Getting the most bass out of a 4.5" Vifa?

[swin1]

I have a pair of Vifa P11WH-00-08 midbass drivers. Apart from the Vifa recommended enclosure sizes for this driver, I think better bass is achievable as they have favorable specs:

52-6000Hz
Fs 52Hz
Qts .21
large magnets 415g

currently they are in a 5L box tuned at 95hz, this seems pretty high seeing how low this woofer can go, what would you suggest I do if I want to get the most bass possible while still keeping it at bookshelf size? Thanks

[rabbitz]

I wouldn't expect to get a great deal of bass out of these. Running out of Xmax is going to one of the main problems. Looks like they are tuned to give a peaky mid bass response

You could always tune to 70Hz using a 39mm x 99 long port to flatten the response a bit and see how it goes or extend the existing port with a carboard tube or PVC pipe as an experiment.

[swin1]

they have a 3mm Xmax which isn't too bad for such a small woofer, I am also willing to up the box size if necessary, thanks for your reply 70Hz would be a big improvement, how did you come up with that measurement?

[joensd]

If you want bass...
what about a mini-TL?
Of course you´d have to give up on some SPL but well that also depends on taste and what you´ll use them for.
I´ve TL´s with 6.5" that also have 3mm-xmax and that´s plenty for my listening room.

I´m no expert at this but could try to put your TS-parameters(if you´d post them) in Martin´s worksheets and see what they can do.

[swin1]

I had considered a TL but have had no experience building those. Where are Martin's sheets? Here are further TS parameters:

rms power: 30W
dc resistance: 5.4ohm
Vas: 10.3L
sens: 88db

Thanks

[planet10]

Originally posted by joensd
what about a mini-TL?

Q is awefully low for a TL... a miniHorn maybe (althou that is a bit of an oxymoron)


dave

[GM]

Assuming the specs are ~accurate, with an 8ohm series resistor it sims max flat in 10.29L/51.5Hz, so F3 should be around 45Hz. Since it's only rated 30W, it just barely runs out of Xmax and peaks at ~100dB/half space. Short of a huge back horn, this is about as good as it gets and still be able to use its wide BW.

GM

[swin1]

so you are saying I could tune this woofer down to 45Hz in a ported enclosure? That would be pretty cool, but I would need a box close to the VAS in size? Would like to know more if you are willing to offer further information. Thanks in advance GM

[rabbitz]

Originally posted by swin1
they have a 3mm Xmax which isn't too bad for such a small woofer, I am also willing to up the box size if necessary, thanks for your reply 70Hz would be a big improvement, how did you come up with that measurement?

3mm Xmax is quite good but to pump out bass you need volumes of air to be moved and the diameter of the driver comes in as well (2x the diameter increases driver area and effective volume by 4x). 3mm Xmax in a 4" woofer is different to 3mm in a 8" woofer. Compared to a 4" woofer, a 6.5" will have 2.4x the area, a 8" will have 4x the area and a 10" will have 5.6x the area.

Someone correct me if I'm wrong, but if you increase the box volume you also increase the cone excursion (which can then run out of Xmax) and reduce the speaker efficiency.

I got my figures from LSPCad but I suggest you get a copy of WinISD and play around. I'm not trying to put you off but trying to let you know there will not be bags of bass and you could run into cone excursion limitation.

Experiment and have fun. Just try retuning the port first (making it longer) with a cardboard tube.

[GM]

Originally posted by swin1
so you are saying I could tune this woofer down to 45Hz in a ported enclosure? That would be pretty cool, but I would need a box close to the VAS in size? Would like to know more if you are willing to offer further information. Thanks in advance GM

Yep, though as I previously noted, with considerable series resistance and the limited output it implies. Plug these into MJK's ported worksheet to see the half space sim:

Fd = 52 Hz
Re = 13.4 ohms
lvc = 0.38 mH
BL = 5.4597 n/a
Sd = 58cm^2
Vd = 10L
Qed = 0.645
Qmd = 1.1
(it will calculate Qtd)

L = 30.38"
zdriver = 10.81"
zport = 15"
SO/SL = 26.736"^2
density = 0.2lbs/ft^3
rp = 0.75"
Lp = 4"

GM