The feasibility of DIY subwoofers with with bookshelf speakers

[trains are bad]

I will preface my post by saying that I know almost nothing about home audio, but I know an awful lot about car audio.

I have energy C-3 bookshelf speakers and a Pioneer Elite A35R amp. In my new apartment, I'm astounded at how well they sound. The room makes a big difference indeed.

Anyway, they don't have good bass extension, being bookshelf speakers and all. Does anyone know of any plans for DIY subwoofers? I only want a small one, I'm not looking for volume, merely extension. The first issue is whether it's possible to integrate a subwoofer with the bookshelf speakers at all and get good results. Most of the music speakers I see seem to be full range speakers. Is a separate subwoofer a home theater construct and not suitable for music?

What I could do is buy a subwoofer driver from parts express, build my own MDF box, and figure out some way to amp it. When I was into car audio we just did sealed boxes, but I know home audio generally goes ported, which I can't do unless I have plans. In home audio you also have the crossover built into the speaker and run a full range signal to it.

Of course if there are inexpensive commercial subwoofers available I would just buy one of them, but I haven't seen any that didn't seem awfully expensive, considering what you can buy parts for.

 

[Wodgy]

Quote:

Originally Posted by trains are bad I will preface my post by saying that I know almost nothing about home audio, but I know an awful lot about car audio. I have energy C-3 bookshelf speakers and a Pioneer Elite A35R amp. In my new apartment, I'm astounded at how well they sound. The room makes a big difference indeed.

You've already got a great setup going there. Both of those are great pieces of gear.

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Anyway, they don't have good bass extension, being bookshelf speakers and all. Does anyone know of any plans for DIY subwoofers? I only want a small one, I'm not looking for volume, merely extension. The first issue is whether it's possible to integrate a subwoofer with the bookshelf speakers at all and get good results. Most of the music speakers I see seem to be full range speakers. Is a separate subwoofer a home theater construct and not suitable for music?

You won't find as many complete plans for DIY subwoofers as for other types of home speakers, but that's not because people don't build them. It's because subwoofers are relatively easy to model with software, so you don't really need plans. Just download WinISD (or Unibox if you want to get very detailed info), input your driver specs, choose whether you want sealed, ported, or something more exotic, and it will calculate optimum box sizes and port lengths for you, which you can then adjust. (Stick with the old version of WinISD rather than the Pro version, because the latter can be a pain for entering driver information.)

Most of the plans online are for quirkier unconventional subs, like this one, meant to be small:
http://www.rjbaudio.com/Cerberus/cerberus.html
or this one, meant to slide under a sofa:
http://www.partsexpress.com/projects...man/index.html

But here are two good conventional designs:
http://www.partsexpress.com/projects...ake/index.html
and
http://zaphaudio.com/archives-20.zip
You could come up with those designs yourself just by using modeling software.

In response to your sound quality question, it is definitely possible to build a system with good sub/sat integration. A sub combined with bookshelf mains is in many ways a better compromise than a medium-sized floorstander. Just as a practical matter, you'll probably find that it's easier to get good integration with a sub by stuffing the ports in your bookshelves and crossing a little bit higher. This is because the phase angle spins around so dramatically at a loudspeaker port's tuning frequency.

Note that for music, the "chest thumping bass" actually comes from strong output in the 60-85 Hz range. The 20-35 Hz range mostly just shakes stuff and is unnecessary for music for the most part (except pipe organs). With a good low distortion sub, you'll be surprised by just how little audible sound is generated in that region. (With a lot of commercial subs, what you're hearing when you play a 25 Hz tone is just second or third harmonic distortion products, which are louder than the fundamental.) So ultimately your goal for music only needs to be decent extension down to about 30 Hz, perhaps with a bit of a bump around 75 Hz.

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What I could do is buy a subwoofer driver from parts express, build my own MDF box, and figure out some way to amp it. When I was into car audio we just did sealed boxes, but I know home audio generally goes ported, which I can't do unless I have plans. In home audio you also have the crossover built into the speaker and run a full range signal to it.

Yup, basically all you need to do is buy a driver from PE and build a box. Take a look at Zaph's project I linked to above (the zip file). That's a good, solid design using a good value PE driver.

Most home subs are ported because people want dual use for home theatre, and thus require extension to 20-25 Hz. However, if sound quality specifically for music is your goal, a sealed box is still the best choice for home use, because it's the fastest sounding design (lowest group delay). The tradeoffs are decreased extension and the requirement of needing a larger woofer. You won't be satisfied by anything smaller than 12 inches if you go sealed. Many sub plate amps (e.g. some of the ones at PE) have a bit of a low end boost designed to match nicely with sealed boxes, giving them a little more low end oomph. If you do go ported, watch the group delay in WinISD and don't get too crazy. You can make most drivers go very low by pushing up the group delay, but then you get that slow tubby bass sound you hear from Radio Shack subwoofers.

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Of course if there are inexpensive commercial subwoofers available I would just buy one of them, but I haven't seen any that didn't seem awfully expensive, considering what you can buy parts for.

If your goal is saving money or bang for the buck, just get the low end AV123 X-series sub, designed by Danny Richie. For $199 you can't come close by buying the parts separately, even if you just leave the box as unfinished MDF, rather than finished real wood veneer. If you want a truly good sub for a decently low price, consider picking up the Dayton RSS315HF from PE along with one of their mid-range plate amps with bass boost for sealed boxes, then build a sealed MDF or baltic birch ply box and you're good to go. This will compete with any of the best commercial music subs out there, at any price.

 

[ooheadsoo]

I was going to suggest the subwoofer I have, using GR-Research's driver and passive radiator, but their site seems to be down for me, right now. It's -3db at 20-21hz depending on if you do the little plate amp eq mod. Either way, it's not a big deal, whether it's 20hz or 21hz. The lower you cross over, the better for this subwoofer, but it can perform higher if called for. Danny Richie, the designer, recommends 50hz or lower for the best results, and I agree. On the flip side, there really isn't much going on below 50hz, so if thump your chest bass is what you're looking for, this won't help unless you turn it up disproportionately loud. It performs adequately at higher frequencies, in my experience, as well as or better than anything I've personally integrated. Better than a dual 10" sealed sub of my own design, at any rate. You can also experiment with using the GR driver in a sealed box without the passive radiator. One of my friends has told me that it does the higher frequencies very well in that sealed configuration.

 

[trains are bad]

I know when I was doing cars (I was strictly into SQ, which is why I no longer do anything with cars), I never did ported boxes because group delay was just too hard to eliminate. Even using 3way front speakers with separated components the high frequency group delay was enough to smear cymbols all over the place.

I do use my system for HT, but it's strictly second priority. I don't ever sacrifice its performance in the least bit for HT concerns.

What I'm mostly missing with my bookshelves is the very low bass lines in dub and other flavors of electronica. You can hear it enough to follow it if you know it's supposed to be there, but it's not as prominent is it should be. It's also true that I don't have visceral bass drum effect, but that's not what's driving me to want a sub as much.

I am, indeed, looking to get out as cheaply as possible, being a working college student. I was considering a 12v battery+a car amp I already have. If you can't tell by now, I don't care how it looks, only how it sounds

One of my speakers is sitting on physics texts.

I'm still confused about crossovering. In cars I always used DSP to implement active crossovers and seperate amps (I had 5 amps in my truck at one point). Right now I'm running full range to my bookshelves, which have an internal xover. If I get a sub+amp, I assume the amp will have an active xover, but then should I just let my bookshelves roll off at the lower end? Or is the port stuffing trick intended to be a highpass?

I really appreciate the plans and stuff.

 

[trains are bad]

I've been playing around with WinISD. What amount of group delay is considered acceptable or noticable?

 

[ooheadsoo]

Not to criticize Wodgy, but I don't trust WinISD. I've used it extensively, myself, and it gives different results from what I get with unibox, which is a tool that many more experienced designers use. It is simple to use, though, but I'm not sure how accurate the results are.

As for phase angle/group delay on bass, it's debatable. Some people think that any delay is unacceptable beyond 10ms. Others say that as long as you keep things together until you are below 50hz or so, your ears can't tell the difference.

Here's the link to my sub: http://www.gr-research.com/drivers/sub_pr.htm

 

[Wodgy]

Quote:

Originally Posted by trains are bad What I'm mostly missing with my bookshelves is the very low bass lines in dub and other flavors of electronica. You can hear it enough to follow it if you know it's supposed to be there, but it's not as prominent is it should be. It's also true that I don't have visceral bass drum effect, but that's not what's driving me to want a sub as much.

Soundstage has a good set of measurements for the Energy C3. They're down -3dB at about 70 Hz, with the standard -24dB/oct ported rolloff. That's why you're missing the visceral bass thump as well as the low end basslines. This is pretty standard for bookshelf speakers. A sub will definitely solve your issues. Note that if you choose to stuff the ports, the -3dB point will move up to about 90 Hz. That sounds like a high crossover frequency, but you'll find with a quality low-distortion DIY sub, that it's probably the best approach.

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I'm still confused about crossovering. In cars I always used DSP to implement active crossovers and seperate amps (I had 5 amps in my truck at one point). Right now I'm running full range to my bookshelves, which have an internal xover. If I get a sub+amp, I assume the amp will have an active xover, but then should I just let my bookshelves roll off at the lower end? Or is the port stuffing trick intended to be a highpass?

Many people just feed a full range signal to their bookshelves and do not use any form of crossover on them. A sealed (stuffed) set of bookshelves will naturally roll off at 12dB/oct. A ported set of bookshelves will roll off at 24 dB/oct. Subwoofer amps come with built-in variable frequency crossovers. Some will have a 12dB/oct filter, others will have a 24dB/oct filter. Generally you want to pick one whose crossover matches the speaker rolloff. Most of the mid-range PE plate amps have 12dB/oct filters, which is another reason why it makes sense to stuff your mains for proper integration with the sub.

Note however that you can increase the power handling and lower the distortion of your mains by using an electronic or electrical crossover on them too. This can dramatically reduce the distortion of smaller drivers, but for a speaker like the Energy C3 with relatively large woofers, it's not so much of an issue. The simplest crossover is just a capacitor inline, which gives you an additional 6dB/oct rolloff, but then it becomes more difficult to match with your sub amp, which will almost always be restricted to just 12dB/oct or 24dB/oct. There aren't that many good audiophile-grade electronic crossovers available because people feel they're impure and color the sound. How much of that is reality and how much of that is audiophile perception is debatable, since they can potentially lower distortion. Home theatre receivers can often highpass the mains in the digital domain, but then you're restricted to the DAC in your receiver, and most of the time the highpass filters only function in Dolby processing modes, which munge the sound for regular audio. The bottom line is that you can probably get away with running your mains fullrange, like most people do.

 

[trains are bad]

Excellent info. This WinISD is way, way cool, but I'm not sure whether I should believe it. With a DAYTON SD270-88 it's saying that I could use a box as small as .04 cu.ft. I don't even know if the driver would fit in a box that small. I should probably just buy a ready-made subwoofer.

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There aren't that many good audiophile-grade electronic crossovers available because people feel they're impure and color the sound. How much of that is reality and how much of that is audiophile perception is debatable, since they can potentially lower distortion.

Yeah I noticed that, and it's very weird. At my shop we had real time analyzers and calibrated mics and we could tweak crossover slopes, points, and (gasp) equalize for flat frequency response. The improvement was not subtle. I also have a background in pro sound. When I got into home audio I was surprised that I don't see nice all in one DSP units that can auto room correct and feedback destroy. It's almost like home audio is lagging behind the times.

 

[Overheat]

maybe your problem is that your speakers aren't actually "bookshelf", but standmount speakers that seem to be lacking suitable stands. You should be able to pick up some good quality stands for cheaper that creating a sub and they'll have a similar effect but shouldn't dominate your music as much as a sub would. Your setup really shouldn't need a subwoofer!

 

[Wodgy]

Quote:

Originally Posted by trains are bad Excellent info. This WinISD is way, way cool, but I'm not sure whether I should believe it. With a DAYTON SD270-88 it's saying that I could use a box as small as .04 cu.ft. I don't even know if the driver would fit in a box that small. I should probably just buy a ready-made subwoofer.

That sounds strange. You might have entered one of the driver params incorrectly.

Quote:

Yeah I noticed that, and it's very weird. At my shop we had real time analyzers and calibrated mics and we could tweak crossover slopes, points, and (gasp) equalize for flat frequency response. The improvement was not subtle. I also have a background in pro sound. When I got into home audio I was surprised that I don't see nice all in one DSP units that can auto room correct and feedback destroy. It's almost like home audio is lagging behind the times.

Home audio tends to be fad and belief driven. People do things and buy into philosophies based on imagined principles or by following groups. e.g. People believe things like "crossovers are evil" even though the majority of single driver crossoverless designs sound pretty bad to an impartial listener. And, of course, that's not even getting into cables....

There are actually at least two commercial DSP crossover/room equalization/correction systems on the market (DEQX and TacT), but they're pretty expensive. Still, the DEQX is getting a little traction. In the bass region, the situation is better. The Behringer Feedback Destroyer Pro is inexpensive and fairly popular for dealing with bass room modes as well as handling sub crossover duties.

 

[trains are bad]

Quote:

Originally Posted by Overheat maybe your problem is that your speakers aren't actually "bookshelf", but standmount speakers that seem to be lacking suitable stands. You should be able to pick up some good quality stands for cheaper that creating a sub and they'll have a similar effect but shouldn't dominate your music as much as a sub would. Your setup really shouldn't need a subwoofer!

So are you saying that using stand would increase my bass output? Dramatically?

I did indeed have the units wrong for that sub calculation.

1.2 cu ft sounds a lot more reasonable.

 

[Romanee]

Wodgy -

The Drake project looks nice, though I wonder how much LF energy the 4.5" driver produces.

I'm tickled by the "boogieman under-sofa subwoofer". Looks promising for under our bed to supplement the $30/pr Insignia speakers (on 31" Sanus stands). Talk about motion on the ocean.....

 

[ooheadsoo]

Quote:

Originally Posted by trains are bad So are you saying that using stand would increase my bass output? Dramatically? I did indeed have the units wrong for that sub calculation. 1.2 cu ft sounds a lot more reasonable.

You should definitely use something better damped than text books. Try cinder blocks.

Keep in mind that winisd will give you the phase and FR info, but it doesn't tell you much about the other parameters that affect what we hear, such as energy storage problems and harmonic distortion. Sometimes, a driver sounds bad despite a good FR/low group delay.

Romanee, I've lived with a dual 4.5" subwoofer for a year or two about 8 years ago. It can definitely create a lot of chest impact when properly configured, but perhaps not as much as you would desire if you actually wanted flat response, and it won't go deep.

Btw, the GR sub I have is the cheapest way I know of to hit 20hz with relatively low group delay, keeping it basically below 50hz.

Here's the link to the FRD Consortium where you can find unibox and subwoofer (like unibox but specifically for modeling subwoofers.)

 

[Romanee]

Quote:

Originally Posted by ooheadsoo You should definitely use something better damped than text books. Try cinder blocks. Keep in mind that winisd will give you the phase and FR info, but it doesn't tell you much about the other parameters that affect what we hear, such as energy storage problems and harmonic distortion. Sometimes, a driver sounds bad despite a good FR/low group delay. Romanee, I've lived with a dual 4.5" subwoofer for a year or two about 8 years ago. It can definitely create a lot of chest impact when properly configured, but perhaps not as much as you would desire if you actually wanted flat response, and it won't go deep. Btw, the GR sub I have is the cheapest way I know of to hit 20hz with relatively low group delay, keeping it basically below 50hz. Here's the link to the FRD Consortium where you can find unibox and subwoofer (like unibox but specifically for modeling subwoofers.)

I look into GR Research and didn't see the 12" sub. Found FRD Consortium.

 

[ooheadsoo]

My post above has a link to the GR subwoofer.