Question on "amp in the room" parameters

[Hektor]

It is my feeling that as far as amp modeling and effects, current technology came a long way to a point that most of us feel comfortable to use it in recordings. Having said that, I still feel that the weakest link in the chain is the speaker/cab/IR part especially for live performance when the "amp-in-the-room" experience is required.

So I have a somewhat theoretical question to all the speaker/cab/IR gurus:

1. Assume that we have an ideal FRFR speaker cab
2. Assume that we have a specific guitar speaker cab
3. Lets now measure the freq response of this guitar cab using an ideal reference mic in an open space (i.e. no room related effects) and translate it into a high-res IR.
4. I assume that if we now measure the response of the IR+FRFR system in similar conditions we’ll get practically similar response as measured with the guitar cab.

My related questions are:

1. Are these two systems going to give the same “in-the-room” experience? (you can assume the guitarist is standing in the same point as the ref mic, if needed)
2. If not, what are the factors that still differentiate these systems ?

In other words, assuming similar frequency response, what are the main speaker and cab characteristics that differentiate one system from another, and how they affect what we hear and feel while playing. I know there are many speaker/cab parameters so please focus on those that have a major impact on the “in-the-room” aspect.

 

[Gencives]

maybe the quantity of air the cab is moving ?

 

[Jay Mitchell]

So I have a somewhat theoretical question to all the speaker/cab/IR gurus:

1. Assume that we have an ideal FRFR speaker cab

A huge assumption, and a critical one.

2. Assume that we have a specific guitar speaker cab

Check.

3. Lets now measure the freq response of this guitar cab using an ideal reference mic in an open space (i.e. no room related effects) and translate it into a high-res IR.

Done and done. Three of the factory cab sims are fully compliant with 2. and 3.

4. I assume that if we now measure the response of the IR+FRFR system in similar conditions we’ll get practically similar response as measured with the guitar cab.

Correct.

1. Are these two systems going to give the same “in-the-room” experience?

They will come very close in the case of a closed guitar cab, less so if the cab is open back. See viewtopic.php?f=13&t=14673&p=138339&hilit=acoustic+dipole#p138339 for more detail on the open-back effect.

I describe a way to create the open-cab effect with a FRFR system here: viewtopic.php?f=11&t=11773&p=112366&hilit=acoustic+dipole#p112366.

 

[barhrecords]

Jay,

Can an IR create the effect of an open-back cabinet from a listening position that avoids the bad artifacts of an acoustic dipole?

I was curious if the desired (subjective term but meaning avoiding the unpleasant acoustic dipole artifacts you mentioned) open-back cabinet sound can be perceived by listeners in a live performance venue using a mono FOH PA and an IR.

Thanks,
Richard

 

[Jay Mitchell]

Jay,

Can an IR create the effect of an open-back cabinet from a listening position that avoids the bad artifacts of an acoustic dipole?

In "a listening position that avoids the bad artifacts of an acoustic dipole," the sound is no different than the sound from a closed cab would be.

I was curious if the desired (subjective term but meaning avoiding the unpleasant acoustic dipole artifacts you mentioned) open-back cabinet sound

The "desired... open-back cabinet sound" to which you refer is specifically the result of dipole behavior, and it is only evident to the player and (possibly) others on the bandstand. Playing through an open back cab offers no advantage to any member of the audience.

 

[LMO]

2. Assume that we have a specific guitar speaker cab
3. Lets now measure the freq response of this guitar cab using an ideal reference mic in an open space (i.e. no room related effects) and translate it into a high-res IR.

Done and done. Three of the factory cab sims are fully compliant with 2. and 3.

Which three?

 

[Hektor]

Thanks Jay.

Based on your answer, I understand that if two closed-cab systems have similar freq response at a specific point, both will project similar “in the room” effect (assuming the listener is at the same point). This is regardless of other speaker characteristics that may still be different.

OK, so let’s limit the discussion to closed-cabs and assume an ideal ref mic, single position and no room effects. Would the following be correct:

1. In a case of non-ideal FRFR system, would it be possible the measure its freq response and use that IR in conjunction with the target guitar cab IR to get better results ?
2. If we take this one step further, based on the above process, can a guitar cab A emulate a guitar cab B, assuming guitar cab A has a wider freq range than B ?

My point is, would the IR of the actual cab/FRFR used, once manipulated with the target IR, be helpful in achieving better results ? Has anyone done that ?

 

[randocaster]

I'm simplifying here for those of us who can not design our own high end speaker system and create our own ir's perfectly suiting their needs from years of engineering experience. (basically everyone except Jay) :mrgreen:

FR sounds like a mic'd speaker cab though a P.A. Even the flat mic is still a mic.

A 4x12 cab in the room sounds like a 4x12 in the room.

They are very different, and trying to force one to essentially 'be' the other is not going to ever "get you there 100%".

If you can't live without a cab n the room, just use a cab in the room.

If you like how your tube power amp colors your sound, use it.

The axe-fx is so versatile, because you can define so many ways to use it.

Just my opinion based on my experience. I'm sure there are flaws in my argument though. There always are. :mrgreen:

 

[Hektor]

They are very different, and trying to force one to essentially 'be' the other is not going to ever "get you there 100%".

This is clear. I'm sure most if not all of us experienced this.
I'm only trying to understand why they are very different. Is it only freq response related, or there are other factors involved ?

I was under the impression that there is another important factor other the the freq response which I can only describe in a no-scientific way as an "attack response". Anyway, according to Jay, which I respect his opinion, it is only freq response related.

 

[Jay Mitchell]

I'm only trying to understand why they are very different.

They are a lot less different than the armchair acousticians are claiming.

Is it only freq response related,

No.

or there are other factors involved ?

Yes, but response is by far the dominant one. If you really and truly get that parameter right - which would appear to occur only rarely - you can get the "in the room" effect.

I was under the impression that there is another important factor other the the freq response which I can only describe in a no-scientific way as an "attack response".

You mean transient response. Transient response is determined by frequency response. A properly-acquired IR of a speaker contains the speaker's transient response.

Anyway, according to Jay, which I respect his opinion, it is only freq response related.

I never said that.

 

[Hektor]

Anyway, according to Jay, which I respect his opinion, it is only freq response related.

I never said that.

Sure, my bad. I should have said "it is mainly freq response related"

Any comments on my previous post ?

 

[Jay Mitchell]

Any comments on my previous post ?

They are in the post you just quoted.

 

[barhrecords]

Thanks Jay.

I hadn't thought about the open cabinet effect being only percieved by the player and the other musicians on the bandstand vs. what the audience hears and I wasn't sure if an IR could deliver that effect to the audience or not.

Makes great sense.

I really appreciate your posts and taking the time to reply.

Richard

 

[randocaster]

It never occurred to me that a speaker system designed to be used in full range PA applications would sound, and more importantly feel like a traditional guitar cab. The sound is coming from multiple drivers. And the woofers in a full range system are very different from a regular guitar speaker. It seems unlikely they could ever really give you the the same experience. Sorry if I was nitpicking.

 

[Jack Napalm]

How much 'in-the-room' feel do you get when you are out on stage moving around? I seems to be missing something in this argument that seems to be latest against modelers. I can understand it while rehearsing with band in a room but not out on a stage. I guess maybe a small stage in a small bar but that's about it.

 

[Hektor]

Any comments on my previous post ?

They are in the post you just quoted.

I'm reffering to this:

"OK, so let’s limit the discussion to closed-cabs and assume an ideal ref mic, single position and no room effects. Would the following be correct:

1. In a case of non-ideal FRFR system, would it be possible the measure its freq response and use that IR in conjunction with the target guitar cab IR to get better results ?
2. If we take this one step further, based on the above process, can a guitar cab A emulate a guitar cab B, assuming guitar cab A has a wider freq range than B ?"

 

[joegold]

It never occurred to me that a speaker system designed to be used in full range PA applications would sound, and more importantly feel like a traditional guitar cab. The sound is coming from multiple drivers. And the woofers in a full range system are very different from a regular guitar speaker. It seems unlikely they could ever really give you the the same experience. Sorry if I was nitpicking.

I think Jay actually said this: "They will come very close in the case of a closed guitar cab."

So, you're both right.
It will never be exactly the same as playing through a real guitar cab, but with an ideal system you could get it to sound something akin to the "in-the-room-experience, and it might be close enough that any perceived differences wouldn't matter to you.

I don't think you can get the feel of a wall of 4 X 12 cabs through a pair of 2-way FRFR speakers.
I think that with more than 2 FRFR speakers you could probably get closer though.

Etc., etc.

 

[joegold]

I don't think you can get the feel of a wall of 4 X 12 cabs through a pair of 2-way FRFR speakers.

Actually, rethinking this a bit....
With an ideal FRFR stereo system, having the L & R speakers sufficiently widely spaced, and a really good IR, you probably could get real close to the feel of a wall of 4 X 12 cabs.
Not exact. But real close.

 

[Jay Mitchell]

1. In a case of non-ideal FRFR system, would it be possible the measure its freq response and use that IR in conjunction with the target guitar cab IR to get better results ?

In some cases. Not all deviations from ideal response are equalizable. Some FRFR speakers have substantial response variations depending on your location relative to the speaker. Equalizing the response to flat at one location may actually make it worse at other locations.

2. If we take this one step further, based on the above process, can a guitar cab A emulate a guitar cab B, assuming guitar cab A has a wider freq range than B ?"

If you have the required instrumentation and expertise, this would be possible in principle. Again, directivity is the enemy. Equalizing the signal going into a speaker is only helpful to the extent that the response of the speaker is consistent over a relatively broad angle. This is never the case with 12" speakers operating full range (i.e., with no HF element and crossover).

 

[Hektor]

Thank you Jay. This is very helpful.