One note bass

[richidoo]

I heard the one note bass!

I have been frustrated with the dillemma of too much reverb in my main room and no way to fix it without painting the place with absorbtion. Physics are tough to outsmart.

So I moved the stereo into my office as a gesture of surrender, grasping for sanity and an attempt to move forward. I suspected the Ushers would be a bit too much in the little 12 x 11 x9 room  , and sure enough they were. But mostly because of the one note bass, not so much the SPL, but that was a little too strong also, due to small closed field volume. But I was able to make some interesting observations about the bass anomalies.

I am set up along the longer wall (12) to best accomodate the door. I have 64 sq feet of 5" absorbtion on the rear wall, 32 sq feet on the left wall, the diy holy diffusor panel on the front wall between speakers. Plus stereofools 6" thick 2x4 FG panels in corners, and the 2 giant bass traps (cardboard boxes full of absorbtion) in the rear corners. I will be experimenting with placement of all this stuff, but it is in there now so results are probably at least 80% of potential.

Lots of fussing with speaker position yielded this which was just barely starting to give solid center image. It's just too damn close for these speakers which IME are not laser imagers anyway.



The modes start at 47Hz or so. But obviously the speakers are playing below that frequency. I hear the dreaded one note bass at every location in the room except smack dead center on all three dimensions. In the dead center of the room, bass is a little too loud, but tuneful and clear. Move a foot away in any direction and I can start to hear the smearing, echoish almost, layers of reflections graying up the music. It is really grungy indistinct energy.  As I move farther away from the dead center, the grunge gets more smeared until it is many reflections all melted into one, making the sound of 99 Maxima playing Tupac full volume.

My question is about the frequencies below the modal region. Is there any chance for music down there, or is it just dead man's land, where no music can be had? The one note also seems to be triggered on notes above 47Hz. Maybe the modes are what I'm hearing. I've read that below modal frequencies it is just non-directional pressure.

I can fill all 12 wall corners of the room with large bass trap absorbtion. But I would like to know if this will cure the one note bass before I try it. How low frequencies can a 2x2 foot triangular wedge of solid cotton absorb? If not low enough for 47Hz, how to kill that mode? Tuned trap?

Having heard how the one note bass thing changes with position, I'm wondering if what is happening is that the wavelengths larger than room dimensions fold back on each other and create many pressure peaks in the room, which are perceived as the room dimension's wavelength, with all three wavelength of the major room dimensions smearing together like a low freq muddy chord.

I know that I can't apply absorption thick enough to affect even the first mode, requiring absorption 6 feet from the wall to reach quarter wave peak velocity of the reflection. So I'm starting to wonder if it's possible to make full range music in a small room. EQ can manage the bass level, and your head can be in the least reactive spot in the center, but that is not practical in a very small room.

Cool little freq/wavelength calc: http://www.mcsquared.com/wavelength.htm

What is the potential for massively treating the corners with absorbtion? Can the one note be effectively eliminated?
All opinions are very welcome!
pics:





Thanks
Rich

[bpape]

Actually, below the primary axial modes, it's not possible to have true modal activity.  That said, there are still tangential and oblique modes that can be lower but they're generally not as intense - unless they happen to overlap each other closely.  You can have plenty of music down low

Where are you noticing the one note down low?  The upper ones are easier to see around 250 and 320 Hz.  There's another that could be perceived in there around 95hz. 

The placement you have in that room is going to give strong SBIR from the side walls which isn't helping either. 

Have you tried anything on the wall behind the listening position and potentially along the wall/floor boundary (try the 2 boxes...)

Bryan

[richidoo]

I will sing along to figure out where the one note lies.  Could be 95 or even higher. It is so non musical it doesn't really sound like a note, but it must be.

I am willing to treat everything and anything if it will let me keep those speakers until I get a room that can handle them properly.  Not sure the soundstaging can every be right though. I can literally cover every surface 8" deep if it will help, but not about to go to that length without some guidance. As always I appreciate your endless fountain of help.

I haven't tried anything other than in the pictures so far, just moved in there yesterday. I usually prefer traps along the floor beside speakers, so I'll try that. Also I want to try more traditional dead front, live rear. Might help with the soundstage depth.

The wall behind the listening spot has the 4x8 panels cotton in kraft paper, but nothing directly behind the listener in the 3' gap between the panels. The stuffed chair blocks my head from that bare wall behind me, but I will probably get a chair with no head support and use diffusion behind.

I will experiment some more with the trap placements and run a FR scan.
Thanks Bryan
Rich

[richidoo]

One other thing I have been wondering, will it damage the crossover to disconnect one of the woofers, and make a pseudo Be10? The woofers share chamber volume so the unpowered would move.

It seems that removing a driver in parallel raises the load impedance so should be no problem electrically, but probably won't sound as clear as both powered.

EQ/biamp would fix it more properly but is it safe to try?
Thanks

[bpape]

I have no idea about the speaker disconnection - sorry.  Logically I wouldn't think it would hurt anything unless they're wired in series which I doubt - which would drop the impedance.

Try the boxes on the floor behind the listening position against the wall.  That will hit both the even harmonics of the width and any potential tangentials involving the wall/floor intersection.  Might work, might not.  There's so much else going on in the room it's hard to say.  If it was me, I'd pull everything out in terms of treatment and play for a day or 2 with speaker and seating location to see if you can pin it down any better without potentially masking something.

Bryan

[miklorsmith]

Wow, sorry about the issues Rich.  I thought you were happy as a pig in mud, just a pig needing a killer, big SS amp.

Do you have the hardware to do in-room FR and impulse decay measurements?  Stereophile test tone CD? 

[Bigfish8]

Hi Rich:

Sorry to hear you are having bass issues.  Honestly, I cannot imagine those BE-20's in that room.  You must be able to generate SPL's that would make a rock band take notice. 

Good luck on finding the issue and I look forward to seeing you next week in Denver.

Ken

[richidoo]

Thanks Bryan, geat idea to start empty. Also pad behind listener.

Mike, I am happy as pig in mud! I have a great system now. Unfortunately midrange reverb in 46 x 26 x 10 hard surface room with open doorways to another 4000cu feet is impossible to tame. I just want a break from that big room that has no perfect solution. After a while it makes me crazy to keep thinking about it.  I have gear to measure the room, but I need a new laptop.  Without midrange reverb the Ushers sounded unbelievable last night on stuff with no bass. It will be fun to work the small room out and then the big room doesn't seem so make or break.

Ken, you're right the Ushers are too much for that little room, but it's what I have on hand right now.  I will be trying the Feastrex horns in there tonight. They are good to 50Hz, probably will sound a bit better in some ways, not as good in other ways. I will eventually put the Ushers back in the big space, but for now, trying some new ideas that are simpler than continuing the fight with the big room. I just need a change. Me too looking fwd to RMAF!

The weird thing is the small pine cabinet Feastrex single driver speakers needed NO acoustic treatment. The reflections from the room were warm from the wood and clear enough not to disturb the flow of music so I didn't mind them. Removing treatment made the room sound better, but there was little bass anyway. I'm building the new larger cabinet for Feastrex in pinewood now. So maybe it is crossover phase issues in the Ushers, or their near perfect monopole behavior, or god knows what. The drivers have no material signature. In many ways they are perfect. In other equally important ways, like usability in less than perfect space, well, I don't know yet. As I work with them I will learn more.
Rich

[miklorsmith]

Looking at the website, it appears the XO to the woofer is about 550 hz.  I would try a Behringer or similar parametric EQ off the second set of preamp outputs, run that to a big SS amp (or preferably monos with very short speaker leads) and gain full control of the bass range that way.  That's similar to what I'm doing though I'm only going to 100 hz or so.  Generally I think this range is insensitive to the possible nasties of DSP and the benefits are incredible.

This could fix your SS amp problem too.  I replaced a single Crown K2 (giant) with two much smaller and cheaper Behringer A500s and took a significant step forward.  My two Behringers were $340 total delivered and control the 4x10"x2 sub drivers per side, no problem.  They blend with the snootier mains amps too.  If you go this way, balanced cables (or adaptor) to the EQ, balanced cables as long as needed to the bass amps next to the speaks, 12" heavy gauge speaker leads.

I LOVE this setup and wouldn't consider anything else at this point.  It really delivers it all.  Being able to decide what bass character you want to achieve AND getting it in the room is a luxury I wish upon every audiophile.  And, even if you had to buy everything new you're in the $500 range total.

Yeah yeah, you mentioned midrange echo which I can't help with at all but had to take the chance to get on the soapbox.   

[Carlman]

   You've been busy! 

I don't think there is a way to 'eliminate' the physics issues of ginormous speakers in a small room.  Even with something like a TacT it's tough to get it to sound right.  BUT you can tame it quite a bit.  I think some vinyl sheet-covered panels with absorption behind them is probably going to work best.  It is important that the bass get as trapped as possible.  Also, bracing under the house will be a big factor too.  It'll help tame the resonance of the room even more than the other room you were in.

That room is a good size for your Feastrex speakers, though.. I can't wait to hear that setup.

I know all too well the bass wonk of that sized room.  I would be very happy to help you move it 90* so it's setup on the short wall if you want to try it that way... I've got a few panels lying around you can 'borrow' also.

Give me a shout and let me know a day that works for some experimenting.

-C

[richidoo]

Hey Mike, I like that idea! Behringer makes some very useful products, I like my crossover. Def2 has no built in bass amp?

Thanks for the tips Carl. Maybe next week?

Amazingily I did get the Feastrex playing music in there tonight. I was able to just sit back and relax and enjoy some music. The one note bass grunge of the room was just starting to kick in a little on some fender bass lines on smooth jazz stuff, so 50-100Hz area. But not half as bad as Ushers. Maybe because ushers play lower, maybe because they are absolutely monopole, while these horns leak sound in every direction. I also moved a box trap down to the floor corner.

With all the treatment out of the LR the kids were all screaming to play with the echos. 

[_Scotty_]

Rich, I think I have an idea for you to try that might put your Ushers back in the big room. In as much as you cannot acoustically treat the walls of the big room to your satisfaction you  might try intercepting a portion of the energy that would have rebounded off of the walls before it gets there. To that end you might try placing GIK 242 Elite
on either side of both speakers so that the midrange and high frequency drivers are placed in a horn formed by the sides of the acoustic panels. To maybe make this work you will need the panels at least as high as the tweeter if not a little higher. You have a lot lot of acoustic absorbers in your small room that might be pressed into service to test this idea. The 2x4 FG panels would be a good place to start if you have 4 of them. you can place the panels off to one side or in another room when they are not in use.
  The speaker woofers cannot be disconnected. The speakers are designed as a system and the enclosure is sized and designed to have two driven woofers in it for the bass to have the proper transient behavior and extension. Part of your problem in the small room is room gain below a 100Hz. Below a certain frequency in the bass region you will gain bass output at about 12dB/oct in that room. You might try a simple 12db/oct roll off in the bass region. Your software might be able to tell you at what frequency you start to gain output, this would tell you what frequency your 12dB/oct slope would need start at. I don't want to be negative about your situation in the small room but I don't really see your large speakers working all that well in this size room. You are right about being too close for the speakers to image properly. They probably won't generate a proper Gaussian wavefront where the output of the drivers blends together evenly until you are about 8ft. away from them. Good luck with resolving
the issues with your system.
Scotty

[richidoo]

Great stuff Scotty, thanks.  I'll think about how to biamp/EQ with what I have on hand. I have used that principle to kill it early successfully before.  Putting absorbtion near the speakers can work well. My woofers play up to 550Hz so the whole thing needs to be horned, it's a good idea. I know the Ushers are just too big for the office, but it's worth a try to learn what happens. So I will probably move them out soon. Julie wants to decorate the LR now, which means drapes which will help. She was not interested in decorating it before.  I'll wait till she gets it really nice looking then surprise her one day when she comes home with the speakers back in there!

[Carlman]

Julie wants to decorate the LR now, which means drapes which will help. She was not interested in decorating it before.  I'll wait till she gets it really nice looking then surprise her one day when she comes home with the speakers back in there!

Oh wow... Can you video her reaction and put it on youtube? hahahaha   

[miklorsmith]

The 2's do have sub amps built in.  They have plenty of pop, decent definition, and sound pretty impressive that way.  I need to measure response with them set up that way.  However, compared to the EQ'd setup they sound lumpy and don't go nearly as deep as when EQ'd. 

The setup as now includes a dbx Driverack 260 which allows Left/Right independent equalization via parametric or graphic.  I do the left channel, measure, tweak, measure, tweak, etc, then the right channel.  When I have them each set up basically "flat" I have a separate, summed parametric that finalizes the whole system response exactly how I want.  I've read a gentle rise toward 20 hz is generally preferred and I find that to be excellent at low-to-mid volumes.  I have a flatter preset that I usually use for higher volumes which doesn't shake the house or load the drivers quite as much.

The final upshot is while the speaker itself does have a bass amp and attenuator which allows *more* tailoring between the speaker and room than your average bear but still nowhere near the level of the EQ'd system.  I can even minimize reverberant modes (which I have too) by decreasing output at those narrow bands.  It might not look quite as "flat" in a measurement but it's worth the tradeoff and besides our ears are nowhere near as "flat" as we'd like to believe.

This arrangement might be just as useful in your big room too.