Hi,
My names Jim and I'm just starting to learn the basics of speaker cabinet design.
Our first project is a man portable PA built into a British army bergen (rucksack)
I'm trying to get my head around calculating the dimensions of an ordinary sealed cabinet.
The drivers we will be using are here (PDF), because they're cheap, cheerful but come with a set of thiele small numbers.
I've used a calculator I found here (web page)
That worries me though because it's completely black box and is named as a designer for subwoofer enclosures. I don't know whether the maths is different for full range speakers.
Anyway, the bag minus batteries and amp leaves us with about 50liters of space for the cabinet.
Now, putting the numbers into that calculator get me a Qtc of 1.
So far I've read that you're supposed to aim for 0.707 but 0.5 to 1.2 is a usable range.
Unfortunately I don't have all the measurements and dimensions to hand, but I keep not getting round to making this post so I'm just taking the plunge.
Sound quality is not top priority in this project, it's just slightly behind:
1) Cost, apart from the fact nobody has much cash to throw around, the Mark 1 Noisy Bag is intended to be followed by more refined designs so we don't want to spend too much on something that will probably be just the first attempt.
2) Just Getting It Done. Seriously, we've been procrastinating for about 2 years now. It's time to get the hammers out.
3) And then sound quality, because there's no point in putting in all this effort/money if it's going to sound bad.
In fact it's really about striking a balance between all of the above 3 factors.
Speed, Quality and Cost.
Hmm, wait a minute, that reminds me of an old adage... ;-)
Anyway, I'll try to draw up and post some more details this evening (can I upload napkins and fag packets, back of? Does that work
)
Anyway, thanks for reading the ramble.
J.
My names Jim and I'm just starting to learn the basics of speaker cabinet design.
Our first project is a man portable PA built into a British army bergen (rucksack)
I'm trying to get my head around calculating the dimensions of an ordinary sealed cabinet.
The drivers we will be using are here (PDF), because they're cheap, cheerful but come with a set of thiele small numbers.
I've used a calculator I found here (web page)
That worries me though because it's completely black box and is named as a designer for subwoofer enclosures. I don't know whether the maths is different for full range speakers.
Anyway, the bag minus batteries and amp leaves us with about 50liters of space for the cabinet.
Now, putting the numbers into that calculator get me a Qtc of 1.
So far I've read that you're supposed to aim for 0.707 but 0.5 to 1.2 is a usable range.
Unfortunately I don't have all the measurements and dimensions to hand, but I keep not getting round to making this post so I'm just taking the plunge.
Sound quality is not top priority in this project, it's just slightly behind:
1) Cost, apart from the fact nobody has much cash to throw around, the Mark 1 Noisy Bag is intended to be followed by more refined designs so we don't want to spend too much on something that will probably be just the first attempt.
2) Just Getting It Done. Seriously, we've been procrastinating for about 2 years now. It's time to get the hammers out.
3) And then sound quality, because there's no point in putting in all this effort/money if it's going to sound bad.
In fact it's really about striking a balance between all of the above 3 factors.
Speed, Quality and Cost.
Hmm, wait a minute, that reminds me of an old adage... ;-)
Anyway, I'll try to draw up and post some more details this evening (can I upload napkins and fag packets, back of? Does that work
)Anyway, thanks for reading the ramble.
J.
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Hi Jim,
I'm not going to ask quite why this is to go into a bergen, I'll just presume you're a noisier than average member of the rambler's association. I should tell you that it's so long since I designed a speaker box that my information came off printed pages and I used a handheld calculator.
Sealed box and vented box are ok for your purposes, bandpass isn't. Are you going for sealed box because it's the simplest? A vented box will get lower cutoff frequency for a given volume, or smaller volume for given cutoff.
Vented box design is more involved and there's less protection for the speaker from damage by being fed high levels of signal below cutoff.
All this is jumping the gun a bit though, you've decided on a driver unit, but the link you give is actually to a specification for two different speakers, Slick 69.2, a 140W and Slick 69.3, a 160W version.
Maybe if you say which you're talking about, and quote the figures from those specs that you've put into the calculator you've used you'll get more replies on here?
The other thing that I notice is that the specs don't give a figure for where the top end, frequency-wise, of these speakers is - you really need to know that. Googling on "slick 69.2 speaker specification" brings up a few different units, you're appparently talking about a round one, 220mm dia.
The oval 6" x 9" units have a concentric built in tweeter, and are supposedly ok up to 25kHz, high enough - maybe the round 220mm ones do to?
Given the lack of information, the quip about fag packets probably sounds:
1. A bit lazy to British readers
2. Something very different to Americans!
Hope this helps!
I'm not going to ask quite why this is to go into a bergen, I'll just presume you're a noisier than average member of the rambler's association. I should tell you that it's so long since I designed a speaker box that my information came off printed pages and I used a handheld calculator.
Sealed box and vented box are ok for your purposes, bandpass isn't. Are you going for sealed box because it's the simplest? A vented box will get lower cutoff frequency for a given volume, or smaller volume for given cutoff.
Vented box design is more involved and there's less protection for the speaker from damage by being fed high levels of signal below cutoff.
All this is jumping the gun a bit though, you've decided on a driver unit, but the link you give is actually to a specification for two different speakers, Slick 69.2, a 140W and Slick 69.3, a 160W version.
Maybe if you say which you're talking about, and quote the figures from those specs that you've put into the calculator you've used you'll get more replies on here?
The other thing that I notice is that the specs don't give a figure for where the top end, frequency-wise, of these speakers is - you really need to know that. Googling on "slick 69.2 speaker specification" brings up a few different units, you're appparently talking about a round one, 220mm dia.
The oval 6" x 9" units have a concentric built in tweeter, and are supposedly ok up to 25kHz, high enough - maybe the round 220mm ones do to?
Given the lack of information, the quip about fag packets probably sounds:
1. A bit lazy to British readers
2. Something very different to Americans!
Hope this helps!
The drivers you have choosen will not make a box with Q < the Qts of the driver, both of which are greater than max-flat 0.707.
As car speaker they ar edesigned to be mounted somewhere where they are in essentially a large leaky box.
The Vas parameter is in an unknown unit -- for now i'll assume it is meant to be litres.
The lower Vas unit alsohas the higher Q, but with a limited size box you'll end up in about the sameplace... you are best to make the box aperiodic.
dave
As car speaker they ar edesigned to be mounted somewhere where they are in essentially a large leaky box.
The Vas parameter is in an unknown unit -- for now i'll assume it is meant to be litres.
The lower Vas unit alsohas the higher Q, but with a limited size box you'll end up in about the sameplace... you are best to make the box aperiodic.
dave
I'm just going to suggest buying a plastic foam-insulated picnic cooler from a charity store. That would get you a light-weight but reasonably stiff enclosure. Pack it with pillow stuffing to reduce/eliminate the honking from internal standing waves. As for lightweight speakers, some OEM car systems come with incredibly lightweight speakers using neodymium magnets. Those may get chucked out by car audio installers who install aftermarket speakers.
Hello Jim, and welcome to AudioAddicts anonymous.
Seriously though, is this going to be used mostly for speech or music? I ask because the requirements for good speech intelligibility are rather different than for decent quality music reproduction.
Indeed, I'm probably going to start with sealed as it's the simplest.
Also it's a reference point, we're actually going to try to build it so the speaker it just a box bolted to other boxes and you can change it for a different design.
Whoops, we're going to use the Slick 69.3.
We're going to be using the 6x9, 160W version.
Sorry, I just have limited time to get this stuff done, but I've now written up the napkins into something like a design (see above post)
Indeed it does!
Thanks,
J.
Thanks Dave, the software kept complaining that the Q had to be more than the Qts of the driver, now it makes more sense why.
I'll go Google aperiodic!
J.
Thanks guys, but the game was always going to be building it into a backpackers rucksack.
Thanks!
Almost always music.
Going to write a bit more about the project:
This all started a few years ago (took us a while to get going) when we lamented the fact that people just don't lug around good music equipment any more.
In the summer we spend a lot of time on the common next to the sea having beer and bbq on a Saturday or Sunday.
Friends turn up with a mobile phone and plug it into a pair of 20mm speakers powered but some tiny little battery.
So we decided we would design and build a man portable (ish) sound system in a British Army Bergen. Because their cheap, plentiful, waterproof (England!) and we wouldn't mind cutting holes in one.
We got together (or are still getting) the following bits and bobs:
1 x Crossfire CFA402 2x100W amp
1 x British Army bergen (we didn't pay that for ours!)
6 x 7ah 12V Sealed Lead Acid batteries
1 x Bluetooth audio receiver
Misc bits for adding a line in, line out, guy ropes, second speaker out, power switch, project box, solar panel, wind turbine, FM transmitter to second bag, etc.
(The batteries and the amp weigh 19kg, this will not be light)
OK, that's enough rambling for now.
J.
Compactness is indeed an issue. Design of the cabinet is almost moot, the volume is the volume, unless any of you can fold space.
My design apparently gives me 24.6l of volume.
Using this calculator (the sealed version, I won't link the EXE directly), I think that gets me a Qtc of 1.06.
If somebody could validate this, that would be great. Here's the relevant information:
Here's the manufacturer numbers:
Code:
Slick 69.3
Revc = 3.4 Ohm
Fo = 58.663 Hz
Sd = 20.931 m M
Md = 18.200 g
BL = 4.675 T
Qms = 3.421 8
Qes = 0.911
Qts = 0.719
No = 0.618 %
SPLo = 89.9 dB
Vas = 28.836 m M
Cms = 463.526 u M/N
Krm = 3.558 m Ohm
Erm = 0.716
Mms = 15.879 g
Mmd = 14.138 m Kg
Kxm = 11.605 m H
Exm = 0.597
480 watts peak
160 watts RMS
MIN.input 80 watts RMS
Mount depht 75mm
Mount DIA 220x150mm
Code:
Qtc = 1.06 (found by trial and error, you can't put in a volume)
Qts = 0.719
Qes = 0.911
Fs = 58.663 Hz (assumed Fo was Fs)
Vas = 28.836 l (assumed Vas units was litres)
Pmax = 480 watts
Diameter = 185 mm (Averaged 220 and 150, just a guess)
Xmax = 6 mm (left at default)
Code:
Vb = 24.5732 l
Fb = 86.4851 Hz
F3 = 66.3566 HzLooking at pages about aperiodic enclosures, I see how that would be very useful in my situation. However the following is a problem:
1) I don't have software for that
2) I can't find anywhere that sells these "damped ports"
Many Thanks,
James.
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Hi,
Yorr numbers seem very reasonable and I wouldn't worry about the
slight bass bump, as your outdoors and haven't considered BSC,
(baffle step compensation). If you have any EQ options involved,
and you should to allow for very disparate volume levels, and
disparate placements, e.g. free standing / against a wall, not
really a practical issue. Basically you simply want a sealed and
well stuffed box that is around the driver Vas in effective volume.
It seems what your forced to go with fits the bill .......
Aperiodic loading won't really help at all IMO in this application. For
reasons I don't really want to go into / have to explain / argue about.
rgds, sreten.
A driver with Q of near 0.7 will have a Q of near 1 in a box = to Vas.
Yorr numbers seem very reasonable and I wouldn't worry about the
slight bass bump, as your outdoors and haven't considered BSC,
(baffle step compensation). If you have any EQ options involved,
and you should to allow for very disparate volume levels, and
disparate placements, e.g. free standing / against a wall, not
really a practical issue. Basically you simply want a sealed and
well stuffed box that is around the driver Vas in effective volume.
It seems what your forced to go with fits the bill .......
Aperiodic loading won't really help at all IMO in this application. For
reasons I don't really want to go into / have to explain / argue about.
rgds, sreten.
A driver with Q of near 0.7 will have a Q of near 1 in a box = to Vas.
Last edited:
I think this should beat those 20mm speakers you found a bit lacking into a cocked hat.
I'm wondering how long you think you'll be out playing music for at a time, 6 batteries, each 7Ah, 12v, so about 500 watt-hours ....... the more I hear of this, the more I'm thinking it sounds like a peculiarly British version of the helicopters playing Ride of the Valkyries in Apocalypse Now
What the hell, the Real bass amps have tubes thread are talking about building bass amps using ex soviet GU-50 valves, based on the Ampeg SVT. Apparently originally designed as tank transmitter valves, I'm resisting the temptation to ask if they've got a tank to transport them on...
I'm wondering how long you think you'll be out playing music for at a time, 6 batteries, each 7Ah, 12v, so about 500 watt-hours ....... the more I hear of this, the more I'm thinking it sounds like a peculiarly British version of the helicopters playing Ride of the Valkyries in Apocalypse Now
What the hell, the Real bass amps have tubes thread are talking about building bass amps using ex soviet GU-50 valves, based on the Ampeg SVT. Apparently originally designed as tank transmitter valves, I'm resisting the temptation to ask if they've got a tank to transport them on...
Me again,
Well, things are progressing slowly, but are progressing.
We have all the bits now, but another key decision has to be made and I'd like some advice.
I have access to a CNC laser cutting machine so we could make our box using that.
However, I've been informed that it works best with 6mm ply.
Which sounds a bit thin to me.
We're going to reinforce the load bearing sections with glued in blocks (base, catches, handles, etc)
But is 6mm too thin for the speaker box?
If I need to make the sides thicker/stiffer, will bonding sheets of foam or ply solve that?
J.
PS: We're going to make it with a FRICKING LASER BEAM!!
PPS: I thought I'd replied after SimonB and sreten had posted, obviously I forgot, my apologies.
Thanks for the feedback, I'm now much more confident that I'm on the right track.
Once into said cocked had, I'm going to set it on fire.
Well, things are progressing slowly, but are progressing.
We have all the bits now, but another key decision has to be made and I'd like some advice.
I have access to a CNC laser cutting machine so we could make our box using that.
However, I've been informed that it works best with 6mm ply.
Which sounds a bit thin to me.
We're going to reinforce the load bearing sections with glued in blocks (base, catches, handles, etc)
But is 6mm too thin for the speaker box?
If I need to make the sides thicker/stiffer, will bonding sheets of foam or ply solve that?
J.
PS: We're going to make it with a FRICKING LASER BEAM!!
PPS: I thought I'd replied after SimonB and sreten had posted, obviously I forgot, my apologies.
Thanks for the feedback, I'm now much more confident that I'm on the right track.
Once into said cocked had, I'm going to set it on fire.
MDF? This is an ideal application for good quality plywood. Light, strong, stiff (12mm is as stiff as 3/4" MDF and has less energy storage issues).
In this application low weight i would assume is crucial. With careful bracing you could probably get away with 9mm. 12mm is a lot easier to build with.
dave