Monacor SP-310CX build

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Docfoster
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Monacor SP-310CX build

Unread post by Docfoster »

In recent weeks I've got going with the latest project.
I've been impressed with the performance of the compression driver in the Tannoy 295/8. I wanted to progress that favourable impression into a meaningful new project.
My current favourite speaker manufacture, Monacor, make a range of Tannoy-style dual concentric drivers. The SP-3CX series. 8 inch, 10 inch and 12 inch models.
I bought a pair of the SP-310CX 10 inch model for a good price (£120 each).

Image

I spent a long time calculating the cabinet.
Based on the driver's specs SP-310CX been designed to work in a ported cabinet. Previously I have always gone for drivers that I know will work well in a sealed cabinet. I'd rather avoid something that it's possible / likely for me to get wrong. And I've heard a few speakers that have got the port wrong. But a few that seem to have got it right. So for this one, as well as calculating cabinet volume I had to learn a bit about ports and how to calculate them (lengths, diameters, and their displacement effects on cabinet volume). A satisfying new challenge.

I used 25mm MDF, screwed and glued. Pretty straight forward once dimensions had been calculated.

But the crossover for this was as much art as science.

The main driver for my trying this specific driver was because I like the sound of the compression driver in the Tannoy. It operates down to 1000Hz. And to my ears it provides dynamics and clarity at that frequency better than any of the midrange cones I've tried. I wanted the Monacor dual concentric to do the same. The frequency curves for the driver show that this is possible.
Problem #1: Monacor recommend a crossover frequency of 1800Hz. However, I suspect that this may in part be for power handling reasons. The driver is rated up to 400 Watts; or rather the woofer part is rated 400 watts. The compression driver tweeter is rated to 100 watts. I imagine that 400 Watts overall would be fine for the compression driver with the crossover set at 1800Hz. Obviously reducing the crossover frequency means more of the power is routed to the compression driver. Possibly putting it at risk with the speaker fed with a total of 400 watts. But, this isn't a problem for me. My SECA is rated 20 watts. So theoretically the compression driver should be able to handle, from a power POV, the whole frequency range from my amp.
Problem #2: The frequency curve of the woofer is a little shaky 1000-2000Hz. I know from experience that graphs aren't everything, but I wanted to avoid the woofer in this range, and ignore Monacor's suggested crossover frequency.
Problem #3: The frequency curve of the compression driver is still rising at 1000Hz. It only has about 4dB to climb, but this was troubling, given my plan.

I considered building a Butterworth crossover, as this results in a 3dB lift at the crossover frequency. But in the end decided to go for a Linkwitz-Riley, which is flat, as this is the type I've built previously.
I should have been more adventurous.

With the build's first incarnation completed a few days ago, I was able to listen.

Image

I had been most worried about the bass. This is the first ported type I've constructed. So far all good there. In fact I've been genuinely and pleasantly surprised. From the limited listening to date bass is impactful and tuneful. A good amount of air moving through the port. Really pleased with that. As mentioned above, the port was a design complication that would have been easy for me to get wrong.

First thing to tweak was the attenuation on the tweeter. Once the physical crossover is in place I can do this digitally using a digital high-shelf in JRiver, set at the crossover frequency. -15.1dB sounded good.

But, as my worries predicted, there is definitely an issue with a slight lack of output around 1000Hz. I can correct it digitally, and the speakers sound great. But obviously I want the speakers to sound great in their own right.
So it was back to the drawing board with the crossover. I ordered the capacitors and inductors for a Butterworth crossover to give me that 3dB lift at the crossover frequency where the problem happens to be.

This improved things markedly.
But not enough for my fussy ears. My next plan is to drop the crossover frequency for the compression driver so that it is higher still when the signal to the compression driver hits that 1kHz frequency.

Anyway. I'm enjoying this one. :-)
These users thanked the author Docfoster for the post (total 3):
savvypaul (Thu Jul 09, 2020 9:30 am) • Fretless (Thu Jul 09, 2020 9:35 am) • antonio66 (Thu Jul 09, 2020 4:59 pm)
System 1: JRiver MC24 > Dell Latitude 7270 > Asus Xonar Essence One Muses Edition DAC & pre- > One4 Class A power amp (with Dynamic PSU boards) > DIY Monacor SP-310CX speakers & DIY Dayton Audio SD315A-88 bass cab.
LC Audio Technology mains DC filter > Sovereign MTBPS balanced power supply
TQ (Wonfor) Ultra Black cables.

System 2: Anything with a headphone socket > Inca Tech Claymore > DIY Monacor SP-308CX speakers

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karatestu
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Re: Monacor SP-310CX build

Unread post by karatestu »

Well done. :clap: Not much love for ports round these parts but don't let that stop you. Looking forward to your future updates.

I couldn't design a decent xover for toffee so it's just as well I don't have to :lol: Monacor do some good drivers. A member here mentioned them on diyaudio and I have to say that on paper the 8" and 5" from the range I have seen look very well behaved indeed.

:epopc:
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Re: Monacor SP-310CX build

Unread post by NSNO2021 »

karatestu wrote: Thu Jul 09, 2020 6:44 pm Monacor do some good drivers. A member here mentioned them on diyaudio and I have to say that on paper the 8" and 5" from the range I have seen look very well behaved indeed.

:epopc:
That would be me but I think someone else on here nudged in Monacors direction to start with. I will go back through my messages and hopefully establish who it was. Interesting post Doc and I am looking forward to further updates 👍
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Re: Monacor SP-310CX build

Unread post by karatestu »

That would be Simon Hickie by any chance ?
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Re: Monacor SP-310CX build

Unread post by Latteman »

Great post, could u share a bit more on the cross over build please👍🏼
Analogue Source -
Denon DP47f- Ortofon mc20 supreme
Ifi Zen Phono
Doug Self balanced Pre amp
Akai 4000DS mk2 R2R
Digital Sources- IfI stream, Ifi Neo idsd Dac; Tidal / Radio Paradise
Amplification Nva 30vdc mono blocks
Speakers Lii Audio F-15 in Open Baffle; Ls6
Weiduka AC8.8- for digital sources
Mini BMU for analog sources

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Re: Monacor SP-310CX build

Unread post by Docfoster »

karatestu wrote: Thu Jul 09, 2020 6:44 pm Well done. :clap: Not much love for ports round these parts but don't let that stop you. Looking forward to your future updates.

I couldn't design a decent xover for toffee so it's just as well I don't have to :lol: Monacor do some good drivers. A member here mentioned them on diyaudio and I have to say that on paper the 8" and 5" from the range I have seen look very well behaved indeed.

:epopc:
Thanks.
I don't really design crossovers. I use a free online calculator to do that... 8-)

https://www.diyaudioandvideo.com/Calcul ... Crossover/

Then I use a high-shelf (set at the crossover frequency) to find out subjectively, via listening, what level of attenuation I like best for the tweeter...

Image

Once I've decided, I use a free online L-Pad calculator to design the L-Pad for the desired dB level...

http://www.sengpielaudio.com/calculator-Lpad.htm

I you ask me how any of these things work, I would be unable to tell you. But I know they do work (for me)!
nilsatisnisioptimum wrote: Thu Jul 09, 2020 9:02 pm
karatestu wrote: Thu Jul 09, 2020 6:44 pm Monacor do some good drivers. A member here mentioned them on diyaudio and I have to say that on paper the 8" and 5" from the range I have seen look very well behaved indeed.

:epopc:
That would be me but I think someone else on here nudged in Monacors direction to start with.
I must say I think they are a great manufacturer. Produce loads of drivers in different designs at different price points. Haven't had a had a bad one for them yet. :clap:
System 1: JRiver MC24 > Dell Latitude 7270 > Asus Xonar Essence One Muses Edition DAC & pre- > One4 Class A power amp (with Dynamic PSU boards) > DIY Monacor SP-310CX speakers & DIY Dayton Audio SD315A-88 bass cab.
LC Audio Technology mains DC filter > Sovereign MTBPS balanced power supply
TQ (Wonfor) Ultra Black cables.

System 2: Anything with a headphone socket > Inca Tech Claymore > DIY Monacor SP-308CX speakers

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Re: Monacor SP-310CX build

Unread post by Docfoster »

Latteman wrote: Fri Jul 10, 2020 8:43 am Great post, could u share a bit more on the cross over build please👍🏼
Thanks. Yes. Happy to. :-)

I started with the 1000Hz crossover as this worked well for me with the Tannoy 295/8.

I choose 2nd order simply because this is the one that conventional wisdom holds is the best balance of simple and effective.
I have not yet tried a build with a 1st order. I should probably do so!
A 1st order simply has a single in-series capacitor on the tweeter and a in-series single inductor on the woofer. The signal for both descends at 6dB per octave.
A 2nd order adds an in-parallel inductor to the tweeter, and an in-parallel capacitor on the wooder. The signal fort both descend at 12dB per octave. So, a sharper drop.

I chose a Linkwitz-Riley curve as theoretically, and all other things being equal, this seems best to me as the curves sum to flat.

Image

I use a free on-line calculator for which one inputs driver impedence and desired crossover frequency.

https://www.diyaudioandvideo.com/Calcul ... Crossover/

One gets a nice neat design...

Image

Obviously I round the values to the nearest convenient. In this case, 10uF capacitors and 2.5mH inductors.
I order from Willy's hifi. Good products at fair prices. Friendly service and speedy delivery.

Once arrived I try to make the crossovers as compact as possible. I just use a scrap of MDF as the base board and attach the components with cable-ties. I try to create a layout that allows me to solder the tails directly. In this case I did need to use a short strip of wire to connect the negative ends of things. Take 1...

Image

It worked fine. But as noted above, there was a drop around 1kHz that the graphs for the driver prophesied.
So, I decided to try a Butterworth crossover, which (see graph above) sums to a +3dB lift at crossover frequency (which happened to be 1kHz).

The online calculator gave me values for which the nearest convenient values were 15uF caps and 2mH inductors. A bit of trial error on the online calculator suggested that these values would produce a crossover frequency of 930Hz. Close enough, I reckoned, so back to Willy's Hifi website.
The result, Take 2...

Image

The cables attached there are the ones heading off to the driver.

This did improve things, but not enough.

So, my next thought for further boosting the overall signal around 1kHz was to lower the crossover frequency of the tweeter whilst keeping the 930Hz butterworth filter the same on the woofer. A bit of jiggery and pokery on the online calculator suggested that a Butterworth 2nd order crossover at 700Hz would, for the tweeter, be 20uF cap and 2.5mH inductor. Fortunate as that meant I could recycle the components from my first crossover (above): the 2.5mH inductor and the 2x 10uF caps which in parallel create 20uF.

So, Take 3...

Image

And yes, it's working. :guiness;
Only issue is that I'm staying with my parents atm, so I've got only a minimal system (lappy headphone socket > Incatech Claymore). Moreover I'm listening in my parents lounge. Lovely room, but one with whose acoustics I am totally unfamiliar. Things sound fine, BUT obviously I want to wait till I get back to the big rig at home to make any definitive judgements.
If OK, I'll spend time listening to determine the attenuation level, and then make up some L-Pads accordingly.

(Incidentally, I am using some NVA speaker cables that I bought for my Dad ten years ago, that I've just pinched from his study. :grin: )

Image
These users thanked the author Docfoster for the post:
Latteman (Fri Jul 10, 2020 9:32 pm)
System 1: JRiver MC24 > Dell Latitude 7270 > Asus Xonar Essence One Muses Edition DAC & pre- > One4 Class A power amp (with Dynamic PSU boards) > DIY Monacor SP-310CX speakers & DIY Dayton Audio SD315A-88 bass cab.
LC Audio Technology mains DC filter > Sovereign MTBPS balanced power supply
TQ (Wonfor) Ultra Black cables.

System 2: Anything with a headphone socket > Inca Tech Claymore > DIY Monacor SP-308CX speakers

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Re: Monacor SP-310CX build

Unread post by Latteman »

Chairs- lol 😂
Analogue Source -
Denon DP47f- Ortofon mc20 supreme
Ifi Zen Phono
Doug Self balanced Pre amp
Akai 4000DS mk2 R2R
Digital Sources- IfI stream, Ifi Neo idsd Dac; Tidal / Radio Paradise
Amplification Nva 30vdc mono blocks
Speakers Lii Audio F-15 in Open Baffle; Ls6
Weiduka AC8.8- for digital sources
Mini BMU for analog sources

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Re: Monacor SP-310CX build

Unread post by Docfoster »

Latteman wrote: Fri Jul 10, 2020 9:38 pm Chairs- lol 😂
Yes. I was disappointed to learn that a 75 year old woman's speaker stand collection is limited at best.
System 1: JRiver MC24 > Dell Latitude 7270 > Asus Xonar Essence One Muses Edition DAC & pre- > One4 Class A power amp (with Dynamic PSU boards) > DIY Monacor SP-310CX speakers & DIY Dayton Audio SD315A-88 bass cab.
LC Audio Technology mains DC filter > Sovereign MTBPS balanced power supply
TQ (Wonfor) Ultra Black cables.

System 2: Anything with a headphone socket > Inca Tech Claymore > DIY Monacor SP-308CX speakers

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karatestu
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Re: Monacor SP-310CX build

Unread post by karatestu »

Hey Doc.

Glad to see you are not going overboard with the xover. No notch filters, baffle step correction etc etc etc :clap: If I was doing it they would be first order all the way but I have learned that the average 1" dome tweeters sound much better when using a single capacitor if the filter knee frequency is as high as possible or you use more than one tweeter to share the work and drastically reduce distortion.

At least you don't have to worry about woofer / tweeter time alignment :dance:
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