crossover and so

Bert · « **on:** 19 Dec 2003, 08:19 pm »

Hello,

I have ordered 2 AKSA amplifiers (1x55W and 1x100W). to drive my speakers (2 subwoofers and 2 satelite speakers).
But I have some questions about pre-amping and crossovers.
I would like to use the GK-1M as pre-amplifier, but a friend of mine ill advised me that because I would use the GK-1M to drive a crossover and that would screw back the quality of the system because the crossover would be driven with a signal that is to small.
According to him, I should build the following:

input selection => 2 way crossover => buffers => 4 channel attenuator => Amps

Does anyone have a simular system? Is it through what he says about the signal being to small for the crossover?

What is the best thing to do when you want to bi amp with active filters?
I am planning on building a Linkwitz-Riley filter.

All tips, experiences and help is welcome.

Bert

AKSA · « **Reply #1 on:** 19 Dec 2003, 08:45 pm »

Quote

input selection => 2 way crossover => buffers => 4 channel attenuator => Amps

Does anyone have a simular system? Is it through what he says about the signal being to small for the crossover?
What is the best thing to do when you want to bi amp with active filters?
I am planning on building a Linkwitz-Riley filter.

Hi Bert,

Just received your order, my thanks; I'll post it off on Monday (today is Saturday morning here).

Interesting questions; check your seat belt, this could be uncomfortable...

A signal coming off a CD/DVD player is at line level. Nominally this is 0.775Vrms (2.2Vpp) with a source impedance around 100R, and often lower. A preamp is designed to accept this voltage, give it a tiny amount of gain, maybe 1.5 to 5 times (3.5-14dB), and pass it on to a power amplifier.

The typical opamps in active crossovers, and including Seigfried's designs, are powered from +/-15V supplies (some go up to +/-22V but they are unusual) and the output can go to at least 27Vpp, which is 9.5Vrms. They are usually unity gain. So they output precisely what goes in, at least throughout their passband.

If a preamp is inserted between the crossovers and the source, then it will actually output a little more signal to the crossovers than they'd get directly from the source.

Now, why use a preamp?

Firstly, source selection. It gives you this very important option, rather than hardwiring from just one source, which is highly inconvenient.

Secondly, a good preamp will process the signal, making it more engaging and adding an organic, human dimension which once heard, can never be ignored again.

Now, the uncomfortable bit.

Have you considered what happens to the sound after passing through the active crossover? It adds phase disturbances, inevitably, at and around the crossover frequency. They all do; it's actually what they do in order to be frequency specific.

This disturbs imaging, and in many cases, blows it out of the water.

You need to check a working version of this design before you commit. Check it permits good imaging.

Sometimes imaging can be restored by fitting impedance correction to each and every driver, because absence of impedance correction will also change the phase of the output to the driver and cause damage to the image.

Only then should you move forward with your plan. Imaging is VERY important, and once discovered, not something you'd want to give up.

Cheers,

Hugh

andyr · « **Reply #2 on:** 19 Dec 2003, 10:36 pm »

Hi there, Bert.

Your friend appears to be a sub-species of "audiophilia pura" entitled "passivistus absolutus" ... ie. he thinks the best "preamp" is a volume pot.

There is no point trying to reason with such people (just like there's no point trying to make a Jehovah's Witness acept that there's merit in any other religious belief) ... you just have to be polite to them and ignore what they tell you.

I run a 3-way Linkwitz-Riley active setup ... I used Rod Elliott's PCBs (go see at www.sound.au.com). My preamp feeds the right and left crossovers and then 3 x ICs go from each crossover into three AKSA monoblocks (25w/55w/100w). It works absolutely fine!

I am in the process of building a GK-1 ... which will make it all sound even better!

Now, I know Hugh believes active crossovers do not provide good imaging (this is an on-going project of mine - to produce an active crossover which he approves of!!) but in a sub-woofer setup, you can't go passive ... you must have an 18dB or 24dB active LP filter (as the coils and caps required are simply too large!).

However, you do have a choice for the satellite HP filter - either:
* a matching 18dB/24dB HP active slope, or
* a cap in series with the input of the AKSA which powers the satellites, to roll off their low frequencies at the appropriate point.

Good luck!

Andy

Malcolm Fear · « **Reply #3 on:** 19 Dec 2003, 11:36 pm »

I run something similar, but use a different approach.
CD player (or any other source) go into a GK-1.
I have 2 sets of "pre out" RCA sockets on the output part of the GK-1.
One set goes to an AKSA 55 power amp. From there the output of the AKSA 55 drives a pair of full range drivers. I do not introduce any filtering into this leg. The speakers roll off at about 70 to 80 hz, naturally.
The other set of pre out RCA's on the GK-1 go into a sub woofer pre amp, then onto a power amp and sub woofer.
Works for me, and I don't have any extraneous crap in the main signal path (no active crossover, no crossover components at all).

Bert · « **Reply #4 on:** 20 Dec 2003, 11:37 am »

Hi,

Thank you for the replies.

Hugh, It was a bumpy ride, but you have cleared any doubts I had about using a pre-amp.

I was planning on building Rod Elliott's Linkwitz-Riley filter. However my satelite speakers are full range. So maybe I should connect them directly to the AKSA 55, and only build a subwoofer filter? Or build a complete crossover filter and listen to the difference in sound with or without it?

Thanks again for the replies.
For those of you that are interested here's a picture of my speakers.

AKSA · « **Reply #5 on:** 20 Dec 2003, 11:53 am »

HI Bert,

Your speakers are very nice! Should be extremely fast and clean. I believe you follow the active arguments perfectly!

My thanks to AndyR for his explanation!! (Andy, your crossovers are MUCH better than most, but yes, the quest goes on!)

Personally, I opt for a two way, with limited bass, rolling off around 45Hz. I use a single 55W AKSA (although right now I'm listening to a 1.5W 6EM7 SET amp I've just built for experimental purposes through my AKSonics), and use 3rd order 2,500 Hz crossover on the two way. If I want more bass, I couple in a sub through a 100W AKSA (2 x 12" isobaric, 130 litres, VERY loud!) via a 3rd order filter with corner frequency around 95Hz.

In recent times I've not felt the need for more bass. I believe one loses interest in overblown bass as one ages. God knows why!

By avoiding an active crossover at line level, this does not damage the image, which is an important part of my own enjoyment.

Cheers,

Hugh

Jens · « **Reply #6 on:** 20 Dec 2003, 05:15 pm »

Hi Bert,

I agree with Hugh that active crossovers can wreck havoc with imaging.

However, that is mostly true when they are used for the treble and mid (this is where the imaging occurs).

So, the solution is to use the active crossover for the bass only! I've used this with great succes in my own system and have taken the whole thing a step further by using active equalisation as well for the bass extension. This allows me to utilise closed systems for the bass. This does indeed render bass much, much more precise than any vented system can hope for. You get ultrafast slam that is extremely well controlled! None of the vented system booooooom!

There are details on my web page about my system that might give you some inspiration (also in English).

Cheers,

JohnR · « **Reply #7 on:** 20 Dec 2003, 09:37 pm »

Could someone post a more detailed explanation of how exactly active crossovers destroy imaging? After all, passive crossovers have phase shift too, and any impedance funnies in a tweeter and mid are well below the crossover region.

andyr · « **Reply #8 on:** 20 Dec 2003, 10:43 pm »

Quote from: Jens

.... and have taken the whole thing a step further by using active equalisation as well for the bass extension. This allows me to utilise closed systems for the bass. This does indeed render bass much, mu ...

Jens, I would like to know more about your subwoofer setup. Are you using Siegfried Linkwitz's crossover/equalisation circuit? Could you send me the URL so I can access your web site?

Thanks,

Andy

AKSA · « **Reply #9 on:** 20 Dec 2003, 11:47 pm »

John,

As you know, I don't really get into the math too much - a weak point of mine. I do a lot of moving around, listening to others systems, and a lot of reading and playing around with circuits.

You are right that active and passive systems share much in common and should have very similar effects on image. But they don't. I would suggest the reason for this lies solely in impedance correction, which is a standard feature of well designed passive crossovers but almost never implemented with active systems because of the usual wish to avoid any reactive elements at the driver. Of course, there is a hugely reactive element at any dynamic driver - the voice coil, typically of a couple of mH or more, and we are stuck with it. Its phase shift should be corrected with increasing frequency to get the best from the driver, since the feedback regime normally used on SS amplifiers takes its cue from voltage, not current, and phase shift dislocates the two, leading to strange feedback anomalies. This is particularly important at the midrange and higher frequencies, where imaging information is found, but probably not too important at bass frequencies.

As you might guess, there are a couple of chapters of explanation in all this; forgive me if I go no further so I can finish my Christmas shopping!!

Merry Christmas and Happy New Year to you, your family, and all AKSAphiles the world over. You've all been very good to me, and 2004 looks like it will be an even better year!

Cheers,

Hugh

Jens · « **Reply #10 on:** 20 Dec 2003, 11:59 pm »

Hi Andy,

No, I'm not using the Linkwitz crossover, but something similar. It's a beautifully made unit from THEL in Germany. I haven't had a close look at the Linkwitz, but I bet they do more or less the same thing. If you can read a bit of German, there are details here: http://www.thel-audioworld.de/module/saw/saw.htm

Access to my website is easy, just press the 'www' button at the bottom of my post. On the opening page, press the 'English' link, and you're there.

The basic setup of my system is passive xovers between tweeter and midrange AND a passive roll-off of the midrange (working in conjunction with the midrange unit's own acoustic roll-off). Bass roll-in and equalisation is done by the THEL unit. Don't be fooled by the size of the speaker system - I have a large room. This setup will work beautifully with a smaller system as well.

The high/mid is powered by an AKSA 55 Nirvana, and the bass system is powered by a 2 x 250 watt ICEpower PWM module from Bang & Olufsen.

If you have further questions after visiting my website, please do not hesitate to get back to me.

Cheers,

Oz_Audio · « **Reply #11 on:** 21 Dec 2003, 10:22 am »

Bert, what are the main and sub speakers you are planning to use for this? Do you alraedy have these or are you planning to build some?

Sub integration is not easy when the speakers are not used in the way the designer intended. Most people just add a sub to "Full Range" speakers and it may not work. I use main speakers that are designed to roll off at 80hz (no high pass crossover) and the sub starts at 100 hz (active 18 dB/octave).

Mark

Bert · « **Reply #12 on:** 21 Dec 2003, 05:01 pm »

Hi Oz_Audio,

The speakers I intend to use on the AKSA system are units I have build with Monacor speaker chassis. The speaker units are made and build to work togheter. here is a picture of them

The satelites are full range speakers. The sub is added for a deeper and more civilized bass.

I will post more specs, but I can't right know because I left them at work.

Greetz, Bert

fred · « **Reply #13 on:** 22 Dec 2003, 01:43 am »

Quote

As you might guess, there are a couple of chapters of explanation in all this; forgive me if I go no further so I can finish my Christmas shopping!!

That reminds me: I'd better start my Christmas shopping. For the first time, it occurs to me Aussie Christmas Carols evidently avoid reference to snow and sleighbells (being the middle of summer). I wonder, do they (instead) reference swimming, sweat, and heatstroke? Just curious.

AKSA · « **Reply #14 on:** 22 Dec 2003, 01:54 am »

Fred,

In fact, no, they don't. They rather play down the cold and snow, but don't replace it with swimming, heat, and dust. It seems the Limey heritage dies very slowly, a pity. We've not got a lot of Christmas Carol composers in Australia - just now passed 20 million souls - but I can see there's an opening here. Hmmm. I'll ask around, I have a composing friend.

Cheers,

Hugh

fred · « **Reply #15 on:** 22 Dec 2003, 02:14 am »

Inherited from fair England, eh? Does Father Christmas make his way down there, still wearing the fur coat? (Perhaps he sheds it as he nears the equator, and dons shorts and sandals).

Sorry for the digression, but you are enriching my culturally impoverished mind.

EchiDna · « **Reply #16 on:** 22 Dec 2003, 08:42 am »

Quote from: fred

Inherited from fair England, eh? Does Father Christmas make his way down there, still wearing the fur coat? (Perhaps he sheds it as he nears the equator, and dons shorts and sandals).

Sorry for the digression, but you are enriching my culturally impoverished mind.

Santa/Father Christmas or whatever your culture calls him still wears the red fur trimmed coat in Oz, and here in Singapore (right on the equator itself!) as well

it is even weirder than in Oz here as there is 'snow showers' at a lot of the big shopping malls - the 'snow' is actually a shower of bubbles coming out of the decorative Christmas themed facade stuck on the outside of the stores!

you get hundreds of kids and their families playing in the bubbles wearing shorts and sandals every day

Oz_Audio · « **Reply #17 on:** 22 Dec 2003, 09:12 am »

I love it when threads get highjacked!!!! Makes one read everything.

About 20 years ago when my very English grandparents died, we started having a Seasfood, mainly Crayfish (lobster) Xmas lunch instead of the roast.

Now Seafood Xmas lunch is the latest fashion. Nothing better, Cold Cray, Prawns, Crabs, cheese and Beer!! Pissed by 11am and sleep all day while the kids go ape.

Any way, back to the topic. Bert, good looking speakers, keep us informed.

Mark

stvnharr · « **Reply #18 on:** 22 Dec 2003, 05:53 pm »

Where does Christmas Lunch come from?
Having spent a few Christmas down under, I got myself in real trouble over the concept of Christmas Lunch, when I am used to Christmas Dinner at a more reasonable hour.

EchiDna · « **Reply #19 on:** 23 Dec 2003, 08:33 am »

Quote from: stvnharr

Where does Christmas Lunch come from?
Having spent a few Christmas down under, I got myself in real trouble over the concept of Christmas Lunch, when I am used to Christmas Dinner at a more reasonable hour.

Christmas lunch gives us time to get two big meals and two rounds of drinking into the day... or one long continuous meal/drinking session!

origins? very good question... what else would you do in the middle of Christmas day? eat sandwiches??