Ah yes, that'd be Clark Johnson and his crank book of misapplied physics and selective misquotations, yes? The Audio Critic demolished it, and his ridiculous self-aggrandising letters back in the early '90s. I'm glad one copy still appears to survive though, to serve as a warning from history.
Audible differences can certainly exist sans gaskets. But Clark's argument, if it was for the reason you mention, is borderline cretinous in engineering terms, since it's not physically possible to get a perfect seal between driver basket and the mounting surface. Neither are perfectly flat, so air-leaks are inevitable. Not always a bad thing; for example, it can be used in some cases to bleed off an excess of pressure, but this is at best something for specific circumstances and gone into for a specific reason. In other circumstances -well, that's what gaskets are for.
I wondered about damping between the driver and cabinet, apparently the driver should be "grounded" to the cabinet for best results.
@nicoch58 - Yay! Sounds like my thoroughly modern amplifier is on the way too! :')
@scottmoose - small world, eh? Thanks for reminding me his name - that's the guy - it's certainly been a while. I've long lost my copy of the book.
I took the basic idea to heart, that of a kick drum makes a pressure wave, a tympani a rarefaction and such absolute phase relationships can switch back and forth recording to recording, even on the same disc. However, I dont have a phase switch in my system though.
The idea extends to some awareness around reversing the + / - on my assistant woofers, in order to get flat frequency response through the crossover with certain order filters. Ideally, I'd prefer to have both speakers in phase and I spose that's what the 24db LR design is for. Or does it really matter given the crossover could now be 4-5X higher than, say, the 60-ish Fs of the F15 - which was my target of the line-level passive network I had in place?
Thanks,
@scottmoose - small world, eh? Thanks for reminding me his name - that's the guy - it's certainly been a while. I've long lost my copy of the book.
I took the basic idea to heart, that of a kick drum makes a pressure wave, a tympani a rarefaction and such absolute phase relationships can switch back and forth recording to recording, even on the same disc. However, I dont have a phase switch in my system though.
The idea extends to some awareness around reversing the + / - on my assistant woofers, in order to get flat frequency response through the crossover with certain order filters. Ideally, I'd prefer to have both speakers in phase and I spose that's what the 24db LR design is for. Or does it really matter given the crossover could now be 4-5X higher than, say, the 60-ish Fs of the F15 - which was my target of the line-level passive network I had in place?
Thanks,
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Well, LR4 wasn't designed for that reason, but certainly it does require the drivers to be wired in the same electrical polarity, assuming appropriate physical offset. LR2, LR6 and LR8 often require inverted polarity on one element though. This is primarily in the electrical domain though; in practice different offsets, placements etc. usually require either a degree of asymmetry in the transfer functions to provide flat summing, or electrical delay to one or more elements. Absolute phase is somewhat different to phase rotation caused by the crossover, though since they're both phase, they are in that loose sense related.
Well, after an initial go with having both low and high pass filters, the best sound seems to be crossing very near the F15's Fs...
The miniDSP makes my system sound like a mass-market receiver from the 80s... I cant run the high pass through it - wrecks whatever magic was happening between the Liis and the Jolida LM1875 amp.
So it's now a LPF for the assist woofers, with 70 Hz LR4 - and a rising response to 25 I tacked on via the parametric EQ part. The F15s running full range with no EQ and a direct signal path from the DAC sounding best to me. No measurements yet...
I'm going to have to fix this. I assume line level ADC / DAC (internal) I/O for the mini is centered about 2.5V - hence the caps to bring it back to about 0. Sure wish I had a schematic for the Aune - line level offset measures a fraction of a mV, but I have no idea if it's a capacitively coupled output - or an Op-Amp with a safety resistor. Sigh.
The miniDSP makes my system sound like a mass-market receiver from the 80s... I cant run the high pass through it - wrecks whatever magic was happening between the Liis and the Jolida LM1875 amp.
So it's now a LPF for the assist woofers, with 70 Hz LR4 - and a rising response to 25 I tacked on via the parametric EQ part. The F15s running full range with no EQ and a direct signal path from the DAC sounding best to me. No measurements yet...
I'm going to have to fix this. I assume line level ADC / DAC (internal) I/O for the mini is centered about 2.5V - hence the caps to bring it back to about 0. Sure wish I had a schematic for the Aune - line level offset measures a fraction of a mV, but I have no idea if it's a capacitively coupled output - or an Op-Amp with a safety resistor. Sigh.
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@dave: "In our miniOnkens we have a brace from the driver to at least 3 other sides accomplishing the same thing"
How would the back of a driver be attached to, such that you can put a force on it that would put the basket in tension, i.e. pull the speaker harder against the baffle? Or perhaps it's easier the other way around; push a force on the driver to make it want to raise up off the baffle? Probably want a gasket in that case - but the mounting stiffness loss due to that is mitigated through the driver itself being in screw force tension or compression within the cabinet.
Set them up fresh from the shipping container using a torque wrench!
How would the back of a driver be attached to, such that you can put a force on it that would put the basket in tension, i.e. pull the speaker harder against the baffle? Or perhaps it's easier the other way around; push a force on the driver to make it want to raise up off the baffle? Probably want a gasket in that case - but the mounting stiffness loss due to that is mitigated through the driver itself being in screw force tension or compression within the cabinet.
Set them up fresh from the shipping container using a torque wrench!
The holey driver brace fits tight up agsinst the magnet, firmly, but with no force placed on the basket. This catches the rear-ward force reaction of the basket, if you want the other way as well you would need to use ready rod to attach the front of the driver to the back (or better to another driver).
Some drivers like the one pictured, KEF has built some, and i have seen others, where there is a mechanism to mechanically couple the drivers in both directions.
dave
Some drivers like the one pictured, KEF has built some, and i have seen others, where there is a mechanism to mechanically couple the drivers in both directions.
dave
Is that good then?
I ran my f15 in open baffle with a little assistance from a sub and ribbon tweeter, no crossover, very good and something I could live with if I had the space, which I don't.
@dave, come to think of it, I once owned a pair of 104/2s, which had the metal bar inside and between the "coupled cavity" woofers. One day a tweeter stopped working...KEF made the MTM module unrepairable, so I replaced both tweeters and sold 'em - stating the tweeters had been replaced with non_KEF units.
My thought was if there's a brace already for the driver to push against, how would it be to add a little tension/compression preset force into that mechanical system?
@paulfk; OK, it's not good. It seems the Lii "wants" to run towards full range, rather than be more like a 15" tweeter. I understand and have no issue with simply eliminating the infra frequency signals from getting to its voicecoil.
Of course I'd prefer it if the miniDSP were as transparent as a wire, but that's not the case as...even I thinks I can hear it. More of a difference than moving from a FLAC stream to a 64K one - which can still sound pretty good through the F15s...
As soon as those caps come in the post, I'll push onward with it. Hopefully I'll be able to use it for the high pass as well. Using it for just low pass - as a tool to tune the woofer assist part of my OB design - is fine if that's how things work out.
I realize I could modify the LM1875 amp (driving the Liis) to give me a fixed HP function, from two cascaded 3 db filter opportunities I see inside it. However, I usually consider such modifications in lieu of a possible future "top amp" swap or eventual sale; ideally that HPF comes about without having to modify the amp - one reason I bought the miniDSP!
My thought was if there's a brace already for the driver to push against, how would it be to add a little tension/compression preset force into that mechanical system?
@paulfk; OK, it's not good. It seems the Lii "wants" to run towards full range, rather than be more like a 15" tweeter. I understand and have no issue with simply eliminating the infra frequency signals from getting to its voicecoil.
Of course I'd prefer it if the miniDSP were as transparent as a wire, but that's not the case as...even I thinks I can hear it. More of a difference than moving from a FLAC stream to a 64K one - which can still sound pretty good through the F15s...
As soon as those caps come in the post, I'll push onward with it. Hopefully I'll be able to use it for the high pass as well. Using it for just low pass - as a tool to tune the woofer assist part of my OB design - is fine if that's how things work out.
I realize I could modify the LM1875 amp (driving the Liis) to give me a fixed HP function, from two cascaded 3 db filter opportunities I see inside it. However, I usually consider such modifications in lieu of a possible future "top amp" swap or eventual sale; ideally that HPF comes about without having to modify the amp - one reason I bought the miniDSP!
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you can put a small but good caps at the input of the amp to cut some bass out.....or build the Nelson jfet xo Analog Crossover Network – diyAudio Store
PS
Or mod the input amp caps that most probably have
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Yep, that's what I would target; just use the MiniDSP to get the required crossover amd equalisation settings then build Nelson's crosover with those parameters.
I have a pair of Lii Audio Fast-10S drive units that I'm thinking of using in a Neson Pass SLOB open baffle; if I proceed with the build I will get the crossover from the DIY Audio store (I'm still considering my options for using the units - part of me says use it full-range in a suitable cabinet and avoid the issues of integrating a bass helper).
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ie a PLLXO.
I suspect that you are hearing the miniDSP. A PLLXO will add no electronic haze to the 15.
dave
What if this guy was right? Generally I like your ramblings in LS applications but targeting as cretinous engineering one of the basic principles of structural solidity is too much
Yes, when all is said and done, the Chinese population bearing the brunt of this ordeal are ordinary people like you and I.
He may very well have been...but not right enough for me to go home and take my speakers apart to remove the thin, squished piece of closed cell foam from behind every driver.
What he was getting at I still consider a first principle; that of substantial stiffness/mass for an audio driver to push against. Coupled to the cabinet as it may be, typically mounted upon or to the back of a baffle; the folks who build with 1.5" thick front baffle boards do so out of respect for his, or the idea.
The "dam" I made on the backs of these OBs used spare of the same material as the boards, a 1.25" laminated mdf. Glued on edge in an extended semi circle around the F15, they add substantial mass at the top of the tombstone. They also got the Lii's down to 60.
I'm going to leave them in place, regardless of where I'll eventually end up with the crossover frequency. I'll probably definitely consider the PLLXO after I work out the bugs manufactured into this miniDSP. I want to give it a shot at the high pass job again. At least two tries, one to go direct from my PC to its I2S input.
If it works out, I guess I'll miss the little Aune with its tube in the audio signal path. Looking around for a schematic for the Aune, I ran into a headphone site where they talked about this thing a lot, regarding rolling tubes. One fellow mentioned trying such tube and his head-system getting real holographic in presentation...
I looked them up and happened to have a pair of those in Amperex clothing; low voltage triode for car radios. I tried to sell them on ebay, but none wanted 'em. Just plug in one tube for the other and turn it on...
The guy was right - it changed the character of how instruments appeared within the soundstage. Maybe even added a little distortion - or was that dynamic range? Anyway the F15s resolve that level of change very nicely and I would miss the chance at all the tube rolling fun should the miniDSP work out.
I spose...I could always add the same kind of unity gain tube stage after at least two of the miniDSP outs. Looks like I better start looking for an enclosed chassis.
What he was getting at I still consider a first principle; that of substantial stiffness/mass for an audio driver to push against. Coupled to the cabinet as it may be, typically mounted upon or to the back of a baffle; the folks who build with 1.5" thick front baffle boards do so out of respect for his, or the idea.
The "dam" I made on the backs of these OBs used spare of the same material as the boards, a 1.25" laminated mdf. Glued on edge in an extended semi circle around the F15, they add substantial mass at the top of the tombstone. They also got the Lii's down to 60.
I'm going to leave them in place, regardless of where I'll eventually end up with the crossover frequency. I'll probably definitely consider the PLLXO after I work out the bugs manufactured into this miniDSP. I want to give it a shot at the high pass job again. At least two tries, one to go direct from my PC to its I2S input.
If it works out, I guess I'll miss the little Aune with its tube in the audio signal path. Looking around for a schematic for the Aune, I ran into a headphone site where they talked about this thing a lot, regarding rolling tubes. One fellow mentioned trying such tube and his head-system getting real holographic in presentation...
I looked them up and happened to have a pair of those in Amperex clothing; low voltage triode for car radios. I tried to sell them on ebay, but none wanted 'em. Just plug in one tube for the other and turn it on...
The guy was right - it changed the character of how instruments appeared within the soundstage. Maybe even added a little distortion - or was that dynamic range? Anyway the F15s resolve that level of change very nicely and I would miss the chance at all the tube rolling fun should the miniDSP work out.
I spose...I could always add the same kind of unity gain tube stage after at least two of the miniDSP outs. Looks like I better start looking for an enclosed chassis.
Casually advocating the removal of all sealing between driver and mounting surface, with zero advance knowledge of, or consideration for, the form and surface conditions of either is cretinous in engineering terms. Only an audiophile tweaker of the daftest sort would advise people to do any such thing without giving an iota of consideration for such matters. 'Structural solidity' is a fine principle in and of itself, but if you in the process introduce a leak path by removing the seal (almost inevitable unless both basket and mounting surface are perfectly flat and evenly torqued down, which they never are), you have introduced a problem in order to address what is in the majority of cases a non-issue in the first place. Now, you can actually use this to bleed off some excess pressure in cases where the enclosure is overloading a given space; the point is, you don't go around casually advising everybody to rip out gaskets, which have a job to do and are very necessary in most cases, for specious reasons of idealised structural engineering without consideration of the consequences on other, typically more critical, aspects of behaviour.
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