Help Understanding Speaker Impedance (with IRs)

[zafreemusic]

Hey Friends,

I looking for some help understanding the Speaker Impedance settings with IRs.
I have found that the proper Speaker Impedance settings are important to getting a good sound IMO.

So, I am wondering how you guys are setting this with IRs?

My other question is some of the defaults seem off (unless I'm missing something) shouldn't the low resonance be above the speakers Ls?
Examples:
1x12 Deluxe Verb - How can the Low res be 63 hz when pretty much all Jensens, Oxfords and Fender speakers have resonance around 90hz?
1x12 Tweed - 62 Hz same thing as above.
2x12 Class A 30W - 56 hz low resonance, Celestion Blues, Greenbacks have resonance of 75 hz?
2x12 Match Chief - 61 Hz same as above, Matchless G12M25 and G12H30 have 75 hz Ls?

I'm sure there are more, but those are some that I use that just seem wrong, any ideas?

Thanks!

 

[FractalAudio]

They are measured values of the speakers in the actual enclosures. The values on a spec sheet are with the speaker mounted on an "infinite baffle".

 

[zafreemusic]

They are measured values of the speakers in the actual enclosures. The values on a spec sheet are with the speaker mounted on an "infinite baffle".

Thanks for the timely response.
I understand they are measured values, I guess I'm more just confused how the low resonance gets lowered when placed in the enclosure? From my understanding the resonance freq increases when put in a cab? Are you able to explain why this happens?

 

[zafreemusic]

Think I may have found my answer through googling "infinite baffle"

"One of the biggest things that you can see is that the resonant frequency is actually shifted down when the speaker is in the cabinet as opposed to in free air. In the graphs, above, the F(s) of the speaker in free air is about 58 Hz, while the F(s) of the speaker in the cabinet is about 53 Hz."(Source: courses.physics.illinois.edu/phys406/sp2017/Student_Projects/Spring01/PPoongbunkor/Piya_Poongbunkor_TS.pdf)

"This means that for larger box or cabinet sizes, a lower resonant frequency can be achieved with a given loudspeaker unit. " (Source: electronics-notes.com/articles/audio-video/loudspeaker/infinite-baffle-speaker-cabinet.php)

Is this correct?

 

[boyce89976]

Think I may have found my answer through googling "infinite baffle"

"One of the biggest things that you can see is that the resonant frequency is actually shifted down when the speaker is in the cabinet as opposed to in free air. In the graphs, above, the F(s) of the speaker in free air is about 58 Hz, while the F(s) of the speaker in the cabinet is about 53 Hz."(Source: courses.physics.illinois.edu/phys406/sp2017/Student_Projects/Spring01/PPoongbunkor/Piya_Poongbunkor_TS.pdf)

"This means that for larger box or cabinet sizes, a lower resonant frequency can be achieved with a given loudspeaker unit. " (Source: electronics-notes.com/articles/audio-video/loudspeaker/infinite-baffle-speaker-cabinet.php)

Is this correct?

Correct.

 

[zafreemusic]

Correct.

Awesome thank you, out of the rabbit hole and back to playing

 

[RDH]

It depends on the enclosure, open back has a lower resonance value than closed back. Closed back usually shifts the resonance upward.

 

[boyce89976]

Awesome thank you, out of the rabbit hole and back to playing

There are some other factors involved besides internal cabinet volume (such as open back or closed back design, port tuning, etc...), but in general, yes that's correct.

 

[Joe Bfstplk]

Closed back usually shifts the resonance upward.

...and damps it a bit, too, due to the resistance of the air in the box to changing pressure. The smaller the box volume, the more of a factor this is.

 

[JJunkie]

Hey guys, just wondering if the impedance values for the various factory (and maybe 3rd party) IRs are published together anywhere? Cheers

 

[IronSean]

Hey guys, just wondering if the impedance values for the various factory (and maybe 3rd party) IRs are published together anywhere? Cheers

They would have to be individually measured. And since they weren't measured when the IRs were made there's not much that can be done. Going forward they can be captured by people when they make IRs if the IR makers are willing (although I can't remember if we can add our own in the current UI). The current best is just to pick a curve for a cab that seems to match the cab the IR was made with.

 

[Smittefar]

It would make me happy, if the different curve names indicated, what kind of speaker is inside the cab. Most of them just state the brand name and the speaker configuration.

 

[edo]

They are measured values of the speakers in the actual enclosures. The values on a spec sheet are with the speaker mounted on an "infinite baffle".

Does this mean that for authentic accuracy, one should select the speaker curve preset based on the ir he’s using? Eg, if I were using a brit800 (defaults to 4x12 Brit800 speaker impedance curve) with a 4x12 greenback ir, I should select the 4x12 Brit greenback curve?

 

[Smittefar]

Yes that would be the most authentic.

Try them out. The differences are quite big.

 

[DLC86]

It would make me happy, if the different curve names indicated, what kind of speaker is inside the cab. Most of them just state the brand name and the speaker configuration.

FWIW I can tell you the speaker model for one curve since I personally measured it and sent to Cliff:
2x12 Bassbuster is a Fender Bassbreaker cab loaded with two 8 ohm Fane F70 speakers

 

[edo]

Yes that would be the most authentic.

Try them out. The differences are quite big.

Oh, yeah, I know! It would be useful to
know something more about the different curves for similar cabs (for example, what’s the difference between a 4x12 Brit tv vs a 4x12 Brit basketweave etc?)