Comments on: The Mini Convertible active loudspeaker: design

By: John Reekie

John Reekie — Sat, 06 Jun 2015 14:51:13 +0000

Ah, yes, that is true, that with DSP you can achieve a steeper crossover than you can with analog filters, which – as I understand it – will reduce the frequency range over which vertical lobing occurs. I’m not sure I understand the significance of the horizontal shift though…

I don’t know of any plate amps that can have FIRs programmed into them. It would be cool if there were…

By: Janis Irbe

Janis Irbe — Tue, 02 Jun 2015 13:30:50 +0000

“You may be wondering at this point how DSP and controlling directivity are related. The answer is that they aren’t..”

Different crossover types and their order severely impact lobing, so If we consider lobing being part of directivity/dispersion problem domain then relation actually exists.

My recent observation was that with very steep crossover slopes effect of horizontal physical shift of HF driver (aka time alignment) to be almost inaudible compared to that of LR phase linear 4-th order filter probably because with steep filters lobing doesn’t change much. The steepness must be at least 8-th order, I used Hypex A2.100d amp for this and sequenced 4 second order IIR biquad filters. Even better results can be achieved with so called brickwall FIR filters, as suggested and explained here: http://www.prosoundweb.com/article/a_useful_tool_creating_applying_fir_filters/P1/
In this article Rephase tool was used together with miniDSP and OpenDRC 2×2.
PWR-ICE125 uses ADAU1445 SigmaDSP. Can it also be used with this software?

If not, Sigma has their own DSP programming software. Has minidsp OEM-locked the DSP chip? If not, reprogramming with Sigma tools could void warranty but also open up more features, like creation of brickwall FIR filters (see mentioned article) resulting in significant reduction of vertical lobing.

Unfortunately I haven’t yet found plate amps with built-in DSP and convenient software that provides FIR crossover filters and Room EQ in the same package. Any suggestions?

By: John Reekie

John Reekie — Sat, 30 May 2015 05:05:25 +0000

Hi, no, not a problem. The drivers are connected to different channels. The maximum output power for the 8 ohm driver will be less (about half) but as long as that is not a problem, it’s fine. With this driver, 65W is plenty.

By: Adrian

Adrian — Fri, 29 May 2015 06:57:36 +0000

Okay, thanks.
But I have another question, the Chassis u’re using have an different impedance.
Is this relevant or a problem when u connect them both to the same Amplifier?
Regards,
Adrian

By: John Reekie

John Reekie — Thu, 28 May 2015 01:00:25 +0000

Hi Adrian, the volume control is, I think, really intended for when you are using one amp for a subwoofer. For stereo use, set the volume control on the amps to full on and control the volume “downstream” i.e. in a preamp (for analog in) or in computer/digital source.

By: Adrian

Adrian — Wed, 27 May 2015 18:04:34 +0000

Hey John,
Your project looks great!!
I have just a question, I’d like to think that u’ve made stereo speakers.
But each amplifier has an own volume control, the question is how u Balance the volume?

Regards,
Adrian

By: John Reekie

John Reekie — Mon, 09 Mar 2015 01:45:51 +0000

Hi, to be honest for sound reinforcement I would use separate fan cooled amps, these are not thermally designed for continuous high power operation. I forget the thermal ratings exactly but they are in the B&O datasheet. You would have to ask miniDSP for the noise spec.

My pair are not currently operational as I’ve disassembled them to finish the boxes nicely. And, well… it’s taking time 🙁

By: Conrad

Conrad — Sun, 08 Mar 2015 23:47:40 +0000

Hey John,

Thanks for the excellent review!

I’m building a horn loaded sound system for sound reinforcement purposes, and these amps look like an excellent way to go. My only real hesitation are with the noise spec’s: [2 x 120W @ 1% THD+N, 20Hz – 20kHz, 4Ω, SE (both channels driven)], seeing as how a main goal is to have as good sound quality as possible (ribbon tweeters, biamped, dsp).

After listening to your system, what are your thoughts on this?? And has the system been stable??

Much thanks in advance,

Conrad.

By: John Reekie

John Reekie — Wed, 14 May 2014 08:31:51 +0000

Hi Bruce, thanks for the kind comment and your enquiry. The construction article is held up waiting for me to build another pair so I can take some decent photographs that reflect my current dimensions/drawings…. The ported base has been revised to include it’s own woofer to make a 2.5 way, similar to the concept I posted for the Convertible here: https://johnr.hifizine.com/2014/04/the-convertible-active-loudspeaker-revisited/

I’m sorry, woodwork is a very slow process for me…

By: Bruce

Bruce — Tue, 13 May 2014 06:56:53 +0000

Hi John,
How are the follow up articles (i.e. Parts 2 & 3) of the project coming along? Looking forward to seeing them.
Keep up the good work.
Bruce M