Building a 2-way small active speaker with software crossover

[pma]

Building a 2-way small active speaker with software crossover

1. Goal

To try software crossover method for a 2-way, active speaker

2. Software and instrumentation used

Per @dualazmak hint, I will use EKIO software crossover. It is very easy to use and it is free up to 2 IN/4 OUT channels.
For acoustical SW measurements, I am using REW software in combination with VituixCad , VituixCad is also used for crossover and acoustical simulations.
For acoustical HW interface, I use Behringer ECM8000 microphone with the calibration curve, iConnectAudio4+ soundcard and Roland Duo-Capture Ex soundcard.
As an audio amplifier, I use my A250W4R or AIYIMA A07.

3. Speaker cabinet and drivers

The speaker cabinet used is made from 18mm MDF, dimensions 180 x 280 x 170 mm (w x h x d)

Woofer is a 4" Magnat MW 111 CP 754-I (no link unfortunately)

Tweeter is a Monacor HT-88 horn loaded PA driver

4. Connectors

I need 4 wires to bring to the speaker, so the 4-way Speakon-like Cliff connector is used.

5. Crossover

I plan to use 48db/oct LR filters for the woofer and the tweeter. This will be completed with baffle step compensation shelf filter and necessary slope filter for the tweeter, with gain compensation between the low frequency and high frequency crossover sections. The goal is to get as flat on-axis response as will be possible. With the tweeter used, the useful HF range will be restricted to some 12kHz-15kHz, but I do not care, it fits to my hearing limit, being near to 70 years old .

As already stated, the main goal is to try software crossover method. The passive R-L-C crossover with baffle compensation and air-core inductors would be that big that it would not fit inside the cabinet. And, the SW crossover is much more flexible for changes, and, is able to provide necessary filter slope to cut parasitic driver behaviour.

I am not posting the preliminary simulations, I will wait for first real measurements and post them then.

 

[mcdn]

I like the offset tweeter position. Did you model that in VituixCAD to balance out the baffle diffraction effects?

 

[pma]

Yes, I did, and also made some preliminary measurements. However, I would like to wait for the first real world results, hopefully in about 2 days.

 

[restorer-john]

The Two Eggs matches are for burning the whole thing if you don't like it?

 

[dualazmak]

Very interesting, and I hope much good luck and success for your project.

I very much like your simple 2-way (2-SP-driver) concept and design "to start with" for DSP(EKIO)-based active system.

I believe you will establish not only nice XO/EQ but also perfect time alignment between the SP drivers as well as L & R at your listening position, like I did it intensively.

I assume possible addition of L & R subwoofers would be also your target, right?

 

[ppataki]

@pma
EKIO looks great!
Alternatively you can use Jriver with whatever VST plugin you want for the EQ, crossover, delay, etc.
With that you can even have linear phase crossover.... (probably not 48dB/octave due to pre-ringing but 24dB shall work fine with something like the T-Racks Linear Phase EQ)
In Jriver I recommend using DDMF Metaplugin to manage your plugins for each channels

 

[Deleted member 21219]

The Two Eggs matches are for burning the whole thing if you don't like it?

I thought they were for speaker burn-in.

Jim

 

[dualazmak]

Only in case if you would be seriously interested in using tone burst test signals I prepared and used in my time alignment studies (summary here and here), and/or the intact tracks of my "audio reference/sampler music playlist" including all the tracks of "Sony Super Audio Check CD" (summary here and here), I will be more than happy sharing them with you through PM communication.

 

[restorer-john]

I thought they were for speaker burn-in.

Jim

All I know is I want "two egg matches".

Over here we had Redheads.

60 matches:

Inflation kicked in, down to 47 matches:

 

[pjug]

All I know is I want "two egg matches".

Over here we had Redheads.

60 matches:
View attachment 313358

Inflation kicked in, down to 47 matches:
View attachment 313359

It looks like they increased the hair though.

 

[pma]

It looks like they increased the hair though.

I would be grateful if you guys could stop posting these OT posts . In case you have nothing to add on the subject, please do not post in this thread. Thank you.

 

[restorer-john]

I would be grateful if you guys could stop posting these OT posts . In case you have nothing to add on the subject, please do not post in this thread. Thank you.

Only if you tell us about the two egg safety matches.

 

[tmtomh]

Yes, I did, and also made some preliminary measurements. However, I would like to wait for the first real world results, hopefully in about 2 days.

Love the elegance of a simple design concept and software crossover network. Looking forward to seeing how they perform!

I know you want to wait to post real measurements, but can you tell us if you have a rough idea of the bass extension you expect, or that you are aiming or hoping for? I'm just curious what those 4" midwoofers might be capable of.

Thanks!

 

[pma]

I know you want to wait to post real measurements, but can you tell us if you have a rough idea of the bass extension you expect, or that you are aiming or hoping for? I'm just curious what those 4" midwoofers might be capable of.

Yes, no problem. Nearfield response of MW 111 (in a similar closed box), without SW crossover, without DSP looks like this

With the SW crossover, which includes bass-boost circuit, the LF will be extended down to 70Hz, of course at the expense of lower max. SPL in this area. You can see similar tricks in Neumann small monitors, like KH-80, and many other small monitors.

This project is not intended to create the SOTA speaker, it is rather about learning and evaluation of SW xover and DSP approach.

 

[KSTR]

This project is not intended to create the SOTA speaker, it is rather about learning and evaluation of SW xover and DSP approach.

Hhm, the filter section of EKIO looks very limited to me. No variable Qs for highpass/lowpass is pretty restrictive, you'll have to work around that with additional PEQs etc.

The strict top-down filter design approach is:
- define final acoustic target functions (which is already an art in itself, though managable for a two-way)
- find out the required electrical filter functions by dividing those targets by the raw acoustic functions (after some pre-processing of these like smoothing)
- find a good fit to that electrical target for a set of parametric-valued filter blocks after setting up an educated guess for the types and numbers of filter blocks
(- find a good fit and simple realization for that electrical target with analog crossover circuits, another art in itself, not needed when DSP-based, of course)

I've been using LSPcad for all of this, and I think VituixCad might be able to do the same (does it have an optimizer)?

Of course one can simple us the filter banks and play with them and re-measure the outcome in real-time over and over to slowly iterate to a good result and there is some fun and learning in doing this... but is a very non-engineer-like and tiring approach, IHMO.

 

[MAB]

I plan to use 48db/oct LR filters for the woofer and the tweeter.

These are the electrical responses I assume. As KTSR mentions, the electronic filter response is in addition to the natural acoustic responses of the drivers (I'm pretty sure you know this, tell me to stop if I am too elementary here...). I usually decide on a target response for my filters, and develop the electronic filters so that speaker response + filter response = target.

Looks like fun. You will be able to do lots of experiments with filters. And of course, lots of software is available to assist your project. I like this tutorial, if you hadn't seen already:

How to make quasi-anechoic speaker measurements/spinoramas with REW and VituixCAD

Quasi-anechoic measurements are a way to capture the 'real' frequency response of a speaker without the influence of a room. They are called 'quasi-anechoic' because they have the potential to get you really close to the results one might achieve with a non-reflective environment like an...

www.audiosciencereview.com

 

[voodooless]

Do you have any TSP on the little Magnat? From your plot is looks like it’s rather high Q in that box, which I find surprising given the apparent box size. TSP would open the door for reflex loading it for better power handling, lower distortion and more low end output.

Otherwise, cool project . I would probably not recommend that tweeter for a serious project for various reasons, not the least because it contains ferrofluid, but for a learning project, that should not matter.

 

[DVDdoug]

Normally and "active" speaker has the amplifier(s) and crossover built-in.

It looks like you're building a bi-amplified speaker a with customized active crossover.

And it looks like a lot of work for speaker with a tiny 4-inch "woofer", but that's just my personal bias/prejudice.

 

[pma]

Hhm, the filter section of EKIO looks very limited to me. No variable Qs for highpass/lowpass is pretty restrictive, you'll have to work around that with additional PEQs etc.

The strict top-down filter design approach is:
- define final acoustic target functions (which is already an art in itself, though managable for a two-way)
- find out the required electrical filter functions by dividing those targets by the raw acoustic functions (after some pre-processing of these like smoothing)
- find a good fit to that electrical target for a set of parametric-valued filter blocks after setting up an educated guess for the types and numbers of filter blocks
(- find a good fit and simple realization for that electrical target with analog crossover circuits, another art in itself, not needed when DSP-based, of course)

I've been using LSPcad for all of this, and I think VituixCad might be able to do the same (does it have an optimizer)?

Yes, VituixCad has an optimizer. The other way is to generate an impulse response (rePhase) and use a convolver or to send filter coefficients into DSP. EKIO is tempting to me as you do not need a DSP machine to upload the filters there. EKIO works with one additional ASIO soundcard in the chain, analog-in channels and analog-out channels, in a real time. I need to buy nothing to my current system. I only had to manage cabinet production (EUR 80) and bought a tweeter at EUR 28. Almost no expenditures to start a project for fun.
BTW I do not understand your remark on Qs of LP and HP filters. The choice is Butterworth, Linkwitz-Riley and Bessel, which I find appropriate.

I can also make a direct comparison of VituixCad filter simulation with same configuration of filters in EKIO and loop feedback test of FR in REW. The results are identical, VituixCad simulated filters and EKIO real time loopback test. You just need 2 soundcards, one as a generator/recorder and the other one as a real time filter processor with analog I/O. The filters are already tested in real time and will be modified as necessary, according to measurements of drivers in the cabinet. It is not a trial/error method.

I already have the drivers measured in a similar, but not the same cabinet. So anything would be a rough speculation at the moment. Without the drivers having been measured in this final cabinet, there is no basis for final crossover design.

 

[pma]

Do you have any TSP on the little Magnat? From your plot is looks like it’s rather high Q in that box, which I find surprising given the apparent box size. TSP would open the door for reflex loading it for better power handling, lower distortion and more low end output.

Free field impedance (resonance) and impedance of MW 111 measured in a closed box are almost identical. I only have TSP calculated from those measurements. I am not planning to use the vented box.