Tuba 60 Hi Pass Filter Setting

[5meohd]

Manual says "The signal to the amp must be high-pass filtered at 25 to 30Hz, to prevent excessive power and/or excursion below the cab pass band."

But what slope/topology do you folks prefer? Does it change with 4 cabs? And what about 4 cabs in a 2x2 cube vs side-by-side 1x4 "horizontal" configuration?

Thanks!

Long time no speak. Hard to believe we are prepping to celebrate 10 years of our system!! It's surely a little sad that I didn't try harder

[Seth]

I have a T39. In my plans it says to use the steepest slope available in the DSP processor. In my case, that is 48dB/octave. But, as my mind tends to do, I wondered... what if my processor had a maximum slope of 24dB/octave? So, I listened to recorded music with bass that challenged the high pass frequency, content above and below the HP frequency, and found that I much preferred the sound of the 24db slope.

In your case, there's not likely to be many songs in your library that challenge the high pass frequency. But, you could give a listen anyway.

I did my best at unfolding the SketchUp model of the T60 and used that to reverse engineer and enter the dimensions into hornresp modeling software. Disclaimer; I'm not a pro at SketchUp and I'm not a Pro at using hornresp... grain of salt. In my modeling of the T60, even a 6dB slope set at only 20Hz keeps excursion less than xMax at 50 volts. I only mention it to make the point that I'm convinced the high pass settings aren't super critical with this particular design. If they were mine, I'd probably do 25Hz on a 24dB slope.

[Bill Fitzmaurice]

At 50 volts a 2x12 T60 will reach 31mm excursion at 22Hz. If you use a 25Hz high pass at 24dB you would exceed xmax if there was significant content at 22Hz. Luckily there isn't. Still prudence dictates that with a 25Hz filter you should use as much slope as you have available. If you use less slope compensate for that by moving the knee frequency higher. I would not go lower than 25Hz no matter how many cabs you have. There's nothing down there to hear, so there's no reason for it. I have yet to come across a pro-touring rig of any size that didn't high pass at 30-35Hz. They see no reason to double their sub and amp count to provide what can't be heard, and neither should you.

[5meohd]

Thank you both for the detailed responses.

We have the single driver LAB 15 builds.

Does that change much?

I will try 25Hz at 48dB and 30Hz at 24dB and see if there is a subjective preference.

We certainly listen to a lot of experimental bass music with energy down there. I've said that from the beginning. However, I've definitely transitioned from wanting to be able to "hear" at all costs, to wanting to protect the equipment from it.

[Seth]

Woo wee... thank goodness for Bill. I'd have sent you down the road for blown drivers and upset without him. Guess I've got a little brushing up to do in hornresp. I think it may be that I'm not accounting for a driver chamber. I do get similar results modeling a 30" 2x12, within a few millimeters. The numbers I quoted were a model of 28" 1xLAB15, which I assume is slightly off too.

[Fastskiguy]

Why can you go a little lower with multiple cabs? I mean….it’s not like they “know” they are in a group of, say, 4 vs all alone. Do they?

Joe

[Seth]

Mouth area.

[Bill Fitzmaurice]

With multiple cabs the low frequency sensitivity increases. It takes eight cabs to realize flat response all the way to the 26Hz low frequency corner.

[5meohd]

Thanks Bill.

BTW do you have GLL files for the T60?

Or does anyone have very trust worthy Frequency Response files that I could use to compare against?

Prepping to do ground-plane measurements May 24th-26th.

[Bill Fitzmaurice]

What's a GLL file?

[5meohd]

https://www.afmg.eu/en/gll-loudspeaker-file-format

[5meohd]

https://www.youtube.com/watch?v=pCecKOc3Mnc

https://www.youtube.com/watch?v=MU3fRV2TT-w

[eshadeol]

But what slope/topology do you folks prefer? Does it change with 4 cabs? And what about 4 cabs in a 2x2 cube vs side-by-side.

Hello, long time, no speak as well. My hunch is that ground loading 4 - 1x15" T60's "side by side" would be better because decoupling 2 of those from the ground to create the cube would be loosing the ground as a boundary load,,, but, I could be wrong?¿ ... I say this , because I tried both , and not just because it's easier to load lide by side but, because my ears are hearing better response, musically at least , when side by side... I tried 3X , once at a wedding in South Mountain Park open-air , under a vibrating metal sheet-roof ramada because , on that day it rained for the party briefly, didn't want speakers getting wet, even though they did get wet 8 years later , still working good , knock on wood.

[Bill Fitzmaurice]

There's no de-coupling of the upper cabs from the ground when stacked. Side by side or in a cube they all combine to become one.