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Revel M105 Copy DIY build

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McFly

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It was with everything. Even watching TV. Purely subjective I know. But the paper woofer has been a revelation (no pun intended). The 15W8530 is one hell of a woofer
 

D!sco

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How's the bass since the update? Does the lower Fs justify a new box?
 

Paweł L

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Getting back on the M105 copies;

After living with the M105 'copies' there is something that bugs me - it's like a sheen/glare over the entire midrange. I kept trying to ignore it but eventually I couldn't and it bugged me. Perhaps I failed to supress the woofer breakup sufficiently. I suspected the woofer and have since swapped it for a paper cone scan speak - if the problem goes away I will provide updates with the scan speak unit. Here's preliminary quick data

View attachment 200672

;)

View attachment 200675
I'm working with 17NBAC 4ohm version, and yeah while nice there's hint of 'metal cone' coloration. Slapped RLC trap to reduce 4-9kHz area, capacitor across coil to remove the cone breakup hash, but while quite clean and detailed, there's something there, a glare as you described it. I guess it's just the way they behave, sort of like alu done tweeters vs fabric domes.
This paper Scan looks well behaved, without the 'hash' of alu SB midwoofers.
 

Tangband

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I'm working with 17NBAC 4ohm version, and yeah while nice there's hint of 'metal cone' coloration. Slapped RLC trap to reduce 4-9kHz area, capacitor across coil to remove the cone breakup hash, but while quite clean and detailed, there's something there, a glare as you described it. I guess it's just the way they behave, sort of like alu done tweeters vs fabric domes.
This paper Scan looks well behaved, without the 'hash' of alu SB midwoofers.
Very interesting building and this 17NBAC youre mentioning seems to be very good . Maybe you have to do a crossover with at least 24 dB/oct slopes because there IS a nasty breakup higher in freq and a notchfilter in my opinion doesnt do any good for the sound .

My suggestion would be trying a mini dsp or such and try 24-48 dB/oct filtering , because on paper the 17NBAC looks better than 15W8530K00 if optimal crossed .

In my work with the active HYBRID and seas er18rnx I noticed that a perfect dsp notch filter with a 12 dB/oct crossover sounded worse than a plain 24dB/oct linkwitz riley crossover .

Lesson learned for me - If the driver has a nasty breakup such as in seas er18rnx or 17NBAC its probably much better to do steep crossovers than start to implement notch filtering .

17NBAC has no more than about 3 mm linear extension so it should also be crossed at about 80 Hz or higher.

Maybe metal coned midranges are better suited for steeper active crossovers , even if they look quite good on raw measurements ? B95E92E9-55F4-4E00-BAE7-CDAF06774AF6.png
 
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Paweł L

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Very interesting building and this 17NBAC youre mentioning seems to be very good . Maybe you have to do a crossover with at least 24 dB/oct slopes because there IS a nasty breakup higher in freq and a notchfilter in my opinion doesnt do any good for the sound.

Lesson learned for me - If the driver has a nasty breakup such as in seas er18rnx or 17NBAC its probably much better to do steep crossovers than start to implement notch filtering .

17NBAC has no more than about 3 mm linear extension so it should also be crossed at about 80 Hz or higher.

Maybe metal coned midranges are better suited for steeper active crossovers , even if they look quite good on raw measurements ?
It is 24dB/oct. IMO most 6" drivers need this, I'm actually a bit sceptical how J.Bagby used 12dB in his Satori builds. Seas ER18 maybe isn't as bad as it looks. The SB17NRXC isn't easy to hammer into LR4 either, shooting into Himalayas past 4kHz but I hear it. So definitely paper must dump the resonances better. You might be right about something steeper than 24dB/oct for some alu cones, 36 might work nicely, just the parts count will high.
 

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augerpro

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I know the breakup is extended on the SB, but you might try a notch in series with the woofer, and closer to it than the rest of the network. Per Lars at Purifi this will also remove the harmonic distortion related to the breakup. Other forms of filtering do not have this property. I asked specifically about the cap across the first inductor as I like that method a lot. His answer was really technical but amounted to "no".
 

Paweł L

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Thanks Auger. Hmm, I looked at Lars network for his Purifi 6" paper cone and couldn't figure out why he used series RLC this way, when there are easier ways to hammer the freq resp into specific transfer function. Back to drawing board and some head scratching.
thx again
 

Elfsberg

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@McFly

Interesting build!

Would you care to post FRD and ZMA for your drivers?

Thanks
 

augerpro

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McFly

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Hi all, I haven't forgotten this thread. Life has just been, well , life in early 30's. Much life admin and other projects. I will follow up soon.
 

Paweł L

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McFly,
it would awesome if can you make frd zma files available. I would like to check what are the possibilities other than x-over you presented (more filtering above 4k, where Alu cones show their character). And of course I'm interested what the sb26adc in augerpro vaweguide can do.
 

Paweł L

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With active, especially DSP, there are more possibilities than passive. With passive we are married to driver's freq response characteristics, impedance and the way crossover parts interact with them. Also with large excursion and higher than average signal level certain parameters change their nominal value and might affect the crossover network (slope). The amplifier sees the combined impedance of the crossover and transducers, with all the impedance dips and peaks, plus phase changes. DSP can add specific EQ, notch filters, time delay, it's mostly immune to parameter change of the drivers with signal level, and drivers are directly coupled to amplifiers. So, I would say that active crossovers should actually have better distortion performance and better control over the driver(s) transfer function. Most studio monitors are active in design for a reason.
 

phrog

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With active, especially DSP, there are more possibilities than passive. With passive we are married to driver's freq response characteristics, impedance and the way crossover parts interact with them. Also with large excursion and higher than average signal level certain parameters change their nominal value and might affect the crossover network (slope). The amplifier sees the combined impedance of the crossover and transducers, with all the impedance dips and peaks, plus phase changes. DSP can add specific EQ, notch filters, time delay, it's mostly immune to parameter change of the drivers with signal level, and drivers are directly coupled to amplifiers. So, I would say that active crossovers should actually have better distortion performance and better control over the driver(s) transfer function. Most studio monitors are active in design for a reason.
Active is certainly better overall. I was just noting that this is one particular advantage that passive has over active. The optimal setup might be an active setup that also has passive series notch filters to tame breakup-induced distortion.
 

Elfsberg

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I've seen some of this kind of thinking the last months on this forum and I don't agree.
I'm under the impression that if a crossover can be made passive it should be. It is pretty much always the most cost effective option and some properties can't be achieved through active filtering. These properties isn't news to electronic engineers as shown clearly by Purifi in their public filtering note. If a passive crossover is not possible other drivers should be used.

Though, active crossovers are to be preferred for subwoofer duty: the coils are huge and in some they might end up more expensive than the subwoofer drivers themself if the system designer wants snake oil components.

Equalization is another thing entirely.

I am experimenting with active filtering too but it should not be made a secret I know pretty much nothing about circuit design.
 

LTig

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It seems like this is an inherent advantage to using passive crossovers over active crossovers. I've never considered this.
Just read the paper and I don't see any advantage for a passive crossover. All filters can be implemented much more precisely in DSP, and since the driver is connected directly to the power amp its very low output impedance can control the driver better than through a passive network.
 

D!sco

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Yup, read the note too. It claims that the passive crossover is capable of lower distortion than an active solution early on but never gives data to back it up. All I see is the same high-range, wide band and nicely smoothed graphs I'm used to from manufacturers using passive filters. Likewise, this filter is similar to an active, asymmetrical third order filter used by the maker of VituixCAD in a number of designs by combining a second order filter with a later first order to achieve a more precise roll-off. The tech is neat, but the claim isn't.
 

Elfsberg

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See section 1.3. ;) You want to alter the actual impedance not just the SPL of problem area.
 
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McFly

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One thing I like about passives that isn't often spoken about, is the ability for others to use the speakers.


McFly,
it would awesome if can you make frd zma files available. I would like to check what are the possibilities other than x-over you presented (more filtering above 4k, where Alu cones show their character). And of course I'm interested what the sb26adc in augerpro vaweguide can do.
Will take a look for you soon.
 
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