[matix]

Thanks.. certainly helps.    Come to think of it,  already having some bass problems when the double bass hits the real low notes... I don't think I want to hear those notes below 40...

[ScottMayo]

Thanks.. certainly helps.    Come to think of it,  already having some bass problems when the double bass hits the real low notes... I don't think I want to hear those notes below 40...

Yes, you do! Deep bass conveys part of the emotional impact of music. For some music it's a huge part of the story. I listen to a mix of things, from classical to Frippertronics, and even though I have full range speakers, I'm not shy about adding the sub in when an album calls for it.

People talk about getting accurate tweeters and getting a flat response up to 50kHz, and the fact is, many people can't hear much past 16kHz. But everyone can hear down to 25Hz or lower, and you can feel things down to 8Hz or lower. Don't rob yourself!

Yes, it generally means treating a room, but rooms ought to be treated anyway.  

[warnerwh]

This is just my opinion but I think that the sound and feeling of a live event is the best gauge.  This is where having good low frequency output comes into it's own as most speakers just can't get that bottom octave weight and power.  It's actually amazing how much sound is down there. Once you have it you'll not want to go back.  My sub Only plays below about 45hz so there must be an awful lot of music down there because if I turn off my main amp I can hear that my sub always has something going through it.

[James Romeyn]

This method of eliminating up to two bumps/dips in the bass range is affordable, improves cosmetics, utilizes no room treatments, &   increases system SPL & decreases distortion (especially in the bass range).  In fact, my particular room's bass bumps are so big that inserting enough bass traps to cure the bumps sucked all the life out of the rest of the music (I tried two 4' tall x 4' diameter Tube Traps, their largest).  Bass traps can kill a patient while curing his symptoms.

My room has a 12 dB bump at 30 Hz (20 dB in the corner) & a similar bump at 80 Hz.  Because this technique provides such flat bass response in this room, I think of fullrange-only systems as inherently & anavoidably inferior (except for the rare room without bass modes).      

An amplified sub & w/ a parametric EQ like VMPS' will cure one bump/dip.  Corner-siting the sub provides the earlier mentioned SPL/distortion benefits, increases output (in my room equaling 50x the amp power), & eliminates the transient distortion produced when direct output is quickly followed by reflected wall output (as when fullrange speakers are sited out into the room).  The cosmetic benefit results from the ability to use smaller main speakers w/ minimal bass capabilities.      

Use of a good HT pre-pro or receiver has several benefits.  When used with good satellite speakers it allows stereo sources to be converted to Pro-Logic IIx with stereo rear surround channels, better on most CD's (especially live), than stereo playback.  (I was untill about a year ago a diehard two-channel-only fanatic.  I still audition the best two-channel & am rarely impressed.)  Active bass steering also allows the satellite speakers to be high-pass crossed about 1/2 octave above the highest bass mode.  This lowers distortion, increases output, minimizes amplifier power requirements & maximizes the effectiveness of the sub's parametric EQ by eliminating overlap.  If there is no high-pass XO (main speakers run fullrange) & the size of the bass mode exceeds the boost/cut of the sub's parametric EQ, the main speakers' bass cutoff should be higher in frequency than the room's mode.  Toward this goal the main speakers should be sited away from boundaries, side-mounted woofers should fire away from boundaries, speaker height can be increased, & ports/PR holes can be plugged.          

The active bass steering makes for two low-pass XO's in series on the sub.  When the HT pre-pro/receiver XO is set about 1/2-1 octave above the XO point in the sub amp, midrange output is minimized without increasing transient distortion.  

My corner-sited sub provides linear response & output magnitude is beyond the pain threshold without audible distortion.  Bass output is effectively limitless & without room overload.  20 dB of gain mean the sub amp's 2700WRMS is effectively multiplied about 50x for 135kWRMS.  That's some power.  Consistent with this gain is the -10 dB sub calibration within the pre-pro & the sub input gain set at 1/4 max rotation.  

The other benefits described above also acrue.  My pre-pro has variable sub distance & the sub amp has a continuously variable phase control.  If there's a better solution than this I'm ready to believe, just like the Ghostbusters.  FYI till I tried this medicine I was a full-range speaker only diehard, just like some of you are now.    

If there is a second bass problem area & it is a bump, some type of high-pass XO is required for the main speakers, such as an outboard XO or the active bass steering in a HT pre-pro/receiver.  Tune the low-pass sub crossover frequency below the bump.  Set the main speaker high-pass XO above the bump.  You just tuned out the bump.  Believe me, it works.  My 10-12 dB 80 Hz bump is dead gone after some tweaking.    

If there is a second bass problem area & it is a dip, the sub & main speakers must overlap in the range of the dip to minimize its effect.  The only way I know to do that is to drive the main speakers fullrange & use the main fullrange speaker outputs to drive the sub.  If the sub has no speaker level inputs, attenuators can be easily fabricated.  Set the sub XO frequency just at the upper range of the dip.  If a bass control is present, try turning it up.  I never tried this because I never had a dip to deal with, but I believe it will be at least moderately succesful or better.

For a dip in the second range, & if bass steering exists, & the sub & main speaker XO can be seperated (never seen): XO the main speakers at the lower range of the dip & XO the sub about 1/2 octave above the upper range of the dip.  

BTW, in the end I chose to use one 4' tall x 4' diameter Tube Trap, which helped produce the bass performance I'm now enjoying.

[ScottMayo]

In fact, my particular room's bass bumps are so big that inserting enough bass traps to cure the bumps sucked all the life out of the rest of the music (I tried two 4' tall x 4' diameter Tube Traps, their largest).  Bass traps can kill a patient while curing his symptoms.

Misapplied traps often do harm, yes. If a trap is is sucking the life out of a room, it's absorbing the wrong frequencies. One reason I'm a fan of homemade traps is that they are easy to adjust; if a bass trap is sucking up too much HF sound, it's easy to open it up and add paper or cardboard or vinyl sheeting as needed, to make it reflect the HF back out while still absorbing the bass.

A 4' diamater trap is quite large, for most rooms. The surface area is roughly equivalent to *6* standard flat traps; that's a fair amount of absorption. I'd be looking at other approaches - resonators come to mind - if I felt the need for that much absorption at narrow, specific frequencies. A trap can be too broadband.

There's definitely an art to it. I just came out of a movie theater, which followed all the rules - in order words they had some drapery up to control echo, and an acoustic ceiling, and all those chairs. I'm sure the room was billed as treated. The room's RT-60 was probably a reasonable value. The sound was terrible - harsh and uneven, with problems making out the dialogue at some points. And the sad thing is, it probably wouldn't take all that much to fix it.

[James Romeyn]

Can resonators correct narrow 12 dB bumps centered at 30 & 80 Hz?  How much is the approximate cost & dimensions?

[ScottMayo]

Can resonators correct narrow 12 dB bumps centered at 30 & 80 Hz?  How much is the approximate cost & dimensions?

Helmholz resonators are something you usually build yourself, to size. It's a wooden box with a port in it; people who build speaker enclosures will immediately recognise a ported enclosure. The usual trick is to make it slightly larger than you need, and pour sand into it to tune the center frequency, and then put fiberglass into it to widen the frequency band. Widening the frequency is important; a tightly made resonator is a very narrowband device. It eats the given frequencies; put the mouth at a modal point and the model point more or less dies. A room will generally want a few, generally in the corners.

If you can cut wood, cost is low. If you need a carpenter to build the box (for example, if you want it pretty), you pay finish carpenter rates. Boxes are easier than spheres (and are a little more broadband, in practice.)

The box doesn't have to be huge, even for a low frequency. A quickie calculator can be found at http://www.vk2zay.net/calculators/helmholtz.php and there are more involved calculators available.

Instead of wood you can experiment with large clay vases and urns, with sand and sawdust inside and a narrow mouth. This trick goes back to the Greeks; they used to embed vases and clay pots in their theater walls, mouth outward, half filled with ash. There are other ways to do it: I have a low table in my room with a 2' diameter sonotube for a base, which is more than it appears.

[James Romeyn]

Very helpful, thanks.

For rooms having only one or two bumps, it appears to by purely advantageous to use only a parametric eq & no mechanical solutions to eliminate the bump(s).  The inverted EQ of the bumps decreases subwoofer distortion & increases output capability, sometimes very dramatically.  A Helmholtz resonator will mechanically eliminate the bump, but offers no SPL/distortion advantage.  Plus resonators take up more space & must be integrated with the decor.  EQ is easier to hide.  EQ can also solve most dips.  Is there any mechanical solution for dips?  

Parametric eq seems in every way preferable, more capable, & more useful than mechancial solutions, but I want to learn more of opposing positions.

[warnerwh]

A Behringer DEQ 2496 will help with bass peaks and also help with other room issues and/or tastes.  For three hundred bucks including the ECM 8000 microphone I consider it the best tweak of the decade.

[ctviggen]

No amount of Parametric Eq can correct modal ringing (and this includes any type of digital correction).  This doesn't mean that Eq isn't beneficial, just that -- like everything else -- there are limits to what it can do.

[James Romeyn]

Modal ringing is?  Is there an internet audio dictionary?

[ScottMayo]

Very helpful, thanks.

For rooms having only one or two bumps, it appears to by purely advantageous to use only a parametric eq & no mechanical solutions to eliminate the bump(s).  The inverted EQ of the bumps decreases subwoofer distortion & increases output capability, sometimes very dramatically.  A Helmholtz resonator will mechanically eliminate the bump, but offers no SPL/distortion advantage.  Plus resonators take up more space & must be integrated with the decor.  EQ is easier to hide.  

EQ is easier and smaller, no question. And it can be cheaper. My only objection is that you're using electronics to fight the room, and while that works, it only works at one listener position. If you're a single listener with a favorite chair, EQ can do what you need. If you don't move much.

But if you want the room in general to behave well, it's not good enough. And EQ can't do what's needed to solve problems like overall room ring time (RT60). If it tries, it will make very big changes in the output, leading to even more sharply localized effects. The bigger the room, the messier this can get. You end up in a 24x31' room of which about 2'x2' is usable.  

I use no EQ. I consider it from time to time, but ultra-flat FR isn't the top of my list; imaging and clarity are. I don't disrespect EQ - I just don't think it's any sort of cure-all, just as room treatment isn't a cure-all. I just think fixing a room - while undeniably more work - is the place to start, and EQ is more of a place to end.

[warnerwh]

In my LEDE room with bass traps I think that having a digital equalizer helps quite alot.  More than I could have guessed. No an equalizer won't fix everything but neither will room treatments.  That's why I use both and think both are necessary if at all possible.

If I remember correctly Scott you had Rives help in doing your room. I'd very much like to see room measurements.  In my room which is not very reflective at all with room treatment I"m still getting plus or minus 10db in a few spots.