TOPIC: S12-65 IR coolness

S12-65 IR coolness 3 years 3 months ago #13727

I’ve been helping a friend choose a speaker for his amp, and I just experimented with mic positions on the S12-65 IR using my sine sweep wave and an SA plugin to see what really happens. I found that at 2” directly on axis in the 1x12” “California Combo” cab (on which I EQ’d up only the two cab dips and one peak below 2kHz for a full-bodied sound), the SM57 mic rounds the highest relevant speaker peak off & up to 6kHz for sweeter detail (retaining the ~5kHz dip which reduces brittleness), while it brings up the 4-4.5kHz chime to a more audible level, and dips ~3kHz a few dB to reduce ice-pick. It’s a sort of ideal guitar speaker sound, and just needed a 2dB bass boost to balance the spectrum. Moving the SM57 1”off-axis rolls off the high end peak a bit from 5.5~6khz for slightly less detail, while moving it to 1” on-axis reduces ~3kHz more for a pillowy fat high end. Once fine-tuned with some guitar samples, the combined settings made for a full, clear & sweet sound. The Speaker Cab SA Graph png files and ReaEQ “fix” banks are here: www.mediafire.com/folder/4s6co0cdy2bm4/Spkr_Cb_IR_EQ_fix

I then looked up the G12-65 and found a Robin Ford Rig rundown video. Low and behold, he has an SM57 at ~1” on axis. It seems that from 1-2” away, and up to ~1” off axis is the “magical” tuning area for the G12-65 with an SM57. The other mics don’t have the same fattening affect. Is it just a set of musically fortunate coincidences, or was the speaker designed specifically to utilize the SM57 qualities, or did Robin Ford somehow will it to happen? Lol.
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S12-65 IR coolness 3 years 3 months ago #13730

Greg,
I too was inspired by that same Robin Ford Rig rundown and its part of the reason I bought two G12-65's for my old Fender Showman. I put them in an old 2x12 black Bassman cabinet I've had for many years. I also built an open back for the cabinet to tame some of the bass that cabinet and amp produce. It sounds really nice as a backend to S-Gear (no convolver) or Helix. I had changed the tone controls in the Normal channel to FRFR many years ago to get more flexibility from the amp. I can use that channel with amp sims, or use the Vibrato channel with a typical front of the amp pedalboard. Helix works well for this.

My friend Nate had a old Fender Tremolux with Oxford 10K5's that sounded really fantastic. So I thought I'd try to create my on IRs from these cabinets. To reduce the number of IRs to deal with, I chose my most typical mic and placement configurations. I used an SM57 (my first mic purchase in 1969), and a AT4047 condenser, both placed at 1.5" and at cap-edge. I used a Hafler power amp and Logic Pro X Impulse Response Utility. These are 48kHz, 24bit, and 2048 samples so I can use them directly in Helix. They were made in my garage, so there's likely some room noise. I placed some blankets towards the front and back of the cabinet to minimize the noise, but it wasn't an ideal environment.

You can really hear the impact of that open back. the bass from G12-65's is nicely rolled off while the 10K5's in the Tremolux closed back cabinet have a fuller, perhaps approaching muddy bass response.
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S12-65 IR coolness 3 years 3 months ago #13739

Cool, man. I'll check them out and give you some feedback. I might do cab eq presets. Is that 1.5" from the face of the speaker or the cab face? Technically, the wide felt cap edge on the G12-65 isn't the 1.75" diameter coil edge. It may be a bit "far out, man" hehe. I’ve been working with someone on a speaker project. I tested the damping factor of some thick bath towel layers. I believe 2 to 4 towel layers stapled loosely over the back of the speakers would effectively eliminate any significant cab affects. I highly doubt the speakers can overheat, but I've never tried it. 4 layers measured -10dB at ~1kHz & -6dB at ~500Hz. It should then be -10dB at ~500Hz after coming back through to the cone. I’d think you wouldn’t need more than that for any guitar cab I know of.

The IR’s sound great, jams...and quite loud. Hopefully you didn’t clip or trigger limiting in your A/I unit. I set the speaker Z to 5 to compensate for the SS amp (as inferred from Red Wirez suggestions). It does look centered a little lower than the Scuffham 1x12” G12-65 on the SA graph.

The 10k5’s have a nice gritty sound with great 4~4.5kHz chime. The bass seems fine in the SM57 file. The low end may just need rolling off in the AT4047 files. The close proximity boosted the bass in both mic files - - probably for the AT4047.

If you can do it again, secure some towels over the speaker backs and close up the G12-65 cab. Place the SM57 direct center on the cap, and record at 1”, 1.5” & 2”, and at 96k if you can - - not crucial. One of those files should have the best balance of chime and ~3k dip, as well as more high end detail than the cap edge files. The closest one should have the most dipped ~3k and more bass for a warmer/softer jazz sound. From the Rig Rundown video, it looks like that’s where Robin Ford mics his. You could do 1” off center for each distance as well for less high end.

Not sure if the same applies for the 10k5’s, but it might be nice to have the choices. Seems to me that the most natural sound comes from setting the mic equidistant from all parts of the cone. That should be 2~3” from the edge surface, and best with a small diaphragm mic. Subtract the baffle thickness from that, and you have it. The lifted high end of the SM57 balances the proximity boost pretty evenly at ~2” with just a slight mid dip.

The stronger proximity, virtually flat AT4047 sounds bass heavy in comparison. It’s really not good for close-micing a large guitar speaker, and you would need to set it fairly far back to get a natural speaker sound. Not sure what that would be, but there may be a formula involving the depth of the cone.

Very sensitive mics also deliver speaker resonance spikes in tact with the other fine details. There’s a trade off. I’ve learned, mainly through using amp modelers, that small diaphragm dynamic mics are better for amp distortion sounds - - the SM57 being the reference. However, I do like the U67 for added sizzle. Small ribbons like the Beyer M160 may be OK for mild amp distortion, but crisp speakers can sound too...crisp. Can be very good on the G12-65, though.
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Last edit: 3 years 3 months ago by GCKelloch.
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S12-65 IR coolness 3 years 3 months ago #13754

I did the sweeps multiple times and made sure there was no clipping in the interface or in the Impulse Response Utility (which provides meters during the sweep). But maybe they're still a little to hot.

I have the back for that Fender Bassman cabinet, and can put it back on. But I also ported that cabinet, so I'd probably need to plug the ports too to make the cabinet fully closed.

I use 48kHz because that's what Helix IRs require. That should be fine.

I'll make some more IRs on axis with the SM57 when I get a chance. Its surprising how easy it is to get reasonably good results. And I could include preamp and power amp responses too.

I think My Fender Showman has too much negative feedback. I changed the output transformer to a Marshall transformer years ago so I could get different output impedance taps. And I think I need to adjust the negative feedback as a result. The gain is a little low, and the clipping seems a bit abrupt. More things to experiment with. I'd need to fix that before including that power amp in the IRs.
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S12-65 IR coolness 3 years 3 months ago #13772

Yeah, there may not be any gain compression at all. They are just louder than other IR’s. Even digital meters don’t always catch everything. Some are better than others.

If you ported the Bassman cab ~1 octave below the cab resonance, I’d be curious to hear that. Either way, I’d try it with at least a few towels over the speaker backs.

Yes, 48k is perfectly fine. I can easily convert to 96k. The files you shared are 44.1k. I think Mac Audio defaults to 44.1k when you go on the internet and what not. My brother had that issue. It takes some digging into to get a handle on it. I hope you have the 48k versions for yourself.

I’m not interested in amp IR’s for use, but I may end up using your cab IR’s if there is less cab coloration than the S-Gear ones. I ended up EQing out a lot of it from the IR’s I use, but I can’t do anything about the lower level ER’s that don’t obviously alter the spectrum. I don’t know why people like untreated cab’s. I find much of the coloration detracts from the body and sweetness, and I can use inharmonically tuned multitap delays with better results than random cab ER’s, if I want that effect.

Again, the excess bass you hear is from the proximity. Assuming your 1.5” placement is ~5” from the cone, there is 3dB or so bass boost in the SM57 files, and more with the AT4047. Not to worry - - that’s the case with the IR’s I know of. It can easily be EQ’d down for a given situation. The bass boost actually somewhat balances the 3~6kHz ~6dB boost on the SM57. The AT4047 is only up ~3dB at 6k. Find proximity charts for the mics to see how to EQ them flat. Comparing with the lower frequency peak of the Beta SM57, I’d still use the standard SM57 for the 6k detail...they got it right the first time.

MEMS mics have uncolored response, like a ribbon mic, with SPL levels over 130dB now. SNR is only up to ~67dB at this point, but it will surely improve in future. They are only 1~2mm wide, so there is much less proximity effect (if any), and no off-axis phase smearing. Your cell phone may well have one. If so, it may be worth recording an IR for comparison. There may be no more need for ribbon or condenser mics at some point. Passive dynamic mics will still be good for smoothing off rough edges, and for rugged stage use.
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Last edit: 3 years 3 months ago by GCKelloch.
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S12-65 IR coolness 3 years 3 months ago #13780

Jamsden,

Try making some longer IR's. I.e. don't truncate to less than 5000 samples @ 44.1KHz even if the tail is zero's. Too small an impulse will reduce the low frequency accuracy of the resulting frequency response. This is because the FFT frequency pots become too coarse at low frequencies.

Cheers,
Mike
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S12-65 IR coolness 3 years 3 months ago #13794

Jamsden may not be aware that this topic was moved here. I sent him a PM about it. He has to truncate for the Helix.I hope he saves originals in longer resolution. I looked up more info on MEMS mics, and it looks promising. The self noise of MEMS mics is only down to ~33dB at this point, but the dynamic range is over 100dB b4 clipping. That means you need peaks at the mic of 133dB for 100dB SNR. That can be closely achieved if you consider the SPL at ~6" from the cone for a speaker with a highest peak of ~108dB/1watt@1M, and the SPL increases 6dB per every 1/2 distance, and the peak wattage of your amp. New Samsung phones apparently have very good MEMS mics. This device also is a very good MEMS mic: www.ikmultimedia.com/products/irigacoustic/

MEMS mics like that are omnidirectional, so you might hang two thick towels at right angles to each other behind the mic to damp room slap back. To avoid room nodes, maybe play pink noise through a speaker in the room, and find a spot for the mic without obvious bass variations using a tablet or phone SA app.
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