Testing speakers in room

Hi Newbee, nice post. It would do well to know what is happening between 20hz and 40hz as you only have one measurement (32hz) within this octave. As well as between all of the other measurements since 60hz to 80hz is a 20hz span, a lot can be happening there as well.

I also suggest getting rid of the old skool pencil and paper and using the free computer program Room EQ Wizard at the Home Theate Shack. Besides a much more accurate picture of your freq response in room it will also show modal ringing in the waterfall plots along with RT60 times etc..

Bob

"What is good enough".....

For me, +/- 3db is good enuf, but I have mine down to +/-2db except for a room dimensionally induced dip of 4/5db at 45hz (depending on room temp I think) which shows up in tests at 40/50hz levels, and this is referenced to flat FR at 200 and 1000hz.

Now for you, a couple of comments.....

Re test disc's. The test disc's are putting out 1/3 octave tones, the related frequencies, by number are not linear. For example, starting at 32db one octave higher is 64db, the next octave higher is 128db, the next octave is 256db, it just keeps on doubling, so by the time you get to 10K to 20K your deviding up 10K Hz difference into 1/3d octaves. The numbers make it sound big, but its not.

Rives is right about dips being caused by cross overs at or near the cross over points. They are benign, usually, because they are neither too deep or too wide to be exceptionally noticible. And just cause the speaker's cross over point is, say 200 hz doesn't mean its flat (or not) there or nearby.

Re high frequency roll off - this could be a result of test equipment as well as the distance from the speakers when the tests (yours and the manufacturers) were made. Usually we sit a lot further from the speakers than the manufacturer when the testing occurs and the high frequency roll off is going to be more prominent. That all of the instruments you mention sound fine is because all of their primary, and most of the overtones, are well below 10K. (O/T a great 'tone contol' is one that rolls the upper mid range (1500 to 3000Hz) and leaves the highs 'flat'.) What you might miss from the rolled highs is that, with a well set up system and speakers with good resolution, is detail in the recording of room ambience caused by the upper frequencies (overtones) emitted by the instruments.

FWIW, assessing the impact of irregular FR - One db differences are barely, if audible to most anyone except when you are listening very critically. 2db is barely audible under normal listening conditions. 3bd will make a very noticible difference. 6db can make it or break it. But, how the differences can change is even a 12db difference can make little, or no difference, IF it is very narrow and does not appear in a critical location of the FR spectrum. You might not really notice such a peak in the upper bass, lower mids where it would add a tad of warmth but not be clearly distinguishible, but at say at 2500 to 3000 hz, with a trumpet playing a solo it could put an edge on the sound that would take your ear off.

That was all just a stream of consciousness, so to speak, as a preliminary to this.......If you want some specific advise you might be well served by telling folks very specifically what your actual frequency spectrum is. When you talk about "75 and 85bd but with peak at 93db" at 184 hz what are you referencing the peak of 93db to? 80db at 1000hz, 200hz? What exactly?

For example, and just dealing with the bass, what I would say if I owned the questiojn, is that my room is 13x19x9, my speakers are 66 inches from the wall behind them, 9 ft apart, toed in until the axis crosses in front of my listening position 10 ft back. Referenced to 80db at 1000 and 200 hz, which are flat or measure:

32db +3db
40db -2db
50db -4db
60db +1db
80db 0db (flat)
100db +1db
125db -1db
160hz -2db
200hz 0db (flat)

Seeng this, especially in graph form, helps to understand how big and where the deviations from flat may occur, and help determine whay they occur, and what you can do to fix them. Some times as simple as moving a chair or your speakers, or both in combination, less than a foot.

I hope that helps you a little bit. Something to think about anyway. Oh BTW, there are no quick and easy fixes, but by doing a lot of experimenting first with things as simeple as moving stuff about you can save a lot of money trying to find quick and easy 'fixes'. You just need some graph paper (a lot perhaps) and even more patience. :-)

Don't forget, you are really measuring room response to your speakers. The published specs for speakers are done under anechoic conditions. I'll second Acousta6's recommendation for RoomEQ Wizard. It takes a little while to figure out how to use it, but nothing really that complicated. And, best of all, it works and is very helpful with tuning the room.

Hello,I wrote, "4) The difference between 75 and 80 db is twice as loud!"

Actually it is the difference from 75db to 85db.

Bob

Thanks, guys. I will check out the REW program and persevere in my efforts to improve the sound!

Hi Magister, The way you are measuring is not a high enough resolution and it is only part of the story. You also need to see waterfall plots and RT60 times.

The best way to do this is with the FREE program REW (Room EQ Wizard) available for FREE at the Home Theater Shack. ITS FREE!!!!!

1) plus or minus 5db is good, plus or minus 3bd is exceptional, You can always plan on a few large peaks/nulls that are part of your house sound (along with the sound of your equipment)

2) you "can't" do anything about the sound of your equipment, so buy quality. You did:). Your ears do have the ability to compensate depending on the Q and levels of the peaks and nulls. But dont expect them to compensate for a 10db peak/null.

3) Radio Shack meter is not accurate at these frequencies.

4) The difference between 75 and 80 db is twice as loud! 93db is definitely giving you bass boom.

5) It's all frequency-related. Base peaks limit the volume you can listen at. They also affect the sound of recordings where some may appear skewed.

The answer to your question is bass traps and broadband absorbtion of enough size and quantity to effect a change in room.
Bob

Most of your issues could be fixed using an equalizer, give that a try. And 10db is a big peak (or trough). You'd probably like the system's sound better if you could get those leveled out to no more than 4-6db.

Merry Christmas!

-RW-