MemX

Push Pull Slot Loaded quad SI HT18s

81 posts in this topic

Hey all,

 

Just thought I'd post some pics up of the boxes I have commissioned for my 4 x 18" SI HT drivers.

 

Should be roughly 7.5 cu ft per box, and I will run the D2 drivers to show a CV5000 2Ohm per channel, which should mean 2500wRMS is available for each pair of drivers.  (I am aware that Bosso is not keen on the similarly constructed Marathon IIRC? but the CV5000 is the lowest cost option over here without going for a Clone, which I am reluctant to do for warranty reasons!)

 

I've modelled them as only really coming close to 22.5mm XMax around 8Hz and below, and as the amp is -3dB at 5Hz and the drivers XMech is about 30mm, roll off and the extra few mm between XMax and XMech should mean the drivers are relatively safe...  assuming I don't cook the coils, of course...

 

I've not heard a PPSL sub before so I hope I like the apparently very clean sound (although the odd-order third-harmonic dominating the harmonics it does have may be an issue) but there is enough room in the design to swap the 'out' driver back to 'in' if I hate it.

 

They should hopefully be complete in 3 or 4 weeks time, then I just have to buy a mic, REW my room, identify if I need an EQ solution, order all the cabling and connections, possibly run cabling to the airing cupboard if I can't get the amp in the same room without it being too noisy (I am reluctant to swap fans out for warranty reasons), and then spend what I'm sure will be a while tweaking things to get a flat response down to as low as it can go (fingers crossed).

 

The other main issue is that I'm going to be stacking them with some risers, so the driver centre-lines are at 1/4 and 3/4 room heights, but as each sub is going to be about 17 stone and the amp is 6 stone (and may go in the centre riser), I'm not entirely sure how I'm going to get them stacked... lol

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Few more pics.

 

Veneer is looking to be damn expensive!

 

 

 

 

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That's going to be a beast, mass balanced drivers is a nifty design. Looking forward to the finished product :)

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Another quick update!

 

My legend of a handyman who is building them has sweated buckets this weekend getting the drivers fitted to the first box due to the inaccessibility of the rear of the slot :blink:  :D

 

He's done a great job on it, though, I can't thank him enough for his care and attention to detail  :)

 

I don't envy him having to do the second box now... lol

 

Some idea of size relative to the real world!

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I think we're going to try and get some output measurements before I get them back to my place, although now they take 3 people to move because they are so heavy, I'm not quite sure how easy it is going to be to get them upstairs into my apartment, and then get the second one stacked on top of the first... :blink: lol

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Nice looking build. I bet that is heavy. I'm interested whether you can hear any motor or suspension noises from the inverted driver once you start pushing them a bit.

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haha  I think we calculated them as being something like 17 stone each... :lol:

 

 

Going from the comments on your review of the SI HT18, I am hopeful that they should be very 'clean' and exhibit very little motor noise, especially on music which is mostly over 30Hz!  Unless I'm playing music at house-breaking levels, like 130dB :wacko: , excursion should be minimal compared to the XMax, nevermind the XMech. 

 

The graphs seem to indicate 22mm excursion max at 30Hz at 126dB if I run them without a LT, but that is crazy levels which I'm sure I will never approach playing music because the police will be called!  :blink:  lol  Even if I play at 100dB, that is -26dB from peak available output, which should mean the cones are barely moving... (?)

 

 

Movies will probably be a little different, but if the graphs are correct I should have 115Hz (groundplane) output down to 15Hz, so with 12dB/octave room gain I should hopefully be able to have Reference level capability (either 115Hz .1 channel only or c.127dB all channels) all the way down to wherever my system starts to roll off, which my etch-a-sketch graph (also attached) should hopefully illustrate! 

 

(Note that the title is wrong and I've got the 10dB and 12dB per octave room gain colours mixed up - obviously the higher line of dots will be the 12dB gain, d'oh!)

 

I don't think it's often that there is <20Hz content with little else over the top, so if there is any driver excursion noise I am hopeful that it will be masked by general content from the speakers... *crosses fingers*

 

(That said, I am assuming that Reference capability is effectively 0dBFS on the recording being played back, and there is not that much content that hot, is there?? :unsure: )

 

I have considered lining the slot itself with accoustic foam if driver noise is distracting - the theory being that it should absorb any higher-pitched driver noise but leave the bass output untouched because it will just travel through the foam as if it wasn't there...

 

 

When I can sort a van out I will be able to get this one back home and give him space to do the other one, but I've a feeling that I will leave it unplugged so I can setup both at once when they are both ready, to give me maximum "Oh.  My.  Goodness." factor when I first crank them up :lol: lol

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MemX, love this, just monstrous ... thanks for sharing.

 

 

JSS,  +1  beautiful area. 

 

I've looked at ppsl designs, etc., but anyone care to share links to some of their favorite discussions, outstanding build/testing documentations?      

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I shall pass on the compliments on the garden :D lol

 

I am hopeful that this build should cure 'upgradeitis' until myself and the lady can afford a house and a dedicated room!  In the meantime, I pray to all the gods that my early-20s downstairs neighbour with an active social life and a tendency to be out most evenings, continues to live below me and doesn't move out and pass the place on to a moody, short tempered, complaining hermit :laugh: lol

 

 

 

This is probably the biggest source of PPSL info anywhere:

http://www.diyaudio.com/forums/subwoofers/177905-thread-those-interested-ppsl-enclosures.html

 

djk seems to be the original and most vocal of PPSL proponents, and welter sys is very pro-PPSL as well, having built his own and found they are unlike any other subwoofers because they are so clean.  They are both on other forums as well but, TBH, I simply don't have time to go on all the forums!

 

I've never heard one so I hope I like it... lol

 

I think it's in that thread that someone posts a whole load of graphs showing the considerable reductions in 2nd Order Harmonic Distortion from PPSL, but I have the links somewhere on a spreadsheet if you can't find them, just let me know.

 

I'm happy to try and answer any questions but I can't guarantee I'll know the answer or get it right when I think I do :D lol

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Oh, and it's ~7.5 cu ft internal but the slot takes up something like 3.6 cu ft IIRC (including all the wood that fills in the internal volume) so they are about 11 cu ft overall external size :)

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Just quickly (because I've stumbled on it and this will save finding it again) post 535 of that thread has a good graph illustrating the bandpass properties of a PPSL design.

 

I would copy and paste the link but for some unknown reason I can't paste into the reply box today... stupid computers!!

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MemX, I appreciate all that. I don't go there that often, however I've read much of diyaudio's content on ppsl. You're right, it's seems to be some of the best stuff out there. Just curious about more discussions. 

 

I've been contemplating a small, modest ppsl project myself. 

 

Thanks

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An injection of reality usually gets the response that I'm anti-whatever the latest sub fad is, but it is only an injection of reality, I assure all.

 

The link to Wayne Parham's test results shows same drivers on a baffle, one pair in push-push and then the same pair in push-pull.

 

I've always been a fan of Wayne's stuff. But, the test is a sine wave at 30 Hz to 105dB. Instead of building a rather huge box of a high degree of complexity, one might consider buying the LMS-U and putting it in a simple cube of 1/3 the size or less.

 

Josh's results show 106dB with less than 3% THD at 30 Hz. In-room, that number will be even lower, depending on the final FR. If building a large and complex box to reduce THD by lowering the even number harmonics makes someone happy, then I'm all for it because happy is good.

 

But, if that same person rushes to DIY Audio and tells the world it sounds noticeably cleaner, I'd have no choice but to roll my eyes a bit. :rolleyes:

 

I experimented with push-pull sealed a decade ago. It was fun but the results were by no means noticeably cleaner through human ears and the additional required box size pushed over my personal limit.

 

The point here is that the mechanical behavior of the system rests solely on the shoulders of the driver. The single LMS-U trounces the performance of the pair of whatever driver Wayne used in his test at 30 Hz, and, I suspect, at every other frequency as well, box size and complexity notwithstanding.

 

Four of them in 1/2 the box size will play any source cleanly to reference level in any room.

 

Consider what we listen to before declaring the reproduction clean, regarding harmonics. Here is a spectrograph of a plucked E-string of one of my bass guitars. It was close mic'd with no amplification.

 

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One graph is full range, the other is zoomed to 1-240 Hz.

 

It appears that the instrument has its own harmonic "distortion", which is instead more accurately called "overtones". It also runs well into the mains, past the crossover point with the 4th harmonic overtone actually louder in dbSPL than the fundamental.

 

Now, that's before preamp/amp distortions and before mix/master distortions are introduced. Again, with time restraints what they are, the point here is that a pure sine wave input yields far different results than a rock band or full orchestra with explosions and gunfire. Saying one presentation sounded cleaner than another regarding harmonic content is dubious, IMO.

 

I also wanted to comment on the first post mention of the Marathon... I have no problems with the amp as a value item and I still use one to power my surround speakers. My problem with Marathon was the complete lack of communication from them when the amps were on back order and in never responding to questions of any sort regarding their products. It's just an old-tech, big iron, very heavy, 3RU amp. There are plenty of those available. They just don't compare to other, higher-tech amps that are readily available today.

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Mr Bosso, I always appreciate your input, be it positive or 'constructive criticism' ;)  lol, and I won't take it personally!

 

 

Comments noted re: Sine waves not being true content, that 'real world' content does have harmonics within it, and that empirically evidenced reductions in distortion are not always audible.

 

Perhaps it is just a case of PPSL or similarly low-THD setups (however they are achieved) being 'cleaner' (either audibly or captured via electronic equipment) because they do not introduce their own harmonics on top of the real world content's harmonics?

 

 

 

With regards to LMS vs PPSL using another driver, is LMS-U short for LMS Ultra, the one that is almost $1k?  I know they are supposed to be very clean and play in very small boxes, but they were way over my budget, personally speaking  :blink: lol 

 

I just thought it would be cool to try something different  B)   I have the space within an alcove to play with, the drivers were cheaper than anything available over here in the UK and the amp was shop-soiled so cheaper, so it's not too expensive an experiment.  :)

 

 

Thanks for your comments on the Marathon also, they're much appreciated :)  Hopefully the newer tech will start to trickle down into more affordable equipment in the near future as a lot of the big power / small size stuff is still $$$$!  A Clone was on my radar but warranty / reliability was my main concern on that front, and I'm not electronically minded so didn't fancy a DIY fix via email across several time zones... lol

 

 

 

Updates?

JSS

Well, I have the first box now in place and wired up!  We'll gloss over the fact I'm an idiot and spent about an hour chasing a fault that didn't exist, just because I didn't twist the speakon in properly at the amp end :rolleyes: lol

 

It is running nicely and I've run Audyssey XT32 on my Onkyo 818.  First impressions are it is sooo much tighter than my old ported SVS - I know XT32 is supposed to time-align everything, but I think it was struggling with the ported sub.  With this being sealed it seems so much snappier, and now the sub blends into the mains rather than having the mains playing and then a sub playing obviously below them.

 

There is also the added depth I was looking for; the SVS had 16Hz tune and did well but it seemed to lack the lower end 'weight' sometimes.  I think I do need to bring the bottom end up in output, though, as it's not quite as weighty as I'd like, so next plan is to REW everything and see if/where output tails off.  I think XT32 only EQs down to the system's -3dB point so MiniDSP or SEQSS is on the radar for low-end duties, should I need it. 

 

The amp is only seemingly tickling the -10dB lights even on very loud scenes so I think I need to run some sinewaves and check output through the system to sort out the gains.  That said, I set the gain attenuation dial on the amp according to the 75dB requested by Audyssey (although it was 78dB in the end as the next notch on the amp dial brought it down to 72dB) and the dial is at -22dB IIRC, only 2 or 3 notches off the very bottom of the scale, yet seems to be fine.  I don't listen to Reference very often (barely ever TBH) so perhaps it's not a surprise that I'm not lighting all the amp's input signal lights!

 

I can't wait to get the second one in, the cones on just one box are barely moving on even very loud music content so distortion must be minimal (other than that within the content itself ;):lol: ) and on some of the big bass scenes it all seems pretty effortless, with the cones moving perhaps half an inch in each direction, which should reduce with the second one going in.

 

 

I think my only issue is the neighbours - the guy downstairs (who is rarely in as he is young and goes out most evenings and weekends) is selling up to, presumably, get a bigger place with his girlfriend, and so far I've seen what looked like a 60 year old woman with her 80 year old mother looking at the place...  :rolleyes:  Kill.  Me.  Now.

 

Apparently I also kept the neighbour in the next block along awake the other night, even through my closed double glazing, his closed double glazing, and the concrete block and brick construction of the place... :huh:  I think perhaps I had the back bedroom windows open, which must have been leaking sound - I always have the internal door closed to minimise treble carrying through the second, front door and into the stairwell, but perhaps it was travelling out through the bedroom windows that were open.  I might have to knock it back a bit or finish watching sessions earlier!  Although if some granny moves in downstairs, who never goes out and whinges at the slightest noise, I am in trouble... lol  At least now I can have a couple of hours in an evening and in the morning when people are all at work!

 

 

None of the above covers the PPSL benefits, though...  lol  but I have a fellow AV person coming round shortly so I will post his opinion up when he's visited!

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Actually, I just pull the LMS-U up from habit over the years. The SI-18s are similarly low THD at 106dB @ 30 Hz, as are most of the pairs of subs and drivers of interest in these parts, compared to Wayne's measured example. :)

 

Again, the 'push-pull' part of the equation is not noteworthy in my own tests over the years, at least not up to the many recent comments on the merits of that configuration.

 

The more interesting part is the 'slot-loaded' aspect. There doesn't seem to be a formula for the 'slot' and I can't find any measurements that might tell us what the exact advantage to the design are.

 

Changing the loading of the driver in a sealed sub affects the performance. Of course, just placing the sub in the corner of a room changes the loading vs outdoors in the case of any front-firing sealed sub. But, if the sub fires down or into a faceplate, as all of my subs have for 12 years, that changes the loading outdoors as well.

 

The question is how it changes the loading. :ph34r:

 

Years back, I measured the difference in output of the driver up-firing into the room vs the same firing into a solid top plate:

 

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Almost 1dB added output per driver. In an 8x15" driver system, that's not trivial.

 

In addition, the air spring of the sealed box causes asymmetrical throw in that the inward 1/2 of the cycle is shorter than the outward 1/2 of the cycle. This causes 'air spring distortion', which is mostly 2HD. By adding a top plate or down firing the driver into the floor, this ASD can be reduced because the floor/plate restricts the outward throw somewhat, depending on the distance/Sd.

 

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I suspect that these are results that are also possibly seen as a result of the 'slot loading' part of PPSL.

 

Of course, measurements with/without are needed to confirm/deny any of these claims. In my case, I've seen measurable differences, but I don't think I've ever claimed that it was audibly noticeably "cleaner" or any of the typical subjective comments being made.

 

My premise has always been that there are other benefits to up/down firing and using a solid top plate (or face plate in the case of the FF config) such as protection for the drivers, proximity of the drivers to a corner, no need for a grill cloth that adds distortion, is hard to clean, etc. The additional benefit of added output and lower 2HD are things I put in the category of better is good, whether it's audible or not, as long as it doesn't require something drastic like doubling box volume.

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Ok, just dumping links from my phone here so I can find them later when I do a proper reply on a proper keyboard!

 

 

Link to post with graph showing Bandpass properties of the slot:

http://www.diyaudio.com/forums/subwoofers/177905-thread-those-interested-ppsl-enclosures-11.html#post3966460

 

Thread with links to posts/webpages stating +9dB output from a slot compared to a baffle, and also a substantial lowering of Fs:

http://www.diyaudio.com/forums/subwoofers/242775-driver-parameter-changes-ppsl-ripole.html

 

+9dB (close mic measurement) mentioned:

http://www.enjoythemusic.com/diy/0911/slot_loaded_open_baffle_speaker.htm

which becomes +2.5dB @ 3m, with a graph.

 

Reduction of Fs mentioned (from 27Hz to 16Hz (!) in this example):

http://www.diyaudio.com/forums/multi-way/195734-nelson-pass-slot-loaded-open-baffle-project-11.html#post3279971

but no graphs from what I can see.

 

I think one of those links also details some cancellation at certain wavelengths due to the front and back of the slot interacting, but only at something like 500Hz IIRC.

 

On my work computer I have the link to the graph showing the bandpass effect of the slot (and hence reduction in harmonics if they are above the bandpass effect because the slot therefore attenuates them) - I'll post it up later when I get a chance.

 

 

I think I understand the principles behind equalising pressure on both sides of the cone to make it more linear, but I don't think I get how output is increased / more efficient, be it by 1dB per driver due to top plates or +9dB in the slot example - a driver can only have a set maximum output within the constraints of its physical properties, surely(?) so it seems any output increase is from the increase in velocity and pressure of the wave due to squeezing a given volume of air through a more restricted space within a same time period, but it seems like voodoo, like you're creating extra energy over and above the driver output from nothing, which is surely impossible in physics! :lol:

 

Surely it's just down to channelling energy into limited directions and therefore reducing the radiating area, meaning more output per area channelled into, but which would mean a reduction in output in the area the sound is channelled away from?  e.g.  if measuring a box (with a top plate, for example) from the side, output would seem to be increased, but if you laid the box down and measured in line with the driver but with the top plate between the mic and the driver, you'd get a substantial decrease, surely?  Likewise, a slot would seem to be more directional if off-axis of the slot is having output restricted due to the driver/slot layout?  How does my logic square with bass being said to be omni-directional below 80Hz (IIRC)?

 

It's way too early for this, my brain hurts :lol: lol

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You are putting a little too much thought into the plate...Think about how a horn or bandpass system works. No laws of physics are broken. I am a bit surprised at a gain being shown over such a large bandwidth even if just 1dB or slightly less.

 

Dave how far was the mic from the sub and what was its general placement for those measurements? I still haven't looked at this like I need to.

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Actually, my son did the exercise. I wasn't there at the time. As I recall, the measurements were done near field, or, IOW, within 1 foot. The mic was on a tripod and wasn't moved for the test. The only thing that was changed between the 2 traces was top plate vs no top plate with the sub being a 1X and firing up.

 

I've been struggling with the 'velocity' thing.

 

I know it must be a simple matter to grasp since so many people refer to it so matter-of-fact-ly. The speed of sound is a constant and velocity is just another word for speed. So, how does the velocity (or speed) of sound increase?

 

I happened upon Nelson Pass at CES a dozen years ago and he had 4 small FF sealed subs, 2 stacked in each corner, with the drivers facing the corners. Someone walked in and immediately asked, "Why do you have the drivers facing the corners like that?" and he said "It changes the loading".

 

I had already been building up-firing (with a glass top plate) and down-firing sealed subs by then, but hadn't considered the distance from the top plate-to-driver or floor-to-driver. The following year, circa 2003, I built the 1st in a series of dual opposed, up/down-firing and it was then that I looked at the distance between driver and plate/floor.

 

There was some discussion about it at HTS regarding the distance between driver/floor when building a down-firing sonosub, and I seem to recall Seaton suggesting that the area should be equal to Sd. Since I personally dislike HTS and its dictatorial chief moron, I didn't follow or participate in the discussion, so I don't know what the general consensus ended up being or if anyone posted measurements of any kind.

 

I've experimented with from 30% to 75% of Sd. IMO, 100% of Sd is no different than FF with no plate. I never published my test results regarding THD and/or increases in efficiency/output, I only mentioned on occasion that dual opposed and plate loading and up/down firing and stacking are all beneficial and the benefits are additive.

 

So, help me out with the velocity thing?

 

And, is there any difference between 'slot loading' and plate loading? IOW, take the slot loaded sub and compare it to a FF, same-Vb version that has a plate in front of the drivers at a distance that is calculated to equal area of the slot. And, the same sub in a down-firing config with legs calculated for same area as well.

 

I've always thought it would be a worthwhile test outdoors to compare a DF sub with various length legs (different size support blocks under your stock sealed cube with the driver facing down) vs the same sub in FF config.

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I may be able to do something like that....I'm building 8 sealed boxes right now.  Hornresp could probably sim it with its newer capabilities.

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You are putting a little too much thought into the plate...Think about how a horn or bandpass system works. No laws of physics are broken. I am a bit surprised at a gain being shown over such a large bandwidth even if just 1dB or slightly less.

I think this is where my knowledge gap is evident :lol: I think I understand something about how the volume of the air inside a horn effectively acts as one and the mouth being larger than the driver itself therefore gives more output (unless I am completely wrong, which I fear I am...)

 

More reading required!!

 

 

 

I've been struggling with the 'velocity' thing.

 

I know it must be a simple matter to grasp since so many people refer to it so matter-of-fact-ly. The speed of sound is a constant and velocity is just another word for speed. So, how does the velocity (or speed) of sound increase?

Ditto those comments/thoughts.

 

Over the weekend I was pondering the assertions made elsewhere on this. Is it a case that the air being forced through a smaller slot makes it denser, therefore soundwaves travel faster through it? Does the restriction, effectively, 'couple' the air to the driver's cone?

 

I might stick a post up on DIYAudio as the confused n00b that I am :lol: lol

 

 

 

I had already been building up-firing (with a glass top plate) and down-firing sealed subs by then, but hadn't considered the distance from the top plate-to-driver or floor-to-driver. The following year, circa 2003, I built the 1st in a series of dual opposed, up/down-firing and it was then that I looked at the distance between driver and plate/floor.

 

There was some discussion about it at HTS regarding the distance between driver/floor when building a down-firing sonosub, and I seem to recall Seaton suggesting that the area should be equal to Sd. Since I personally dislike HTS and its dictatorial chief moron, I didn't follow or participate in the discussion, so I don't know what the general consensus ended up being or if anyone posted measurements of any kind.

 

I've experimented with from 30% to 75% of Sd. IMO, 100% of Sd is no different than FF with no plate. I never published my test results regarding THD and/or increases in efficiency/output, I only mentioned on occasion that dual opposed and plate loading and up/down firing and stacking are all beneficial and the benefits are additive.

 

So, help me out with the velocity thing?

 

And, is there any difference between 'slot loading' and plate loading? IOW, take the slot loaded sub and compare it to a FF, same-Vb version that has a plate in front of the drivers at a distance that is calculated to equal area of the slot. And, the same sub in a down-firing config with legs calculated for same area as well.

 

I've always thought it would be a worthwhile test outdoors to compare a DF sub with various length legs (different size support blocks under your stock sealed cube with the driver facing down) vs the same sub in FF config.

Check out this post on AVForum, showing some hornresponse modelling of different distances of a front/base/top plate:

http://www.avforums.com/threads/decisions-decisions.1876156/page-10#post-20855553

 

Hope it is interesting/of use! :)

 

IMO slot- and plate-loading must effectively be the same thing - it must surely just present a reduced available area of expansion to the driver's cone, regardless of whether the 'escape zone' is circumferential or just to one side??

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With many thanks to 3ll3d00d for his patience and helping me out, and his excellent tutorial / guide on AVF (which links to and gives full credit to the other helpful posts on HTS and AVS), I have just about managed to get a Behringer UCA202 soundcard calibrated on REW, get a RadioShack meter setup and calibrated, and have just about got the hang of it...  I think... :blink:

 

So, first graph and first problem - it looks like the calibration on the setup only really goes down to 15Hz usefully, as the sweeping line (SPL Meter OFF) seems to suggest when compared to the captured output graph (SPL Meter on) which seems to stop capturing actual output at that point...

 

As per 3ll3d00d's recommendation, I shall have to order a CSL mic as that's calibrated to 5Hz and is not as expensive as the Bosso-approved mic! :D

 

 

I will do some MLP captures tomorrow, hopefully, as I've been at this screen for about 12 hours trying to get this bloody program to play ball, and I am now somewhat tired... lol

 

Respect to anyone who uses REW a lot - it is powerful and an amazing shareware, but it is not very user-friendly to get setup initially, seemingly!

 

 

Oh, and a big thank you to James, who was kind enough to lend me the mic and soundcard :)

 

 

 

EDIT:  I forgot to say I was slightly confused - the calibration graph of the soundcard (done via the loopback method) seems to suggest -3dB at around 4.5Hz, so I don't know why I'm not capturing down to that point?  (graph attached)

 

EDIT EDIT:  I'm having weird deja-vu like I've written this before, but I am 100% sure I haven't... lol

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