Finding the Low Res Frequency

HarrySound

HarrySound

Power User
Hey guys. I've literally spent an entire week just purely jamming on a Vibrolux with split coils on my PRS and now it's time to make some dirty tones.
I've been doing some reading and i'm trying to follow Cliff's example here...

  • Here's how to find the correct resonating frequency:
    1. Put a Filter block after the Amp block.
    2. Set the type to Peaking, Q to 5 or so and Gain to 10 dB.
    3. Start with a Frequency of around 50 Hz. Play some chugga-chugga and slowly adjust the Frequency until you hear and feel the cabinet resonate. You need to do this at loud volume level to notice it. Make a note of the frequency.
    4. Remove the Filter block and set the Amp block SRF to match.
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My question is when do I know when i've found it. What does this actually sound like?. My first thought was when it started woofing but that can't be right.
My settings so far on most occasions has left the 7th and 8th fret E string (B# and C note) woofing while everything else seems "ok" so i'm doing something wrong.
 
using the stock cabs in the AXE itself
EDIT: sorry . Using a set of KRK RP6 monitors.
 
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HarrySound said:
Using a set of KRK RP6 monitors.
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The whole point of studio monitors is not to have any resonant frequencies or at least dampen them as much as physics and economics will allow. So there will be a boost wherever you set that peak on the speaker page. If the speakers can handle that frequency, if course.

With guitar cabs it's different - they are built to emphasize that frequency, not dampen it. Effect will be much more prominent.
 
yek said:
If you're not using a guitar cab, finding the low freq resonance is not as important.
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IMO, it IS important, but it becomes more of an additional EQ thing. You can more or less set it wherever you like. With a guitar cab importance is different in that if the value is wrong, the cab won't sound great.
 
Thanks for the info! I'm singing myself up for many months of learning with this thing and i'm starting at the bottom.
I would still like to know what the resonance actually should sound like and how to pick it out.
 
HarrySound said:
I would still like to know what the resonance actually should sound like and how to pick it out.
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You'll need to play through a guitar cab for that. Plug it into a tube amp and you'll know. :)

The simplified point is that at a certain frequency a speaker begins to "overreact" to whatever comes from an amp. When this happens, it starts driving the output of the amp with it's own generated signal. Tube amps cannot dampen this completely, so they start "grooving" together with the speaker, and the whole system resonates, thus giving a healthy boost.

Solid state amps dampen this by design to be more linear, aiming to give true representation of the signal they amplify. Modern speaker systems also dampen that resonance to be flat. With guitar sound, this perfection sounds kind of dull and lifeless, not what people are used to hear from a guitar cab. To compensate for that, there's the Speaker page.

The flipside is that, because solid state amps and good modern speakers are much more "perfect" devices, you can sort of make them sound any way you like. Just set that boost wherever it sounds good to you and don't worry about it. :)

Oh, and one more thing. In a way, you've heard it a million times. Many hifi amps have a "loudness" button. It does something similar to this resonance effect. And actually, you already hear it through your monitors because the Speaker page defaults to something non-neutral.
 
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I have read in previous post that a good starting point is to find the low res frequency of the speaker that you are using. You can find this usually on the manufacturers website. And then add a value of 10 to that for closed-back cabinet. What would you add for an open back cabinet?
 
bdrepko said:
I have read in previous post that a good starting point is to find the low res frequency of the speaker that you are using.
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I personally find this strange and rather useless. For example, Celestion V30 speakers have it at 75 Hz, if I'm not mistaken. Add 10 and you get 85 Hz. I doubt you'll find a cabinet with the resonant frequency so low. Moreover, that's too low to be useful in a mix, you usually don't want to boost it at all. The cabinet itself affects the overall resonance too much to pay any attention to this spec, IMO.

It also has no practical value. It's not like you spend an hour per Hz or something. Just do a sweep as Cliff suggests, starting as low as you like, and find the sweet spot. There's no real point in looking up speaker specs for that.

As for the theory, I think that open back cabinets should be closer to the pure speaker spec than closed ones. But that's just my common sense guess, not any specific knowledge.
 
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vangrieg said:
I personally find this strange and rather useless. For example, Celestion V30 speakers have it at 75 Hz, if I'm not mistaken. Add 10 and you get 85 Hz. I doubt you'll find a cabinet with the resonant frequency so low. Moreover, that's too low to be useful in a mix, you usually don't want to boost it at all. The cabinet itself affects the overall resonance too much to pay any attention to this spec, IMO.

It also has no practical value. It's not like you spend an hour per Hz or something. Just do a sweep as Cliff suggests, starting as low as you like, and find the sweet spot. There's no real point in looking up speaker specs for that.

As for the theory, I think that open back cabinets should be closer to the pure speaker spec than closed ones. But that's just my common sense guess, not any specific knowledge.
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Thanks for the info. I guess I need to find a free afternoon and play around for a while. I agree with your suggestion that the open back cabinet would most likely be closer to the speaker lo res.
 
If only it was this simple. :confounded:

First of all that tutorial for finding the resonating frequency only works when you're running a real cabinet. It does not work with IR's after shooting them with current techniques that remove the power amp color. If you do this test without a real cabinet you'll (unsurprisingly) find that this resonating frequency is the exact same frequency where your speaker page low res freq is set. If you disable this frequency you will not find a resonating frequency right?

I've heard about these math equations also but the fact is that even the difference between 104hz or 105hz may make or break your palm mutes and feel. A Mesa 4x12 Traditional (Cab Pack 7)has it's low resonance frequency at 106hz with a Q of around 2 but the Mesa 4x12 Oversize (Cab Pack 13) (which has the same type of speakers in it) has it's low resonance frequency at 103hz with a Q of 1. Completely different low end responses on both cabinets which many would describe as just a "Mesa 4x12". So take to account that you'll most likely have to struggle to get this information.

The good part of this is that you don't have to find "the right" low resonance frequency but instead you can find something that works really well with your setup. Some people change their amps and cabs because they hate the uncontrollable low end and want something tighter. For us it's just a turn of a knob. The default settings are always really good starting points. Fine tune them to fit your guitar and sound and you should be good to go. :)
 
ML SOUND LAB said:
A Mesa 4x12 Traditional (Cab Pack 7)has it's low resonance frequency at 106hz with a Q of around 2 but the Mesa 4x12 Oversize (Cab Pack 13) (which has the same type of speakers in it) has it's low resonance frequency at 103hz with a Q of 1. Completely different low end responses on both cabinets which many would describe as just a "Mesa 4x12". So take to account that you'll most likely have to struggle to get this information.
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And those numbers you provide (100+ Hz) should put this weird Speaker Res Freq + 10 idea to rest, I think. It's not anywhere even close.
 
ML SOUND LAB said:
If only it was this simple. :confounded:

First of all that tutorial for finding the resonating frequency only works when you're running a real cabinet. It does not work with IR's after shooting them with current techniques that remove the power amp color. If you do this test without a real cabinet you'll (unsurprisingly) find that this resonating frequency is the exact same frequency where your speaker page low res freq is set. If you disable this frequency you will not find a resonating frequency right?

I've heard about these math equations also but the fact is that even the difference between 104hz or 105hz may make or break your palm mutes and feel. A Mesa 4x12 Traditional (Cab Pack 7)has it's low resonance frequency at 106hz with a Q of around 2 but the Mesa 4x12 Oversize (Cab Pack 13) (which has the same type of speakers in it) has it's low resonance frequency at 103hz with a Q of 1. Completely different low end responses on both cabinets which many would describe as just a "Mesa 4x12". So take to account that you'll most likely have to struggle to get this information.

The good part of this is that you don't have to find "the right" low resonance frequency but instead you can find something that works really well with your setup. Some people change their amps and cabs because they hate the uncontrollable low end and want something tighter. For us it's just a turn of a knob. The default settings are always really good starting points. Fine tune them to fit your guitar and sound and you should be good to go. :)
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Yes this is for a 2x12 cab with Celestion speakers driven by a Matrix GT800 power amp.
 
ML SOUND LAB said:
If you do this test without a real cabinet you'll (unsurprisingly) find that this resonating frequency is the exact same frequency where your speaker page low res freq is set. If you disable this frequency you will not find a resonating frequency right?
Click to expand...

I always wondered if you shouldn't be turning the low res freq all the way down temporarily when doing this test with a real cab as well for the exact same reason...wouldn't that run the risk of resulting in a false positive even with a real cab? Not to mention the risk of mistaking the sound resonating the walls in your room rather than your cabinet hitting that peak. I'm just very skeptical of that test providing anything definite if you're using a solid state amp, and a much better way I think to find out for sure is to use a tube amp...which of course then the results would vary given the different transformers/output sections etc...

SO that pretty much circles back to using what sounds best with the stock settings as a starting point :yum:

I guess if you're well equipped to use a multimeter and other measuring tools along with a high level of maths you could figure it out exactly independent of an amp?
 
If I understand the nature of this phenomenon correctly (which may not be the case), transformers shouldn't affect this frequency, at least directly. The negative feedback circuit in a particular amp will determine the dampening factor, i.e. the "amount" of resonance, however, so that will skew the result. Amps without negative feedback should get "pure" results, and their output voltage will rise with the speaker impedance. It'll still be a tedious process with a multimeter though. :)

I guess it's relatively easy to make an op-amp based device that'll send a frequency sweep and measure its own output for accurate results.
 
ML SOUND LAB said:
I've heard about these math equations also but the fact is that even the difference between 104hz or 105hz may make or break your palm mutes and feel. A Mesa 4x12 Traditional (Cab Pack 7)has it's low resonance frequency at 106hz with a Q of around 2 but the Mesa 4x12 Oversize (Cab Pack 13) (which has the same type of speakers in it) has it's low resonance frequency at 103hz with a Q of 1. Completely different low end responses on both cabinets which many would describe as just a "Mesa 4x12". So take to account that you'll most likely have to struggle to get this information.
Click to expand...

Hey @ML SOUND LAB thanks for posting these. Have you considered posting a single thread with the LF resonance frequency / Q listed for each of the cabs you have shot? It would be a very helpful resource if you have the information.
 
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