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Old 28th September 2005, 05:42 AM   #41
Byrd is offline Byrd  South Africa
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Quote:
Originally posted by Scottmoose
....
Why are the simulated and measured outputs different? Well, the curves are basically very similar. Did you remember to apply to the MathCad charts the +6db boost gained in system efficiency for having paralleled drivers when comparing to the measured data?

Regards
Scott
All response graphs are similar - IE they are curtailed at both bottom & top end

But seriously I still don't see what you see. I am not talking here simply of amplitude but a fundamental difference. Look at the 30 Hz Dip in Driver output & 35 Hz Peak in Port output as predicted by the sims. There is no evidence of this in the measurements taken by D'Appolito.

There is something causing this difference. Either the sims are wrong (No offence intended here please, just object discussion), or they are being fed different parameters to what actually exist in reality, or the worlds * "foremost expert of speaker measurement" has fudged the results.

I wish D'Appolito were here to state his case.

* Wherever this title comes from I don't know but it has been bandied about often enough.
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Old 28th September 2005, 09:35 AM   #42
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As do I. It would be interesting to get his views on the matter. Oh -no offence taken by the way. Life would be very boring if we all went around taking umbridge at every objective observation! Besides, I don't claim to be infallible by any stretch of the imagination -I might have been off with the vent dimensions, but I don't think it was by more than a few mm -not enough to make a major change. The best way of ascertaining this is to try it yourself -the worksheets are on Martin's site, along with a free version of MathCad Explorer 8 if you don't own the full version (works just the same, you just have to cut & paste into something like Word if you want to save).

I think the important thing we need to keep in mind when considering all this, is, whether you go with the simulated or the measured data, Thor looks poor, especially considering its high price. If I wished to build a speaker in that price range, and I saw only the measured data for example, I would be very wary, especailly when I saw the crossover.

OK, why the differences, if we're assuming for the moment that my simulation is in the ball-park? Well, firstly, keep in mind that the measured data has clearly been heavily smoothed -speakers are not that flat in real life, and this disguises response aberrations. Looks like 1/3 or 1/2 octave smoothing to me. Note that the dip in woofer output circa 30Hz is still there on the measured data -it's simply been flattened out, which confirms this, at least to my satisfaction. Ditto the peak in vent output, though apparantly on the measured data it occurs a little lower, suggesting a slight error on my part on the vent dimensions -I hold my hand up on that one. It's not that significant though in the overall scheme of things. Staying with the vent output, the remaining climbs, dip and peak just after 100Hz are all still there on the measured plot, albeit flattened out, as is everything post that, though it's not easy to compare at first glance, with such odd values being used in the measured data graph. The rapidly rising response predicted by the sim to 1KHz will be mitigated slightly by the presence of the correction applied to the woofers in the crossover, which is not enough to negate the overall rising trend indicated -there's peaking at circa 1KHz in both sim and measured data for example.

Below 100Hz in room, you won't get a huge performance boost. It'll be better than the anechoic response of course, but the vent output is too low, and being mounted high up, and firing horizontally rather than vertically it can't drive the room as well as a low mounted vent a la Lynn Olson's Ariel. Worse, you'll still have the 3-4db baffle-step losses Martin mentioned, which the crossover does not correct. And just to add a further fly in the ointment, the cabinet is full to the brim with a very heavy quantity of stuffing, which itself will cause the bass to sag further. Whichever way you look at the data, Thor will be significantly down at low frequencies. Only by listening to it in your own room however, will you be able to determine if it works well enough for your taste in your home. Depending on what you listen to and how large your room is, an alternative speaker you might like to look at is Bob Brines FTA-2000. It uses a single Fostex F200a full-range driver, and is pretty much flat in room from 30Hz - 20Khz. It'd cost a fair bit less than Thor too. You'll find it here: http://www.geocities.com/rbrines1/Pa...2000/Main.html
Perhaps not ideal for thrash metal or a very large room, but most anything else, it's a winner. The Ariel is also very good -no deep bass, but Lynn always stated it didn't, which is nice and honest of him, and it simulates and measures well. Both are cheaper, which means you could add a decent subwoofer from REL, or perhaps a pair of Linkwitz Thor (I kid you not!) monopolar subs, or the open baffle subs from his Phoenix project. That'd be what I'd do anyway!

Cheers
Scott
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Old 28th September 2005, 11:37 AM   #43
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Quote:
Originally posted by Byrd

I wish D'Appolito were here to state his case.
D'Appolito would probably respond to a letter to AudioXpress (in which the article appeared.)
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Old 28th September 2005, 12:26 PM   #44
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Default Improving Thor

I have been following this thread with much interest.

After several months of research I descided that the Thor TL was the speaker for me.

Now I'm having doubts, but I admit I am somewhat confused. Please forgive my ignorance as I am a neophyte.

Is the performance issue that Scottmoose is questioning related to the actual driver selection in this particular TL geometry or is it a combination of the driver(s) and geometry ?

I ask this question because I was going to change the design and substitute a Seas 27TDFC for the Excel tweeter, and replace the drivers with Extremis 6.8's bi-amped with an active XO at 3.5 or 4.0 kHz. The Extremis doesn't have a cone breakup mode (at least I don't hink so), and the poly cone should soften the sound a bit for the type of music I listen to.

I used the original article as the basis for my substitutions. Plugging in the extremis specifications into the calculations, the Thor dimensions actually work out to the "arbitrary" resized dimensions, which should result in the "full" bass response.

So my big question then is this:
Will my driver substitutions result in exceptional speakers or is the Thor design just pre-destined to be an "OK" speaker no matter what.

Feel free to ridicule my assumptions, maybe I need a dose of reality here, or do I actually have some potential as a DIYer.

Thanks.
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Old 28th September 2005, 12:58 PM   #45
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Forget ridiculing. An active crossover is always a good step forward; pity they aren't used more often, but of course, they mean another box, more amps etc., which is probably why they're relatively rare.

When designing a TL, you have to consider the geometry, dimensions and driver T/S parameters as a whole, and whether simulated or measured, I find Thor wanting, so I suppose it's your second point -combination of drivers and enclosure that I dislike. Basically, as you know, you start with the drivers you wish to use, and design a cabinet specifically for them using alignment tables or the available software, and that's where it all goes pear-shaped for Thor in my view, bacause the tables / theory it's based upon are decidedly rocky. There's much better information and software available, like Martin's, which will yeild superior results. As you seem to have settled on the drivers you wish to use (I don't know them myself), I'd suggest you plug their parameters into his worksheets and design an optimised cabinet for them that way rather than the alignment tables Joe used when designing Thor, which aren't overly accurate. Also, if you haven't already, read some of Bob Brines guides to designing a TL. While he sticks with single drivers (as I usually do), the same theory is equally applicable to multi-ways, and Bob is a master at refining designs; they make Martin's MathCad sheets easier to understand, and give you a good starting point rather than trying things more or less at random.

Cheers
Scott.
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Old 28th September 2005, 01:48 PM   #46
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I don't believe it. You know I mentioned in previous posts that a TQWT enclosure seems to produce the best response with these Seas Excel drivers. Well, try this on for size. You know what the dimensions are? Groan. They're the same as Martin's Project 2 ML TQWT, but with a 3"x2" (WxL) port. That's it. So=1Sd, Sm=7Sd. TL length is 60". Driver height is half the TL length. I've mentioned the port dimensions.

It's got a slightly rising response that'll need bringing down somewhat, but nothing like as bad. As before, add 6db overall for the drivers being paralleled. There's a slight peak at cut-off which will add a little weight to the sound. You could try either a folded or version or straight. Remember to make allowance for baffle-step (unlike the original). Not a small enclosure, but the best TL response from these drivers I've seen so far.

Scott
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Old 28th September 2005, 02:44 PM   #47
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Well this is comforting.

Seeing you're having so much fun with this simulation, would
you care to post the results using the Extremis parameters ?

I'm curious to see what the difference would be.

Thanks


Extremis 6.8

Nominal Impedance: 8 Ohms
Usable Bandwidth: 30-5000 Hz
Rated Power: 100W RMS
Peak Power: 300W
Rated Efficiency: 86 dB
Moving Mass: 23.3 g
VC Diameter: 40mm
Compliance: 1.2 mm/N
Linear Travel: 26mm p-p
Maximum Travel: 30mm p-p
Driver Weight: 2.5 kg

Inductance: 0.13 mH
DC Resistance: 7.02 Ohms
BL: 9.0 N/A
Resonant Frequency: 30 Hz
Cone Area: 140 cm2
Vas: 33.2 L
Qms: 2.54
Qes: .383
Qts: .332
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Old 28th September 2005, 04:06 PM   #48
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As in, in the Thor cabinet? It shall be done. If I'm feeling generous, I'll see what I can come up with as optimised dimensions for them as well.
Give me half an hour or so. (and in case anyone is wondering why I've so much spare time at present, I'm currently in limbo: I'm waiting on my supervisor to send back his suggestions on the final draft of my Master's thesis.)
Cheers
Scott
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Old 28th September 2005, 04:46 PM   #49
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Frequency response of Thor cabinet with above drivers. Remember to add 6db overall for the paralleled drivers, and then subtract 4db from everything below 100Hz due to baffle-step loss.
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Old 28th September 2005, 05:01 PM   #50
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Very much appreciated Scott.

I guess the response isn't that good with these drivers.
Or might it just require that the stuffing density be changed ?

Thanks again.
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