Tannoy system 15 DMT II

Fair enough. So long as you are happy with the results you get.

FWIW I don't use digital EQ, but would not hesitate to do so for bass duties having heard the results. And I run a very purist valve and vinyl set up.

 

Hi,

I am not not entierly sure what is attempted to be said with that, but it makes zip sense electrically. What I THINK is referred to is electrical damping, that is the ability of the amplifier to SINK (absorb) reverse induced currents from the driver, which in turn apply an electrical "break" to the cone (if rather ineffciently).

If you use a suitable single ended amplifier the damping is in essence fixed by the valves anode impedance, transformed down by the output transformer. An optimally matched SE Valve Amplifier ALWAYS has a daming factor of 2.6, you can about double that, if more damping is required by connecting an 8 Ohm Speaker to the 4 Ohm tap, in this case you loose around 30% of the maimum power or 1.5db maximum SPL capability.

Continuing on my Corner Yorks (which are not miles off in various ways from a 15 DMT, though they used mch superior quality alnico drivers with the "pepperpot" phaseplug fron the days when workmanship was top notch) with a similar tuning as the DMT's extended well into the upper 20Hz range without significant attenuation.

Shown here is the equalisation curve from one speaker using a Behringer DEQ8024 digital equaliser (heavily modified):



This is in fact the inverse of the actual frequency response of the righthand speaker, in room, uncorrected. If you look closely, you can tell that the resultant in room response falls into a 6db (or +/-3db) wide tolerance field (the whole range is +/-12db or 24db in total) between 30Hz and 16KHz, with a gentle top end rolloff (near ideal conditions).

Despite having a range of subwoofers available I felt no need to use them at all, though I used the Digital EQ to equalise the system flat to 25Hz with around -6db at 20Hz.

As the DMT 15 is intended for soffit mounting a placement near corners is essential to get a balanced Low frequency response, free field spacing will produce an uneven and bass light sound. It would then be hard to integrate subwoofers at all and make the system extremely twitchy to tune "just so".

I would suggest to experiment with open cell foam in the ports if the bass is a little overbearing in a corner position, thus somewhat damping the port action, this can be used to very precisely "tune in" the low frequency response. My Corner Yorks where about as old as I am and instead had their internal stuffing optimised and much increased over Tannoy's original specification, which in essence has had the same effect.

Probably. However you would probably be better off DIY'ing a suitable sub using some serious drivers in "URPS" and using something like a Behringer Feedback Destroyer as crossover/equaliser. By clever placement and use you could actually use the subwoofer output to "reverse correct" problems (including room modes) caused by the main speakers and you would not have any requirement to place a digital EQ into the direct forward path of the system.

I would keep the 15 DMT's running fully open (no highpass) with their ports tuned to give really good response and follow up with a pair of Eminence Magnum or Kilomax 18" Subs in a small sealed enclosure (22" cube), using the classic ELF style analogue processing and some whopping big amp's (think Kilowatt into 8R), place them relatively far away from the main speakers and use a suitable digital EQ fed directly from the 15 DMT's speaker input (with an L-Pad if you use amplifiers above 10VA output) to produce the neccesary "anti room EQ".

Most likely you would have to invert the polarity of the Sub, which in the main would become actually an active room mode suppressor and would extend the very low fewquencies of the 15 DMT to basically however low you like. With a Magnum or Kilomax 18" per side I'd have few qualms setting the ELF EQ to 12Hz LF cutoff....

Ciao T

 

As a slight side issue (and without intentionally deflecting the theme of the thread), I'd be interested in reading what you replaced the original stuffing with, as I've been meaning to do the same to my Cheviots. I temporarily stuffed a load of sheeps wool in which improved things a bit, but I need a better and more permanent solution.

 

Hi,

Actually, I did not do the tuning. The gentleman who did in the 1960's used sheeps wool (Mr Baily's extra longhaired extra virgin sheeps - so probably not from Wales or NZ ) held in place by coarse burlap fabric stapeled over the wool, the stuffing was arranged to leave a free path between driver and ports but covered the whole interior. Based on another friends corner york experiences this methode was very effective.

Ciao T

 

Thanks for the info Thorsten, so I wasn't going too far wrong when I used sheeps wool then! I want to strip out all the old foam anyway as I understand that it can harden with time, and I'll start again with more sheeps wool in canvas 'cushions' and see how I go....

Baa.

 

Hi,

I suspect that modern engineered acoustic foams would offer a better performance and utility, but the quaint old methodes are still quite good and also rather satisfying, moreso perhaps than cutting foam blocks....

Ciao T

 

You are right but what I was thinking is that IF you want bass, using a big efficient sub like you have there would indeed be a substitute for needing huge amps and pushing the Tannoy's.

All I'm really getting at is that the frequencies below 100Hz generally need more power than anything else in the music so if you hand that over to a dedicated sub you can normally get away with less power for the main speakers, as long as you high pass them.

 

Interesting, that is very much the method some transmission line designers prefer, while others insist on stuffing all though with wool.

 

hm, i've noticed that 215's go pretty cheap on some markets, probably due to size and ugliness.

i don't mind about both so a possibility that you can have a pair for say 1200-1300 quid started getting me hooked.

my only issues are a room size and positioning.

can i bring in 4x15" monsters into 24m2 room, 3m high without endangering the statical stability of my house?

can 215 be practically wall mounted? considering their size and weight - as well as an old wooden suspended floor - i think the only safe place for them is a thick, outer wall (20" bricks), 3,3 m wide, firing nearly 5m towards a listener.

i know this is hypothetical but maybe someone more clever and experienced about room acoustics can see if this can be put under control.

re amps, i think i would go for a cheap SS for bass, something like alesis R150, with some nice SET or gaincard or altmann's BYOB for DC driver. first in bi-amped mode, later active.

any thoughs? how far are 215 from classic or prestige tannoys?

 

My present system uses Tannoy 15DMT II loudspeakers, and I have found due to their high sensitivity and not too difficult load/impeadance that a large variety of amps can produce a good sound from these speakers. I have used low powered SET 300B amps (around 8 watts), low powered digital amps (Trends 15watts), higher powered digital (Nuforce 100 watts), and high and medium power transistor amps (Gamut & Pass Labs), all sound excellent. I have found the small Trends digital amp and the higher powered NuForce digital amps to be particularly succesfull. Biamping the speakers also pays dividends, making the soundstage in particular much wider and deeper.

If anyone is interested I have a pair of the smaller Tannoy 12DMT MKII speakers for sale which are in excellent condition and come with their original boxes.

 

I'd be more interested in your 15 inchers.

 

if steve hoffman is to be trusted, it's the 215 from DMT series that should be looked for....

http://www.stevehoffman.tv/forums/showthread.php?t=50180