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m_ms

MicroWrecker build thread

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They're alive! That is - it's still a very early sound-draft, so to speak. There's a lot of optimization in the wait, and so any impressions may only tell you so much. I won't be able to supply measurements anytime soon (I know you guys crave seeing them data), but I hope they'll land eventually.

I had no success with the removal of the fan of my Crown Macro-Tech 1200; from the bottom of the amp we were able to safely pull off the fan from its spindle/axle, but when I fired up the Crown this way, with speaker load, it turned very hot quickly, and not soon after shot down one of the channels. So, the fan went back in, and properly fan-cooled one barely registers any heat on its chassis, if at all - even when cranking the MW's a bit.

So, with the proviso of a noisy background level from the Crown fan, B&C drivers that aren't yet run-in, and no elaborate optimization other than crude level-matching with the mains and a preliminary HPF/LPF at 90Hz, here're some early impressions:

The MW's in my particular setup are a different animal compared to the SVS SB16-Ultra, that's for sure. At first I found them surprisingly "civilized" or delicate even, and after switching polarity in one channel found a more satisfying (but not altogether) level to match the mains. They still sounded a bit recessed, in a way, as if not really kicking into gear. I've since had them playing a good many hours for the last two days, and yesterday while seeing "Mission: Impossible - Fallout" on Blu-ray I noticed how they suddenly started loosening up and subjectively gaining in volume level. This tendency has continued throughout today with a fuller, more tactile sound, so much indeed that I needed to re-calibrate their volume.

Compared to the SB16 the MW's provide a noticeably smoother and more "liquid" presentation of the lower band, and a livelier mid-bass. Moreover the bass from the MW's is much more wholly immersive, like an omni-presence. What's interesting is hearing how the bass of the MW's can truly sound like the lower registers of an instrument (like strings), where the SB16 sounded congested by comparison and more obscured "bassy." There's indeed an obvious thickening of the bass from the SB16, from my recollection. The MW's have more roar and texture in the mid-bass to mate more seamless with my mains, while subjectively rolling off earlier in the lower bass compared to the SVS, but this is a bit tricky to assess. With up-beat techno material the SVS had more emphasis on the lower bass to the point where you felt it to stumble a bit, whereas the MW's are more agile with no drag, more impactful and yet fuller sounding, but with more emphasis on the mid-bass. There's no sense of the MW's lacking in the lower bass as such, where there's the sensation of them shaking the air very effectively, but I suspect the SVS to dig a little deeper. 

Pics later, and more impressions to come as the optimization process kicks into gear..

 

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Would like some views from you guys on the matter of a high-pass filter, and whether it's really necessary in my case with the MW's?

Well, I've just applied a 20Hz 48dB/Oct HPF just to be sure. I take it this is more a measure relating to distortion than protection of the drivers per se, being that I can't see myself going beyond SPL's of 110-115dB's (short bursts, like from watching Blu-rays). Playing a scene from "Ready Player One" towards the end (of the game) is some "doomsday device" being set off, resulting in some very low-frequency rumbling as the destruction unfolds. In this scene, at my usual playback level, the excursion of the SVS driver was clearly visible, but playing the same scene with the MW's at the same SPL I can't see the driver move at all, apart from very small cone vibrations - quite impressive. Perhaps the frequencies here are sitting in the vicinity of the tuning fs of the TH..

OTOH, many Blu-rays contain frequencies indeed much below 20Hz - at full level - so if the MW's don't produce much worthwhile information below 20Hz anyway I don't see any reason for them to work, unloaded, with infrasonic information. That's certainly the argument in favor of using a HPF here. 

MW 22.jpg

MW 23.jpg

MW 24.jpg

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On 1/17/2019 at 3:20 PM, m_ms said:

Sound like beasts. What's the in-room low corner from a pair of those, and how big is your listening room (in square meters)? 

They are boosted to be flat (or rather optimized to target response) to about 6 Hz.  I'm not sure how to answer your second question.  The living room is open to the rest of a modest sized 3 bedroom ranch.  If I only include the commons areas, which are connected by large openings, I'm at around 45 m^2, all with 8 foot (2.44 m) ceiling.

12 hours ago, m_ms said:

Would like some views from you guys on the matter of a high-pass filter, and whether it's really necessary in my case with the MW's?

It's probably a good idea, even though you may not play them hard enough for it to matter.  A 48 dB/octave filter is extreme though.  You can probably get away with like 12 or 18 dB/octave.  I suggest going back and look at what's recommended on the build thread.

The filter is probably a lot more important for movies than for music being that movies are more likely to have < 20 Hz content and at a high enough level to be a potential problem.

That RP1 scene is pretty crazy, especially considering how long it lasts.  Of course I'm running with BEQ, so no steep filter at 20 Hz.  I don't know if that matters much though.  Even if there is ULF, it seems to hit harder across the rest of the bass range.  Going by my level indicator display, the effect seems to consist of a rapid, chaotic succession of short bursts that goes for several seconds.  The voltage output peaks are pretty high, but it doesn't ever blink the yellow lights like King Kong does.  Assuming it's mostly in the 20-60 Hz range, my subs probably aren't seeing much power there, but that suggests the SPL is pretty high, easily well into the 120s dB SPL.

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16 minutes ago, SME said:

It's probably a good idea, even though you may not play them hard enough for it to matter.  A 48 dB/octave filter is extreme though.  You can probably get away with like 12 or 18 dB/octave.  I suggest going back and look at what's recommended on the build thread.

How can the HPF slope here be (too) "extreme"? Is it potentially detrimental? 

Quote

The filter is probably a lot more important for movies than for music being that movies are more likely to have < 20 Hz content and at a high enough level to be a potential problem.

Certainly my assessment as well. My line of thought is why you'd bother sending info to the MW's they can't reproduce anyway, so might as well keep the HPF for music as well as for watching films.  

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2 minutes ago, m_ms said:

How can the HPF slope here be "extreme"? Is it potentially detrimental?

A steeper slope will ring more.  This is likely to be noticed much more with movies because most music is filtered higher up.

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26 minutes ago, SME said:

A steeper slope will ring more.  This is likely to be noticed much more with movies because most music is filtered higher up.

Can you elaborate a bit on the "ringing" - how is this noticeable?

Btw, @lilmike at an earlier juncture advised me to use a HPF at 20Hz for the MW's, "minimum 4th order," so 24dB/Octave at least. Question is whether his recommendation entailes an implicit upper limit for the slope used..

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And this has to be said clearly: thank you, @lilmike, for taking the time answering my endless questions and supplying free plans to a TH that by all accounts appears to be an excellent design :) 

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On 1/25/2019 at 3:48 AM, m_ms said:

@lilmikeCan you elaborate a bit on the "ringing" - how is this noticeable?..

It's basically a perceptual emphasis of frequencies in that area and possibly a bit of overhang to the sound, whenever the content goes that low.  If the content is filtered a lot higher, like > 30 Hz as is typical for music, you probably won't hear much difference.  So it's probably more a thing with movies that extend to at least 20-25 Hz.

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12 hours ago, SME said:

It's basically a perceptual emphasis of frequencies in that area and possibly a bit of overhang to the sound, whenever the content goes that low.  If the content is filtered a lot higher, like > 30 Hz as is typical for music, you probably won't hear much difference.  So it's probably more a thing with movies that extend to at least 20-25 Hz.

Interesting. From my understanding on the subject of high-passing subs a certain degree of slope steepness is needed for it to have an effect (i.e.: to actually be a protective measure to the driver), and going by lilmike's recommendation of a 4th order minimum it would follow that an even steeper slope is advisable. This advice may come in the wake of the relative nature of what exactly needs to be high-passed: horns generally gain from being used within a rather narrow bandwidth, and with a tapped horn both the low- and high-pass section would seem critical; the HPF for protection of a driver unloaded (in free air) below its tuning frequency, and the LPF to quench any looming peaks in the upper band. 

As is I'm using a 48dB/octave Linkwitz-Riley LPF at 90-100Hz (presently at 100Hz) on the MW's, and a corresponding 48dB/octave Linkwitz-Riley HPF on my main speakers (all-horns). Later I'll try out a 24 or 36dB/octave L-R crossover at 80Hz and see how that fares. The HPF on the MW's is 48dB/octave Butterworth at 20Hz, but I'll try a HPF down to 24dB/octave - slope type unchanged. 

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7 hours ago, m_ms said:

Interesting. From my understanding on the subject of high-passing subs a certain degree of slope steepness is needed for it to have an effect (i.e.: to actually be a protective measure to the driver), and going by lilmike's recommendation of a 4th order minimum it would follow that an even steeper slope is advisable. This advice may come in the wake of the relative nature of what exactly needs to be high-passed: horns generally gain from being used within a rather narrow bandwidth, and with a tapped horn both the low- and high-pass section would seem critical; the HPF for protection of a driver unloaded (in free air) below its tuning frequency, and the LPF to quench any looming peaks in the upper band.

Any amount of slope is enough to provide some driver protection compared to no slope, but how much is needed for "bulletproof" operation depends on the design and also on where the filter cuts. This case being a horn, the unloading of the driver may result in a more dramatic increase in excursion than a typical vented alignment.  That would definitely explain why a 4th order is needed.

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Sorry for the late reply, just getting back online after a vacation.

The 4th order recommendation was based on simulations of the performance of lower-order filters. The lower-order filters do not provide sufficient protection from overexcursion below the horn's tune. Once at 4th order, things look OK, higher than 4th looks a bit safer, but as SME mentioned, higher-order filters come with other issues, like ringing and phase issues.

That was all done in simulations, which are predictions of large-signal performance based on a set of small-signal parameters that do not scale linearly as signal increases. My experience is that excursion tends to not be as much of an issue as Hornresp predicts. Usually, there are warning signs before the bad noises happen, and so far, I've not killed any drivers in tapped horns (though, I don't set out to do so). I haven't had a chance to actually measure the excursion of a driver in a tapped horn yet, but I hope to be able to do that before too much longer. I do have most of the gear and software, just need to get it all configured. 

The highpass recommendation was my effort to try to make these cabinets as bulletproof as possible for other people. I would hate to have someone kill the driver in their newly-built sub while showing it off in a demo because I didn't recommend a highpass to protect the driver and minimize distortion. I run 20 Hz at 4th order in my system, and I definitely twist the volume knob to silly on occasion. The sub has moved itself out of the corner several times. So far, only warm voice coil aromas, no bad noises or other complaints from the sub. The rest of the system was running out of gas at that point, but I am working on that.

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The 4th order HPF sounds pretty conservative.  I do know that @deepthoughts reported that driver excursion can be unexpectedly high (vs. simulation) in ported alignments at levels that cause a lot of port compression.  I guess the port, when it's compressing, is not providing enough loading on the driver.  Port compression can also be difficult to see in measurements because the output from the driver itself increases, helping hide the drop in output of the port.

I don't know enough about tapped horns to be able to guess whether something similar can happen due to losses in the expansion, but I'd expect it'd be less of a problem if it is at all.

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I've done some rudimentary testing with other drivers and found that I could put a lot more power to them in the tapped horn than in a free-air situation. The driver I was working with (Shiva X2) would make mechanical noise (tapping) at really low frequencies at about 100 watts applied free-air. The same driver in a tapped horn was able to take 500 watts without any noises. Not totally scientific, and certainly not what I have planned for my future efforts, but at least it showed that there is some loading on the driver below the horn passband and at least some difference between the displacement predictions and actual performance in that case. 

I have also found that my tapped horns tend to measure a little flatter at higher output levels than they do at a watt. 

In the case of a ported box with an undersized port, the excursion increasing as the port compresses makes total sense to me. In the vast majority of cases the ported box is larger than a  sealed box would be for the driver in question and the port essentially becomes a large leak once compression sets in and the port is no longer functioning as a proper resonator. 

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On ‎2‎/‎9‎/‎2019 at 9:18 PM, lilmike said:

Sorry for the late reply, just getting back online after a vacation.

The 4th order recommendation was based on simulations of the performance of lower-order filters. The lower-order filters do not provide sufficient protection from overexcursion below the horn's tune. Once at 4th order, things look OK, higher than 4th looks a bit safer, but as SME mentioned, higher-order filters come with other issues, like ringing and phase issues.

That was all done in simulations, which are predictions of large-signal performance based on a set of small-signal parameters that do not scale linearly as signal increases. My experience is that excursion tends to not be as much of an issue as Hornresp predicts. Usually, there are warning signs before the bad noises happen, and so far, I've not killed any drivers in tapped horns (though, I don't set out to do so). I haven't had a chance to actually measure the excursion of a driver in a tapped horn yet, but I hope to be able to do that before too much longer. I do have most of the gear and software, just need to get it all configured. 

The highpass recommendation was my effort to try to make these cabinets as bulletproof as possible for other people. I would hate to have someone kill the driver in their newly-built sub while showing it off in a demo because I didn't recommend a highpass to protect the driver and minimize distortion. I run 20 Hz at 4th order in my system, and I definitely twist the volume knob to silly on occasion. The sub has moved itself out of the corner several times. So far, only warm voice coil aromas, no bad noises or other complaints from the sub. The rest of the system was running out of gas at that point, but I am working on that.

Sorry for the late reply as well, and thanks for getting back to me, @lilmike.

I see clearly were you're coming from with your HPF recommendation for the MicroWreckers. My 8th order BW HPF for the MW's was perhaps somewhat exaggerated, not least in light of my not all that commanding use of them, so today I've dialed it back to a 4th order Butterworth HPF. I believe it actually sounds better this way, but I won't bother any of you with details to describe it. The most I've seen those B&C units move was with a recent Blu-ray showing of Blade Runner 2049 where they "jumped" 2 mm's perhaps during the scene where K's being downed in his hovercraft from a strike of lightning - and that was running the system volume 6dB's hot.. Yes, that's all they move with my typical use, but the SPL could most definitely be felt!

The first weeks of use (actually until rather recently) the MW's sounded somewhat lean and lacked impact, but slowly and steadily they're really getting around to it, though I suspect running them in properly will take months. Those rugged cloth surrounds of the B&C 15TBX100'a are quite stiff, and the little they are being worked out from the limited in-use excursion won't see rapid burn-in progress.

As is, after finally finding their proper on-the-side-lying placement along each side wall, I'm really pleased with the result; the MW's provide a totally effortless, uninhibited, smooth and enveloping bass that blends in extremely well with my all-horn mains - indeed they seem like a perfect match. I'm surprised they're so informative as they are. The bass is so present, clear and even liquid in a way that makes it extremely easy to follow bass-lines, and they refuse to "solidify" the way I felt the SVS SB16-Ultra did; this is bass that energizes the air, shakes it even, and is more of an enveloping, floating kind. 

What follows now is a rather lengthy process of fine tuning delay, PEQ, crossover frequency and slope, and subtle changes in placement (from a general outset that won't change). Right now I cross over to the mains at 91Hz 42dB/octave Linkwitz-Riley, and as mentioned above 4th order HPF Butterworth on the MW's. 

Great design, @lilmike - kudos :) 

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Had a rather big break-through today with the aid of friend, who helped optimize the MW's. Actually, he deserves sole credit for totally rearranging the delay and other aspects via the Xilica unit in the wake of honing in on an 80Hz (still 42dB/octave Linkwitz-Riley) cross-over that we settled on. The high-pass of the MW's remains unchanged. Also, the MW's remain hooked-up in true stereo mode. 

He had "fallen in love," as he put it, with the MW's for their "clean, fast, non-signature, hard-hitting bass" that "wholly integrates with the mains" (he uses a pair of Electro Voice TL880D cinema subs in his own setup). He has extensive experience with and knowledge of horn subs, and found the MW's the best horn subs he'd yet heard. Not too shabby.. :) 

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