Ampeg Isovent - Jack Plate Circuit Board.

[Wasnex]

No.

The first Radiator is Powered while the other operates Passively in reaction.

FYI, The owner's reference guide infers both drivers are active. See attached.

 

[farace]

No.

The first Radiator is Powered while the other operates Passively in reaction.

No, on the SVR cabs both the front- and rear-facing drivers are powered. There is a crossover so that only the lowest lows go to the rear, and above that to the front (don't remember the spec but if I find the catalog I can check). There is also a front-facing horn with on/attenuation/off switch. No passive radiators on these cabs. (I did have a pair of Panasonic Thrusters stereo speakers in college that used passive radiators, though.)

 

[farace]

FYI, The owner's reference guide infers both drivers are active. See attached.

I had that manual but sent it along with the cab when I sold it. According to the manual, the front/rear crossover is 150 Hz.

 

[S-Bigbottom]

Trouble is, I still use this, in part or whole

 

[Nicholas Orick]

This is my first GK. I'm very happy with it, and it's very easy for me to dial in a good sound. I still have some Ampegs--a '68 B-15N, '72 B-15S, a '67 Jet guitar amp, a Sound Cube and even a Buster, the last two being battery/AC practice amps. Then there are several Ampeg basses, a guitar, and a bunch of pedals. I won't be divested from Ampeg until I'm cold in the ground.

LOL.

I can understand that.

Ampeg for life.

I like Ampeg but I also like GK and Mesa so ...

 

[Nicholas Orick]

After riding along with this. I remember doing silly things too! My tri-amped system

Um er - Since when did you lose your mind?

.

 

[Nicholas Orick]

Just kidding, you know. But I thought we got it from two relevant sources (not the OP) and one of them had looked in the ports of his own box. I actually had written a whole response challenging the theory that it was horn-loaded box since there isn't much room and I couldn't figure where the 'mouth' was. Then I didn't post it because I thought I might look foolish (imagine!) and erased it. I've seen plenty enough cab designs that appear and/or claim to be horn-loaded but aren't truly operating as horns, and I was afraid that it might a one of those cases. I looked at both the sales lit and the owner's manuals on-line ages ago (page 1) and there was nothing there about a rear-loaded folded horn. But then, there was virtually nothing about the bi-amp inputs either, and that knowledge could have actually been useful, as opposed to more marketing hype. Anyhoo...hadn't meant to cast aspersions.

LOL.

"(NOT the OP)",

Very Funny.

Actually the Isovent is NOT a Horn Loaded Cabinet.

Basically the chamber containing the clamshell loaded 15s is standard ported bass cab.

Yes it has an open mouth but the chamber containing the 15s is NOT a folded horn by any means.

Just a slightly odd shaped box with two ports - one on each side of the speaker cones.

The 210s sit in an upper sealed chamber.

 

[DJ Bebop]

Um er - Since when did you lose your mind?

.

Since I saw the Grateful Dead

 

[Nicholas Orick]

Since I saw the Grateful Dead

LMAO.

Okay - Now I get it.

Very Good.

Very Funny.

Finally Phil Lesh has gone to Hartke, and I guess Larry Hartke has talked Phil into making some order out of Chaos.

 

[Nicholas Orick]

This is considered isobaric

View attachment 3681790

Basically this is the layout of the Isovent.

Yes the overall box is odd shaped for the 210s and the clamshell 215s are angled in a little bit but overall this is the concept.

 

[Wasnex]

LOL.

"(NOT the OP)",

Very Funny.

Actually the Isovent is NOT a Horn Loaded Cabinet.

Basically the chamber containing the clamshell loaded 15s is standard ported bass cab.

Yes it has an open mouth but the chamber containing the 15s is NOT a folded horn by any means.

Just a slightly odd shaped box with two ports - one on each side of the speaker cones.

The 210s sit in an upper sealed chamber.

Here is the rear of the cab to show the ports.

So the front part where 15 is connected does not open in the the rear chamber?

The baffle goes all the way to the back or bottom of the cab like this?

Instead of opening into a port like this?

 

[Nicholas Orick]

I am not saying it's a folded horn. My contention is it's an experiment that is caught somewhere between ported, folded horn, and tapped horn. IMHO it's neither of these in a pure sense. It's closest to what we commonly call a sub scoop.

It's most like an EV T18, EV SH-1800, or JBL 4530 except it uses isobarik loading.

T18
View attachment 3681792 View attachment 3681793

SH-1800 Basically the same cab at the T18, but different woofer in a different orientation.
View attachment 3681784
4530
View attachment 3681794 View attachment 3681785


Electro Voice SH-1810L-ER literature say the box operates as a horn for much of it's range and works as a ported box in the low frequencies. The box is described as a "SubScoop".

I believe the JBL 4530 is supposed to work the opposite. The driver functions as direct radiators at the top of the cabs range and the horn takes over at the bottom of the range. The length of the horn is much longer on the JBLs.

See my other post Ampeg Isovent - Jack Plate Circuit Board.

And here's what the inside of a 4530 looks like.
View attachment 3681786

A folded horn basically takes what would be a big long horn, and by folding it in on itself, attempts to develop a horn that is far more smaller and compact.

The inside of folded horns can range from fairly simple to Very Complex, there is a lot of mathematics, physics, and trial & error involved.

.

 

[Nicholas Orick]

Here is the rear of the cab to show the ports.
View attachment 3682010

So the front part where 15 is connected does not open in the the rear chamber?

The baffle goes all the way to the back or bottom of the cab like this?
View attachment 3682004

Instead of opening into a port like this?

My ports are on the front on either side of the 215s.

 

[frankie5string]

My ports are on the front on either side of the 215s.

So how are things going with your friend who's working on the IsoVent? Have you made any determinations about your theories on the jackplate/filter/circuit?

 

[Jim C]

So back to the real action:
Wasnex and Andy,
Many of us really appreciate the time you both spent presenting drawings and engineering data as well as design concepts and opinions to this thread.
While the original title and direction of this thread is not important, thank you for the continuing education on speaker design.

 

[jthisdell]

So after 23 pages my feeling is that a well engineered modern ported design will sound better, go lower, be more articulate and weigh a lot less and fit in my Miata. Folded horn designs were developed to produce low end efficiently when amps were not as powerful. All that has changed for the better.

 

[Nicholas Orick]

So how are things going with your friend who's working on the IsoVent? Have you made any determinations about your theories on the jackplate/filter/circuit?

He has ordered parts for ReWiring the Isovent, according to his partner - is working on the cabinet, but other parts won't be In until next week, so we will just have to sit tight until probably the middle of of next week at the earliest.

I called simply because I am curious, but I am NOT going to make a nuisance of myself calling them every 20 seconds, and until then I have plenty of music and bass playing to be practicing, plus my job, and so on, so I will just concentrate on that, and NOT worry about the Isovent.

He has worked on cabinets many times before, did many road shows and concerts, he knows gear, he is also a luthier, and I am confident when he does call, and I go over there, he will probably have something interesting to show me.

So I am NOT sweating it.

Probably by the middle of next week we should know something.

 

[Wasnex]

My ports are on the front on either side of the 215s.

Okay I went back to your first post and pulled a photo.

Weird that some have the ports on the back, and some have them on the slanted baffle that holds the 15s.

 

[Nicholas Orick]

Really? I don't think you are familiar with that cabinet, certainly not crossed over to get rid of the gank in the mid bass and up.

Something else that's misleading is that the written specs do not match the published on axis graph, which is why it may appear better in the low end than it actually is, and also why it works better at a 100Hz crossover frequency.

https://www.electrovoice.com/binary/T18_Engineering_Data_Sheet.PDF

If you look at the written specs, it claims -3dB at 45Hz and -10dB at 33Hz. Yet, it you do the math from the FR graph, and use the average sensitivity from the graph over the published 250Hz bandwidth, you will quickly discover that the average sensitivity is just about 101dB, the -3dB point is 60Hz and the -10dB point is 40hz. (the absolute sensitivity does not matter as everything is relative in this spec)

The other thing that should be striking is what's happening in the mid bass (remember that I had mentioned that the mid bass artifacts are a particular challenge with many of these "folded horn, horn loaded vented", and other non-conventional designs???). Ignoring the 4th order 250Hz LPF that's been inserted into the graph, look at what's happening at 100 to say 250Hz (extrapolated w/out the LPF obviously). There's a 10dB peak at 150Hz (it's probably higher and wider, extending upwards to 250Hz), which is EXACTLY the type of artifact you are experiencing with your proverbial "F-bomb". A conventional bass reflex cabinet with appropriate tuning does not have this artifact.

All the "wide eyed infatuation, arguing and obtuse (plus being totally incorrect) justification can't change the physics of whats happening acoustically. The engineering relationship is basically the same as gain-bandwidth product, where you trade-off gain for flatter and broader bandwidth. What's ironic is that the math is very similar to that in electronic filter theory and in fact we use filter theory models when describing what's happening.

This is also why I suggested that you listen to those who do know more about this than you do. You might actually learn something. Your tank experience means nothing in this field, zip, zero, nada, and I think you have finally proved this to us as well.

I think the T18 will be a good cab for just doing gigs and trashing it.

I know there are far better and more expensive speaker systems, but for a far lesser expensive, and for bass players just gigging on a much lower budget, the T18 makes an excellent choice.

Obviously the T18 is No Match for the newer far more and much more expensive systems of today.

For example the T18 is No Match when compared to the JBL VRX, but for a modest club or venue, the T18 is NOT a bad speaker to consider.

However the T18 is NOT High End Gear.

I know this already.

That said, what would you recommend?

For a basic system I think my Bag End does okay.

Good basic and NOT too expensive.

Now if I had a whole lot of Extra Money, Bag End has come out withthe Quartz bass speaker, and I would probably consider one of these.

What would you recommend for lower budget and for higher budget?

Just curious.

.

 

[Btbp]

Dang that is a lot of plywood, more than I'd want to carry, memories of my Acoustic 301....

If childhood memory serves, that there's a PushmePullyou.