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Now a Soviet Era Drivers for the Mets

Hari Iyer

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#1
I started looking for a new pair of drivers to replace the Fostex for my Mets and since past 3 months have been looking around. Though there were plenty of options, the one that could fit the requirements of parameters, cost and delivery was not more. Typically its said that if you look around too much for a particular thing, then at the end you purchase more with your heart and intuition rather than your head and logic. I think this is what happened to me when I ordered the Soviet era driver from the 1980s. I have gone to the extent of looking at Lowther, Voxativ, AER drivers which was miles above my budget. Also considered many vintage Alnico types etc. But the Alnico would require a subwoofer as they are more for mids and highs. Also was reconsidering Fostex and the Dayton point source full ranger. Both the Fostex and Dayton are more technical sound and I knew what to expect from their associated hype. Finally came across this driver. It was purchased on intuition and there are plenty of DIY speakers with this driver ranging from BLH, Horn, TQWT, Sealed, OB etc. This driver like any Russian product is built like a "Tank" with a thick cast iron basket (no painting) and looks pretty heavy (unlike the thin basket used in Chinese driver which needs to be painted to avoid rusting).

Like my project this driver is also DIY. Typical TS parameters are not given much importance. More importance to the driver material - paper used, suspension used, glue used for sticking the spider, suspension and cone at the voice coil. Details of the voice coil, guage of wire used, number of turns, number of layers etc. are mentioned in the specs other than the usual TS parameter. Also surprisingly, harmonic distortion of this driver gets mentioned above all. Another surprise when I ordered this driver was - the seller asked me if I want some changes in the driver like the suspension used and the colour of the suspension required. So this driver is not over the shelf, but is made after ordering - a true DIY driver but has many followers in Russia.

The driver after its modification will be shipped in a weeks time and will post impressions after I have worked with them.

Thanks for looking.
 
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Hari Iyer

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#7
My broad band driver with new hangers (suspension) are now ready for dispatch. There were 3 to 4 colour options with different Qtc and Fs. I opted for the white colour ones as they were with lower Qtc and higher resonance.
 

keith_correa

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#8
My broad band driver with new hangers (suspension) are now ready for dispatch. There were 3 to 4 colour options with different Qtc and Fs. I opted for the white colour ones as they were with lower Qtc and higher resonance.
Qtc?
 

Hari Iyer

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#9
Orange colour hanger Qtc = 1.03, white colour hanger Qtc = 0.71 (Total Q)

Qtc = Qes*Qms/ (Qes+Qms)
Where Qes = Electrical Q
Qms = Mechanical Q

Typically for a ML TQWT or BLH, the Qtc should be preferrably low (less than 0.5) to enable low stuffing, else the low frequency gets compressed. But if the resonance is lower, you can still go ahead with moderate stuffing to get a flatter low end. Much will depend on the box loading. Also over damping can help with higher Qtc driver (> 0.7 and < 1). For Qtc > 1 OB or sealed enclosure is preferrable.
 
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keith_correa

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#10
I think you're confusing Qts with Qtc. They're different.
 
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keith_correa

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#12
Total Q is Qts. Qtc is the resonant behavior of the driver in an enclosure.

And no, AFAIK they're not interchangeable.
 

Hari Iyer

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#14
I am planning some diy activity for this driver. The published Qts for this driver is around 0.71. But i am planning to keep the Qtc around 0.7 for the speaker system. This means i will need to lower the Qts of the driver. As Qts is a function of Qes, i shall be reducing Qes to achieve this. This can be done either by adding more stuffing to the cabinet or by inducing electical damping to the voice coil. As i will be using these drivers with my SET tubes, adding a resistance across the driver terminal will add additional damping and there by help to reduce Qes (there by reducing Qts). I am planning to reduce the Qts to around 0.55 so that the overall Qtc is around 0.7 for the cabinet+ driver. From network theory we know that a Q of 0.7 gives a maximally flat frequency response.

The Mets have a cabinet volume of around 36 liters. With Qts of 0.55 and desired Qtc of 0.7 and with the published Vas of 23 liters gives me a cabinet volume of around 36 liters. Looking at the videos of the driver, it seems the stiffness of the spider + suspension of this driver is quite low.. That means its a high compliance driver (compliance is inverse of stiffness). Hence the cabinet compliance should be low to get an overall lower compliance of the speaker system. Adding more stuffing can increase the cabinet compliance. It wiould be quite tricky to get the right stuffing to get a overall Q of 0.7.

Adding the resistor in parallel to the driver can reduce the sensitivity a bit and also reduce the VC resistance. To counter this i will be adding additional dual magnets salvaged from a Peerless tweeters to increase a dB or 2 on the SPL. Have not done this before hence keeping my fingers crossed.

Thanks for looking.
 

yogibear

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#15
Why not just play this driver in Open baffle first with no crossover and played from your SET ? This will give you an idea of what this driver is capable of and then do your box thing and compare the sound ?

After all, everything you do is about the sound, what you hear.
 

Hari Iyer

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#16
Why not just play this driver in Open baffle first with no crossover and played from your SET ? This will give you an idea of what this driver is capable of and then do your box thing and compare the sound ?

After all, everything you do is about the sound, what you hear.
Its good suggestion and can be thought off. But the Qts is not high enough (0.71) to warrant for an OB. Probably a Qtc of > 1 would be suitable. I may receive the driver by end of this week and only the measurement will confirm the actual values.
 

yogibear

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#17
No Hari, Qts of 0.7 in fact is just perfect for OB. Its a myth that Qts of > 1 is good for OB. In fact, sonically, Qts of 0.7 is perfect for OB in case of a full range driver. Trying to make a full range driver do the low end duty in OB takes its toll on midrange magic. So just try it before attempting your driver in a box.

Your driver specs state that it does fine 60-20,000 Hz. I presume, it will do great 100Hz to 16K practically. An open baffle width of 24" will be fine. Atleast it will tell you the sonic quality of your driver and how capable it is when driven with no crossover, no box damping effects, driven by your SET.

You may end up going back to OB after all your "driver in box" iterations. Atleast you will know the difference in sound.
 

Hari Iyer

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#18
An open baffle width of 24" will be fine.
This looks great but has poor WAF for me due to space constraint in my home otherwise i would have tried them for sure as it will NOT be acceptable to family to block the room space. I dont have a luxury of separate listening room for the time being.

In the meanwhile i did a LA simulation of the same driver with a modified Qts = 0.51 and i got very good bottom end with my current Mets volume off 36 liters. I have simulated without ML and kept the entire terminus open with heavy stuffing density. Posting the image.
 

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