SS 18W8535-00 questions

[andrew01]

Hi,
Can someone explain to me the differences between software calcs and real world usage of this driver.

for example :

DIY Proac 2.5 has ~38L volume with 75mm x 140mm port , which
seems to be tuned to around 42Hz , this gives a large bump in the bass response.

Another design has volume of 30L and 62mm x 190mm port , tuned to around 35Hz....bit smaller bump in bass response.

If I stick the T/S parameters into WinISD it comes up with dimensions of 59L with 75mm x 233mm port tuned to 27Hz.....with no bump in bass response.....

Why the large differences / discrepancies ? Which is better or ideal ?

Any help appreciated.
Andrew

[tktran303]

I have confirmed by measurements that the 18W/8535-00 in a 38L vented box with 200g/m^2 density Dacron stuffing material on all walls except the front (as per www.geocities.com/diyproac25 directions) gives a port tuning of 38Hz. And IIRC, based on my own computer simulations, there is a mild bass boost of about 3dB, centred at 50Hz.

As for different box sizes and tuning, yes the software is always a little different to the actual. You may find that even different software will give you different results!
I have found that Unibox gives me the most reliable approximations.

Obviously the best way is to measure actual port tuning after building it, and shorten/length to taste.

According to Troels Gravesen, who has probably spent more time with this driver than anyone else in DIY-land, you can kill two birds with one stone using a smaller box and lower port tuning for a more controlled bass response.

I'd go with 25-28L tuned to 28-30Hz, however what is "best" is usually a personal preference, and largely depends on the speaker placement relative to the rear and side walls.

[Notax]

Originally posted by andrew01
Hi,
Can someone explain to me the differences between software calcs and real world usage of this driver.

for example :

DIY Proac 2.5 has ~38L volume with 75mm x 140mm port , which
seems to be tuned to around 42Hz , this gives a large bump in the bass response.

Another design has volume of 30L and 62mm x 190mm port , tuned to around 35Hz....bit smaller bump in bass response.

If I stick the T/S parameters into WinISD it comes up with dimensions of 59L with 75mm x 233mm port tuned to 27Hz.....with no bump in bass response.....

Why the large differences / discrepancies ? Which is better or ideal ?

Any help appreciated.
Andrew

You can look at this tread, and continue there.

calcualtions

[Notax]

Like you can see in that tread I have some corrections of calculatiuons with Thiel/Small parameters. In this case, with that corrections I got:

Vb=31 L
Fb=34 Hz
Dt=53 mm
Lt=145 mm

Its with catalog values. For the real and exact, unit must be measured, and then all calculate with measured T/S.

[rabbitz]

Originally posted by andrew01
DIY Proac 2.5 has ~38L volume with 75mm x 140mm port , which
seems to be tuned to around 42Hz , this gives a large bump in the bass response.

A pseudo BSC method which can be very effective and I used a similar tuning (40Hz) with a 18W8531G00 and made a huge difference to the tonal balance.

I found a flat response sounds.... er... flat in the bottom end and needs BSC in the filter network or the hump in the bass.

[tktran303]

IMHO, it's just a form of BASS BOOST, pure and simple.

You can argue til the cows come home where it's a good or bad thing.

[rabbitz]

Who's arguing?

[andrew01]

Thanks Gents,
Got an idea whats going on now.
I also discovered that the port length from s/w calcs is too long - need to mult. it by ~0.7 to get the real length........

so correct me if I'm wrong....

the 18W/8531G-00 should go in a 28-33 L box not 40L , and be tuned to ~33Hz....not 31

[Notax]

Originally posted by andrew01
Thanks Gents,
Got an idea whats going on now.
I also discovered that the port length from s/w calcs is too long - need to mult. it by ~0.7 to get the real length........

so correct me if I'm wrong....

the 18W/8531G-00 should go in a 28-33 L box not 40L , and be tuned to ~33Hz....not 31

You are wrong. Simulation are correct for relation between Vb, Fb, Dt and Lt, but are not in every case exact and usefull for Vb.

[rabbitz]

Here's some suggested box sizes and tuning from Scan Speak on the 18W8535-00 (as supplied to resellers and I haven't tried or modelled any of these).

Vb=47 litres
2"x6" port
F3=32Hz

Alt

Vb=53 litres
2"x5" port
F3=29Hz

FIY, the suggested box size for the 18W8531G00 is between 37-45 litres.