| Scottmoose |
I've been sorting through my notes that have been building up on the hard drive over the past 18 months or so and thought this might come in handy / be of interest for anyone out there. Nothing overly new of impressive, but someone might find it of some use, hense the post.
The Lowther Club of Norway 'Voigt Pipe' (Not that poor old P.G.A.H Voigt had anything to do with it). It's the entry for many people into the world of full-range DIY speaker-building -not sure why, probably because it looks dramatic and it's easy to construct.
Pity that, as it stands, it is, quite frankly, rotten. Below is the MathCad simulated response for this enclosure with the Fostex FE206E, which, rightly or wrongly, I suspect is the most popular driver that finds its way into these enclosures. (If you're interested, the response looks almost identical with the FE207E, FF225K, FE166E, FE167E and FF165K. With the Lowther PM6C drivers it was designed for, it looks even worse.)
But what if you've put a lot into your LCofN Voigt pipes, both in time and effort, and don't want to scrap them? Well, you're never going to have the best enclosure in the world I'm afraid. But I can suggest something that might help a bit: see next post. |
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| Scottmoose |
Still with me? OK, now if you ask anyone who is used to modelling quarter-wave enclosures with Martin's MathCad worksheets to pick one single thing they hate about the LCofN 'Voigt Pipe' above anything else, I would put money that it will be this:
They are an So=0 design. For those who haven't a clue what I'm on about at this point, So is the area of the top of the pipe. Now normally, when designing a Mass-Loaded TQWT enclosure, we say never use a top area less than the surface area of the drivers.
Thing is, in this case, that isn't the major problem. The drivers that frequently find their way into these things tend to be low Q designs. And they actually appear to be less affected than the higher Q drivers in this regard -in some ways, they seem to like the extra gain it provides. Gregreferred to this some time ago I believe?
What is a major issue is that although these things are mass-loaded (although I seriously doubt the thought even occured to the designer: he just set the vent area to the same surface area as the intended Lowther driver, or as close as he could get) -it's not enough.
Here's the same enclosure, same driver, everything the same. But instead of the large vent, there's a 3" wide, by 3" long circular port, 4" up from the bottom. OK, it's not perfect by any stretch of the imagination, but it's a heck of a lot better than having big peaks and holes all over the place.
This works wonders for every driver I tried it out with. The lowest Q types need a bit of series resistance as you can see: I'd say 2ohms or so, to bring the response down, as it rises a bit. Ripple is mostly flattened, and on average, you suddenly get an extra 20Hz of bass. These assume 0.25lbs ft^3 of stuffing from the top to just below the driver by the way.
Oh yes -a BSC filter would be of use too, in-room. I'd try the one from Martin King's Project 2 MLTQWT which should do the job fine.
Hope some of this is of use. I figured I'd put it up here before I delted it all.
Best
Scott |
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| coredump |
Scott,
very nice! Thanks for the effort. :-)
Best,
Oliver |
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| steenoe |
Thanks a lot for the nice writing, Scott. I had my eyes on those Voigt pipes from Norway, among others:) It's very nice to have the additional info you provides here.
Steen:) |
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| Kuei Yang Wang |
Konnichiwa,
I'd note a few things about the LCONVP.
1) LF extension is limited, but at high efficiency, basically that thing is 95db/W/m down to 70Hz, not bad.
2) The first really nasty mode is at 300Hz, where a simple counter resonator or even likely just the right kind of stuffing could limit the "big dip" and likely flatten out the feever curve higher up.
3) Given the kind of FR evidenced by the FE206 toeing these in strongly or pointing them straight on so that the listener is off axis would probably give a quite even tonal balance.
So, with a little luck in stuffing and listening off axis the LCONVP could make a surprisingly decent speaker..
For the modified design we see that efficiency is traded for bandwidth, by reducing the resonant behaviour of line, the result is a rather early but shallow LF rolloff, which despite having a lower -6db point (~40Hz) than the LCONVP (~55Hz) would likely sound rather strident and forward with lean tonality, unless the speakers midrange is pulled down by around 5db to bring it in line with the LF.
I suspect persnally I would probably prefer a reasonably sorted version of the original to the "fixed" one.....
Sayonara |
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| Scottmoose |
You're welcome guys -hope it's of use to someone. Note: I do not recommend constructing this cabinet. If you wish to build a TQWT for your driver; do yourself a favour and design a decent one, from scratch, in Martin's MathCad worksheets. It will reap major rewards. This mass-loading is just a boot-strap, quick fix for people who've already constructed the wretched thing and discovered the frequency response is all over the shop, and bass is serverely lacking.
Kuei -You make some very fair points. I agree with you regarding the toe-in, or listening off-axis. This would likely mitigate against requring series resistance; though I'd still advise using 24AWG or 30AWG wire with a low-damping factor amplifier, and a resistor with a high damping-factor amp or eveything under 120Hz or so is going to vanish.
Good luck if you think you're going to sort out the massive response issues this cabinet has via stuffing however. No chance. Promise. Stuffing exists only to damp harmonics that cannot be otherwise engineered out of a cabinet. There is a 20db hole in the response and that's just the one at 285Hz or so: you won't loose that by shoving more stuffing into the pipe, and for the love of heaven don't believe the myth that all additional stuffing does is clobber the efficiency. It will start to absorb the Fundamental, which is the whole reason for using a QWR in the first place. The mid-Q drivers like the FE207E and FE167E don't have this rise. Me, I'd rather have a flatter response than 20db holes and savage comb-filtering.
Be aware that whatever you do, this cabinet needs baffle-step correction. Active or passive, take your pick. Without it, you're going to run into even more problems. Passive will need a 2mH inductor with 4ohm resistor, approximate (minimum) values.
Best
Scott |
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| steenoe |
Well, I was wondering... How come those Cain's Abby's got so fancy reviews? They look an awfull lot like those norwegian "pipes" Except for the port, being made like Scott suggests:confused: Well, more or less at least?
Steen:) |
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| MJK |
| quote: | | How come those Cain's Abby's got so fancy reviews? |
If you look at my Project #2, you will find the design details behind this type of ML TQWT enclosure. My earlier design has a strong ressemblance to the Abby. I would assume the performances of both are very similar. |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by steenoe
Except for the port, being made like Scott suggests:confused: |
The port appears the depth of the front wall and appears to have a width nearly of the whole pipe and sign ificant hight. Looks more like a cosmetic cahnge than an acoustic one....
Sayonara |
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| steenoe |
Thanks a lot for responding, MJK. Just visited your homepage and realised that I have some reading to do;) I see what you mean, your project 2, looks a lot like like the Abby's. Just shaped a little different. Come to think of it, I guess I could pop my Coral Flat 6-II into those boxes? They shouldnt be too different from those Fostex, should they? Sorry if this is a stupid question, but I really dont know that much about speaker-units:xeye:
Steen :)
Kuei... Crossposting:D I love that:)| quote: | | Looks more like a cosmetic cahnge than an acoustic one.... |
So you mean that fancy looking venthole in the Abby's are more or less a cosmetic showoff? Well, being in the process of planning a pair of speakers for my Pass F2 clone, I sure would like to get this just right from the start!! Could the venthole be just circular as in MJK's lovely box?? With the correct diameter, ofcourse:) |
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| Scottmoose |
I gather Terry chose the port shape for fluid air motion or something of the kind which I confess I haven't a clue about. Personally, I doubt there's any difference between that and a circular port, and indeed, I seem to recall Terry saying something to that effect. But his speakers are a real craftsmans product and designed to look good as well as sound good, which is fair enough. That's not to say I don't think Martin's Project 2 ML TQWT doesn't look good: I do. In fact, I like it as much as the Abby. Mine are in a nice, rippled sycamore veneer if you're interested, with 4 coats of lemon oil rubbed in (took forever -I'm the world's worst veneerer!)
I remember Terry stating on Bob Brines forum that it is not an So=0 design, despite external appearences. OK, this is a place for conjecture... Looking at the external dimensions, I'm going to take a stab here about the approximate internals of Abby. It's 68" tall externally, and comes to an external point at the top. So my guess is that it actually has an internal line length of about 60", or perhaps just a touch more, which probably means the So is around 0.7Sd, give or take. With external dimensions of, I believe 9" x 9" at the base, I'd reckon on an Sm of 3Sd or thereabouts. The driver position looks a bit high, but Terry knows what he's doing -Nelson (Pass) has some frequency response measurements of Abby that don't look too shaby. Martin's cabinets easily match them in this though, and completely stuff them in the bass (they go a good 15Hz lower), though they are less efficient. I've built 3 pairs of them so far, which says it all.
Best
Scott |
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| steenoe |
| quote: | | I've built 3 pairs of them so far, which says it all. |
I better stick to those then. The only thing I am sure of, after reading all this, is that I do not know enough about the subject:D Well, I better stick to a ready made cookbook project;)
Thanks a lot guys for your replies:)
Steen:cool: |
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| Scottmoose |
You won't go wrong with Martin's Project 2 speakers. They are the most versatile enclosure I know of. Period. Best the with Fostex FE167E (the replacement for the FE164 he originally used, which was discontinued). Do let s know if we can help out, it's what we're here for!
You mention some Coral drivers. I can't speak for their quality, but if you have their T/S parameters or can give me a link to a site that has them, I'd be happy to run a MathCad sim on them in this enclosre and find out what modifications would be needed to the original design for you.
Best
Scott |
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| talatnat |
Scottmoose:
<<You mention some Coral drivers. I can't speak for their quality, but if you have their T/S parameters or can give me a link to a site that has them, I'd be happy to run a MathCad sim on them in this enclosre and find out what modifications would be needed to the original design for you.
>>
I'm glad I stumbled across this thread -- because like, Steenoe, I have a pair of Coral Flat 6's that I was thinking of putting into a TQWP. And, like Steenoe, I've been wading thru' masses of material and websites (including Martin's), and am confused about whether I can pull it off. Anyway, the person who sold me the drivers had his (a different pair) measured as:
T/S Parameter Coral Flat 6B
Fo 68Hz
Qms 5.671
Qes 0.433
Qts 0.402
Vas 31.346 L
The Coral Audio brochure lists the following specifications, which are somewhat different from the above (Qo of 0.52 and Fo of 45 Hz).
Nominal size: 6.5 in.
Impedance: 8 ohm
Min. resonance frequency (Fo): 45 Hz
Power input: 10 W
Sensitivity: 98 dB
Frequency response: 45 ~ 20,000 Hz
Magnetic flux density: 11,000 Gauss
Qo: 0.52 (45 Hz)
Equivalent mass: 0.23 oz
Diameter: 8 in.
Depth: 2-9/10 in.
Dimension of baffle opening: 5-3/5 in. (7 in.)
Mounting hole dimension: 6-1/10 in. (7-2/5 in.)
Magnet weight: 14 oz.
Total weight: 3 lbs.1 oz.
The bass-reflex cabinet they suggest:
Dimensions: 10-4/5 (W), 20.5 in. (H), 7-2/3 in. (D)
The driver is mounted in a 7-in-dia baffle opening located 5-9/10 in. from the top. The port is located 4 in. from the bottom, and is a square of 2-3/5 x 2-3/5 in., and 4-in long.
The Coral's I have (apparently) been unused, but their vintage status (~20 years old) may account for the discrepancies.
The Frequency Response curve in the Coral brochure shows a gradual LF rolloff from about 150 Hz. They also have a broad, shallow dip between 1,000-1,500 Hz (about -7 dB, or so), and dip a little raggedly (-5 db) between 3,500 - 5,000 Hz, and finally rolloff very gradually above 10,000 Hz. The Freq-Response curve that was scanned in the brochure is of such low resolution that I'm making some big guesses here.
I've tried simulating in Martin's Mathcad program, but given that I am fairly clueless (this is my first post!!), I know I'm doing most things wrong.
Scottmoose, I'd appreciate it if if you could run these through your simulations, and let me know the results, and how to proceed, then I may be able to duplicate your results myself on Mathcad and start learning how to use it.
Thanks a lot in advance,
Talanat |
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| steenoe |
| quote: | | Do let s know if we can help out, it's what we're here for! |
Thanks a lot Scott, most kind of you:)
| quote: | | I'm glad I stumbled across this thread |
I am glad you did, too;) You have more parameters than I was able to find.
Talatnat, are yours Flat6's the "II" version?
Many people says that the Corals sound better than the Fostex's.
But I wouldnt know, since I never compared them. Nonetheless, I think the Corals has a very good reputation. I posted some questions about mine some time ago, here you can see the drivers: http://www.diyaudio.com/forums/show...9879&highlight= I tried them in the recommended bassreflex box and they sound pretty good, indeed. Take a look here: http://www.diyaudio.com/forums/show...7590#post797590
I will post the parameters I have if they differ from talatnat's.
This thread is getting pretty interesting, indeed:)
Thanks Scott:cool:
Steen:) |
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| Scottmoose |
Right, this is what I've come up with for the Coral Flat 6II.
First up, I'll say I've had to fudge some of the data as I can't find the full T/S parameters. However, the most important: Vas, Qe/m/t are a start. I calculated the Bl factor using Martin's check-sheet as 9.771; the rest aren't quite so important, so we should be at the very least in the ball-park here.
Enclosure is 42" tall, 9" wide, 10" deep (internal). The driver is set 11.25" from the internal top, the port is 4" x 2" (WxD) and set 3" from the internal base on the front baffle.
2ohms of series resistance were applied: you can do away with that if you can cope with the slightly rising response or your room is bass-heavy. Just use a run of high-resistance wire: a single pair of 24AWG extracted from a length of Cat5 would be ideal, or a run of 24AWG magnet wire.
0.35lbs ft^3 of stuffing. Stuff from the top down to just below the driver. Predicted frequency response is shown below.
They'll need a BSC circuit, like most enclosures do. Try a 2mH inductor with a 4-8ohm resistor.
All dimensions were made in the latest (as yet unreleased) version of Martin King's Ported Box worksheet. You can do the same with the existing sheet, though adding the series resistance is a bit trickier. This isn't actually a reflex enclosure, but an MLTL. I don't think these drivers will work too well in an ML TQWT, I'm afraid.
Best
Scott |
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| talatnat |
Thanks Scott!!
Those curves look pretty good! Tks again...
Steen: The Coral's I have are Flat 6B, 15 W, 8 ohm (these are what's printed on the back -- and the speakers don't have the sticker specifying the model that yours do). I haven't seen the B's mentioned too much, and don't have any specs on them. The manufacturer's numbers I posted are for just Flat 6 (no suffix) and the only thing I can make out is that it differs in the input power, which is given as 10 W, 96 dB; I also have Coral's Flat 6 II specs listed as as 30 W, 92 dB. So, maybe these reflect some continuum series of power ratings/sensitivity.
The measured T/S numbers I posted were for Flat 6 Bs.
Nice F-2 clone!
Now, to get to work figuring out Scott's numbers... |
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| GM |
| quote: | Originally posted by Scottmoose
Right, this is what I've come up with for the Coral Flat 6II.
First up, I'll say I've had to fudge some of the data as I can't find the full T/S parameters. However, the most important: Vas, Qe/m/t are a start. I calculated the Bl factor using Martin's check-sheet as 9.771; the rest aren't quite so important, so we should be at the very least in the ball-park here.
Enclosure is 42" tall, 9" wide, 10" deep (internal). The driver is set 11.25" from the internal top, the port is 4" x 2" (WxD) and set 3" from the internal base on the front baffle.
2ohms of series resistance were applied......
All dimensions were made in the latest (as yet unreleased) version of Martin King's Ported Box worksheet.
I don't think these drivers will work too well in an ML TQWT, I'm afraid. |
Greets!
Well, I don't have the same PORTED WS, but FWIW, using these specs in your pipe I get a very rolled off response below ~100 Hz:
Fs = 68 Hz
Re = 8 ohms
Lvc = 0
BL = 9.46 NA (calc'd)
Sd = 214.0834 cm^2 (6.5" nom.)
Rs = 2 ohms
Vas = 31.346 L
Qed = 0.433
Qmd = 5.671
Qtd = 0.494 (auto calc includes Rs)
To get something with as much LF gain as yours I had to use a large, fast taper ML-TQWT:
L = 72"
zdriver = 36"
zport = 69"
SO = 9"^2
SL = 180"^2
rp = 2.75"
Lp = 0.75"
GM |
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| Scottmoose |
Well, I'm blowed if I can figure that one out Greg! Thanks for the warning. I've just plugged the specs back into the sheet, this time using the ones you calculated and posted above as you've more experience at figuring out T/S parameters from older drivers than me. But the predicted response has come out practically the same, with only minor changes due to the slightly different driver parameters entered. So I've honestly no idea what's going on there. Do you have a set of response curves you could post? Perhaps we could then send them off to Martin for comparison: as I'm using the new sheet this might indicate there's a bug in there somewhere. I'll have a go in one of his existing sheets and see what happens in that too. Very odd. I'll get back in a few minutes. Oh yes -I had a look at your ML TQWT too; looks good to me! I tend to get hung up on only going to a 2" radius maximum for the port, which is obviously limiting the options a bit! Something I need to be more careful about doing as it clearly rules some possibilities out, many thanks as usual.
Best
Scott |
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| Scottmoose |
Very interesting indeed. They don't match. Rather than using the current Ported Box sheet, I tried it in the ML TQWT sheet. This is what it suggests for the Coral driver (GM's calculated parameters) and the MLTL enclosure without any series resistance.
Doesn't look so good here. But it doesn't look too bad either -I've seen a whole lot worse, and as a theoretical exercise, there doesn't appear to be much that couldn't be sorted by juggling some port dimensions and adding the 2ohms series reistance we both went for to get it flat. Strange -any thoughts?
Best
Scott |
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| GM |
Greets!
No, not really beyond he apparently continues to 'streamline' his math like programmers have done to T/S box calculators, with the consequent reduction in accuracy. In the scheme of things, these differences mean nothing to folks who don't measure drivers, their room, speakers, and the speakers in-room since they have no way to correlate what they're hearing to the sim. Factor in that down low our hearing acuity sucks and even what looks like gross differences below ~150 Hz in a sim would be hard to detect in an in-room A/B comparison.
Still, when 'bench racing' sims, it would be nice for everyone to be using the same 'rules' and that they ~mirror any properly done nearfield measurements.
BTW, I use to have real problems with getting consistant results (i.e. what I expected to see) regardless of which WS I used, even after a computer upgrade to Win XP pro/MC 2001 pro, until I started (re) calculating them by clicking on 'math/calculate worksheet'. For whatever reason neither 'refresh' nor 'ctl R' has worked at all in either the demo 8 or licensed program and after several recalculations, scrolling down to update the various plots quits working correctly on the one we look at most, the 'far field' plot.
Anyway, using whatever version of the PORTED WS I have (downloaded 2-6-04), once I reduce the stuffing to 0.2 lbs/ft^3 with none below position 'L01' I get a 'close enough' looking sim to yours once the difference between the PORTED and ML-TQWT vent orientation is accounted for.
GM |
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| Scottmoose |
Bingo. Yeah. I've just had an email from Martin -I'd asked him to take a look, and that was his observation, so we're in the clear after all, albeit with a slightly 'off' stuffing level.
Cheers
Scott |
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| talatnat |
Thanks Scott and GM. Great input for someone new at this game!
Interestingly, I ran across another thread:
http://www.diyaudio.com/forums/show...&threadid=42409
where Martin and GM did some sims for Coral Flat 8s. It appeared that an ML-TQWT might be suitable for the Flat 8s, and it looks as though the T/S's for 8s are not that very different from those for the 6s.
Scott, you mentioned that the ML-TQWT design could be fixed using a 2-ohm resistor and varying the ML. Were the figures you posted based on GMs quick-tapering design? Alternatively, any chance of optimizing the ML-TQWT and re-posting the design (since you have the newer worksheets, and are so much better at it). I'd like to go with a ML-TQWT if possible, since the Coral's are old, and I may have to replace them at some stage.
Thanks again to both of you (and Martin, of course). |
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| Scottmoose |
No, they were for the same straight, untapered MLTL I came up with before (Martin's ML TQWT sheet can model straight, as well as tapered enclosures you see). The only updated sheet I currently have is the Ported Box sheet which can't model tapered enclosures, so I'm using the current sheet for those, same as GM's using.
As you clearly like the tall ML TQWT enclosure (and why not?), I've played around with some dimensions a bit more. GM's fast tapering job looks like it provides the best response for the Corals of this particular tapered geometary with 2 ohms series resistance applied. However, if you're willing to increase that a bit to around 4 ohms, which isn't out of sight (I've used 10 ohms before now and as resistors are cheap, you can afford to experiement a bit!) then Martin's original ML TQWT enclosure, ironically, will also work quite well: http://www.quarter-wave.com/Project...TQWT_Design.pdf
You'd just need to increase the port radius to 2" up from the original 1.5" Response rises somewhat, but the series resistance will sort that, and you need to remember the boost room-gain will provide -the room is the major factor low down, with box speakers at any rate. Frequency response of that enclosure is below. GMs generally looks similar, just a bit flatter.
Best
Scott |
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| talatnat |
Great!
I just plugged in GM's numbers (minus the 2 ohm resistor, I couldn't figure how to do that, I guess I'll have to hit the books some more), and managed to duplicate something along the lines of what you had posted... Good so far, and then Macdemo crashed...!!
Following your lead has got me up to speed much faster; and GM's tip about refreshing via Math/Calculate worksheet helped, I think I was chasing my tail for awhile.
Thanks again to all. |
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| sharpi31 |
I finished building my voigt pipes on friday. I used Scott's port design.
Drivers are FE207E, cabinet is LCON dimensions (except for port), damping applied as suggested except 'bumpy' foam used directly behing driver to soak up driver reflections.
One point to note: I couldn't find 3" pipe locally for the port, so I designed a rectangular port with the same cross-sectional area and length as Scott's suggestion. This is still centred 4" up from the bottom of the baffle.
Coming from my previous speakers (modded Loth-X BS1) these things are already like a breath of fresh air. The loth's are very good at what they do, but clearly offer a very narrow window onto the performance. Both HF and LF are curtailed compared to the voigt's, which also have a cleaner mid.
I have assembled the drivers as described above, but not yet played around with stuffing etc. I don't see any point in tweaking until drivers etc. settle down.
Having said that, I did assemble both a LR (1.5uH/8ohm l-pad) filter (parallel in series with the driver) and a RC (16.4ohm/3.0uF) (series in parallel with driver) filter.
I have plugged both of these networks in to give me some smoothing of the driver while it runs in. Once everything settles down I will try alternative options.
The amp is a recased and highly modded t-amp. So far I cannot fault these £200 speakers! The bass is focussed and even, despite my large living room. Imaging is holographic and transparency rivals my old Magnaplanar MG.5QR.
Thanks a lot Scott. Fully recommended design!
(photo's to follow...) |
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| talatnat |
| Another coincidence. I'm just modding a Class-T myself to use with these ML-TQWT's, so it's good to hear that the combination works. |
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| Vix |
Hi!
I have an ML TL with Fostex FE206 E (MJK's project 5).
It sounded a bit "hot " at first. Adding some series resistance helped a bit, but at a cost of reduced efficiency.
Then, just as an experiment, I tried something else: I connected the secondary of an 220v /12 v 50W mains transformer in series with the speaker. At the primary side (200v) I connected a 20K pot.
Well, this tweak made Fostex sound much more pleasant. Don't ask me why, try it! :cool:
regards,
Vix |
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| GM |
| quote: | Originally posted by Scottmoose
No, they were for the same straight, untapered MLTL I came up with before (Martin's ML TQWT sheet can model straight, as well as tapered enclosures you see). The only updated sheet I currently have is the Ported Box sheet which can't model tapered enclosures, so I'm using the current sheet for those, same as GM's using. |
Greets!
Huh?! You're saying you can't load SO (top) and SL (bottom) separately with different areas into the new WS?
GM |
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| GM |
| quote: | Originally posted by talatnat
I just plugged in GM's numbers (minus the 2 ohm resistor, I couldn't figure how to do that, I guess I'll have to hit the books some more.........
Thanks again to all. |
Greets!
You're welcome!
Unless I'm missing an obvious 'trick', changing the WSs each time you opened them would be more trouble than it's worth since you can't save them in the demo, so make a little spreadsheet to calc the new T/S parameters to load into the WSs:
Qed' = Qed*(1+Rs/Re), where Rs is the series resistance and Re is the driver's DC resistance.
The WS will auto recalc Qtd.
Qmd, Vas, Lvc is unchanged.
Re becomes Re+Rs.
BL changes only fractionally, so not enough to be worth the effort to recalc.
If you want to know the new, lower efficiency rating without doing a sim:
n0 = 9.6352*10^-10*Fs^3*Vas(liters)/Qes'
SPL = 112.018+10*Log(n0)
GM |
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| Scottmoose |
Good question. I've just put some examples up for all of 5 minutes, but I've wiped them temporarily as it might not be quite fair if it's a bug -this is still a test sheet afer all. I'll ask Martin about that one and get back to you. Suffice to say at the moment however, in my experience, it throws a fit if you try to model a tapered enclosure.
Regarding the latter -that's a really useful tip that I'll use myself until I get a full, decent version of MathCad. Thanks!
Cheers
Scott |
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| Scottmoose |
OK, I've found out what it was. The new sheet can indeed model tapered enclosures (I checked with Martin to be sure), but it was being thrown out when I ran it by a modified ham radio program running in the background (I'd borrowed a PC from my Dad temporarily). I've run a few checks with different drivers and cabinets on my own system now, and they match to the current sheet almost perfectly.
Problem solved. Thought it was a bit odd!
Cheers
Scott |
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| talatnat |
Scott, that's good to know.
After a few crashes, I figured Macdemo to be a resource hog, and now shut down as many other applications I can live without, and then run it. Seems to behave just fine now.
As an aside, in playing around with the designs that you and GM came up with, it seems that a very low So (~0.1 Sd) and a large Sl (~10) yields a somewhat flatter curve. Elsewhere, Bob Brines has suggested (after suitable qualifications) using the "shortest, fattest" pipe to meet the bass cut-off goal, and the "smallest diameter, shortest port" to meet both the bass-cutoff goal and reduce unwanted higher harmonics. I've also read that a low So isn't recommended, and that one shouldn't stuff beyond 0.25 lb/ft3, and so on.
I was wondering whether someone had put together any rules-of-thumb of what works better in actual practice. For example, is it better (or acceptable) to use a somewhat rougher FR vs. shooting for a truly flat FR if criteria X, Y and Z are met. This doesn't detract from the value of doing the sims, but I'm curious whether the collective wisdom of those who have actually built ML-TQWT's enables them to recommend some design constraints under which to optimize the sims.
I guess the reason I'm asking is that the more I read up on this, the more I realize how little I know! Thanks in advance for any suggestions... |
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| talatnat |
There are some good pointers in the article:
http://www.t-linespeakers.org/desig...mies/index.html
But I am shooting more for the sort of suggestions that brought about this thread on the FR of the LCON pipe, and again why some prefer it to a flatter FR. In other words, what are the tradeoffs one should keep in mind? |
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| Scottmoose |
Why do some like the original? Personal taste I suspect more than anything. Fair play -they're the one's listening to it, and they have to like the sound!
Efficiency is the primary one I suspect. Take horns for example. 99% have a terrible measured and / or predicted response -don't they? Well, yes. And no. It depends on the criteria you have. Some people value efficiency above everything else. They love the scale, the sense of immediacy, the subjective dynamics (note: no rear loaded enclosure can improve the dynamics of a driver, but the combination of other factors makes it sound like that) that horns provide, and could care less if the frequency response is rough, or the bass response is weak. However, for me, 20db holes in the response is starting to get beyond 'reasonable' levels. GM has pointed out that our hearing acuity drops with frequency, so you can get away with having a fairly rough response in the lower registers without noticing, particularly since as our hearing is amplitude based, and we'll key off the peaks. I'm not sure I'd risk that much over 100Hz though.
I'd modelled these enclosures a few months back and found them on my hard disk when I was cleaning it out, and thought I'd put them up as they might be of some use to someone. The mod I suggested will give a much flatter response, and deeper bass, at the expense of reduced efficiency. 91db is pretty good though in my book: 1w will be fine for ordinary listening.
A few general ML TQWT ideas. This is not the only way, but some find it a good starting point. Firstly, I'll note that it depends on the driver you're using. I try not to aim for a specific cut-off, at least not initially, but concentrate on trying to get the flattest response possible. Note that what is flat in anechoic terms will not be in-room, but it's a good place to start.
I wouldn't bother with a line-length of more than 60". Longer lines will likely give deeper bass, but there are other ways of achieving that.
So. This is a tricky one. Nomally, I would say don't go for an area less than Sd. However, if your choisen driver has a Qts of less than 0.3, and after you've tried everything else the system looks like it needs some more gain, try reducing this a bit, down to 0.5Sd, and adjust in increments.
Sm. Minimum area 3Sd. Maximum area 7Sd. Don't try going for more than that, you'll just run into issues such as a sag around 100Hz etc. Now, be wary. Say you're using an FE207E 8" full range driver. That's got an Sd of 31"^2, give or take. So 7Sd will give the base a surface area of 217"^2. Say your cabinet is 10" deep, that would mean that the width at the base would be a monstrous 21.7". So you need to keep the physical dimensions in mind; you could hit upon a magnificent response, but if it's not going to fit in your room, it's not going to be of much use to you!
Start with a driver position at 0.5 the line-length and if there is a spikes or dip at around 100Hz-200Hz, try moving it up and down slightly to flatten that out. 0.5 is a good general compromise and starting point though. Stick with 0.25lbs ft^3 of stuffing initially. if it needs more, don't go beyond 0.5lbs ft^3. If it needs more, the cabinet dimensions will want a re-think.
Ports. Start with a small, 1" radius port as short as possible, and increase the length in increments to try to flatten the response out, up to, say, 6" in length. Keep it close to the bottom: 3" from the base is a good starting point. If you get no joy, increase the port radius to, say, 1.5", reduce the length to the shortest possible and repeat this. Then again for a 2" radius port. Only ever change 1 variable at a time so you know which has affected the response.
OK, say you've got a good combination, but you want more bass, the driver can go lower (don't generally try to go more than 10Hz, maximum, lower than the driver Fs and preferably not that much), and you have the room. OK, increase the area of Sm, and adjust the port dimensions, if necessary, to flatten the response.
As I say, this is a long proceedure, and there are other ways, probably better too, but it works and it gets you used to using the worksheets and seeing how the different variables affect the response. |
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| talatnat |
| "There is always light at the end of the pipe." |
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| steenoe |
Talatnat, Scottmoose; I am still following this thread;) I hope you come up with a pretty good enclosure for the Corals for sure;) I dont understand half of the acronym's you use, but just hope a nice box will be the result of these discussions:) I cant contribute with a lot, sorry;) But I will be happy if you post a nice box for those Corals:) I sure would like to hear them baby's sing at their best;)
Steen:cool: |
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| talatnat |
Steen: OK, I'll keep you posted as things progress.
As of now, Scott and GM each came up with a design that look very close to best-of-breed for that particular configuration. Scott's is a ML-TL, a 42-in.-high tower, and GM did a 72-in. ML-TQWT, which is a tapered triangular box. Both reach low frequencies of around 45 Hz, unaided by room effects.
If you are looking for detailed projects, you can use MJK's step-by-step accounts at http://www.quarter-wave.com/Project03/Project03.html , which is similar to Scotts design, and http://www.quarter-wave.com/Project02/Project02.html , which can be substituted for GM's design. These two projects will give you a good basis for what Scott and GM recommend.
At the moment, I've gone back to scratch and am planning to break in my speakers (awaiting the the class-T amp, which is almost done), and to then measure the T/S parameters to see if either of these designs need any tweaking. I am somewhat uncomfortable using Coral's published T/S params, or the ones given to me that I listed earlier, since the speakers are 20-25 years old, and I'm unsure of their condition. Also, this is an excuse for me to learn how to do everything from the basics...
I'll post as I learn more about the Coral drivers themselves. |
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| talatnat |
Just for kicks -- I realized I should have done it earlier -- I did a sim of Coral Audio's recommended bass-reflex box using the ported-box WS and GM's params. Even unstuffed (and minus 2-ohm series resistor), it looks like a surprisingly clean FR curve, decent LF, with just a couple of sharp dips (standing waves?). FR curve attached below.
The Coral dimensions: 10-4/5 (W), 20.5 in. (H), 7-2/3 in. (D)
The driver is mounted in a 7-in-dia baffle opening located 5-9/10 in. from the top. The port is located 4 in. from the bottom, and is a square of 2-3/5 x 2-3/5 in., and 4-in long. GM's params: Fs = 68 Hz
Re = 8 ohms, Lvc = 0, BL = 9.46 NA (calc'd), Sd = 214.0834 cm^2 (6.5" nom.), Rs = 2 ohms, Vas = 31.346 L, Qed = 0.433, Qmd = 5.671, Qtd = 0.494 (auto calc includes Rs).
Dimensionally, it's about the same as Scott's design (So, Sm = 90 in.^2), and about half as high (20.5 vs 42 in.).
As a start, would it be prudent (for a neophyte) to just build the Coral box, since it seems to provide decent LF response, especially if will be used in a small (bassy) 13x13 ft room?
And, this is just curiosity (and DIY fun): Next, once things settle down, would it be possible to couple the Coral box to a daline-type TL? There were a couple of threads re: dalines a few years ago, but nothing conclusive. GM outlined a personal system for such daline-type designs, noting that they require low Qt/Fs drivers (not exactly Coral's strengths). Some mentioned splitting the volume to 1/3rd box, 2/3rd TL. And, interestingly, MJK mentioned that he did not seem to have much success modelling the dalines with the Mathcad WSs.
Questions:
1. I was just thinking that if the daline experiment didn't work, I'd still be left with a pair of decent Coral boxes. Is this feasible, or would the basic Coral box just not work for a daline?
2. Will using a rear-firing port for the Coral boxes to accommodate (aesthetically) the daline TL be a mistake?
3. Can just modifying the length of the daline TL pipe enable one to tune the LF output to suit a room, or is this just my pipedream?
I'd appreciate any suggestions and advice. |
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| GM |
Greets!
MathCad isn't currently working for me, but in theory, 19.30" x 11.93" x 7.37" with the driver down 8.93" and the vent near/at the bottom will be even smoother, though probably not audibly so, especially once a little damping is used. Anyway, the notches are the vent comb filtering with the driver's output, so easily damped.
Whether to build them or not is up to you. It's simmed response assumes it will be ~up against a large wall at ~ear height, making it much more rolled off perched on stands well away from any, so it boils down to how much efficiency you're willing to trade for a ~flat in-room response.
Yes, you can convert it to a Daline tuned to ~48 Hz, though all things considered, bottom firing seems the best option. Typically, damping the vent exits is the way to fine tune them to the room, just like a TL.
GM |
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| talatnat |
GM: In case you were curious about how your optimized design looks in MJK's Ported Box WS, I've attached a .jpg below. The comb spikes are minimized mucho, and after playing around a litte bit with the vent radius and length, it looks like you hit it right on the head (or is this what you had in mind?).
Here's what I used (not stuffed, no 2-ohm resistor), in addition to your original T/S params: zport = 19.3 in. (bottom?), So & Sl = 87.92 in^2, Rport = 2.75, Lport = 0.75.
I'm a little more adept with computers than with TL design, so if I can reciprocate, I'd like to help with your MathCad problems. Unfortunately, I haven't used it rigorously since Version 6, so I may still be out of the loop. Macdemo is working fine for me when I minimize using other applications (my trusty steed is a 5-yr-old laptop). Let me know... |
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| GM |
Greets!
Not really, I just plugged your Vb into a spreadsheet to possibly give you a theoretically better alternative using the golden ratio. If it were me, I'd just start with one of the larger cabs.
WRT MC, I have 2001 pro, so quite a bit newer than V6. Anyway, it's been working OK until the latest round of MS and NAV updates and I still have a few things to try before I reach my knowledge limit. Anyway, thanks for the offer and I may yet take you up on your offer since I have a profound lack of desire to learn anymore than I absolutely have to keep my computer functioning.
GM |
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| steenoe |
| quote: | | Steen: OK, I'll keep you posted as things progress. |
Thanks a lot, Talatnat:)
Steen:) |
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| gychang |
I am a newbie but very interested in building ML TQWT, where can I find a picture of Martin's Project 2 that many folks are referring to?
| quote: | [i] That's not to say I don't think Martin's Project 2 ML TQWT doesn't look good: I do. In fact, I like it as much as the Abby. Mine are in a nice, rippled sycamore veneer if you're interested, with 4 coats of lemon oil rubbed in (took forever -I'm the world's worst veneerer!)
Best
Scott [/B] |
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| MJK |
| Follow the link below. Look under the Projects link on the main page. |
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