Can someone explain

[Ron G]

I have an Ampeg BA-115HPT, I installed the caster wheels straight out of the box and I notice that my amp did not sound like the one I played in the store I thought it was because of the tube the one I played was BA-115HP.

Yesterday after telling my wife I regret buying my amp, when I got home I removed the caster wheels and have it resting on the floor it sound so much better, the way I thought it should.

Why?

 

[billfitzmaurice]

You have to lift the cab at least a foot for there to be any difference, so wheels versus no wheels doesn't matter. But moving the cab closer or further from a wall will make a big difference, as will the size of the room you're in.

 

[Ron G]

I have the amp in the same room/ spot, I just took the wheels off.

 

[Rick Auricchio]

Two possibilities:

1. You're feeling more floor vibration, or the floor is acting as a sounding board.

2. It's a psychological effect.

 

[stiles72]

I always remove the casters from my Ampeg B100R and my 63 Portaflex. Some people will say it doesnt make a difference - but it does to me. Here's some info from the old Ampeg Portaflex manual that you might find interesting reading:

"As mentioned, models B-15N and B-12X are factory equipped with detachable, shock mounted dollys. IMPORTANT: Remove dolly while amp is in use. Since the dolly will absorb vibration, it will also absorb sound waves. There is a definite gain of power if the amp has a solid footing. You may seemingly get enough power with the amp on the dolly, but the speaker is working harder than it should be. You are in effect, spinning your wheels on the ice."

And this is from the Barefaced cabinets site regarding mechanical coupling of a cab with a stage or floor:

"With mechanical coupling the stage/floor is excited by the vibrations from the cabinet or by the acoustic output from the speakers/port and the floor itself becomes a resonating surface like a giant drum skin or speaker cone. The acoustic output from the resonating floor is very unpredictable, centred around the modes of resonance of the floor, which almost always results in a boomy onstage sound and unpredictable offstage sound (depending on how it reinforces and cancels the output from the speaker cabinet)."

 

[bobcruz]

The speaker will sound different/louder/better as it breaks in so perhaps you're just breaking it in more the more you play. The one at the store was undoubtedly more broken in. Breaking in loosens up the stiffness of the springy suspension of the cone and allows it to move farther and faster, I believe. Anyway, enjoy your new amp!

 

[Ron G]

I always remove the casters from my Ampeg B100R and my 63 Portaflex. Some people will say it doesnt make a difference - but it does to me. Here's some info from the old Ampeg Portaflex manual that you might find interesting reading:

"As mentioned, models B-15N and B-12X are factory equipped with detachable, shock mounted dollys. IMPORTANT: Remove dolly while amp is in use. Since the dolly will absorb vibration, it will also absorb sound waves. There is a definite gain of power if the amp has a solid footing. You may seemingly get enough power with the amp on the dolly, but the speaker is working harder than it should be. You are in effect, spinning your wheels on the ice."

And this is from the Barefaced cabinets site regarding mechanical coupling of a cab with a stage or floor:

"With mechanical coupling the stage/floor is excited by the vibrations from the cabinet or by the acoustic output from the speakers/port and the floor itself becomes a resonating surface like a giant drum skin or speaker cone. The acoustic output from the resonating floor is very unpredictable, centred around the modes of resonance of the floor, which almost always results in a boomy onstage sound and unpredictable offstage sound (depending on how it reinforces and cancels the output from the speaker cabinet)."

Thanks, Mechanical coupling.

 

[billfitzmaurice]

"As mentioned, models B-15N and B-12X are factory equipped with detachable, shock mounted dollys. IMPORTANT: Remove dolly while amp is in use. Since the dolly will absorb vibration, it will also absorb sound waves. There is a definite gain of power if the amp has a solid footing. You may seemingly get enough power with the amp on the dolly, but the speaker is working harder than it should be. You are in effect, spinning your wheels on the ice."

I've seen that before, and it's absolute BS, written by someone in their marketing department who had not the slightest clue how sound waves function. At least, I hope he was in the marketing department.

And this is from the Barefaced cabinets site regarding mechanical coupling of a cab with a stage or floor:

"With mechanical coupling the stage/floor is excited by the vibrations from the cabinet or by the acoustic output from the speakers/port and the floor itself becomes a resonating surface like a giant drum skin or speaker cone. The acoustic output from the resonating floor is very unpredictable, centred around the modes of resonance of the floor, which almost always results in a boomy onstage sound and unpredictable offstage sound (depending on how it reinforces and cancels the output from the speaker cabinet)."

I'm surprised to see Alex referencing 'mechanical coupling' from cabinet vibrations. It only exists when the cab is so flimsily built that it should be considered defective. I'm sure that's not the case with Alex's cabs. Floors will vibrate, of course, the source of what causes them to vibrate is the acoustical output of the cab, and where that's concerned Alex's comments are spot on.

 

[Ron G]

all I know before I removed the wheel I was going to buy a amp, I had my ampeg for about 8 month's. It sounds different to me.

 

[Pilgrim]

Don't underestimate the effects of:

1) The rooms acoustics, and;
2) Placement in the room

The more hard surfaces in the room, the more sound bounces, which makes these effects more audible. The store you played in and your home are sure to be totally different acoustic environments...therefore the amp will sound different in each one.

If it didn't sound different, THAT would be worthy of comment.

 

[Jim Carr]

EQ?

 

[UncleBalsamic]

I'm surprised to see Alex referencing 'mechanical coupling' from cabinet vibrations. It only exists when the cab is so flimsily built that it should be considered defective. I'm sure that's not the case with Alex's cabs. Floors will vibrate, of course, the source of what causes them to vibrate is the acoustical output of the cab, and where that's concerned Alex's comments are spot on.

The rest of the info on Alex's website:

The key point to understand regarding coupling is that there are two forms of coupling - mechanical coupling and acoustic coupling.

With mechanical coupling the stage/floor is excited by the vibrations from the cabinet or by the acoustic output from the speakers/port and the floor itself becomes a resonating surface like a giant drum skin or speaker cone. The acoustic output from the resonating floor is very unpredictable, centred around the modes of resonance of the floor, which almost always results in a boomy onstage sound and unpredictable offstage sound (depending on how it reinforces and cancels the output from the speaker cabinet).

You should generally try to avoid mechanical coupling and this can be done by using a well-braced speaker cabinet which vibrates less, isolating the speaker cabinet by reducing the amount of physical contact with the floor (isolating foam/tilting cab/raising onto beer crate) and placing the cab at a more solid part of the stage (i.e. a corner). If you are on a small hollow stage see if it's possible to place the cab off the stage - also make sure that the PA subs are not on the stage, though any sound engineer with a clue will not have done this.

He goes on to explain acoustic coupling as well.

 

[jnewmark]

So, is there a rule of thumb when it comes to raising a cab? I have always done this, just to hear myself better. But, i have read where nothing changes by raising it a foot; others have said that 2-3 feet makes no difference in sound or tone. Does it depend on the cab size, or other factors? I have either used an amp stand or milk crate and it seems like I can always dial in my sound easier from room to room, as opposed to having the cab on the floor.

 

[billfitzmaurice]

So, is there a rule of thumb when it comes to raising a cab? I have always done this, just to hear myself better. But, i have read where nothing changes by raising it a foot; others have said that 2-3 feet makes no difference in sound or tone. Does it depend on the cab size, or other factors? I have either used an amp stand or milk crate and it seems like I can always dial in my sound easier from room to room, as opposed to having the cab on the floor.

Lifting the cab does two things. It makes it easier to hear the mids and highs, which travel in an arc that narrows the higher in frequency you go. It also acoustically de-couples the cab from the floor, with the frequency of the de-coupling dependent on how high off the floor it's lifted. In the case of 3" wheels that de-coupling would occur above roughly 1khz, but that's up where the radiation from the cab is directional and there is no coupling with the floor anyway. The highest frequency where floor coupling will occur is about 200 Hz; de-coupling at 200 Hz would require lifting the cab 1.4 feet off the floor. The most effective use of de-coupling is to limit boom, which occurs roughly from 100 to 150 Hz. That requires lifting the cab between 1.8 and 2.8 feet.

 

[jnewmark]

Lifting the cab does two things. It makes it easier to hear the mids and highs, which travel in an arc that narrows the higher in frequency you go. It also acoustically de-couples the cab from the floor, with the frequency of the de-coupling dependent on how high off the floor it's lifted. In the case of 3" wheels that de-coupling would occur above roughly 1khz, but that's up where the radiation from the cab is directional and there is no coupling with the floor anyway. The highest frequency where floor coupling will occur is about 200 Hz; de-coupling at 200 Hz would require lifting the cab 1.4 feet off the floor. The most effective use of de-coupling is to limit boom, which occurs roughly from 100 to 150 Hz. That requires lifting the cab between 1.8 and 2.8 feet.

Thanks, Bill. BTW, picked up my Jack 210 yesterday !