Can somebody check my understanding please? (DIY speaker)

[Magic Matt]

I'm not sure if I am going to build the speaker or not yet, but in order to cost things up I am trying to learn what I can and plan out what I might do.

I currently play through a Peavey TKO 115 Sheffield, which is coincidentally also rated 75 watts, but into 8 ohm 15 inch speaker. No ext cab facility, and it's heavy!! Built like a tank - I like the sound, although it's nothing special. I've seen it described as a reliable solid tank for getting the job done with a good but not outstanding tone - seems like a fair description to me, I just don't like lugging it about.

Hence I have acquired a Polytone Mini Brute which is a 75 watt into 4 ohm, that has a facility for an ext cab. which I've confirmed would also be 4 ohm. The amp itself actually contains a 3 ohm 12 inch speaker (weird!) but if it says it is designed to take a 4 ohm ext cab, that's probably the best thing to plug onto it!

My aims are:

1 - Good efficiency. Low powered amp driving 4 ohms, so the more efficient the output the better.
2 - Tone - not sure. The polytone on its own is great at lower volumes, but when you start to crank it, the low end starts to vanish too much. The Peavey is nice, but a little muddy on the bottom end to me. I'm hoping that combining a 12" and 15" might give me what I want.
3 - Lightweight (ish). This is intended to be a nice easy carry, and should fit in the boot with the polytone, so no fridges.
4 - Not too worried about power - The Peavey is ok most of the time, though it's driven just over half full volume and gain. I expect I could DI into the PA if I had to, but I'd rather not. I figure two cones will be louder than one, so I shouldn't need to drive the amp as hard as I do currently to get the same volume.
5 - Looks - I want something that looks a bit different from the usual black box. I like the idea of putting the wood on show
6 - Cost - Low cost without being silly. I had in mind a figure of £100-£150 for cab and speaker.


Hopefully I've not made any daft decisions so far.

Cab will be a very basic vented model - I figure with my modest skills it should be achievable.

Simple things out the way first - looks and construction. Does varnished ply look good? I actually wondered if I could stain it deep blue or something, and varnish that. I dare say it's been done before, but I like the idea. I figured perhaps making a frame from planed softwood then using screws and glue to attach the plywood, and sealing joints inside with decorators caulk. Stick foam to all the ply panels inside.

Frame - Planed softwood, 32mm x 32mm

I don't really understand ply... I think Marine is big and heavy, and might be overkill for the volumes I use. 18mm ply seems to be the most popular, but I don't understand the different types. I got the impression Baltic Birch is the material of choice, but I suspect this may be horribly expensive. Is there a cheaper alternative that would suit my needs? Am I right in thinking the standard ply in DIY stores is probably not up to the job?


Speaker

Torn between the Basslite 12" and 15"... I've put them together in WinISD and as far as I can tell the 15" has some advantages, even in a small cab... the main one being it's 4ohm rather than 6ohm, so is 3dB louder across most of the scale (see graph). Even in a small 100L cab, the 15" seems to be better on the graph to my uneducated eyes. What I can't understand is the drop off - is the 12" better or the 15"? Am I going to find that the low E has much less apparent volume compared to the rest of the notes, when compared to the 12" which will be quieter overall, but more even?

[6v6]

[quote name='Magic Matt' timestamp='1382363721' post='2251185']
Hence I have acquired a Polytone Mini Brute which is a 75 watt into 4 ohm, that has a facility for an ext cab. which I've confirmed would also be 4 ohm. The amp itself actually contains a 3 ohm 12 inch speaker (weird!) but if it says it is designed to take a 4 ohm ext cab, that's probably the best thing to plug onto it!
[/quote]

So just to state the obvious, you know that if it's designed for a 4 ohm minimum load, you'll only be able to run the extension cab and not the internal speaker (because the combined impedance would be 1.7 ohms) right?

[quote name='Magic Matt' timestamp='1382363721' post='2251185']
My aims are:

1 - Good efficiency. Low powered amp driving 4 ohms, so the more efficient the output the better.
2 - Tone - not sure. The polytone on its own is great at lower volumes, but when you start to crank it, the low end starts to vanish too much. The Peavey is nice, but a little muddy on the bottom end to me. I'm hoping that combining a 12" and 15" might give me what I want.
[/quote]

AFAIK the general consensus is not to mix different sizes of speaker, or you can get phase related issues which cause dispersion/phase-cancellation issues.

So if using multiple speakers then they should be the same size of driver, vertically stacked for best results.

[quote name='Magic Matt' timestamp='1382363721' post='2251185']
3 - Lightweight (ish). This is intended to be a nice easy carry, and should fit in the boot with the polytone, so no fridges.
4 - Not too worried about power - The Peavey is ok most of the time, though it's driven just over half full volume and gain. I expect I could DI into the PA if I had to, but I'd rather not. I figure two cones will be louder than one, so I shouldn't need to drive the amp as hard as I do currently to get the same volume.
5 - Looks - I want something that looks a bit different from the usual black box. I like the idea of putting the wood on show
6 - Cost - Low cost without being silly. I had in mind a figure of £100-£150 for cab and speaker.
[/quote]

If you want a natural finish, then you want top-quality void-free birch ply. I used 15mm in my cab, which helps keep the weight down a bit compared to 18mm, but it's only stocked by good/larger timber merchants. This sort of ply is good but expensive - I paid over £50 for an 8x4 sheet including vat and cutting.

IME you'll be doing very well if you manage to build and cover the cab for £100 (wood, glue, fixings, finishing materials, grille, wiring, handle, corners, wadding, foam gasket, etc etc - it all adds up). That's before you start thinking about the driver - DIY cabs aren't a way to save money (but they are fun to build! )

You may be interested in my build thread, and the thread linked where I got some great advice before starting out on a similar project:

[url="http://basschat.co.uk/topic/200152-1x12-diy-cab-build/"]http://basschat.co.uk/topic/200152-1x12-diy-cab-build/[/url]

[Magic Matt]

[quote name='6v6' timestamp='1382368562' post='2251299']
So just to state the obvious, you know that if it's designed for a 4 ohm minimum load, you'll only be able to run the extension cab and not the internal speaker (because the combined impedance would be 1.7 ohms) right?
[/quote]

No, the ext cab for it is in parallel, the amp is designed to happily drive 2 ohm loads apparently - the speakers that used to be available for it were 4 ohm and worked in parallel..

It may be a mute point. I'm being swayed in favour of not using it, and buying a second hand head at some point, as apparently it's tuned specifically to their cabs for the compact size, which I didn't appreciate.

[quote name='6v6' timestamp='1382368562' post='2251299']
AFAIK the general consensus is not to mix different sizes of speaker, or you can get phase related issues which cause dispersion/phase-cancellation issues.

So if using multiple speakers then they should be the same size of driver, vertically stacked for best results.
[/quote]

Ok... I must be missing something as I'd seen the combination of a Barefaced Midget and Compact being a lovely combination, and as far as I know that's a 12" and 15" respectively. Perhaps different because they're tuned to be able to work together though?

[quote name='6v6' timestamp='1382368562' post='2251299']
If you want a natural finish, then you want top-quality void-free birch ply. I used 15mm in my cab, which helps keep the weight down a bit compared to 18mm, but it's only stocked by good/larger timber merchants. This sort of ply is good but expensive - I paid over £50 for an 8x4 sheet including vat and cutting.

IME you'll be doing very well if you manage to build and cover the cab for £100 (wood, glue, fixings, finishing materials, grille, wiring, handle, corners, wadding, foam gasket, etc etc - it all adds up). That's before you start thinking about the driver - DIY cabs aren't a way to save money (but they are fun to build! )
[/quote]

Hmm... hadn't considered all the extras! I've already got some stuff (handles, glue, screws, etc. but not things like a speaker grill). Thanks for the heads up!

[quote name='6v6' timestamp='1382368562' post='2251299']
You may be interested in my build thread, and the thread linked where I got some great advice before starting out on a similar project:

[url="http://basschat.co.uk/topic/200152-1x12-diy-cab-build/"]http://basschat.co.u...-diy-cab-build/[/url]
[/quote]

Very much so, yes!
I've been reading as many threads as I can find on the forum.

[6v6]

[quote name='Magic Matt' timestamp='1382378781' post='2251500']
Ok... I must be missing something as I'd seen the combination of a Barefaced Midget and Compact being a lovely combination, and as far as I know that's a 12" and 15" respectively. Perhaps different because they're tuned to be able to work together though?
[/quote]

I'm a novice at cab design, so I can't help with the details (there are experts around here who no doubt can tho), but Barefaced do state on their website that the Midget and Compact have been specifically designed for compatible phase response.

[Mr. Foxen]

Knobs turned up half way doesn't mean half power.

18mm ply is popular for crude unbraced cabs, but you can use thinner if you use other means to make it stiff and non-resonant.

[LukeFRC]

or buy this..... http://basschat.co.uk/topic/213386-l180-bfm-omni-12-tallboy-2x10-full-range-cab/

what you want, or better than spec- more or less on budget, can be used with either of your amps... and without you having to learn to build a speaker yourself!

[discreet]

[quote name='LukeFRC' timestamp='1382392909' post='2251741']
or buy this... [url="http://basschat.co.uk/topic/213386-l180-bfm-omni-12-tallboy-2x10-full-range-cab/"]http://basschat.co.u...full-range-cab/[/url]
[/quote]

+1 Suit you, sir! I'm always amazed at the low price of BFM cabs second-hand.
Must be because they don't have any evidence of 'branding' on them and thus are seen as 'home-made'.

[LukeFRC]

[quote name='discreet' timestamp='1382393137' post='2251749']
+1 Suit you, sir! I'm always amazed at the low price of BFM cabs second-hand.
Must be because they don't have any evidence of 'branding' on them and thus are seen as 'home-made'.
[/quote]

[ShergoldSnickers]

[quote name='LukeFRC' timestamp='1382392909' post='2251741']
or buy this..... [url="http://basschat.co.uk/topic/213386-l180-bfm-omni-12-tallboy-2x10-full-range-cab/"]http://basschat.co.u...full-range-cab/[/url]
[/quote]

I'd honestly give this serious consideration. It will be very efficient at converting watts to sound, so it should go very loud if required, but do so cleanly as well. If I didn't have a Barefaced S12T already, I'd be looking at this.

[Magic Matt]

[quote name='ShergoldSnickers' timestamp='1382427047' post='2251873']
I'd honestly give this serious consideration. It will be very efficient at converting watts to sound, so it should go very loud if required, but do so cleanly as well. If I didn't have a Barefaced S12T already, I'd be looking at this.
[/quote]

Still worth it even though it's going to be around £45 in fuel to go and get it? I know nothing of how expensive they are to make...

[LukeFRC]

[quote name='Magic Matt' timestamp='1382457293' post='2252384']
Still worth it even though it's going to be around £45 in fuel to go and get it? I know nothing of how expensive they are to make...
[/quote] how much has your planned build been costed out to? How valuable is your time? add them together... if more than that cab and petrol money... then yes

[xgsjx]

If I had a spare £200, I'd have bought that BFM already. I'm gonna get plans for a sub off him one day.

[Phil Starr]

Hi Matt, there's lots of issues here but the first one is to try and sort out what you are trying to achieve. If it is the best sound on a small budget then sadly self build isn't the way to go. Second hand will always be cheaper. For example there have been several Peavey BXBW 15's with the better Black Widow speaker on Ebay which have gone for comfortably below £100. The bare speakers cost nearly half as much again without the cab! There are lots of other used bargains too, and you can try them and hear the sound yourself before you buy.

If you want to build as a learning experience then that is a different matter. You can get something quite usable at a price not too much more than used and a lot of knowledge and satisfaction. If you are looking for something high end then it is possible to build and save money over a new speaker. There are lots of people here who will give you advice and support and if you follow that advice it is unlikely to go completely pear shaped but it just isn't the cheapest option.

So, build and learn or Ebay and play?

Edited October 23, 2013 by Phil Starr

[6v6]

[quote name='LukeFRC' timestamp='1382462119' post='2252488']
how much has your planned build been costed out to? How valuable is your time? add them together... if more than that cab and petrol money... then yes
[/quote]

IMHO it's not that simple - for most folks who make DIY anything, it's not the cost that's the main driver, it's the satisfaction of fully understanding how to make something from scratch, and the enjoyment of realizing the end result from the raw materials.

As for the low price of DIY cabs second hand (even if they're made to plans which have been professionally designed), I guess the reason is you don't really know anything about the quality of construction, so it's much more of a risk than buying from an established manufacturer. I think anyone building a DIY cab in their shed (myself included) knows the resale value will be relatively poor.

I'm sure that BFM cab linked is really awesome, but FWIW I think you'd need to spend some time sorting out the wiring, as it (IMHO) looks, uh, a bit dodgy:
- None of it is secured, so it will rattle about and eventually wires will fall off.
- Same goes for the crossover, which should be constructed on a bit of fiberglass or phenolic board with turrets/tags, not a bit of ply which can absorb moisture and become conductive.
- The components in the crossover (capacitors in particular) have non-secured long bits of wire hanging off them which will vibrate and eventually the component legs will fall off.
- Also, for some reason, it seems to have a 12v bulb from a car interior light wired into the tweeter part of the circuit, I assume instead of a resistor, only bulbs filaments will fail with vibration whereas decent wirewound resistors won't.
- The wires on the right are close to the speaker cone, so will probably make a buzz and eventually fall off due to vibration

Sorry if that sounds harsh, I'm sure the cab is otherwise awesome, and I'm very aware that no DIY cab is perfect (mine isn't, but I like it!)

[LukeFRC]

[quote name='6v6' timestamp='1382515535' post='2252970']
IMHO it's not that simple - for most folks who make DIY anything, it's not the cost that's the main driver, it's the satisfaction of fully understanding how to make something from scratch, and the enjoyment of realizing the end result from the raw materials.

As for the low price of DIY cabs second hand (even if they're made to plans which have been professionally designed), I guess the reason is you don't really know anything about the quality of construction, so it's much more of a risk than buying from an established manufacturer. I think anyone building a DIY cab in their shed (myself included) knows the resale value will be relatively poor.

I'm sure that BFM cab linked is really awesome, but FWIW I think you'd need to spend some time sorting out the wiring, as it (IMHO) looks, uh, a bit dodgy:
- None of it is secured, so it will rattle about and eventually wires will fall off.
- Same goes for the crossover, which should be constructed on a bit of fiberglass or phenolic board with turrets/tags, not a bit of ply which can absorb moisture and become conductive.
- The components in the crossover (capacitors in particular) have non-secured long bits of wire hanging off them which will vibrate and eventually the component legs will fall off.
- Also, for some reason, it seems to have a 12v bulb from a car interior light wired into the tweeter part of the circuit, I assume instead of a resistor, only bulbs filaments will fail with vibration whereas decent wirewound resistors won't.
- The wires on the right are close to the speaker cone, so will probably make a buzz and eventually fall off due to vibration

Sorry if that sounds harsh, I'm sure the cab is otherwise awesome, and I'm very aware that no DIY cab is perfect (mine isn't, but I like it!)
[/quote] not going to disagree with any of that... but... isn't a bulb used quite commonly as a fuse to protect the tweeter?

[6v6]

[quote name='LukeFRC' timestamp='1382526967' post='2253155']
not going to disagree with any of that... but... isn't a bulb used quite commonly as a fuse to protect the tweeter?
[/quote]

Well I never, google says it's true!

You learn something new every day. I still wouldn't want that nice hot bulb tie-wrapped to a big bit of flammable ply personally..

[discreet]

[quote name='6v6' timestamp='1382528950' post='2253198']
Well I never, google says it's true!
[/quote]

So it MUST be true! [size=4] Seriously though, I did not know that a bulb could be used as a fuse. We live and learn.[/size]

[Bill Fitzmaurice]

[quote name='6v6' timestamp='1382528950' post='2253198']
Well I never, google says it's true!
[/quote]Google is wrong. Bulbs aren't employed in crossovers as fuses, although they will in effect act as fuses if the cab is over powered or fed with very highly distorted signals, which can blow them out. Bulbs are used as simple compressors. As the filament heats with higher power input the resistance of the filament goes up, reducing the voltage delivered to the tweeter.
[quote]Same goes for the crossover, which should be constructed on a bit of fiberglass or phenolic board with turrets/tags, not a bit of ply which can absorb moisture and become conductive.[/quote]There is no reason to use fiberglass or phenolic other than that they can be made with conductive traces, which speeds the construction process in high volume operations. Making a board with conductive traces slows the construction process in typical DIY production runs of one or two cabs, even assuming the DIYer has the capability to make traced boards at all. Wood as a material for crossover boards has been used since the first crossovers were constructed circa 1920, with no ill effect.

[Magic Matt]

Yes, you can use bulbs as fuses... they don't make very good fuses though, and it's cheaper and more efficient to just to buy a fuse..They do start to light up though, which can act as a visual warning. I only know this because that's how a pair of old HiFi speakers I used to have were working.

I didn't realise bulbs were still used as compressors - I thought LEDs were generally employed in that capacity now. I know the optical compressor in my mic pre-amp is an LED based optical compressor. Seems to work well.

I would think if the ply was damp enough to start conducting any current or voltage that would affect the operation of the crossover, then the speaker cones are probably buggered from the damp already. I'm not against sorting out wiring if I have to - I like electronics. Are we saying that doing using the wire-wrap method, then securing components with a small amount of potting compound into a mini enclosure would be better?

I really like the idea of building something. It's got a lot of appeal, I'm just not sure I have the skills. I'm wondering if it might actually be smarter to save a bit more money, buy something second hand, and then do it up cosmetically.

At the moment my issue is also not really knowing what I want to achieve. Mainly a reduction in weight from the Peavey, but without losing the nice deep sound it has... but the more I think about it, the more I think I want something a bit unique... a bit unusual... a bit more "me"... I'm a blues man at heart, but I like unusual things with character, and the big black boxes, as great as they sound, are just a bit boring looking...

[Magic Matt]

*double take* ... um ... Hi Bill...

[6v6]

[quote name='Bill Fitzmaurice' timestamp='1382533209' post='2253271']
Google is wrong. Bulbs aren't employed in crossovers as fuses, although they will in effect act as fuses if the cab is over powered or fed with very highly distorted signals, which can blow them out. Bulbs are used as simple compressors. As the filament heats with higher power input the resistance of the filament goes up, reducing the voltage delivered to the tweeter.
[/quote]

Very interesting, thanks! Seems live a very crude method, but I guess whatever works!

[quote name='Bill Fitzmaurice' timestamp='1382533209' post='2253271']
There is no reason to use fiberglass or phenolic other than that they can be made with conductive traces, which speeds the construction process in high volume operations. Making a board with conductive traces slows the construction process in typical DIY production runs of one or two cabs, even assuming the DIYer has the capability to make traced boards at all. Wood as a material for crossover boards has been used since the first crossovers were constructed circa 1920, with no ill effect.
[/quote]

Gulp... I hate to to disagree with someone of your unquestionable experience, but I maintain that wood is a poor choice for anything but very low voltage circuit construction.

In the 1920's I'm sure it was used because more modern materials (e.g FR4 epoxy or PTFE sheet) did not exist - the dielectric properties of wood (particularly if it absorbs any moisture) are not good when there are high voltages involved (admittedly, I come from a tube amp background ie 300+v, but 500w into 8ohms is still going to be ~60v in that crossover right?).

Most of these materials are also somewhat more resistant to components getting hot, so probably a bit less likely to catch fire when you're putting loads of power through a lightbulb attached to it...

I wasn't advocating conductive traces at all, but saying some sort of GRP or similar board, with turrets or tags (connected by wire traces) would be electrically and mechanically better than the construction method in the photos. Something like [url="http://www.qtasystems.co.uk/loudspeaker-components/crossover-boards.htm"]this[/url]

Edit: grammar

Edited October 23, 2013 by 6v6

[Magic Matt]

Looking closer at the pictures, I don't think it is conductive traces... I think it's just wire soldered to the components leads. I don't even thing the wires are in contact with the board - more likely slightly above it.

[6v6]

[quote name='Magic Matt' timestamp='1382571377' post='2253949']
Looking closer at the pictures, I don't think it is conductive traces... I think it's just wire soldered to the components leads. I don't even thing the wires are in contact with the board - more likely slightly above it.
[/quote]

I think Bill was saying there was no reason to use fibreglass board over wood unless you wanted to make a PCB with copper traces. As mentioned in my response IMHO that's not true, there are plenty of advantages to using it for turretboard point-to-point construction with wire connections.

In the pictures it is just wires hanging off the component leads, which was the reason I mentioned it - that's not a durable construction method for something which will be vibrating at bass frequencies for hours every time you use it (IMHO). I'm sure it sounds great tho, and could be easily fixed!

Edited October 24, 2013 by 6v6

[Magic Matt]

I can't quite see how it would be less durable than the weight of the components hanging by their leads from a fibreglass board... I'll just have to take your word for it.

[6v6]

[quote name='Magic Matt' timestamp='1382625088' post='2254596']
I can't quite see how it would be less durable than the weight of the components hanging by their leads from a fibreglass board... I'll just have to take your word for it.
[/quote]

The components aren't hanging, and they don't have 6" bits of speaker wire waggling on the end of their legs anymore.

Something like [url="http://www.turretboards.com/images/PRODUCT/boards/marshall_18watt_lite_v2.jpg"]this[/url] - the component can be attached to the board with tie-wraps or silicone, then the component leg is much shorter and goes right into the turret. Tube amps have been made like this for years.