Ampeg Isovent - Jack Plate Circuit Board.

[frankie5string]

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.

 

[fdeck]

At the time I went in, players were still pretty much outfitting themselves with their own rigs, but by the time I got out, anything considered to be a rig had become basically a glorified stage monitor, with most bands opting for these more rapidly growing array sound systems. Now many musicians use IEMs, which you will Never see me use because I hate having things stuck in my ears.

Strictly as an aside to this conversation, JimmyM posted an interesting poll recently:

POLL: Who needs an amp on some gigs because of vocals-only PA?

There have been quite a few threads on "bass amp as stage monitor." Sure, how the really big acts manage their sound is an interesting aspiration, but it's not a reality for most of us. My own impression from reading the comments of many bassists, is that a lot of us are producing most or all of the bass that reaches the audience, from our stage amps.

 

[agedhorse]

All folded horn cabinets have that mid bass peak, the consumer grade horns especially. It's a byproduct of the horn's geometry and one of the tradeoffs that result from the quest for higher sensitivity. The other tradeoff is the lack of low frequency extension compared with a high quality bass reflex cabinet (at 1/2 the size and 1/4 the weight).

I am very familiar with the Cerwin Vega folded horn cabinets as I was one of the system techs for their touring earthquake systems that were used for technology demonstrations. I also managed a service center that was one of the largest Cerwin Vega service centers on the west coast back in the late 1970's and early 1980's.

 

[Charlie Tango]

Dunning/Kruger Effect is a thing for a reason! It is on full display with the OP.

Not very far from where I am typing this reply temporarily resides A Very Stable Genius who exhibits the phenomenon on a 24/7 basis.

 

[DJ Bebop]

Not very far from where I am typing this reply temporarily resides A Very Stable Genius who exhibits the phenomenon on a 24/7 basis.

On full display

 

[Wasnex]

All folded horn cabinets have that mid bass peak, the consumer grade horns especially. It's a byproduct of the horn's geometry and one of the tradeoffs that result from the quest for higher sensitivity. The other tradeoff is the lack of low frequency extension compared with a high quality bass reflex cabinet (at 1/2 the size and 1/4 the weight).

I am very familiar with the Cerwin Vega folded horn cabinets as I was one of the system techs for their touring earthquake systems that were used for technology demonstrations. I also managed a service center that was one of the largest Cerwin Vega service centers on the west coast back in the late 1970's and early 1980's.

I have heard a couple of systems in small clubs running a quad of Cerwin Vega EL36s, and they were tuned to sound real nice. But they don't get much respect in the various threads I have read about them. The response plots I have seen show them to drop off quickly below about 50hz.

IMHO, a folded horn should be crossed over over below the mid bass peak.

If I were running the Isovent I would try crossing it over at 100hz.

From what I have read, the Growler trades some efficiency for extended low frequency response. They start to drop off just below 45hz. I have read some threads where measurements were taken that suggest performance wise they really are very close to the JBL SRX718S and VRX918S. The Growler weighs 88lbs VS 81lbs for the VRX918S. JBL lists 95dB sensitivity, but this is with whole space loading. With half space loading, the sensitivity of the JBLs is reported to be about the same as the Growler.

If anyone is interested, here's an in-depth technical review of the 2015 Growler from Data-Bass.com.

dB v2

 

[agedhorse]

When folded horns are stacked in a quad or more, the effective horn mouth area increases and the efficiency of the acoustic coupling between the source and the free air improves. This increases sensitivity and decreases F3.

Crossing over the folded horn before the mid bass hump improves the performance as a sub, but this doesn't help with bass guitar applications.

 

[DJ Bebop]

For the folded horn guys...
For Sale - Acoustic 360/ 361 Bass Rigs USA Made with Cases (6 Available)

 

[Wasnex]

Crossing over the folded horn before the mid bass hump improves the performance as a sub, but this doesn't help with bass guitar applications.

Since the Isovent has a pair of sealed 210s, I would think applying a crossover at 100hz over would significantly smooth the response in the lower mids. What I am missing?

Per Ampeg, F6 is listed as 32hz.

 

[Redbrangus]

I suggested bi-amping with an 80-120 Hz crossover point in post #8. I had trouble believing that there was any sort of horn-loading going on in this box because there is so little internal volume behind the 15s. So maybe I was wrong about it being a horn-loaded box, but I don't think I was wrong about the problem with the amount of space involved.

Think about this design decision: Besides the obvious advantage of having two motors in parallel, the primary supposed benefit of the isobaric principle is that it doesn't need as much internal volume behind the driver to load it properly. Maybe I don't fully understand the principle, but it seems to me that benefit only accrues to a bass reflex enclosure...the stiffer compliance offers no advantage if the driver is in the throat of a horn, folded or otherwise. Does it? Or even if were to, is there any other way that the performance of a bass horn benefits from a reduction in size? And it is a tiny little horn, such as it is, which dictates a relatively high LF cut-off frequency. So I suspect that the horn contributes relatively little to the overall LF performance and that in the lowest octave, the direct radiation from the front side of the driver pair is what is being heard. And I find all those LF specs a little bit suspect...does anyone else have trouble accepting that this enclosure is only 6dB down at 32 Hz?

The road to decent audio performance is littered with concepts that didn't find acceptance for whatever reason...usually the reason is that the disadvantages of the design outweighed whatever supposed advantages they offered. And I get the idea of keeping a rare old bird alive, for whatever eccentric reasons, but if I had an old carbureted, mechanical-ignition car, I'd have to be ready to accept the performance limitations of the outmoded design.

Anyway...I look forward to seeing the results of whatever mysterious solutions you and your buddy-who-has-extensive-experience-working-on-speaker-sounds-systems have come up with. That sounds intriguing...keep us posted.

 

[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.

As usual the Tweeter needs to be ripped out.

I Never use Tweeters anyway.

.

 

[agedhorse]

Since the Isovent has a pair of sealed 210s, I would think applying a crossover at 100hz over would significantly smooth the response in the lower mids. What I am missing?

Per Ampeg, F6 is listed as 32hz.

I was commenting on folded horn cabinets by themselves in general. The isovent is not a folded horn.

Yes, crossing over a folded horn at 100Hz is important for controlling the mid bass peak as well as dealing with the lack of real mids.

 

[Redbrangus]

As usual the Tweeter needs to be ripped out.

I Never use Tweeters anyway.

.View attachment 3681294

Yeah, that makes real sense. You do get that this isn't a speaker system that's been optimized for bass performance, right? But it does have a pretty good complement of very expensive mid and HF components that would need to be ditched, along with the rigging hardware, which is the single most expensive part of this system. So you'd be paying about $3500 for a box that you're going to throw away more than half the value of...that would NOT perform all that well as a bass box in the first place. Why do you imagine this would be a good course of action?

Edit: Everything in the design of a line array box is optimized to function in an ARRAY...there is nothing particularly advantageous about the performance of an individual element by itself. In fact, the performance of 'onesies' is typically pretty compromised, particularly if operated in the wrong axis, as you continue to show it.

 

[Redbrangus]

The isovent is not a folded horn.

Wait...is this right? That was my initial thought, but there seemed to be authoritative info that it WAS, including the OP speaking eloquently about his affection for folded horns...and he's had the box apart. So was I mistaken when I decided I was mistaken about it not being a rear-loaded, folded horn?

 

[frankie5string]

Wait...is this right? That was my initial thought, but there seemed to be authoritative info that it WAS, including the OP speaking eloquently about his affection for folded horns...and he's had the box apart. So was I mistaken when I decided I was mistaken about it being a rear-loaded, folded horn?

When I looked inside I just saw an angled baffle with the push-pull speaker arrangement and the space in the box designed for it. I didn't see any sort of folded horn in there when I took one apart.

You can look right in and see the bass drivers. They're not obscured by any horn.

 

[Redbrangus]

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?

 

[frankie5string]

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?

Lol! I was wondering that too... although the OP did mention those old-fashioned CV bass horn clones...

 

[BassmanPaul]

For me the biggie with the Isobarik alignment was that you needed to use two drivers and twice the weight, to get the volume of one!

 

[BassmanPaul]

Okay a kind of strange thing happened to me. I was in the Army for many years, and at the time I went in, folks were doing things one way in music, but by the time I got out over a decade later, the whole paradigm had changed, only I didn't know it.

On a different tack I'd like to thank you for your service. You made a positive difference to this world. of ours.

 

[agedhorse]

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