Newb Q: Avoiding damage to driver

[zafdor]

I'm embarking on my 1st project. What does one need to watch out for in order to prevent damage to either the amp or driver. Clearly the driver should not exceed its rated power, but does the box design come into play here? I've seen some references to exceeding Xmax, but WinISD does not give me a plot of cone excursion, I supplose one of the variables is unknown...

I plan on putting the Dayton RSS265HF in a 1.9ft^3 box with a 17" port and driving with the PE 250W amp. Should be a safe combo (?).

[David Gatti]

Download Unibox which will clearly show your cone excursion versus frequency.

[zafdor]

Tx Dave, Unibox does indeed calculate cone excursion with freq. It shows the Xmax being hit at ~18Hz. But I'm still not clear if this is a problem.

[paulspencer]

or get the pro version of WinISD which will show excursion

you really need a rumble filter for movies if you have a vented box

have a look at the wiki pages on subwoofers, especially on rumble filters and how to design a sub with win ISD.

[damo21]

So is a highpass filter at 17Hz unnecessary for a closed box? Does the air pressure inside provide enough spring?
I already have an amp with 17Hz hp, but I'm thinking I want a closed box arrangement...(looking for a driver)
Unless there is a way to tune a vented box to 18Hz without generating delay?
I just want nice tight bass reproduction for classical/jazz music.

[damo21]

On this same topic, is it ok to design a closed box which will exceed the Xmax (12.5mm) of a driver by 2.5mm at frequencies 15-25Hz? Or will I likely destroy it?

I did some models on WinISD Pro comparing the Peerless XLS, XXLS and Shiva. It seems that the shiva is a much better driver than either of these, but the XXLS will work nicely (in theory) if u allow a little overexcursion...
I am trying to find a replacement for the Shiva which is now out of stock/production.

[paulspencer]

IMO XLS is superior to Shiva, a more articulate driver.

You probably don't need a rumble filter for music, but I don't think it's going to hurt since the GD is affected down low. You could argue that music doesn't go down that low, but if that is true in your case then you won't have GD issues.

A few mm beyond xmax isn't going to kill a driver, usually the suspension can go beyond xmax. My drivers have an xmax of 23mm and an xsus of 30mm. The XLS has a generous surround for a driver with a 12mm xmax, I'd say it could go well beyond xmax without being in danger of mechanical damage.

The air spring in a sealed box does help. My subs are sealed at the moment, but I prefer to be safe and have the rumble filter on. I don't notice a different, except in cone excursions.

[damo21]

Really? The XLS is better... Hmm well I just ordered one.

What is your experience with big vented boxes for music?
I read somewhere that you have to keep the velocity below 16m/s through a port to prevent the turbulence from resonating the pipe, so making it bigger in diameter and flaring the ends will fix that.
What about a 200L vented box tuned to 13Hz... would that be good for music reproduction? I don't see any problem except WinISD says the group delay at 20Hz would be around 25ms (which is the same for my closed box simulations with all the filtering) but shoots up to 37ms at 17Hz.... If that is acceptable, then it would be worth building
The response is flat down to 15Hz and the velocity through a 110mm diameter x 700mm port doesn't exceed 13m/s

[damo21]

I designed a sealed box that ended up with a Qb=0.3 ...... is that bad? What does this mean?

[paulspencer]

Damo,

The audibility of GD is a debatable issus, higher values are considered acceptable as you go down lower. In general, you can't avoid higher GD as you get deep extension, in fact if a sealed box has eq to match the response of vented, then the GD is about the same but the output is 6db lower.

Tuning lower makes it behave more like a sealed box, until you tune it at 0 Hz and have a sealed box effectively.

That's a very large box! That is a low amount of damping, and it's not a bad thing. Typical values are 0.7 (maximum) or 0.5 critically damped considered better. As you go lower, you start to approach infinite baffle.

Acceptable vent velocity varies depending on the aerodynamics of the port. 34m/s can be achieved but most don't make flares big enough to pull it off. Even 16m/s can be too high if you don't have flares!

Collo did some experiments to find out what works before you get chuffing of vents, and I put in some links in the wiki pages in the sub section ... follow the links in my signature ...

Which version of XLS did you buy?