For someone trying to get a handle on the whats and whys on their rooms bass response I think they are invaluable. Especially so when initially setting up speakers. FWIW, I suspect very few who are really serious about set up are without one.
What surprised me most when I first starting using one was the extent of bass abnormalities that could be cured by simply moving the speakers or listening chair a little bit. I had heard folks talk about small movments making big differences but I thought they were FOS.
Huge changes in bass response depending on small changes in seating position. Less than 12" forward or back affected bass by as much 10db.
Everyone should try it if possible. Cheers,
I tested my system and room from 10-300hz by 1hz increments from my listening position and was startled by the results.
Response varied by 15-20db in very narrow ranges (+-10HZ). Just by moving my head 1-2 feet there were huge differences. Nulls all over the place.
I am not sure how to interpret the results, because they varied from place to place.
It also takes a while. 290 readings at 10sec each takes an hour. Moving speakers by trial and error then remeasuring could take some time.
I am told that to do it right you should use 1/3 octave pink noise and a spectrum analyzer.
Yes, some measurement of frequency response is valuable, but, there is simply no comparison between using a SPL meter with a test disc vs using a spectrum analyser (like a Behringer DEQ2496). The spectrum analyser gives you an immediate indication of any changes (like speaker or listener position). It gives you a much clearer idea of the whole spectrum.
Ditto to Newbee & Sbank's responses. The small differences in listening position will be particularly true in small to mid sized rooms, especially ones where the dimensions reinforce the same frequencies (a cube is the extreme example where the opposing surfaces are equally spaced). The meter was also instructive to me since, for example, my initial views of a flat bass response were really not correct.
I totally agree with everyone's sentiments. I use Room EQ Wizard to generate my test tones and graph the response from my Rat Shack analog spl. I guess if I was really serious I would get a better spl.
I own two Hsu Research TN1220 HO subwoofers with their Model 500A amp with 24db per octave high and low pass x-overs at 51hz. I sit midway, [in the center of my listening room], between the subs, in which one is near the middle of my front wall between my speakers and the other is in the rear of my room near the middle of the rear wall.
My listening room, including the dining room and kitchen due to large open spaces is roughly 23 x 23 x 8.
Using a Rat Shack digital sound level meter, with corrections, and the Hsu Research CD-R with 1/3 octave warble tones and a 100 hz reference:
I have a broad peak of about + 7 db at 16hz! and 20hz,
a -4db dip at 25hz, a -3db dip at 31.5hz, same as the 100hz level at 40hz and 63hz, a -2 db dip at 80hz, and a big + 8 db peak at 50hz.
With both subs along the rear wall I have a broad +7 to +9 db peak at 16 to 25hz, a -3db dip at 31.5hz, same as 100hz at 40hz, a -2db dip at 63hz, a -4 db dip at 80 hz, and still have the +8db peak at 50 hz.
The 50 hz peak surprised me because running the speakers full range without the subs or high pass filter resulted in the same +8 db peak as when using the subs, mains, low pass, and high pass filters all together!
I expected the 50 hz peak to be reduced in level by about 6db by using the latter due to the natural -6db dip at the x-over point using 24 db per octave filters, but it was not reduced at all!
Very strange indeed.
I use a Radio shack analog spl meter with the Rives test response disc. The good thing about that disc is that there are a set of tracks that compensate for any false readings that the Radio shack device may give.
Kenyonbm...Your results are not unusual. And what a lot of work!!! (Get yourself a Behringer DEQ2496). By the way, did you try repeating the meter measurement several times at the same spot? I bet that some of the veriation is simply the measurement. Low frequency should not vary much over a short distance. High frequency will vary.
Would you please tell us some more about using the spectrum analyser? What other equipment is required, microphones, sources etc.
Any suggested reading?
Nice to read everyone's responses so far.
Tbooe, the Rat Shack meter, IMO, is fine for this task. I have an analog one, as well as a calibrated digital unit from Monarch Instruments (Model 321 @ $259). Both read quite similarly head to head.
Obviously, I'm a proponent of this sort of objective assessment of one's system. Loudspeaker/listener position changes to mitigate room modes on the bass end, as well as effects of room treatments and subwoofer integration all benefit, in my experience. It is revelatory simply to measure, albeit somewhat imprecisely, the in-room performance of one's painstakingly-assembled components. My, what our ears/brains must accept simply in the frequncy domain as "faithful" reproduction!
Panacea - hell no, but anyone integrating a subwoofer/pair will likely be very surprised at the imprecision of plate amp crossover/phase/parametric EQ adjustments, for one. I recently spent a number of hours dialing in stereo "sub"woofers (10 inch Focal woofers with Adire ADA300 Class D plate amps - DIY))to even out terribly uneven 30-160 Hz in-room response with fairly inflexible loudspeaker/listener positioning constraints. The Adire plate amps are among the elite of their ilk, with dual crossovers, continuous phase adjust and 2 band parametric EQs (16-80Hz freq range and continuous Q adjust). Nonetheless, the physics of my listening room proved more complex and unforgiving even for this array of "tools". I did achieve +/- 6.5 Hz from 30-12,000Hz compared with +/- 12Hz before adding/dialing in the powered woofers. Subjectively, vastly more enjoyable.
Kenyonbm...There have been many (too many?) postings about the Behringer DEQ2496. You can also download the complete users manual from the Behringer website, as well as the sales brochure.
i tried a spectral analyzer, but the quality iwas not sufficient for the task. i believe the use of a well designed spectral analyzer at the listening position, using white noise can give a clue as to stereo system frequency response imbalances. then one has to figure out if the room is responsible and or the components.
I have a Behringer, and ran the auto eq and was done. How do i use it as a spectrum analyzer? Do i just play a test cd and watch the values? Then move things around to get things closer to flat? Thanks.
Okay, I am going to out myself a little bit. I own a company which rents and sells SLMs, FFTs, RTAs, various spectrum analyzers,etc. As far as the perfect measurement and alignment goes, you would use a sound source like a Bruel and Kjaer 4204 or 4205, measured by a Real Time Analyzer with at the very least 1/3rd octave analyzer and preferably a 1/32nd with a calibrated preamp and microphone. The sound source has known values in an anechoic chamber and the frequencies it puts out are compared via the RTA to the ones measured in the free field. I cannot count the number of times I have seen "acoustics experts" not even make corrections for the pressure response curve of a measuring microphone above it's actuator drop-off value(the difference between using an electrostatic actuator directly on the diaphram and the actual response of the microphone in air) which is over 10dB oftentimes at 20kHz. Once the room is defined, then one would do whatever you could to equalize the room nodes, before even starting with the speakers. Ideally one would feed two channels of 1/4" microphones into a test torso at the listening position. Once the room was treated appropriately, one would use full spectrum pink noise or even better, a continuous swept sine wave with relatively high harmonic content, averaged, on auto-continuous, and watch the display as one moves the speakers, chair,etc for a better reading.
However, it is well known that most people do not pschycoachoustically "like" a flat response. (read Gundy curve) When one has a rectangular room, any number of simple programs will project the room nodes with great accuracy, and it is well known that the first reflection of the tweeter is very important to ameliorate. I have found that when I have measured friend's room, if the bass nodes are taken care of, reflective surfaces are minimized, and the first reflection of the tweeter is absorbed, the rest is generally up to user tastes. The biggest problem my staff sees when we help friends, is that generaly the speakers are just waaay too close to the rear walls. The confusion in sound propagation caused by that, or by setting the speakers in a null spot, are terrible.
I see Bruel and Kjaer 2032s, 2033s,2133 and 2144s on ebay for under a grand, preamps and microphones for less than a few hundred, if you really really want to maximize your room/speaker interface, seems like a cheap price to pay relative to most people's systems.
It seems to me like people who want you to spend 50 grand (dealers and manufactureres) on a pair of amps would spend a few thousand to help ALL of their customers maximize their listening experiences. In my opinion, considering they might have to buy one unit, it would be a small, teeny tiny little cost. On the other hand, the experienced guys dial in speakers pretty well without the measuring devices, but dang, if they are gonna make a big deal about 1db difference in an amp response, and there are room nodes of 15dB, it sure wouldn't hurt them to have this stuff.
I do high end audio
for fun and a hobby, which is why I have been loathe to comment on these types of forums. This is my getaway from work, I will be more than glad to help my fellow audiophiles where I may, which is a joy to me. I want to stress though, that if you are in my area, I'll bring some audio measuring toys over for fun to help, but I have no desire to take a dime from anybody in this hobby. (unless, of course, I am selling my used audio components) :):)
Streetdaddy...With the white noise signal playing,just look at the RTA display before you do any equalization. If you have a test disc you could play that instead of the built-in noise signal. You can watch the response gradually become flatter as the equalization process is performed. As Chrisla notes you may prefer a response that is shaped (not flat) in some way, and that is easy to achieve by setting up the target curve before you do the auto eq.
No doubt the professional room tuning equipment and procedures the Chrisla describes are more accurate than the simple 1/3 octave corrections done automatically by the Behringer (unless you take the trouble to use the "feedback destroyer" function which is as sharp as 1/60 octave). But in practical terms the Behringer, properly used, comes so close to optimum results that I don't think the ear could tell the difference. Certainly the variation depending on listener position will be greater than the difference between professional room tuning and the Behringer result.
I will be more than glad to help my fellow audiophiles where I may
Now, THAT is a princely offer...
B&K's, calibrated mics + pres... wow! This is serious stuff...