Dual DTS-10's and dual CS 18.2's - Page 24

If you want to see how awesome your room is compared to mine, I posted some info here. The second graph shows close mic vs lp

I have like no room gain

Well despite that I think you're puttin up numbers that anyone would be happy with. I'm sure only you would know if you had any weakness from top to bottom cause I can't see any.

Man, I wish it were true, but the truth is, I give up on this one. I haven't found 2 traces anywhere that even resemble each other. I've done literally hundreds of close mic measurements and all of them were +/-1dB from the quasi-anechoic measurements.

Here's MKT's previous trace, his latest trace and the CHT model that they claim is 'more accurate than a close mic', which supposedly has the EQ boost applied. I could put 10 posted traces on this graph and no 2 look like the same sub.



A while back I used my digital RS meter, 1/12 octave sine tones and an old correction file against my mic and it was accurate enough to convey a close mic measurement that could be used for this exercise, so I just don't know what the malfunction is here, but I'm certain that the latest trace is not accurate enough to crunch the numbers.

Bosso

Yup, I don't know what is going on with these close mic measurements.

Your comparison above was with a model that had bass boost applied. MKT does not use the bass boost because of his room. Regardless, I am not sure why you tried that exact comparison. MKT is not trying to prove the model.

You said " I've done literally hundreds of close mic measurements and all of them were +/-1dB from the quasi-anechoic measurements." How did each of those measurements compare with the model?

There seems to be a question about how difficult it is to take an accurate close mic measurement.


Just for fun, I tried a few close mic measurements of my NHT 2.9 speakers. This speaker is a 4-way speaker with a 10" sealed driver that uses a passive crossover at 100 Hz. For the measurement microphone I used my RS Digital SPL meter set to the 100 dB C scale, and applied straight standard SPL C scale compensation factors. Close mic sweeps.

SPL level was calibrated for REW and TrueRTA. REW used 250Hz as the upper sweep level.

My room has little room gain.

Sweeps vary below 13 Hz because of room gain and whatever.

General conclusion. It is difficult to measure FR below 15 Hz in my room (little room gain). Also, the Stereophile reference varies from my close mic measurements around 70 to 100 Hz.

I suspect that room gain in MKT's room shows up in his close mic measurement. Then again, he may be doing something else that I do not have any knowledge about.




True RTA

Top curve is average of 5 sweeps, smoothed to 1/6 octave.

Middle curves are 5 sweeps overlaid. I took more sweeps, but tossed out the ones that looked real jagged below 15 Hz.

Bottom two curves shows Pink Noise with 100 averages compared with the top curve (averaged smoothed sweep). Same results.









REW

9 sweeps. Variations at frequencies below 13 Hz.









From Stereophile

Looks like we have 2nd party confirmation on CHT subs being tested by Ricci:

if you do close mics, you may be better off doing it with doors open and the sub lifted off the ground. lower levels may help as well

Good point. Kind of hard to move that sub off of the ground. MKT could try to leave the doors open to his room and lower the SPL test levels.

An outside measurement would be better, but it is still winter up north. It snowed last night and this AM!

I used the 100 dB C scale on the RS SPL meter with C scale factors in REW set to on.

At the close mic position, for REW I activated the SPL calibration set to slow. With the SPL meter placed at the close mic position I measured 95 dB SPL C scale on the SPL meter and set the REW SPL meter to that calibration value.

I did the REW sweeps with a -15 dB FS sweep level, with an upper frequency limit of 250 Hz.

I used -15 dB FS for the pink noise test also. Not very loud at all!

In addition, do at least 9 sweeps and see how they line up. Throw out the crazy ones. Then take an average of all of them. Two charts would be nice. One for the Average and one for all 9 curves overlayed.

That's great....now some things can be put to rest.

I don't like the "looks" part though.

MKT, at his point all you are doing is an academic exercise and gaining experience in close mic meaurements.

Room gain varies by frequency. Your room gain at 10Hz is about 18 dB if your baseline is accurate. What is it at 20 and 30 Hz? Hard to know unless your baseline close mic is accurate.

30 Hz has a wavelength of 38 feet, so I don't see what raising it off the floor would do, and levels are lower by default at .5" distance to avoid clipping the mic/SC.

I wonder if MKT used a neutral amplifier he might get a better representation of the naked response?

I also never use the SW out for close mic measurements because they usually have a global LPF in line. If you set your mains to large and use one of the FR/FL outs, you'll get an unfiltered signal to the amp.

I've never used the RS meter as a mic, so I'm no help in that department.

Bosso

Good point. I forgot about that issue. MKT will have to answer the question on how he connects the subwoofer power amplifier to his PC audio output.

I suppose one could move the R & L crossover as high as it can go. That would be 200 Hz in my receiver. Then again, I do not use the subwoofer output jack.

Actually you don't have to worry about most of this. It's all academic but interesting to know!

You know what is funny here is that I intend on TRYING to redesign my room to something similar to what MK has.

Also this is just MK's adventure and he SHOULD be allowed to post what he wants but there should be clarifications so that others do not misread what he has posted. To use MK's measurements/discussions as a comparison of sub designs will lead to inaccurate conclusions.


There is only one conclusion for......


Im still envious of his room and setup

You can check to see what your receiver does between the audio input and subwoofer output by connecting the subwoofer output jack of your receiver into the PC audio input. Just unplug the RS meter and plug in the receiver SW output and do a sweep. Make sure levels are low enough so you do not clip the PC audio board input.

I assume that Audyssey is not being used.

This is a fun thread.

You get to learn a lot on someone else's nickle.

... to add, and not that you're implying this, many do comment that the LMS5400's SQ is above what they've experienced with other subs regardless of measurement comparisons. E.g., Paul's recent review of the FW12.0 sub ...


I'd love to hear one compared to another sub in the same room (level and FR matched,bla bla bla), preferably in some sort of blind test to see how true the above statements holds.

I agree, I recall how tough it was to pick the sub with the best SQ when a few of us blind tested the PB13/JLF113/EP600/DD18 (after trying to match the FRs using an SMS-1). Having said that, it may have been easier with a "lesser quality" sub (whatever that means) than that line up.

I recall some guy trying to sell me his $1k or $2k DAC and trying to convince me it would sound better than my AVR at the time (Onkyo 886 or Integra 9.8?). I was flipping back and forth between using the AVR DAC and the external, and after a while try as I might couldn't tell a difference or if I did it was so minute I couldn't tell if it was actually there or in my head. At one point the guy started to say "see how much tighter the bass sounds right now and how much more air you're getting from the recording" or some nonsense like that, at which point I politely said "actually I'm still on the AVR DAC"... needless to say, I told him I wasn't interested in the DAC.

Interesting comments on in room close mic testing errors.


http://www.avsforum.com/avs-vb/showt...4#post20253774