[drphoto]

I'd like to try an active crossover to high pass my Merlin monitors. The brands I'm aware of are:

Bryston
Marchand
NHT X2
Paradigm x30
vintage Audio Research

Which of these is the most neutral and transparent? Seems like the Marchand is pretty highly regarded. Is the tube version worth the added cost? Is there anyone modding any of these?

NHT doesn't  show the X2 (which is the version for non-NHT speakers on their website) Is is still available?

As the Merlins are a sealed design, what crossover slope would I want?

What about the passive high pass filters from ACI?

Thanks for any insights.

[Davey]

If all you want to do is high-pass your speakers a couple of capacitors and resistors will do the job fine.  Probably cost you about $10.

http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

Davey.

[woodsyi]

What is the roll off characteristics of your monitors?  Can you just low pass the sub and blend the monitors in?  I have had good sucess with 24 db slope for woofer/mid filter.  I use a XM44 3way and like it but XM9 is supposed to be good too.   XM126 is too expensive and i wanted the x-over to be as neutral and clean as possible since I already use tubed pre and amps.

[audioengr]

I'd like to try an active crossover to high pass my Merlin monitors. The brands I'm aware of are:

Bryston
Marchand
NHT X2
Paradigm x30
vintage Audio Research

Which of these is the most neutral and transparent? Seems like the Marchand is pretty highly regarded. Is the tube version worth the added cost? Is there anyone modding any of these?

NHT doesn't  show the X2 (which is the version for non-NHT speakers on their website) Is is still available?

As the Merlins are a sealed design, what cross ...

Neutral and transparent?  They all have coloration, mostly due to coupling capacitors and cheap op-amps.  The DEQX is good when used through the digital input.  I have modded this one, but I can mod any of them.

[Aether Audio]

drphoto,

I'd like to try an active crossover to high pass my Merlin monitors.

I agree with audioengr's advice. In theory, an active circuit is the way to go for a number of reasons, but the "devil is always in the details."  By the time you add the filter and buffer stages, it's almost as if you were adding another preamp in line - but usually worse.  If you can find a really good one then I'd say go for it, but I can't make any recommendations.

Seeing that your monitors are sealed designs to begin with, a passive high-pass is easy to implement.  To create a 4th order Linkwitz-Riley alignment, all you need to know is the monitor's -3dB frequency point.  Assuming the box has a standard Butterworth 12dB/oct. rolloff, select a series inductor followed by a shunt capacitor that gives a second order (12dB/oct.) Butterworth high-pass response (into the same impedance as the monitor) with the same -3dB frequency as your monitors.

If you select a good air-core coil and use some decent film caps in parallel with the electrolytics (which you will need to use as the cap values will be large), you can avoid all the active X-O issues and end up with really excellent results.  You'll gain at least 3dB of low frequency power handling at the X-O frequency, more below (obviously) and a little above that point as well.  A secondary benefit is that you won't have to worry at all how the low frequency rolloff of the monitors will interact with the high-pass transfer function of an active, were it to be set to a higher frequency.  In this case, your monitor's frequency response is part of the total filter transfer function to begin with.  

Add a sub with a 4th order low-pass at the same frequency and you're done.  With a fourth order alignment set to such a low frequency (which it's bound to be unless the Merlins have virtually no extension to begin with) you won't experience the "mushy" bass that reults from the larger group-delay of such a filter used at a higher frequency.  On top of all that, the steeper slopes mean less driver interactions, making sub/monitor placement less of an issue.

Well, that's my 2 cents worth.  Hope it helps.

Have fun!:D
-Bob

[Jon L]

I have used several active crossovers, including Purist Audio, Krell, KMF Audio, and now Bryston.  I can confirm that active crossovers do have "colorations," but a lot of it can be avoided if the integrated volume controls are not used.  Used this way, Bryston is superbly transparent.

I would also opine that although I prefer active over passive, that's when an active is used to remove a passive x-over.  In your case, you're not removing any passive x-over but ADDING an active crossover.  No matter how good the active x-over, this will not sound as pure as nothing added.  

In your case, I would tend to run your Merlins (TSM?) full-range, then try to blend in the sub at low frequency and high slopes, experimenting with phase, placement, etc.

If you have access to a good DSP crossover, that may be a better option, but that'll require some investigating.  Even something as cheap (FREE) as Foobar crossover plug is more transparent than any active (or passive) crossover network I've heard of...

[bhobba]

drphoto,
I agree with audioengr's advice. In theory, an active circuit is the way to go for a number of reasons, but the "devil is always in the details."  By the time you add the filter and buffer stages, it's almost as if you were adding another preamp in line - but usually worse.  If you can find a really good one then I'd say go for it, but I can't make any recommendations.

SP Pres is correct.  A DEQX has been mentioned.  And while it does signal processing it is in the digital domain and does much more than simply splitting the frequencies for the drivers.  I does room, frequency and phase correction including time alignment of all drivers that, to the best of my knowledge, can not be achieved by any other means.  Expensive - yes (although considering what some spend on pre amps maybe not) - but the way of the future.

Thanks
Bill

[Davey]

Did you guys even read my suggestion?  He simply wants to high-pass his monitor speakers.  It's very simple to do this at line-level with a passive network.
Why in the world would you want to perform this at speaker level?  Or with a full-blown active crossover?  Or with a mega-buck unit like the DEQX?  Or with some other gadget?

Cheers,

Davey.

[Scott F.]

I'd like to try an active crossover to high pass my Merlin monitors. The brands I'm aware of are:

Bryston
Marchand
NHT X2
Paradigm x30
vintage Audio Research

Which of these is the most neutral and transparent? Seems like the Marchand is pretty highly regarded. Is the tube version worth the added cost? Is there anyone modding any of these?

NHT doesn't  show the X2 (which is the version for non-NHT speakers on their website) Is is still available?

As the Merlins are a sealed design, what cross ...

There are a couple that you didn't mention. The vintage Pioneer SF 750, 850 etc, and the vintage Sony TA 4300. Heathkit also made a tubed XO.

The Pioneer isn't too bad but the Sony is definately more 'transparent'. good luck finding one. I've only seen one in the past six or eight years and I bought it (and sold it).

Anything vintage you get will need new caps. The vintage Audio Research EC series will need more. The coupling caps need to be replaced with a better cap. The multisection power supply caps need to be replaced also. Don't touch the silver micas or the old Allen Brady resistors. This crossover can sound extremely good with some resoration but it is damned pricey plus you have to feed it four 12ax7's for each band (low, mid, high as is the case with my EC3). Tubed units are not for the faint of wallet. If you can swing one and are willing to rebuild a vintage one, you'll fall in love with it.

Tubed crossovers (as it is with most tubed gear) can add tons of life to your system (if that is what you are looking for). Right now my EC3 is in the shop since I can't find the time to fix it. I'm using my Pioneer SF750. It's not bad but I miss my EC3. The system sounds dead without it. Steer clear of those cheap pro-sound and DJ versions of an active XO. You get what you pay for with those things.

I can't really comment on the other pieces you mentioned as I've not heard them.

The one thing to consider with the plug in, line level high pass filter you mentioned, make sure that your preamp has a pair of line outs, one for the amp driving the Merlins and one for your new sub. The next thing, the preamp will need to have a healthy amount of gain (and current). There will definately be some insertion loss associated with the inline piece. Not to mention, if you use the second line out for your sub, the ouput voltage of your pre will stay the same but the current will halve. This is a big reason most people use a true active crossover (somehting with an internal gain stage).

An active crossover is a wonderful thing. It's not as bad as some would lead you to believe. What you gain in dynamics, clarity and overall headroom (or aparent power) far outweighs any of the pitfalls IMO (even from less than 'transparent' models). I've been bi or tri amping with active XOs for as long as I can remember (almost). I'll never go back to standard monkey coffins again.

[Watson]

Seeing that your monitors are sealed designs to begin with, a passive high-pass is easy to implement. To create a 4th order Linkwitz-Riley alignment, all you need to know is the monitor's -3dB frequency point. Assuming the box has a standard Butterworth 12dB/oct. rolloff, select a series inductor followed by a shunt capacitor that gives a second order (12dB/oct.) Butterworth high-pass response (into the same impedance as the monitor) with the same -3dB frequency as your monitors.

SP Pres, thanks for this informative post!  Forgive me if this is an overly simple question (I don't know much about filters), but wouldn't I use a series capacitor followed by a shunt inductor instead of what you said (basically the opposite)?

Another question...  On this page:
http://www.t-linespeakers.org/tech/filters/passiveHLxo.html
they suggest creating a second order highpass filter by putting two CR filters in series.  Correct me if I'm wrong, but doesn't this create a 2nd order Linkwitz-Riley filter instead of a 2nd order Butterworth filter?  So the approach on that page, if used, wouldn't combine properly with a sealed speaker's natural rolloff to produce an LR4 filter?

If I wanted to create a 2nd order Butterworth passive filter that goes between my preamp and amp (rather than between the amp and speaker), is there any way I could do this?  If I tried to use a series capacitor followed by a shunt inductor, assuming an amp's input impedance of 20k and a desired 100Hz crossover point, it looks like I'd need a 45 Henrie inductor!  I don't think that's practical.  Is there another easy way to create a 2nd order passive Butterworth filter that might work?

[Davey]

It's very difficult to achieve Q's greater than 0.5 (Butterworth=0.707) by cascading RC filters so it would be difficult to achieve a combined LR4 rolloff.  However, that's assuming your speakers actually have Q=0.707.  If the speakers are somewhat underdamped (Q > 0.707) then in combination with a second-order filter with a Q=0.5 or smaller you might ultimately achieve a target of LR4 or Butterworth 4.

Yes, passive filters using inductors at line-levels would yield some very high values.  Check out Phil Marchand's XM46 crossover which uses ferrite potcore inductors in the 1 to 3 Henry range:

http://www.marchandelec.com/xm46.html

http://www.marchandelec.com/ftp/xm46man.pdf

This type of LC crossover could end up being a difficult load for some preamplifiers as well.  

Cheers,

Davey.

[drphoto]

Thanks for all the great info guys.

Yes, as some have suggested, I want to do the high pass in order to gain more headroom. At even moderate volumes, material w/ very low bass is too taxing on the mid/bass of the Merlins. I've got a sub rolled in on the bottom now.

I think I'll give ACI passive line level filters a shot for now. They're pretty cheap, so I won't be out much if they don't work. Hopefully, as per Scott's comments, the Tempest pre will have enough grunt to make up for the insertion loss.

I can solder fairly well, but I don't have the electronics knowlege to make up custom units. I'd pretty much have to have a picture of the circuit and the values to do it. Working from a schematic only is a 'bit above my pay grade'.

BTW: Scott, I saw a guy on ebay was asking $1K for one of those old AR tubed units.....wow.


cheers

[Aether Audio]

Watson,

...but wouldn't I use a series capacitor followed by a shunt inductor instead of what you said (basically the opposite)?

BUSTED!  Aaarrrggghhh!  I can't believe I did that. I guess I had "low-pass" on the brain.  You're exactly right...series cap, shunt coil.  Duh.

Other than that obvious screw up, I still prefer to go passive at the amp output.  The parts aren't cheap and they're pretty big but I think the advantages out-weigh the disadvantages.  If you compare the cost of the passive parts to that of a good active, well...you just can't do it much cheaper.  The cost of both filters, even with expensive caps, should easily run less than $200.00

First advantage, seeing that it's not in series with the monitor, the inductor doesn't have to be "the best" as long as it doesn't saturate.  Madisound http://www.madisound.com/inductors.html has their "Sledgehammer" inductors at a pretty reasonable price.  They're high Q, low resistance, steel laminates that are rated to 500 watts.  I've used them and never detected a tinge of saturation.

Second, unless you wire something wrong (i.e., a short circuit), it's pretty hard to screw up or damage anything.

Third - no insertion loss.

Fourth, the amp still benefits as it sources less current.  This is because of the rising impedance it sees from the passive filter at low frequencies below the filter -3dB point.

Fifth, the passive parts are far less likely to cause any degradation, especially if you use a couple of good film caps in parallel with the electrolytics.

Sixth, the filter is pretty easy to tweak to get the proper system Q.  Just adjust the values a little one way or the other by adding/subtracting paralleled caps and/or adding/subtracting turns from the coil.  For the cap, start with a smaller value and add as needed.  For the coil, start with one bigger than needed and remove turns.  True, it really helps to have an analyzer of some type, but textbook values should get you real close.

The hardest part is finding your speaker's impedance at the -3dB point.  There's several ways to do that, the easiest being getting it from the manufacutuer's impedance plots.

An active will get you dialed in faster, but in lieu of some sort of test equipment, you're still stuck with the analyzers hanging on each side of your head.  Refined levels of engineering still take time, no matter which way you go - even with the new digital gizmos.

-Bob

[Scott F.]

Thanks for all the great info guys.

Yes, as some have suggested, I want to do the high pass in order to gain more headroom. At even moderate volumes, material w/ very low bass is too taxing on the mid/bass of the Merlins. I've got a sub rolled in on the bottom now.

I think I'll give ACI passive line level filters a shot for now. They're pretty cheap, so I won't be out much if they don't work. Hopefully, as per Scott's comments, the Tempest pre will have enough grunt to make up for the insertion loss.
 ...

Klaus' Tempest should do just fine driving the passives. Be sure not to judge too quick, those passive parts will need a bit of break in time. I'd expect about 40 or 50 hours before the sound 'opens up'. If you like the sound, maybe buy an extra one and dissect it. Then build one out of nifty parts (that hopefully sound better).

One thing, after you have it installed, be sure to swap the polarity of your speaker wires back and forth. I'm not sure if those things invert the polarity or not (I suspect they do). Check it both ways (by ear without the sub turned on) and see which you like better, then play with the polarity of your sub until they blend well.

BTW: Scott, I saw a guy on ebay was asking $1K for one of those old AR tubed units.....wow.

I've seen them go as high as $1200 bucks. Thats absolutely insane for an unrestored piece of kit. I got lucky when I bought mine. I paid $600 bucks for it about 5 years ago. That was just about the time they started creeping up in price.

Have fun!

[suits_me]

Gee, if I had great speakers like Merlins I wouldn't want to mess them up with cheap, passive inline filters.

How loud are you playing them so they bottom or whatever? Wow.

I would agree with the others who suggest supplementing the bass with a woofer and not messing with the Merlins, but you say it won't work for some reason....

A lot of subs include stuff to filter the mains if you hook them up to do that. And a lot of av receivers have simple 100hz bass management options.

Other externa; crosssover options which are far from perfect but affordable and better than the inline passives are available from Paradigm (they're monos, so you buy two,) the external box from Hsu, the (pending?) unit from Curt Wishman, and some of the Behringers. av123 has an x unit coming out with a crossover and Cello Pallette like function, but they tend to slip product announcements.

If money is not object then the analog Rives crossover would be the choice, although, as I said, no crossover would be my choice for this application.

[drphoto]

Suits-me,   you know you're right. I'd probably just screw things up, as the Merlins sound pretty darn great now, especially as I got the Straley speaker cable installed today.

Oh well, it was an interesting discussion.

[Watson]

Gee, if I had great speakers like Merlins I wouldn't want to mess them up with cheap, passive inline filters.

How loud are you playing them so they bottom or whatever? Wow.

The goal of using a high-pass filter isn't necessarily to prevent the woofers from bottoming out or to increase SPL.  The goal is to reduce distortion, thus improving sound quality.

A driver's distortion (across the frequency spectrum) increases as its excursion increases.  By forcing a woofer to handle the lowest frequencies, you thus increase distortion.  This can end up muddying the midrange or making the upper midrange sound harsher than it should.  In many cases the measured harmonic distortion with a high-pass filter is only one fourth what it would be without the filter.

Ordinarily, introducing extra components into the signal path isn't a good idea.  But this is one of those situations where a few extra components can significantly reduce total distortion, making it a win.  If you've never tried it, give it a try (people with home theatre receivers and subs can do this experiment easily).  I've always been impressed by the improvement.

[konut]

I'm with Watson on this one. I'm currently running a Toshibs SD6980 universal to a Creek OBH12 passive remote attenuator(3 input, 1 out) to a Behringer CX2300 analog active crossover to a pair of Kenwood KM-X1000 monoblocks driving Omega Aperiodic 8s. The mono sub out is going to a Rocket UFW-12. The CX2300 is an older Behringer model I purchased in '97 for $329. It has a fixed 24db per octave slope each way and its lowest crossover chioce is 90hz. There is a newer model CX2310 which has greater flexability and goes for about $100. While Behringer is not a highly regarded brand, it works as advertised. By avoiding the sharp impedance rise of the woofer at the tuning frequency with such a steep slope, the amp see a simpler load. This is in addition to the advantages Watson cited.  
      As the Behringer is primarily intended for the pro sound reinforcement market the need for adapters from XLRs to RCAs is required adding to cost. It is also built to withstand and output higer input and output voltages required in pro audio and even with a passive attenuator that I use I find the unit very clean. IOW I'm using it well below its limits.
         I have been using line level, both active and passive, crossovers since the '70s. I've found improvement over passive in every situation I've tried them in.

[Davey]

konut,

Point of clarification:  The use of an active or line-level crossover does nothing to avoid/aleviate "the sharp impedance rise of the woofer at the tuning frequency."  The amplifier will see exactly the same load/impedance curve as it would otherwise because these impedance fluctuations are the result of the driver itself and its interaction with the box.
Yes, the use of a line-level crossover means the amplifier is driving the speaker less hard at these frequencies, but the impedance curve is unchanged.

I've seen some crossover networks that use conjugate networks with large component values to try and reduce the resonant peak(s) of the driver-in-box, but these are few, and far between.

Cheers,

Davey.

[konut]

The impedance rise remains but the amp doesnt 'see' it. If you have a 4 wheel drive vehical but only use it in 2 wheel drive the engine never 'sees' all 4 wheels.