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Settings for tri-amping an '82 Belle with an active digital crossover


Chris A

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Bass group delay effects on the sound is fairly subtle to many people that might have acclimatized to that sound over their listening experiences, and is usually only audible at higher loudness levels.  One demonstration that I witnessed, given by Roy in the listening room next to the chamber, was the professional series ported woofer boxes having 1, 2, and 4 woofers compared to a Jubilee bass bin.  The fewer the number of woofers, the more noticeable the "thumpiness" or heaviness of the bass when playing heavy bass music with lots of kick drum transients.  At four woofers in the box, the differences become less pronounced but still audible (a certain "wood splintering" sound on the kick drum impulses from the ported boxes, and overall heaviness of sound).  The horn-loaded bass bin (Jubilee) never overemphasized the bass sound and was always clean, while the ported boxes all sounded heavy, somewhat fuzzy (not as impulsive) and overemphasized...to my ears.  This is likely all attributable to bass group delay growth, also known as phase curve steepening, due to the ported box effect on bass response. 

 

As far as using analog or digital filters to correct loudspeaker frequency response--in general, if you're applying those upstream EQ filters wisely, then the resultant phase and impulse response will have inaudible characteristics.  However, there is some difference of opinion as to whether higher order crossover filters (e.g., 48 dB/octave Linkwitz-Riley) introduce "harshness".  There is a thread over on the diyAudio Multiway forum discussing that subject presently.

 

Chris

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28 minutes ago, Chris A said:

Bass group delay effects on the sound is fairly subtle to many people that might have acclimatized to that sound over their listening experiences, and is usually only audible at higher loudness levels.

I do listen to amplified live music a couple nights a week, and have grown to be tolerant of variations and distractions so that I can enjoy the overall experience. As for my home system, the tri-amped Klipschorns have been a pleasure to live with.

 

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4 hours ago, Khornukopia said:

I do listen to amplified live music a couple nights a week, and have grown to be tolerant of variations and distractions so that I can enjoy the overall experience. As for my home system, the tri-amped Klipschorns have been a pleasure to live with.

 

5a3193741fd60_P1020600-Copy.JPG.138f18fdd15fe16c8ee7370cf19498a0.JPG

I would have to agree with this, since going active and tri amping my khorns I listen to a lot more music even FM radio... Using REW to get the phasing correct and time alignment of all the drivers I can hardly turn it off once I turn it on...

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On ‎12‎/‎13‎/‎2017 at 6:11 PM, canyonman said:

since going active and tri amping my khorns I listen to a lot more music

 

It is good to know that you are enjoying your tri-amped Klipschorns. I am thankful that Chris A has provided information and guidance to us and all the bi-amp Jubilee owners who are also enjoying the full performance from their systems.

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Thanks for the kind words.  Note that "paying it forward" is the real story here.  My original information on use of DSP crossovers all came from Roy--showing a few guys how to use them on Jubilees. 

 

Nowadays, I think that the use of DSP crossovers represents that quantum step up in loudspeaker performance that many horn enthusiasts had been waiting for.  It enables the next generation of horn loaded loudspeaker performance that's been the holy grail of those horn loving hi-fi enthusiasts for decades, since perhaps the mid 1940s when home hi-fi really came into being.  You can now get it all: time alignment, true concert-level dynamics with inaudible modulation distortion, flat frequency and phase (group delay) response, controlled coverage directivity, and point source performance (using multiple entry horns).  DSP crossovers are the enabler, and now they've become the economic choice among those wanting true hi-fi sound reproduction performance.  PWK's vision for horn-loaded loudspeaker performance has finally arrived...70 years after he launched his company. 

 

Chris

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Chris A, I have a question - 

 

  Is it typical to use a capacitor on a midrange and a tweeter in an active-crossover system for safety reasons?  For example, in case the crossover points are accidentally modified or corrupted, this would prevent bass content or from being presented to the tweeter or midrange.

 

Thanks

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I don't use blocking capacitors on the tweeter channels for the following reasons:

  1. The limiter within the DSP crossover is fast...fast enough to protect the tweeter diaphragms  (@Cantilope used this capability with his tri-amped Belles) but only if you set to protect the tweeters
  2. I typically use 2" compression drivers for 425-20000 Hz., which can absorb almost as much electrical power as the woofers, so protection really isn't an issue
  3. I don't use amplifiers that often fail with DC output (i.e., tubes)
  4. I find that it actually isn't that easy to make the kind of mistakes that lead to blown diaphragms.  Visual verification is apparent of crossover settings before using them at high power

I've not blown a diaphragm or fried a voice coil yet.

 

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Thank you, Chris.  I'm using a Modulus-86 amp and it has a servo to make sure DC is zero.  I was just curious; I had never heard anyone talk about this potential issue.  Sounds like it is a non-problem.

 

I'm planning on building 4 more channels of the Modulus-86 and I have a DCX2496.  At first, I'll run it as-is, but I have plans to change out the output op-amps to get rid of noise.

 

What filter topology and slopes do you typically run?  Do you time-align?  What delays do you use (on a KHorn)?  Sorry if this has been asked before.

 

Thanks,

code

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I'm using 48 dB/octave Linkwitz-Riley overlapping at 425 Hz center frequency on the Jubs, and 475 Hz on the K-402-MEH.  But I'm about to try out a Harsch (4th order Butterworth, 2nd order Bessel) to improve phase response in the interference bands.  I don't currently run tri-amped Khorns, but Greg Oshiro did it a while back in this thread:

 

Note that the delays are a function of the type of crossover filters used and their order.   If you change the filters, the delays have to change, too.

 

My time alignment is pretty good, but I'm thinking the Harsch crossover schema will align even better.  Once I get everything dialed in, I'll post a step response and spectrogram of the results.

 

Chris

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On ‎12‎/‎16‎/‎2017 at 3:33 PM, codewritinfool said:

I have a DCX2496

That unit has an Auto Align function. Plug a mic into input C, select Auto Align, short delay. Make sure to mute the speaker that is not being measured. STORE the settings any time an adjustment is performed. Details are on page 9 of the owners manual.

 

On ‎12‎/‎16‎/‎2017 at 10:03 AM, codewritinfool said:

Is it typical to use a capacitor on a midrange and a tweeter in an active-crossover system for safety reasons?

I also would like to know, what is the industry standard for tweeter protection within a self-powered loudspeaker system? I don't have any capacitors between my amplifiers and tweeters. My wires are color coded and clearly labeled, so there has not been a problem.

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2 hours ago, Khornukopia said:

That unit has an Auto Align function. Plug a mic into input C, select Auto Align, short delay. Make sure to mute the speaker that is not being measured. STORE the settings any time an adjustment is performed. Details are on page 9 of the owners manual.

 

I also would like to know, what is the industry standard for tweeter protection within a self-powered loudspeaker system? I don't have any capacitors between my amplifiers and tweeters. My wires are color coded and clearly labeled, so there has not been a problem.

Excellent, didn't know about the auto-align.

I would also like to know about your second point.

Thank you!

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Ok, I've looked at the manual for the DCX2496, page 9 and have a question.  Does this simply adjust for time arrival at a listening point?  There is no indication I can see, anyway, that if you configured it for 2-in, 6-out that it will independently adjust the three outputs for a given channel to time-align independently, i.e. 4.x ms mid delay and 6.x tweeter delay.  Sorry if I'm just confused.

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It has been a couple years since I used a DCX, but as I recall, the microphone is placed in front of one loudspeaker and the ping is sent to the woofer, squawker and tweeter and the arrival time is calculated for the two delayed drivers. Be sure that only one loudspeaker is playing, but do LINK the crossover settings to both left and right channels. Do you have a mic and XLR cable so you can experiment? Parts Express has the EMM-6 #390-801 that should be compatible with the DCX.

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  • 4 weeks later...
On 1/5/2011 at 4:27 AM, Chris A said:

Total upgrade cost to tri-amp the Belle = ~$600 (US) including Dx38 crossover, cables, and Crown D-75A amplifier. (Actually, I already had these items in-hand.)

EDIT: By the way - to upgrade a pair of Belles or La Scalas to the "JuBelle" or "JubScala" configuration via bi-amping, the cost would be the $600 above + the cost of the K-402/K-69-A or K-510/K-69-A horns/compression drivers from Roy Delgado at Klipsch (roy.delgado@klipsch.com).

The difference in sound quality from the JuBelle/JuScala upgrade from their stock configurations is difficult to quantify.

Suffice it to say that you will hear a "really BIG difference".

Chris

Any info on this jubelle comb? I recently purchased a set of k402s/510 combos that I will be setting on top of my diy Belle bass bins and would like to know a good starting point for eq/crossover. 

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Chris,   If I may quote you here,   "Whenever you use higher order (steeper) crossover filters, the time delay for the higher frequency channel  has to be increased by 1/4 wavelength for every order of filter used (i.e., 6, 12, 24, 36, 48 dB/octave filters each need, respectively, 0, -1/4 wavelength, -1/2 wavelength, --3/4 wavelength, -1 wavelength) in addition to the delay needs to physically align the acoustic center of the drivers."

 

So, if I change a crossover slope, then I need to re-calibrate the time delay between the affected drivers? That would explain why my time delay settings are not consistent with the physical lengths. This is very helpful to my understanding of time delay settings.

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One of the performance measures of loudspeakers that's really gotten my attention over the past couple of years is their phase/group delay response.  It turns out that the clarity of the music or sounds played depends strongly on flat phase group delay curves above about 100-200 Hz--all the way up to 3-5 kHz or so.  This was demonstrated for me using the online demonstration tracks from that linked presentation. 

 

I ran into the phenomenon of clarity after I partially dialed in the K-402-MEH and was startled by its increased clarity for both spoken dialogue and music that it added to the setup as a center channel.  As it turns out, most of the measured phase/group delay growth in loudspeakers is due to the crossover filters that they use.

 

If there were any rules of thumb that I now look for in outstanding hi-fi loudspeakers for home use, they would be:

  1. controlled and flat directivity indices/coverage angles vs. frequency down to 100 Hz
  2. flat phase/group delay response from 100-5000Hz
  3. low amplitude higher-order modulation distortion sidebands (measured nominally 100-105 dBC at 1m)
  4. all acoustic drivers within 1/4 wavelength vertical and horizontal separation at their crossover frequencies (preferably on the same horn aperture in order to achieve coupling without acoustic lobing occurring)

These four factors are really only mutually achievable using fully horn-loaded loudspeakers with coaxial re-entrant drivers (as in a multiple entry horn) using very well-designed and implemented crossover filters. 

 

Note that flat frequency response on-axis is not on the list.  This is because on-axis frequency response can be EQed flat quite effectively, which also partially corrects the phase/group delay response...but not all of it.

 

Chris

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Using a two way bi-amp system for example, crossed over at 500 Hz, both slopes at 6 db/octave and the drivers time aligned, what happens if I change just the high pass filter to 48 db/octave? Did I introduce a one wavelength delay to the tweeter signal, the equivalent of physically moving the tweeter backwards 2.26 ft.?

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