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post #1 of 16 Old 10-14-15, 11:10 PM Thread Starter
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Help me decide path...

Hi all,
I've been doing some research lately, trying to figure out which path to take.

I'd like to build a custom subwoofer box. I've done it many times for car audio, but not for home theater.
I'm trying to figure out if I:
- need to get a subwoofer driver made for home theater or if I can use any, off the shelf car audio subs available.
- What kind of amplifier could/should I use? A plate amplifier to screw onto the sub box or a component amplifier such as the Behringer EUROPOWER EPX2800?

Also, how low should I tune a box (Hz) to get a really effective/flat response down to about 20 Hz. How does the port tuning affect frequency extension.

I'm not after SPL, like it was in car audio. I want smooth, clean, accurate and low bass response. No need to move the house off the foundation.

Size of the room, at this point, doesn't matter. If I want more bass I'll simply build another.

I've looked at many pre-made available subs (Polk, Klipsch, etc.), but looking to build my own.
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post #2 of 16 Old 10-15-15, 12:52 AM
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Re: Help me decide path...

This is a heavily loaded question...

How big a box are you willing to deal with? And in turn, what size driver do you want? Stereo Integrity has a screamin' deal on the HT18 18" subwoofer right now. Not exactly "off the shelf", but do you have to be able to touch the shelf with your own fingers?
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post #3 of 16 Old 10-15-15, 01:48 AM Thread Starter
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Arrow Re: Help me decide path...

OK, yeah it's a loaded question, but very open to options.
The Stereo Integrity HT18 18" does look interesting, but only half the goal; what to use to power it?

I was looking at a bare minimum of 12", perhaps a 15", but 18" is still doable.
Box size, I'd like to keep it under 8 cu. ft. Perhaps a single 18" or 2x 12"s.

Budget: Well, depends.
Plate amps for each sub, ~150-200 each
Component stereo amp able to drive more than one sub (like the Behringer): up to ~$350
Drivers: up to $200.00 each

I figure that for $500-1000 I could build something better than what's available in-store, but we'll see what kind of plan I can come up with.

No "wife" factors involved. Aesthetics, I could build it or them into a TV stand, end tables, stand-alone, etc.

The rest of my system is as follows:
Receiver: Pioneer VSX-1120-K
Fronts: Polk RTi10's
Center: Polk CSi3
Surround: Polk RTi6's
Surround Back: Polk RTi4's
Home theater PC and basic blu-ray player.

It sounds awesome, but it simply lacks the really low bass below 40Hz.

Car audio seems easier at this point. Maybe different when I learn more about home theater and room boundaries, modes, etc.

Thanx for the help and don't be shy about suggestions.
The road is, perhaps, more fun than the destination.
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post #4 of 16 Old 10-15-15, 01:03 PM Thread Starter
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Re: Help me decide path...

To the moderators, could you please move this post.

I just noticed that I posted this in the wrong section "Subwoofer Amps | High Pass Filters".
It should be in the "Ported Subwoofer Build Projects" section.
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post #5 of 16 Old 10-15-15, 08:34 PM
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Re: Help me decide path...

Driver selection is going to be the determining factor for most of the rest of the build. The T/S parameters are going to provide guidelines for how you should design a box, and how best to provide power.

For instance, if you're in the $150-$200 range for a plate amp you're looking at amps generally rated for 200-300 Watts into a single channel at 4Ω. (I'm sure there are exceptions... but 30 seconds of research gave me that ballpark figure) A standalone amp (like the Behringer, or a Crown/QSC/Crest etc) can deliver much more power for the price... Crown XLS 1500's will put 525W x 2 into 4Ω, and for about $200.

The plate amps will usually have some useful signal processing on board, like variable crossovers, level control, polarity control, and maybe a bass boost option. Many pro amps will have similar options, minus a bass boost.

So the first question to answer is this: How much power do you need? That's going to be answered by the driver you choose.

The issues of room boundaries and modes and such won't be avoided by using a car subwoofer, as they are the result of physical properties of air and the propagation of waves. As far as I'm concerned, you can build a perfectly acceptable HT sub using automotive drivers... all it will do is alter box volume/dimensions, port parameters, etc. And there's not really general rule to follow in comparing one breed of speakers to the other because in both, the options are equally vast and varied.

Read up on T/S parameters and you'll start to see how specific numbers manifest in a driver's performance, and how that affects its application. Here's an enlightening read about Qts:

http://www.loudspeakersplus.com/choo...t_speaker.html

That's not the only parameter that matters, but it's good information.

The conceptual approach to building a HT sub isn't inherently different than a car sub... so don't throw out the knowledge you already have just because it's tagged differently. What's your process for selecting a car sub?
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post #6 of 16 Old 10-16-15, 08:53 PM Thread Starter
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Re: Help me decide path...

Just as an example, I'll suggest the JL Audio 12W0v3-4.

Also, back when I built the boxes for cars, I did the calculations with pencil, paper and a calculator. Guess how old I am?

Anyway, I'm looking at this speaker for a number of reasons (feel free to correct me if I'm wrong).
It has the following:
Free Air Resonance (Fs) 28.43 Hz
Xmax: 11.4mm
85.64 dBSPL (would like this higher, but it is what it is)

The ad states the following:
Ported Enclosure Specifications:
  • Wall Thickness 0.75 in / 19 mm
  • Front Baffle Thickness 0.75 in / 19 mm
  • Volume (net int.) 1.75 cu ft / 49.6 L
  • External Width (W) 17.5 in / 445 mm
  • External Height (H) 14.75 in / 375 mm
  • External Depth (D) 16.25 in / 413 mm
  • Internal Port Diameter (ID) 3 in / 76 mm
  • Port Length (L) 14 in / 356 mm
  • Tune to 26 Hz
  • F3 30.8 Hz

I've entered the data available (T/S parameters) into WinISD and simply cannot come up with the same box specs as the manufacturer listed.

Mind you, back in the day of pencil and paper, I didn't know what any graphs looked like. Maybe I'll find some of my old documents and see what happens in the graphs.

Let me know what you think or have other suggestions/ideas.
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post #7 of 16 Old 10-16-15, 09:53 PM
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I have to say, my lifelong friend owns 2 of the states most highly regarded car audio stores and JL drivers are special. Having said that though, unless I'm all wet, drivers have a hard time playing much lower than their fs. Not that they can't(or that it's the only consideration)but it's hard for them and easier to damage them. Also a custom built sub with an f3 of 30hz is just too high. Maybe if it were sealed and the room were the right size, room gain would help keep it flat to about 23hz. I think tuning it much below its fs is just asking to unload it and bottom it. A lot. Especially with 11mm of X max. IMO, car drivers are built to hit around 30hz(give or take), and that's great, but in s theater setting, that would be annoying and boomy. Exactly what you said you don't want. 30hz buzzing bass takes less excursion than 20hz and below. If I'm way off, I'd be glad to be corrected, but I think you want a different driver, and a lower tune. I've seen lots of spectrographs of modern movies with content down to single-hz. As you know from experience, you'll want to do it right. Just .02
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post #8 of 16 Old 10-16-15, 10:19 PM
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Re: Help me decide path...

Quote:
ziggy1971 wrote: View Post
Just as an example, I'll suggest the JL Audio 12W0v3-4.

Also, back when I built the boxes for cars, I did the calculations with pencil, paper and a calculator. Guess how old I am?

Anyway, I'm looking at this speaker for a number of reasons (feel free to correct me if I'm wrong).
It has the following:
Free Air Resonance (Fs) 28.43 Hz
Xmax: 11.4mm
85.64 dBSPL (would like this higher, but it is what it is)

The ad states the following:
Ported Enclosure Specifications:
  • Wall Thickness 0.75 in / 19 mm
  • Front Baffle Thickness 0.75 in / 19 mm
  • Volume (net int.) 1.75 cu ft / 49.6 L
  • External Width (W) 17.5 in / 445 mm
  • External Height (H) 14.75 in / 375 mm
  • External Depth (D) 16.25 in / 413 mm
  • Internal Port Diameter (ID) 3 in / 76 mm
  • Port Length (L) 14 in / 356 mm
  • Tune to 26 Hz
  • F3 30.8 Hz

I've entered the data available (T/S parameters) into WinISD and simply cannot come up with the same box specs as the manufacturer listed.

Mind you, back in the day of pencil and paper, I didn't know what any graphs looked like. Maybe I'll find some of my old documents and see what happens in the graphs.

Let me know what you think or have other suggestions/ideas.
Back in the old days, you did not have the plots and you had to select box size/tuning for different "alignments" like SBB4, QB3 etc. with each alignment having its pros and cons. Sometimes the only tabulated info was -3dB point. WinISD allows to plot various small- and large-signal output parameters for any box, but still proposes standard alignments by default. The default alignments normally achieves max-flat response (lowest -3dB point without FR ripples) but considering the room gain the -10db point might be a better optimization target (while keep the excursion & power in check). You may change box size and tuning to see if you match JL Audio's box.

I never heard the JL audio driver mentioned but at 200$ I believe there are several better options in the 12-18in range. The high Qes denotes a not-so-strong motor, thus the driver requires a large box and is not particularly efficient. Many 12in drivers delivers better combination of efficiency, Xmax and fs.

The SI HT18 at the current price is a good choice for HT, it needs a big box but you seem to be capable to accommodate it. If you are after SQ you might want to get two of them to get more uniform response across the listening area. A 500W amp is about right for this driver. The PA amps like the XLS1500 are well-suited.
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post #9 of 16 Old 10-17-15, 10:03 PM Thread Starter
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Re: Help me decide path...

The Stereo Integrity HT18 don't ship to Canada; just the continental US.
I've been reading about the various T/S parameters all day; will take time to get a grasp of it all. All I knew back then was that they were needed to calculate enclosure size and port dimensions.

Now, I gotta learn what they mean and which ones are important.

I think I read somewhere in my car audio magazines that the Fs was a significant factor in the type of box/frequency extension one would be able to get, I may be wrong.

There is a JL Audio 15W0v3-4 available locally and seem to have much better WinISD results than the 12" sub listed above.
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post #10 of 16 Old 10-18-15, 09:26 PM
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Re: Help me decide path...

Sorry I did not know the HT18 did not ship to Canada. On the south shore of Montreal there is solen.ca that sells pretty much the same stuff as madisound in the US (mainly home audio). Look for Dayton audio Ultimax or Reference series subwoofers (e.g. RSS350HF, UM15 etc...). For pro-audio, I've have good experience with qcomponents.ca.

To help your decision process, the website data-bass.com is a good reference about subwoofers.

You are right about Fs being a significant (small-signal) parameter. As DgMcClain mentioned, Qts is very important to define the box size. As for large signal, you mainly need to keep an eye on Xmax and Power ratings.

If you like reading, reprints of the original articles by Thiele & Small easily found over the internet:
Closed-Box Loudspeaker Systems Part I & II (R. Small)
Vented-Box Loudspeaker Systems Part I & II (R. Small)
Loudspeakers in Vented Boxes: Part I & II (N. Thiele)
Loudspeakers in Closed Boxes: Part I & II (N. Thiele)
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