My various SPL charting sessions.

[WB]

Will be adding to this thread over time as I make more charts and BF cabinets. Will also compare to several commercial cabs that I have, at some point. Mostly interested in electric bass backline amplification. Comments, suggestions welcomed.

Build pics and charts can also be found here:
http://web.mac.com/wb12/iWeb/WB%20/SPL%20Charts.html


June 15th, 2008

O15TB Sub, with and without baffle mod. Warning, Y axis is not 1W/1M.
Same as above, but with crossover engaged. Warning, Y axis is not 1W/1M.

Sept. 17th, 2008

O15TB Sub, 3015LF

June 24th, 2009

Omni subs and direct radiator comparison.

August 9th, 2009

These charts are 4 meter at 11.32 volts (1W/1M). I angled the top box down so the vertical alignment was on axis with the mic.

DR250, checking tweeter array polarity.

Comparing the sealed DR250 to the OT112.

Comparing my O15TB sub with the O15TB modular sub which has two 3012's.

Sealed DR250 with O15 modular sub, no crossover.

Close up view of crossover area.

Comparing sealed DR250 with ported, 5 different port areas, thru the plastic handle. My idea, not in the plans. I did this so I could easily revert back to sealed status without touching the cab.

I choose this port.
Port handle inside view.
Port handle outside view.

[Ron K]

What testing software are you using? Even outside unless you are in a very wide open field you can get secondary reflections into the measurement mic that may drastically skew your measurements. Reason I ask is I never saw that drastic dip @ 1.1K with an O-top 12 without a coherency issue being present even though my dip is at a bit higher frequency.My measurement technique was almost the same as yours but again not done in a lesser echoic environment.



The red trace at the top shows no less then 4 coherency issues (most likely drawn by secondary reflections). If these sounds enter the measurement mic out of time they could also enter out of phase and significantly cause measure errors. This is using SMAART which also has a time window (gate) that helps keep out unwanted secondary effects from being measured.

[WB]

What testing software are you using?

I wish I was. But so far I'm doing it manually using a TENMA Audio Sine Geneator 72-455A.

I'm using the Behringer reference mic into a second DEQ2496 and using the RTA/MIC-IN screen to read the actual SPL figures. I used a Phonic PAA3 to calibrate a test tone to verify that the readings are correct.

Even outside unless you are in a very wide open field you can get secondary reflections into the measurement mic that may drastically skew your measurements.

I think that's what I was experiencing, but didn't realize it would be so drastic.

I never saw that drastic dip @ 1.1K with an O-top 12 without a coherency issue being present even though my dip is at a bit higher frequency.My measurement technique was almost the same as yours but again not done in a lesser echoic environment.

I did have that drastic dip on the OT112, but was pleasantly surprised that it wasn't there on the DR250.

That's a very good looking plot of the OT12 you have there. It looks a lot smoother than I've been able to measure. So far all the direct radiator cabs I've measured have been smooth but inefficient and all the BF cabs have been peaky but efficient.

[Sydney]

Even outside unless you are in a very wide open field you can get secondary reflections into the measurement mic that may drastically skew your measurements.

On a related note:
A good portion of Chapter 12: Adjacent-Boundary and Loudspeaker-Mounting Effects ( from Sound reproduction: loudspeakers and rooms By Floyd E. Toole ) is @ Google Books.
It discusses boundary effects and how field measurements compare to theoretical predictions.

[gdougherty]

On a related note, there was some discussion a while back about drastic dips in OT12's being related to cancellations off the rear port of the driver onto the access panel. I put 1/2" wool carpet padding on the entire rear surface of my panel and I still have that dip. I've thought about putting a wooden cone or pyramid centered on the port to reflect everything sideways instead. Still haven't gotten around to it to see if it makes a difference.

[Bill Fitzmaurice]

On a related note, there was some discussion a while back about drastic dips in OT12's being related to cancellations off the rear port of the driver onto the access panel. I put 1/2" wool carpet padding on the entire rear surface of my panel and I still have that dip. I've thought about putting a wooden cone or pyramid centered on the port to reflect everything sideways instead. Still haven't gotten around to it to see if it makes a difference.

I've confirmed that dips in the 800-1200 Hz range are products of horn loading. They can be addressed with some changes in the horn, but at the cost of overall sensitivity, so it's not worth it.

[Ron K]

Actually since I re-padded the inside of the O-Tops and added the compression Drivers with a bi-amp the overall O-top 12 curves are even better then what I have showing in those old charts.If I ever get some extra time I'll see if I saved the screen shots the second time I measured the boxes after an extensive re-padding, foam lining the grills and changing of the HF components. I don't believe I did as time was tight that day and my goal was a quick look and EQ to my set curves. It was before an outdoor gig so I really couldn't play like I normally would.

The only problem is I use a modified Fletcher-Munsun curve as my final EQ goal so the end results after EQ never look flat. Flat Q's sound absolutely horrible IMHO!

Mine end up with a big peek or hill around 100hz with a smaller valley around 1K and a smaller peek around 8K. Sort of a big hill ,small valley , small hill smooth roller coaster curve. That seams to be where my hearing is most accurate.

I do polar's from a flat EQ but that's about the extent of anything that gets flat!

[WB]

Flat Q's sound absolutely horrible IMHO!

I agree.

The room correction option on the DEQ's Auto EQ function does a nice job of taming the flat eq. also.


August the 15th, 2009

DR250 full space pink noise response

After Auto EQ'ing 315 Hz and up.

The resulting graphic EQ curve.

Quiet country backgound with crickets chirping.

August the 19th, 2000 and 9

Comparing DR250 50 Hz porting with my handle port, and sealed.

September 4th, 2009

Wedge10 sine wave comparison with Berg EX112 with modified W10 porting for electric bass.

W10 pink noise, full space, no EQ.

Same as above, but with Auto EQ by the DEQ2496.

The resulting graphic EQ curve.

Wasn't happy with August 15th's DR250 results so I did them over:

DR250 full space pink noise response, no EQ.

Same as above, after Auto EQ.

The resulting graphic EQ curve.