[Felipe]

Hi all, i hope this is not too long, plz read and post an opinion!

I built an AKSA 100w almost a year ago now and have been very happy with it. I have been using it with a pair of Proac Response 2s speakers (8ohm).
For a while i've been wondering how would the AKSA behave with my old Mission 782 (4 ohm) wich i now use for surround speakers in my HT system. I decided to give it a try....put the Proac in surrounds and the Mission in front mains...

These are the specs and chars of both speakers :

Proac Response 2s :

- $3000 US dollars  (2 years ago)
- 8 ohms
- HIGHS: extremely transparent , very accurate bass, smooth highs, crystal voices
- LOWS : sometimes too transparent (shows defects), not very big presence or body....maybe the room is too big ?
- MUSIC PREFERRED : Acoustic guitar, wind instruments

Mission 782 :

- $1000 US dollars  (15 years ago !!)
- 4 ohms
- HIGHS : presence
- LOWS  : slow bass, not transparent at all, voices shallow, as if with a cloth or a curtin covering them.
- MUSIC PREFERRED : anything


Ok...looking at each one specs its easy to see that the Proac is much beter...and it is. But...how do they sound with the AKSA ?
What changed when i putted the Mission back ?

Many things...most beeing what i referenced before. With the Mission's i had covered voices, the bass was slower and not as deep (but not bad..we are talking about an AKSA here !!!) , and most important the mystic of the acoustic guitar and the flutes and violins was gone. The Mission just plays music like an ordinary speaker. At least compared with the Proac.

SO...WHATS THE FUZZ ABOUT ??
Well...i dont know if its because the Mission is 4ohm and the Proac is 8 ohm, but with these Missions riding the AKSA, i thought my house was going to explode. What a sense of POWER. I noticed that the AKSA had power..but never this kind when i connected it to these speakers.

Sure, it didnt had magic, the sound was overall worse, but in 5.1 surround i tend to believe (and now even more) that what matters is power.
It just sounded better ...liveler...stronger. My living room was filled of music for the first time.
This was with 5.1 music though, because with stereo the strong power is just not enough to beat the crystal voices and the controlled bass, etc.
I think that is why so many ppl have separate systems, each one requires diferent combinations! But i cant have that ...


So the question is :

Is it because it delivers 200W in 4 ohms now instead of 100w in 8 ohms???
Is the AKSA best suited for low impedance speakers ?
Do my Proac need a 200w AKSA ?

Does anyone else has a similar experience ?

Sorry for the long post...

[Larry]

These are the specs and chars of both speakers :

Proac Response 2s :

- $3000 US dollars  (2 years ago)
- 8 ohms
- HIGHS: extremely transparent , very accurate bass, smooth highs, crystal voices
- LOWS : sometimes too transparent (shows defects), not very big presence or body....maybe the room is too big ?
- MUSIC PREFERRED : Acoustic guitar, wind instruments

Mission 782 :

- $1000 US dollars  (15 years ago !!)
- 4 ohms
- HIGHS : presence
- LOWS  : slow bass, not transparent at all, voices shallow, as if with a cloth or a curtin covering them.
- MUSIC PREFERRED : anything

What are the sensitivities of each speakers ?

[Felipe]

I am not sure about the Mission's....i cant find any paper related to them.
But the Proac's are  86dB i think.

[AKSA]

Felipe,

It is difficult to put an explanation on this.  However, the following might be useful:

1.  The power of the AKSA into a 4R load is almost doubled over an 8R load, so dynamic headroom is immediately enhanced.
2.  Speakers are not purely resistive, they are reactive, and if the impedance curve is flat, the amp will always sound better since phase shift is controlled more effectively and this will enhance short term stability on any SS amplifier with a global feedback loop.
3.  The quality of 'lifeforce' in amplified music is related to stability issues on the amplifier voltage amplifier which are greatly impacted by the feedback factor and the speakers used.  Consequently, if the reactance of the speaker is well controlled, then the feedback factor is more consistent, and qualities like presence, 'life' and vitality are improved.

These sonic qualities are only now being discussed in the hifi world since the nineties, and their relationship with the design of the amplifier is still being investigated.  All I can say is that I have indeed done a lot of R&D in this area, as I seek to design the most involving amp possible, and while I have some of the answers, my information is empirical and not fully understood.

I cannot overstress the importance of the crossover in a loudspeaker.  It is absolutely crucial to the sonics.  Get it wrong, and so many do, and the poor interaction with the amplifier will make the speaker sound flat and lifeless.  This is one very good reason certain amps and speakers go well together.

Cheers,

Hugh

[cmscott6]

Hmm... So has anyone out there found a particularly synergistic combination of AKSA and speaker (including Aksonics)?  I realize this is purely a subjective point, but I'm just curious.  I have a pair of home-built two-way transmission line speakers, which sound very nice with AKSA 55N and GK-1.  Granted I also have a small room, but the imaging,  height and depth of the music is phenomenal (even more so since changing C3 on AKSA to a Black Gate. Thanks Hugh!).

[Darren Thomas]

Hmm... So has anyone out there found a particularly synergistic combination of AKSA and speaker (including Aksonics)?  I realize this is purely a subjective point, but I'm just curious.  I have a pair of home-built two-way transmission line speakers, which sound very nice with AKSA 55N and GK-1.  Granted I also have a small room, but the imaging,  height and depth of the music is phenomenal (even more so since changing C3 on AKSA to a Black Gate. Thanks Hugh!).

I've heard several speakers on my AKSA 100 and must say I haven't found a speaker that didn't sound incredible paired with it, of course the speakers I've built are from very good kit designers. I've listened to the Ellis 1801's, Adire Kit 281's, GR-Research AV1+'s, AV1's, and will soon listen to the Criterions, and the Diluceo's. All so far have sounded great with the AKSA 100. These speakers have extremely high end crossover parts and are designed very well.

My favorite pairing so far would be the Ellis Audio 1801's with the AKSA 100.

Darren

[cmscott6]

Did you like the Adire Kit281's?  I've been thinking of building those this Summer.  Ideally I'd like to build the TL option, but so far I can't find anyone who has tried it.  It's always hard to shell out the money for a speaker I haven't heard...

[Darren Thomas]

Did you like the Adire Kit281's?  I've been thinking of building those this Summer.  Ideally I'd like to build the TL option, but so far I can't find anyone who has tried it.  It's always hard to shell out the money for a speaker I haven't heard...

I have listened to the sealed and vented version of the Kit281's. My personal opinion is that they place too much demand on the tweeter to fill in the mids. This is my opinion, I could be out of line. They crank like nobody's business and are far superior to many commercial speakers at much higher cost but I'm not partial to their sound. I prefer the 1801's to all the speakers I mentioned except for the Criterion's and the Diluceo's because I haven't heard those two yet. If you are going for a more refined sounding speaker I'd consider the GR-Research AV1's or AV1+'s. My opinion is that they are a bit more laid back and involving. Both speakers are detailed and very accurate, I just prefer the less "in your face" speakers. The 1801's are also much more involving in my opinion. They all have their place though. I haven't met a DIY design I didn't like yet

Darren

[PSP]

Hi Darren,
I'm very interested in your comparison of the GR Research AV1+ with the Diluceo... I expect "no contest", but the Diluceo is way more expensive and I'd like to build a GK-1 too.  Please post your impressions on these speakers when you get a chance.

My main amp is a 55w AKSA and I have a spare 55w AKSA that I can use for biamping... I know that I can biamp the Diluceos; can I biamp the AV1+ without messing with Danny's crossover design?

Thanks,
Peter

[Darren Thomas]

Hi Darren,
I'm very interested in your comparison of the GR Research AV1+ with the Diluceo... I expect "no contest", but the Diluceo is way more expensive and I'd like to build a GK-1 too.  Please post your impressions on these speakers when you get a chance.

My main amp is a 55w AKSA and I have a spare 55w AKSA that I can use for biamping... I know that I can biamp the Diluceos; can I biamp the AV1+ without messing with Danny's crossover design?

Thanks,
Peter

I also expect it to be no contest but you are correct, the price difference is significant. Yes, you can bi-amp the AV1+ without modifying the AV1+ crossover. A different binding post setup would be necessary but easily done. I am wiring a pair of Diluceo's for bi-amping currenlty for a customer. It would be the same procedure for the AV1+'s.

I'll definately post my impressions. I expect them to be nothing short of amazing.

Darren

[Carlman]

I have a pair of Revel F30's with similar specs to the ProAc's mentioned.... except the resistance is 6 instead of 8 ohms.  I listened to the ProAc's A/B'd to the Revel's using a Marantz receiver as the source.  This was at a shop with a nice sound room.  The ProAc's sounded like they needed double the power they were getting.  The Revel's sang with authority.  The AKSA almost seems like overkill for my amp-friendly speakers.  However, the clean detailed nature of the amp, lets everything else in the system shine through.

I have also connected the amp to 2 other pairs of DIY speakers and found the results very musical.  The amp gets out of its own way very well.  On a pair of 8-ohm line array types, the amp wasn't struggling but, didn't produce the full potential of the speaker, either.  It sounded good but, not great.  Some guy in Florida made them.  I haven't ever heard that pair of speakers sound great though, the person who owned them said they needed a lot of power to sound good.  So be it.

I think the ProAc's are real power suckers.  But, that's my limited experience.  Bi-amping your ProAc's would probably be a great idea.  Whereas bi-amping my Revel's would probably be a waste.  

I found a lot of small differences with speaker cables.  I don't know what's best for anyone but, by experimenting I've found Kimber's 4TC to gel it all together fairly well.  Audio Magic works, too.  (Silver coated copper)... I found some home-made Canare to be too much.  NOT good speaker cable for this combo... but, a great combo for my old amp.

-Carl

[Felipe]

Thanks Carl, i found your comments to be very usefull.

Yes i too think my Proac's are "extremely power suckers".
At the shop, they usualy connect them to Krell or Mark Levinson's from 200w to 400w or up. This for solid state amps...

But this is not all....because when Proac trully shine ... is with tubes....and tubes dont have 200w of power...lets talk more like 50w for a good tube power amp.

So...if Proac works well with litle power with tubes...why does a solid state need to have 200w to really make the speakers alive ?
Since i bought them i have that feeling...they are great...but they can give MORE!

What do you think is best , put in a Nirvana TLP to introduce tube sound in the Proac's....or put in a 55w in the tweeter and bi-amp the suckers ??
I am a litle insecure ..... Hugh can you help here?

If bi-amp is the way to go....how do i do it? How do i get 2 pre-outs to feed both the amps ? Do i need to build a crossover ?

Thanks guys for helping....

[AKSA]

Felipe,

Can't help much here because I don't have ProAcs, and I'd need them to find why they sound as they do with the AKSA.

I would not be surprised to find impedance anomalies in the ProAcs.  This would account for the apparent sonic equivalence of 200W SS and 50W tubes - a dead giveaway.  I'd suggest the ProAcs bring a little instability to SS amps with global negative feedback - that is, most of them - and this may be what you are hearing.  My experience tells me this sort of problem makes the system very sensitive to cable selection....

The solution to the problem, I hate to say it, is a redesign of the crossover on the ProAc, not something you really wanted to hear!  You'd start by doing an impedance plot - it should not rise above about 12R at any frequency, and if it does, you've isolated the problem.

Cheers,

Hugh

[Felipe]

Hello all,

Thanks Hugh for giving your help here.
Something like that would force me to open up the speakers cabinet and mess with the crossover right? Well, that is out of the question, because i am not experienced enough to play around with a 3k us.dollar speaker.
And i find it hard to believe that a 3k speaker has poor crossover design.

Nevertheless how do i do the impedance plot ? Should i just chek with the multimeter across the +/- at the speaker while music is playing?

And another thing that maybe you missunderstood.... the Proac's do not give equivalent sound with 200w solid state and 50w tubes....Its very diferent ! I think that the tube romance that a Proac can give through a valve amp is something that makes everything else disapear...
The Proac still needs a big power amp to drive them properly, and in s.s. the 200w or up do the job. At least the Krell did.

[AKSA]

Felipe,

I can understand your reluctance to mess with the ProAc crossover.

However, I KNOW categorically that many expensive speakers have poorly designed crossovers;  remember, it was designed by a human being.  Actually, those designed by computer are almost always worse.......

I have a friend with ProAc towers.  They cost even more, full of ATC drivers.  He drives it with a Cary 805, SET with the 845 (he also uses an AKSA 100W to drive the woofer, but that's another story.)

He has had the crossover professionally altered and it is now a better speaker, at least that's what he says - and he has good ears.

You need to factor in the compatibility issues;  some amps just don't cut it with good speakers.  The Apogee, the Grand Slam - these are very expensive speakers but they are compatible with only a few amps.  The fact that your ProAcs sound best with a 200W Krell says something about the impedance curve of the ProAcs, and I can promise you that this bears some research.  If you want the answer, you have to take the first step, remove the crossover, plot the schematic at the least, then study the technology.

No one ever said this was easy.  Imagine your pleasure if you should find you can actually improve on a ProAc!!

Cheers,

Hugh

[AKSA]

Felipe,

I almost forgot;  impedance curves.  I found this on the net from one Pat Brown, a designer of loudspeakers.  You can find others like it on the net under 'impedance plot' in Google.

"Since the impedance of a loudspeaker is a frequency-dependent parameter, it must be measured at multiple frequencies to get a true picture of what the amplifier is “seeing” at its output terminals. While very sophisticated methods and instruments exist, you can get a pretty good idea about the impedance curve of a loudspeaker with a standard real-time analyzer.

You will need a pink noise generator (or audio signal generator, much cheaper) and voltage source of at least 10 volts RMS to drive the loudspeaker. A small power amplifier with at least a 12.5 watt rating into 8 ohms works well for this purpose, or you can use the AKSA itself.

Place a 1000 ohm 1% metal film resistor in series with the amplifier output. This value will allow impedances up to 100 ohms to be measured (most loudspeakers).  The voltage across this non-inductive resistor gives you a direct reading of the impedance;  the closer this voltage approaches the output of the amplifier (which you must also measure) then the lower is the impedance of the speaker.  
With this configuration, the voltage across the load will be proportional to the impedance of the load. The impedance measurement will be made by measuring the voltage across the load with a voltmeter or real-time analyzer.  You can use a quality DMM on AC as long as it is certified to 20KHz;  not many are, however.

To calibrate the setup, substitute an 8 ohm noninductive load resistor for the loudspeaker under test, and adjust the analyzer for a nominal reading at 1KHz, the standard frequency. This reading should correlate with an 8 ohm resistance.

Substitute the loudspeaker under test for the resistor. You will now be viewing the impedance curve of the loudspeaker as you sweep from low to high frequencies.  The AKSA will deliver a flat response from 20Hz to 20KHz as long as the audio signal generator output is flat also.  

If you have say 10 volts output from the amplifier, and you have calibrated the speaker with an 8R non-inductive resistor, then you will have 9.92 volts across the 1000R resistor, and just 7.94mV across the resistor.  This is 8R impedance.

If you then leave the output of the amp the same, and measure 15mV, the impedance of the speaker is 15.2R.   (15.2/1015.2 = 15mV)
 
Hope this is helpful,

Hugh

[Felipe]

Hello,

Hugh, thank you so much for the time and caring.    
I will try that method to try and seek the impedance curve of the Proac's.

But i came up with a diferent approach  :  

Lets say the Proac's have that impedance curve pretty unbalanced.
In regardance to what you said :

"it should not rise above about 12R at any frequency, and if it does, you've isolated the problem. "

...i saw some impedance plots of a group of various speakers and usually all of them rise well above 12R at least 1 or 2 times !!! So i think those 12R upper level is a bit low...almost every speaker rises to 20 or up at some frequency, at least the ones i saw, of course there are exceptions.

That said, i thougth of a way to reduce this slop . Lets say i put a Resistor of 17 ohms (of 17W in order not to burn) across the loudspeaker terminals. This would reduce the curve a lot ! If i had 30 ohms at a certain frequency i would have now about 11 ohms ! So this would eliminate any rise of the impedance...and keep the impedance plot more stabilized !

The downcoming of this would be that i would be asking more power from the amplifier...but the AKSA has lots of it...and maybe this would be a nice alternative  ???        

Hugh, i think i need your opinion here.....a must have really.  

Thank you so much for helping !


Felipe

[Oz_Audio]

Not all speakers have large peaks and troughs in their impedence plot.

Here are my DIY speakers plot (total cost less than $400USD):

http://homepage.mac.com/tlinespeakers/TLS/projects/tlB/images/tlb_imp.gif

The top plot is the phase shift and the bottom plot is the impedence.  As you can see it is almost flat at 5ohms.

These work very well with an AKSA 55, image sensationally and I highly recommend them.  They are a very unusual design and I also use a Linkwitz Phoenix Peerless dipole woofer for below 100hz.
http://www.t-linespeakers.org/projects/tlB/index.html

Mark   [/img]

[Oz_Audio]

Not all speakers have large peaks and troughs in their impedence plot.

Here are my DIY speakers plot (total cost less than $400USD):

http://homepage.mac.com/tlinespeakers/TLS/projects/tlB/images/tlb_imp.gif

The top plot is the phase shift and the bottom plot is the impedence.  As you can see it is almost flat at 5ohms.

These work very well with an AKSA 55, image sensationally and I highly recommend them.  They are a very unusual design and I also use a Linkwitz Phoenix Peerless dipole woofer for below 100hz.
http://www.t-linespeakers.org/projects/tlB/index.html

Mark