rePhase, loudspeaker phase linearization, EQ and FIR filtering tool

[Barleywater]

Originally Posted by kgrlee

A speaker isn't a 1D transmission channel. It has 1D input but 3D output.

You need to consider what happens at other listening axii/positions and also what the speaker is shoving into the room.

Is Linear Phase Worthwhile? and Polar Response Errors in Digital Crossover Alignments discuss some of the issues. I don't agree with everything Dr. Greenfield says but his is a good overview.

I was external examiner for some of the U of Essex papers on digital stuff including digital xovers so I've been playing with these for longer than most.

Probably the most evil factor is you don't really want the directivity of your speaker to change abruptly. This was identified as long ago as the 50's by the BBC and my own experience only confirms it.

A zillion dB/8ve xover to a sub at 80Hz in your domestic room is probably OK ... especially if you correct the phase.

Having said that, a somewhat lesser slope is OK too for "improved IMD performance, power handling, bla bla .. ".

Andrew, would you care to tell us your experiences, good or bad, with steep slope xovers?

1ch in, in 1ch out. All measurement points can only be correlated to single input, a design axis is chosen that is representational of design application.

Crossing over between two drivers with large differences in directivity at chosen crossover point is perfect example of poor design choice, if off axis performance is priority (a great one IMO with omni and dipole speakers). Use of steep crossover results in abruptness, but shallow slope seeking concept of smooth blend results instead in increasing ripple off axis in overlap region due to differing change.

I've posted two-way fully active DSP PC based design utilizing direct inversion of driver IR for linearization; DSP Pluto Clone. I've applied crossovers as IIR filters from 24dB/octave to 192dB/octave both as minimum phase filters and as linear phase filters and also FIR filters of various tap counts to create range of crossover slopes.

Going from 24dB/octave to 48db/octave nets some measurable and audible improvements in distortion performance, and further improvement to 96dB/octave with IIR based filters. Minimum phase crossover at 96dB/octave didn't sound as good to me as linear phase version and the linear phase version didn't perform as well as FIR with same number of effective taps, i.e. filters truncated to length where sample values are 100dB below peak value.

Speaker with full linearization passes arbitrary waveform within bandwidth, and music playback, in particular acoustic music and voice, is most natural sounding that I've heard from any loudspeaker. Closest comparison is electrostatic headphones.

Regarding latency: My understanding is JRiver Media Player has controls for video delay, and certainly an integrated video/audio DSP approach is possible.

[kgrlee]

Originally Posted by Barleywater

I've posted two-way fully active DSP PC based design utilizing direct inversion of driver IR for linearization; DSP Pluto Clone.

Thanks for the link Barley. Got more details of Pluto?

If I may ask a few naive questions ..

• What distance is the measuring mike from the speaker? What mike?
• What axis?
• Is this anechoic?
• What measuring software?

Got any off axis measurements of the same system including impulse responses ?

Also at slightly different height?

Bit suspicious of your "speaker response looks when one of the drivers has leads reversed". All the fuzz has gone.

[thierry38efd]

Originally Posted by CopperTop

I have a choice to use an external set of correction filters e.g. generated by REW, .

hi,

be careful with REW export,IR is not time windowed.
with REW,you need to add delay and cut the lenght of IR.(if you take a look at IR,it's start at t=0)
i've used to.
open audacity,add a silent...etc
the better and simple way is to use HOLM.you can limit negative and positive number of sample when you are exporting a IR.
just a advice to avoid issues.

[kgrlee]

Originally Posted by kgrlee

Got any off axis measurements of the same system including impulse responses ?

Also at slightly different height?

Found the Pluto site.

Impulse response & response eg 100mm above & 100mm below your 'design' height for your version please? [edit] Make that +15, +30 & -20 degrees to compare with his. [/edit]

Linkwitz uses a 1kHz xover which I see you've followed. That should certainly alleviate certain evils in high slope xovers but I'd be interested to see your impulse responses at different heights and also the frequency responses to compare with his.

Gotta admit I'm impressed by Pluto. It is the most innovative of Linkwitz's designs and I nearly forgive him for appropriating a xover configuration that speaker designers have known about for years before he turned up and put his evil name to LR.

Would still like to know the answers to ..

• What distance is the measuring mike from the speaker? What mike?
• What axis?
• Is this anechoic?
• What measuring software?

[bohdan1232000]

Originally Posted by john k...

Hi Bohdan,

Also, aren't the latencies you are quoting for linear phase? If phase linearization is not engaged latency still goes down in V4 as it did in V3, correct?

Hi John,

I have been reading posts for a short while only. I am glad to see such interest in linear-phase technology. Coupled with HBT equalization, it's the most powerful processing there is for loudspeakers.

Yes, the latency figures I quoted are for linear-phase only. Minimum-phase latency is around 65ms for 8192 and 130ms for 16384bins. FFT length is controlled by the UE buffer size automatically.

Best Regards,
Bohdan

[Pano]

Has this wandered off into crossover design, or are we still talking about rePhase software?

[CopperTop]

Originally Posted by Pano

Has this wandered off into crossover design, or are we still talking about rePhase software?

I think it's still more-or-less on topic as long as it wanders back to rephase now and again.

I would be very happy to use rePhase-generated filters if I actually knew how to use the tool... It's not obvious to me how I load a raw impulse response and view the phase/amplitude result of it convolved with the filter. Currently it seems like a tool that can generate a filter if I study a graph of phase/amplitude of my driver in another tool and type the values into rePhase. Have I got this wrong? (version 0.9.2)

[Barleywater]

Originally Posted by kgrlee

Thanks for the link Barley. Got more details of Pluto?

If I may ask a few naive questions ..

• What distance is the measuring mike from the speaker? What mike?
• What axis?
• Is this anechoic?
• What measuring software?

Got any off axis measurements of the same system including impulse responses ?

Also at slightly different height?

Bit suspicious of your "speaker response looks when one of the drivers has leads reversed". All the fuzz has gone.

I've got matched pair of Earthworks OM-1 microphones.

Design point is 9" from tweeter face. Tweeter axis is angled about 5 degrees up from horizontal, and microphone is placed slightly below tweeter axis.

Measurements are in living room.

Main software is Cool Edit Pro 2.1. Familiar with Praxis, Holm, ARTA, REW, and Audacity. Inverse transfer functions are created with Kirkeby transform.

Off axis responses and phase are posted here and here.

From perspective that speaker response is flat to fractions of a degree at design point, with driver linearization prior to crossover filtering, the reverse null is fuzz free too, along with image coherence through crossover region.

[CopperTop]

Originally Posted by kgrlee

I was external examiner for some of the U of Essex papers on digital stuff including digital xovers so I've been playing with these for longer than most.

Probably the most evil factor is you don't really want the directivity of your speaker to change abruptly. This was identified as long ago as the 50's by the BBC and my own experience only confirms it.

@kgrlee

Aha! So you might know something about the so-called Stochastic Interleave alignment described here:
http://www.essex.ac.uk/csee/research...ssing%20LS.pdf

...which does seem relevant to what you say above.

The aim seems to be to mix up the comb filtering between drivers through the crossover region, allowing you to have shallower crossover slopes without obvious audible artefacts. I've coded it into my crossover system, but haven't been able to try it for geographical reasons (it's Christmas and I'm staying elsewhere from where my system is :-( ).

Does it work?!

[thierry38efd]

Originally Posted by CopperTop

I think it's still more-or-less on topic as long as it wanders back to rephase now and again.

I would be very happy to use rePhase-generated filters if I actually knew how to use the tool... It's not obvious to me how I load a raw impulse response and view the phase/amplitude result of it convolved with the filter. Currently it seems like a tool that can generate a filter if I study a graph of phase/amplitude of my driver in another tool and type the values into rePhase. Have I got this wrong? (version 0.9.2)

you can use HOLM.
export IR as .txt file from rephase.
import the IR.txt from HOLM

you can do math.AxB or A/B...you need the files with the same extension.
(2 .txt file or two measuremnt).