1x12 practise amp, how do you work out the tuning.

[fatgoogle]

Hi
Im going to build a 1x12 200 watt practice amp with an extension, ie im going to put a small power amp in the back of one and use a tech 21 Vt or aguilar tone hammer as a preamp.
Now from other cabs ive built with help on the design, i understand to work out size you take its recommended cubic space for a vented enclosure do the relative sums and get the measurements for HxWxB.
But the tuning i still haven't got, ive been meaning to get vance dickinsons book on cabinet making, but its quiet expensive and i haven't got around to getting the library to get it in for me. So how do you work it out.
Im intending to use A fane sovereign 1x12 as i liked the 1x15 400 i used in my first few cabinet experiments.

Thanks
Sam H

Edited January 7, 2010 by fatgoogle

[Mottlefeeder]

[quote name='fatgoogle' post='704821' date='Jan 7 2010, 09:34 PM']Hi
Im going to build a 1x12 200 watt practice amp with an extension, ie im going to put a small power amp in the back of one and use a tech 21 Vt or aguilar tone hammer as a preamp.
Now from other cabs ive built with help on the design, i understand to work out size you take its recommended cubic space for a vented enclosure do the relative sums and get the measurements for HxWxB.
But the tuning i still haven't got, ive been meaning to get vance dickinsons book on cabinet making, but its quiet expensive and i haven't got around to getting the library to get it in for me. So how do you work it out.
Im intending to use A fane sovereign 1x12 as i liked the 1x15 400 i used in my first few cabinet experiments.

Thanks
Sam H[/quote]
The specifications for a speaker are an indicator of how it will resonate in a specified box, with a specified port (or no port). They are intended to be used in equasions that you can use to calculate the volume and the port tuning. I believe that the book you refer to gives you the equasions, but you can also find them free on the web.

One of the more popular programs that uses these equasions is WinISD, which is a free download. It comes with a database of speaker types, and allows you to play with box volume and port tuning, and see the effect that has on a graph of the frequency response. However, unless you understand what you are looking at, moving a line on a graph does not get you much further forward. If you want a cab to experiment with, then you can check out how the different tunings sound, but if you just want to build and use, my advice would be to pick a Fane recommended cab design, and build that.

David

Edited January 7, 2010 by Mottlefeeder

[fatgoogle]

Ive had a mess with WinISD but as you said i didn't know what the graph corresponds to.

The fane specs give a recommend size but i cant see anything on tuning.

[fatgoogle]

Looking at the Fane, it seems to want a very big cab if i see this correctly.
Vas Litres 104, i would have though it would closer to 80 maybe 70.
Also the 98db sensitivity looks good.

[stevie]

I can help you with this. I've just modelled it on the PC. The best driver to use is the Sovereign 12-300 - don't bother with any of the others. You need a cabinet of around 50 litres (45 to 60 litres is OK) tuned to 48Hz. Use two ports 125mm long with an internal diameter of 70mm for 50 litres net internal volume. If you can get flared ports (inside and out) use those in preference. The system will handle 200 watts before you exceed xmax.

The best material for your cab is probably 15mm birch ply, if you can get hold of it. I've attached a jpg of the design for a 50 litre cab. It's large so that you can see the detail.

[fatgoogle]

Thanks you very much Steve just what i was looking for.
Just to confirm if i make internally 18"x16"x18" will give me 51 litre cab.

Now im thinking if i wanted to mount a power amp in the back of it i would need to extend it so maybe if i made it 18x16x19, to give a bit extra room. Or will a standard 2u preamp not take up enough room to make a difference.

Also front or rear mounting the speakers, does it make a difference. Ive only front mounted so far.

[bigjohn]

I reckon it equates to a a great big box..

The bigger the box, the smaller the port you put in it unless you want to smash yer winders.


I once cracked my bedroom windows putting a 100w solid state head through a 20" odd PA speaker.

I dunno how. But I did. Bbbbbbrrrrrhh..... crack.


The window was open though. And the frame was rotten.

[stevie]

[quote name='fatgoogle' post='705027' date='Jan 7 2010, 11:59 PM']Thanks you very much Steve just what i was looking for.
Just to confirm if i make internally 18"x16"x18" will give me 51 litre cab.[/quote]

Sounds about right.

[quote name='fatgoogle' post='705027' date='Jan 7 2010, 11:59 PM']Now im thinking if i wanted to mount a power amp in the back of it i would need to extend it so maybe if i made it 18x16x19, to give a bit extra room. Or will a standard 2u preamp not take up enough room to make a difference.

Also front or rear mounting the speakers, does it make a difference. Ive only front mounted so far.[/quote]

I don't think a 2U power amp would make all that much difference, but you should really take its volume into account. You normally deduct the volume of bracing, handles, the speaker and so on when you calculate the net volume figure. Try to avoid having any two dimensions the same or very close in value, by the way. 18" by 18" will reinforce resonances and standing waves. Better to do 20" x 17", for example, instead.

I've always front mounted speakers, too. Rear mounting means having a removable baffle or rear panel, which is not always what you want. One of the benefits of a 12" speaker is that it allows you make very transportable boxes. I'm not sure I'd want to detract from that by making it into a combo - but you obviously know what you're after.

Edited January 8, 2010 by stevie

[fatgoogle]

I just thought it would be even more portable to have it slotted in the back
And thanks again for all your help.