Single 12" bass Cab

[Count Bassy]

[quote name='Phil Starr' timestamp='1495956179' post='3307691']
Since then working on the Mk2 we've found that a single port gives a lot less port noise than a group of four with the same cross sectional area. I'm not keen on four corner ports for that reason, but it does help stiffen the cab. Balloon wrestling again.
[/quote]

One thing (possibly the only thing) I remember from my Physics degree is that at the same pressure doubling the diameter of a pipe will increase the flow by a factor of 16, not the 4 times that the actual area might suggest.

So, although 4 ports of diameter X will have have the same area as a single port of diameter 2X, the flow through the single large port would would 16 times that of a single port at X, or 4 times the flow of 4 ports of the same total area.

[Phil Starr]

[quote name='Count Bassy' timestamp='1496183854' post='3309468']
One thing (possibly the only thing) I remember from my Physics degree is that at the same pressure doubling the diameter of a pipe will increase the flow by a factor of 16, not the 4 times that the actual area might suggest.

So, although 4 ports of diameter X will have have the same area as a single port of diameter 2X, the flow through the single large port would would 16 times that of a single port at X, or 4 times the flow of 4 ports of the same total area.
[/quote]

I have a distant memory of studying fluid dynamics 40 years ago and some 'interesting' maths. It should have been obvious but it's easy to get complacent when using computer models . I guess that narrow ports are more resistive and you get turbulence at lower port velocities.

[Phil Starr]

[quote name='Thunderpaws' timestamp='1496179548' post='3309432']
Is it the volume of the port that matters? For example, if corner triangular prisms were used, should the volume of the prism be the same as the volume of the cylinder that makes a circular tube port?
[/quote]

Yeah, as Beer of the Bass says you need to calculate the ports for each cab and tuning but in a practical sense the length of the port depends upon it's cross sectional area so if the corner ports are the same area as the round ones their length will be the same. There's a slight complication because the termination of the port has a different impedance against the walls of the cab so there will be a small end correction to apply. In practice the cab would work OK but you probably wouldn't hit the tuning exactly.

[Phil Starr]

[quote name='Bill Fitzmaurice' timestamp='1496144686' post='3309067']
I don't know about Linden, but American Basswood is too lightweight for speaker cabinets. It's considered a junk wood, not suitable for construction or furniture. It doesn't even burn well.
[/quote]

It's just not something we see over here as a plywood so I've no experience of it. My son lives in Japan and when we visit I grab the chance to look at Japanese joinery. I don't recognise many of the timbers and like everything in Japan they try to use Japanese materials. The ply I've seen is fantastically good quality but was being used for finish work so you'd expect that.

DIYJapan you need to just chat with your timber merchant about it's suitability, you don't get to do anything in Japan without a hell of a lot of training so they are likely to be knowledgeable about timber even if not speaker cabs.

[DIYjapan]

Phil, I'm looking into the linden ply which is 7 ply at 15mm. Also found an importer of Latvian birch 11ply at 15mm. It costs a little bit more, double actually, but would probably look better.

Contacted a Russian Waterproof birch ply importer too but I'm still waiting for a reply from them. Right now I'm leaning towards the Latvian birch.

[Jus Lukin]

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Edited February 24, 2022 by Jus Lukin

[Marty Forrer]

With all due respect to Mr Bill Fitzmaurice, I have just built a Greenboy Fearful 12/6 from scratch, not a kit. I have pumped 500 watts RMS of double bass signal (huge transients and organ re-arranging bass) and have no problem with the spine bracing. I will be stone deaf before I hear any rattles or vibration. Each to his own.

[Bill Fitzmaurice]

[quote name='Marty Forrer' timestamp='1496374873' post='3310886']
With all due respect to Mr Bill Fitzmaurice, I have just built a Greenboy Fearful 12/6 from scratch, not a kit. I have pumped 500 watts RMS of double bass signal (huge transients and organ re-arranging bass) and have no problem with the spine bracing. I will be stone deaf before I hear any rattles or vibration. Each to his own.
[/quote]With all due respect, I've done extensive testing of both, in the same cab configuration, side by side. Panel to panel bracing is at least four times as effective as spline bracing, with less weight. Modal analysis bears that out, but I prefer to rely not on analysis alone. Your results may be acceptable, but unless you have built both configurations you have no basis for comparison.

[DIYjapan]

[quote name='Bill Fitzmaurice' timestamp='1495813099' post='3306832']
Panel to panel braces are far more effective, and allow you to build a cab from 1/2"/12mm plywood for a lightweight cab.
[/quote]

I've been redrawing my plans with light spline bracing and panel bracing Left to right side and front to back.

I have a question in regards to the wood for this purpose. I will probably use leftovers from the original plywood. In case I run out would cheap pine from the home center work? They also have some nice lightweight spruce (18x18mm) that looked way better than the pine and not much more price wise.

[DIYjapan]

In regards to the spruce: it also came in larger sizes, 24x24, 30x30, and 12 x (18, 24 or 30).

[Bill Fitzmaurice]

Panel to panel braces can be made from whatever is handy. There are no flexing forces exerted on them, only compression and extension, so stiffness isn't required. When I use spline braces, only if there's no place to put a panel to panel brace, they're plywood, at least and inch and a half wide, because they do require as much stiffness as possible.

[DIYjapan]

Help with winISD.
So I downloaded this software and have been playing around with it for about a week now, don't let my wife know, and man is it great. I entered the stats for the Eminence Beta 12a-2 and I even entered them correctly I hope. Here is a screen shot of the response I get for the basic 1 watt input. I've designed this cab and considering the internal bracing the internal volume will be about 57.5 litters. The plan calls for a vented port out the front. It will be divided in half so I input 2 ports into the software. The will be 4cm tall, 18.5 wide and it looks like 19cm long. Those measurements give me this graph result. Looks like a nice curve to me. I can get it to bump at the 100hz area by shortening the vent but I didn't think a huge bump was a good thing. Anyone with more experience with this let me know if my graph looks acceptable? Thanks
[attachment=246795:57L4CM19CM.jpg]

[DIYjapan]

Here is a mock up battle between an Eminence Beta 12a-2 (white), Delta 12(pink), and a Delta 12lf(green). To me the green Delta 12lf would be the best choice. So only problem is I can't get the old driver and will have to put in new stats for the newer 12lfa version. But, (again, maybe I'm reading this graph all wrong) it looks like that is the best choice for the box I'm designing.

[Phil Starr]

Well done, now you have access to the software you can answer a lot of your own questions.

That 3dB hump is fairly typical of a lot of commercial designs. In practice it gives a good solid bassy thump to your sound. It's caused by a lack of damping of the cone at low frequencies. Bigger magnets on the speaker and bigger air masses from having a bigger box will damp the excursion and flatten the curve which is what the Delta and 3012HO will do for you. Hence the rule that you can't have cheap, deep and lightweight. The flatter deeper curve will give you a cleaner more detailed bass but can excite room resonances when used live in smaller venues. That is easily solved by rolling off the bass in most situations.

It's worth your while looking at the port velocities and excursion graphs too. Input the maximum power you will operate at and see where your speaker exceeds Xmax on the excursion graph. Limiting the size of the box will give you a bit more power to play with at the expense of a little less bass. If you tune high you usually get good handling down to the tuning frequency but problems below that with excursion. If you tune low then the excursion low down improves but you can get problems in the 80-100Hz region opening up. Don't tell your wife, I can spend hours fiddling to get just the right compromise.

the problem with the Delta is that it has an extraordinary spike in response around 1-2kHz (from memory) and the DeltaLF has little midrange output as it is designed to work with a tweeter. Only use the LF if you are going to use a horn. The 12A-2 has a nice peak with quite a wide span which with the bass hump in your model gives the speaker a nice smiley face response curve, the classic old school bass response.

Finally that 57litres, have you taken of the volume of the speaker and the bracing? It might have a volume close to 50l by the time you allow for all that.

[DIYjapan]

The 57L is with the bracing. Without I was about 62L.
As for port velocity: I was looking for that but haven't found it yet on the software.
Also went and looked at the SPL running at 250watts. The max of my little Tc electronics BH250. Looks like I may get in trouble if I crank it up. There was a spike below 50hz and another bump over the red line from 100hz area. Worrisome?

[Bill Fitzmaurice]

Of the three I greatly prefer the green. The white will be boomy in the midbass and weak in the lows. What they don't show is response above 200Hz. That you can only find by comparing the charts on the Eminence data sheets. The Delta 12LF will be weak in the mids. You also should be looking at the SPL chart, not the transfer magnitude chart, which doesn't take into account sensitivity. For comparison this is the measured response of the 2512 plus tweeter in my Simplexx 12:



You can see the midbass hump is slight, so boom won't be an issue, and the low end is stronger as well.
You're also missing two charts that are of equal importance to the SPL chart, the maximum SPL chart and the rear port velocity chart. The port velocity chart, which needs to be calculated at the maximum power of the driver, tells you how large the port area must be to keep port velocity below 20m/s to eliminate port noise. Too much area isn't good either, it makes the port longer and therefore the cab larger for no reason.

[Phil Starr]

[quote name='DIYjapan' timestamp='1496757303' post='3313666']
The 57L is with the bracing. Without I was about 62L.
As for port velocity: I was looking for that but haven't found it yet on the software.
Also went and looked at the SPL running at 250watts. The max of my little Tc electronics BH250. Looks like I may get in trouble if I crank it up. There was a spike below 50hz and another bump over the red line from 100hz area. Worrisome?
[/quote]

That increase in excursion below the port tuning frequency is shown by all ported designs. I've put up a thread about it which a lot of the techie BC people contributed to. It might be worth a read. It's not a problem if you use a good low frequency filter like a Thumpinator or you avoid boosting those frequencies which are pretty much out of our hearing range and not particularly prominent in the output of your pickups. It doesn't cause a problem for most of us but people do sometimes blow speakers if they are unaware of it and do strange things to get 'more real bass' You need to be aware of it is all.

The higher peak, midbass peak if you like is what is causing the over excursion in that area. The 12-A2 doesn't have the super excursion that the better drivers like the 3012HO have. Have a look at the maximum power charts and you'll see there is quite a reduction in the maxumum power. Whether it's a problem depends upon how you use the speaker. There's a little safety in that the safe mechanical limit is 11mm so brief peaks aren't going to damage the speaker. The 12A-2 is pretty reliable for most of us. Long term flat out use with lots of bass boost might cause the speaker to overheat though.

Try modelling it in a smaller box and you'll see that the maximum power will increase at these frequencies as it will if you raise the tuning frequency a little.The trouble is that both changes will give you less bass but that might be acceptable. We spent a long time tweaking our designs to get where we did.

I don't thrash my speakers and quite like that midbass warmth but that's a personal thing. It wouldn't worry me but it's something to note certainly. If you are concerned it may be worth going for the more expensive driver and a smaller box.

The excursion wouldn't worry me

[DIYjapan]

Air velocity with the amp pumping 250 watts. WOW. I blew it off the chart. crud.

[DIYjapan]

Here we go with the amp pushing out 50 watts. This looks more reasonable. Will definitely have to reduce air noise on this thing somehow. What a difficult thing this balloon wrestling. Feels like some one greased the balloon. I guess that is part of the fun.

[Bill Fitzmaurice]

If designing speaker cabinets was easy everyone would do it. Just to complicate matters further, it looks like you're using WinISD Beta, or perhaps an old version of Alpha. I can't tell which from the photos, as they're too small to make out details, and in any event I haven't had either of those for quite a few years, so I have nothing to compare to. You should be using WinISD 0.7.0.950.
http://www.linearteam.org/

[DIYjapan]

[quote name='Bill Fitzmaurice' timestamp='1496838355' post='3314185']
If designing speaker cabinets was easy everyone would do it. Just to complicate matters further, it looks like you're using WinISD Beta, or perhaps an old version of Alpha. I can't tell which from the photos, as they're too small to make out details, and in any event I haven't had either of those for quite a few years, so I have nothing to compare to. You should be using WinISD 0.7.0.950.
[url="http://www.linearteam.org/"]http://www.linearteam.org/[/url]
[/quote]
I downloaded the winisd pro alpha. I can't recall the release date but I did notice that a lot (all) of the newer eminence drivers kappalite 3012, beta12a-2 (which I am modeling) are not in the database. I had to input the driver specs myself. Will look into downloading an updated version. Thanks for the heads up Bill.

[DIYjapan]

Still a newbie question: I have subtracted the bracing that I will be using from the internal volume but I didn't take into account the dampening materials. I haven't found anything that I can use yet here locally so I'm not sure what I'll be using. I've found, well I think I have, a good source of wool dampening material and some decent looking eggcrate stuff made for sound cancellation. Found other egg crate stuff that look really cheap too but thought that the denser stuff would work better.
Right, question: Do I need to subtract the space of the dampening materials too?

[Bill Fitzmaurice]

Damping doesn't take up acoustical space.

[DIYjapan]

The sheet of plywood 15mm will be more than enough for a single cab so I'm contemplating making a second cab out of the leftovers. Does anyone have a 12" they'd recommend for a smallish (+-40L) sealed cab?

[DIYjapan]

12mm or 15mm? Opinions and reasons behind those reasons please.
The best option for birch ply is 12mm sheet for $118.
Or 15mm for $141. Shipping for either would be the same.

I was leaning towards the 15mm for the extra stability and gives me a little extra stiffness in case I mess up/ under brace the box.

A plus for 12mm is a slightly lighter box and a little easier on the wallet (but, not too much). I would have to get the bracing right and I'm pretty sure that's doable. I know the fearfuls are all designed for 12mm so it's probably fine.

But, bagends look rugged as heck and they are thicker 18mm not 15mm. 18 is out of the question for me.