JF Vented Horn

I was going to start a thread disscussing ported horns dropping their tnuning when stacked, but i havent had the time yet. I have been thinking recently and i predict that if the cabs were stacked with ports next to each other then the port would act longer and drop the tuningexactly as much as the difference between a regular port and a shelf port...

I'll explain again... i think that if you had two ports next to each other they would each act as though they are longer, half their width longer.

L+(W/2) = newvirtual length of port

L=length of port
W=width

Would anyone agree?

The port as it is, is 305mm long, the next 3 i make i'll make them 270mm or something, that should do it. then when i do this gig i'll have to do it with one odd tuned cab.

jsg wrote: Jake

A few points:

1. You can always try adjusting your original model to match your current measurements. I think Chris suggested this earlier. It's a good idea because if you don't object to the frequency response, phase response and excursion behaviour you actually have, then maybe you don't have a problem at all

Thats a good point, although i know that i will suffer in the 50Hz region with excursion problemsif the chamber/port is tuned too low. I'd ratherthrow awaya cab that took a lot of work to build than build 4 im not entirely happy with.

jsg wrote: I'm sorry that my three observations all seem to lead in different directions - that's the nature of the game I'm afraid. It's the choices you make at this stage that define your personal style as a speaker designer and hence make you unique and not just another sheep.

I already have a rather cool idea in the pipeline that is a much better version of this ported horn, so i wont fuss over this one too much, but i'll need to save up for wood again and that sort of thing.... this was my first (non reflex) build by the way, its agood learning oppertunity.

Just a quick thought about the tuning, would it not be possible to add a couple of circular ports to the front panel and use tubes to change the tuning, the added holes will sum with the main port to give a new tuning frequency.

Also for future builds if using the same port design then maybe make the 'lid' of the port none permanent and fit different lengths, and make the sides of the port longer than you are going to need.

JaKe

Maybe you should do another prototype of a slightly different design, compare the two, then decide which one you actually want to go with. I know it's a lot more work but I think if you want to get something which you're really happy with you're going to have to go round the design process a couple of times.

Personally, I think port assisted horns work better with a smaller
front chamber (going by simulations anyway) and less bandpass effect. You can probably also fit more horn length in that way.
Martin do all of theirs that way too. So if you do build a different one, I'd recommend trying that.

Regarding the port tuning/lengthening thing. I don't think the coupling of the ports themselves will have that much difference on the tuning, although it might to a small extent. I think it's more likely the cab as a whole that does it.

Edit: Making it sound marginally more on-topic!


Edited by: chaudio

SubSoniks wrote: Just a quick thought about the tuning, would it not be possible to add a couple of circular ports to the front panel and use tubes to change the tuning, the added holes will sum with the main port to give a new tuning frequency.

Also for future builds if using the same port design then maybe make the 'lid' of the port none permanent and fit different lengths, and make the sides of the port longer than you are going to need.

JaKe

(i forgot that subsoniks was you JaKe!)

I actually built the port too long and cut it down until i got the right tuning. I then had to add a brace and glue most of the top down to stop the port vibrating and make it properly airtight. I knew the brace would make the tuning lower but i didnt know how much, I had a guess and cut off a further 2cm from the port to compensate, but alas twas not enough.

The tubes in the front thing would definatly be an idea though, and was something i have been thinking about for a next design anyway. I think for now i'll leave it and build the other 3 slightly higher then build a fourth.

Unfortunatly Chris i have to provide a soundsystem on the 13th of september and its not built yet so i dont have time to try different prototypes. B&Q Fked me over with wood last night and seriously held stuff up so i'll be hard pushed to finish this now I dont even own any leads yet, im sat here soldering loads of plugs on leads from scratch...

Nothing like a bit of pressure to get things done, does help if the paints had time to dry though, built my first subs with a African Headcharge gig that I had been booked for - wasn't gonna miss that, sweat and blood - good times.
Jake

I remember putting the final touches to Chris's punishers in a marquee a few hours before setup while he fetched more gear[img]smileys/smiley4.gif[/img]

Everything went well! I finished building them the night before the event. and i set up the proccessor settings for the first time at the venue. they sounded ***king A!

Pics and stuff to follow!.....

Jake_Fielder wrote:
Everything went well! I finished building them the night before the event. and i set up the proccessor settings for the first time at the venue. they sounded ***king A!
<div></div>
<div>Pics and stuff to follow!.....</div>

[img]smileys/smiley32.gif[/img] Well done my good man!

Bravo, bravo.

Here:

Good work, its great when things come together like that.