What's to chat about?

[Bruce Weldy]

Envisioning the cabs, a 24x24x48 cab sounds a bit easier to move than a 20x30x39

Yikes! No.....the T39 is extremely easy to move. Rolls easy and is tall enough to roll without having to bend over.....I'm 6'1" and it's no problem. T48s are pretty danged big. A buddy of mine built some - I was amazed at how much bigger they are than the T39.

If you really need the extra 5hz, fine. But, if you are mixing live sound - there is no need for it.

[Seth]

Yikes! No.....the T39 is extremely easy to move. Rolls easy and is tall enough to roll without having to bend over.....I'm 6'1" and it's no problem. T48s are pretty danged big. A buddy of mine built some - I was amazed at how much bigger they are than the T39.

If you really need the extra 5hz, fine. But, if you are mixing live sound - there is no need for it.

I see your cabs aren't 30 wide. What is the width of your friends T48's? It's the footprint that "seems" more manageable. Although, neither occur as unmanageable.

[Seth]

... and really, my main inquiry in the whole thing is; will a 24" wide T48 loaded with Delta 12LFA have enough of an edge in sensitivity when compared to a 30" wide T39, to make the size increase worth it?

Is there likely to be a 2-3dB average advantage with the T48 in these widths? Or, closer to 1dB? Or, a wash and the only benefit is the additional extension?

[Bill Fitzmaurice]

T48 isn't inherently higher in sensitivity than T39, it just goes lower.

[Seth]

Thank you Bill. That's what I assumed.

I've noticed the widths of the cabs have a lot to do with average sensitivity, like the graph below shows for the T39.



My question isn't so much one cab design compared to the other, so much as it is "design @ width" compared to "design @ width".

I haven't seen a chart for the 24" T48 option, is it safe to assume that your statement also covers the specific width/cab combos I mentioned too?

[Bill Fitzmaurice]

Horn length determines low frequency extension, horn mouth area determines sensitivity. If you only increase length you only lower response. If you only increase mouth area you only increase sensitivity. To do both you need to go longer and increase mouth area.

[Bruce Weldy]

Yikes! No.....the T39 is extremely easy to move. Rolls easy and is tall enough to roll without having to bend over.....I'm 6'1" and it's no problem. T48s are pretty danged big. A buddy of mine built some - I was amazed at how much bigger they are than the T39.

If you really need the extra 5hz, fine. But, if you are mixing live sound - there is no need for it.

I see your cabs aren't 30 wide. What is the width of your friends T48's? It's the footprint that "seems" more manageable. Although, neither occur as unmanageable.

4 of mine are 25 inches and my friends were 24 I think. It's not just the additional height, but the extra depth that makes 'em quite a bit bigger. I considered those when I was building, but I'm glad I went with the T39. For live sound, they do everything I've ever needed.

[Seth]

Horn length determines low frequency extension, horn mouth area determines sensitivity. If you only increase length you only lower response. If you only increase mouth area you only increase sensitivity. To do both you need to go longer and increase mouth area.

The mouth area for the two options mathed out...

30" T39 - 5 Ft²
24" T48 - 4.9 Ft²
30" T39 V coupled - 5.65 Ft² each (Half of the total combined mouth area of 2)
24" T48 V coupled - 5.54 Ft² each

Darn near a wash. Thanks for filling in the (my) blanks Bill


Now I just have to decide how important the extra extension is. For my personal listening it's fairly important. But it's not too important for my PA needs. Hmmm.

[Seth]

4 of mine are 25 inches and my friends were 24 I think. It's not just the additional height, but the extra depth that makes 'em quite a bit bigger. I considered those when I was building, but I'm glad I went with the T39. For live sound, they do everything I've ever needed.

Thanks for sharing your experience Bruce. I appreciate it quite a bit

[Seth]

Apart from the above that was mentioned, one thing I do is run aux fed subs. My main mixer outs go to my driverack and only go to my tops. Any channel I want in the subs I set up an aux out and that goes to a third input on my driverack (dbx360) and that then goes to my subs. That allows me to pick and choose which channels gets sub support - usually kick, bass, keys, floor tom and break music. Where this differs from a normal highpass is that a mixers highpass is usually 12 db/octave where by aux fed subs the slope is infinite, if I don't put a channel in the sub aux, nothing from that channel will every make it to the subs. The other way, even if you highpass every channel, with 14 open mics on stage, you will be getting bass from stagewash into the subs as a highpass is a slope, not a cliff.

This also allows me to adjust how much of that channel to feed the subs, if a bass has too much low end I can dial back that channel in the sub aux out rather than use an eq on that channel. I can also adjust the subs overall output from the mixer rather than from the driverack which is useful when you are playing in different venues with different setups.
AuxFedMainGraphicLayout.jpg

So, I've rolled this around and digested it quite a bit. I've read about aux fed subs a bunch of times before, but you put it in a way that's a little different than I've heard before and I like it. I can better relate to it.

What I'm hearing from you is, it's a great way to eliminate unneeded LF content that could otherwise muddy up the low end from the subs altogether.

What I'd read in the past... or understood from what I read in the past, is it's a great way to add more thump as needed. Bass on demand.

My mixer (M32C) has a Main LR mix Bus and a separate Mono/Center bus and can do exactly what you're saying without using up an aux bus. And I can have the levels on the "aux" channel be dependent on the level in the main mix and maintain the integrity of the balance of harmonics between the subs and tops as the levels are adjusted throughout the show.

One thing I had worried about is, I like to record the shows I do. I'd worried it may effect the recordings. But, on further thought, if I just record LR out it will have an intact signal being as it's prior to any outboard EQ and Crossovers.

I'm for sure going to give this strategy a go next opportunity I have. Thanks again CO

[CoronaOperator]

I'm for sure going to give this strategy a go next opportunity I have.

See if you like it, for the smaller loud stages I do it really cleans up the low end so it is worth the extra config for me and I can adjust the sub level from the mixer too. If you mix using subgroups then you might want to ditch the idea (VCA's are okay) as when you adjust the subgroup fader/compression/gate/etc the change won't go to the aux unless you route that subgroup there instead of the channel fader. In which case if you route the whole drum subgroup then that kind of defeats the purpose of using aux fed subs to begin with. I guess it still keeps the low end out of the vocal and guitar mics.

https://www.youtube.com/watch?v=JHNzXSGrE7Y I think this video should walk you through the m32 setup for aux subs.

[Seth]

Horn length determines low frequency extension, horn mouth area determines sensitivity. If you only increase length you only lower response. If you only increase mouth area you only increase sensitivity. To do both you need to go longer and increase mouth area.

I know you've thought of nearly everything and you've done an absolutely fabulous job with all your plans... but I gotta ask. Is there any more sensitivity to be had in a T48 loaded with a 12 by going even wider than the max stated 24"? Would a 30" wide version be a complete waste of time and money if my goal is to get nearly every bit of sensitivity there is to gain?

[Tom Smit]

I've looked at several old plans and originally, the max width for a 12" was 19". These were top-load cabs. Front load cabs appear to always have been limited to 24", which also happens to make the best use of a 48" wide plywood sheet. Now, if your asking about a 15", you can go as wide as 36".

[Seth]

I've looked at several old plans and originally, the max width for a 12" was 19". These were top-load cabs. Front load cabs appear to always have been limited to 24", which also happens to make the best use of a 48" wide plywood sheet. Now, if your asking about a 15", you can go as wide as 36".

Thanks Tom. I'm inquiring specifically about the 12" loaded cabs.

I've chosen to use the lower powered Delta 12LFA drivers and start with a foursome of cabinets. I'd like to explore what options are available to squeeze every bit of sensitivity out of them, then weigh all the options before making my final cab choice.

In the current plans, 15" is the minimum width for both, the T39 and the T48. The T39 goes up to 30"... well, 28" in the new plans. I'm just curious if the T48 could make use of that width and pick up a couple dB average too.

I don't know, perhaps it's not any sort of coincidence the max widths currently stated in the plans equate to essentially a 5 Ft² mouth area. Maybe that's a thing? Maybe there's some reason it can't/wont be able to take advantage of more? I'm not curous enough to need to know WHY it's possible or not possible to squeeze a couple more dB out.

Don't need a lengthy explanation.

Just a statement like "there's no gain to be had going wider than X".

[Bill Fitzmaurice]

I don't know, perhaps it's not any sort of coincidence the max widths currently stated in the plans equate to essentially a 5 Ft² mouth area. Maybe that's a thing?

It's not. As the cab is made wider the mouth grows larger, but so does the throat. If the throat is too large you lose sensitivity at the upper end of the horn pass band. The maximum width is determined by that factor.