Ampeg Portaflex cab/dolly question

JimmyM · #1 11-23-2010, 09:02 AM

one of our portaflex club regulars, beans-on-toast, posted this excerpt from the manual that came with portaflexes:

"Important: Remove the dolly when the amp is in use. Because the dolly will absorb vibrations, it will also absorb sound waves. There is a definite gain in 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."

i asked about how much real world effect the dolly has because it seems like mine pretty much sounds the same and has as much power whether on the dolly or on the floor. beans suggested i throw it to the speaker experts. so i am...

does the dolly really affect it to where i should be taking mine off for gigs?

stiles72 · #2 11-23-2010, 10:38 AM

What I notice is that when the dolly is removed, the cab causes the floor/walls etc... to vibrate more from the low frequencies, creating the perception of more "Umpfff" (rattling things off the wall). The old Portaflex manual also says that by not removing the dolly is like "a car spinning it's tires on ice". I think thats a bit extreme - but from reading the baby bass and portaflex manuals you can tell they encouraged any method that made for a bigger deeper sound, whether the terminology used was "scientifically correct" or not. Since you don't shoot for a booming sound - you probably won't notice as much of a difference as I do with mine.

stiles72 · #3 11-23-2010, 10:42 AM

Forgot about this thread also:

Can someone explain

fu22ba55 · #4 11-23-2010, 10:54 AM

The troubling quote from the manual for me is "the speaker is working harder than it should"

That implies to me that the speaker has to work harder to move the cone when it's on casters. As if the cab is attempting to roll in the opposite direction of the cone every time it moves.

Looks like BFM already called BS on this in the thread stiles72 referenced.

Sounds better on the floor? Sure, yes, to my ears. But I don't think the speaker would be any less efficient when on casters. Sounds like cork sniffing to me. (Or glue sniffing.)

Sounds like another Mythbusters episode: Measure SPL with identical amp settings on casters, wood stage, concrete stage, suspended with filament...

beans-on-toast · #5 11-23-2010, 11:26 AM

Just to be complete, I'll crosspost this.

Quote:

Originally Posted by JimmyM

hey, let's revisit this for a second. is this really how it works? because if it is, i can't hear it. how much vibration could the dolly absorb to where it affects the cab's performance negatively? i do mostly one nighters so i just leave it on the dolly.

Quote:

Originally Posted by beans-on-toast

That's what they claim, I figure that they must have a reason for stating this. In theory, the energy needed to make the dolly vibrate, is going to come from the sound waves and this would translate into lost sound energy and the speaker would have to work harder to produce the same sound level. In practice, as you ask, how much energy would you really loose and could the extra energy needed to compensate for the vibrating dolly be enough to put the driver at risk of blowing.

I usually remove the dolly and place the amp on a vibration isolator called a Gramma from Auralex. I find that the decoupling helps to keep the low end clear, especially on spongy surfaces like you can find on some of those old stages. A dolly can be acting like a spongy stage. There are a lot of isolation products being marketed and people use them. There must be something in all this.

Since you stack two cabs, maybe the additional weight would make any negative effects caused by the dolly vibrating less apparent. I think that it would be more noticeable at higher volume levels.

coreyfyfe · #6 11-23-2010, 11:28 AM

I took that statement (speaker working harder) to mean that if you are trying to pump out the bass, you'd be better placing the amp on the floor, getting a bit of flood coupling so to speak, and a bit of a bass boost. Where that would make an audible difference more than a few feet from the amp isn't clear, but if the amp is just a monitor for the player then it's possible that they would hear better with a little added bass.

Either way, I don't take mine off of the dolly. I like the way it sounds overall and I think the bass response is fine. More would probably be too boomy actually.

coreyfyfe · #7 11-23-2010, 11:30 AM

Quote:

Originally Posted by fu22ba55

Sounds like another Mythbusters episode: Measure SPL with identical amp settings on casters, wood stage, concrete stage, suspended with filament...

That would be something. Hmm, they do take suggestions....

Caca de Kick · #8 11-23-2010, 11:41 AM

I always take the dolly off my Portaflex and it's extension cab, and both sit on the floor. I can definitely tell the floor coupling helping out as much as possible in *my* situation of a low powered rig and a loud rock band. Actually my drummer was the first to notice it as some clubs he relies on the drum riser's feel of bass frequencies than just what little he ends up getting in the drum monitor...he said there's a huge loss of bottom with the cabs on the dolly.

OldFenderPlayer · #9 11-23-2010, 01:49 PM

Its enough work just to get my B-15N to a gig, but to take it off the dolly once I'm setting up ... I don't think so! But .... when I use my Port-A-Flex its for low-volume jazz or coffee house gigs. If I'm in a situation where I need more volume from them amp, I'll definitely give sans-dolly a try.

JimmyM · #10 11-23-2010, 03:30 PM

OFP, i feel about like you do on the subject. but it's just one of things i got more curious about once i heard it, so i just wanted to see if i'm really degrading the performance and don't know it. but at this point, i'm kind of feeling like it's all academic since i usually have enough guns with the dolly on not to worry about it so much.

greenboy · #11 11-23-2010, 03:44 PM

As far as "working harder", there's hardly enough energy being exerted there to be a factor.

Do the dollies rattle? Are they soaks? If not, other than direct contact sometimes exciting hollow floored areas/stages or rattling stuff a little more because of mechanical transmission, there's not going to be any big change in actual acoustic coupling. Though perceptual/subjective changes will be noted and/or argued ; }

A few inches is just not enough raising to cause any audible loss of wavelength-related bass coupling, though for really short players the change of distance to the midrange sourcing may make it seem like something changed in the bass. But it didn't.

JimmyM · #12 11-23-2010, 03:55 PM

glad you chimed in, greenie. nice to know it's nothing to worry about. the dollies aren't any sort of soaks as far as i know. just a piece of wood with casters, a thumbscrew, and some rubber legs.

love the happy christmas sentiments, too!

greenboy · #13 11-23-2010, 04:06 PM

Yep, the dollies on the ones I've played were just fine. Actually before I was a bass player and was setting up a studio with a partner, it was one of these babies we snagged for our venture. So I do have a little time in with them...

It was good talking with you the other day, Jimmy. But what I told you about the weather? Well, it got nastier up here ; }

pgk · #14 11-23-2010, 05:49 PM

i made an ampeg style tray for my bag end cab, with the knurled knob and everything. but i used primo 4" blue rubber Guitel casters for it simply because they're the greatest. so it's the wheels, the tray, 2" hard plastic spacer feet between the bottom of the cab and the top of the tray. it raises the whole cab up 7" and i can definitely feel and hear the improvement, esp on wobbly and/or hollow stages. to my ears it's more decoupled from the stage than without the tray, for sure. i feel the sound going out into the room more, rather than the low end going down into the floorboards as much as without the tray. maybe i'm smoking crack i dunno, or maybe i can simply hear the cab better, but i for one think it works great and that tray never comes off

JimmyM · #15 11-23-2010, 06:35 PM

Quote:

Originally Posted by greenboy

Yep, the dollies on the ones I've played were just fine. Actually before I was a bass player and was setting up a studio with a partner, it was one of these babies we snagged for our venture. So I do have a little time in with them...

It was good talking with you the other day, Jimmy. But what I told you about the weather? Well, it got nastier up here ; }

time for ice fishing!!! it's gotten cold here, too. at night it's been down in the mid 50's

the tradeoff for not having mountains.

good talking with you too, bro.