The MB2S PMC speakers you refer to here is like two stacked XB2 subwoofers, these subs are passive and around £5000 a piece so that a pair will set you back about £10k, which is about $15500, and as these are passive you need sub amps in addition.
[imghttp://www.pmc-speakers.com/sites/default/files/xb2-00.jpg[/img]
It is hard based on just these things to have any opinion about quality, and price / value proposition, but if you compare to competing brands it's certainly not winning on price. However, there's always been something very different in a positive sense with TL's and as such... it's probably hard to find better anywhere else, but the price of these things
XB2 is not their top of the line product, there's also an XB3 sub....
Even REL, that seemed to be quite pricey to mee is cheap compared to these things....
Yes BBC uses PMC, so does David Gilmour (Yes, that! Mr. Gilmour)
XB2 | PMC Loudspeakers
You can get a set of Vienna Acoustic, The Music for the price of these two subs, if you just add some extra money.... or you can get Thiel CS 3.7 plus a pair of subs from SVS... probably also Vandersteen model 5.... so competition here is tough....
I guess it would be interesting to have a qualified look into these PMC products by someone very qualified, is it so much better that it's worth this price penalty?
Yes, TLs are worth the trouble and price. They have always been expensive, the IMFs were and the Radfords before them. TDL speakers commanded a high price. John Wright of TDL was a very nice guy, and not in the business of ripping people off. Back 30 years ago his top model sold for just under $24,000 per pair.
Over the years a lot of poor commercial designs have come and gone. This coupled with a bunch of misinformation has added to the fog. Basically a correctly designed TL is a tapered stopped pipe, with a speaker placed to avoid exciting the third harmonic and critically damped to suppress one peak of impedance, but only just! The pipe must have the correct length and volume to optimally load the driver. This is easy to say but hard to accomplish.
That is why TLs have in the main been the preserve of DIY designers and builders like myself.
As far as PMC, I have only heard one set of their speakers. I liked it very much, but I have seen third party data on some of their models and they are not correctly damped.
Since you are interested in TLs here are the impedance and phase angles of the five lines in my studio here. There are 9 lines in all with only the center not being paired.
First the right and left mains which are dual lines.
The
mid line exits at the port just above the upper 10" driver.
Note there is a broad peak of impedance from around 30 to 80 Hz. There is one peak of impedance so the line is critically damped and rolls off 12 db per octave. The impedance peak correlates well with the region of driver support.
Now the
bass line which exit either side right at the top of the speaker.
You will note a peak of impedance centered at 32 Hz with the base of the peak from 18 Hz to about 50 Hz. So there is driver support in this region. For measurement I had to parallel the two 10" drivers, but they are driven from two separate amps, both operate below 60 Hz and the upper driver carries the BSC for the mids.
Note that the peaks of impedance of the two lines are one half octave apart. This is a trick of John Wright. This leads to very smooth bass support in this system from 20 Hz to 80 Hz.
Now the center line.
This shows a peak of impedance at 49 Hz the base is from about 24 Hz to 75 Hz. Again I had to parallel the drivers, but again they are driven from separate amps, the upper driver providing BSC for the lower driver, which has the coaxial tweeter connected.
Now the rear backs.
The mid line driver is the Dynaudio M75 with a lower response limit of 90 Hz. This is a biamped speaker, with the first crossover at 180 Hz third order. So the goal of this line is to damp this mid driver and avoid any hint of "boxiness". The line is over damped and tuned to 90 Hz.
The
impedance curve shows a small peak of impedance at 95 Hz. The line exits from the slit between the top KEF B139 and the M75.
Note the crossover performance. This is the crossover that was 10 years plus in development, and the longest in gestation of any of my designs. The crossover to the upper three drivers is almost purely resistive. It is a first order crossover and the first crossover is an unusual series crossover the 5 kHz crossover is parallel. The drivers are time aligned
The amps don't have anything to complain about with this crossover.
These strange animals are very good speakers indeed. They were my monitors for a quarter century.
The bass line exits at the top of the speaker.
The KEF B139s are tricky to load. They have a gentle roll off beginning just above 50 Hz, first order, and then fall away faster below 30 Hz.
So this line cheats a little. As you can see there is a peak of impedance just below 60 Hz to assist the drivers, the line is very slightly under damped to extend response down below 30 Hz. You will note a very small secondary peak of impedance at 25 Hz. This arrangement keeps the B 139s pretty much flat down to about 33 Hz and with highly significant extension below that. In fact they sound better than the vast majority of subs.
Now the surrounds.
These are 2.5 way sealed Qb2 boxes, using Dynaudio drivers.
As expected there is one peak of impedance and it is centered on 90 Hz.
The F3 is 53 Hz with second order 12 db per octave roll of.
Now a ported box. These are the speakers in the first level great room.
As expected there are two peaks of impedance associated with the LF tuning at 12 and 38 Hz, which puts the system tuning at 30 Hz.
You can see three way crossovers are tricky. To make the significantly negative phase angles coincide with peaks of impedance took 27 components per crossover. The speakers are easy to drive as you can tell from the curves.
As you can see the studio TLs are quite a juggling trick.
However I think it was very well worth the trouble. Bass is deep and without bloom. This allows for a piano for instance to sound exactly like a piano, totally convincing.
Yet when the grandchildren arrive with the BS they have saved for there are peals of delight. They were here with Real Steel recently. The robots walking about shook the floor, like they were in the room.
The boxing matched caused peels of delight from the children. As Ethan pointed out you really know where your liver is.
In the final boxing match the effects were superb, and you felt as if you were in the arena. Giving joy to the grandchildren like that is just icing on the cake.
The spls were pretty high but nothing sounded stressed and the amps only just got warm. Despite this huge power and effect, the LFE channel is set -3.5 db below the rest of the system.
So yes, I firmly believe good TLs are worth the trouble and expense.
I have chosen not to publish this much detail, on the off chance someone might want a set. However they really are so complex the cost would put off all but the most devoted and wealthy souls.
