speakers are in phase with one another. Next try adjusting your crossover point higher to remove your mains from the equation so they are not adding to your woes. Years ago (and several times since) the woofers in my Advents had deteriorated foam rings and sounded terribly muddy. As you can tell I don't think it is the sub causing the issue, (unless it is damaged) but more of how the sub is interacting with your system and the room. As stated before, I have the predecessor to the X12 but the design is very similar. I get excellent response from it for both music and HT.