Advice for a budget Subwoofer project

[peter_m]

Hello,

I might be helping someone build a HT around Zaph's http://zaphaudio.com/ZBM4.html for a 16x14 room located in the basement. We are still in the early planing stage and need advice for the Sub. My questions is what would be a good matching sub design in terms of power/price? Is about 300$ for the driver and the plate amp realistic? I guess it's safe to call it a budget system.

Should it be a sono-tube or cube MDF enclosure? Sealed or ported? Would it be better to have two driver firing in opposite directions to minimize enclosure vibrations?

Peter

PS: One more detail, can it be idiot proof? Teenagers might crank it up all the way just to see something move/vibrate and I'm afraid they might blow the sub.

[brent_s]

Do you have any box size limitations? How much output are you looking for? For my tastes, especially in that size room, $300 will definitely yield a satisfying result.

In ascending order of output:

Dayton RS315-HO in 2.2 ft^3 net, tuned to 22hz. PE BASH 300 watt amp. F3=22hz. Good for 105+db from 20hz up at 1m ground plane...expect more in room. Amp limited design so the amp will shut down before the teenagers can kill the driver...repeatedly doing this may be detrimental to the life of the amp. About $280 for driver amp. Biggest problem may be fitting a suitable port into that small of a box. I have one of these in the parts closet, but haven't finalized how I want to actually build the cabinet.

Dayton RS315-HF in 3.0 - 4.0 ft^3 net, tuned to 20hz. PE BASH 300 amp. F3=22hz in 3 ft, F3=19hz in 4ft. At 3 ft^3, good for 105.5+db from 20hz up. At 4 ft^3, 107.5+. The 4 ft^3 alignment just kisses Xmax so it's safe from the teenagers...and there's still some Xsus left beyond Xmax. I'm currently building a 3.5 ft^3/20hz tune of this myself...box waiting for me to find time to paint it.

Dayton DVC15 in 6ish ft^3 tuned to 17-20hz. BASH 300 for budget, although it should safely handle a 500 watt amp for a relatively insignifcant 2ish db gain...you need to change the rumble filter on the BASH 500 if you choose that option. Not as flat anehoic, but may actually compliment room gain better than a flat to 20hz design...f6 is 20hz or so. With 300 watts, 108db @ 20hz, 112@30, 114@40. I'm currently running a DVC15 in 5.9 ft^3 tuned to 17hz. According to REQW measurements, corner loaded in my 22x16 theater, flat down to 10hz with a 100db test signal is no sweat...driver barely moves. At my typical listening volume of 10 to 15db below reference, low frequencies still stress the sheet rock and send tremors to the other end of the house...some may want more output, but I don't see the need.

You might could squeeze the RS390 series into your budget.

Sono or box is up to you, whichever fits your aesthetic. Tubes are probably easier. The 12" RS drivers are technically suitable for downfiring, but they're on the upper end of recommended cone sag. The RS 15"ers are a no go for downfiring, IIRC. Personally, I stay away from downfiring since it's never really a good thing for a driver unless it was designed with a coil offset.

-Brent

[peter_m]

Brent,

Thanks for the multiple suggestions. For box shape and size it's up in the air right now. We are just looking at options I've seen some interesting stuff with hiding a sub in a coffee table or big ottoman. A vertically oriented sub might be also acceptable tucked away in a corner. So size is really limited by what can be hidden by the previously mentioned options... without going overboard... We still need leave some room for people to sit and watch...

What about sealed enclosure like Zaph's 2.0 ft^3 sealed Dayton setup? Heard it should yielded tighter base then ported?

BASH amps are better the the Dayton line?

[rco3]

What a coincidence!

I just built ZBM4's, and then built a sub to go with 'em using a Dayton RSS265HF in a 1.5 ft^3 sealed MDF box powered by a BASH 300. Hard to imagine doing much better for the money. The wife is perfectly happy with the cabinet size, too.

Rough estimates predict in-room response that has a 2-3 dB hump in the mid-30's, relaxing to flat at 20 Hz and rolling off from there. I'll be measuring that later, after the newness wears off and I can stand to stop listening to the system. I don't listen all THAT loud, so I'm using a crossover around 100 - 110 Hz.

Sounds like somebody's getting a pretty nice little HToB (Home Theater on a Budget).

[brent_s]

Peter,

there's certainly nothing wrong with Zaph's sub design if size is a concern. I plan to throw together a sealed box for my RS315-HF at some point. Iron law is loud, low, small...pick 2. For HT, you're really looking for extension with adequate desired output. A ported alignment will have significantly more output near its tuning frequency relative to the same driver sealed at the expense of a larger enclosure

You don't really want to open the sealed vs. ported can of worms. Searching here and other forums should yield plenty of discussion on this topic. IMO, sealed alignments don't inherently have better sound quality than ported; as with most endeavors, it's all in the implementation. FWIW, my DVC15 replaced dual sealed subs using the original (not Madisound clones) NHT1259 drivers and I feel the single ported DVC15 is an improvement in every way.

Comparing RS12-HF in 2 ft^3 sealed vs. 3.5 ft^3/20hz tune with 300 watts each: Sealed f3 is 37hz, it's -11.5 @ 20hz. Ported f3=20hz. Sealed output...98db@20hz, 104@30, 107@40. Ported output...106@20, 109@30, 109.6@40. All 1m ground plane sims. Effectively, you'll need two of the sealed subs to equal the output of one ported below 30hz. Room gain will effect both. Potentially, the ported could be a bit bottom heavy if there's enough gain, but that hasn't stopped people from singing the praises of SVS offerings with 20hz F3 points.

There's nothing wrong with the Dayton amps, but the HPSA series doesn't fit your $300 budget and 500 watts leaves the 12" drivers vulnerable to the teenage damage concern. That only leaves the SA240 as an alternative, but it doesn't have the LFE input (Xover bypass) found on the BASH-300.

My WinISD models also suggest John's 2 ft^3 sealed/500 watt alignment would not meet your teenager safe constraint. John's project notes imply that it would and he's probably forgotten more about speaker design than I've managed to learn in the past 20 years, but the 2db increase from 300 to 500 watts is not worth the risk in your scenario, IMO.

-Brent

[peter_m]

Thanks for you posts guys,

We will plan for the 12" Dayton RS in a ported enclosure with the 300w BASH. I guess it's not that important for me (or us) since the sub will not be used for critical music listening. 99% for movies and at best just the occasional house party for background music. So what IF the sound quality is slightly lower with a ported enclosure. It's not worth the effort to search, read and make an opinion on the subject. Thanks for the simple solution.

RCO3: How do you like the sound of your new ZBM4s? Also, how loud do you feel comfortable driving them? I only ask because I recently replaced some 4" drivers on a friends system with low end parts and the flexible conductor broke because it was too short (factory defect) after only a few days of use. Is this something that might happen with the MCM drivers? Is it worth the time money and effort over something like this?

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=302-019&CFID=6742144&CFTOKEN=42466192

[Dave Bullet]

PS: One more detail, can it be idiot proof? Teenagers might crank it up all the way just to see something move/vibrate and I'm afraid they might blow the sub.

The most common way toblow a sub is over excursion. You could put a line level highpass 12dB (or preferably higher) filter at approx 20Hz to reduce cone excursion if they crank it, especially with the synthesized bass heavy tracks most youngsters like these days.

David.

[rco3]

Hm. I just wrote and then erased a really long post, because it got to be more of a life story than an answer to your question.

I like the ZBM4's a lot. Very clean, open, good imaging, broad dispersion. Not a lot of bottom, but they're 4's and need a sub no matter what IMHO. I may need to check to make sure there aren't any air leaks, that may be contributing. The wife likes the size and the sound, and is getting close to liking the finish on 'em. I haven't heard the MTXs, but I'm just doubtful that a pair of complete 5-1/4' two-ways that cost - after markup - less than the drivers and crossovers for the ZBM4s will have the same attention to performance as the ZBM4s. My 75 WPC Denon has yet to run out of steam, nor have the speakers, and I've never thought, "Man! I wish these were louder!" *I* have no reason to think that the MCM drivers will be a reliability liability, but I'm hardly an expert on the matter. The hardest thing about the build was the tweeter cutout, and a little "manual customization" of my Jasper Jig resulted in a hole that's a near-perfect press-fit.

I'd rather have these and the RS sub than pretty much anything I've EVER heard at a Worst Buy.

I'll tell ya the biggest problem I've had with the ZBM4s - the tweeters. Not because of poor QC or design, but because they are apparently IRRESISTIBLE to toddler fingers. I've had at least two, perhaps three different toddlers invert the domes (you'd think I would eventually sense a pattern, right?). I've had to use really sticky tape on the end of a pen to pull 'em back out, the vacuum cleaner trick wouldn't do it. I've got replacements enroute, but right now the L and R tweets look like topo maps of Colorado. Still sound good to me, though. I'm thinking that when the new ones go in, I'll put some thin grill cloth material over the tweet first so that the press-fit keeps the material taut.

[JonP]

Dayton RS315-HF in 3.0 - 4.0 ft^3 net, tuned to 20hz. PE BASH 300 amp. F3=22hz in 3 ft, F3=19hz in 4ft. At 3 ft^3, good for 105.5+db from 20hz up. At 4 ft^3, 107.5+. The 4 ft^3 alignment just kisses Xmax so it's safe from the teenagers...and there's still some Xsus left beyond Xmax. I'm currently building a 3.5 ft^3/20hz tune of this myself...box waiting for me to find time to paint it.
-Brent

A side question, but maybe not, since it sounds like Peter is picking this choice...
What kind of port size do you think one can get away with here?

I got a buddy who finally decided to have me build him a sub, have a 3.0 cu box and the RSS315HF. I found 18-20Hz to be good looking tunings... but we're talking 32-24" of port in a 18" box using 4" port tube!! 3" would be so much shorter, and of course, so much higher air velocity...

Any practical pointers as to port size? I bought a 4" Precision Port.. need to make it longer (and with an elbow) if I'm not going to return it and live with a 3"

I have run the numbers with a few programs, don't have them off the top of my head...

[brent_s]

JonP, is the box 3 ft^3 net after subtracting driver/port/bracing or is that 3 ft^3 gross before putting stuff in ala a PE pre-built box. The port is treated as a solid cylinder and tends to eat up space in a hurry. Treat the driver as 0.1 ft^3 for guestimating.

I'm not an expert in vent air velocity and I didn't stay at a Holiday Inn Express last night. I would suggest you look at your friends likely SPL levels vs. simulating with max power. For instance with a 3" port, below about 26hz the 315HF in 3 ft^3 @ 20hz with 300 watts exceeds even the 34 m/s velocity recommended in a Peerless white paper I read once upon a time. Now folks are recommending 17 m/s or even less, depending on frequency and port size. At 150 watts (3db reduction) you're under 34 m/s down to 20hz...all before taking any rumble filter effects into account. How much time is your friend likely to spend above 150 watts or so?

FWIW #1) SVS uses a 3" Precision Port with in their 10" model. Their driver probably has as much or more displacement than the 315HF due to enough excursion to offset the Sd difference. Don't recall seeing anyone complaining about port noise with these.

FWIW #2) I use a single 4" Precision Port with a DVC15 and no rumble filter, more Xmax and Sd. Haven't heard any port noise even at reference level (typical listening is more like -10/-15 reference) in a 26x16x9 room. The sims have it exceeding the 17ms recommendation in the mid 20s as well, but not as badly as the 315HF with 3". Granted, I did make the port downfiring into the carpet.

FWIW #3) Assuming your 3 ft^3 box took some port volume into account, you might want to try the 24hz tuning you'd get with a single 4" PSP. The transfer function is still +/- 3db from 20hz up. Just with a nice broad peak from 30ish up. Otherwise, the 3" 18hz tune looks like a better option than the 20hz tune, at the expense of nearly double the port length.

BTW, if that's a 3 ft^3 gross box, you may want to consider the 315HO instead. In 2.5 ft^3 tuned to 20hz with 300 watts, it'll give up about 2db to the 315HF according to WinISD. Still the same potential problem with port noise.

-Brent

[JonP]

JonP, is the box 3 ft^3 net after subtracting driver/port/bracing or is that 3 ft^3 gross before putting stuff in ala a PE pre-built box. The port is treated as a solid cylinder and tends to eat up space in a hurry. Treat the driver as 0.1 ft^3 for guestimating.

Sorry I've been so #$%$ busy with work and stuff, and haven't gotten back here.
Well, it is the PE box, and it does seem a bit larger than the "3.0cu". I'm getting about 19 1/8" x 19 1/8" x 18 3/8" for the actual box, the MDF is slightly smaller than normal at about .74" (maybe 18mm + truckbed paint?) There is a single brace of a MDF 1" x 3" x 17 5/8", across one pair of sides. (Hmmm.. it needs another.. and some damping...) This comes out to a bit over 3.0 cu, in Bass Box Pro, with a net of 2.9 in a sealed with the brace and driver.

Vented comes out more like 2.68 cu with 4" x 23" port (suggested 22hz tune) or 2.81 cu with a 3" x 12" port. I get about 24m/s at 17hz with the 4", and about 15m/s for the 3". I've got my WinISD files at work... as I recall, I got rather different velocity factors between the two... there isn't something obvious like one of them not calcing for the port volume or something?

I'm not an expert in vent air velocity and I didn't stay at a Holiday Inn Express last night. I would suggest you look at your friends likely SPL levels vs. simulating with max power. For instance with a 3" port, below about 26hz the 315HF in 3 ft^3 @ 20hz with 300 watts exceeds even the 34 m/s velocity recommended in a Peerless white paper I read once upon a time. Now folks are recommending 17 m/s or even less, depending on frequency and port size. At 150 watts (3db reduction) you're under 34 m/s down to 20hz...all before taking any rumble filter effects into account. How much time is your friend likely to spend above 150 watts or so?

Good point. I don't have a feel for how much lower a more real world level would be below max output. Even though I have a sub, I don't know how hard my speaker output drives it, and I rarely have it turned very high. And, it's sealed... There's always building a test box and listening to it, but that takes more time...

[QUOTE=brent_s]FWIW #1) SVS uses a 3" Precision Port with in their 10" model. Their driver probably has as much or more displacement than the 315HF due to enough excursion to offset the Sd difference. Don't recall seeing anyone complaining about port noise with these.

FWIW #2) I use a single 4" Precision Port with a DVC15 and no rumble filter, more Xmax and Sd. Haven't heard any port noise even at reference level (typical listening is more like -10/-15 reference) in a 26x16x9 room. The sims have it exceeding the 17ms recommendation in the mid 20s as well, but not as badly as the 315HF with 3". Granted, I did make the port downfiring into the carpet.

If I was getting the same, lower, number in all sim programs, I'd just go with the 3" port, and figure between lower music listening volume / HT noisyness covering things up.. he'd be fine. I worry that my higher numbers might be real...

FWIW #3) Assuming your 3 ft^3 box took some port volume into account, you might want to try the 24hz tuning you'd get with a single 4" PSP. The transfer function is still +/- 3db from 20hz up. Just with a nice broad peak from 30ish up. Otherwise, the 3" 18hz tune looks like a better option than the 20hz tune, at the expense of nearly double the port length.

BTW, if that's a 3 ft^3 gross box, you may want to consider the 315HO instead. In 2.5 ft^3 tuned to 20hz with 300 watts, it'll give up about 2db to the 315HF according to WinISD. Still the same potential problem with port noise.

-Brent

Well, the HF is already bought. Another thing, the depth of the box is less than 17" inside, and a bit over 17 5/8 sideways, very little room for the 17" Precision at full length. The PP guy I talked to said you might get away with an inch or so, rather than the "1/2 or one full diameter" of the port I often hear. But I don't even have that much on the 4", without shortening and going higher. Hence, my eyeing elbows at the hardware store...

I'll go over the numbers again, in a few different calculators, then bring the results back.

[brent_s]

With the box volumes and port choices you've listed, I'd go with the 4" port and use an elbow to fit. There's negligible difference in response/spl between 2.68 and 2.81 at the nearly identical tunes, but the air velocity difference is drastic...53m/s v 29m/s @ 20 w/300 watts. Finding an elbow to work with the PSP may be tough, but some have done it. An elbow will increase port turbulence some, but I'd still pick a 4" straight PVC with elbow over a 3" PSP in this model; WinISD doesn't account for flaring in the port velocity calculations.

BTW, the 3" and 4" PSP ports are 18" assembled, but for tuning purposes, you treat them as 17" ports. You probably realize this, but your next to last paragraph raises the question.

-Brent

[JonP]

I'll look close at the net volume after port, that may explain why I was getting such different velocities for the "same" box and tuning in different programs. If they weren't all on the same page as to what the net volume was, that would explain it.

On going 4" with the elbow... yeah, that's pretty much where I've been pointing myself going over this. The 3" full length (or the 4") is just too long for the box... straight, they'd have to be 3" shorter... a no go.

Will be a bit tricky, missing the brace, and the back of the woofer, especially that I want to use the inner flange from the PP if I can. And, it really should have another brace in there, too...

I thought I mentioned here, maybe not.. I've found a thinner schedule of PVC pipe at the local HW stores, its SDR 35 (350?) and is a much thinner walled stuff than Schedule 40 or the identically sized sewer pipe black ABS. That stuff is .25" thick! The Precision Port tube is .090" it's quite a gap to the ABS/Sch 40 PVC fitting. But, this SDR35 stuff is only .115" or something close, it's not snug but you'ld use a lot less RTV or other sealing cement to fill the gap.

There will still be the fun of tuning, in that with the elbow, you always have to guess and see how much length it will equal.. I'll be measuring the driver impedence response anyway... shouldn't take more than a few cut and measure cycles...

Or, was that measure and cut cycles? :W

<On topic content/> I got a batch of cute little Al woofers in the mail from MCM the other day...

[brent_s]

If the budget will allow an additional $80, you could look at a passive radiator alignment. The PE 15" DVC PR (295-194) with 750g added will get you a 19.5hz tune in 2.8 ft^3. No port noise. There's also a 12" DVC PR, but you'd need two at $65/each.

-Brent

[JonP]

I appreciate the idea, but Murphy is just not allowing flexibility on this project. :M

A PR would be an idea for low tuning... would have to talk my friend into the extra $$. But... the real problem is, the single 1x3" brace this box has. And how I've cut the amp hole in the back already... And how said brace goes from side to side now... If I hadn't already cut the amp hole, I could have rotated it and had side(s) to cut into. Now I'm stuck...

Ah well, I've just about got the on paper layout done, using 4 elbows 8O to not hit driver, brace, amp, and still get 26" or so in there. Amazing how small 3 cu ft can get... Wondering if four elbows will have a noticable effect on port noise, one way to find out. It sounds pretty good right now as a sealed... but the port should give it +6dB or more, from the high 30's down to 17-18Hz or so... Definite HT improvement.

[brent_s]

You could place the amp in a separate enclosure, if the funding is available for the PR.