Dayton DCS380-4 15" in THT, should I set HP filter at 20Hz?

[vann]

Hello ppl,

I first posted this at Parts-Express forum (since Dayton DCS380-4 is sold by their web-shop) and later also on AVS forums, but it seems that the post didn't gather much interest...


Anyway, I want to use the Dayton DCS380-4 15" subwoofer driver in Tuba HT folded horn cabinet. To power this I would like to use the Foster wf-100k Plate Amplifier which I bought some time ago from Jack Hidley's NHT surplus sale. (115W into 4ohms, 80W into 8ohms. 4th order (24dB/octave) low pass adjustable from 50-200Hz. 0-180 degree phase switch)
The thing is that the amp has a 3rd order (18dB/octave) high pass filter set at 29Hz with a Q of 0.707 built in. Since THT cabinet is tuned to go very low so I think I should modify the high pass filter to whatever the Dayton DCS380-4 can safely work with.

Does somebody here have experience with DCS380-4? Specs say range is 20-500 Hz, so should I go for 20Hz cutoff frequency?
Or something safer, like 25Hz...?

Also should I modify the Q variable to some other value more appropriate to the combination of the Dayton DCS380-4 and Tuba HT cabinet? (I'm not sure I understand the Q parameter, but changing this to some other value or just to zero seems well documented in the amps docs)

[Bill Fitzmaurice]

THT does not require a HP filter, as it reaches maximum excursion at 22Hz, dropping below that.

[vann]

So, in other words the cabinet itself doesn't require a HP filter but I can still set one around 22Hz to protect the driver, right?

[Bill Fitzmaurice]

So, in other words the cabinet itself doesn't require a HP filter but I can still set one around 22Hz to protect the driver, right?

Protect it from what? Read my post again.

[gdougherty]

What Bill is implying is that unless you intend to use this outdoors with a high power amp, you're likely not at risk of burning it up with a 100W plate amp. You'll probably kill either the house or the plate amp first.

EDIT: well with only 350W max, maybe you could burn it up. Chances are though you'll find the output more than you need.

[Bill Fitzmaurice]

What Bill is implying is that unless you intend to use this outdoors with a high power amp, you're likely not at risk of burning it up with a 100W plate amp.

Nope. To reiterate,
THT does not require a HP filter, as it reaches maximum excursion at 22Hz, dropping below that.
High pass filters are used to protect the driver from over-excursion below the intended pass band. Below the intended pass band THT excursion does not go up, it goes down.

[gdougherty]

Ok, so limiting would still be appropriate though to prevent power input damage? I thought as you decreased frequency excursion increased to where it would more easily damage a speaker with low frequency content. Guessing that's only an issue to prevent additional power input from the low frequencies. Is that by design, or an interesting side effect of electromagnetic physics that it won't move as much at frequencies it can't reproduce?

[vann]

Thanks for taking the time to explain.

So in this case there's no need of HP filter and I can remove it altogether? On the other hand, if there's a HP filter at the lowest frequency the driver is specified (driver specs says the range is 20Hz-500Hz) -does this somewhat lower the everyday wear and tear of the driver without much of an audible difference?
My Foster plate amp already have a HP filter @29Hz + boost, it was made to work with another driver and in another cabinet. I have to tweak it anyway...

My apologies for for bothering with such questions, I've been reading much in last two years on DIY audio yet I'm aware I don't know much.

[Bill Fitzmaurice]

Thanks for taking the time to explain.

So in this case there's no need of HP filter and I can remove it altogether? On the other hand, if there's a HP filter at the lowest frequency the driver is specified (driver specs says the range is 20Hz-500Hz) -does this somewhat lower the everyday wear and tear of the driver without much of an audible difference?
My Foster plate amp already have a HP filter @29Hz + boost, it was made to work with another driver and in another cabinet. I have to tweak it anyway...

My apologies for for bothering with such questions, I've been reading much in last two years on DIY audio yet I'm aware I don't know much.

The only way a HP filter does anything with THT is if it's set to no lower than 30Hz, which makes having built a THT a bit of a waste.