Another Electro Voice Interface D/Sentry VI thread.

Hi Guys, This forum has given me lots and lots of information of several owners so thank you all for sharing your insights and most of all pictures.

I would like to build a speaker based on the interface D. I ran into a nice set of two VMR and ST350b speakers and suddenly images from my youth popped up. I have been an Electro Voice fan since my teens end 70's and have actually I build a copy of the Sentry III in that time frame. The Interface D was lost in the dungeons of my brain ready to pop up after seeing the VMR.

I have the luck that my nephew has a great wood shop with CNC machines that was owned by his father (my uncle) and his father (my grandfather), so building speakers has been a passion for over 35 years and I have build many models in the HiFi and PA space.

I am not an absolute vintage geek, love those old designs but I don't need to actually recreate the original. I do want a good sonic reproduction of the design so I am looking for the original stuff.

What I want to change is the geometry of the enclosure. I want to give it a slightly more modern appearance but still remain truthful to the original design. This means that I want to make the unit the same height but a more shallow front panel but deeper. This will give a width of about 15" with a depth of 22" with the original height of 32". (this is actually the enclosure 90 degrees turned). I don't want the passive crossover in the open on the bezel, but keep that clean.

The advantage is a nice speaker to look at in the living room (higher WAF) with a better dispersion as there will be less interference from the front panel.
Volume will remain the same so the LF properties will remain unaltered. I need to find a 12" speaker that will be up to the task (thinking on a Sentry 500 driver).
I am also considering making the unit powered with a dual amplifier module and keeping the VMR/ST350b combination passive.

A few questions that maybe some of the forum members who own an int.D can answer;
1. What is the distance between the bezel and the enclosure (the height of the gap)
2. What is the size of the port? I have seen a round one that seemed to have no depth, and I have seen a square one in two parts that had a dept of something in the range of 8" to 10".
3. I have the schematic of the very straightforward crossover but some of the values are unreadable.

Can anybody help me with these questions?
Thanks.
Peter
The Netherlands

Hi Guys,

A small update:
I have made a first attempt to define the dimensions of this new design which I named “Interface E” as an ode to the original.
To make the unit not overly deep and get the sweet spot of the mid/HF section closer to the ear when sitting I increased the height to slightly over a meter (43”)

Attached a PDF of the original and the new design. Because I really don’t like the open filter in the base I want to make a small section in the back, covered by a plexi-glass plate like the filter section in the Patrician II.
What do you think?
Peter

Very cool project! I want a pair!

Looks very cool - keep us updated!

Good luck on the project!!

If you can find original woofers (or foam for the originals) please post it. I'd like to get the woofers on my D's refoamed but have not yet been convinced that whomever I might have do it can get them back to (true) factory spec.

How I love the paper surrounds on my other speakers. The paper has been going strong since 1979 whereas the surrounds on the D's has already been replaced once and needs it again.

Hi CoyTee,

There is a guy here in the Netherlands that can recone or re-foam these speakers.

I found a website where they have this foam:

http://www.simplyspeakers.com/ev-speaker-foam-edge-repair-kit-fsk-12a.html

If you don't want to do it yourself I am sure there is somebody closer to you who can perform this task with the above foam.

I am looking for some pictures that show a disassembled ST350b (or ST350a).
I wonder if the horn comes off as a bare metal device that maybe could be spray painted?
With a T35 this is the case, but can't find anything on the ST350.

PeterSchut said:

I am looking for some pictures that show a disassembled ST350b (or ST350a).
I wonder if the horn comes off as a bare metal device that maybe could be spray painted?
With a T35 this is the case, but can't find anything on the ST350.

Click to expand...

Be careful removing the horn, many times the original diaphragm gets stuck to it and you'll destroy it trying to remove it as the voice coil lead-in wires are hair thin and will snap. :sigh:

Coytee said:

Good luck on the project!!

If you can find original woofers (or foam for the originals) please post it. I'd like to get the woofers on my D's refoamed but have not yet been convinced that whomever I might have do it can get them back to (true) factory spec.

How I love the paper surrounds on my other speakers. The paper has been going strong since 1979 whereas the surrounds on the D's has already been replaced once and needs it again.

Click to expand...

Try Jim at http://circuitshop.com/

Hi dgwojo,

Be careful removing the horn, many times the original diaphragm gets stuck to it and you'll destroy it trying to remove it as the voice coil lead-in wires are hair thin and will snap.

Click to expand...

Is the constuction the same as with a T35 in this movie:
https://www.youtube.com/watch?v=Slbru4arSCQ
but then where the little horn is replaced bu the baby cheek horn?

thanks

PeterSchut said:

Hi dgwojo,



Is the constuction the same as with a T35 in this movie:
https://www.youtube.com/watch?v=Slbru4arSCQ
but then where the little horn is replaced bu the baby cheek horn?

thanks

Click to expand...

I haven't done an ST-350 in a number of years but I think the horn assembly lays against the diaphragm, personally, I'd just mask the working driver with masking tape and spray paint what's visible with satin black paint.

The set arrived today, in pretty good shape.
Need to do a bit of work.
A bit of kit between the plastic front plate of the VMR and the metal case.
Change the wires that are different and flimsy
And one of the ST350b terminals has a bad contact to the voicecoil on the outside.

Now all I need is an appropriate woofer (Sentry 500?)
I did see an easy available unit called EVS12B but I can't find the specs

I posted this picture in 2005 of the EV Interface D components, maybe the woofer numbers will help? :scratch2:

Thanks dgwojo,

I actually have this picture (I saved all I could find on the web)
The number that is readable on the magnet is more a production stamp very typical for all EV products.

There are however a few questions I have on this set:

The VMR has these cardboard quarter circles on them where the VMR that I have and seen were always front mounted and use a plastic ring.

What is also typical is that the woofer in your picture has the magnet assembly of the EVM12S, with the correct shallow (S) aluminum basket. In my findings the Interface D uses indeed that basket but the smaller magnet assembly of the force series.
Yours have the foam surroundings but the magnet seems to strong for the task (these magnets increase the efficiency but only above the lower octaves). I would classify this unit as an EVM12S reconed with Sentry 500 cone assembly.

I am investigating alternative LF units and will report soon on them.
Cheers.

The search for a good LF alternative;

The original Senty VI/Interface D woofer is rare and there are is no data available on the web.
I believe that the main responsible components for the sound are the VMR and the ST350b. Sure the woofer is responsible for the foundation of the system but because it is down firing it loses a bit of its harmonic character and acts as a true foundation to the fairly low starting VMR.

In the attached picture you see three graphs.
The white one is a Peerless XXLS unit 12" designed for the lowest octaves in a big enclosure.
The yellow one is a Beyma unit that resembles the EV unit. It is designed for a medium size enclosure, a bit louder but not capable of the lowest octave.
As a reference I added the Electro Voice EVM12L but in a small enclosure of 20 liter, no LF at all but very loud in its working area.
As a reference I added a 350Hz 2nd order low pass filter as used in the Interface D.

In my opinion the unit in the Interface D has a slightly higher efficiency as the Beyma of 97 dB 1W/1m but has a poorer lower octave capability that is corrected with the external equalizer.

So for the lower octave (the Interface D equalizer adds +6dB at 32Hz) the efficiency is actually only 91 dB and the amp does need to compensate for that........
So a 94 dB system with the Beyma is actually more efficient (seen for the amp) than the Interface D as most energy is needed in the lower octaves.

An alternative is using the Interface E (my design) in a Bi-Amp mode where a low power (single ended Triode) amp is used for the middle/top section and a 10 times more powerful amp for the lower octaves and use the Peerless unit where a natural frequency response up to as low as 24 Hz (-3dB) is possible.

Choices, choices......

PeterSchut said:

Thanks dgwojo,

I actually have this picture (I saved all I could find on the web)
The number that is readable on the magnet is more a production stamp very typical for all EV products.

Click to expand...

I think the first two groups of numbers are possibly a model number and the last set of digits like a production number, I notice this pattern on the T-35 tweeters. :scratch2:

Thanks dgwojo
I did dig into it and indeed the number points to a specific speaker but I haven't been able to find any.

An update.
My digging is paying off.

I have enough information to reconstruct the filter.
The poor schematic in one of the other threads and a bit of help allowed me to get the total schematic.
I will post the schematic as soon as I have drawn it on my computer.

Some other information:

With the exception of one picture that showed a round non ported hole in an Interface D I can add the following.

As you might have seen and owners can confirm, there is a possibility to partly close the down firing bass vent.
In doing that you lower the tuning frequency of the system but the output (volume) in that part of the frequency spectrum will also lower as a result.
Open, the system is tuned to about 44 Hz. When the port panel was installed in the Interface D it lowered the tuning to about 31 Hz and it then used the +6 dB equalization boost also at 31 Hz with the external EQ.

Apparently the Sentry VI did not have this option so the result was that the Interface D had extended bass, going a half octave lower than the Sentry VI, but needed some help from this EQ in front of the power amp.

Cheers,
Peter

The different VMR versions and the Interface D schematic

Hi,

I found some extra information about the different VMR's?
There are 4 versions with a 2,5" voice coil, and there is the 2" VC VMR II used in the interface C, The Interface Gamma and the Interface 300 (the last one I have just bought, and should arrive in a few weeks)

1803-9864 – This is the hi-fi version from the Sentry VI and Interface D

1803-9943 – This is the original pro version with a voice coil made from round wire. The repair manual says to rebuilt using the voice coil from the 18030595 below.

1803-0037 – This is the same pro version as the 18039943, except that the part number for the plastic ring was different. My suspicion is that this is the white ring stating VMR you see in some pro cabs.

1803-0595 – This is the later pro version with higher power handling with a voice coil made from rectangular wire. As near as I can tell, this coil has the same impedance and performance as the round wire coil from 18039943 and 18030037, except that it has higher power capability.

What this exactly means with respect to the sound is not clear. They are all quite similar but will most likely be different one way or another.

Cheers,
Peter

Update

Two weeks ago I bought a Swiss made Interface Delta. This is the licensed version of the Interface D build by Electro Voice SA.

The foam surround of the 12"down firing woofer was close to being powder. It has been refoamed and the units are playing again.

The enclosure is in an OK shape, but not good enough to be allowed in the living room (no, not my wife, myself)

The plan is to redo the filter by using all air inductors and high quality Mundorf polypropylene caps. This should make the unit sound better and if good enough I will rebuild the enclosure to a less wide but deeper and taller (same volume) shape bringing the tweeter in a better position.

A week before that I purchased an Interface 300 (equal to the Interface Gamma and very close to the Interface C)
This speaker is still in transit but that could be the base for a nice set of surround speakers (also in a new enclosure). I will experiment combining the 10" woofer, VMR II with an ST350 replacing the dome to get more synergy in the total setup.

That leaves me with the original bought VMR (pro versions as seen in my previous post) and 2 ST350b's. one of each has to end up in a new to be designed center speaker where the LF unit has to be determined completing the VMR and ST350.

Cheers,
Peter