Going to active xover

[maxserg]

Hi everybody! Just want some hints about time align via the Berhingher DCX 2495. There I is an option for the auto align between woofer and horn mid tweeter(JBL 2420) I was thinking that the dcx needs to listen or it is just misaligned coils measured in inches.... sorry for my English...

[BMWCCA]

I could give more credence to time-alignment if instruments and vocalists (and orchestras) were two-dimensional. Otherwise I just don't understand the extra layer of processing for what amounts to at most a 10-inch deviation. I'm sure I'm wrong and that someone will tutor me on its importance!
:dont-know:

[speakerdave]

It does seem to be a debate. Time alignment, I think, was developed for, or was early applied to the UREI monitors, which used coaxial drivers, a very important detail. With drivers spread around a baffle alignment can at best exist in one spot.

Single driver speakers are inherently time-aligned, though of course they have their own limitations. But to get a sense of the point source/time-aligned effect a listening session with some full range drivers might let you see what people are shooting for. Imaging can really be a lock with them.

I have two sets of Tannoy 2558 coaxial drivers. One set is in the stock SGM10B cabinet, the other in the Manley cabinet with the time-aligned crossover. It really does make the music more coherent, if the recording is coherent.

You get close to an important point when you point out different location of instruments, but I think it is actually the microphone placement which matters. Multitrack studio recordings of electric rock and jazz are unlikely to benefit much from time-aligned speakers, whereas simply miked stage recordings of acoustic classical, folk and jazz music very well could.

Simply put, whatever coherence exists in the recording can be preserved in the listening with time-aligned speakers.

[Mitchco]

Many years ago, I recorded/mixed for a living for 10 years. Loved those Urei 813 series time aligns better than any other studio monitor I used at the time (large format or nearfields).

Today's audio DSP software is very sophisticated running on powerful computers. Time alignment can be achieved with a high level of accuracy and precision. Here as an article time aligning JBL 4722 cinema speakers: https://www.computeraudiophile.com/ca/ca-academy/audiolense-digital-loudspeaker-and-room-correction-software-walkthrough-r682/

I performed many experiments with time alignment and if you know what to listen for, it becomes easier to hear the difference, especially with subwoofers which usually are delayed 3 to 5ms behind mains in a typical home stereo setup. Several of these experiments were blind testing of switching digital FIR filters in near real time in a music playback system, with one filter set with no delays, and the other time aligning the drivers. Frequency response was the same for both filters.

The eBook in my sig goes into great detail and shows time alignment is not just for one mic position, as I was able to show time alignment in 14 measurements across a 6' x 2' listening area.

If going active, worth the effort to time align as well. If using linear phase digital XO's one can time align so that the direct sound arrives at ones ears all at the same time, and in phase. All good listening fun!

Edit: Go for it! Give it a try. Even try adding too much delay to get a sense of what it sounds like, not only timing wise, but tonally as well. I have found no amount of eq can get rid of a tweeter arriving first and always having that in your face sound...

[1audiohack]

I could give more credence to time-alignment if instruments and vocalists (and orchestras) were two-dimensional. Otherwise I just don't understand the extra layer of processing for what amounts to at most a 10-inch deviation. I'm sure I'm wrong and that someone will tutor me on its importance!
:dont-know:

Since this train jumped the tracks right out of the station, what the heck. maxserg sent another. :)

I think you have it right. On one side anyway.

Mic or direct record something or someone and play it back through a speaker system with more than one radiating element and all sorts of issues creep in, time delay distortion being one of them. This is the other side of the coin.

I am with Mitch, getting it right has value. Being familiar with the sonic signature of well aligned sources makes poorly aligned sources difficult for me to truly enjoy.

Like any engineering project, one chooses what to pursue and how far to pursue it.

Barry.

[Ian Mackenzie]

Hi everybody! Just want some hints about time align via the Berhingher DCX 2495. There I is an option for the auto align between woofer and horn mid tweeter(JBL 2420) I was thinking that the dcx needs to listen or it is just misaligned coils measured in inches.... sorry for my English...

It’s a fun idea to play around with but simply attempting to time align the voice coils is not the whole issue

Your only scratching the surface.

Loudspeaker drivers, crossover network and a b c location of drivers all cause a culmination of delay and what is termed group delay.

Fixing it is neither easy or in expensive if you don’t want to degrade the audio signal.

On top of that you have the whole room interaction thing going on as well.

There are systems like Acourate (or other DSP programs that generate FIR filters), the Dirac and packages like DEQX that combine the hardware and software. They are not easy to use for the average person and tend to over promise on benefits.

Here is a simple approach

Grab your 4 way Jbl and let your HT receiver do the full Monty on room and loudspeaker correction
I did this with my Pioneer LX 83

I then look at the corrections. The frequency response and group delay and levels were largely smoothed out.
On some program material it was subjectively an improvement.
But when compared to the unprocessed signal with high quality DACs and amplifiers there is a loss of fidelity with the processed signal.

Not everyone cares or is concerned about the impact of signal processing so you need to pick the route and go from there. It’s entirely up to the user.

[GoldcountryJim]

Kind of been waiting for this topic. Driverack 260's have become pretty affordable and I'm thinking of stepping into this arena.

Where the output of two drivers overlap at or near the crossover point, there is the possiblilty of a cancellation of sound waves. This assumes the drivers are not in the same plane. This would be most noticable if the high pressure wave of one driver meets a low pressure wave from another driver at the same frequency. Even if its slightly off, there will be some effect. The harmonics could also be distorted by this process. Half of the sound waves for the next octave could be cancelled.

The type of xover and the rolloff for the lower and higher drivers would define the range of frequency affected. The steeper the rolloff, the smaller the range of frequencies affected, except for the harmonics. The perception of harmonics may be impacted outside this range. If a second harmonic is cancelled you my hear a fundamental and the 3rd harmonic more strongly, which would color an instrument somewhat.

I would expect some soundstage and location information to be lost. However, I've noticed more of a tonal change to specific notes when bi-amping my bass. Moving the drivers (in separate cabinets) can change the tone for some notes. I'm crossing at 800hz, so its the harmonics getting cancelled. The fundamentals are all far below that.

Barry, I remember seeing a thread on time alignment where you were trying to dial your system in. Sounds like you had some success.

I'm guessing how intolerable this is depends on an individual's hearing and listening skills and whether they can pick off these effects. If so, it probably is worthwhile to do the alignment.

[rusty jefferson]

I have no experience with active crossovers, but have had the pleasure to watch 2 active systems (one a 4 way custom studio monitor, the other a 3 way diy planer/open baffle woofer array/subwoofer system similar to the Infinity IRS) that were installed by knowledgeable people and tweaked for many hours. Then, each was tuned by the deqx tech over the interweb, and significantly improved in about an hour each. Both involved slight adjustments to time alignment differently than the installers had performed. It's fly fishing.

Learned about the service in this thread.
http://www.audioheritage.org/vbulletin/showthread.php?29281-Some-thoughts-on-Deqx-and-their-products

[1audiohack]

Hi Jim!

What you describe listening to a single instrument and the harmonic content or balance of it is one of the big ones for me.

In one of the audio platform measurement classes I took an instructor held a small pair of near field monitor speakers together side by side, one in each hand. Facing us with pink noise as a source he slid them fore and aft about two inches over and over again and the alteration of the signal was staggering.

Just as you have surmized, this miss alignment will cause issue in reproduction. It’s easy to hear when its done like the class demo, but when you know the source well, like your bass, you can find these issues in a static system, as you have. Piano that cuts through a crossover is an acid test as are plucked strings and percussives.

Getting it really right is work, and worth it in my book.

Did you see the graphs in Mitch’s links?!? I have achieved some pretty smooth magnitude and phase measurements but,,,dang!

Barry.

[1audiohack]

Hi Rusty;

It’s a joy to witness a master at work isn’t it. :)

Barry.

[maxserg]

My system is a k-145 with a 2420 on a small horn-lens, I want to cross it at 1kHz... just for the discussion...��. The K-145 is a bass reflex of 4.5 cu ft from original plans from JBL.

[maxserg]

By the way many thanks for some hints! I know that this is not simple. I made myself a recording of my Yamaha C3 with two Km 184 in a ORTF configuration. So I know very well how it sounds while playing the piano. Headphones are good for reference, and ORTF is good for mono compatibility too.

that will be my reference because the information in the 1kHz split point... with the piano.

By ear I doubt that I come with the perfect timing but it is a starting point...

[retro soulman]

i use active crossover on my system for around 3 years . What i can say to you is : Be ready for some hiss noise, be extremely patient untill you will find the right gain adjustments and different crossover points .

[maxserg]

Yes! Thanks for the advice. I’m quite used to the gain chain. I know that the output ok the el. Xover has to be set at max volume and the amps adjusted to optimal gain🙂

[Ian Mackenzie]

A few tips
Unlike woofers a compression driver on a horn is largely a resistive Load.

Therefore you can insert a 10 dB fixed pad on the driver to improve the s/n.

A woofers considerable inductance means it will behave very differently when removed from a passive network and used in an active situation.

If you plan to emulate a passive network the voltage drive with the woofer connected need to be traced or plotted.

The active voltage drive then requires fitting to the passive curve.

This is not easy and involves a lot of trial and error.

If you are creating a system from scratch use a measurement tool to get a ballpark crossover slope using the acoustical measurement.

Then flip the woofer driver polarity with the horn in phase.
Adjust the amplitude so both acoustic output are close
Then move the horn forward or back until you have a uniform notch around -20 dB.

Flip the woofer phase back and measure. Both drivers will sum correctly but more importantly the system will image correctly

You should do that test at a reference point that is the listening height.

[GoldcountryJim]

Barry,

I did see them. Actually, I've been to most of the threads I could find on the subject. I was looking to see who was getting the best results and how they were doing it.

I think Ian has a point about the listening position. Where the drivers are stacked vertically and aligned, moving around the components probably doesn't have an effect on the alignment. However, if the drivers are not vertical (stacked from bottom to top and centered) moving from one point to another could alter the result. It would depend on the baffle configuation. As to listening height, there would be some change from sitting to standing, that's probably going to have a more subtle effect, depending on how close you are to the drivers. An alignment issue would be present, but more difficult to pick out during a musical composition. Its really about what you can hear. That's going to be unique to each individual.

Maxserg, I'll being watching to see how you get along with this.

[Ian Mackenzie]

Sorry my explanation may not have been clear.

If the drivers are stacked vertically the crossover region is not effected moving in the horizontal plane if dispersion is linear in the region.

However when stacked vertically the crossover region sums like a lobe. The lobe shape depends on several factors - dispersion of the horn and woofer @ crossover point, the order of the crossover slope and so on. The steeper the slope the less interference. There can be several lobes at different angles.

So ideally the design point should be the listening height.
The Jbl 4430/4435 brochure has graphic representation of this.

If the position is moved up or down it can have a significant impact on either a dip or peak in the crossover region.

When Drivers are not time aligned summing flat at the crossover point can be compromised.

[GoldcountryJim]

Ian, that was pretty clear!

I noticed a good graphic put up by Frank23 in an earlier thread. Here it is:

http://www.audioheritage.org/vbulletin/showthread.php?32426-I-measured-the-time-alignment-of-JBL-2123-and-2420-2344

[Ian Mackenzie]

Great thread

It’s an interesting problem.

In my own experience the realities or physical possibilities dictate how much movement can be tolerated.

For example with a 15 inch woofer you can indent it about 50mm before everything goes to hell.

The pink noise is a great idea in the absence of test equipment. Trust your ears!

But like using 2123 is actually a bit tricky.

The 2123 diffracts with any baffle or horn obstruction like hell in the 600-1200 range due to its wider dispersion.
You hear it as ghosting. So the best option is to tweak the crossover rather than move the horn forward to get the reverse phase suck out.

I agree with Mr Widgets comments in that thread.

[Ian Mackenzie]

I have attached some images to illustrate the effect of correct summing at the crossover point.

The first 2 images are vertical polar based on actual measurements at 10 degree intervals.
Those measurement were then uploaded into LEAP to display polar response curves with the crossover.

With a bit of screwing around I was able to obtain a uniform reverse phase notch at the design point.

The left image is out of phase, the second image is in phase.
The deep notch is the reverse phase at the crossover point (800 hz). The slopes are 36 db per octave so there is not much impact either side of the crossover point whom is what you want in theory.


The deep nodes are normal either side of the central node and their location will depend on a number of factors.
My design point was slightly below the centre point.

The other two curves are out of phase frequency response and in phase. Green is the summed response.

This is a 2 way design using a 15 inch woofer and a large horn.

You don't need this precision but its kind of cool to see what happens.
Getting it right does make a significant difference subjectively. The rules are the same for passive or active crossovers. Ideally you want an adjustable active crossover with independent adjustment of Low and High pass crossover points like the analogue First Watt B4 or a dsp crossover.

BTW the acoustic centre can be deeper than the woofer voice coil due to the group delay of the low pass filter possibly 0.2 ms or more.

So if your horn is deeper than the woofer don't stress.

[GoldcountryJim]

Ian,

Great images! The verticle images are really interesting, with the green line showing a really smooth response on those 10 degree intervals. Even if it is summed, that's got to sound smooth.

Awesome!

[Ian Mackenzie]

It’s tedious getting it just right.

I always do reverse phase once the crossover slopes are good.

Don’t rely on or aim for an in phase smooth response (only)

If you can swing it buy a measurement device from like Parts Express and start on getting some measurements. It’s not hard and you will doing the real deal as opposed to talking to people about what works in no time

[Epplerd]

Has anyone measured the voltage drives to the 4430 transducers via the passive crossover. I have a pair of 4430's minus crossovers for which I'd like to create an active crossover. The voltage drives to the transducers via the passive network would be a useful starting point .

[Robh3606]

Take a look here second post. This gives you the woofer curve. The top you are going to have to sim or look for this is a biamp with passive CD comp in place.

http://www.audioheritage.org/vbulletin/showthread.php?1159-5235-Network-Plug-In-Card-52-5130&highlight=4430+5235

Rob:)

[Ian Mackenzie]

Further to Rob's post read this and check the RC values for the 4430/4435 cards values
http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/JBL-5235%20manual.pdf

NOTE: You will need to build the Horn high pass section of the 3135 networks for to implement the biamp functionality.

Its not appropriate to attempt creating the horn voltage drive with the EQ.

You will find the active horn EQ to be too noisy.

[Robh3606]

Here is the passive voltage drive both systems in JBL Standard test fixture. L pads at max 4435 good as a reference. Courtesy of 4313B

Rob:)