Hello all!
I'm fairly new to the world of DIY audio and currently working on my first pair of 2-way desktop/bookshelf speakers. I hope this thread is not misplaced, since I don't know yet whether my problem is software-, speaker- or brain-related... probably the latter 🙂
Browsing for a suitable chassis, I read a lot about Paul Carmody's DIY Speedsters, which I'm sure are well known around here (perhaps even a DIY classic?).
I won't replicate this exact build, but I have my eyes set on the Tang Band W4-1720 in vented a 6 litre enclosure paired with Dynavox AMT-2.
As per the official pages:
A 40ish F3 with a 4" woofer in cabinet that small? Impressive! Surely I can aim for a similar result, once I get a hang of this whole DIY thing? And so I decided to feed the T/SP, box and vent data into WINISD to verify that this could actually work. WINISD won't let me specify the port length but everything else, and in fact recommends an even longer port. This is how it looks:
That's nice and smooth graph for sure, but with a steep and early dropoff. Nowhere near 45 Hz at -3dB! The Speedster's crossover doesn't seem to play a role in that (or does it? I'm only just learning how crossovers work, with XSim and SPL trace and everything, so keep in mind that I am exactly as clueless as it seems). Anyway, I've looked for other explanations. Incorrect TSP (or units) were the prime suspects. But they are all in line with the specsheet.
Except... this posting on parts express' techtalk caught my attention:
Not that smooth anymore, but it looks more in line with that infamous F3. Air speed looks good... cone excursion not so much, but that also applies to the original VAS. Now, all this reeks of confirmation bias. A woofer so widely used and nobody except one dude noticed this? Don't think so. What am I missing?
Maybe I should just call it a day, move on to a different chassis and work it from there. But I'm trying really hard to understand the basics and not go by feel. Can you help me with that? 🙂
Thank you kindly,
v3
I'm fairly new to the world of DIY audio and currently working on my first pair of 2-way desktop/bookshelf speakers. I hope this thread is not misplaced, since I don't know yet whether my problem is software-, speaker- or brain-related... probably the latter 🙂
Browsing for a suitable chassis, I read a lot about Paul Carmody's DIY Speedsters, which I'm sure are well known around here (perhaps even a DIY classic?).
I won't replicate this exact build, but I have my eyes set on the Tang Band W4-1720 in vented a 6 litre enclosure paired with Dynavox AMT-2.
As per the official pages:
(Alas, there is very little on that later.)
A 40ish F3 with a 4" woofer in cabinet that small? Impressive! Surely I can aim for a similar result, once I get a hang of this whole DIY thing? And so I decided to feed the T/SP, box and vent data into WINISD to verify that this could actually work. WINISD won't let me specify the port length but everything else, and in fact recommends an even longer port. This is how it looks:
Except... this posting on parts express' techtalk caught my attention:
Changed the VAS in WINISD, and sure enough:
Maybe I should just call it a day, move on to a different chassis and work it from there. But I'm trying really hard to understand the basics and not go by feel. Can you help me with that? 🙂
Thank you kindly,
v3
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Most folks just build DIY kits and enjoy 😉, so recommend calling it a day and use a larger format, more rigorously designed speaker such as some of these to reverse engineer: Troels
Vas can be hard to measure accurately, especially tiny drivers, and its spiders can take a long time to break in, so the pioneers determined that a closed box that raised Fs at least 1.56x would be most accurate, ergo with a raw driver its Fs needs to be pushed at least 1.56x lower, which can bottom out a small, low Fs driver, so 'caught between a rock and a hard place'.
Vas can be hard to measure accurately, especially tiny drivers, and its spiders can take a long time to break in, so the pioneers determined that a closed box that raised Fs at least 1.56x would be most accurate, ergo with a raw driver its Fs needs to be pushed at least 1.56x lower, which can bottom out a small, low Fs driver, so 'caught between a rock and a hard place'.
The most thorough tests of the W4-1720 that I've seen were performed by John Krutke (Zaph) here: http://www.zaphaudio.com/smalltest/compare.html.
PS - That page requires Javascript to be enabled
PS - That page requires Javascript to be enabled
Thank you so much guys.
@ernperkins: Zaph measured Vas = 1.93l = 0.68cf! More evidence that the factory specs are off. Also, Fs seems much higher than specified (75 vs. 60Hz). Another possible explanation is, as suggested elsewhere, that TB altered the drivers at some point in the past. Depending on which is correct, the port length suggested by WINISD varies a lot. Will have to give it some thought and compare with other woofers.
@GM: I'm a bit stubborn when it comes to that, but yeah, maybe I should resort to just picking a kit 😉 Troels' pages are fascinating though. Lots to take in there. A bit intimidating, too ("crossovers cannot be calculated"!) ...
@ernperkins: Zaph measured Vas = 1.93l = 0.68cf! More evidence that the factory specs are off. Also, Fs seems much higher than specified (75 vs. 60Hz). Another possible explanation is, as suggested elsewhere, that TB altered the drivers at some point in the past. Depending on which is correct, the port length suggested by WINISD varies a lot. Will have to give it some thought and compare with other woofers.
@GM: I'm a bit stubborn when it comes to that, but yeah, maybe I should resort to just picking a kit 😉 Troels' pages are fascinating though. Lots to take in there. A bit intimidating, too ("crossovers cannot be calculated"!) ...