Active, DSP, REW, Xilica 101

[Rudy81]

Chris,

Thanks for the horn loaded Heil paper.  While reading on the AMT I started wondering what would happen it you put....say an Oris horn, in front of one.  It is small enough to fit in the Oris back chamber.  I may just buy one for the hell of it and try it.  They are pretty inexpensive.

 

My one issue is that the Bass bins I built have a port resonance of about 515hz. I'm not knowledgeable enough to know if I should cross the bins above that frequency.  I do know the bass bin will go well above 1kHz, but not sure about distortion etc. 

 

 

[Chris A]

Here's a harmonic distortion plot of an AMT-1 at ~90 dB on-axis:

 

 

I run the AMT-1 crossed at ~650 Hz on top of the surround Belle bass bins.  Their performance subjectively exceeds the stock Belles by a large margin.  Just note that you're not going to get low distortion at 100-110 dB/1m.  Surrounds work very well with the AMT-1s.

 

 

Chris

 

[Chris A]

6 minutes ago, Rudy81 said:

I may just buy one for the hell of it and try it.  They are pretty inexpensive.

Yes, cheap enough to try--which is just what I did last year when they lowered the price to $140 each (they're $170 now, I believe the last time I looked).  The AMT-1s are still here doing surround duty as two-ways, but I swapped out the Cornwall bass bins I initially used for Belle bass bins in order to get better directivity control.  Nothing wrong with the Cornwall bass bins--they actually have a lower bass extension and smoother FR to EQ out.

 

8 minutes ago, Rudy81 said:

My one issue is that the Bass bins I built have a port resonance of about 515hz. I'm not knowledgeable enough to know if I should cross the bins above that frequency.  I do know the bass bin will go well above 1kHz, but not sure about distortion etc. 

Test it and find out.

 

Chris

[Chris A]

14 minutes ago, PrestonTom said:

Chris, I can't look for the specific threads over at DIYaudio, but there were some conceptual arguments and empirical data that were at odds with this configuration.

 

Perhaps a potential designer would want to look at those before investing the money. As I recall, those tweeters were not inexpensive.

 

Good Luck,

-Tom

Tom, in this case, your hearsay is a bit off the mark...

 

And I don't think a lot of the opinions over at diyAudio too much.  If I'd listened to them, I never would have built a K-402-MEH (...except for one guy over there who encouraged me--Art Welter.  He's someone to pay attention to, I've found.)

 

Chris

[PrestonTom]

2 minutes ago, Chris A said:

Tom, in this case, your hearsay is a bit off the mark...

 

And I don't think a lot of the opinions over at diyAudio too much.  If I'd listened to them, I never would have built a K-402-MEH (...except for one guy over there who encouraged me--Art Welter.  He's someone to pay attention to, I've found.)

 

Chris

I have corrected my mis-quote (or whatever you want to call it).

You are correct, Art Weller is a good source of information. There are a number of other capable folks there also. 

[Chris A]

I don't post at diyAudio any more.  Ask me why...

 

Chris

[Chris A]

Here's a phase plot of the three configurations: AMT-1 only (red trace), with Cornwall bass bin (green trace), and with Belle BB (blue trace):

 

 

I'm using the Danley-style crossovers in the blue and green traces.  The Cornwall bass bins have a particularly flat phase response--rivaling the Jubs with Danley-style crossover filtering.

 

Chris

[Khornukopia]

7 hours ago, Chris A said:

I don't post at diyAudio any more.  Ask me why...

 

Chris

 

Why?

[Chris A]

Lack of effective moderation to keep the trolls at bay.  There are many trolls that ply their wares there because of that.

 

Chris

 

 

[rplace]

Would changing the gain on the input side of Xilica have no effect on the rest of what you already have dialed in (Phase, Group Delay, etc.) beyond simply lowering/raising the volume? I've got a hand full of presets that all sound pretty good across two very different sets of amps (3.5 watt SET 2A3 and 60 Watt KT88). My goal now is to get them all close in volume so when I switch between them for evaluation purposes it is a more fair comparison.  As most of us know all things being equal you will typically gravitate to the "louder" one as a favorite. Try as I may I find I can't discount the volume differences when trying to pick what I like better.

 

Any reason to not do it on the input side? I'm thinking that is easier than the output side. Any reason not to do it all and leave the differences between presets I've developed?

[Chris A]

There should be no significant difference in phase/group delay response when changing relative gains on the output channels--other than a minuscule effect that minimum phase plays around the crossover interference band.  Changing the gains on the input channels only changes the left-right balance in a stereo loudspeaker setup. 

 

Chris

[rplace]

19 minutes ago, Chris A said:

Changing the gains on the input channels only changes the left-right balance in a stereo loudspeaker setup. 

 

If I only changed one side, yes. My thinking was to find the "quietest" of the presets in question then use the input gain, both right and left, to bring the rest of the presets down to the same level/output. Then when I switch between presets I would not have to try and adjust the volume manually to get close to what the previous was.

 

I just thought for a 2-channel stereo preset (not my HT settings for 7.2) that doing 2 (right/left) on input was simpler than 4 (2X HF and 2X LF) and less chance to mess things up. I use the same solid state crown amp for the LF bass bins no matter 2-channel, HT, or which HF amps. But when dialing in the difference between the 3.5 Watt SET amps and 60 Watt VRDs there is a huge change on the gain settings on the output side for HF channels.

 

Interesting side note that I am not really sure why. For the last year I've almost exclusively used the 3.5 watt amps for the HF Oris horns. I could never really get the VRDs to my liking no matter the XO point from about 200-800 or the XO type (Bessel, LR, Butterworth). Since giving the PEQ only XOs a go over the last couple of weeks I've come up with 3 very good sounding presets for the 3.5 watt amps and 2 really, really good presets for the VRDs.

[Khornukopia]

On 11/30/2019 at 12:10 PM, Chris A said:

I don't post at diyAudio any more.  Ask me why...

 

On 12/1/2019 at 1:17 AM, Chris A said:

Lack of effective moderation to keep the trolls at bay.  There are many trolls that ply their wares there because of that.

 

I understand. Lucky for us that the Klipsch forum has the best members and the finest moderators.

[Chris A]

46 minutes ago, Khornukopia said:

Lucky for us that the Klipsch forum has the best members and the finest moderators.

Unfortunately, I think it boils down to locally acceptable behavior based on underlying culture: what's acceptable to say and do in person and on-line. 

 

People don't treat other people the way you see in that other forum here, I believe, because of where this forum's membership predominantly resides (i.e., linked to local geographic culture and generational age represented here).  Apparently, it's culturally accepted elsewhere to treat people as you see at that other forum in the parts of the world that are predominantly represented there.  That's the only explanation that I see why their moderators do nothing about the identified behavior. 

 

So they really don't need me in that forum. 

 

Chris

[Rudy81]

On 11/30/2019 at 12:58 PM, Chris A said:

Yes, cheap enough to try--which is just what I did last year when they lowered the price to $140 each (they're $170 now, I believe the last time I looked).  The AMT-1s are still here doing surround duty as two-ways, but I swapped out the Cornwall bass bins I initially used for Belle bass bins in order to get better directivity control.  Nothing wrong with the Cornwall bass bins--they actually have a lower bass extension and smoother FR to EQ out.

 

Test it and find out.

 

Chris

 

My order is in for a pair to play with.  In the mean time, I have found that Hawthorne audio once added a horn to and AMT.  Currently, the Pure Audio Project uses the Heil AMT in one of its open baffle offerings. Very interesting driver.  Beyma also sells a similar driver with a horn that goes down to 800hz or so.  Who knew?  Goes to show that you don't know what you don't know. 😁

[rplace]

I found something new to me on the Xilica interface. "Plot Options" has a Phase checkbox. If you take the Magnitude off so it is not so cluttered it looks something like below. What if anything can we learn here? It can't be the actual phase because that would need to be measured. As you turn the PEQs off the phase line(s) flatten just like the magnitude. Is this just Xilica's best guess at what it will do to your phase given the PEQ you apply?

 

I'm having a hard time seeing the benefit but I don't think it would be there if useless. Any insight on how to use/understand it?

 

[Rudy81]

I am not certain, but I suspect it is a method of plotting phase, which you may have modified using the Phase 1, Phase 2 options in the same box where you select PEQ, Hi Shelf and Lo Shelf.  I researched that a little when I got my Xillica, but could not find anything.  My other xovers have the capability of incremental phase change, not just inverted polarity. For example, my Behringer has phase changes by degree increments.  If you select Phase 1 or Phase 2 in the PEQ box, you can make changes up to 180 degrees IIRC.

 

Of course, I could be totally wrong.

[Chris A]

3 hours ago, rplace said:

What if anything can we learn here? It can't be the actual phase because that would need to be measured. As you turn the PEQs off the phase line(s) flatten just like the magnitude. Is this just Xilica's best guess at what it will do to your phase given the PEQ you apply?

You've ventured into the land of minimum phase filtering theory ("IIR" filters). 

 

When you add a PEQ at a certain frequency that has a significant gain (either boosting or attenuating), you will also see a little wiggle in the phase plot around the center frequency.  This is something that comes with IIR filters: phase shifts.  You'll notice that the phase goes the opposite direction, turns around, and then returns to zero for a single PEQ filter.   This is the coupling between PEQ amplitude and phase that I might have mentioned in an earlier thread.

 

If you select a single ramping filter on a channel, like a high shelf or a low shelf, you'll notice that the phase doesn't return to zero.  This is also the effect of crossover filters--they shift phase between channels (which is usually not desirable).  That's why I have advocated PEQs instead of ramping filters (and REW's EQ facility doesn't handle ramping filters, either). 

 

If you select "Phase 1" for the filter type, you will see the phase shift, but not the amplitude.  This is the so-called "all-pass filter" (AP-1) which is a first order filter.  You can also try the "Phase 2" filter (second order all-pass) and see the effect on phase.  I recommend playing around with this to see the effects.  It may be that you might come up against a situation where all-pass filters can be used (probably a first order all-pass).  I've not found such a situation, and there is little documentation on this subject other than the following from the XP series DSP crossover manual:

 

Quote

BW:
The EQ bandwidth ranges from 0.02 to 3.61 octaves in steps of 0.01 octave.  The equivalent Q value is automatically shown besides the octave value.  For 1st degree all-pass (AP-1) filter, the bandwidth will sets the phase shift at the centre frequency. This phase shift is gradually changed from 180 degrees above the centre frequency to the specified value.

Chris

[Edgar]

39 minutes ago, Chris A said:

You've ventured into the land of minimum phase filtering theory ("IIR" filters). 

 

Just to be pedantic; not all IIR filters are minimum phase, and the best example of a nonminimum phase IIR filter may be an allpass filter.

[Chris A]

While you're here, can you recall an instance where you used an all-pass to correct phase?  Or a ramping filter... 💡

 

Chris