1st Speaker project - uni student help pweez :(

[MCGroves]

Hey im new to this forum, and the diy world! My names Mark and im from south wales im 19, studying civil eng!!

Being a student i have far to much time on my hands, onest, and spend too much money on alcomahol!!

I started reading up on loudspeakers after i was given sum old pa speakers, an amp n cables off a dj m8 of mine. ( turns out there is 2 20 yr old H|H drivers, and 2 unknown drivers about 180w ) any ways, ive blown 1 H|H messing about, and the other has been put bk in it cab, and is just sitting in my room dien to make noise ( it does go boom boom pritty hard ).

I decided i would like to build my own speakers for my room, with the possibility of them being used for house parties!!
My funds are realy limited ( around £200 MAX ) but wood, and construction will be totaly free to me. I was thinkin about mounting two 8" woofers with a tweeter in a dual ported box of around 100-120L, with a max height of about 1m.

I did a few calculations with winisd, the ports came to around dia=4.7cm length=8cm, using "HIGH POWER WOOFER WITH KEVLAR CONE skytronic 902.426" drivers. ( T/S can be found here http://www.skytronic.com/rsc/doc/thielesmall_902127.pdf ) the charts looked good to me, but i realy was jus working in the dark after reading a very basic guide.

I can pick these speakers up in the UK for around £22 a pop which suits my budget :P and i was only drawn to them as i like the bright colours lol ( small minds ... ) and fancy leaving the front uncover.

I'm not sure of the quality of these drivers, and if its ok to simply wire the woofers in series , and connect the tweeter in parrallel? would i require a crossover? and shud i look at a mid range, instead of 2 woofers? Also if i wontd a tuning freq of around 30Hz would i need a sub or could i gt it all from the speakers ?

All ill be using the speakers for is to play loud music, nothing fancy. I've looked at kits, but they all seem to be more expensive, and aim for high quality sound.

does this sound like a feasible idea?

A little help and suggestions please, it will be much apresheated!! Cheers, Mark

[EC8010]

Welcome to the forum. It's worth bearing in mind that the people on the forum who have the knowledge to help you are likely to be old farts (like me) and they don't like being addressed in misspelt textspeak. If you write in a form acceptable to your lecturers you will get a much better response...

Yes, you will need a crossover for your proposed project. However, if all you want to do is to make a loud noise that annoys the neighbours and results in a Noise Abatement Order then I suggest that you buy eight 7" x 4" (or similar) drivers for about £3 a piece and put four each in a pair of big strong cardboard boxes well-sealed with parcel tape. This has the great advantage that when your equipment is impounded, it's no great loss. We used to do this for parties when I was a student.

Alternatively, if you want to spend time and money to achieve something that won't embarrass you in three years time, do a few searches for high-efficiency drivers and perhaps have a look at the full range forum. WinISD is great for helping with bass alignment, but crossovers are much harder to get right; especially if you're not an electronics engineer.

[MCGroves]

Thank you very much, that’s great. Sorry for the text talk.

Great idea EC8010, sounds like fun, and cheap, but wouldn’t it be a fire hazard :P

Very strong (I mean very strong) cardboard boxes won’t be an issue, my father is a design for a UK corrugated card company, he has made office desks and chairs from it in his spare time. If I invest in some 7" x 4" drivers, what type of output can I expect from them, can I get loads of bass (seem to have an unhealthy craving for it) and how would they be wired, also would it be ok to run them off a 350w channel?

I would still like to make a half decent effort at building my own speakers though. Any help on the above would be great.

EC8010, how much would high efficiency drivers cost me, and could you point me in the right direction? Funds are limited at the moment, and I don’t fancy spending too much money on a first project that could go horribly wrong, I looked at cheaper drivers to bodge about with for the time being, then if I do really get into DIY speakers, and like what I can produce, maybe blow some of the student loan and give it a good go.

Thanks again Mark.

[sreten]

Hi,

perhaps I can help here, but right at this moment I don't have
enough time to write a full answer due to the many issues you
are probably unaware of.

I'll be back ..........

/sreten.

[sreten]

Hi,

Using multiple 7"x4" will give you high efficiency, which is whats
needed if you don't have much power, but not not much bass.
In the days when 7x4's were common (e.g. in radiogram's) so
was power handling of a few watts, with 350W on tap I don't
think they would last very long.

I presume the main purpose of the speakers will be to be capable of
producing what I'd consider vomit inducing levels of bass frequencies.

The most important parameter is volume displacement, that is
cone area x cone excursion. For a 100L cabinet with a choice
of those skytronic drivers I'd go for a 2x12.

The sort of bass alignment you get is common is PA speakers.
Reflexing is used to increase power handling not bass extension.
At low frequuecies the port effectively doubles the number of
drivers (compared to using the drivers in a sealed box).

So with a pair of speakers at low frequencies you'll end up
with the equivalent of 8 12" drivers with 6mm excursion.

Should do for the average students room.

When considering the whole frequency range it should be noted
you are flying blind with drivers you don't know the frequency
response of, so what follows are what I'd consider possibilities :

I'd make the two twelves a 0.5 way. Adding a switch that connects
various resistors in parallel with the 0.5 way inductor will give you
a midrange level control.

For the top end in the interests of being simple (but crude) and
servicable if it gets fried you should source a piezo midrange horn
and a screw-in Motorola midrange driver.

At this point I'll refer you to the excellent wiki on piezo crossovers.

The c/o frequency and level of the horn will need adjusting
to suit the capabilities of the the top 0.5 way 12".

I'd also check the prices of the skyelectric drivers, should be cheaper.

/sreten.

[MCGroves]

Hi

Good guess sreten

“I presume the main purpose of the speakers will be to be capable of
producing what I'd consider vomit inducing levels of bass frequencies.”

I looked into the volume displacement for the 12” skytronic speakers, and came across the 902.222, should the 150wrms put me off? (I have a 2 chan amp 350w) I messed about on ajvented and winISD, and came up with a 200L box (a compromise on the 300 odd suggested, and the maximum size I would like.) tuning freq of around 29, f3 of around 30.5Hz, and a square vent ([10.21x10.21]x10.13cm) using the SBB4 alignment. Does this sound ok?

Sorry for my ignorance, but I am a total noob, (only have so much time on my hands, with uni studies, I will have a break at Easter though, hopefully start ordering and building) I don’t understand what you mean by “I'd make the two twelves a 0.5 way. Adding a switch that connects various resistors in parallel with the 0.5 way inductor will give you
a midrange level control.”

I have two Motorola piezo (from older pa cabs), and I have been looking at piezo horns, would a Wide Dispersion Piezo Horn Tweeter be what I’m looking for? Or could you suggest a midrange driver to me?

Also is there any simple way for me to get the crossovers I need? Building them probably isn’t an option for me (I solder like someone with elephant feet). I’m also struggling to find mountain dimensions for the drivers (going to get the wood pre-cut)


Ps, u was right about the price, cheers.

[sreten]

http://www.wle-shop.co.uk/modules/sh...79&rangeid=407

Hi,

some further info :

use the 12" wide (315mm) x 4" horn or 15" x 4" if your cabinets wide enough.

A motorola piezo mid driver is £10 from maplins, you could try the
cheaper ones on the above link, don't know how good they are.

The 902:176 has higher efficiency and power handling over the 902:222.

200L is a massive box - are you sure ? If you have a decent graphic
EQ you could quite possibly get away with 125L tuned to 30Hz.

You'll also need someone who can solder and understands the
rudiments of electronics and acoustics if your going to be able
to do some listening tests and adjust the design to suit.

Someone who understands crossovers and can look up 0.5 way on the net.

/sreten.

[Emiel]

Let me elaborate on the 0.5 way a bit(correct me if I'm wrong):

A driver will theoretically drop 6dB below a certain frequency (f [Hz]) depending on the baffle width (BW [m]), rule of thumb: f=115/BW. If you ad another driver below this frequency, you'll compensate for this baffle loss.
The second driver is thus only covering a part of the frequency range of the first driver: this is were 0.5 comes from.

Ciao

[sreten]

I'd make the two twelves a 0.5 way. Adding a switch that connects
various resistors in parallel with the 0.5 way inductor will give you....

Hi,

Maplin do a £5 subwoofer crossover board with
moreorless the correct inductor value (~7mH).

This is assuming your box is not a lot wider than the 12" drivers.
the 12"s are obviously vertically aligned with the 4"x12" horn above.

The top 12" is wired directly to the input.

Remove the capacitor from the c/o board and connect the
board between the input and the lower of the 12" drivers.

I'd only worry about adding resistors if - god forbid - there is too much bass.

The procedures for the piezo mid/treble are somewhat more complicated.

/sreten.

[MCGroves]

Wicked! Thanks very much sreten.

That’s made the most of it very simple, just to crack the piezo mid/treble. Help any one??

One last thing, I wonder if you could post me the links to the "12" wide (315mm) x 4" horn", "motorola piezo mid driver is £10 from maplins" "£5 subwoofer crossover board with
moreorless the correct inductor value (~7mH)"

I’m sure I can keep the cab to around 12" wide if that’s what’s needed, and what you said before about the EQ, can this be don’t through my pc, seems that’s what I’m using as my player.

Thanks again ( I might actually get this off the ground!! )

Mark !!