Tony Gee did it, it's on Data-bass...should I do it?
 

Well, the "Serious Sub" looks like a great option to me for a new subwoofer build. Granted it would need a lot of power and EQ but I was wondering what everyone thought about going the route of using a 21" PA driver for a subwoofer.

I like the idea of going this route since the cone doesn't have to move as far for the same output and will give a much more effortless sound to the bass frequencies.

I don't see many builds like this so I dont want to rush into it. Especially considering the many Tapped Horn designs out there that are also worth considering.

Different tradeoffs that I can recognize right away are:

Tapped horn: Limited extension, large enclosure

Sealed 21" PA: limited SPL compared to TH, Massive power needs, needs EQ.

Any input into the different approaches would be appreciated.

Thanks.

oh, it's been done
and also by members here

the only problem I see is the high cost of these big monster woofers

A large TH can reduce excursion considerably, and can extend in to the 10 Hz range with a fraction of the power and driver expense of a good 21" driver in a sealed enclosure.
It really comes down to budget, tolerable cabinet size, and desired SPL at X low frequency.
I find a pair of sealed moderate Xmax 12" adequate for my SPL needs down to the low teens in my home, if I wanted more output would simply add more.
Since I find even short exposure to much over 100 dB at 20 Hz to make me feel sick for a while, I have no desire for more LF output than I have.

best advice is to do some enclosure modeling to get a starting point, seeing as your "easily recognizable" trade-offs are not set it stone in either enclosure. With each enclosure type, you can manipulate the evil triangle known as Hoffmans Iron law. A tapped horn need not have a large enclosure, but if you make it too small sensitivity and low end extension may suffer. Each one has tradeoffs within themselves that you can easily see with enclosure modeling.

Which actual models have you produced/investigated?

A few observations about the serious sub design:

- Weight of each sub is about 265lb including driver. That's pretty darn heavy. Take any sub design and put that much mass into it and it will sound better.

- Overall outer dim's seem to be about 25" x 23" X 20", which is pretty compact and smaller than many ported 15's people build. 110L internal sealed seems a bit low for this driver IMHO.

- There is a bunch of parametric EQ being done, to flatten room response and boost the low end. IMHO this induces pretty noticeable phasing issues. When given the choice between a bit of minor uneven frequency response (+/- 3-5db in room) vs. eq induced phasing issues, I would rather have the minor uneven response because it will sound more natural and clear than messed up phase. Phase issues in the upper bass and midbass are VERY noticeable in your dynamics/tranisent response, say from 50hz to 300hz.

- I would rather have a ported box (with a correctly designed port) than sealed plus EQ, even though it would probably end up much larger with this woofer.

- The Sd is equivalent to two 15" woofers. Xmax of the PD is about 10.5mm, so a single long throw (21mm+ xmax) 15's could match it in output.

- I can't imagine the cone is particulary rigid. Do you prefer your distortion from the cone flexing (21" sub) or from the motor/spider/surround movement (long throw 15")? The industry & market has been saying for quite some time that long throw smaller drivers are much more practical, and can sound quite good if done properly.

- He may have a point about the accoustic coupling of the large woofer to the surrounding air. You get a sensitivity boost by stacking multiple (usually) horn subs together to get better coupling, so I would imagine a single large driver does better than a long throw smaller driver in that respect.

- IMHO the mdf, lead, and bracing is not very efficient for the weight and complicated build. 1" thick birch plywood with 1/8" bitumen on the inside would probably be as stiff and damp while being less than half the weight and much easier to build. The bracing is overly complex, two 3" slats (no holes) along each wall with 2" cross braces would be just as effective and much simpler to build.

Once the box gets small enough, the tapped horn will have the same sensitivity and frequency response as a ported design of the same size. Always model your driver from a tapped horn design in a ported design of the same volume.

As tapped horns get larger they can trade low frequency extension for sensitivity and output while maintaining a relatively flat frequency response.

Whereas ported designs mostly improve their low frequency extension (a bandwidth increase), and drop in sensitivity.

Hi,

You'd get more choice and better value using 2x18"ers.

2x21"ers are really about bragging rights domestically.

What you actually need size wise is again another matter.

2xLAB12's in 100L each tuned to 20Hz, 500W each,
is more than enough for nearly all domestic systems.

rgds, sreten.

Some one else commented to me the other day that 15" would be more than enough as well.

I have yet to build anything as I keep reading and studying the books I have on audio design etc.

I think my problem is that I don't know what compromises I like best.

I am limited by size and the one that I can fit in my room is the T6 tapped horn that only really reaches about 28hz which is still enough for the majority of movies but the ones that go lower I think I will be missing something as even with my current sub that reaches 20hz, I feel like there are alot of times that there is content that I am not getting like in "How to Train Your Dragon" and other movies.

A dual 15" in a sealed cab will most likely meet all my needs but like what was mentioned earlier, the EQ can cause phasing issues.

an LLT is too large for me for the most part as well and can suffer from chuffing if not done right.

I currently run a PC12-NSD and I have thought about doing another ported cylinder for the easy sealed sub with dual 15" or just going to a 15" tuned lower to about 15-17hz. However, my wife would like me to go to something a little more eye friendly...So then I have looked at sealed boxes and ported boxes. But to really get a little bit lower of extension in a ported sub the boox usually ended up pretty large. So I then looked at PR designs and I dont like the extra expense...

GAH! audio is such a pain sometimes....maybe i'll just get a divorce ahah!

When I ran my recent project of a pair of dayton HO 15's as sealed (plugged the ports) with big EQ, they ran out of headroom/xmax @ 20-25hz in a moderately sized living room watching movies. For dedicated HT use I would want more, so a ported design tuned to around 18hz or so.

To get below 40hz with a tapped horn at high sensitivity (98-100 db/w/m/2pi horn resp sim), it seems that you get into increasingly huge boxes. An efficient 20hz tapped horn is going to be HUGE, if it is small it will have have the same sensitivity of a ported box of the same size.

If you are willing to compromise, there is tons of bass presence (physical shake) in the 30-40hz range, so if your response is strong there it can pass as deep bass for the casual observer. Several of the larger diy tapped horns acheive that well.

I know people LOVE tapped horns here, but I think a well designed and constructed ported box is more practical and effective for all around home music and HT use.

What is your room size and your current equipment. What sort of overall listening levels in db?