Hi,
I'm building a subwoofer and have a plate amp (DAYTON SA240 240W SUBWOOFER AMPLIFIER). There's not a lot of documentation on this thing.
One review says "A built-in “rumble filter” attenuates the lowest audio frequencies to help conserve amplifier headroom and protect drivers. The “rumble filter” is actually a 12 dB/octave high-pass filter that is centered at 20 Hz, the F3 is 18.2 Hz. Since most source material does not contain information below 20 Hz, usually we are not missing anything. But, in cases where information is available this low, we generally need to protect our drivers from this potentially damaging information. Since excursion demands increase with decreasing frequencies, even the beefiest sub can start to run into overexcursion problems. This is particularly a concern in vented subwoofer systems where overexcursion occurs rapidly below the tuning frequency."
I'm having trouble determining whether this thing has any sort of a high-pass equalization filter that I can use in my box calculations. If it does, does anyone know how exactly would I figure this into my WinISD Calculations.
Thanks!
Greg
I'm building a subwoofer and have a plate amp (DAYTON SA240 240W SUBWOOFER AMPLIFIER). There's not a lot of documentation on this thing.
One review says "A built-in “rumble filter” attenuates the lowest audio frequencies to help conserve amplifier headroom and protect drivers. The “rumble filter” is actually a 12 dB/octave high-pass filter that is centered at 20 Hz, the F3 is 18.2 Hz. Since most source material does not contain information below 20 Hz, usually we are not missing anything. But, in cases where information is available this low, we generally need to protect our drivers from this potentially damaging information. Since excursion demands increase with decreasing frequencies, even the beefiest sub can start to run into overexcursion problems. This is particularly a concern in vented subwoofer systems where overexcursion occurs rapidly below the tuning frequency."
I'm having trouble determining whether this thing has any sort of a high-pass equalization filter that I can use in my box calculations. If it does, does anyone know how exactly would I figure this into my WinISD Calculations.
Thanks!
Greg
If you're using the WinISD beta, your first step is to download the WinISD Pro alpha version.
In WinISD Pro, you go to the "Effects/EQ" tab, click Add, and select a highpass filter, order = 2, cutoff = 18.2. I would assume a Butterworth filter unless there's evidence to the contrary.
You'll see that you'll lose a couple of dB above 20 Hz, but the cone excursion will be greatly reduced below 20 Hz. That will keep the woofer from bottoming out when your movie soundtrack goes bananas at 10 Hz.
Take a look at this thread on another board. Plots from the movie "The Incredibles" show some strong output in the 5 Hz range. Good reason to have a filter on a vented woofer!
In WinISD Pro, you go to the "Effects/EQ" tab, click Add, and select a highpass filter, order = 2, cutoff = 18.2. I would assume a Butterworth filter unless there's evidence to the contrary.
You'll see that you'll lose a couple of dB above 20 Hz, but the cone excursion will be greatly reduced below 20 Hz. That will keep the woofer from bottoming out when your movie soundtrack goes bananas at 10 Hz.
Take a look at this thread on another board. Plots from the movie "The Incredibles" show some strong output in the 5 Hz range. Good reason to have a filter on a vented woofer!
jaygeorge1979 said:
So we can see what it will closely look like in real life.
Yes.
A rumble filter will drop the low end faster than without one. At the rumble filter frequency, you've lost 3 dB.
It's not absolutely necessary to consider the rumble filter, but it's a good idea. Some could even use it to tweak the design. You could use the rumble filter to tame a 3 dB peak at the tuning frequency caused by a too large box for example.
bcycle said:
Hence my struggle. The above statement is from a review of the amp that I bought. The software I'm using (Bassbox) has fields for inputting an Fx and a Qx parameter. I'm not exactly sure which values are entered in these fields but when I select the software to "suggest" a box size using the "Vented Box with Active HP filter" it yields a dramatically smaller box ( 2.381 cubic feet) with 19.67 F3! Bassbox calculates a Qx of 16.78 and an Fx of 16.78.
Given the amp description should design this with the "Vented Box with Active HP filter" setting?
I've attached some pdfs showing my calculations. Some of them seem a little wacky, especially the group delay. (I'm still not savvy with all the graphs as yet.
As always, I appreciate the help!
Greg
jaygeorge1979 said:
I want to know both the small signal response (how low does it play), but also the large signal behavior - how loudly will it play without bottoming out or melting? One of my design criteria is, can I build something my family can't break, even accidentally?
WinISD lets you graph max power, max SPL, cone excursion and port velocity vs. frequency. The high pass filter changes those behaviors quite a bit at very low frequencies.
For instance, when I was trying to design a woofer for my system I considered using a 12" Dayton Titanic in a vented box tuned to ~21Hz. Above resonance, it would (theoretically) handle 500 W and play deafeningly loudly. More than i would need, right? But, without a high pass filter, a 60 W signal @ 10 Hz would bottom the woofer! I could see that happening too easily with movies (60 W = 102 dB above 30 Hz., and I have a big room to fill).
A little fooling around in WinISD tells me that a 3rd order hipass @ 18 Hz woud control the cone excursion well enough that bottoming would never be a concern at any drive level, thus meeting my 'can't bust it' criterion. The effect on F3 would be minor. The group delay would look a lot worse, but there are no free lunches.
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