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pegodk 22nd April 2013 10:09 PM

Project SPH-30X/8
7 Attachment(s)
Hi guys

I've just finished a pair of small desktop speakers with the driver Monacor SPH-30X.

This little 3" full range has gotten some pretty good reviews and I must say it sounds promising and with surprisingly good bass.

Although it sounds promising the frequency response reveals that the sound can probably be improved even more. See the attached graph(s).

Before measuring the response I would have guessed that a strong notch around 10khz and then some baffle step attenuation would have done the trick, but since it has a dip around 3 khz that I dont want any deeper i'm now leaning towards multiple notch filters.

The solution I have so far includes 3 notch filters, but since two of them deals with the dip at 10 khz, maybe it can be done more effectively. I'm hoping that some of you guys will take a look and tell me what you think :-)

I've uploaded my frequency and impedance measurement, but also the lspCAD project file, and REW measurements to my site:

Please note that the site is kinda outdated and not really finished, so its not allowed to look around :D


Ivo 23rd April 2013 04:40 PM

My first reaction would be DSP. I am thinking you could shelve the response (down) from about 400 Hz to 2.5 kHz, then from 2.5 kHz to 3 kHz (up). Then you are left with that 10 kHz peak to sort out with a notch. Maybe you can do the same thing with analog networks, I wouldn't know. DSP was a step to avoid learning analog stuff. I haven't regretted it. :-)

Ivo 23rd April 2013 04:42 PM

Nice speakers, by the way. I have used these drivers in the past as well, I loved them. I used them filterless, with baffle shapes designed in Edge to compensate for response anomalies. I changed philosophies somewhat...

pegodk 23rd April 2013 05:26 PM

Thank you :-)

Well i have thought about digital signal processing, but i dont have much experience in that field. How is that easily implemented? The idea of these speakers, being desktop speakers, was also the possibility of playing music via an ipod and a cheap class d amp.

I already have some of the filter components, so i think i will try to do it passively, but i can imagine that it would be easier to do digitally..

Bill poster 24th April 2013 06:34 PM

I've a pair in black (4 ohm), I've removed the dustcaps as an experiment (for use in an omni type design) but havent got around to finishing the project yet

pegodk 25th April 2013 10:51 PM

2 Attachment(s)
If anyone is interested I have now built the (triple!) notch filter. I used components that i had just laying around, but the impact was minor.. Anyways, I think it looks very promising, but I still haven't done any listening tests :-)

Below are pictures of the simulated effect and the actual measured effect of the notch filter (looks surprisingly alike imo)

v-bro 15th August 2013 10:42 AM

I've built these speaker drivers in many different boxes and have a couple of correction filter options that work well with them, if you're interested I could dig them up...

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civcapitan 4th August 2014 08:54 PM

V-bro, would you mind sharing your blueprints for the mega mini? Your original post at has not been accessable for some time now...

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