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Another Electro Voice Interface D/Sentry VI thread.

This is a very interesting thread. I posted on another forum with some some questions about this design, and Pete B helped my understanding quite a bit.

My thought was to create a workalike by modifying the econowave design to use a 6" or 8" midrange speaker and then use a automotive subwoofer driver as the woofer. The big sticking point for me (though I'm pretty much a novice at speaker design) was I didn't really see a way to match the efficiency of the original system. It seems like modern woofers are much less efficient, or else they can't reach as low. Bi-amping will solve this, but I didn't want to bi-amp.

But even more than that, I'm a terrible woodworker and realized they would turn out hideous.

Anyway, I lost interest. It would be a pretty fun project. I've been thinking about implementing the ideas in other ways - basically retune the port on a speaker to 1/3 octave below FS and then use a eq to boost it back up. If the woofer can handle it, you gain the 1/3 octave in downward range.
 
Hi Forum

An update with some measurements.
Please see the attached file where I measured 7 ST350’s, 4VMR’s and two speaker systems.

I guess the measurements speak for themselves.

The biggest surprise is the difference between VMR pro 1 and VMR pro 2. This will also be visible in the frequency plots below. Not two drivers that you want in a stereo setup. Luckily I only need one that will be combined with the ST350a-C as a center speaker.

The STR350’s are all within a very decent range equal to each other. Very consistent behavior I have to conclude.

The plots are measured with the free program from Audionet called Carma. The absolute accuracy in the LF domain is hard to determine but repeating measurements on the same device under test showed remarkable consistence.

All driver measurements were done with exactly the same volume and measuring distance of 60 cm (approximately 24”)
For the ST350 measurements I used a 1,5µF series capacitor with a 0,42mH inductor parallel that is exactly as is used in the Interface D filter.
The VMR – L and VMR – R are also measured with a LPF consisting of 1,5mH and 9µF to give some indication what happens with the top-end of this unit.

The VMR-1 and -2 are VMR’s I bought on Ebay.
The VMR-L and –R are VMR’s from the Interface D.
The ST350b’s are all bought on Ebay.
The ST350a-C is bought on Ebay and was taken from a Bass guitar cabinet.
The ST350-L and –R are also from the Interface D.

I also had some time to listen to the speakers. I used a fairly low cost 45W Denon integrated amp and a budget DVD player as a CD source. Anything but High End and just setup in the office where I performed the measurements as can be seen from the pictures in the attached PDF.

But wow …… the Interface is a very special speaker. I will love it once it is rebuild and connected to a slightly better source and amp. The dynamics are awesome; the highs are clean and very honest. Voices are pure, and extremely honest as well. But the power and unlimited dynamics is what struck me most even with this modest amp. Up till now High End audio (and I had some really awesome speakers like the Avalon Eidolon) can be great transparent and with awesome soundstage but sound compressed and canned compared to the “D”. People on this and other forums raved about these speakers and they are all right.

The Sentry 500 is a nice speaker as well, but in a different league with respect to these dynamics and sounded less fat with thinner voices and a different low and top end, maybe slightly more in the direction of what we call HiFi … but I will be very happy with the Interface Delta.
 

Attachments

PeterSchut said:
Hi Forum

An update with some measurements.
Please see the attached file where I measured 7 ST350’s, 4VMR’s and two speaker systems.

I guess the measurements speak for themselves.

The biggest surprise is the difference between VMR pro 1 and VMR pro 2. This will also be visible in the frequency plots below. Not two drivers that you want in a stereo setup. Luckily I only need one that will be combined with the ST350a-C as a center speaker.

The STR350’s are all within a very decent range equal to each other. Very consistent behavior I have to conclude.

The plots are measured with the free program from Audionet called Carma. The absolute accuracy in the LF domain is hard to determine but repeating measurements on the same device under test showed remarkable consistence.

All driver measurements were done with exactly the same volume and measuring distance of 60 cm (approximately 24”)
For the ST350 measurements I used a 1,5µF series capacitor with a 0,42mH inductor parallel that is exactly as is used in the Interface D filter.
The VMR – L and VMR – R are also measured with a LPF consisting of 1,5mH and 9µF to give some indication what happens with the top-end of this unit.

The VMR-1 and -2 are VMR’s I bought on Ebay.
The VMR-L and –R are VMR’s from the Interface D.
The ST350b’s are all bought on Ebay.
The ST350a-C is bought on Ebay and was taken from a Bass guitar cabinet.
The ST350-L and –R are also from the Interface D.

I also had some time to listen to the speakers. I used a fairly low cost 45W Denon integrated amp and a budget DVD player as a CD source. Anything but High End and just setup in the office where I performed the measurements as can be seen from the pictures in the attached PDF.

But wow …… the Interface is a very special speaker. I will love it once it is rebuild and connected to a slightly better source and amp. The dynamics are awesome; the highs are clean and very honest. Voices are pure, and extremely honest as well. But the power and unlimited dynamics is what struck me most even with this modest amp. Up till now High End audio (and I had some really awesome speakers like the Avalon Eidolon) can be great transparent and with awesome soundstage but sound compressed and canned compared to the “D”. People on this and other forums raved about these speakers and they are all right.

The Sentry 500 is a nice speaker as well, but in a different league with respect to these dynamics and sounded less fat with thinner voices and a different low and top end, maybe slightly more in the direction of what we call HiFi … but I will be very happy with the Interface Delta.
Click to expand...

Try them with tubes...you will be amazed!!
 
Thanks for the measurements, Peter. I'm not sure which versions of VMRs I have. They do really open up with tubes! Definitely give it a shot, if you haven't tried. I'm not sure what you mean by, not drivers for a stereo setup?
 
absolve2525 said:
Thanks for the measurements, Peter. I'm not sure which versions of VMRs I have. They do really open up with tubes! Definitely give it a shot, if you haven't tried. I'm not sure what you mean by, not drivers for a stereo setup?
Click to expand...

The two drivers I bought on Ebay (VMR- 1 and 2) were originally meant for a stereo setup and are very different (even though they have the same model number on the back). So one left and the other right would have given a serious imbalance in the 'stereo' setup. At closer inspection one seems to be re-coned.
 
Any kind! I have push-pull 6v6 and 6aq5. That mid just jumps out. I think the horn tweeter opens up too with tubes. It's unreal.
 
I never had tubes when I was using my D's as my primary speakers. That said, when mated with some power (and I'm presuming you know this), they will absolutely shake the foundation of the house.

I had mine mated with a pair of Klipsch LaScalas (EV's bought 1978, LaScalas bought 1979 and I still have both)

The LaScalas would pound you in the chest like the EV's never could but, the D's would shake the foundation like the LaScalas never will.... so it was a wonderful match made for me as I scampered off to college and had some fun in my dorm! (yes, all crammed into a dorm with 120 watts/channel... Yamaha 2040)
 
Hey coytee,seen may posts by you on the ev'D's since I got my pair a couple yrs back.I drive mine with tube amps by the way.Being a long time owner you must where I can find the d eq box??
 
Other than once/twice on eBay, I don't think I've ever seen one for sale. The circuit HAS to be able to be copied if someone were motivated enough???
 
I've been watching ebay for at least a year, maybe two at this point. I don't remember seeing any I-D eqs unless they were with a set of speakers, and I think that happened only once.

They are rare speakers, and it seems many people just tossed the eq rather than bother with hooking it up.

I'm pretty sure you just need to swap a few parts to turn any of the other Interface eqs into a I-D eq. If you're handy with a soldering iron, should take about 5 mins. I've seen several of the other Interface eqs on ebay, so that is certainly your best option.

There's a post somewhere on AK with all the info, and if you can't find it, revive this thread when you have an eq and I'll repost the info.
 
I will be receiving my Interface A eq tomorrow (with the Interface 300). If I am well informed I only need to change 4 resistors.
Eventually at home I will bi-amp the "D" and might decide to put the eq only in front of the LF section. I will check the insertion loss of the unit for the mid-high and compensate that as well.

Mine came from Ebay Germany (I live in the Netherlands) and I saw two Interface A EQ's for sale in the US yesterday.
 
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Just wondering... if you were going to biamp....

Could you put the curve into the active crossover that the EV eq does and achieve the same goal?
 
Coytee said:
Just wondering... if you were going to biamp....

Could you put the curve into the active crossover that the EV eq does and achieve the same goal?
Click to expand...

I am sure a parametric Eq or a modern active x-over like EV's DC one could do the same.
The curve looks quite normal.
See attached picture that I found on the web that shows some graphs.
 

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  • Sentry-Interface EQ schematic.jpg
    Sentry-Interface EQ schematic.jpg
    94.3 KB · Views: 106
youd think one would become available at some point,ive been running wanted ad's on canuck audio for some time with only one response and it was an A box and buddy wanted 150.00 for it...lol
 
I'm quite certain most parametric crossovers could match the curve, especially one of the newer digital ones.

From what I've read, it's a 6db boost with Q=2 at the specified freq, which is supposed to be the FS of the box (which is 1/3 lower than the FS of the speaker).

As for the high end, I found the I-B eq I'm running with my L150As actually boosted the high end a bit, so I run it in the 2 position to flatten the highs back out. I put it in as an experiment, and it boosts the low end in a way I like, so I left it in. Note that the JBL L150 series have a pretty famous roll off below 50hz, so the boost below that is welcome. These are the speakers that I've been thinking about pulling the passive radiator, putting a port in where the radiator was, and tuning the box to use an eq to boost the lows. I figure there will be no permanent damage to the cabs, and it should be an interesting experiment.
 
I really hate to add anything to the circuitry as I believe the simplest circuits sound the most realistic to live sound recreation.Hence ive never considered a eq especially with my tube gear.The problem being the original manufacturers recommendations NOT to use the Ev D's without there designated eq.I found a obscure post concerning removeable port covers on the series 1 EV D which mine are and upon inspection discovered these ports on the underside next to the down fireing woofer.Some one had posted with this model of D the eq was not needed if you removed the port covers.thats how ive been running them ever since.any info on this dr mordo??
 
I'm pretty sure the whole removable port thing is not true.

First, I haven't personally seen it in the literature, and I've read all I can find.

Second, it just doesn't make sense when considering basic speaker design. I'm a little out of my depth here, so hopefully this makes sense.

A port is tuned by both the length and width of the tube. If the length stays constant, a larger diameter lowers the pitch of the port.

An Interface D is tuned to a box FS that is 1/3 octave lower than the FS of the woofer. To tune the box to the speaker, you'd have to make the port smaller in diameter or much longer.

So opening a port to raise the pitch of the box makes no sense as far as I can tell.

If you want your I-Ds to work as advertised, you need to use the eq.
 
When I first pulled the port covers I found an increase in bass response when driven by my Dynaco mkiv tube mono blocks.These can be a bass heavy speaker as is.I run tube preamp as well with the bass/treble set flat and find the music reproduction top notch.I make sure I don't over drive the speakers even tho they seem to proform excellent at all volumes.I will keep an eye out for the elusive ID eq thankx Mordo
 
Dr. Mordo said:
I'm pretty sure the whole removable port thing is not true.

First, I haven't personally seen it in the literature, and I've read all I can find.

Second, it just doesn't make sense when considering basic speaker design. I'm a little out of my depth here, so hopefully this makes sense.

A port is tuned by both the length and width of the tube. If the length stays constant, a larger diameter lowers the pitch of the port.

An Interface D is tuned to a box FS that is 1/3 octave lower than the FS of the woofer. To tune the box to the speaker, you'd have to make the port smaller in diameter or much longer.

So opening a port to raise the pitch of the box makes no sense as far as I can tell.

If you want your I-Ds to work as advertised, you need to use the eq.
Click to expand...

Dr Mordo;

The formula works opposite. The tuning frequency is depending on indeed diameter and length. The bigger the hole the higher the tuning frequency at a given length.
A bigger hole is better as there will be less air noise, but the length of the port will become unpractical long.

I have been fortunate to have a contact (loudspeaker Engineer) at EV that has been there since 1985. Unfortunately he started at the end of EV HiFi and has been doing mainly PA design. He alse shared all the different VMR data that I have posted before. But he could tell me that the design filosofy was to have two modes. The first mode was where the two ports are open. A bit strange at first but that increases the tuning frequency to 44Hz. With one port covered the tuning frequency lowers (at the cost of some increased port air velocity) and then the eq comes in. Port and eq are tuned at 31Hz.The interface C,B and A could not be tuned and you should use the Eq. The Interface 300 (a Swiss made Interface C) was tuned higher to omit the Wq for the European market. The Sentry III had a same construction with a dual port and the EV SEQ. I can confirm that my Interface D has two ports combined into one large square tube. Google on Interface D and you see a lot of pictures with one of the two ports covered.
 
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