Care to critique my customized Voxel design w/slot port?

[hv6478]

Hey all,

Long time lurker, first time poster. Really appreciate this community and any help I may get for this upcoming project.

I plan to build 2 subwoofers for my office / desk setup. I was thinking of maybe starting with 1 and seeing how it goes, but figured it would be more economical to go for 2 in one shot and why not have 2 anyway!

This system is strictly for music. My mains are Micca RB42s which I'm quite impressed with and will probably keep for a while. That said I have an aging Energy ES-8 subwoofer (20+ yrs) and the amp is on its way out.

I found Paul Carmody's fantastic Voxel design and wanted to integrate the amp into the cabinet and try to get down to 30-32 Hz f3. My width and depth limit are 11" or so, and height up to 20". I decided to go with the Dayton SA70 plate amp.

I went with a slot port to help with chuffing as even a 2" port was peaking close to 23 m/s at 35W power. With a 3/4" x 8.5" (full width) slot at almost 30" long, this goes down to below 11.3 m/s. At the full 70W it is under 16 m/s. Much better.

That said, 35W is the highest I can go in WinISD with this design while obeying x-max, after adding in the 18 Hz highpass filter that is apparently built into the SA70 (according to a Q/A on the product page). I figure (hope) I won't pump more than that as I already have my current setup turned quite low. I like bass extension to fill in the lows but not high volume or "obvious" bass. That said even Paul's original design seems to exceed x-max at one point, so hopefully this will be a non-issue in the real world.

Here are some SketchUp drawings:

And some WinISD screenshots:

Full pack of pics:
hv6478's take on the Voxel - Album on Imgur

The 3 "slats" at the bottom to form the port are from 1/2" material rather than 3/4" like the rest. This helped me stay more comfortably under my 20" height limit, but if I end up "having" to use 3/4" material, I'd end up at 19 3/4" (to keep the interior volume the same, that is).

I'd really like to know if this generally looks like a good approach. I know it's conceptual in this form and I look forward to building these, but I'd like to be as best prepared as possible beforehand. Any critique, suggestions, big red flags or alike would be greatly appreciated.

I'll be building with a very experienced friend, and I'm not too bad around a shop though I consider my woodworking skills quite basic, hence my friend's help.

The plan is to cut a 45" angle around all the edges of each face as you'll see in the sketch. I feel like this would provide a cool look, and it will "hide" the butt seams too. I'll be using 3/4" void-free Baltic Birch (the proper stuff, 5' x 5' panels) from a local lumber yard. I plan to stain them a dark chocolate brown.

Thanks,
hv

 

[GM]

Greets!

The vent's aspect ratio is > 9:1 and combined with all those 90 deg bends it will be somewhat aperiodic, so expect a more rolled off response than predicted.

GM

 

[hv6478]

Thanks very much for the greetings and reply!

I imagine you mean a steeper roll off on the low end?

I was worried about that. Was considering going narrower and taller.

Would something more like 1x4 combat those bends enough?

I thought that the much higher velocity of a 2" round port would leave me worse off. I do have some plans for that as well (ends up being 2" shorter as well).

Otherwise I suppose the built-in amp is making it a bit harder to make a simpler and more effective slot port. Perhaps a modest outboard power amp would work if I could figure out a good way to hide it in the setup.

Thanks,
hv

 

[Brian Steele]

I hate plate amps with a passion. IMO they're a solution for consumers who want to buy a hassle-free all-in-one add-on subwoofer for their system, not for a DIYer who wants to build their own subwoofer. And if the thing blows, you're stuck with a hole in the back of the box that's likely not to fit any other plate amp than the one you cut the hole for. Then there's the likely humming caused by running a line-level signal several feet to the subwoofer. I recommend going with a separate standalone amp instead.

I've had a look at the Voxel a couple of times. I think if I was going to build it, I'd probably opt to go with two PRs instead, rather than a vent. Yes, it makes the overall cost a bit more expensive, but you don't run into any issues that could be caused by trying to fold a long narrow vent into the box.

 

[hv6478]

This is why I'm glad I posted here.

You're right on the cost as well, it will certainly drive it up a bit especially with PRs and a separate power amp. That said I'd rather do it once and do it right. This system gets some use every day, ranging from 1 to 6 hours really based on how my day goes in terms of phone calls.

Maybe meeting in the middle with an external power amp "better" slot port design (due to lack of internal plate amp)?

One thing that worries me with power amps is the high pass filter, or lack thereof, at say 18 or (even better, in my case) 20-25 hz or so. Is this something standard on most power amps? This has been tough to confirm.

I'm also not adverse to looking at a different driver. However I found it very difficult to find anything that seems to compare to the capabilities of this TangBand W5-1138SMF, without getting considerably larger (and pricier overall).

And funny you mention that hum or buzz -- especially when idle with nothing playing, that drives me nuts. I'm very sensitive to it.

 

[chris661]

I hate plate amps with a passion. IMO they're a solution for consumers who want to buy a hassle-free all-in-one add-on subwoofer for their system, not for a DIYer who wants to build their own subwoofer.

While a little off-topic, IMO the one thing every HiFi system should be is hassle-free.

I've gone from a tri-amped system with DSP, active subs, etc, to a pair of passive 2-way systems driven by a store-bought HiFi amp. I went from "I'll just play music out my laptop, the stereo is too much hassle" to having the music playing from breakfast until bed.
The sound may or may not have improved, but my enjoyment is much greater.

Chris

 

[hv6478]

I see what you mean. I went through a similar pattern with cell phones a while back. Convenience is a real world factor for sure.

As of right now I'm using a Yamaha amp to power my mains and have the LFE port running to the sub. Sounds wonderful to my ears, I went through a few different amps. I like that this one is pleasant, quite accurate, not harsh and balance with some warmth which I really enjoy.

I suppose my concern is the overall approach, layout and whether my bracing is adequate. I can switch to a 1x4 port and have it just under 20", which saves at least one pair of 90-degree bends.

I tried modeling some PRs, even some pairs, and it seems that I can't really get the f3 down below 40Hz, not sure if I'm doing something wrong.

 

[chris661]

Add mass to the PRs to drop the tuning frequency.

Chris

 

[Brian Steele]

While a little off-topic, IMO the one thing every HiFi system should be is hassle-free.

I meant hassle-free purchase, not hassle-free use

The truly hassle-free solution here is just to buy a powered sub, but the OP has chosen not to do so. They are building one instead.

And in terms of hassle-free use, it depends on who is being hassled. Case in point: I'd lent my brother an old 5.1 receiver to use to power his bar system (two sats and a passive subwoofer). It received a feed from the bar's mixer via its AUX-IN. Well, almost every other day I had to go and help him out because someone pressed the wrong button or turned the wrong knob on the receiver. So I replaced it with two amps with nothing on the front panel but power buttons and a DSP408 to do the EQ and filtering. The only thing the bar staff could do is turn them on or off. No more calls, no more hassle .

For a DIYER, since you've already made the choice of going through the hassle of building your own subwoofer, going with a separate amp rather than a built-in one really doesn't add much if any additional hassle. If that "Yamaha amp" that the OP referred to has some decent built-in DSP processing, there's no need for the subwoofer amp to have any. It could be a simple box like the Monoprice Unity 100, which can be used to drive the subwoofer with its channels bridged.

 

[hv6478]

I meant hassle-free purchase, not hassle-free use

The truly hassle-free solution here is just to buy a powered sub, but the OP has chosen not to do so. They are building one instead.

And in terms of hassle-free use, it depends on who is being hassled. Case in point: I'd lent my brother an old 5.1 receiver to use to power his bar system (two sats and a passive subwoofer). It received a feed from the bar's mixer via its AUX-IN. Well, almost every other day I had to go and help him out because someone pressed the wrong button or turned the wrong knob on the receiver. So I replaced it with two amps with nothing on the front panel but power buttons and a DSP408 to do the EQ and filtering. The only thing the bar staff could do is turn them on or off. No more calls, no more hassle .

For a DIYER, since you've already made the choice of going through the hassle of building your own subwoofer, going with a separate amp rather than a built-in one really doesn't add much if any additional hassle. If that "Yamaha amp" that the OP referred to has some decent built-in DSP processing, there's no need for the subwoofer amp to have any. It could be a simple box like the Monoprice Unity 100, which can be used to drive the subwoofer with its channels bridged.

Glad they got up and running more smoothly.

I have a simple Yamaha Natural Sound RX-V385. It does have some built-in DSP presets you can switch between, but there seems to be no DSP customization options beyond that. Their mic and YPAO room calibration seems to work quite well.

For this application I was hoping to not need to worry about any additional DSP. I was considering doing a powerful pair of sealed subwoofers with some Linkwitz DSP goodness to get something tight and musical while avoiding pre-fab boxes like the SVS SB-1000 for example. However it seems the cost goes up considerably due to the extra power needed and a DSP-capable amplifier as well.

I figure at lower volumes and near-field, I should (hopefully) be able to get solid performance out of a ported design and save quite a bit of cash. Especially because these are only for music and I really just want the presence of the low end filled in, not boomy, never that loud. For reference I have the sub's volume on the amp turned all the way down to -10.0dB and the gain knob on my current subwoofer barely at 2 out of 10 (old Energy 8" 100W not sure if that's RMS).

I'm also not married to this design. Though it took a while to figure out SketchUp and I've revisited it many, many times, I will happily (and without emotion) scrap it for something better.

Re: amp, I agree, and my initial decision was mainly because of my concern for high pass filters when using power amps. I don't believe my Yamaha has that built in with the LFE port (please correct me if I'm wrong and this is some sort of standard behaviour I may now know about). While there are various Samsons and Behringers that are reasonable, I'm not sure they'll have that built-in. But I'm not trying to go for a CAD$500-600 amp with DSP and what not for this setup.

 

[wolf_teeth]

Look up my Triumph design. 9.5" cube with 2 PRs. F3 of 40Hz, and lower room loaded. You can use whatever amp you like.
Wolf

 

[hv6478]

Look up my Triumph design. 9.5" cube with 2 PRs. F3 of 40Hz, and lower room loaded. You can use whatever amp you like.
Wolf

Hey Wolf, thanks for chiming in, and for sharing your designs and wisdom.

Your Triumph (or Biumph) was one of the first ones I found actually. Really love the design and the "cube-ness" of it. The f3 is what ultimately deterred me -- that at the fact that the Dayton SA25 plate amp does not have an auto-on feature which is a deal breaker for me. Though perhaps with the SA70 or a different outboard power amp that would be a non-issue.

I also noticed the TB driver in your design is not available to me (I have to shop on solen.ca fyi). I wonder if the SMF version would do well in your design. The other tough part is that it's nearly impossible to predict what the in-room extension would be. I definitely "need" it to go to 30-32Hz f3 to satisfy this system and to make this whole project worth doing in my case. I like a variety of music, but especially with certain bass guitar, piano, double bass and other low instrument parts, the low 30s are very important.

That said, I can't help but wonder if the Triumph would dig down deep enough in-room and sound better overall with music, even though it doesn't have as low of a modeled f3.

 

[hv6478]

Add mass to the PRs to drop the tuning frequency.

Chris

Totally missed this response -- great point and thank you. I will dive a bit deeper into PRs and their mass and do some more research. I've see mixed opinions on PR performance, not sure what to expect as I've never heard one.

 

[chris661]

A good PR system will sound like a good ported box, but with subtle differences:

- So long as you have enough PR cone area, they won't compress at high levels
- A PR box tends to be smaller because you're not trying to fit a 1m+ port in there
- PRs will add a little harmonic distortion as excursion increases, just as the main driver will. That will probably lead to a more even distortion profile.

When I say "distortion", we're talking a couple of percent THD, but it will be level-dependent. I've pushed drivers to >100% THD before now, but it doesn't sound pretty.

Chris

 

[Brian Steele]

PRs will add a little harmonic distortion as excursion increases, just as the main driver will. That will probably lead to a more even distortion profile.

I hadn't thought of the distortion again, but yes, seems to be correct based on measurements of my current build. Luckily we're not very sensitive to distortion at low frequencies, particularly when it involves music rather than sine waves.

BTW, that driver seems to have quite a bit of excursion potential. I wonder if a passively-assisted design for it might work? I'm actually about to try just that sort of alignment with two 12" drivers that I have lying about. Lots of decent Xmax and they will be used nearfield, so I will likely not be running them anywhere near max linear output anyway.

 

[GM]

Thanks very much for the greetings and reply!

I imagine you mean a steeper roll off on the low end?

Would something more like 1x4 combat those bends enough?

Perhaps a modest outboard power amp would work if I could figure out a good way to hide it in the setup.

You're welcome!

No, a higher F3, slower roll-off; the bend's cumulative friction adds a resistive component.

A 1.273:1 rectangular ratio is the optimum with up to a [1.273*9]^0.5 = 3.3848:1 not much worse, so 4:1 is fine and one I often used in the 8 - 30 ft^3 towers I use to build, still recommend for Altec, et al low tuned HE vented alignments [aka MLTL in recent decades].

It won't be a 'Voxel' anymore, but this type alignment tends to perform better overall morphed into an inverse tapered TQWT and if needing fine tuning can add a 'stub' vent [ML-TQWT].

Definitely recommend a separate dedicated amp.

GM

 

[hv6478]

A good PR system will sound like a good ported box, but with subtle differences:

- So long as you have enough PR cone area, they won't compress at high levels
- A PR box tends to be smaller because you're not trying to fit a 1m+ port in there
- PRs will add a little harmonic distortion as excursion increases, just as the main driver will. That will probably lead to a more even distortion profile.

When I say "distortion", we're talking a couple of percent THD, but it will be level-dependent. I've pushed drivers to >100% THD before now, but it doesn't sound pretty.

Chris

Great info here and I'm going to consider those options. Maybe start with one due to the cost.

I hadn't thought of the distortion again, but yes, seems to be correct based on measurements of my current build. Luckily we're not very sensitive to distortion at low frequencies, particularly when it involves music rather than sine waves.

BTW, that driver seems to have quite a bit of excursion potential. I wonder if a passively-assisted design for it might work? I'm actually about to try just that sort of alignment with two 12" drivers that I have lying about. Lots of decent Xmax and they will be used nearfield, so I will likely not be running them anywhere near max linear output anyway.

Seems to be quite a lot of love for PR and other builds have successfully used this driver for them as well, so definitely going to consider this an option. Would shrink the footprint a bit as well. Are you doing dual 12" passives with a single driver in your setup? And is it mostly for music as well?

You're welcome!

No, a higher F3, slower roll-off; the bend's cumulative friction adds a resistive component.

A 1.273:1 rectangular ratio is the optimum with up to a [1.273*9]^0.5 = 3.3848:1 not much worse, so 4:1 is fine and one I often used in the 8 - 30 ft^3 towers I use to build, still recommend for Altec, et al low tuned HE vented alignments [aka MLTL in recent decades].

It won't be a 'Voxel' anymore, but this type alignment tends to perform better overall morphed into an inverse tapered TQWT and if needing fine tuning can add a 'stub' vent [ML-TQWT].

Definitely recommend a separate dedicated amp.

GM

This is awesome, and before some research I didn't understand it all. Makes a whole lot of sense and I'm glad that a 4:1 is an option, if I stay with a slotted design I will go for that ratio at most.

This design and modeling it though, is difficult for me to grasp. Not sure how I would determine the correct angle and length, positioning, need for a port, etc. I can't seem to find that option in WinISD but I apologize in advance for my potential ignorance. A bit of a start on some guidance on this would be awesome and I'm curious!

For the dedicated amp, I'm running into one snag trying to figure out a subsonic / high pass filter for the driver to protect it from xmax especially at the lower frequencies. It seems the DSP-integrated ones all have this feature as standard, but that would take this project a bit beyond its original scope of pricing and also have a LOT of extra power. I know it's good, but it would be extreme amounts of headroom that seems unnecessary for this system. Any insight on this would be greatly appreciated.

Great to see some action in this thread and I really appreciate it. Can't wait to get them (or it) built. Will be posting some new revisions with a 4:1 vent port without an internal amp, as well as maybe a PR version.

 

[Brian Steele]

Are you doing dual 12" passives with a single driver in your setup? And is it mostly for music as well?

"Passively-assisted" doesn't involve the use of passive radiators. Basically you add a whole bunch of capacitance in series with the driver mounted in a sealed box. Get the amount right, and the result is an extended response (the graph I provided is one such alignment). It also seems to knock down the inductance hump a bit. The graph is a sim of 12" drivers in a 1 cu.ft. (!) box. Basically the speaker baffle for the box will be just slightly bigger than the speaker itself.

It's the first time that I'll be trying it out. But the sims look good. The plan, if it comes to fruition, is to mount each 12" passively-assisted subwoofer on each side of the couch in the living room, for some nearfield subwoofer goodness.

 

[hv6478]

"Passively-assisted" doesn't involve the use of passive radiators. Basically you add a whole bunch of capacitance in series with the driver mounted in a sealed box. Get the amount right, and the result is an extended response (the graph I provided is one such alignment). It also seems to knock down the inductance hump a bit. The graph is a sim of 12" drivers in a 1 cu.ft. (!) box. Basically the speaker baffle for the box will be just slightly bigger than the speaker itself.

It's the first time that I'll be trying it out. But the sims look good. The plan, if it comes to fruition, is to mount each 12" passively-assisted subwoofer on each side of the couch in the living room, for some nearfield subwoofer goodness.

Were I a bit more brave I'd love to try this myself but I will patiently await your outcome (if it happens) and maybe use it for a future project. The world of audio/speakers is extremely fascinating.

Have been a bit busier than usual with work (no complaints!) but will get some new drawings out soon. For simplicity and given that this is my first build, I'm leaning towards sticking with a 4:1 ratio slot port and finding the right external amplifier for it. The Monoprice 100W simple one seems like it would fit the bill quite nicely (65 WPC at 4 ohms) though I don't think it has a high pass / subsonic filter built in.

 

[Booger weldz]

I did this(yellow pic) with that little tangband and it simmed as the red response curve in the bare cabinet using horn response. The blue was what I got from the RTA in REW(with smoothing drawn). I considered redoing it with a smaller throat chamber and without the expansion, but it’s all broken in now and is pretty fun for a 5.25”. Pretty sure you’ll enjoy it. If I see one @ parts express restock or on sale I’ll be jumping for another.

I used a plate amp on it... yuck. Try the 100w t3116 Chip amp?