Another Electro Voice Interface D/Sentry VI thread.

[PeterSchut]

Things are getting out of hand

Hello Forum,

Things are getting out of hand …. (that is not new for me ….)

I have been working a lot on the design of an EV based surround system and want to share what all happened.
It all started after I bought 2 VMR’s and 2 ST350b that I mentioned at the beginning of this thread.
Since then I bought:
- A set of Swiss made Interface Delta’s – The foam surrounds are renewed
- A set of Swiss made Interface 300 (close equivalent to the Interface C)
- I found a single ST350a in perfect shape (future center speaker)
- And last weekend I ran into a Sentry 500 and 2 extra ST350b’s that I couldn’t resist.
(see attached pictures)
The 500 is quite a nice speaker and the woofer is the closest thing to an Interface D woofer, but still different. As you can see in the pictures it is a shallow or short basked with magnet structure from a Force 12, were the original Interface D woofer is the longer/deeper basked and magnet structure from the famous EVM12L.
The tweeters of the 500 are the well known HiFi tweeters from the Sentry 100a and Interface C but then mounted to a very pretty wooden horn. I have no real plan for the 500 parts but the enclosure has seen better times, and I might try to put it in an enclosure like my Interface E design but then as a 2 way front loaded system.

The design of the Interface E is getting more and more shape see attached PDF.
The filter parts are ordered for a full rebuilt of the passive filter with all Mundorf high end caps and air conductors.

So far for an update.

Peter

 

[PeterSchut]

Things are getting out of hand (cont)

And some more pictures ....

I forgot ... I found and bought an Interface A EQ that will be modified to an Interface D EQ

Peter

 

[dgwojo]

The dome tweeter used in some versions of the "C" was actually a good sounding tweeter with nice dispersion, most of them have deteriorated foam diffusers by now though, Dave.

 

[absolve2525]

How are you finding these awesome EVs that I've never seen here in the US? Lucky guy! Have you had any experience replacing diaphragms on ST 350? For some reason I had one that sounded brighter than the other, and wondering if you ever noticed variations.

 

[totem]

Peter, great thread of your EV speaker project.

 

[tomlinmgt]

The dome tweeter used in some versions of the "C" was actually a good sounding tweeter with nice dispersion, most of them have deteriorated foam diffusers by now though, Dave.

The foam diffusers on my C's are still in great shape. I'd sure like to know if there is anything I can put on the foam to preserve them. :scratch2:

 

[PeterSchut]

How are you finding these awesome EVs that I've never seen here in the US? Lucky guy! Have you had any experience replacing diaphragms on ST 350? For some reason I had one that sounded brighter than the other, and wondering if you ever noticed variations.

I can't tell yet, I did remove a full magnet/VC assembly from an ST350b and that was easy. What I have seen replacing the diaphragm doesn't seem to complicated but the wires are flimsy. And the loose diaphragms I can get are all after market ... not ideal I guess.

But all the drivers are US made. So EV Switzerland got the drivers from the US and then made Swiss enclosures with sometimes some small variation.
As I now have 7 ST350 (3x a and 4x b) I will investigate them.
It seems that tightening the screws can influence the volume by optimizing the “0” spot of the coil/
If you don’t notice it, it might be over tightened and you need a new filler between magnet structure and coil assembly. I have not checked that but it makes a lot of sense. I will know soon.

 

[PeterSchut]

Hi dgwojo,

I did see some US based suppliers still have the foam. I believe these are 2 parts inner and outside part ($ 25 a set .....)
I guess that the horn should give a similar result but will be louder. It is by the way hardly a horn as it is very flat. I do like the look of it and that probably made me buy the set.
A new set could look like this: (see pdf)

 

[totem]

Not to derail your D direction but I am curious if you have played with the Sentry III series for comparison.

 

[PeterSchut]

Not to derail your D direction but I am curious if you have played with the Sentry III series for comparison.

Not realy but i did built a clone 33 years ago, and at that time I loved it. Today the physical shape will not make it into the living room as it is to wide an not tall enough. I alo think that the VMR will do a better job on voices. It can be used on a much lower x-over and will never sound nasal. But i know there are quite a few fans out there.
Bottom line, the Intface D configuration is just more appealing to me (taste)


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[Pete B]

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......

What is the internal volume of the Interface D woofer section?

 

[absolve2525]

Peter, thanks for the info about the diaphragms. I bought an ST-350 pair recently from some Sentry speakers and they both sound the same. I don't know the history on my other set. I replaced the diaphragm on one, after destroying the one it came with when I attempted to open it up for examination. I'm always hesitant about opening up horn drivers, for that reason! I bought the aftermarket diaphragms from a Simply Speakers on Ebay. The tweeter leads were enameled where they are supposed to be soldered, making it difficult to install. I used a soldering iron to scrape it off. I reused the original cardboard gasket. I was not aware of overtighening being an issue, let me know if you encounter that. Thanks

 

[PeterSchut]

The original Interface D vollume is 111 liter, my design calculates to about 120 liter


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[Pete B]

I should have asked, do we have T&S specs for the original Interface D woofer?
Is the crossover schematic online somewhere?
I'd like to know the DC resistance in the path from the input terminals to the woofer - it would be nice to see the rest of the XO also.

Nice work by the way!

 

[Pete B]

Is this the correct schematic?

 

[PeterSchut]

Is this the correct schematic?

Yes, that schematic is correct.
Woofer 4mH series, 90u paralel, 1,3mH and 2.5 ohms Series!!!
Mid 1,3 series 9u paralel, 17,7 series, 4,3mH paralel
High 1,5 series, 0,42 paralel

There are no TS parameters that I know of the woofer

Peter

 

[Pete B]

The original woofer was 4 ohms I take it since the system was somewhere
around 6-8 ohms?

Do you know if all the drivers are wired in phase? All negatives to negative at
the input terminals?

The 2.5 ohm resistor significantly raises the effective Qts of the woofer to make it
match the vented bass alignment better. It is like having a weaker motor or magnet.
Is that 3 Watt rating correct? Can't be, it would burn up.

Sure would be nice if someone would measure the woofer and VMR T&S
parameters next time some are being worked on.

 

[PeterSchut]

The original woofer was 4 ohms I take it since the system was somewhere
around 6-8 ohms?

The 2.5 ohm resistor significantly raises the effective Qts of the woofer to make it
match the vented bass alignment better. It is like having a weaker motor or magnet.
Is that 3 Watt rating correct? Can't be, it would burn up.

Indeed my woofer measures 3,8 Ohm DC
And the 3 Watt is 30 Watt on my system (and it looks like 30W is mentioned in the component description on the schematic)
See attached file for basic schematic with the tube socket connections removed.

 

[Pete B]

Thanks for the diagram, that all makes more sense.

 

[hunter00]

I run my EV D's with an old dynaco st70.very efficent and lovely tone.Just need to find the EQ,just about had one but was not fast enough on e-prey