So I tried my hand at this today. For now, just the on-axis measurements to make sure I'm doing all this right. In my shop I have an ancient pair or Proac Tablette 2's! The Tablettes are quite legendary, here is the history of these little speakers.
1979 – named changed to ProAc and first Tablette released to international acclaim
1987 – Super Tablette introduced
1989 – Response series first released
1991 – Tablette 2 introduced, Response series updated to ‘S’ models
1993 – Tablette 3 introduced
1997 – Response updated to ‘SC’ and floorstanding 2.5/3.5 models released
1998 – Tablette 50/50 Signature introduced
1999 – Tablette 2000/2000 Signature introduced
2000 – Future series released, the first models to use ribbon tweeter
2001 – Response ‘D’ series introduced to great acclaim, new Tablette Reference released
2007 – ribbon tweeters introduced to the Response ‘D’ series with introduction in D38R
2008 – Carbon Pro series introduced, ProAc’s largest and most expensive designs yet
2010 – Tablette Anniversary released to celebrate 30 years as ProAc
2011 – K6 released, the first speakers to use the newly available Kevlar cone material
2015 – K8 released bringing Response series to its culmination
2016 – Tablette 10 released
2017 - DT8 & Tablette 10 Signature is released
I think I purchased my 2's around 1993 or '94 on a close out as by then they had the Tablette 3's in stock. Even though these speakers all share the same name, they are all a bit different. I believe the latest incarnation is a sealed enclosure with completely different drivers, but hey the box is a similar size for what that's worth
Here are a couple of pics, front and back.
For my hardware setup, I have an older Edirol UA-25EX Interface that I use for this. I've done the interface calibration and it works pretty well. For a mic I have a Earthworks M23R mic, with the calibration file, although this mic only varies about 0.5db so it could be used without it. I also use one channel as a loopback interface wired directly from output to input. I only measured down to 40hz, I know there isn't anything that low and I didn't want to damage them.
Here's my first measurement, I took it at 18 inches instead of 1 meter. I don't exactly know why I did that! haha But it's a pretty small speaker so I think that's fine.
Then I applied the IR Window at 6ms which seemed like a good place. My shop is pretty big and has a 9ft ceiling. Here are the results.
Next up my nearfield woofer measurement at about 1/4 inch.
Next I measured the port, which is on the back of this speaker and is 2" round.
Next I summed the woofer and port. Since my graphs do not have a nice "alignment point" like the example, I used the calculation method that was mentioned, which was 20 Log (port dia/piston dia). The port dia is 2" and the piston is 3.375", so 20 Log(2/3.375) which gives me -4.54db. When I put that in and added the graphs, here's what I got.
Next I used Vituixcad's diffraction tool to arrive at the following compensation.
Then I imported that into REW and Summed it with the Nearfield and Port summed graph.
Finally I can align the Windowed version with the Woofer+Port+Diffraction.
And the final On Axis response.
While I think I followed the instructions correctly, to my eye/ear, there seems to be something a bit off. The overall response seems about right with the exception of the bass extension. This method shows the -3db point being at around 64hz with the -10db point being around 45hz.
I can tell you, they sound great, but there is NO WAY these things go that low! To be honest, the original non-windowed measurement seems more correct, at around 80hz it shows about 4db lower output than the final merged graph.
So the question is, what did I do wrong? The piece I'm wondering about is the summation of the nearfield + the port. I reduced the port by using the formula which produced -4.5db. But that port is on the back of the small speaker, seems logically to me it might be producing less out in front of the speaker. If you took the final graph and hinged down the line from about 300db taking it down about 3db at around 100hz I think it might be pretty accurate.
So went back and just tried to lower the Woofer+port+diffraction graph by another 3db, then summed it again with the Windowed version. Oddly enough, it didn't really do much of anything. So I don't know what I did wrong.
But this exercise gives me a lot more respect for all you guys who do this so well! It's a tricky thing at least when you don't have any experience.
Edit: Just for fun, here's the original response at 18 inches, with an IR window of 25ms, which is 40hz, overlayed with my final merged graph.