BASH 500: Boost Filter for Dayton RS315HF

[Operandi]

A friends of mine helped me come up with a model in LEAP for my RS315HF and arrived at 2.6cuF with a port tunning of 25HZ. The cabinet is done and veneered and ready to go I'm just not sure about the boost filter in the BASH amp. My crossover and filter knowledge is basic at this point so I could use some advice.

I would like to match the modeled output as close as possible. I assume the Fc is functioning as the rumble filter to protect the driver? I don't plan on reaching crazy SPLs and I will be using this with 90% music so would a Fc or 18-20HZ be safe?

I realize there will be room modes affecting the response but I would just like to get the response of sub to match the software model as much as possible and go from there.

[JonMarsh]

You haven't really posted enough information for anyone to comment intelligently, unless they are using leap and have your software model, and have all the details of the BASH amp.

The problem is that just modeling the anechoic enclosure response and chosing a boost circuit on the BASH amp leaves out the room and woofer position as part of the equation. Starting point would be to go for flat anehoic equivalent response for the sub located at some clean boundary interface, but to really optimize response at the listening position you may need to do some measurmeent, too.

[ThomasW]

Unless PE's tech support people specifically say the unit is designed to function as a HP filter below the boost frequency, I wouldn't make that assumption.....

[Operandi]

You haven't really posted enough information for anyone to comment intelligently, unless they are using leap and have your software model, and have all the details of the BASH amp.

The problem is that just modeling the anechoic enclosure response and chosing a boost circuit on the BASH amp leaves out the room and woofer position as part of the equation. Starting point would be to go for flat anehoic equivalent response for the sub located at some clean boundary interface, but to really optimize response at the listening position you may need to do some measurmeent, too.

Thanks Jon. I do have the LEAP sim in PDF format, would any other info be useful?

I realize that room and woofer placement are being ignored and are big influences. What I would like to do is aim for flat according to the model and make any adjustments after listening and measurements with an external processor, something like the Behringer Feedback Destroyer.

According to the BASH PDF the default has a 3 dB boost between 31-35 which doesn't seem optimal for my sub. Though I'm not exactly sure since it says R18 is 60K which isn't even in the tables. The sim was done assuming no boost so would something with 1 dB of boost from the first PDF table would most accurately match the sim done in LEAP?

Unless PE's tech support people specifically say the unit is designed to function as a HP filter below the boost frequency, I wouldn't make that assumption.....

Ok, well as I will be using this for music at sane SPL levels I think I will be ok.

[brent_s]

I would like to see that model and the assumptions your friend made. A 315HF-4 in 2.6 ft^3 net tuned to 25Hz shows a 1.8dB peak centered at 37Hz in WinISD. F3 is still 25Hz, but I wouldn't exactly call it flat. With the stock filter in the BASH500, you're looking at a 4.2dB peak around 37Hz! This alignment really needs to be tuned to 20Hz to get rid of the natural peak even before any EQ is accounted for.

Assuming the LEAP model is as described with 2.6/25, I'd go with something like 20K/45K for R17/R18 to get a Q=.75 / Fc=24Hz filter...this will shift your peak slightly (1.5dB@40Hz) while protecting you from overexcursion below tuning with 500 watts.

-Brent

[Rick Craig]

Thanks Jon. I do have the LEAP sim in PDF format, would any other info be useful?

I realize that room and woofer placement are being ignored and are big influences. What I would like to do is aim for flat according to the model and make any adjustments after listening and measurements with an external processor, something like the Behringer Feedback Destroyer.

According to the BASH PDF the default has a 3 dB boost between 31-35 which doesn't seem optimal for my sub. Though I'm not exactly sure since it says R18 is 60K which isn't even in the tables. The sim was done assuming no boost so would something with 1 dB of boost from the first PDF table would most accurately match the sim done in LEAP?



Ok, well as I will be using this for music at sane SPL levels I think I will be ok.

Want you need to do is go back and model it as a 6th order alignment. To do that you'll need to input the boost frequency and Q for the filter. The 1db of boost is still going to affect your output because of the highpass function of the boost filter. Being able to measure the output and tune the boost / port functions is the best way to go.

[---k---]

I believe that Jeff Bagby's Woofer modeler program most recent update easily allows for the modeling of amp boost and high pass filters.

Jeff also had a great post on PE once that listed the different high pass filters on various plate amps. They should have made it a sticky. I searched briefly, but couldn't find it. Then I had to do real work.

[Operandi]

I would like to see that model and the assumptions your friend made. A 315HF-4 in 2.6 ft^3 net tuned to 25Hz shows a 1.8dB peak centered at 37Hz in WinISD. F3 is still 25Hz, but I wouldn't exactly call it flat. With the stock filter in the BASH500, you're looking at a 4.2dB peak around 37Hz! This alignment really needs to be tuned to 20Hz to get rid of the natural peak even before any EQ is accounted for.

Assuming the LEAP model is as described with 2.6/25, I'd go with something like 20K/45K for R17/R18 to get a Q=.75 / Fc=24Hz filter...this will shift your peak slightly (1.5dB@40Hz) while protecting you from overexcursion below tuning with 500 watts.

-Brent

It seems relatively flat if I'm interpreting the graphs right. Those settings sound good, and far more appropriate than the defaults. Do you think you could explain how the Q works though?

Here is the pertinent data on the subwoofer sim.

[brent_s]

It seems relatively flat if I'm interpreting the graphs right. Those settings sound good, and far more appropriate than the defaults. Do you think you could explain how the Q works though?

Here is the pertinent data on the subwoofer sim.

Now I get it. He's actually simulated a net 3 ft^3 box because of the 50% fill. His model still leaves you with a 1.6 dB peak centered around 36Hz. See the blue trace in the SPL-Frequency graph...you can see the peak relative to the 80-100Hz level. Once the room gets involved, 1.6dB is probably negligible.

He's also modelling a port with both ends in free space, which is not the way you're actually going to build it...meaning your port can be a bit shorter for the same frequency. I get 4"x15.06".

His assumptions about the BASH500 are all wrong, as you already guessed. First of all, you can use the LFE input to bypass the amp's lowpass altogether. Technically, I still think there's a mild 6dB/octave rolloff starting at 200Hz, based on other BASH designs I've seen measured, but that should be well above the xover frequency you actually use in your processor. On the rumble filter/high pass, it's implemented as a Sallen-Key 2nd order and starts the rolloff 12dB/oct at 30Hz with a 2dB boost up around 36Hz in stock form.

The Q represents the slope of the rolloff. The boost in a Sallen-Key filter is created by having a Q > .7071. In stock form, the Q=1.2. I was just fiddling with the calculator to find a set of values that got close to .7 at the right frequency. The .75 I came up with will still introduce a very slight bit of boost.

If you increase your port to 4"x25", you'll drop the tuning to 20Hz in the same 2.6 (3.0 effective) box. Go with a filter of Fc=18Hz/Q=.7071 (28.42k/56.84k) and you take out all peaking (well, .13dB if you want to split hairs) and excursion still stays within Xsus if your really push it to 500 watts. F3 is still 24Hz with a shallower rolloff than your proposed design...f6=20hz versus his being f10=20Hz.

There is no single correct alignment for a sub. Either design will likely sound great, IMO, but I like the flatter curve of the lower tune. My pair of 315HFs are 3.5ft^3/20Hz with no rumble filter at all.

-Brent

[Operandi]

Thanks for the help brent . Yes, the sim was done with stuffing, I neglected to mention that. Also, I will be using a Reckhorn F-1 so I will be using the BASH's LFE input.

I think I understand what the Q is doing in the filter. The box is already done and everything is a fairly tight fit so the port can't be made any longer without it sticking out the back so your original Fc of 24Hz and a Q of .75 would seem to be what I want.