Manganese - New Deck Speakers

ScottS

In this time of social distancing, our family is continually trying to create more spaces for small scale entertaining or just hanging out. More of our get togethers have been outdoors. As a speaker guy, the general requirement is that every living space should have some sort of sound system. Now that our deck has become more of a living space, it needs speakers. When I set out on this project, the basic requirements were:

• Sealed - keep dirt and critters out.
• Small footprint - the deck isn't that big and now has more furniture.
• Inexpensive - it can't be a life changing loss when the next Tornado, Derecho, crazed pet, or over-served houseguest takes out one or both speakers.

My initial thought was to use a 5" x 5" composite fence post as the primary enclosure, but as I started to think about how I wanted to assemble everything, I decided it would be easier to just use some of the Birch plywood I already had languishing in the garage. I had a 5' by 30" sheet of 1/2" material, so I cut eight 5" x 30" strips, giving an enclosure 5" x 6" x 31" after adding end caps (about 9.8 liters).

For drivers, I was looking for either an aluminum or polypropylene cone woofer with rubber surround and with an OD of 5" or less and low cost (approx. $25 or less). The HiVi M4N has a 1 piece aluminum cone with rubber surround, works well sealed, and is $13 each. It doesn't have huge excursion, so we'll need two. For a tweeter, I have some Peerless DX20BF00-08's that came with a Solen sale order a while ago. I'm not sure if the dome will handle the elements, but they are cheap and the slight horn loading will help keep them out of harms way.

Here's a general idea how these will look.

I'm really not sure how these will do in the weather, but my finishing approach was to put a couple coats of deck stain on the sides and contrasting black stain on the endcaps. I then covered all panels with a couple coats of marine polyurethane. The bottom end cap is 7" x 8" to allow for more secure mounting.

In the next post, well get into the crossover, measurements and related squiggles.

ScottS

I measured all drivers on the tweeter axis at 1 meter using 2 channel measurements to capture absolute phase. The impedance measurements for the woofers were a little messed up, as the cabinet wasn't stuffed and wasn't well sealed due to the wires needing a place to exit. These drivers fell pretty easily into a crossover point of about 2.75 kHz, which should be reasonable for both drivers. Here is where it wound up.

The 0.3 uF cap in parallel with the woofer inductor creates a notch around 9 kHz, which helps some with the M4N breakup. These are gated measurements with a pretty short window (about 3.5 ms), so anything below about 300 Hz probably isn't very accurate. Above that, the response looks to be within about +/- 2.5 kHz. Initial listening went well enough to justify assembling everything and doing final measurements.

ScottS

For final assembly, the first consideration was the enclosure. If you model a pair of M4N's in about 9.5 liters sealed, you get something like a 3 dB peak. Clearly, this will need some significant stuffing or an aperiodic vent, which isn't really what we're looking for in an outdoor speaker. I took a strip of ultratouch R13 denim insulation, pulled it apart in roughly two half thickness strips, and attached that to the interior rear wall. I then stuffed the balance with several handfuls of morning glory fiber fill.

When these were assembled, the first measurement I took was an impedance measurement to get some insight into the alignment.

The peak impedance around 20 ohms just above 2 kHz agrees well with the sim. The resonance between 200 and 300 Hz is gone, and we now have a single sealed box peak around 95 Hz (the smaller peak between 40 and 50 Hz is a measurement artifact I see in most of my other impedance sweeps and can be ignored). The 95 Hz peak is now pretty small. I am able to model a similar impedance peak with a Ql of 20 and Qa of 2 in WinISD. This gives the a Qtc around 0.89 and an F3 around 80 Hz. The peak is clearly under control.

With that, we move on to the full suite of gated measurements.

ScottS

The first measurements were the final on axis measurement coupled with individual driver responses with the crossover applied. All of these were taken on the tweeter axis at 1 meter.

Key features of this are a 2.77 kHz crossover point indicated by the low point in the reverse null and 5 dB between the highest and lowest response point. The final response matched the sim pretty closely, which is always reassuring.

I then took a set of horizontal off axis responses.

I thought the most interesting observation was the off axis response starting to drop off above 1 kHz. I would not have expected that to start at such a low frequency for a 4.5" woofer. Coincidentally, there is a rise in the on axis response in the same area, so maybe that is a good thing...

There is a dip around the crossover point that gets a little more pronounced off-axis. Otherwise, things seem pretty well-behaved.

If any of you follow the Audio Science Review forum, you may have noticed that I submitted a couple of my designs (the Helium and perfectionist mod of the HiVi DIY 3.1) for review over there. I picked those because enough of both have been built that they might be of wider interest. This was, in a way, a substitute for me for DIY events this year. It was also an opportunity to try to up my design and measurement game. With that in mind, I have started messing around with VituixCAD. I did a more extensive set of horizontal off axis measurements than I usually do to support this.

Here are a few results.

The power response is nearly ideal up to the crossover point, there is a dip in the crossover region, then the small horn/waveguide leads to a little too much output from 3-6 kHz and too little above 10 kHz. This didn't stand out as a large issue in listening tests.

The polar response clearly shows the dip around the crossover point. It would be improved by a lower crossover point, but that wouldn't work well for the DX-20 from a distortion/power handling perspective. The DIY 3.1 had a similar issue, but was did very well in distortion testing. I think that is a reasonable trade off here as well.

All-in-all my wife and I have enjoyed listening to these. There could be more bass, but they can play pretty loud without falling apart and the driver cost is about the same as what is in the C-Notes.

Kornbread

Nice build. I've used fiberglass resin to weatherproof mdf with excellent results.

PWRRYD

Cool project Dr.

What's the speaker with the HiVi dome mid sitting behind it?

Wolf

That's not a HiVi dome back there. It's the TB 3" from 2011.

ScottS

Correct, Wolf. That is the never published Vanadium project from 2011. Peerless OX20 tweeter, Tang Band 75-1558SE 3" dome midrange (aka "Tar Ball"), Aurum Cantus AC-200MKII woofer. The Tang Band mid is NLA and if someone bought the woofer, who knows what the T/S parameters would be? FWIW, they were very useable for my pair... I've made a few changes over the years based on better measurements and smoothing out the chamfer edges around the mid, which allowed me to get rid of a notch filter.

4thtry

Nice design. Horizontal polars look very consistent from about 2.5kHz and up!

I read the reviews for your Helium and perfection mod of the HiVi 3.1's over on the Audio Science Review forum. They really liked the perfection mod but had problems with the Heliums. I noticed their measurements were quite a bit different from yours on the Heliums. Why do you think that was the case?

ScottS

I am not quite sure yet. The discontinuities in the midrange from the ASR review are likely either some port noise or reflections from the Klippel NFS. The tweeter level is a little lower than what I measured. It could be that all of my other measurements are from the other speaker and there is just inconsistency in the ND16. The other possibility is that the automated measurement routine couldn't be set to measure something that small and the measurement pattern skewed the results.

I have the Helium back that was tested and still need to get around to taking some close-miked port measurements to see if I can find any artifacts around the problem frequencies and measure the reviewed speaker to check the tweeter level.

ScottS

I published a post mortem on the Helium's over on ASR

https://www.audiosciencereview.com/forum/index.php?threads/sehlin-helium-diy-speaker-review.15518/page-3

I measured the port output by putting the mic about 1/2" inside the port and measuring with no gate. The peaks were significant and aligned with the midrange discontinuities. At some point, I should try throwing a little ultratouch in one of those to see if it helps...

I also found differences in the tweeter response between the speaker I sent and the other one. It is clear that I designed based on the other one as that is what all of my design files match. I will have to actually do some disassembly to take measurements on just the tweeters to determine if the issue was tweeter variation, crossover component variation, or crossover assembly variation. The impedance matches closely enough between the two speakers that I don't think there was a major assembly error.

The key takeaways at this point are:

1. Always measure both speakers.
2. You might not capture things like port resonances in short-gated frequency response measurements.

ScottS

The deck speakers have been deployed for about a month and a half of midwest weather and seem to be holding up fine.

The Helmsman Polyurethane is doing its job and the DX20's so far seem to not be affected much. They are facing east, so that coupled with being a little recessed means they aren't getting much direct water contact.

Here's a wider shot.

For associated equipment, I am trying out a Pyle marine stereo head unit. There is a 12V Meanwell outdoor rated power supply attached.

Also needed to make some weather resistant speaker cables.

So far, everything is working pretty well. The head unit puts out enough power for the deck/patio area. Over the winter, I will give it a more permanent enclosure.

jhollander

I get the point but geez they are only 4 feet from the door.

Kornbread

Put a hat on them.

ScottS

@jhollander said:
I get the point but geez they are only 4 feet from the door.

The use case winds up a lot different for us. I have a boombox type system I can bring out, but we only wound up doing that when we had a get together and only if I set it up. With the current setup, if we decide to bring dinner out to eat on the deck or step out there for a refreshment or two, I just pair my phone and we have music.

ugly_woofer

I like it, I need to do something like this just for convenience.

ScottS

I built a second pair of these for a friend. My wife and I just delivered them last night.

I did a few things different this time. The finish is duratex - 3 coats of white with two additional coats of black for the tops. (friend's house has white siding with black trim). Underneath are two coats of Kilz 3 primer. What I learned from the first build is that the avenue in for the water was primarily the end grain of the birch ply and I didn't want to repeat that issue.

Instead of a separate control box, I decided to mount a marine bluetooth stereo and power supply directly into one of the speakers I chose this one

along with a 12V Meanwell lpv series power supply rated for outdoor use.

The decision to include the radio/amplifier into the speaker was made after the rest was completed, which made mounting the power supply a little awkward. The radio was just a 3" hole saw cut and a rectangular cutout for the iec power receptacle was also needed.

To operate, all you need to do is push the big power button in the middle, pair your phone and control using the phone - just like a typical bluetooth speaker except hopefully the sound quality. Each speaker has standard speaker terminals with one standard speaker cable connecting the two speakers. I'm happy with the ease of operation, and the little Pyle unit can get pretty loud and hold up decently for it's low price. We'll see how long it lasts...

ScottS

I should also mention that I used black expanded PVC sheet for the bases this time.

6thplanet

Nice way to spread the love👍🏼

PWRRYD

Nice work Scott. You coming to Iowa?

ScottS

@PWRRYD said:
Nice work Scott. You coming to Iowa?

I will be there. I have meetings down south on Friday, but will be heading up at the conclusion of that - should arrive around 9 pm.