"Rule of thumb" for modeling?

[fuzzy]

My question is, when looking at Xmax, in Uni-Box,for let's say a 4" driver or two, sealed, in a volume that allows 50 watts at Xmax and 200 watts with about 3mm over Xmax,at say 60Hz,(and now the actual question) would a 2nd order electrical highpass at 300 Hz allow the driver(s) to operate safely, assuming they could handle it thermally, at 200 watts? TIA. Is their a "Thumb- Rule" for this? The thing that led me to this ? Is having a woofer with awesome specs.(rss315hf) and trying to use it in a threeway with mid-woofs I already own.(vifa/jbl buyouts from several years ago). Not that I am really designing for 110db,but that woofer is .......:D

[brianpowers27]

Re: "Rule of thumb" for modeling?

There are few rules of thumb for this. One could easily model this behavior in Jeff B's WBCD.

Here is a good link comparing excursion to various driver sizes.
http://www.diymobileaudio.com/forum/...ker-sizes.html

[JustinG]

Re: "Rule of thumb" for modeling?

There are few rules of thumb for this. One could easily model this behavior in Jeff B's WBCD.

Here is a good link comparing excursion to various driver sizes.

You may want to put the link in brian... :P

[fuzzy]

Re: "Rule of thumb" for modeling?

A link? thnks for responding so quickly,but think computer incompotent if you could,or would and that's me!

[charlielaub]

Re: "Rule of thumb" for modeling?

My question is, when looking at Xmax, in Uni-Box,for let's say a 4" driver or two, sealed, in a volume that allows 50 watts at Xmax and 200 watts with about 3mm over Xmax,at say 60Hz,(and now the actual question) would a 2nd order electrical highpass at 300 Hz allow the driver(s) to operate safely, assuming they could handle it thermally, at 200 watts? TIA. Is their a "Thumb- Rule" for this? The thing that led me to this ? Is having a woofer with awesome specs.(rss315hf) and trying to use it in a threeway with mid-woofs I already own.(vifa/jbl buyouts from several years ago). Not that I am really designing for 110db,but that woofer is .......:D

If you use Jeff Bagby's Woofer Box and Circuit Designer (WB&CD) which you can download at the link below, you can model a variety of high and low pass crossovers in the same program in which you are modeling the driver response. It's free software that everyone should have a copy of!

http://audio.claub.net/software/jbagby.html#WBC

More specific to your question, if it can handle the thermal power and Xmax is not exceeded anywhere, it is OK as far as modeling goes.

-Charlie

[Wolf]

Re: "Rule of thumb" for modeling?

My question is, when looking at Xmax, in Uni-Box,for let's say a 4" driver or two, sealed, in a volume that allows 50 watts at Xmax and 200 watts with about 3mm over Xmax,at say 60Hz,(and now the actual question) would a 2nd order electrical highpass at 300 Hz allow the driver(s) to operate safely, assuming they could handle it thermally, at 200 watts? TIA. Is their a "Thumb- Rule" for this? The thing that led me to this ? Is having a woofer with awesome specs.(rss315hf) and trying to use it in a threeway with mid-woofs I already own.(vifa/jbl buyouts from several years ago). Not that I am really designing for 110db,but that woofer is .......:D

Sorry I missed this-
I use Unibox regularly, with the 1.15 correction for 15% distortion regularly.
For a worst-case scenario, I model for 100dB, as noone would routinely/regularly play them that loud. This varies on wattage per driver.

About Xmax-based xover points, -you can do it that way if the drivers will meet there well, but- I usually will shoot for an octave above where the Xmax breaches, as this is not unlike the avoiding Fs argument for tweeters. I also think that a 12dB electrical would suffice at this one-octave above target.

You're increasing resistance as you approach the Fc of the xover and beyond, and this should attenuate the output and Xmax the lower you go. Since one octave at a 12dB slope is -12dB from reference or nominal output, you should be good.

Hope this helps,
Wolf

[Jeff B.]

Re: "Rule of thumb" for modeling?

Sorry I missed this-
I use Unibox regularly, with the 1.15 correction for 15% distortion regularly.
For a worst-case scenario, I model for 100dB, as noone would routinely/regularly play them that loud. This varies on wattage per driver.

About Xmax-based xover points, -you can do it that way if the drivers will meet there well, but- I usually will shoot for an octave above where the Xmax breaches, as this is not unlike the avoiding Fs argument for tweeters. I also think that a 12dB electrical would suffice at this one-octave above target.

You're increasing resistance as you approach the Fc of the xover and beyond, and this should attenuate the output and Xmax the lower you go. Since one octave at a 12dB slope is -12dB from reference or nominal output, you should be good.

Hope this helps,
Wolf

But why not just do as Charlie and Brian suggested and use software that shows exactly what the excursion vs power vs frequency plot will be when using whatever crossover you plan to you? Woofer, Box and Circuit Designer will do this easily with built-in transfer functions. However, you can also import your actual passive crossover transfer function from PCD into it and see the impact it has on excursion as well (in addition to all other measured features in the box model).

[Wolf]

Re: "Rule of thumb" for modeling?

But why not just do as Charlie and Brian suggested and use software that shows exactly what the excursion vs power vs frequency plot will be when using whatever crossover you plan to you? Woofer, Box and Circuit Designer will do this easily with built-in transfer functions. However, you can also import your actual passive crossover transfer function from PCD into it and see the impact it has on excursion as well (in addition to all other measured features in the box model).

While I understand that your program does what was stated, I also was thinking that he was more familiar with Unibox than the other newer programs out there, and provided him with a usable ROT for use with the program he typically uses.
Some of the newer fellows getting into the hobby might only understand one or 2 spreadsheets well and how they are used. While I also understand that the WBCD is setup a lot like Unibox, I just wanted to give him the option.
Later,
Wolf

[Jeff B.]

Re: "Rule of thumb" for modeling?

While I understand that your program does what was stated, I also was thinking that he was more familiar with Unibox than the other newer programs out there, and provided him with a usable ROT for use with the program he typically uses.
Some of the newer fellows getting into the hobby might only understand one or 2 spreadsheets well and how they are used. While I also understand that the WBCD is setup a lot like Unibox, I just wanted to give him the option.
Later,
Wolf

OK, but you can do the same thing in Unibox and import the crossover transfer function. I'm just saying that you get an accurate answer this way rather than a rule of thumb guestimate.