Bass and room modes test with music CD

If you are frustrated by playing with a Rat Shack meter and test tones (frequency tones, warbles, pink noise, 1/3 octaves etc.) and never quite sure what you should "fix" or what you should just live with (no room is ever perfect)....then this may be the CD for you.

Rebecca Pidgeon, The Raven, Chesky CD.

What follows is taken from Bob Katz excellent book on Audio Mastering. The track "Spanish Harlem" on this CD, in the key of G, uses the classic 1, 4, 5 progression. Here are the frequencies of the fundamental notes of the bass.


Check it out.

In the absence of a test CD with real music I spent hours playing with test tones/Rat Shack meter/PEQ... and initially I went overboard with a PEQ trying to fix everytyhing as near flat as I could in the LF. In the end, I did not like the sound when it was equalized flat and went back to a minimal PEQ approach with a few minor adjustments on the worst offending peaks but never crushing the sound into conformance. (trial and error process playing many CD's)

Yesterday I received the above CD and played Spanish Harlem track. WOW - it works. You can easily HEAR immediately how balanced it is. (Real notes on a real instrument seem far easier to balance in your head than test tones...I can't explain why but that was my experience...perhaps it's the harmonics)

I realized that this CD could have saved me an enormous amount of lets you judge how the room modal bumps, incorrect sub settings and/or placements are actually affecting a real instrument.

Unlike the Rat Shack meter this allows you to gauge the amount of tweaking necessary. For me, a 3 db bump over a 6 Hz interval is much better simply left alone rather than mercilessly PEQ for flat reponse; but a 10 db bump is an audible intrusive problem clearly affecting the balance. In any case, the CD lets one precisely judge the relative effects on music.)

IMHO, PEQ adjustment to get a flat response, whilst easy to do, is far from ideal because it adjusts the primary signal in order to get the combined primary and room modal signal down (the room modal response is the real culprit and, although not always practical, room treatment/design is by far the ideal solution)

...just thought I would share this. Any comments from anyone who faced this issue or perhaps has found another solution or another good test with music CD?
Like you I found the RS meter game to be a lot of frustrating work, and never really effective. My solution is a Behringer DEQ2496 automatic equalizer with spectrum display. (Three of them actually, to take care of five channels). I equalize for the total sound at the middle of my room, but if you wanted to do just the primary signal you could put the mic up close to the speaker. However, if your speakers are any good this would result in very little equalization. Room effects are really what it's all about.
I agree with Eldartford as I also love my Behringer unit. I have found that fine tuning by ear a necessity however.

You say you equalized for a flat response. I hope you didn't try to equalize the bass region flat with the midrange and treble. The reason for this is because it will not sound natural. The bass region must have a slight boost and the treble above 2khz needs to be tapered downward to sound like a live event.

Ethan Winer's site,, has bass frequencies you can download in I think 1hz increments. This way you can get a much better idea of what is going on. He also has a program called "modecalc" for Windows that will calculate your room modes depending on the dimensions. All you have to do is enter the dimensions to the nearest inch and hit enter.

If you're not using Rives cd that is corrected for the Radio Shack SPL meter then you're in error on your readings. This cd will get you much closer to being accurate.

With the Behringer I've been able to tweak my room into a major improvement. My room is LEDE with four large bass traps so is fully treated too. The Behringer properly used can make alot of improvement. For 300 bucks I consider it a steal. If mine ever breaks I'll go straight to a pro audio shop and buy another.

Every room with walls has modes which I can tell you know. There's more than just the bass to worry about. Once you spend some time learning how to get the sound adjusted properly with digital equalization you'll never go back. I'm sure that's why the TACT users so vehemently praise their gear. I would buy a Tact if I could afford one. Prices of the 2.2 are down to 2k these days so I'm looking hard at them.

If you try the Behringer realize you can use it strictly in the digital domain. I output mine to a Bel Canto dac. There's no degradation anywhere and the improvments for the money is amazing. I've discussed other subjects with two audio engineers. In both conversations the Behringer DEQ 2496 came up. Both guys told me how impressed they were with what you get and wished they could offer so much for the money. They both happened to have one in their systems also. One is a digital amplifer, preamp and dac designer. The other a recently retired power amplifer designer.

I know that was long but I don't want to leave much uncovered. The room is too important. Way to many people change gear when the problem is their rooms. Huge differences can be made with room treatments and a digital equalizer. For the money they are cheap.
Warnerwh...You forgot to mention how easy it is to get a non-flat response with the DEQ2496 if that's you want. You simply adjust the "target" curve (what the auto eq aims for) until it looks like what you want. Then do auto eq.

I'm curious about using bass equalization devises and how it can be used without creating issues. For the sake of discussion assume you have 86db speakers and a 100wt tube amp with an output impedence which rises to 3.5 ohms at 60 hz and a room with a 12db dip at 60 hz and you use an equalizer to produce a flat response in the bass. Assume also that your average SPL at the listening chair was about 85db. Would using the equalizer to raise the 60hz dip to flat compromise your amps performance?
Newbee...Frankly, I think that a 100 watt amp with 86dB speakers pumping out a SPL of 85 dB is pushing limits even without any eq boost. However, room eq, insofar as you keep the SPL within the capability of your speakers and power amp, will definitely make an amazing improvement to any ststem.

The spectrum analysis display might help you to minimize that dip in your system's response by different speaker placement, room treatment, etc. Also, if the dip is 12 dB, a lesser boost, like 6 dB will help a lot.

The key feature of the Behringer DEQ2496 is that it is so darned inexpensive ($300 and change including mic and mic cable) that most audiophiles can afford to try it. And try it you must. Don't listen to speculation about how it sounds based only on its price or its digital implementation. Your ears will convince you.

Thanks for your response. I'm not surprised that you would say the 100 wts wasn't enuf - I didn't construct that set of numbers accidentially. But, I also think it is not an unusual situation especially for users of tube amps.

I would agree that having the benefit of any devise for analization of frequency response so that you can quickly find good starting locations for speakers and listening positions, as well as identifing room nodes and nulls is a great benefit - certainly beats a SPL meter and a test disc, much easier, more graphic, less note keeping, etc.

I also agree that the best way to change FR response is thru passive methods such as room treatments and careful placements.

Like the original poster however I've never had success using any type of an equalizer to correct for broadband room problems, unless it was for just a bit of judicious lopping off the tops of narrow bandwidth nodes, which doesn't create a potention for interference with amp performance. Conversely I've always thought a equalizer used in a tape loop for tone control applied to sources (software) was an excellent idea.

Now for someone less anal about resolution it probably isn't as big a deal. :-)
Thanks for all the feedback.

I indeed tend to run LF slightly heavier than flat and roll off the highs as Warren suggests.

I indeed only reduce bumps and do not believe in boosting nulls with a PEQ (or at least any boost must be extremely modest)

I currently use the Behringer feedback destroyer pro....just for the sub as I am ever nervous about applying EQ to the main speakers (worries over creating phase issues, besides I don't believe in an EQ's ability to fix room modes much above 100 HZ anyway, as that is what room treatments are for, although I agree an EQ can nicely shape the overall sound if you need that...shelving rather than filtering...and I have tone controls also for that).

I could not find much info about the DEQ2496 on line.....does it analyze in 1/6 octave increments or only 1/3 octave bands? (I might be tempted to upgrade as you say it costs very little)

Most of my (very modest/minor) adjustments are in the extreme LF and are around 1/6 of an octave in width (Q). Apart from a 40 Hz broad bump, 1/3 octave seems too broad for my needs....any further comments on DEQ2496 automatic analysis ability in narrow bands?
Shadorne,,,The DEQ2496 includes a "cut only" function, "Feedback Destroyer" (ten filters) has a bandwidth range of 1/10 to 1/60 octave. The Parametric Equalizer function (ten filters) has filter bandwidth range of 1/10 to 10 octaves. The graphic equalizer function is 1/3 octave...31 bands. The spectrum analyser display is 1/6 octave...61 bands.
The spectrum analyser display is 1/6 octave...61 bands.

Excellent - that is the kind of resolution that I believe I need. Does it come with a microphone - do you have any recommendations on set up and mike? I am definitely interested.

In my case I would probably want it to "cut only" from 20 to 95Hz in order to smooth the reponse mildy....does it do this credibly and automatically. I would not want it to cut more than 6 db in any 1/6 octave band. And never more 9 db in 1/3 or broader octave band. Does it just run automatically? Or do you still need to fiddle a lot to get what you desire.

Thanks for your feedback/help.
Shadorne...It does not include the mic, because professional users may already have a mic, and may also use several DEQ2496, and they don't all need their own mic. Buy the Behringer mic, and don't forget you will need a balanced line mic cable.

If you want more info you can download the complete owner's manual from the website. It looks complicated, but with a little hands-on experience it ain't that bad.

You seem to have a lot of preconceived ideas about limiting the use of the unit. I bet that once you get one to play around with these ideas will change!

FWIW, I bought mine at

Have fun.
You seem to have a lot of preconceived ideas about limiting the use of the unit. I bet that once you get one to play around with these ideas will change!

Yeah - if I had my way I would use no EQ at all...LOL....but that ain't practical as tons of acoustic panels are not an option due to WAF factor...

Eldartford...thanks for your advice....I will plan on picking up the next DEQ2496 I to the pro music shop this weekend to see if they have one ;-)
Something you may want to try, especially with an EQ in your system, is a free program called RoomEQ Wizard (Google it.) As soon as I get my new (ugh - Vista pre-installed) HP laptop "downgraded" to XP Pro, I'm going to run it to adjust speaker placement. There is some discussion about it on AVS Forum. Good luck tweaking!