Help calculate enclosure volume

[richie00boy]

You can only raise Qts, so the W3 with high Q already at 0.9+ means you will be limited to 1+ in a practical box.

Qts affects box size or VAS scaling factor. Lower Qts means a smaller box but at the expense of bass depth (-3dB point)

 

[lndm]

a Qts of .703 which seems oddly small.

A Qtc of 0.7 is not so unusual (maybe it is not what you want right now?). I have used a Qtc of 0.5 . It is probably too lean for many (unless you have a purpose for it), but sounds very clean.

 

[sreten]

Hi,

the B3 :

Qts = 1.00, Vas=0.8L, Fs=105.

On inspection Qtc will always be > 1, so you will get a peaking response.

shown is 2dB peaking and 3dB peaking.

However all is not what it appears, the B3 should not be used full range.

If it is then at the input of the amplifier the input coupling capacitor
should be reduced in value such that the response is -3dB at ~ 150Hz.
So at least the response will be ~ flat.

However as recommended by Zaph HT filtering should be used.

/sreten.

 

[sreten]

So, after a long day of work, I got home... and got solidly confused again

Attached a screen shot of a comparison between Hi-Vi W5 and Hi-Vi B3S. I stole my t/s params from Zaph's measured data.

I just can't wrap my head around what this... *means*.

I have fixed Qts on both models at 1.08. By my eyes, it looks like:
- the w5 wants a really, really, really small enclosure (good luck getting a 5" woofer in a 0.03 ft^3 enclosure)

- okay, apparently silly Qts for the W5. but still, .1 cu ft gives, a Qts of .703 which seems oddly small.

- uuuhhhh, the 3" woofer has better/lower bass response?!
- the B3S seems hard constrained to no lower than Qtc = 1.01 at infinite volume. What's the deal here? On the other hand, its easto

- I can't wrap my mind around how the differece t in db (efficiency) plays into this chart, or more importantly the actual bass response. It seems that in reality the 5" should be "lifted up" on the chart (to compensate for its extra db)... which would also affectively makeit look like its moving towards lower bass response. I have no idea what the correct apples to apples comparison is.

- I actually keep wonder if I put in one of the parameters wrong, cuz there is just so much that is ... well, 'weird' to me in this comparison. I mean it looks like f3 for the 5" is 125hz, where its more like 88hz for the 3". no way I can wrap my head around that.

So... thanks again for helping the n00b understand volumes and such.

-Silly

Hi,

your sealed target for the W5 should be Qtc = 0.6 to 0.7, as
size is the critical issue you should go for 0.7 = Vbox = ~ 3L.

The F3 point of all the sealed alignments Q < 0.7 is ~ 100Hz.
3L may seem small, but if you want a bigger box, reflex it,
this will also give you much bettter bass extension. With a Qts
= ~ 0.4, a box that is ~ half Vas will always give Qtc = ~ 0.7.

The F3 point of the B3 is somewhat illusory and also irrelevant
as it should be used with bass filtering, if it isn't it will be boomy
and run out of bass excursion capability if you even look at it.

The F3 point for the B3 is lower than the 5" when they are both in 3L.
This is generally expected. If two drivers are in the same box, then
the driver with the lower efficiency will have more bass extension.
As the B3 is 8dB less efficient the amount of extra bass is poor.

But bass extension and bass loudness capability are completely
different things, the 3" can't do bass, the 5" can, relatively speaking.

quoting Zaph on the B3 :

..... Like all other 3" drivers, this speaker has serious harmonic distortion below 100Hz. ....
..... This design has terrible bass distortion and should not be run full range. Period. ....

/sreten.

 

[Sillyboy]

Wow, sreten ... that was some response Thanks a ton.

Let's summarize:
- Dude! Distortion! Sure the low frequency's on the 3" are louder... cuz you are also getting a bunch of high frequencys in there too, in the form of 2nd and 3rd order harmonic distortion!

Okay, again that makes total sense, and I almost feel bad for not reading Zaph's comments on this issue more carefully, but... hey... information overload. The subject is big!

So, lets talk briefly about distortion. Zaph simply measured it directly (however you do that... ). Is it also something that can be calculated/guesstimated, or do manufactorers put out any specs for that sort of thing?

I was just looking at the B3S on parts express and noticed: Frequency range: 300-15,000

That would make some sense, now that I see the distortion below 300! Interestingly, the B3N says... Frequency range: 100-7,000. I really, really, really doubt it. So maybe I simply can't know without measuring.

Might be a lesson learned here that... "until you measure the speaker yourself (or have data from another trusted diy'er)... you don't know *anything* about the speaker".

Okay, sounds like I really, need to buy a mic and mic pre-amp, and start learning to take measurements. Noodle_Snacks suggested these:
mic: behringer ECM 8000
preamp:behringer UB802

Those the best cheap options?

Thanks again, I have learned alot this week

 

[lndm]

mic: behringer ECM 8000
preamp:behringer UB802

Those the best cheap options?

These sound like a good option. A cheap option would be an RS analog SPL meter connected directly to your sound card.