why no sEALed fEARfuls???

[chunkstyle]

Ferrari FF.

I imagine the OP has learned quite a lot from this thread... and maybe even got an answer to his question!

 

[john turner]

Why don't they make Ferrari's full time 4 wheel drive? I like to go muddin' but I like Ferrari's.

ferrari may not make those kind of vehicles, but lamborghini certainly has.

 

[JimmyM]

+1. Ampegs recent woes that Jimmy is too aware of probably stem from overlooking this fact.

Ah, the impedance thing...enlightenment hits my head once again!

 

[will33]

+1. Ampegs recent woes that Jimmy is too aware of probably stem from overlooking this fact.
Who knows? It's not impedance, impedance is not measured in decibels. What's more pertinent is this sealed (blue) versus ported (red) trace:

Tubes don't like higher impedance loads, so the lower maximum impedance of the sealed cab is more tube friendly. SS prefers higher impedance loads as that reduces current demand, so they're happier with ported. But again the skills of the designer (or lack of same) enter the equation, as you can tweak the impedance to suit specific needs.

This and Dukes power/voltage read explains a lot but just out if curiosity, what's happening when I play guitar through my bassman with openback speakers? If the "lack of a box" is letting the impedance be closer to it's free air measurement that's anything but even or low. Or am I way off base with that.

 

[chunkstyle]

ferrari may not make those kind of vehicles, but lamborghini certainly has.

The Rambo Lambo.... Sick sick sick.

 

[44me]

Tubes don't like higher impedance loads, so the lower maximum impedance of the sealed cab is more tube friendly. SS prefers higher impedance loads as that reduces current demand, so they're happier with ported. But again the skills of the designer (or lack of same) enter the equation, as you can tweak the impedance to suit specific needs.

Bill, thanks for providing the plot. It better illustrates exactly what I was referring to.

I would say that tube amps and solid state amps both interact with speakers, but they do so differently. Most speakers are designed for solid state amps, so it seems like the tube amp is the one that's interacting strangely, but arguably it interacts less with the speaker's impedance curve.

Duke, your point about SS amps interacting with the speaker more than tube amps is an interesting perspective. I guess my thinking comes from the other direction since I assume that the cab designer is expecting a low impedance source. If you remove that assumption and think about how widely the current is varying over frequency there’s definitely a lot more interaction with the SS amp. It probably would have been better if I had written that you’ll see more variation in low end response with tube amps than with SS due to cab impedance varying with frequency. That's a good paper you referenced. Besides the technical, the first section was very germane to this thread.

It never ceases to amaze me how emotional people get over these one-or-the-other topics. Every design has tradeoffs, and not everyone agrees how to prioritize the key attributes. It’s pretty clear that the market prefers the general tradeoffs of ported enclosures over sealed, but this doesn’t mean that everyone has to.

By the way, is it better to view this forum on a PC or a Mac? I used to limit my Mac browsing to indie threads, but lately it seems to work better on pop.

 

[chunkstyle]

What's the best computer for death metal?

 

[rpsands]

Exactly. So why would Ampeg want to change an Ampeg SVT 810 into a ported cab, anymore than greenboy making a sealed fEARful?

Pointless. So why the question? Why not ask why Ampeg (or any other maker), why they don't design something other than what they design?

IMHO, it would make a lot of sense for Ampeg to offer a ported 8x10 with port plugs -- why? because it'd offer an extra 3db or so under 100hz for free (at least for solid state amps, I guess? Whatever).

The SVT-3 Pro would probably sound a crapload better on the ported 8x10

 

[rpsands]

What's the best computer for death metal?

Amiga.

 

[JdoubleH]

The Rambo Lambo.... Sick sick sick.

That or this:

 

[seamonkey]

what does this graph illustrate ? damping factor or impedance or frequency response? the tube line looks like a speaker impedance curve.

This was frequency response from the amps into a common speaker load. SS is flat, but as the double blind test showed, it can be EQ'd to that of a tube amp used.

Because the higher output impedance of the tube amp, the frequency response tends to follow the impedance curve of the driver in the box.

If you had a ported cab, you'd have two humps in the bass.

This is simple ohms law. The internal impedance is in series with the speaker. At lower frequencies when the driver impedance is high, then there's more voltage across the driver. At higher frequencies where the driver hits 8 ohms, then there's less voltage across the driver.

 

[kraigo]

In addition to RPSands' response, nobody in bassdom is making 500 cabs a day.

KO

Hey, damping material isn't cheap from a manufacturers standpoint either.

$5 you say? (example, I know you didn't say anything about costs) Try loading 4-500 cabs a day with $5 worth of damping then get back to me. Damping material is relatively expensive for what it is, so $5 is a low ball.

I don't think it's acceptable from a buyers perspective, but from a quality point of view I can tell you all about it.

1. Commercial cabs start with the Acoustics guys coming down to the production QA booth to sine wave the newest and greatest. They develope a production standard from THE standard in a less than ideal environment (some mics placed a meter or so from the conveyor belt in an insulated chamber that run through a O scope).

2. Production begins, but the enclosures do not check to the standard. Instead of a fully lined enclosure, there's now only a strip of insulation stapled to the floor and partial back wall. Acoustics comes back down to approve the new specs. Clear sailing for this run.

3. Run no. 2. The speaker specs have changed, god help us if there's a new vendor. No new vendor, but the speakers are different. Acoustics takes a cab back to the lab, then returns with a thumbs up! Production can continue. Just rewrite the curve....

4. In the middle of this 600 PC run, the sine wave varies wildly! Acoustics is too busy to come by, so the production manager calls the QC chief to tell him the line has to run now! So, that's what happens. Turns out some wrong caps where inserted in the crossover assembly... That's what warranties are for.

Remember, business is about making a profit. Though, sometimes it tough to stomach.

 

[billfitzmaurice]

This and Dukes power/voltage read explains a lot but just out if curiosity, what's happening when I play guitar through my bassman with openback speakers? .

It's actually a ported cab, one with a very large port, resulting in tuning too high for bass, usually around 200Hz. It can subjectively make a guitar sound deeper, but that's only relative to the fact that guitar doesn't go very low anyway. Just as most electric bass content is in the second and third harmonic so is most guitar content. And that's why guitar cabs aren't ported, the frequencies that gain from porting are irrelevant with guitar.

 

[will33]

Cool. I always thought it was too big to really function as any kind of port and just let the sound off the back of the speakers fly out the back and bounce off a wall or something.

So that would also have an impedance spike at this 200hz (ish) port tuning??

Not that matters I guess. It sounds good and hasn't caused any problems in it's 30+ years of operation.

 

[DukeLeJeune]

[An open-back guitar cab] is actually a ported cab, one with a very large port, resulting in tuning too high for bass, usually around 200Hz.

That was my analysis also - that "open back" = "high-tuned port", though I don't think I'd seen anyone else post the same conclusion.

I've read about (though never actually witnessed) what some call a "de-tuned" guitar cab, which is where you remove two speakers from an otherwise sealed 4x12. Same thing - it turns into a big, high-tuned ported box.

 

[will33]

I have seen some B52 and maybe crate guitar 412 cabs that had what amounts to a back that was too short forming a sort of slot port along the back. I didn' know anything about speakers at the time and don't if it was functional/useful for guitar or if it was just a selling point for metalheads the like to detune and crank the bass. May reverse engineer one if I see it again just out of curiosity.

 

[billfitzmaurice]

So that would also have an impedance spike at this 200hz (ish) port tuning??

An impedance null.

 

[PhiDeck]

regardless of the provenence of this particular data, this graph _definitely_ illustrates how graphing a logarithmic quantity on a linear scale can seriously exagerate the quantities being measured and imply to the layman a much greater difference in measurement than is really present.

I assume you're referring to the vertical axis, as the horizontal axis is clearly logarithmic.

The logarithmic aspect of human perception is already captured in the equations for calculating differences in dB:
= 20*log(x/r) for voltage, current or their analogs
= 10*log(x/r) for power and its analogs

Therefore dB measurements are plotted on a linear scale, as in the graph you referenced. Otherwise you would be plotting log(log(x/r)).

r= reference

 

[john turner]

I assume you're referring to the vertical axis, as the horizontal axis is clearly logarithmic.

The logarithmic aspect of human perception is already captured in the equations for calculating differences in dB:
= 20*log(x/r) for voltage, current or their analogs
= 10*log(x/r) for power and its analogs

Therefore dB measurements are plotted on a linear scale, as in the graph you referenced. Otherwise you would be plotting log(log(x/r)).

r= reference

i stand corrected, thank you.

i should probably not attempt to think audio, let alone post about it, when i'm working on microcode for a the state machine of a 32 bit cpu. by hand. heh.

 

[Arjank]

That was my analysis also - that "open back" = "high-tuned port", though I don't think I'd seen anyone else post the same conclusion.

An open-back cab acts more like a transmissionline thats very short. The "port" is in this case the whole cabinet, so you don't have a bassreflex system (helmholzresonator) but a short transmissionine.
Btw. I don't know the "bassman" cab, maybe it is not totally open on the back. If the back has a broad slot (and is not totally open) it will then again act more like a helmholzresonator.