[PierreB]

I'd like to know if it's better to buy a 4B SST or another 2B SST and put it in mono with my 2B SST. I look in different topics but find no real answers. If a 4B SST is better then 2 x 2B SST (in mono) than why ??? By the way I love the sound of my 2B SST and I want to keep that sound. My ProAc D18 need more power than my Response 1SC to sound their best and I know that bigger is not always better. I think about a 3B but it's only 50 watts more than my 2B.
Thanks.

[Elizabeth]

The one issue with bridging an amp to make a monoblock from a stereo amp is the speaker impedance.
Normally a low impedance speaker does not matter, BUT, when you bridge the internals of an amp, the load each side sees is halved. So if you have nominal 8 ohm speakers, that is not a problem, as the bridged amp sees that as a four ohm load.

The problem comes in if you are using 4 ohm speakers. Then, the bridged amp sees that as if it were a two ohm load. and that is not good.
So that is the main reason there might be a problem.

I was going to ask James Tanner about the 7B-SST2 which can be factory built to be a series, or parallel. And one can do 4 ohm loads (or even less) no problem, where the other is 8 ohms
I read about it here, and I just cannot find the reference to it.
Anyway, you could also ask James if YOUR amp, and the new one, could be set up that way???
So it could run a four ohm speaker?

[PRELUDE]

I do not have any experiment with 2B or 3B but I would say they might fit ok in small speakers.But for floorstanding ones your entrance ticket would be the 4B.As far you are staying with two way as D18 is better then a three way in a passive crossover.The bigger is not always better is true,but any passive crossover between the speaker and amplifire introduces significant impedance that can reduce the damping factor that is why we have the 28B for some big boys.

[srb]

But the question is two 2BSST, each bridged to mono which would give 360W/ch @ 8 ohms versus one 4BSST with 300W/ch @ 8 ohms.  Bridging is generally only recommended for 8 ohm speaker loads and usually not recommended for lower impedance speakers because a bridged amp sees half the impedance of the speaker load.
 
The Proac D18s are an 8 ohm speaker (haven't seen an impedance graph to know how much lower and at what frequencies they might dip down to), so they may be an appropriate candidate for bridged amplifiers.
 
I would be curious to hear James Tanner's thoughts on this as he knows both amplifiers well, and may even have some experience with the Proacs.

If I were starting from scratch, I would obviously just buy the 4BSST, but if I already owned one 2BSST ..... ?  However if speakers were changed in the future to lower impedance ones, the 4BSST would certainly be the way to go for future-proofing.
 
Steve

[john1970]

I would definitely look at the impedance graph of the ProAc D18s before going the bridge route on the 2B SST.  I would recommend calling a ProAc dealer and asking their opinion as well.  If you are willing to go used, a 4B SST can be purchased for around $2500. 

Good luck,

John

[James Tanner]

Hi,

I would go with the 4B.  Nominal impedance's are just averages and the 4B will be more comfortable than a bridged 2B.

james

[john1970]

Here are a couple of links to the measurements of similar (Response D2 and D28) ProAc models.

http://www.stereophile.com/content/proac-response-d-two-loudspeaker-measurements

http://www.stereophile.com/content/proac-response-d28-loudspeaker-measurements

From my brief reading, both speakers appear to be a relatively easy load to drive with minimum imdedances of ~6 ohms around 150 Hz.  However, the speakers appear to be relatively low sensitivity of around ~85 dB/2.83V/m.  If it were my decision I would take James's advice and purchase a 4B SST. 


Good luck,

John

[PierreB]

Yes the 6 ohms minimum impedance plus the 85 db sensitivity scare me a little.
The 4B looks the safest way to go so I will begin to save my money.
Maybe I will go with the SST².
Thanks all.

[rajesh]

I'm not sure if the speakers have two binding posts or four. If they have two, that means a single crossover supplies the drivers with the appropriate signal. If there are four binding posts with bridges each in between red and black terminals, it means that the bridge can be removed and the speaker can be bi-wired / bi-amped. In that case, you may use a total of 4 channels available in 2 x 2BSST amps to drive each of the four drivers. However, you may have to do a horizontal bi-amping than vertical bi-amping since the two amps would be from different batches and may not have very identical charecterstics.

[vegasdave]

Yes the 6 ohms minimum impedance plus the 85 db sensitivity scare me a little.
The 4B looks the safest way to go so I will begin to save my money.
Maybe I will go with the SST².
Thanks all.

Yeah, I would go for the 4B too. That way you're not in doubt.