Ampeg Isovent - Jack Plate Circuit Board.

[DJ Bebop]

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

 

[Redbrangus]

^^ Stylin'

 

[frankie5string]

I don't see the isobaric part, I do see a simple push-pull driver pair.

Because the air pressure between the speakers is supposed to be constant?
Isn't the the marketing designation "Isobaric" somewhat loose, anyway?

 

[Wasnex]

So it's a VENT-ed box with an ISO-baric driver arrangement. Hence Iso-Vent. I get it. Didn't someone say exactly that on about page 1? Why has there been all this folderol about folded horns?

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

SH-1800 Basically the same cab at the T18, but different woofer in a different orientation.

4530

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.

 

[Redbrangus]

Because the air pressure between the speakers is supposed to be constant? ….

That's what I understood...but then I'm new around here.

 

[Roxbororob]

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

And you survived to tell the tale!
Im not defending the OP. I see he is overlooking good advice (Ive followed the whole thread), but there is no need for us to get bent out of shape.
Not sayin you in particular DJ Bebop...its just seemd like a good time to chime in.
I think Mr Andy is handling this rather well.

Nicholas Orick please run the test!

 

[Wasnex]

I don't see the isobaric part, I do see a simple push-pull driver pair.

This is considered isobaric

 

[DJ Bebop]

And you survived to tell the tale!
Im not defending the OP. I see he is overlooking good advice (Ive followed the whole thread), but there is no need for us to get bent out of shape.
Not sayin you in particular DJ Bebop...its just seemd like a good time to chime in.
I think Mr Andy is handling this rather well.

Nicholas Orick please run the test!

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

 

[Redbrangus]

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.

Ahhh...the venerable old 4530. It did indeed operate as described, working primarily as a direct radiator with the back-loaded horn supplementing it in the lower range. JBL offered several variations on this concept--with dual 12's and single and dual 15 versions. The horn was more curved than folded. They rocked pretty good for the day, and as direct radiators, sounded pretty good above 150 Hz or so. For the era...

 

[DJ Bebop]

And you survived to tell the tale!
Im not defending the OP. I see he is overlooking good advice (Ive followed the whole thread), but there is no need for us to get bent out of shape.
Not sayin you in particular DJ Bebop...its just seemd like a good time to chime in.
I think Mr Andy is handling this rather well.

Nicholas Orick please run the test!

Thank you for that!

 

[DJ Bebop]

And you survived to tell the tale!
Im not defending the OP. I see he is overlooking good advice (Ive followed the whole thread), but there is no need for us to get bent out of shape.
Not sayin you in particular DJ Bebop...its just seemd like a good time to chime in.
I think Mr Andy is handling this rather well.

Nicholas Orick please run the test!

I still use the Aguilar 1x12 with the 1x18 bi-amped as my imitation mini Phil Leah system
Now that he's gone Hartke though...

 

[frankie5string]

I still use the Aguilar 1x12 with the 1x18 bi-amped as my imitation mini Phil Leah system
Now that he's gone Hartke though...

Isn't he using a bunch of Hartke 12s and a couple of their 15s, now?

 

[farace]

I think someone mentioned a couple of chapters back that they had the specs for the IsoVent; I have the 1992 and 1993 Ampeg catalogs (which I believe it appeared in) somewhere about if anyone wants me to scan something or look up specs or marketing hype.

 

[Wasnex]

Ahhh...the venerable old 4530. It did indeed operate as described, working primarily as a direct radiator with the back-loaded horn supplementing it in the lower range. JBL offered several variations on this concept--with dual 12's and single and dual 15 versions. The horn was more curved than folded. They rocked pretty good for the day, and as direct radiators, sounded pretty good above 150 Hz or so. For the era...

If the Isovent is constructed similar to this,

IMHO it has elements of a short folded horn. Like the EV cabs I listed, the horn probably operates at the top of the cabs range rather than at the bottom.

If the Isovent is constructed similar to this,

then I see it more of a pure vented design.

 

[agedhorse]

The term isobaric is highly misleading, by the same definition a conventional 210 or 410 is isobaric since there is no pressure difference between the front surfaces of the drivers or the back surfaces of the drivers.

IMO, push-pull is a much more accurate description of this configuration.

 

[Nicholas Orick]

It may be worth noting that the Orange Isobaric design sounds much tighter, and didn't have any of the weird headache inducing low-mid honk that the Ampeg cab produced. The speakers Orange put into their boxes are nothing like the push-pull drivers in that Ampeg cab.

Every time I used the IsoVent, it gave me terrible headaches because of how it coloured the signal.
In fact, before I stopped using one entirely, I was taking Tylenol prophylactically.
The 15s in the lower chamber aren't really subwoofers. They're still bass-guitar low-mid drivers.

That B52 looks like a copy of the Cerwin Vega folded horns my DJ buddy used to use. Those have completely different drivers again. Just because something is a folded horn, doesn't mean all folded horns act the same. Those CW folded horns definitely had a "brown note" that rang much louder and harder than the rest. They were pretty peaky.

Also, I was struck by your mentioning those JBL VRX array speakers. You know the tweeters in those will rip right through you, right? They're designed for very, very long throw with knife-sharp projection. Even mounted high up, we still had to dial them back in the controller because they are so powerful. You really don't want to use one as a bass cabinet.

Okay the JBL VRX (with Tweeter ripped out) is a bit Extreme, but it is an Option.

I was just saying in response to you guys asking about getting something "More Modern", that this is asking a Loaded Question, and in Today'a World, has many Newer Possibilities, and you all should be Careful about asking this question.

You might NOT like the Answer.

On a more Rational Note, I could easily take a Self Powered Monitor, or even Several Self Powered Monitors, and put together a Rig for more smaller to moderate sized Gigs.

There are far more Reasonable Possibilities.

In terms of the Isovent, I am just having Fun with it. Am I going to be playing it at Very Loud Levels giving me a Pounding Headache, I doubt it, but if I do find myself in an Extremely Loud playing situation, I will be sure to wear some good Ear Protection to prevent any Pounding Headaches developing.

In the meantime, my inexpensive Harbinger 12 inch Self Powered Monitor could be said to be a "More Modern" approach when compared to my GK 15 inch Combo.

All I need is my bass, Preamp/DI, and Harbinger 12, and I have a good Rig for home practice and small gigs.

Again, the bit about the Ampeg Isovent is just purely for fun.

Will I use it on gigs?

Well my first gig was played through a beatup Mesa 4x10 house supplied amplifier combo, and if I ever do haul my Isovent to a gig, I won't be doing too badly.

I am NOT worried about it.

There are many Options to consider in the World today.

One thing.

The Ampeg Isovent does provide a good amount of sound when competing against a very strong drummer, and one way or another, just for Fun, I wouldn't be doing too badly with the Isovent.

I am NOT Worried about it.

.

 

[Redbrangus]

If the Isovent is constructed similar to this,

IMHO it has elements of a short folded horn. Like the EV cabs I listed, the horn probably operates at the top of the cabs range rather than at the bottom.

If the Isovent is constructed similar to this,
View attachment 3681807
then I see it more of a pure vented design.

Was... I thought we had established that it isn't a folded horn...just a plain old bass reflex, i.e., a 'vented' box. Try to keep up.... Do you need for me to post some giant, irrelevant pics for you?

 

[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

The EV T18 is an excellent choice for a larger rig with good projection.

I have tried a set of T18s in really good condition, and like an Idiot didn't buy them, but also I tested a set if T18s that were beat to crap, and I am glad I didn't buy them.

The T18s offer an outstanding choice if you can find a pair that aren't beat to crap.

I kid you NOT, they sound really good for what they are, and if you can find a pair in really good shape, I would recommend them any day of the week.

For some reason, people take the T18s, drive them at Max Volume Non Stop for years, beat them to crap, and for good measure, drag them through a swamp before putting them for sale on the used market.

So if you have a set of T18s that are in really really good condition, I would recommend you try these for those moderate sized gigs where there is No FOH Sound System supporting the gig, and I assure you, you won't be doing too badly with a set of really good condition T18s.

.

 

[Wasnex]

The term isobaric is highly misleading, by the same definition a conventional 210 or 410 is isobaric since there is no pressure difference between the front surfaces of the drivers or the back surfaces of the drivers.

IMO, push-pull is a much more accurate description of this configuration.

I am not sure why you are arguing this. The term isobaric speakers has been accepted for a long time and it does not describe a conventional 210 or 410.

I agree the term is misleading.

Not that this is a great reference but, From wikipedia

The term “isobaric” points to the somewhat erroneous notion that the air pressure in the sealed chamber between the loudspeaker is constant (the "isobaric" condition), when in fact there will be small changes due to the differences in the drivers technical parameters and the air that each is pressurising. One driver will be pressurising the air in the listening room, while the other is pressurising a smaller volume of air in the speaker cabinet.
​

That doesn't mean we should disregard the accepted naming convention...especially since most of us consider the isobaric design obsolete.

Also push pull speaker can mean something entirely different than isobaric speaker.

From example I believe some would describe this as a push pull subwoofer

Here's another push pull subwoofer (M&K)

Compare to

and

With an isobaric only one driver pressurizes the room. The other pressurizes the speaker box. The space between the drivers is called the plenum.

Not sure why anyone would do back to back. Perhaps for tuning purposes. Probably a lot of BS in this link but i provides an example of back to back isobaric loading DECWARE's House Wrecker Car or Home Audio Subwoofer Cabinet

 

[Wasnex]

Was... I thought we had established that it isn't a folded horn...just a plain old bass reflex, i.e., a 'vented' box. Try to keep up.... Do you need for me to post some giant, irrelevant pics for you?

What has been stated may be a fact, or it may be an erroneous opinion since no one has bothered to show or describe how the box is constructed. I guess you not interested one way or the other, so my apologies for wasting your time and bandwidth .