Ampeg Isovent - Jack Plate Circuit Board.

[Nicholas Orick]

NOT likely to DeTune the fretless six, especially when it uses a 2TEK brdige which prohibits DeTuning, but what you are suggesting reminds me if the Picollo Bass.

Having just typed all that, it occurs to me that maybe you could re-string and re-tune so your lowest note is higher than F. Say, F# standard or G standard. Get up above that problematic resonance. With the right bunch of experimental bandmembers, that could be fun to explore. Find a drummer who uses a small kick, and somebody that plays tenor guitar, or some brass...In the right context, it could sound interesting...let that cab’s limitations or idiosyncrasies be an inspiration in a new direction. Hey, Mark Sandman and his two-string slide bass (tuned D and A, I think) did some cool stuff with baritone sax and drums in the band Morphine.

EDIT: I am pretty far off the “how do I fix this cab’s issue” here but I’m not making fun. Trying to think outside the box, so to speak. See what I did there...Anyway, you’ve mentioned having other rigs, so if the F-Bomb turns out to be an unavoidable acoustic “feature” of this cab no matter what, this is one way you might be able to keep it and have fun with it without the resonance F-ing up your playing fun.

I have a Bag End 18 which does fairly well. Probably I will simplu get the Rolls RPQ, and when combined with a Dyna Comp, I will be able to pretty much Surgically Remove and Flatten Out the F Bomb.

I am NOT going to worry about it.

 

[Nicholas Orick]

I think this has been covered more than once in this thread, but even if I’m mistaken, pretty much all the amps and cabs-related posts on TB address this question if you read them with an eye towards current trends. The modern way involves the fact that big wattage is cheap and readily available now. Mega-high-performance, lightweight drivers—neodymium magnets, take a bow!—are available now. So the modern way uses big watts from light, compact amps to drive power-hungry drivers in tuned, ported boxes. It takes a lot of power, but the acoustic performance is more even and accurate over a wider range.

Whereas in the not-so-distant past, watts were expensive, heavy and bulky and driver technology was not what it is today, so various box technologies like folded horns and isobaric cabs were tried as means to extract maximum SPL from limited watts and driver technology. The tradeoff for the performance boost was bulk, weight, woodworking complexity and the fact that the performance boost only worked over a narrow range of frequencies.

I see this as being analogous to engine technology and performance, in a way. I drive a ho-hum 2014 Grand Caravan. It has a 3.6-liter V6 with nearly 300 hp, which produces something like 90% of its peak torque over most of its operating range, on regular gas, and idles smoothly and quietly while getting mpg in the mid 20s in a vehicle that weighs more than two tons.

It does this because it’s got a bunch of computer control over variable valve timing, fuel delivery, ignition timing, throttle position and a six-speed automatic tranny. It’s pretty good at pulling reasonable performance out of this little engine in this heavy vehicle by juggling a bunch of parameters.

When I was a high-school gearhead, this would have been science fiction. 300 hp back then from an engine that size would have involved a really high compression ratio, a wild cam, giant ports and heavy breathing through multiple carburetors, idling rough and a narrow useful powerband that started somewhere north of 2,000 rpm. And getting about 7 mpg on your way to buy 100+ octane gas at the local airport.

You could have done it with 1980s tech, but it would have involved heavy compromises with significantly worse drivability. And emissions that wouldn’t pass inspection in anything made after 1966 or so.

In my comparison, buying $3.00-per-gallon avgas to get 7 noisy, revvy mpg is your F-Bomb.

And adding additional EQ control to tame that F-Bomb is analogous to swapping in a later-model fuel-injected computer-controlled engine, because you like the car despite its limitations compared to newer cars that handle better and are more advanced in various ways. Some guys like to do stuff like that, even though it’s more work (and involves more work-arounds) than just buying a better-performing new car.

The initial goal was to in some way get the Isovent more or less fully operational at a decent level while retaining as much of the original cab as possible.

In other words with No Artifacts like F Bombs.

I didnt know Eden had something to do with the development of the Heavy Mag Cones, and assumed Celestian was the OEM, so before I began this thread I contacted Celestian, to which they made their recommendation.

Something called a BN-400 X Neo cone.

If the Isobraic system will NOT work then I will consider changing to a Neo cone.

In other words I will do away with the Isobraic loading, use a more powerful single cone, and adjust the cabinet from there.

Retainability is one thing and Usability another.

 

[frankie5string]

Both the Bose and the Apogee (which I did some design work for many years ago) products are based on solid science and the cause of the non-linearities were easily defined and quantified. That made (at least most of) the corrections more practical. The Apogee processing was both eq and dynamics based, most of those products were trying to get the most SPL out of the box. I think that's the project where I learned about IASYS, specifically to quantify speaker non-linearities.

Absolutely. I was only using those two examples of analog signal processing, because I thought the discussion on DSP was just way beyond what was going to help the situation. He seems to like everything about the cabinet except for the wolf-tone he's getting. While there's no accounting for taste, he can probably dial that out.

There's a huge difference between a system which is specifically engineered to work with its components for something where the sum is greater than its parts, and one that's cobbled together based on loose ideas and wishes. However, he really wants to use it, even if it's with an amp that's really not designed to work with that cabinet.

Now when he speaks of dialling stuff back "IN" I just shake my head... does he mean turning the amp up louder?

The Apogee system I had was amazing, and the Bose system - even though I was constantly slagged about it by audio gear heads - made me money and gave me satisfied clients. Now that TOA/ABi rig I had - was not so amazing... That's another story.

 

[Rich Fiscus]

Amen Francis!

How about the guys getting all excited about precision while blowing off accuracy?

A number to the 6th decimal place doesn't matter one bit of the accuracy is only possible to 1 decimal place.

I had never even been taught the definitions of accuracy and precision until my first college electronics class. My kids also made it all the way through high school without it being covered once.

 

[NKBassman]

While we’re on the topic of poor designs, you should ditch the Dyna Comp too and get a compressor that’s optimized for bass.

 

[agedhorse]

assumed Celestian was the OEM, so before I began this thread I contacted Celestian, to which they made their recommendation.

Something called a BN-400 X Neo cone.

If the Isobraic system will NOT work then I will consider changing to a Neo cone.

Why would you think Celestion was the OEM? They didn't even make a bass speaker back in that era.

Why would you use a Neo driver in that otherwise heavy cabinet?

 

[Nicholas Orick]

Read

Why would you think Celestion was the OEM? They didn't even make a bass speaker back in that era.

Why would you use a Neo driver in that otherwise heavy cabinet?

Thread

 

[seamonkey]

At some point in time the Isovent designers must have listened to it and liked it in some situation. I think it was in the SLM days and they had some talented designers.

It'd be interesting to pick up a impulse response of a isovent before the cab and crossover get all hacked up.
Plenty of sites/videos and many high quality plugins can create impulse responses. Maybe some IR lib maker will make one, but I doubt it as people really only want "popular" cabs and not one off designs.

I know many "pro" level software packages can model the cab and they produce charts and impulses to let you hear, but it's too much work to find TS on old custom drivers.

 

[agedhorse]

Back then, there was a well deserved perception to design for the maximum SPL, almost regardless of the tone tradeoffs. Especially trying to do this in a (relatively compact (though heavy) package.

With the limitations in bass amp power (due to both cost and technology), there was a need by some customers to be heard in larger situations, the tradeoffs of being not heard was worse then the artifacts.

The good 'ol days weren't all that great in reality. Time passed seems to make the heart grow fonder and the memory foggier.

 

[BioWeapon]

At some point in time the Isovent designers must have listened to it and liked it in some situation. I think it was in the SLM days and they had some talented designers.

It'd be interesting to pick up a impulse response of a isovent before the cab and crossover get all hacked up.
Plenty of sites/videos and many high quality plugins can create impulse responses. Maybe some IR lib maker will make one, but I doubt it as people really only want "popular" cabs and not one off designs.

I know many "pro" level software packages can model the cab and they produce charts and impulses to let you hear, but it's too much work to find TS on old custom drivers.

TS specs are pretty easy to get. Dayton's DATS software does it in minutes really, the only hassle is pulling the driver from the cab.

 

[redstrand]

At thirty pages, this has been entertaining.

 

[Nicholas Orick]

I think this has been covered more than once in this thread, but even if I’m mistaken, pretty much all the amps and cabs-related posts on TB address this question if you read them with an eye towards current trends. The modern way involves the fact that big wattage is cheap and readily available now. Mega-high-performance, lightweight drivers—neodymium magnets, take a bow!—are available now. So the modern way uses big watts from light, compact amps to drive power-hungry drivers in tuned, ported boxes. It takes a lot of power, but the acoustic performance is more even and accurate over a wider range.

Whereas in the not-so-distant past, watts were expensive, heavy and bulky and driver technology was not what it is today, so various box technologies like folded horns and isobaric cabs were tried as means to extract maximum SPL from limited watts and driver technology. The tradeoff for the performance boost was bulk, weight, woodworking complexity and the fact that the performance boost only worked over a narrow range of frequencies.

I see this as being analogous to engine technology and performance, in a way. I drive a ho-hum 2014 Grand Caravan. It has a 3.6-liter V6 with nearly 300 hp, which produces something like 90% of its peak torque over most of its operating range, on regular gas, and idles smoothly and quietly while getting mpg in the mid 20s in a vehicle that weighs more than two tons.

It does this because it’s got a bunch of computer control over variable valve timing, fuel delivery, ignition timing, throttle position and a six-speed automatic tranny. It’s pretty good at pulling reasonable performance out of this little engine in this heavy vehicle by juggling a bunch of parameters.

When I was a high-school gearhead, this would have been science fiction. 300 hp back then from an engine that size would have involved a really high compression ratio, a wild cam, giant ports and heavy breathing through multiple carburetors, idling rough and a narrow useful powerband that started somewhere north of 2,000 rpm. And getting about 7 mpg on your way to buy 100+ octane gas at the local airport.

You could have done it with 1980s tech, but it would have involved heavy compromises with significantly worse drivability. And emissions that wouldn’t pass inspection in anything made after 1966 or so.

In my comparison, buying $3.00-per-gallon avgas to get 7 noisy, revvy mpg is your F-Bomb.

And adding additional EQ control to tame that F-Bomb is analogous to swapping in a later-model fuel-injected computer-controlled engine, because you like the car despite its limitations compared to newer cars that handle better and are more advanced in various ways. Some guys like to do stuff like that, even though it’s more work (and involves more work-arounds) than just buying a better-performing new car.

@agedhorse

Here is why I thought a replacement speaker cone.

It was Celestian's idea use a Neodymium Mag.

If the Isobraic Loading refuses to work then maybe I will switch to using just one stronger speaker cone.

This is why.

 

[thetragichero]

box dimensions vs ideal dimensions for driver?

 

[redstrand]

Time to buy a new cab, this has been beaten to death and then some.

 

[Jeff Scott]

Trying to think outside the box...

Good thinking, given the problem at hand is the box.

NOT likely to DeTune the fretless six, especially when it uses a 2TEK brdige which prohibits DeTuning...

What so special about a 2Tek bridge that prohibits retuning your strings?

 

[Jeff Scott]

Time passed seems to make the heart grow fonder and the memory foggier.

Why, you young whippersnapper! My mind is sharp as a ......... uh, what were we talking about?

 

[abarson]

Well besides throwing the Isovent away, which I am NOT going to do, what is going to fix the F Bomb problem?

Really?! There were multiple suggestions of using EQ back on page 1. EQ is separate and exterior to the internal crossover. EQ is for treating the entire signal before entering the speaker, and offending frequencies can be identified and filtered before reproduction.

The crossover is specific to discriminating the frequencies it receives and directing them to the appropriate speaker. This is fundamental to any signal path. In your case EQ is required to filter out the offending frequency and that isn't the job of the crossover.

Source -> signal boost (preamplification) -> tone shaping (equalization) -> amplification -> speaker discrimination (crossover) -> speaker

Understand and address each link in this signal chain. Otherwise it's like working on your transmission when your carburetor is clogged.

 

[BigBigGuy44]

I'm really starting to like OP. After the IsoVent is fixed, maybe he can go on to solve even more complex problems like making a shower-installed waterproof electric hairdryer.

 

[Jim C]

I'm really starting to like OP. After the IsoVent is fixed, maybe he can go on to solve even more complex problems like making a shower-installed waterproof electric hairdryer.

Considering the application, I'd think you'd want to start with high voltage / high current to get the job done quickly...

 

[BioWeapon]

Considering the application, I'd think you'd want to start with high voltage / high current to get the job done quickly...

Cmon now! He DID say waterproof!