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toddalin
12-27-2005, 05:30 PM
Today I put the 2235's reconed from 2205's in the L200 cabinets replacing the D130F's reconed as 130A's. The other components include an LE175/HL91, 075, N1200, and N8000. I took pics of the RTA (10 band) before and after. Gradations are in increments of 2 dB.

This first pic shows the RTA of right cabinet with the D130F reconed as a 130A by OCS. No eq is employed but the crossovers were adjusted for the smoothest freq response at the seating position. The RTA is a BSR and the microphone actually rolls off the highs making the highs look lower than they really are. (The highs are actually more pronounced than shown. When my Yamaha RX-Z9 goes through the autoeq, it reduces the highs from the levels you see to achieve a flat response and I have more faith in a $4,500 Yamaha than a $150 BSR.) Still, note the total lack of the 31.5 Hz and 16K Hz bands and the less than stellar response in the 62 Hz band.

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/WITH130S.jpg

These next two pics show the right and left RTAs, respectively, after replacement of the 130s with the 2235s. Nothing else was changed but the crossovers were again adjusted for the smoothest freq response at the seating position.:D

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/RIGHTAFTER.jpg

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/LEFTAFTER.jpg

johnaec
12-27-2005, 05:39 PM
One octave bands, correct? (~31.5, 63, 125, 250, etc.)

John

norealtalent
12-27-2005, 05:39 PM
I'm not just bustin' balls here,ok? I've learned alot around here and am grateful for it. I used to ONLY be of the throw it in and see mindset. Now, thanks to something Rob3606 said that put what I've learned into perspective, I think differently. So here's my thoughts:
Yes, you've got the physics of it, the graph looks much better, but I want to know what it sounds like now, please and thank you. :bouncy:

toddalin
12-27-2005, 05:41 PM
One octave bands, correct? (~31.5, 63, 125, 250, etc.)

John

Yes.

Zilch
12-27-2005, 06:40 PM
Mic is near field?

Now close off one of the ports in each cabinet and see if there is a measurable difference.... :thmbsup:

Robh3606
12-27-2005, 07:01 PM
What's with the 480/960 notch?? That is above where the room is dominant. Where are you crossing over??? That at your seat or nearfield??

Rob:)

toddalin
12-27-2005, 07:20 PM
What's with the 480/960 notch?? That is above where the room is dominant. Where are you crossing over??? That at your seat or nearfield??

Rob:)

That is with the mic set on a pillow on the couch in the seating position about 16.5 feet from the speakers. Crossover is at 1,200 Hz (N1200). Yes, there is a notch at 500-1,000 Hz, but at least its in the range where my Yamaha can eq it out. Unforetunately, the bottom 5 bands of the 31 band peq in the Yamaha are dedicated to the subs so if the mains don't go down there, other than using an outboard processor (and it's residual noise), the Yamaha won't compensate for it other than through its bass control. Also notice that even using the 130As, there is still a broad notch in this area.

Listening reveals a deeper bass and extended frequency response as expected, but the overall JBL sound still comes though with little change.

Robh3606
12-27-2005, 10:34 PM
"That is with the mic set on a pillow on the couch in the seating position"

Is the height the same as your ears?? You need to get the microphone at the same height as your ears.

Rob:)

Zilch
12-28-2005, 01:10 AM
Hi, Todd.

Mini-boom and mike stand go for about $25 at Guitar Center, I believe.

I can get different results from the position of me in the room. (Or, maybe, it's just the position of my ass in the room. ;) )

I'd suspect couch and pillow might be problematic for measurements....

Ian Mackenzie
12-28-2005, 03:04 AM
Todd,

I may help first to determine if the problem is in fact a problem or a measurement anomally (ie speaker or crossover or a function of the mic or a room effect).

If you put the mic right in front of the woofer..say within 12 inches centred and take another measurement, then the same for the horn/lense , then another about 1 yard back with the mic midway b/n the horn and the woofer we will know a lot more. I am not sure if you can run without any eq or auto equ but that would be useful to turn it off.

Depending on the room and location of the mic relative to the floor and ceiling nodes will cause cancellation at 1/2 wavelengths and convey visual depressions on the RTA.

Unfortuntely RTA's typically will not allow time gating to gate out the effect of these reflections so you need to move the mic closer (much ) to see what the speaker is really doing.

Hope this helps a bit...its a mine field otherwise.

The Doctor...Who

toddalin
12-28-2005, 09:06 AM
"That is with the mic set on a pillow on the couch in the seating position"

Is the height the same as your ears?? You need to get the microphone at the same height as your ears.

Rob:)

Yes, pretty much. I take a rectangular pillow set on the diagnol (point up) in the seating position in front of the back cushion that you lean against and set the mic on the "pillow point." Not the most scientific, but a simulation of a soft body sitting at this position.

toddalin
12-28-2005, 09:12 AM
Hi, Todd.

Mini-boom and mike stand go for about $25 at Guitar Center, I believe.

I can get different results from the position of me in the room. (Or, maybe, it's just the position of my ass in the room. ;) )

I'd suspect couch and pillow might be problematic for measurements....

Probably so, and better/different placement would change things. But this is where the listener sits. How about if we all come to some sort of agreement as to how and where measurements should be taken so we can all compare apples to apples?

Consider that probably most speakers on the market couldn't even light all 10 bands with the mic at the seating position under these conditions. These sure didn't with the 130As and I would venture to guess that as poor as their bass response was, it was still better than most commercially sold speakers for home use.

toddalin
12-28-2005, 09:14 AM
Todd,

I may help first to determine if the problem is in fact a problem or a measurement anomally (ie speaker or crossover or a function of the mic or a room effect).

I am not sure if you can run without any eq or auto equ but that would be useful to turn it off.

Hope this helps a bit...its a mine field otherwise.

The Doctor...Who

All testing was performed with the autoeq off and tone controls defeated.

boputnam
12-28-2005, 11:41 AM
The RTA is a BSR and the microphone actually rolls off the highs making the highs look lower than they really are. No-one seems worried about the mic. Maybe I shouldn't, but...

What kind of mic is this, and if a reference mic why does it roll-off the highs?

toddalin
12-28-2005, 12:18 PM
No-one seems worried about the mic. Maybe I shouldn't, but...

What kind of mic is this, and if a reference mic why does it roll-off the highs?

For the RTA pics, its the condenser mic that came with the BSR. I've tried to use other mics, but the analyzer won't accept them. I wouldn't think that this is a "reference-quality" mic but just intended for the casual user to better calibrate his stereo system. But, don't make the mistake of thinking that any mic is perfectly linear for 20-20K, especially one that comes with a <$500 RTA. A good mic could easily cost in excess of $500 by itself.

On the other hand, when I quote dB readings, those are taken with a piece of reference equipment that is factory calibrated yearly and in the 10 years I've had it, it has never been off by more than 0.14 dBL as measured by the factory, Quest Technologies.

Maybe it's not the mic at all. Maybe the mic is accurate. Maybe the pink noise put out by the BSR is different than the pink noise put out by the Yamaha during autoeq (which turns down the highs when referenced to the BSR).

I listen to "pink noise" from various sources (cd, the BSR, the Yamaha) and they are all a little different. Certainly this does influence the readings. Maybe we need a "reference standard" for pink noise and should all agree on what disk to use. But then, how do I know that the cd player is not rolling off the highs or lows influencing their/my reading?

Zilch
12-28-2005, 12:19 PM
How about if we all come to some sort of agreement as to how and where measurements should be taken so we can all compare apples to apples?I see many different protocols in the literature, the most common being 1M, aimed on-axis with the driver under test, or, if a system, aimed at the HF. That may be largely derived from the industry standard specification procedures, and not appropriate for actual listening response. Jean (B&K Man) suggests that, when testing systems, this may be too close for the several drivers to integrate with coherency, and, if I recall, advocates something more like 2M.

As Ian points out, however, the further away from the source the measurement is taken, the more the environment and reverberant field come into play. Thus, while measuring from the listening position may be a good choice for "tuning" a system to a particular space, it's not real useful for making objective comparisons of driver/system response between systems in different spaces.

Generally, I'm only looking at one driver or speaker (one box with multiple drivers) at a time, but I've found it's possible to measure both left and right playing concurrently, IF the mic is precisely aimed to find the acoustic center using the RTA display. Movements as small as 1/8" make large changes in the HF response due to phase interaction between systems. I don't know what that translates to in mic angle, but it's on the order of minutes, not degrees.

Why bother with that? Because the acoustic sum of the two better characterizes the actual response, statistically, through averaging.

I ignore just about everything below about 800 Hz, other than for gross level-setting. As you have also experienced, measuring LF is a different set of parameters requiring a different protocol altogether....

boputnam
12-28-2005, 01:30 PM
But then, how do I know that the cd player is not rolling off the highs or lows influencing their/my reading?I doubt the CD player would do that. If you fear it might, try and pipe the pink noise directly into the RTA. Can you do that?

Alternatively, the issue you are raising is best addressed using a Transfer function - a FFT analysis, which compares the reference signal (= pink noise in this case) with the measured signal (mic).

In general, it's worthless attempting RTA "measurements" while being clueless about what the signal looks like that is actually reaching the speaker. You may end up trying to correct a host of characteristics that are not originating from the speaker, per se.

boputnam
12-28-2005, 01:33 PM
That is with the mic set on a pillow... :scold:

Get a proper mic holder that allows the mic to be way in-front of anything. You do not want boundary effects / reflections from anything near the mic.

boputnam
12-28-2005, 01:48 PM
...don't make the mistake of thinking that any mic is perfectly linear for 20-20KI don't. The Earthworks series are (top image is "typical" M30; bottom is my M30, S/N 4286), and Ian has made some using a Panasonic element that achieves same-same for less dough.

You can get the Earthworks M30 and M30BX for $425 and $716 respectively, off the SIA Smaart on-line store. Good prices, and they relieve these type of headaches...

What you are trying to do is fairly sophisticated and requires requisitely sophisticated equipment. From my experience, your results will frustrate and mislead until you approach this more appropriately.