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PostPosted: January 25th, 2018, 12:28 pm 
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https://www.ebay.com/itm/1-X-NIB-UNIVER ... Swk~ZZ6NWu

He's got two listings, but if you look closely, it's the exact same pictures for both listings...

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PostPosted: January 25th, 2018, 1:32 pm 
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It is even crazier when you look at the linear volume displacement of the driver. Even though it was 30" in diameter it only had .15" xMax. That gives it a total displacement counting both directions of 198 cubic inches. It also required a box volume of 300 cubic feet. Compare to a modern driver like the Dayton Ultimax 15. It has a smaller diameter but the xMax is .75". That results in a displacement of 199 cubic inches and can work in a 3 cubic foot box. And it only costs $225.

Where's the catch? Hoffman's law strikes again.The EV had a sensitivity of 100 dB and the Dayton a sensitivity of 86 dB. That was very important in the days when 6 watts was a monster output from an amp. However, at 86 dB sensitivity, a 125 watt amp will still give you 107 dB. Considering that you can buy a 500 Watt class D plate amp with DSP built in for $300 that is a non issue today.


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PostPosted: January 25th, 2018, 3:59 pm 
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tomp wrote:
It is even crazier when you look at the linear volume displacement of the driver. Even though it was 30" in diameter it only had .15" xMax. That gives it a total displacement counting both directions of 198 cubic inches. It also required a box volume of 300 cubic feet. Compare to a modern driver like the Dayton Ultimax 15. It has a smaller diameter but the xMax is .75". That results in a displacement of 199 cubic inches and can work in a 3 cubic foot box. And it only costs $225.

Where's the catch? Hoffman's law strikes again.The EV had a sensitivity of 100 dB and the Dayton a sensitivity of 86 dB. That was very important in the days when 6 watts was a monster output from an amp. However, at 86 dB sensitivity, a 125 watt amp will still give you 107 dB. Considering that you can buy a 500 Watt class D plate amp with DSP built in for $300 that is a non issue today.


Tom,

I cannot speak of this speaker in particular but, all drivers of pre-solidstate era had small xmax and high sensitivity. That is due to the fact that power was limited with the tube electronics.

Remember the driver you measured for me, Altec 411? It has 7.5mm xmax, which means it cannot play any frequencies below 46Hz at 110dB (assuming power is unlimited). The legendary Altec 416 driver used in VOTTs, has the xmax of only 4mm and it cannot play any frequencies below 63Hz at 110Hz (3dB more for vented enclosures) . kick drums go up to 114dB, so these drivers do need a subwoofer to be effective. In effect, pre-SS era drivers will have limited dynamics and frequency response in the sub region with tube electronics.

After the advent of Solid State Electronics. power became abundant so the, xmax went up and sensitivity went down.


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PostPosted: January 25th, 2018, 5:47 pm 
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Shashi:

That is correct for most of the old drivers. The magnets were not as strong and the available amp power was limited so the designers concentrated any available flux in a short gap to get the highest flux density. Therefore small xMax. It was the perfect solution in those days. They also generally had a high Qts so there was a bump at resonance that would offset the drop in response from transformer limitations in most amps. The answer to low frequency output for them was to have relatively low moving mass and very compliant suspensions. They got low response and good sensitivity but the 800 pound gorilla in the room was the huge VAS requiring monster boxes. It is always about compromises.


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PostPosted: January 25th, 2018, 7:22 pm 
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tomp wrote:
Shashi:

They also generally had a high Qts so there was a bump at resonance that would offset the drop in response from transformer limitations in most amps.


Most of the older pro sound drivers that I've seen published T/S parameters for had fairly low Qts. Most of the Altecs from the 50s were <0.3, some were <0.2. Same with the older alnico magnet JBLs. But yes, Xmax was a lot smaller than current drivers. Of course, there wasn't a lot of low bass in the program material that was available, so it wasn't as much of a limitation as it would be today...

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PostPosted: January 25th, 2018, 7:47 pm 
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I probably should have said the Qts plus high VAS led to the bump in the cabinets that were used. As the box size goes down for a given driver the Qb and Fb both go up.


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PostPosted: January 25th, 2018, 11:12 pm 
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Speaking of weird stuff on Ebay, was looking for used TS GG preamp and came across these Chinese knock off PCBs. Several vendors are selling them. Look at the output coupling caps connections in the middle 12au7. They are connected to the grids, pins 2 and 7 instead of cathodes 3 and 8. Tube pinouts are mirror images, ie: tube sockets need to be connected on the back side of PCB. I wonder how many of their customers are struggling to get this preamp working!

https://www.ebay.com/itm/Ground-Grid-gg-12AU7-Tube-preamplifier-PCB/132439395068?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649


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