Active analog crossover?

James Romeyn · « **on:** 26 Dec 2005, 07:55 am »

I need an active analog stereo 2-way crossover, only to seperate sub-bass & midbass drivers. All signals above about 260 Hz will completely bypass the XO.

High-pass requirements:
Stereo
Pole range about 40-150 Hz, prefer 1 or 2 Hz steps but larger OK, prefer independent from low-pass but ganged OK

Low-pass requirements:
Mono or stereo
Pole range about 40-150 Hz, prefer 1 or 2 Hz steps but larger OK, prefer independent from high-pass but ganged OK

NHT, Bryston, Paradigm, the discontinued Sledghammer or the old Dahlquist? What's on your short list?

Thanks all.

Jon L · « **Reply #1 on:** 26 Dec 2005, 04:38 pm »

This is a very sore point in actively amped audio systems today. There are basically NO active crossovers that are all of the above: transparent, very flexible in x-over points/slope adjustments on-the-fly(Marchand's Achilles' heel), and are priced reasonably.

This is sad b/c most of the cheap "pro" type of active analogue x-overs are not close to transparent and b/c the "pro" digital x-overs that convert A->D->A are not desirable.

The nice x-overs that do purely digital x-over without ADA conversion require a lot of commitment and $$$ to build a dedicated system, usually digitally actively tri-amped, around the digital X-over, i.e. TACT, DEQX. Did I mention $$$?

I still believe actively crossed systems are the way to go, however, so there's the dilemma. First, I would cross NHT, Paradigm, and similar units off the list. These simply do not belong in the same ballpark as the nice ones. In general, I would avoid the ones that have continuously variable volume and/or x-over knobs that use cheap pots for these important functions. These should only be used if used for bass only, rolling off the satelites some other way, not going through the x-over.

Krell class-A active x-over is nice, but at the high price they charge, you might as well get a DEQX. The Bryston, surprisingly, competes well with the Krell at much less price b/c it uses discrete resistors to change volume and x-over point/slope instead of continuous pots. It also has a sledgehammer PS compared to most others (well...except the Krell).

Bryston's weaknesses. B/c they use discrete resistors, the x-over points are kind of far apart. You should look at the "sub" and "standard" model and choose the one that offers the x-over points you have in mind. Bryston also prefers to adjust level on the treble portion! not the bass like others. They say this way sounds better, but I hate it. I'd much rather lose transparency in the bass than treble with volume control. Any time I use the level control, even with discrete resistors, I can hear the loss of transparency.

I get around this by leaving the level control at 0dB and use an EVS Ultimate Nude attentuators to match levels of treble and bass amps, which is far more transparent than level control of Bryston. Used this way, Bryston is superbly transparent with power and slam unmatched by others IMHO.

James Romeyn · « **Reply #2 on:** 26 Dec 2005, 05:17 pm »

I feel your pain regarding transparency, but it barely if at all applies in this unique application. The active XO will NOT be in the signal chain above 260 Hz, zilch, zero, nada, gone, totally absent from that circuit. So really, transparency is needed only up into the midbass & lower midrange tops.

The midrange & up will be filtered by the passive XO inside the speaker, combined with trimming the input filter capacitor of the tube amp used for this range. The active XO will high-pass filter only dual 6-1/2" midbass drivers.

The active high-pass filter on these drivers will accomplish three goals, in this order of importance:
1. Combined with the active low-pass subwoofer XO, upper bass room modes are minimized.
2. Midbass performance is maximized by filtering lower frequencies to the sub only.
3. Midbass power requirements are minimized.

Variable high-pass slope would be sweet, but not absolutely necessary.

Though my first posted stated a desire for a low-pass section, it is an option & not necessary. One stereo (2-channel) high-pass XO in the 40-150 Hz range is all I really need.

Marbles · « **Reply #3 on:** 26 Dec 2005, 05:39 pm »

Jim,

Contact John Casler re: the NHT X2, I think it will meet your criteria and it does sound VERY transparent in my sytem...as long as all the IC's used are identical.

Maybe he can let you demo his.

JonL, the price of the NHT would indicate it would not be very transparent.

Problems often arrise because more pairs of IC's are needed with an active XO and the extra pairs that are used are often not up to the standards of the IC's used in the passive system. If you use IC's that are all the same, I think it will be difficult to tell the NHT from very expensive active XO's....it is transparent enough that lessor IC's made a noticeable difference.

I should note I have only used mine to XO at between 35hz and 70HZ.

J North · « **Reply #4 on:** 26 Dec 2005, 06:15 pm »

I am going through the just about the same process you are right now!
My added complexity is the requirement for EQ (dipole bass).
I also want to keep the mids/highs out of the equation.

Where the digital XO's fall down for this purpose is that the processing adds enough latency to throw the time alignment out a fair bit and suffer loss of resolution at lower signal levels if the volume control is before them.

I have done a bunch of reading on the pro audio boards on XO's and just about everyone is going digital there (BSS, XTA, DBX, Ashly, Behringer etc). The top 2 "reasonably" priced analog XO recommendations are Ashly and TDM. Next are Rane and DBX. YMMV of course.

The problem with the the analog XO's that use pots to adjust XO frequency is that they are not totally accurate, can start to get noisy, and just about impossible to match exactly across two channels which will be more of an issue for a home environment.

My thoughts are now to get my hands on the Behringer DBX, possibly mod ify it (diyaudio.com), use it to experiment and dial in my XO & EQ values, then build Op-amp based active XO/EQ based on those values (ala Linkwitz).

good luck . . .

John Casler · « **Reply #5 on:** 26 Dec 2005, 09:18 pm »

Jim,

As Marbles says, for your use the NHT X-2 could work quite well.

I even tried it on my 626R's (high pass) and found little sonic degradation).

The X-2 also has stereo (for 2 channel) as well as LFE (for HT) inputs that work independantly of each other, and have seperate volume control for LFE.

It has continuosly variable frequency adjustment up to 220Hz.

It is next to impossible to find on NHT's site, but is similar enough to the X-1 that you can get a good idea.

The main difference is that the X-1 has NHT "speaker specific" parameters and the X-2 is best for other speakers.

You might also have good luck calling Phil Marchand who will custom make or modify a design for you.

The Bryston are probably the "best and cleanest" sounding units, but they are also priced to reflect their cleanliness.

For your app, the X-2 might be the ticket

Kishore · « **Reply #6 on:** 26 Dec 2005, 10:01 pm »

You can look at Marchand too..

XM126

XM9

Cheers,
Kishore

woodsyi · « **Reply #7 on:** 26 Dec 2005, 11:09 pm »

Jim,

Call Phil Marchand to design you a XM9 or XM44 2way with a band pass mid(both high and low pass poles) and a low pass on the bass. At least on my 40s the ribbons have high pass passive filter around 275. You can run one (full) signal from your pre to amp(s) dedicated to the ribbons (which will be passively filtered) and another signal through the x-over to handle the woofers and the sub(s). Of course, you have to disable the woofer lowpass filter in your 30s. I am doing this with a XM44 three way and works like a charm.

James Romeyn · « **Reply #8 on:** 26 Dec 2005, 11:51 pm »

WoW! You guys are great, as usual! Thanks for the tips. This is like the Godfather granting my wish on his daughter's wedding day, without having to go to the wedding!

I fear the active xo would add grunge & coloration to the mids. That's why I intend to go active only on the midbass 6.5's & nothing else. A bandpass filter would allow me to bypass the first order passive xo (coil) inside the speakers, but I'd settle for the active high-pass filter, leaving the 6.5's untouched internally (passive low-pass xo intact).

gonefishin · « **Reply #9 on:** 27 Dec 2005, 02:07 am »

Hi Jim,

don't dismiss 250Hz right away (click the link below). There's a ton of instruments that play in that range. Many of the instruments that we normally listen to play much lower than we would suspect.

http://www.psbspeakers.com/audioTopics.php?fpId=8&page_num=1&start=0

dan

James Romeyn · « **Reply #10 on:** 27 Dec 2005, 02:52 am »

Dan
That is a very interesting link!

Dr. Harry F. Olson's classic Music, Physics & Engineering, pg 29, has a similar diagram labeling all notes in the scale of equal temperament, with frequencies identified to the thousandth decimal, from 16.351 Hz, or Co (3rd C below the bass staff) to 16,744 Hz or C10 (5th C above the treble staff). I've studied it in the past, but was surprised on re-reading to notice that 261.63 Hz is C4, middle C, the first fret of the 2nd string (from the bottom) of the 6-string guitar. I bet many audiophiles would pick one or two C's below that for 260 Hz.

My 440 Hz tuning fork rings like a bell (of course it has harmonics well above the fundamental). 440 Hz is the 5th fret of the 1st string on a 6-string guitar, the A above middle C.

JDUBS · « **Reply #11 on:** 27 Dec 2005, 03:17 am »

Jim

From what I've heard, the Marchand units are terrific. A less pricey alternative, which may offer at least comparable (if not better) performance, is the crossover made by Greg Roberts of Home Audio, Inc.:

http://groups.msn.com/HomeAudioInc/activecrossoversandpowersupply.msnw

He does totally customer work and is an incredibly helpful individual.

He's in the process of building me one right now....I should have it within the next 1-2 weeks and will be able to report on it then.

-Jim W.

woodsyi · « **Reply #12 on:** 27 Dec 2005, 05:45 am »

Jim, I hardly hear a difference when I run the ribbons through my Marchand XM44 vs. running direct out from my pre using the passive filter (TRT) in my RM40s. I agree that midbass is very important. I played around with different gain, band frequencies and filter slope to get a taste of what this band adds to instrumental and vocal music. That is why I am bandpassing it with separate amps. The 10" woofers on the RM40 do a much better job in the band when not asked to go below 80 Hz. That's where the 2 largers come in. I don't "taint" the signal through an active x-over from ultrasonic to 280 Hz (or whereever Brians series first order passive filter go down to) on the ribbons. For signal below 280 Hz, my Marchand XM44 filters midbass (280 Hz to 80 Hz) to the 10" woofers run by a pair of 1kwatt amps and anything below 80 Hz is sent to my subs run through a Crown K2. I would recommend the Marchand for this purpose without any reservation.

James Romeyn · « **Reply #13 on:** 27 Dec 2005, 06:36 am »

Woodsyi
Thaks for the in depth reply. I am really surprised how much better I like even the 30's bass with a hp xo. The punch, impact, dynamics, & transparency are all much better. It's funny how many/most audiophiles say they want the mains to go as low as possible. I totally disagree now. Plus, like I wrote earlier, it's great to use the xo to manipulate around modes. Finally, I have absolutely no problem with a single sub (vs. the often recommended stereo), crossed around 65 Hz. Even mounted in the corner way left of the left speaker is no problem. The room modes are flattened by the automated EQ, the sub barely moves with all the boundary multiplication forces, even at ridiculous SPL's.

Doug Ravizza · « **Reply #14 on:** 28 Dec 2005, 07:13 pm »

Quote from: John Casler

The X-2 also has stereo (for 2 channel) as well as LFE (for HT) inputs that work independantly of each other, and have seperate volume control for LFE.

John,

Wouldn't that setup require seperate subs; one for LFE and one, (or perhaps two), for the 2 channel LP outputs?

ctviggen · « **Reply #15 on:** 28 Dec 2005, 07:23 pm »

Doug, the X2 will send the LFE to your one/two subs (and to LFE should you desire that). I have three subs and have the LFE sent to all three and use two subs in stereo mode.

As for single subs, unless they're near the middle of the stereo speakers, I can locate the sub. This drives me crazy and one reason I invested in stereo subs.

Also, any speaker that experiences distortion when asked to play frequencies that are too low will benefit from having a sub play those frequencies. I have not yet crossed over my RM40s and am running them full range.

Doug Ravizza · « **Reply #16 on:** 28 Dec 2005, 10:03 pm »

Bob,

I also have three subs that, until recently, I've been using for HT exclusively. I "bread-boarded" an active adjustable, 12 dB/oct. LP filter that sums the L & R channels and splits the passed low freq. three ways to the subs. It is fed through a "Y" cable that also sends the full range signal to a pair of RM40's. I've been experimenting with this for a couple of weeks for 2 channel music with positive results but I have to switch the subs' inputs from the LP filter to the pre/pro LFE output whenever I want to watch a movie. Movie sound tracks sound better on my system if I just let the pre/pro handle the bass management and bypass the LP filter.

I’m just wondering if the X2 can pass-thru the LFE signal from the pre/pro while shutting off the LP output to the L & R channels, and one can accomplish this from the front panel controls. If so I might just buy one.

ctviggen · « **Reply #17 on:** 28 Dec 2005, 10:21 pm »

Doug, if I can find the manual for the X2, I'll send it to you. I think I have it at home. If you can breadboard, you could also open the X2 and get it to do what you want to do.

John Casler · « **Reply #18 on:** 28 Dec 2005, 10:45 pm »

Quote from: Doug Ravizza

I’m just wondering if the X2 can pass-thru the LFE signal from the pre/pro while shutting off the LP output to the L & R channels, and one can accomplish this from the front panel controls. If so I might just buy one.

Hi Doug,

That is almost exactly what it does. Except you cannot shut off "individual" woofers. All outs are active all the time.

The X-2 has two basic sets of inputs:

1) LFE from your pre/pro

LFE is "pass through" with no filtering. It has a seperate volume control to allow you to trim the LFE bass volume to your needs.

2) Stereo or mono from your stereo preamp.

The stereo input then sends the signal through all the filter adjustments.

All Outputs are active and the system can be run in "summed Mono", Stereo, and the LFE can be distributed via any of the outputs.

It also has XLR ins and outs.

XLR and RCA Lowpass outs are all active, so you can run up to four subs at the same time if you use both (ask me how I know

)

It is quite unique and has great versatility.

I have a two channel system where I use four subs.

I have a seperate HT system in the same room and simply run a long RCA over to the LFE input and Voila the four subs are now doing HT and bass management is done by the Pre/pro.

Doug Ravizza · « **Reply #19 on:** 29 Dec 2005, 01:28 am »

Quote from: John Casler

All Outputs are active and the system can be run in "summed Mono", Stereo, and the LFE can be distributed via any of the outputs.

John,

Sorry if this sounds a little dense on my part but, does this mean that the unit has common outputs that carry both the LP and LFE signals? I was thinking that you would still have to somehow "Y" together the LFE and LP outputs to send to the same sub.

Quote from: ctviggen

Doug, if I can find the manual for the X2, I'll send it to you. I think I have it at home.

Bob,

If you had a link to a pdf that would be great and would probably answer most of my questions. I've tried "googling" NHT and X2 and it returned very few relevant hits and those were in the context of how it integrates with NHT's other products.

Thanks for your help guys,
Doug