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Ricci's Skram Subwoofer & Files


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This is the long delayed single driver sub similar in design to the Skhorn. Overall the performance goals and criteria were quite similar. Big surprise there! The Skhorn works so well at what it does

Ok... report after 3 full days of Skram use.  Josh, thank you for this amazing design! I am simply blown away that this kind of performance can be had through diy designs, you are doing the music worl

So close.  Loading drivers and doing the wiring today 

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2 hours ago, ChikoRomantiko said:

The frequency response is taken from the original pdf 451 and 551 :)

Looks like the conditions for those measurements are completely different. The response will be dominated by the enclosure alignment anyway. I would ignore these.

Either driver should work well in the Skram. I would suggest the 551 due to a little bit of extra power handling and functional xmax. 

Nice build! 

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  • 3 weeks later...

Still looking for something I can get to put in these for a reasonable price in Australia without $1000+ shipping, the best I've found so far is this:
http://www.theloudspeakerkit.com/rss460ho-4-18-reference-ho-subwoofer-4-ohm?fbclid=IwAR1JAm7KnbBwCsonNZ9AorrNEzcOgoq7e0ZhdofCSj_un8zpBBL20hlqiqw

Power handling is obviously a lot lower but I don't have that much power anyway, good sensitivity and a fairly low FS, is it even remotely suitable for bass music in an SKRAM?
 

Nominal Diameter 18"
Power Handling (RMS) 900 watts
Power Handling (max) 1800 watts
   
Impedance 4 ohms
Sensitivity 93 dB @ 2.83V/1m
Frequency Response 20 - 500 Hz
Voice Coil Diameter 76.2 mm
   
DC Resistance (Re) 3.2 ohms
Voice Coil Inductance (Le) 2.24 mH @ 1 kHz
Resonant Frequency (Fs) 18.8 Hz
Mechanical Q (Qms) 4.05
Electromagnetic Q (Qes) 0.35
Total Q (Qts) 0.32
Diaphragm Mass Inc. Airload (Mms) 499g
   
Mechanical Compliance of Suspension (Cms) 0.14 mm/N
Surface Area Of Cone (Sd) 1,164.0 cm²
Volume of Displacement (Vd) 1,484.1 cm³
BL Product (BL) 23.4 Tm
Compliance Equivalent Volume (Vas) 272 liters
Maximum Linear Excursion (Xmax) 12.75 mm
   
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Perhaps those are Aussie dollars which are 1 : 0.76 USD (currently).  Even still!

@h3idrun: Tthat driver should do pretty well.  Dayton also has a new 21" with similar motor and price, albeit 8 ohm vs. 4 ohm impedance.  I don't see it listed at your store, but you might contact them and ask if they are planning to stock it soon:

https://www.parts-express.com/Dayton-Audio-PSS555-8-21-Pro-Subwoofer-with-4.5-Voice-Coil-8-Ohm-295-050

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4 hours ago, SME said:

Perhaps those are Aussie dollars which are 1 : 0.76 USD (currently).  Even still!

@h3idrun: Tthat driver should do pretty well.  Dayton also has a new 21" with similar motor and price, albeit 8 ohm vs. 4 ohm impedance.  I don't see it listed at your store, but you might contact them and ask if they are planning to stock it soon:

https://www.parts-express.com/Dayton-Audio-PSS555-8-21-Pro-Subwoofer-with-4.5-Voice-Coil-8-Ohm-295-050

Yea, but 700AUD is 440‚ā¨ and the 21DS115 can be had for 400 here atm, if you take 4. Last time I ordered I paid 380 per driver (bought 2). Am B&C OEM now thou, so I can order directly. Can't tell those prices for obvious reasons :)

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The B&Cs aren't too much more for the actual driver in AUD, its the shipping that's the killer, I can buy a whole extra Dayton for less than the price of shipping for 4x 21s of any kind that I've found so far. Whereas that store seems to already have Australian stock of the Daytons and shipping is basically free.

@chrapladm me and a friend in Melbourne are planning to get 2 each and hoping to spend around $7-800 or less per driver including shipping.

He's just finished his first cab, followed the plan a lot more closely than my first 2 so will be good to compare!

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  • 3 weeks later...

G'day!

First up, hello, and let me add my thanks to @Ricci for the generous provision of your plans and knowledge.  I've gotten interested in live sound recently after long absence, but this time have carpentry/joinery skills in my back pocket!  I can't wait to build my first Skram once the appropriate number of pennies have been saved for a driver.

 

For @h3idrun, I know your pain as a fellow payer of the Australia Tax!  I've spent quite a bit of time researching buying drivers, so for what it's worth, here are some observations that may help:

- I've found TLHP in France to be by far the cheapest supplier of drivers to Australia.  I haven't used them, but they claim to be the EU's biggest stockist of speakers.  I'm surprised you don't hear about them more, but I guess in the US at least pretty much everything would be distributed there..

- Ordering from TLHP, the sweet spot for 21" driver prices is up to 400 euros.  Once you add shipping and convert to AUD, it gets you just under $AUD1000, which means not involving customs (assuming you're happy buying one at a time).  By the way, if you make an account with them, you'll see ex. VAT prices and be able to calculate shipping.  Drivers under that amount include B&C 21SW115-4, Lavoce SAN214.50, and others by RCF, Beyma, etc.

- In terms of Australian stock, there's obviously very little.. Here's a link to an SB Audio 21" from Wagner Online (no idea about its suitablity); The Speaker Factory stock Eminence drivers, but only seem to have 18" max; then you can also obviously buy through eBay, but you'll have to pay GST and I've only seen prices a fair bit higher than THLP anyway.

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While I'm at it, what are the important considerations for the type of plywood?  Is it just stiffness?  I used some lightweight plywood a little while ago, and from memory it was something like 40% lighter than the usual stuff.  The seller claimed it was as strong as a standard type of plywood, but I don't know by what metric.

I don't know if this is a foolish aim, but I'd love to be able to throw one of these around by myself if necessary..

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5 hours ago, bee_dub said:

While I'm at it, what are the important considerations for the type of plywood?  Is it just stiffness?  I used some lightweight plywood a little while ago, and from memory it was something like 40% lighter than the usual stuff.  The seller claimed it was as strong as a standard type of plywood, but I don't know by what metric.

I don't know if this is a foolish aim, but I'd love to be able to throw one of these around by myself if necessary..

I wouldn't go for a lightweight plywood like that for a design like this. Think of the cabinet like a musical instrument, the stiffness and density of the cabinet will contribute to the sound in many ways. If the cabinet can vibrate and resonate with the driver movement it will color the sound coming from it and you may not be happy with the outcome. If you can't do baltic birch you could get away with mdf as it quite solid and dense, its pretty heavy though. 

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4 hours ago, jay michael said:

I wouldn't go for a lightweight plywood like that for a design like this. Think of the cabinet like a musical instrument, the stiffness and density of the cabinet will contribute to the sound in many ways. If the cabinet can vibrate and resonate with the driver movement it will color the sound coming from it and you may not be happy with the outcome. If you can't do baltic birch you could get away with mdf as it quite solid and dense, its pretty heavy though. 

Sure, thanks.. weight is the main consideration, so I would definitely not use MDF. 

When you say it's like a musical instrument though, instruments like a cello for instance are made to resonate, whereas here we're aiming to prevent it, yes?  

Also, if one theoretically was to attempt a lighter weight version, would it be possible to include some extra bracing, or would this interfere with the properties of the design?

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1 hour ago, bee_dub said:

Sure, thanks.. weight is the main consideration, so I would definitely not use MDF. 

When you say it's like a musical instrument though, instruments like a cello for instance are made to resonate, whereas here we're aiming to prevent it, yes?  

Also, if one theoretically was to attempt a lighter weight version, would it be possible to include some extra bracing, or would this interfere with the properties of the design?

Yeah its more like the opposite in this case. If the box resonates a lot, it will add its own sounds to musical output, which is not ideal.  There are box designs out there that use thinner wood and extra bracing, so to an extent perhaps you could get away with it up to a point. If you are planning to use the recommended driver at the maximum powers the box will have a lot of energy in it, so good bracing is really important

 

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Stiffness is most important, and Baltic Birch plywood tends to be stiffer than most other varieties, not just because birch is a hardwood but because the boards are assembled from a greater number of thinner plies compared to most plywoods.

Higher mass also helps with blocking sound transmission, more for high than low frequencies, but it also lowers the fundamental resonant frequency of the panels at which disproportionately more sound is able to pass through.  Hence, most speaker and sub construction tends to favor higher stiffness and lower mass.

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22 hours ago, bee_dub said:

Sure, thanks.. weight is the main consideration, so I would definitely not use MDF. 

When you say it's like a musical instrument though, instruments like a cello for instance are made to resonate, whereas here we're aiming to prevent it, yes?  

Also, if one theoretically was to attempt a lighter weight version, would it be possible to include some extra bracing, or would this interfere with the properties of the design?

Just to make things clear about the mdf, mdf and baltic birch are the same weight by volume just the baltic birch is far stronger and much more durable. I did make an othorn out of mdf and it performs surprising well but i only did it as a kind of a mock up, id say it will be around a while as it stays on the property, i wouldnt expect it to last too long if it were lugged around to gigs and so on. I have got as couple of pieces of australian plantation hoop pine ply(aracauria cunninghamii, nice trees!) laying around and that stuff isnt too bad assuming the price was right. I think birch is the right stuff for the job. I saying that many have had success with other woods as well.

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Baltic Birch 13ply BB/BB from local lumber yards are a few bucks more than maple, oak, and Southern pine 7 ply and MDF at the box stores in most the USA. ($60ish)

If painting, the BB/BB is a no brainer in my opinion. 

If staining, the BB/BB can work as well if you are able to be selective or properly position your cuts around the patches. 

The AA/XX variety is usually about 100 bucks. 

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On 2/25/2021 at 12:10 PM, bee_dub said:

While I'm at it, what are the important considerations for the type of plywood?  Is it just stiffness?  I used some lightweight plywood a little while ago, and from memory it was something like 40% lighter than the usual stuff.  The seller claimed it was as strong as a standard type of plywood, but I don't know by what metric.

I don't know if this is a foolish aim, but I'd love to be able to throw one of these around by myself if necessary..

I don't know if you saw my skram built on page 26 or so, I built 2 of them, made of popplar plywood with a carbon-epoxy layer around to make it stiffer. Then we made the front out of 25mm transparent acryl glass, just to loose the weight savings due to the 10kg (just a wild gues, I forgott the real numbers) of those fronts haha. We didn't put them on a weighting scale yet, but without the heavy front, they would be ridiculously light! So light that we will make a base filled with sand to make sure they dont move more than the drivers do.

We also didn't fire them up, but that will happen soon, hopefully... so I cannot say anything about the stiffness and if there is anything hearable compared to our baltic birch skram, but I will male a post as soon as that happened. 

We will make 2 more of them, without acryl glass front, because we have the materials, but I also have to say that it is a hack of work to prepare all the plates, and also, it is really expensive of course, so i dont think that we will do this again after those next two.

IMG_20210226_230224_574.jpg

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58 minutes ago, klipsch said:

Baltic Birch 13ply BB/BB from local lumber yards are a few bucks more than maple, oak, and Southern pine 7 ply and MDF at the box stores in most the USA. ($60ish)

If painting, the BB/BB is a no brainer in my opinion. 

If staining, the BB/BB can work as well if you are able to be selective or properly position your cuts around the patches. 

The AA/XX variety is usually about 100 bucks. 

The story is not so pretty down here, im in new zealand and bee dub is in australia i believe.

In nz 18mm birch is nearly 130usd per sheet and the story will be similar in ozy... economy of scale and shipping exspense, it is what it is! Hence a lot of guys down here trying for easier on the pocket options!

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58 minutes ago, menace said:

The story is not so pretty down here, im in new zealand and bee dub is in australia i believe.

In nz 18mm birch is nearly 130usd per sheet and the story will be similar in ozy... economy of scale and shipping exspense, it is what it is! Hence a lot of guys down here trying for easier on the pocket options!

Is that $130 for AA or BB or other quality? 

Cabinet grade Baltic birch is around $120s to 150s depending on thickness 

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Just now, klipsch said:

Is that $130 for AA or BB or other quality? 

Cabinet grade Baltic birch is around $120s to 150s depending on thickness 

Its not the really clean stuff(as i did score a bunch of quarter sheet off cuts of that and it was really tidy faced)... dont know how much that would be...

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Huh, I'm surprised that Birch ply is the same weight as MDF.. I'm always surprised by how heavy 18mm MDF feels.

 

So for a sub that needs to be as light as possible, but not at the expensive of functionality, should it be all 18mm Birch ply? Or could bracing be lightweight ply?

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10 hours ago, menace said:

Just to make things clear about the mdf, mdf and baltic birch are the same weight by volume just the baltic birch is far stronger and much more durable.  [...]

I've always regarded MDF to be heavier than BB plywood, so I decided to try looking it up:

https://www.inchcalculator com/how-much-does-plywood-weigh/

Different products will vary a bit, but the chart there suggests BB is only about 70% as heavy as MDF.  I do agree that BB plywood is stronger and more durable than MDF.  There are other pros and cons.  MDF is more messy and toxic to work with (dust) but also a but more forgiving.  MDF has more adhesives which may improve its damping properties.  Many speaker makers argue that the damping properties of MDF make it superior to BB despite the lower stiffness-to-mass ratio.

My thought is that MDF is OK for things that don't get moved/transported a lot and where weight is not important.  For big subs that get moved around a lot, MDF is not a good idea.

If BB plywood is exceedingly expensive in AU/NZ perhaps look for another high quality hardwood plywood product.  As I noted above, BB tends to have thinner plies than other types.  Another benefit of BB plywood over other stuff is that it tends to be void free.  (Tends to---alas the last stock I bought still has a few small gaps :()

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Guess it should also be noted that here in the States, birch plywood is typically more expensive than Baltic birch plywood (region and species differences similar to the differences between pine VS southern yellow pine).  

If in the Midwest States or you don't have access to Baltic birch in your local area - Baird brothers has good stuff. I'm in the Northeast States and with an order of 10+ sheets, Baird Baltic birch BB plywood delivered to my shop was cheaper with better selection. 

https://www.bairdbrothers.com/mobile/Hardwood-Plywood-C966.aspx

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The MDF I have is 800kg/m³ and my ply is 650kg/m³, which makes the MDF 23% heavier. My dad has some old Klipsch speakers made from plywood which feels like half the weight of the plywood I'm using for my subs, there are huge differences. I worked a lot with MDF lately (for studio monitors) and I'm not a fan of it. Won't hold screws well is my main issue here, since I don't care about the dust (my 7KW dust collector leaves nothing on the cnc). Will probably switch to carb2 CDF for the baffles at least, even thou it's literally 6x the cost.

Those old Klipsch speakers are a mess imo. Light ply with no bracing, no gasket tape on the hatch and the tweeter and mid horns are back-mounted on the 1" baffle...

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