Room Equalization (1 Viewer)

[Kirk Mango]

I have posted questions regarding my room equalization in the past, however, I have something else I would like to ask regarding the numbers I have. First let me give some background again. I have a B&K Ref 30 and am using the -42dB test tone generator to test my room nodes and bass response (reference is 0 on this unit). This test tone is the lowest one available. Their are two other louder tones but for comforts sake I choose the lowest one. My mains are set to large (Mirage OM5's, rated down to 22hz +/-3dB) because I am using both the high and line level connections to my Rel Storm subwoofer. All speakers are powered with B&K 200 watt per Channel amps with the mains having a sepperate 220 watts per Channel B&K amp (the OM5's also have their own built in 250 watt amp per speaker). All other speakers are set to small with the crossover on the Rer 30 set to 80hz. Sub is corner loaded and behind a 60" RPTV. I should also point out that I have a filter set, on my Ref 30, from 40hz-50hz because of a room boost at this level. This boost had the original readings at this hz level at/above 80hz. The first number is the Hz, the second number is my original reading with only the filter applied, and the third number is after adding in the RS meter correction factor. My readings with the test tone are as follows:

Hz, Orig/dB, After RS/meter Correction
2064 72
2266 73
2472 77
2671 76
2872 76
3071 75
3270 73
3470 72
3670 72
3871 73
4073 75
4274 76
4474 76
4674 76
4875 77
5074 76
5271 73
5472 73
5673 75
5874 75
6076 78
6276 77
6476 78
6677 78
6876 78
7076 77
7276 78
7476 78
7676 78
7875 77
8074 76
8272 74
8471 73
8669 71
8868 70
9067 69
9266 67
9463 65
9659 61
9856 58
10058 60


My Question is why is there such a big Drop in dB after 80hz. Is it because the sub is not picking up any bass from my center and 4 surrounds after 80 hz and these speakers are now expected to play this tone. If this is true then why as I get beyond 100 hz do I notice that the dB readings start to rise until they are in the middle to upper 70's again. What do you think? Also, how close to flat is my response considered. I am under the impression that if you can keep all dB readings within a 10 dB span you are doing very very good. Is this true? Below 80hz, using the correction factors, I am easily within this range. In fact I am within 6dB from 80 hz down.

KM

 

[Kirk Mango]

Anybody??????

KM

 

[Wayne A. Pflughaupt]

Kirk,

First we should clear up a misconception - your questions have to do with response, not equalization. Equalization is electronically modifying response.

I am under the impression that if you can keep all dB readings within a 10 dB span you are doing very very good. Is this true?

Not necessarily. A 10dB deviation within the space of an octave or less would not be good at all – especially if there is more than one of them. What’s desirable is smooth response from octave to octave without a lot of up-and-down deviations.

However, in most home theaters it would not be unusual to see an overall 10dB spread between the extreme highs and extreme lows that would sound just fine, as long as the “line” in between was fairly smooth (that house curve thing again).

As they say, a picture is worth a thousand words, so here are a couple of charts:






As you can see with the curve above, there is a 10dB deviation occurring in the relatively small 1/2-octave space between 31 and 45Hz. Spread over another 1/2-octave space, between 71 and 100Hz, there is an even worse deviation of 15dB, even if you ignore the sharp null at about 87Hz. The readings between 100Hz and 25Hz (including the null) show a response deviation of over 35dB.





With this chart you can see a 15dB deviation between 20Hz and 100Hz, but notice how smooth the response is between those two points. It should be easy to see that the first curve will sound much worse than the second.

Now, the house curve thing. It’s generally accepted that depending on the size of the room you’re in, ruler-flat response does not sound good to the human ear. In the smallish-home theater environment, measured response will show an upward tilt of the low frequencies in order for sound to be perceived as flat and balanced – i.e., where the low notes sound to be at the same volume as the high notes. The amount of tilt needed for this perceived balance is greater with smaller rooms than with larger rooms. Thus, it will not be uncommon for say, a 1000 cubic ft. room to show a measured deviation of more than a 15dB between 30Hz and 10kHz, while a 7000 cubic ft. room might show half that much. As noted in the opening paragraphs, much of this tilt will be accomplished with the volume of the sub in relation to the mains.

Regards,
Wayne A. Pflughaupt

 

[DavidLW]

You do not mention whether you have your Mirage OM5 crossed over or playing full range. So I assume you have them crossed over since you don't have a big increase in bass below 80hz. Something that should happen if both your sub and main were producing sound in this range. And yes, if you have your sub crossed over at 80, it will not put out much above that point (depending on the slope).

It looks like you have what's a "hole" in the 80 to 100hz range because your main is crossed over at around 100hz while your sub is crossed over at 80hz. Some people choose different cross over points to avoid the "hump" (a spike in frequency when both speakers are producing the same frequency at the overlap). The "hole" may be cause by having different crossover slopes( one of the slope is too steep). Therefore you don't get enough overlap of the two speakers and a smoothening of the frequencies between 80 and 100hz. It may be cause by the two slopes being too steep for the range between crossover points. Check your crossover points and slopes. Narrow the range of the cross over points (increase the sub or decrease the main) or decrease the slope (from 12db to 6db if possible)to help fill in the hole.

If on the other hand you are playing the main full range, I would be more worry about why you don't have a big boost in bass below 80hz. Your main looks like it will perform pretty well to below 30hz (specially hooked up to a B&K 200w amp). And with your sub kicked in your should see a big increase of bass below 80hz.

This is just from looking at the chart and info given. Obviously there's alot more factors involve. And the solutions offered may not be possible with your equipment.

 

[Kirk Mango]

Wayne,

I do not understand what you mean by 20 readings between 20-40 hz and 40 readings between 40-60hz. I count only 11 for both. Does this have something to do with the way octaves are measured. Please explain, my knowledge bass here is null.

Second, can you show some type of a graph for the numbers I have presented like you did for the SVS subs. I understand the smoothness and the bass response needing to be stronger on the low end to give the perceived balanced or flat response but wonder how my numbers might look if graphed.


Third, how would I be able to get the same kind of house curve that you are showing in the second graph. Is this even possible for me? Should I use the second level test tone, which is stronger, to boost my numbers amd retale measurements just to see if there is a difference because the tone I am using is so low (-42dB? Would this just equally boost all the numbers up the scale?

The B&K Ref 30 only gives on filter which I am already using to nock done a room node between 40-50hz. Any other info would be helpful.

David,

Mains are set to large, full range. They sub connect both with LFE and a high level connection to the mains. The sub will play the full LFE channel and pick up what the mains cannot play below 25hz on the high level. That is where the high level is crossed over on the sub. The Rel offers the ability to support the main, while simultaneously playing all bass below 80hz from the surrounds and the center as well as all the info on the LFE channel. Remember, I am using the lowest level test tone generator on my B&K preamp. Any other info would be helpful.

Kirk

 

[Bill Polley]

Kirk, Wayne is correct about the resolution. An octave is a measurement of frequency. The frequency scale is not linear, it is logarithmic. Human hearing, although it is different for all people (some can hear well above 20khz, while others have a tough time with 10khz, and the same for low frequencies) is considered to be from 20hz to 20khz. This frequency range includes 10 octaves. Each octave doubles in frequency. So the lowest octave of bass that people generally hear (and I know that some people, as myself, have systems that approach 15hz) is considered to be 20hz to 40hz. The next octave is 40hz to 80hz. Then 80hz to 160hz. Then 160hz to 320hz. 320-640, 640-1,280, 1,280 to 2,560, 2,560-5,120, 5,120-10,240, and 10,240 to 20,480. When you look at these numbers, it appears that each octave gets bigger in size. The fact is that each octave takes is the same size on a logarithmic scale. Therefore, the 20 hz range in the first octave is actually the same as the 10,000+ range in the highest octave. When you measure a 1hz difference at 20khz, it would be the same as measuring differences of 1/2000hz at 20hz!

If you look at Wayne's graphs, you see that the distance on the bottom scale is the same from 20-40 as it is from 40-80 and from 80-160. This shows that the difference of a 1db change in frequency is greater at lower octaves than it is at higher octaves.

 

[DavidLW]

You did not mention what kind of center and surround speakers you're driving. After digesting the way you sub is suppose to work, it looks like maybe the center and surround speakers are beginning to taper off at the 100hz range. Your main is doing most of the work between 100 to 80hz. At 80hz your sub kicks in for support.

 

[Kirk Mango]

Bill,

I am running Mirage all the way around. 4 Surrounds are OMR2's my Center is the Mirage OMC2.

Dave,

How then should I be taking my measurement so as to best understand my bass response below 100hz? I want to determine whether I am getting the most out of my equipment in my room.

KM

 

[Bill Polley]

I EQ my sub with the speakers off so as to just be hearing the effects of the sub. Then I turn off the sub and EQ each speaker by itself.

 

[Kirk Mango]

Bill,

Isn't their the risk of cancellation problems from the mains or any other speaker playing any frequency within the subs range if you don't have all speakers active when EQing. I know if I EQ in stereo mode, only mains and sub, then my readings are quite different then when in surround 7.

KM

 

[Bill Polley]

I don't know. I EQ each individually. I set each channel as flat as I can, then I turn them all back on and set the levels. I would think you could only have cancellation if the source is in mono. If the recording is made in stereo or in a multi-channel format, then whatever they record should play correctly through my speakers. I would like to think that if I have a cancellation problem, then they must have heard (not heard???) the same cancellation as they were mixing the recording.

 

[Wayne A. Pflughaupt]

Kirk,

Sorry to leave you hanging – lots going on this weekend with the holiday and all.

Isn't their the risk of cancellation problems from the mains or any other speaker playing any frequency within the subs range if you don't have all speakers active when EQing. I know if I EQ in stereo mode, only mains and sub, then my readings are quite different then when in surround 7.

This is correct – if you EQ the sub separately, then add the mains you will find that (due to phase issues) your measurements are often affected for at least an octave above and below the crossover frequency. So what I do is EQ the sub first, then add the front L/R speakers, then tweak the EQ settings. Usually the phase-induced changes can be equalized away. I only worry about doing this with the front speakers because I’m most concerned with accuracy with music.

Regards,
Wayne A. Pflughaupt

 

[Steven_I Martin]

Kirk, I'm sorry for the delay in my reply, but I had to first go through the registration process. I'm most interested in your setup because I also have the OM5's and OMC2 Center. My surrounds are from the Mirage Omnisat series. I have a Servo-15 Subwoofer and a Yamaha RX-V3300 receiver.

In terms of your setup, I have a few questions and observations. While I'm not familiar with Ref 30 preamp/tuner, I was able to go through a copy of the owner's manual for the Ref 50. I'm hoping this will give me a reference point in terms of terminology and available options in your setup.

First let me give you some observations regarding the OM5's in my 13' by 18' by 9' home theater. I found them to be over powering with a significant peak in the 36hz to 45hz range. I found it next to impossible to integrate the low end with my subwoofer and have since turned the level all the way down and set them to small. Even with all this, my peak between 40 and 45 hz reaches above my reference of 70db.

I currently am using my subwoofer to handle all frequencies below 90hz, using a house curve that rises about 13db from 100hz to 20hz. I'm using a Behringer BFD parametric equalizer on my sub in order to create this house curve. My future plan is to purchase a Berhinger DEQ2496 in attempt to tame the low end on my OM5's and integrate them with my subwoofer.

This brings me to my first question for you. In reading the REF 50 manual, I noted that the test tone only goes to 300Hz. Is this the only source you used to measure the response of your speakers? It is unclear from your numbers as to what your reference point is. Without a reference point it is unclear as to whether your 72db - 76db readings represent a peak, a null or rather they are flat.

In order to accurately measure your system, you will want to establish a reference level using 1Khz. Typically, you would set your SPL meter to read 70db or 80db at 1Khz and use this as a reference against which your other measurements are taken.

In order to better assess your situation, it would also be valuable to get seperate readings for your OM'5s and subwoofer, both without your notch filter. Don't forget to take these readings using a 1KHz reference point. As was pointed out earlier, you can reduce the number of readings. Suggested reading points would be 20hz, 22hz, 25hz, 28hz, 32hz, 36hz, 40hz, 45hz, 50hz, 56hz, 63hz, 71hz 80hz, 89hz, 100hz, 112hz, 126hz, 142hz, 160hz, 201hz, 254hz, 320hz, 403hz, 507hz, 640hz, 806hz and 1khz.

Finally, I thought it was curious that you are using both your high level and line level sub inputs. According to the Rel 50 users manual, you should be able to send the main and LFE information to your sub by using only the line level LFE output and the ULTRA Sub setting.

I look forward to hearing from you.

Steve Martin