Some IRs I made (Pulsonic cone T1281s)


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Dec 28, 2020
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Download link first, for those who'd rather skip the essay.

I know speaker IRs are hardly in short supply, but I've finally managed to get together a pair of T1281s, i.e. 55hz 16 Ohm G12H30 Greenbacks, and thought it would be a good opportunity to record some of my own. Two speakers might not be as good as four, but it does mean you at least get "acoustic coupling" (Johan has a great video on this!)

Here they are, in situ:

The cab is a 1936 (special Thomann run, discussed here). One speaker is a '70 (so pre-Rola sticker), the other is '72 (Rola). The '72 sadly arrived with coil rub. I'll let you decide how that impacts on tone.

As it turns out, making IRs was easier than expected. I used Logic's IR Utility (cleverly hidden inside Space Designer), and the Ownhammer GNR IRs as a reference. After capturing 1s responses via 10s sine sweeps, I trimmed and phase-aligned the deconvolved IRs in Logic by hand (I imagine Ownhammer have a more precise automated method).

As far as equipment, I used the return FX loop in my TAE (which has a very neutral SS poweramp) to send the signal to the speakers. Recording was done via an SM57, with a slightly unconventional larger grill as I misplaced the original somewhere (shouldn't make a difference with the "sine sweep" method). I used my UAD Apollo for tracking, with the Neve 1073 "unison" preamp (EQ section off) and no additional processing.

You can see all that gear here (not the tidiest space - or the most acoustically-refined - but probably good enough for a close mic'ed guitar cab):

I ended up with 4 IRs, each of them 24 bits, 96khz and 200ms long. The placement is less precise. I used the standard technique of looping a signal through the speakers, while moving the mic and listening on closed-back cans turned up loud to find the good spots. There are two positions for each speaker, one on-axis and the other off - vaguely near the center of the respective speaker in each case. Both speakers were playing at all times.

I've also made a comparison clip, although I suspect most will get a better idea simply loading the IRs into their existing setups. It's just a couple of variations on a simple riff, Rickenbacker into JTM 45/100 clone. I've labelled each of the transitions. The Ownhammer example chosen was the closest comparison I could find (modern SM57, on "sweet spot", no EQ processing) - note that the speaker used here was a '71 T1221 (so 25W, 75hz).

Doubt I'll be going into commercial IR production any time soon, but it was a fun experiment, and now I have some new sounds for my home recordings! Enjoy