There's a whole lot of BS in all of this. The whole idea is dopey IMHO...and using this cab is kind of like driving a Model T...kinda fun and quaint, but you can't really do anything with it compared to something that has modern functionality.
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Ampeg Isovent - Jack Plate Circuit Board.
- Thread starter Nicholas Orick
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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.
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. 
I have to admit I was once curious about the Isovent since I have heard some really awesome sounding isobaric HiFi speakers. But 134lbs would be too heavy even if the cab sounded great. From the reading I have done, the Isovent is not well regarded.
It would still be fun to see what I could do with biamping and parametric EQ. But I take sort of a perverse pleasure in tuning speakers that most people don't seem to understand
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- Feb 12, 2006
- 61,047
- 5
- 221,000
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
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.
The Ampeg SVR215 and SVR212 (with rackmount section on top) and Dual Drive 215 and 212 (no rackmount section) have drivers back to back, though they're crossed over so that only the omnidirectional low lows come out the back. I had the SVR215, bought new in '92 and sold just a few years ago. It wasn't a bad cab, but I quickly discovered that you didn't have the option of putting them up against the wall on a tight stage. FWIW, these cabs were introduced at the same time as the IsoVent.
- Feb 12, 2006
- 61,047
- 5
- 221,000
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Does this make that concept another winner that didn't make first base?
- Feb 12, 2006
- 61,047
- 5
- 221,000
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
I still don't like or agree with the term isobaric, I don't think it describes what's really happening... and it doesn't generally work as claimed, nor does it bring any meaningful advantages that outweigh the disadvantages.
Last weekend I picked up an old Ampeg SVR-212 cab with a front speaker and a rear speaker. It is a vented cab
Is that back to back isobaric?
I am just curious and want to now the design/technique behind it.
NCD: Ampeg SVR-212
Is that back to back isobaric?
I am just curious and want to now the design/technique behind it.
NCD: Ampeg SVR-212
@TonH
Those cabs were bipole rather than isobaric. Here's a thread that shows front and back SOLD - Ampeg SVR 215
Those cabs were bipole rather than isobaric. Here's a thread that shows front and back SOLD - Ampeg SVR 215
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Well, yeah, it's not a great term. Ideally what would you call it?
Typical marketing mumbo jumbo, but the US patent office accepted it, and various companies have used the term to describe their speakers. This is sort of like our argument with others on the term biamping...it has an accepted meaning, but some people think it simply means using two amps.
I have attached a US patent that deals with improvement to push pull speakers and it not discussing an isobaric design.
Here's an image from the patent
I am NOT saying my experience with Armored Tanks does or does NOT apply.
The guys were busting my chops, posted a video of The Blind Driver, so in return I posted a video of an M1 running over a car.
It is clear you have the Respect of these guys, which is good, and I am also NOT saying I do or do NOT know anything in this field, and in fact, if Nothing Else, this is a field I find fascinating, and I am Beginning (with Humility) to Delve into.
The issue with the Isovent, again if Nothing Else, is a Learning Experience. It ISN'T going to be the end of the world, the ground ISNT going to crack in two, and the sky ISN'T going to fall, no matter how the Isovent experience goes.
Again, if Nothing Else, the Isovent Experience served as a vehicle that has brought me in touch with you, and of course the Chops Busting Guys, no matter how we look at it, the Isovent is proving a worthwhile experience in that I have now met you guys here on Talkbass.
I say Guys because None of the Women are speaking up.
Regardless of how it turns out with the Isovent, this is working towards opening up a whole new world to me, and again, the Isovent is just for Fun, and believe it or NOT, I am having Fun, despite getting my chops busted.
Naturally the continued conversation is generating questions, which as we continue, I will get to, and overall, no matter how it all turns out for the Isovent, I am NOT going to sweat it.
One thing is leading to another, yes I am interested in this field, the unexpected consequence of doing the Isovent Project is I have met you, and I am damn glad to meet you.
So quit worrying.
And the guys have been funny with their stupid videos.
So with Deference to somebody who knows a whole lot more about this stuff than I do, you are peaking my interest, and again, regardless of how the Isovent turns out, I look forward to continuing to get to know you, and learning in this field.
By the way, a while ago, I purchased the Bag End 18 along with the Mesa Walkabout, and as a combined system, a rig, this did well enough. Later on I purchased the GK 1001RBII and tend to use the GK RBII with the Bag End.
In combination the GK RBII and Bag End sounds good, and on the whole, this is probably a good decent basic system. I like the sound of the Bag End which is why I use it. Basically the Bag End is a well made box with a speaker in it and I use it with the port open.
I probably could have left it at that for a long time, but I found myself getting into it, and when I happened upon the Isovent, I decided to try it, and as we see, with the GK and BE already being a good enough rig, I couldn't leave well enough alone, and now all this with the Isovent.
Oh well such is life.
I couldn't help myself and now I have opened Pandora's Box.
I guess I asked for it and had it coming.
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Ah yes, good ol' double-north-ended-north-bound-llama cabinets.
The fact that I couldn't back it up to the wall was really the only complaint I had with it. I didn't get any wolftones. It was compact, though as I aged (especially my back), it seemed to grow heavier. With the 350-watt SVT-III (non-pro) head mounted in the rack, it was 135 lbs. and a bit unwieldy for me to hoist up into the back of my minivan. I sold it and bought a GK MB212-II, and lost almost a hundred pounds while gaining 150 more watts in the process.
I own a couple of GK amplifiers.
The Combo weighs a lot more than the head.
When the cases are open, I keep my gear covered when not in use, and one way or another, Pickles has found a nice place to rack out.
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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.
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