BillFitzmaurice.info

We know that horn subs in groups/herds will get extension below their high pass setting.

I take it there would be a number of factors affecting the extension that can be achieved.
For example, I assume that a LR48 HP filter will exhibit less extension than a LR24 HP filter.
Since LR24 is the value of filter on the Driverack series, and I can achieve the same setting with the DCX, if I get more extension using that setting, and still maintain my safety factor, that may be very handy for some gigs. However, if it's only going to net me a few Hz, it would hardly seem worthwhile.

I'm sure I could measure extension with my RTA mike, running sine waves below my HP setting and measuring SPL compared to frequencies above my HP, but I'm wondering if there is a theoretical way to calculate extension.

This question has arisen since my first rap/DJ gig over the weekend, where I, and the artists, were impressed at the T39's reproduction of bass drops.
I didn't measure the content of the material being played, but no one said, in essence "I couldn't hear all the content I know is there when I listen on my cans".
That has made me wonder if I was actually covering lower content due to extension...

Here's what I know. LR filters (either 24 or 48) are designed to be -6 dB at the crossover frequency. Dropping at their respective slope thereafter. Butter-worth are -3dB at said frequency, with above mentioned slope. So if you want the max extension and have a Bheringer that supports Butter-worth, go with that.

Background
People consider usable extension to be -6 to -10 dB depending on who you talk to. If you stack 4 of Bill's "v-plateable" designs we have learned that it gives us roughly 5 Hz extension. On the other hand it takes 8 T60's inside in order to make they lower from 25 Hz f3 to 22 Hz. AFAIK this is due to their oblong design. T39's still have basically flat output to 38 Hz in herds (4 or more) thus I'd say you were getting audible notes down to there.

IF you want to experiment, I recommend changing your cutoff to Butterworth 48 (for DCX, 24 for DBX if it can do butterworth) and lower your limiter by a little bit for safety if you end up using 24 dB slopes

Reasoning: it is these borderline frequencies that will drive you into overexcursion and the less steep the slope the more likely that the pesky 35 Hz fully redlined bass that they "accidentally" drop doesn't pop your woofers. I haven't modeled the driver excursion but I'm sure there is a way to do it (that's how bill gets his voltage limits) based on how many T39's you have stacked.

Grant Bunter wrote:
I didn't measure the content of the material being played...

If you have some example material I would be more than happy to run it through my freq analyzer and give you some pictures of what the output looks like (visually) with and without a 24 dB filter at 40 Hz.

MissileCrisis wrote: I haven't modeled the driver excursion but I'm sure there is a way to do it (that's how bill gets his voltage limits) based on how many T39's you have stacked.

Excursion varies little with added cabs, but they do go lower as more are added, that's why there's a different HP frequency for more than two.

Bill Fitzmaurice wrote:Excursion varies little with added cabs, but they do go lower as more are added, that's why there's a different HP frequency for more than two.

Ok, this seems to be the perfect time to ask about something that has puzzled me from the beginning.....(concerning using a lower high pass based on increased number of cabs)....

- The limit on a speaker is fixed. (based excursion limits and power)

- It doesn't know that it is snuggled up to another speaker or two...or eight.

If I lower my high pass below the recommended frequency and apply the same voltage, I'm gonna' blow it.

So, when I see that I can lower my high pass on my T39s from 45 to 40 just because I stack 4 of them together, how do I keep from blowing them if I apply the same power?

If I lower the high pass, do I not need to limit at a lower voltage to keep from blowing 'em up?

Bruce Weldy wrote:
So, when I see that I can lower my high pass on my T39s from 45 to 40 just because I stack 4 of them together, how do I keep from blowing them if I apply the same power?

Because of this:
http://billfitzmaurice.info/forum/viewt ... f=10&t=398

MissileCrisis wrote: If you stack 4 of Bill's "v-plateable" designs we have learned that it gives us roughly 5 Hz extension.

I haven't ever seen this written before. If I had, I probably wouldn't have posed the question.
Can you point me to somewhere where you have seen this in the forum?

MissileCrisis wrote:it is these borderline frequencies that will drive you into overexcursion

Fully understood and also part of why I posed the question.

MissileCrisis wrote:If you have some example material I would be more than happy to run it through my freq analyzer and give you some pictures of what the output looks like (visually) with and without a 24 dB filter at 40 Hz.

Thanks heaps for your offer! All the material played that night was custom mixes (which I don't have access to), so I don't know if content was also manipulated.
However, one song for the main act was (based on) "Feels so close". The vocal line had been dropped and Bam Bam was rapping over it.

Bruce Weldy wrote:If I lower my high pass below the recommended frequency and apply the same voltage, I'm gonna' blow it.

Bruce, I know you HP at 50Hz, for increased safety factor. While it's handy to know the where's and why's, I've always thought, since coming here, that if Bill says you can HP 4 cabs at 40Hz (in the case of T39's), that setting will also include an inherent safety factor.
You could safely lower your HP based on that, but if you don't feel your missing anything doing what you're doing, probably best leaving well enough alone.

Bill Fitzmaurice wrote:Excursion varies little with added cabs, but they do go lower as more are added, that's why there's a different HP frequency for more than two.

At what point does this stop?
Following this line of thinking suggests that there could be a lower HP again for 8 cabs, but as per the plans, the lower HP is stated "for 4 cabs or more".

Thanks all so far...

Grant Bunter wrote: At what point does this stop?

Around 8 to 12 cabs

Following this line of thinking suggests that there could be a lower HP again for 8 cabs, but as per the plans, the lower HP is stated "for 4 cabs or more".

Most of the change occurs with four cabs, beyond that it's not enough to overcome the excursion issue.

Bill Fitzmaurice wrote:

Bruce Weldy wrote:
So, when I see that I can lower my high pass on my T39s from 45 to 40 just because I stack 4 of them together, how do I keep from blowing them if I apply the same power?

Because of this:
http://billfitzmaurice.info/forum/viewt ... f=10&t=398

I've read that page many times in the last three years....I do understand how they can gain extension by being clustered in multiples. But, it still doesn't answer the question of limiting.

If the limit of my cab (according to my plans) is 60 volts at 45hz highpass, will not lowering the highpass to 40hz with the same 60 volts put me outside the safe limit of the cab as you have stated it?

The characteristics of the driver in those speakers don't change just because they are stacked - so if it isn't safe for a single speaker to run lower than 45 hz with 60 volts, how can it be so just by stacking them?

That's what I've always been fuzzy on.

As Grant stated, I've always highpassed at 50hz in order to give me a little more breathing room on excursion.....this is more of an question of theory than application for me.

Oh I'm starting to get it, 4 cabs (t39) excursion wise would be ok to run to 40 Hz not because having 4 reduces the stress on the driver but rather that it is a point at which it can produce those (40-45 Hz) efficiently and requiring less EQ to match the level of the rest of the passband, thus avoiding the pitfall of overexcursion.

MissileCrisis wrote:Oh I'm starting to get it, 4 cabs (t39) excursion wise would be ok to run to 40 Hz not because having 4 reduces the stress on the driver but rather that it is a point at which it can produce those (40-45 Hz) efficiently and requiring less EQ to match the level of the rest of the passband, thus avoiding the pitfall of overexcursion.

But that still doesn't address the additional stress on the driver by lowering the highpass and keeping the same voltage.

Now, I could see that keeping the highpass the same and adding cabs will produce more of the rolled-off bass below the high pass as it declines down the slope.....

+1 what bruce said.

Bruce and MC
Perhaps I'm wrong, but I wonder if part of the answer is coupling and increased mouth area.
Both of those would lead to decreased driver stress with the cabs in groups...

MissileCrisis wrote:Oh I'm starting to get it, 4 cabs (t39) excursion wise would be ok to run to 40 Hz not because having 4 reduces the stress on the driver but rather that it is a point at which it can produce those (40-45 Hz) efficiently and requiring less EQ to match the level of the rest of the passband, thus avoiding the pitfall of overexcursion.

+1.

Ok.....I give up.


Not something that I really just have to know....just curiosity.

Sorry to have hijacked the thread.