Is there a way to quantify extension?

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Grant Bunter
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Re: Is there a way to quantify extension?

#31 Post by Grant Bunter »

Who ever said that?
That quote from Bill himself ages ago in another thread.
And he has now repeated it.
I've seen many people in this forum say something like "with the DCX use LR48". It makes sense to not go past LR24 (with the DCX) when that is the steepest slope on the Driverack series.
A high-pass effectively neuters extension...so it simply doesn't pay to build a pile of cabs without allowing them to deliver their maximum low freq potential. That's the whole point of the design. Get too aggressive with the filtering and you'd have been better off building smaller subs to begin with. In short, don't use 48 dB /oct. :cop:
Have I got this wrong? You set a HP with a slope, let's say at 40Hz. I thought the slope commenced at 40Hz. Even if it doesn't and the slope actually begins at (eg) 41 or 42Hz, you may see a reduction of (guestimate) 1dB at 40Hz and how does this mean I should have built smaller subs?
Isn't the purpose of a HP to protect the driver from over excursion at that point, not stuff with the rest of the frequency range of the cab?
Yes, use a woofer tester to take an impedance sweep of one cab. Note the freq of the spike near Fc. Then assemble the entire stack, wire them all in parallel, and sweep again. Once more, take note of the freq of the spike near Fc. It'll have shuffled down by a few Hz. That'll be how much extension you've picked up by adding cabs. Results will vary depending on model, width, and number of cabs used.
I now wondering, with a result of a few Hz at best (using the method above, thanks for detailing it), if extension is perhaps best left unmentioned.

Pumpsfast, I don't know if path length enters into the extension equation.

Thanks all...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

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Michael Ewald Hansen
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Re: Is there a way to quantify extension?

#32 Post by Michael Ewald Hansen »

Grant Bunter wrote: Have I got this wrong? You set a HP with a slope, let's say at 40Hz. I thought the slope commenced at 40Hz. Even if it doesn't and the slope actually begins at (eg) 41 or 42Hz, you may see a reduction of (guestimate) 1dB at 40Hz and how does this mean I should have built smaller subs?
If you set a LR highpass at 40hz, the slope wont start at 40 hz but will start higher depending on steepness of the slope. A LR filter is down 6db at the crossover point, so with a 24db/oct 40hz highpass the slope will start at around 45-50hz and be down 6db at 40hz.. Butterworth is down 3db at crossover, thats why you get a 3db bump at crossover point between 2 units when they sum.. LR sums without that bump.

This explains it:
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Bill Fitzmaurice
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Re: Is there a way to quantify extension?

#33 Post by Bill Fitzmaurice »

Grant Bunter wrote:
Pumpsfast, I don't know if path length enters into the extension equation.
It does, and it doesn't. Path length determines how low a cab will go. Mouth area determines how sensitive it is. To go as low as the path length allows with maximum sensitivity requires a larger system mouth area than one, or even two, cabs will provide. Four subs will get you reasonably flat response all the way to Fc, indoors. Outdoors, where you don't have boundary reinforcement, it can take as many as sixteen.

sine143
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Re: Is there a way to quantify extension?

#34 Post by sine143 »

This is why i always use bw 24 on hipasses, only 3 db down at hipass point and you are not xovering to anything so there is no sumation to avoid.
Built:
2x Tuba 30s delta12lf loaded (gone)
4x Otop12 d2512 loaded
8x t48s (18, 18, 24, 24, 30, 30) 3015lf loaded
2x AT (1 mcm, 1 gto 804)
2x SLA Pro (dayton pa6, 6 goldwood piezo loaded)
1x bastard XF208

2x OT212 (delta pro 450a loaded, eminence psd)

Grant Bunter
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Re: Is there a way to quantify extension?

#35 Post by Grant Bunter »

Michael Ewald Hansen wrote:
If you set a LR highpass at 40hz, the slope wont start at 40 hz but will start higher depending on steepness of the slope. A LR filter is down 6db at the crossover point, so with a 24db/oct 40hz highpass the slope will start at around 45-50hz and be down 6db at 40hz.. Butterworth is down 3db at crossover, thats why you get a 3db bump at crossover point between 2 units when they sum.. LR sums without that bump.

This explains it:
Excellent, thanks Michael.
I had seen that chart before, but hadn't locked into the memory bank.

Perusing it suggests to me, perhaps it could be better said "With the T39 in a group of 4 or more, HP at 40Hz with a butterworth 24 slope, and extension, you will get useable response to 40Hz".

Bill, thanks...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

Michael Murphy
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Re: Is there a way to quantify extension?

#36 Post by Michael Murphy »

Jeeze, go to smoke 1 cigarette before responding and everyone answered everything already. Grant the PA+ has a little graphical display when switching between crossover points and types, LR vs BW so it was easy for me to understand. Bruce you ready to take the plunge and try a HP @ 40 BW24, with the 50 LR24 you were using before should make a noticeable difference especially with electronic music.

Everything said pretty much solidifies my thinking on that pesky crossover point and type issue. Great thread.

Bruce Weldy
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Re: Is there a way to quantify extension?

#37 Post by Bruce Weldy »

pumpsfast wrote:Bruce you ready to take the plunge and try a HP @ 40 BW24, with the 50 LR24 you were using before
I dunno.....I might take it down to 45 if I stack 'em....tonight though, they will be split 2 and 2....so I think I'll leave it alone.
should make a noticeable difference especially with electronic music.
What's that? :cowboy:

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

Michael Murphy
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Re: Is there a way to quantify extension?

#38 Post by Michael Murphy »

Lol, you have no idea how long I pondered for the right word. Im trying to say bass enhanced music like dubstep.

Bruce Weldy
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Re: Is there a way to quantify extension?

#39 Post by Bruce Weldy »

pumpsfast wrote:Im trying to say bass enhanced music like dubstep.

What's that? :cowboy:

We do have something around here called "Bubstep".....that's when Bubba gets drunk and starts staggering around the dance floor.

Is that the same thing? You got someone named Dubba that does that too?

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

Bruce Weldy
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Re: Is there a way to quantify extension?

#40 Post by Bruce Weldy »

pumpsfast wrote:Lol, you have no idea how long I pondered for the right word. Im trying to say bass enhanced music like dubstep.
Truth is....until I came on this forum a few years ago, I had never heard of dubstep. It's just not that big down here. I'm sure it exists, but there is so much live music available in this area that DJs are pretty much doing their business at weddings and off-nights at the dancehalls.

Being sandwiched between San Antonio and Austin, even our little town has at least 5 venues that offer live music every night of the week. Everything from to Rock and Blues to Country, Americana, and acoustic.

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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escapemcp
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Re: Is there a way to quantify extension?

#41 Post by escapemcp »

Don't stop... very much enjoying this thread

+1 on using BW for the lows... as long as that's OK with Bill :feedback:

Michael Murphy
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Re: Is there a way to quantify extension?

#42 Post by Michael Murphy »

That's what I ran up my system with yesterday, but opted for 42.5hz HP as its only 2 coupled, sounded great with the new amp. And I flogged it for hours.

Rich4349
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Re: Is there a way to quantify extension?

#43 Post by Rich4349 »

Sooo, there could be a chart developed that would cross reference safe frequency cutoffs (for a given speaker) at various voltages, so one could use say a t-39 as a home stereo subwoofer down to lower frequencies, say 25 hz at 10 volts (arbitrary example).
2 DR250s, 2 27" Lab15 T-60s, 2 30" Neo Titan 39s, 1 Autotuba...and looking for more!

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Bill Fitzmaurice
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Re: Is there a way to quantify extension?

#44 Post by Bill Fitzmaurice »

Rich4349 wrote:Sooo, there could be a chart developed that would cross reference safe frequency cutoffs (for a given speaker) at various voltages, so one could use say a t-39 as a home stereo subwoofer down to lower frequencies, say 25 hz at 10 volts (arbitrary example).
Not by me. If you need 25Hz, use a 25Hz capable cab. I'm not going to encourage using cabs below their design limit at reduced power, because that's the kind of advise that invariably results in blown drivers when someone forgets to reset the system when they want to turn it up.

Rich4349
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Re: Is there a way to quantify extension?

#45 Post by Rich4349 »

Fair enough.

Next target to be shot:

If horn length dictates extension, and mouth area dictates the volume AT that frequency...how badly would it work to build a plain old hollow tube of plywood (for argument's sake say 8 feet long) that is 27x30 in cross section, and with speaker gasket, join it up to the mouth of a t60? What would the net effect be?
2 DR250s, 2 27" Lab15 T-60s, 2 30" Neo Titan 39s, 1 Autotuba...and looking for more!

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