Age old question: 15" or 12" for THT?

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shawn_g
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Age old question: 15" or 12" for THT?

#1 Post by shawn_g » Tue Apr 19, 2022 12:38 pm

I recently completed construction on my new family room/home theater (roughly 30'x18') and always told myself I'd build two THTLP's when it was done. For the time being, I have two max width, Lab 12 loaded T39's in the room and they've been great, but obviously not designed for home theater and drop off quickly below 30-35hz. For more context, in my old living room, I had a dual loaded table tuba and a dual loaded T18 (time delayed to match the TT) and had always wanted more output but didn't have the space.

Now I'm conflicted on 12" vs 15" for the THTLP's. The minimum width 12" version would be nice appearance-wise, but I don't mind going bigger if it's a significant difference in output. My goal is to get it as flat as I can down to 20hz and I'll be using a Mini-DSP for EQ/crossover duty. I'll mostly be listening at sane volume levels, but I still want to be able to scare unsuspecting victims and annoy my wife when needed. The T39's have been great output-wise in the 35hz+ region, so whatever gets me close to that level of output but also includes the 20hz region would be preferred. Will the 12" version suffice or will I have regrets if I don't use a 15" driver? Thanks.

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Bill Fitzmaurice
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Re: Age old question: 15" or 12" for THT?

#2 Post by Bill Fitzmaurice » Tue Apr 19, 2022 1:05 pm

It's not the size of the driver that matters, it's the mouth area of the horn that determines how loud a horn is at the lowest frequencies. When you say 'minimum width' you're also saying 'minimum low frequency output, so you should approach it from the standpoint not of how narrow you can make it but from the standpoint of how wide you can tolerate. Whether it's loaded with a twelve or fifteen is a matter of which is specified for the width of the cab.

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shawn_g
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Re: Age old question: 15" or 12" for THT?

#3 Post by shawn_g » Tue Apr 19, 2022 1:44 pm

Thanks for the info, that make sense. I'll do some measuring tonight and plan to go as wide as I can get away with.

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Re: Age old question: 15" or 12" for THT?

#4 Post by wuzzzer » Wed Apr 20, 2022 10:05 pm

I have 15s in my 24x36x36 THTs in a huge open basement. Here's my before and after sweeps in REW:
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Klipsch + dual THTs= :shock:

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Re: Age old question: 15" or 12" for THT?

#5 Post by wuzzzer » Wed Apr 20, 2022 10:07 pm

The reddish line was the initial sweep, the purplish line was after mild EQ and adding a steep 16Hz high pass filter. These things are absolutely nuts.
Klipsch + dual THTs= :shock:

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Re: Age old question: 15" or 12" for THT?

#6 Post by shawn_g » Mon Apr 25, 2022 10:15 am

wuzzzer wrote:
Wed Apr 20, 2022 10:05 pm
I have 15s in my 24x36x36 THTs in a huge open basement. Here's my before and after sweeps in REW:
That purple line looks reeaaallll nice. The T39's I've been using are nearly flat down to 30hz, but they drop like a rock below that. I can get my Table Tuba down in the low 20's, but it's just not very loud when it gets that low.

24" wide is likely what I'll go with, but I need to measure my space and make sure it's a good fit. The Dayton Ultimax's are the same price as the RSS390 HF-4, so I'll probably just go with the Ultimax even though it's overkill. If only the price of plywood would come down.

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Re: Age old question: 15" or 12" for THT?

#7 Post by JensToft91 » Mon May 09, 2022 3:15 am

Shawn. I have 20 Hz extension on my 12" thtlp aswell. Minimum width.
With my tiny 50w board amp, I can sweep about 110 dB at 20 Hz.

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Re: Age old question: 15" or 12" for THT?

#8 Post by JensToft91 » Mon May 09, 2022 3:17 am

Response is with audyssey dynamic EQ and minidsp correction, hence the falling response. (Dynamic EQ boost lows)
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shawn_g
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Re: Age old question: 15" or 12" for THT?

#9 Post by shawn_g » Tue May 10, 2022 8:10 am

JensToft91 wrote:
Mon May 09, 2022 3:15 am
Shawn. I have 20 Hz extension on my 12" thtlp aswell. Minimum width.
With my tiny 50w board amp, I can sweep about 110 dB at 20 Hz.
Oh nice, that looks great. I haven't purchased anything yet because I haven't had much free time (my kids play baseball and soccer). I was kind of set on going 15", but your graph is making me question that.

On a side note, I noticed last night that the T39's I've been using caused a crack on a drywall seam right where they're positioned. So maybe the 12" THT is the better choice for the sake of my house :lol:

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