why doesn't my box size match that of others?

[Euphase]

Originally posted by ScottRHinson


Without actually putting the numbers in, I'd say it's clever specsmanship at best. For bookshelf designs, if the F3 is much below 50Hz the linear excursion limited power handling is usually rotten.


Scott Hinson

I would suggest you to run the numbers. 19lt tuned at 39Hz has minimum 102 db excursion limited output from 42Hz on. I wouldn't call that rotten. In case of CP-737, two woofers have plenty of SPL capability, even tuned as low as 30Hz.

[Jim85IROC]

Originally posted by kelticwizard
I don't see any listing or links to the Thiele-Small specs of the speaker, which would certainly be nice. The link that was given for the frequency response of an enclosure is not working, at least for me.

Here's a linke to euphase audo's measured t/s specs, which line up very closely with other people's measured specs, as well as with Usher's published specs:
http://www.euphase.com/RawDrivers/8945-W.asp

So, without any convenient means to see the specs, I will say only this: your box is tuned to 39 Hz, but you want an F3 of 35 Hz.

That rarely happens.

Generally, well designed commercial boxes use a woofer with a Qts of 0.38 or below, put into boxes that are equal to Vas or less. The F3 is above the tuning frequency. So I suspect that something with this situation is amiss right there.

The bass is snappier the smaller the box is compared to Vas, and the smaller the Qts.

You can build a box with a Vb larger than Vas, a Qts above 0.38, and an F3 above Fb, (tuning frequency). But for the reasons given, they are not generally recommended.

A misprint, perhaps?

I realize that I'm not going to get a 3-dB of 35hz when tuning to 39hz. My problem is that I am unable to model an enclosure that does it even when I tune at 30hz like D'Appolito's original design.

The EBS is something that I hadn't considered, and something I want to try to learn more about. Now that I'm reading a little bit on it, it does look similar to what my modeling had resulted in. Between baffle step and EBS, that 2nd woofer's role seems like it could integrate nicely, but it also seems that I either need to find the proper volume that D'Appolito used, or I need to find a way to model this 2.5 way configuration more accurately.

[sreten]

Some curves :

for the final plot I changed Qts to 0.36 to crudely model
some series resistance in the crossover affecting Q.

sreten.

[Jim85IROC]

wow, that's interresting what a little higher qts will do.

[sreten]

The only thing I'm not taking into account is the baffle step compensation that D'Appolito does with the 2nd sub, but that shouldn't have any effect on low frequency extention... right?

Right - there is no difference in the bass modelling of a 2.5
way and a 2 way speaker with parallel twin bass units.

sreten.

[sreten]

Originally posted by Jim85IROC
wow, that's interresting what a little higher qts will do.

http://www.mhsoft.nl/spk_calc.asp#newqts

Indicates a 0.8 DCR of the inductors will change Q to 0.36.

It will also slightly change the sensitivity which
is not modelled by changing Q, by around -1dB.

Not that I'm saying Q=0.36 is the best value, I'll play with it.

sreten.

edit : shows Q stepped from 0.32 in 0.2 steps,
Q=0.4 = 2R/driver, 2 drivers, left scale = 20Hz.