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Vox Foundation reissue: a morality play

#21
Wasnex said:
My interpretation is the cab is a faithful reproduction of the original Foundation cab. I wouldn't expect it to be ported like the revised 1967 cab, and installing a port would not make it magically work well with the Omega. In order for a cab to work well with a particular driver, you have to take into consideration the volume of the cab, as well as the area and length of the port. In other words everything about the cab is modified to fit the driver's T/S parameters, so it is no longer an authentic recreation of a Foundation.

Someone who is knowledgeable about how the T/S parameters work can review a driver's specs and choose drivers that are more suited to sealed cabs. I believe selecting a relatively high Qes is desirable for sealed cabs. Note the Omega spec sheet lists Qes at 0.32 and Fs of 25hz, JBL list the QTS for the K151 as 0.28 and Fs of 30hz, and the specsheet for the EVM18B lists Qts as 0.376 and Fs of 33hz.

I loaded these parameters into this Sealed or Ported Speaker Box Calculator:
Sealed or Ported Speaker Box Enclosure Calculator
The Omega was indicated as the best choice for a sealed box. The Omega and EVM fall in the Both category and the JBL falls in the Ported category.

I attached the JBL T/S specs for you. Your best bet would be to input the full spec of the drivers into some speaker modeling software along with the volume of the Foundation cab. I believe you will find that none of them produce much output below 100hz in such a small volume. There are various free online modeling programs if you want to do this.

My suspicion is what you like about the JBL is not really the low end, but more related to its midrange response. The Omega Pro 18A is pretty peaky and has a really strong peak around 1.5khz, which will probably sound very ganky (see attached).

I don't have a response plot for the K151, but it's mid range response is probably a lot smoother since it is a musical instrument speaker. I have read reviews that suggest the EVM18B is a bit brighter than the K151 and they are also pretty smooth. I posted the EVM18B datasheet, which includes a response plot, in post #15.

I went through the Eminence 18s available at Parts Express and loaded them all into the "Sealed or Ported Speaker Box Calculator." The only one that registered closer to true Sealed was the Kilomax (Qes 0.49, Fs 32). Unfortunately the frequency response is even worse than the Omega. See attached.

So based on this, my opinion is North Coast built an authentic recreation for you and recommended the best Eminence driver available. There may be more suitable or better sounding drivers if you want to jump down the rabbit hole. Finding one with a nice mid range frequency response will likely be a challenge, because modern 18s tend to be designed for subwoofer duty.
Click to expand...
What I like about the K151 is that it doesn't honk other otherwise emit spurious noise like the Omega does in this cab. The Omega is not a suitable driver for this cab, no matter what it says on paper. It sounds great in my subwoofer cab, but is unbearable in the Foundation. With the K151, I've played a low B through this cab and it carried it well. I appreciate your knowledge of spec sheets and such, but in practice, the Omega just sucks in this cabinet. The JBL may not be the optimum driver for it, but it certainly outperforms the Omega in every aspect.
 
#23
oldfclefer said:
What I like about the K151 is that it doesn't honk other otherwise emit spurious noise like the Omega does in this cab. The Omega is not a suitable driver for this cab, no matter what it says on paper. It sounds great in my subwoofer cab, but is unbearable in the Foundation. With the K151, I've played a low B through this cab and it carried it well. I appreciate your knowledge of spec sheets and such, but in practice, the Omega just sucks in this cabinet. The JBL may not be the optimum driver for it, but it certainly outperforms the Omega in every aspect.
Click to expand...


I don't find it surprising that you prefer the sound of the JBL, as the mid range frequency response of the Omega is pretty atrocious. Of course a subwoofer driver is not designed to operate in the mid range.

Without a suitable modern driver, it's really sort of a dichotomy for the company to sell such a cabinet to people who do not have original drivers to install in them.

You might find it useful to model the K151 and EVM18B using one of the online cab simulators. Rather than just going on Qes and Fs, it's best to model all of the parameters.

Faital makes some drivers that have higher Qes and smoother mid range response. I tend to prefer the rising response of the EVMs personally. I have EVM18B in two sizes of ported cabs and Faital 15PR400s in a Greenboy Dually. The response of the 15PR400s is also very flat. The Dually plays way louder and goes way lower in a small box, but I prefer the sound of the old EVMs.
 
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#24
seamonkey said:
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I'd suggest that cabinet is not suitable for most all modern drivers, and probably the majority of yesteryear drivers as well. It's the luck of the draw if you find one you like so Good for you for finding what you like.

I'd like to find an IR of the original with original driver just to compare it to several other cabs.
Click to expand...
I'm not a purist by any stretch. I'm happy with the cab now. I was fairly upset when it sounded so harsh with the Omega, and a little puzzled by the contention that the bolt pattern of a JBL differs from Eminence. I'm normally a guy who trusts engineers and builders to know their gear well enough to make the best choices for equipment like drivers. I remember this amp/cab sounding so great together. I'm also aware that equipment has evolved substantially since those days. I'm fairly sure that any of my amps outperform the old Foundation amps. I tried it with an Ashdown MiBass 2.0, and a Fender Rumble 350 which are both viable ss amps that I thought could be appropriate for the application, but I couldn't tame the harshness of its sound. Then I tried my Marshall VBA400 with it, which despite its massive power, it's a very smooth sounding amp. Still the cab honked and squealed at certain frequencies. When I installed the JBL, the cabinet seemed to respond to the driver and the driver to it much better. It sounds great no matter which of my amps I use with it.
HPIM4645.JPG
 
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#25
Some of the JBL drivers have a slightly different bolt pattern as well as a slightly larger cutout requirement with less margin between the edge of the hole and the screws. This is a real problem with some of the baskets used.

I believe the cabinet originally came with different drivers depending on when made and the availability of parts back then. I recall Goodwin, Fane, and others. I can't see Community ever being used.

A sealed cabinet might be better with the EVM-18B which is a fairly forgiving driver, but there were also early Eminence, Quam, Oaktron, and even Jensen and Celestion. Modern 18" drivers are generally designed for subwoofer applications where higher power handling is necessary at the expense of sensitivity and high frequency extension. The EVM-18B is the one that I see most commonly, though even this benefits from a mid driver.

Without modeling the driver in the cabinet, there's no way to know what the real world power handling is, as this factors into the specs.
 
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#28
oldfclefer said:
This one has cutouts on each side. Not exactly handles, but a place where you can grip each side. The originals were made for a trolley. I installed casters on mine.
Click to expand...

While I remember some VOX units having trolleys I never saw one for the Foundation cabinet.

It is interesting that Community was mentioned as a driver manufacturer. Both Community and Tannoy were more into commercial PA gear than musical amplification.
 
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#32
BassmanPaul said:
While I remember some VOX units having trolleys I never saw one for the Foundation cabinet.

It is interesting that Community was mentioned as a driver manufacturer. Both Community and Tannoy were more into commercial PA gear than musical amplification.
Click to expand...
I said Community. I'm pretty sure someone told me that long ago. There's been a lot of mileage between then and now. My recollection is probably inaccurate. The foundation trolley was made to tilt back for transport.
 

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