MoFi Sourcepoint 8 or Q Acoustice Concept 50s

So you’re on the hunt for a new pair of speakers and you’re down to a choice of two.  Suggest you buy both from a dealer or retailer that will let you buy and try and return one set for free or for a nominal fee.  A/B test them in your room with your equipment playing the music you love.  Keep the pair you like best and return the other.  The only way to know for sure and not have buyers remorse or FOMO in my experience.  Happy hunting!  

@maam522a, I held off making a recommendation but my recent experience may be useful.

I’ve been in this hobby for decades and have churned through a wide variety of components.  After moving (ie a new room), my system, while of very good quality, didn’t adapt well.  Also, each component was separate (including mono blocs) and I wanted to simplify.

So I started with speakers.  I certainly agree with auditioning before buying but that was difficult with the general decline in brick and mortar stores plus moving to a much smaller community with only one quality audio dealer.  That meant reviewing owner reports as well as reading reviews.  From that my short list included OHM so I took advantage of their factory return policy and ordered a pair to audition.  Unfortunately they didn’t adapt to my room well either so I returned them.  Great folks though.  Then I saw a flurry of reviews for the new MoFi SP 888.  I had heard earlier models designed by Andrew Jones, plus I had listening experience with concentric drivers in Tannoy models.  Fortunately Crutchfield has a 60-day return, so I felt confident and ordered a pair.

The longer I’ve listened to the MoFis the more I enjoy them.  They give a warmish musical presentation.  Without going through the audiophile list of descriptive terms I can just say they are greatly satisfying.  Good recordings of small groups can sound like the performer(s) are in the room.  Larger musician groups, where that is not realistic, still offer a decent live simulation.  I also changed to an integrated amp with 90 WPC which is fully adequate in my 28x19x10 room.  This is mainly with jazz, classical, and classic rock.

So good luck in your search.

@maam522a  Too bad—it seems you missed the chance to audition the QC50 at home. Looking back at its historical selling price ($1,100 to $1,800), it appears the speakers have depreciated significantly, so they may not be ideal for resale either. It’s therefore suggested that you focus on auditioning the SP8 through CF. If the treble turns out to be an issue, as it was with the SP10, and Mofi releases the SP8 ME to address that, you could always swap it out. My take is this: if the high-frequency impedance spike isn’t really a concern, as many audiophiles claim, then why did Mofi include a three-level treble attenuator for it? 

I’ve never seen impedance in the high-frequency region reach that level before. Why would Mr. Jones design its crossover that way?  It really makes me scratch my head.

I went through a similar process myself—I auditioned several speakers at home, including the Wharfedale Linton, and ultimately settled on the Linton. I can’t imagine buying a pair of speakers purely on faith, especially when I’m already aware of their potential shortcomings.  I wish you have fun auditioning speakers at home during the upcoming holidays.  Happy holidays in advance.

@pryso Thanks for the insight.  I have spent 30 years rolling gear and scrounging for older high end components that I could not afford when new and I hope to be at the end of that endeavor.  Just finished the Linn LP12 with better arm, MC cart, and very fine phono stage.  I really enjoy my Magnapans, but they do not fill the house like a vintage Klipsh would.  You know - that sound of live music in the next room.  Now that i have settled on my equipment, it is time to listen to the music (not in just the sweet spot) and stop listening to the equipment.  I will try the SP8 and see if they fit the bill.

If the goal is to address only the impedance rise around 2 kHz (as MoFi did with the SP-10 ME), a more refined approach is required.

There is a Audiogoner who PM me to ask about this.  Instead of replying back privately, I will share here for the benefit of the group.  In order to notch down the impedance spike at a specific frequency, such as 75ohm at 1.6khz in the case of SP-8 (see the above imp.-phase chart), you need a so-called LCR serial components in parallel with the driver, which consist of an inductor, a capacitor and a resistor.  Here is how you design the LCR serial components.  First, since the target impedance we try to notch down is the nominal impedance of 8 ohm, use the voltage divider formula to back track the required resistor value, i.e., R = (75x8) / (75-8) = 9 ohm.  Then select a proper capacitance value, preferably from a higher quality part commonly available in the market, say, C = 10 micro Farad (uF) and use peak freq. = 1/[2 pi (LC)^.5] to back track the required inductance, L, which can be calculated as 1/C/(2 pi peak freq.)^2 = 1.0 milliHenry (mH).  So now you have acquired the 1st set of trial values for LCR, i.e.,

L = 1.0 mH; C = 10 uF and R = 9 ohm;

Next check the resulted Q value which define the shape of spike = peak freq. / bandwidth.  The Q = 1/R x (L/C)^.5 = 1/9 x (0.001/0.00001)^.5 = 1.1, meaning the resulted bandwidth of the notch filter is approximately 1.45 khz which seems to cover the shape of the spike reasonably well.  So this seems a good starting point.  It will take some iterations to ultimately iron out the peak as shown in the SP10 ME but this process should give you a pretty good idea how to design a proper notch filter.