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-   -   Beginner seeks help with “the usual question” (http://www.diyaudio.com/forums/multi-way/2029-beginner-seeks-help-usual-question.html)

Tim Buchanan 22nd January 2002 04:53 AM

Beginner seeks help with “the usual question”
 
Hi ya,

A long time ago I bought some peerless 10” drivers with a view to making a cheap system that would have a good, low-end response. The drivers I bought are the 831727’s (260 SWR). I now have the time to start building the cabinets but don’t know what volume and port measurements to use!

The data sheet for the driver can be found here: http://www.d-s-t.com/peerless/data/831727.htm

I got a some e-mails from E. Francy that were a great help, but I accidentally deleted them when I cleared out my back log of e-mails (sorry Eric)! I think he suggested a box size of about 60 litres (2.1 ft^3).

Is this a good box size for a ported enclosure using this driver? I’ve purchased 66ml (2.6 inch) un-flared ports, how long should these ports be to give a flat but decent low-end response? I could use 100ml ports to be sure to avoid excess port noise, but the cabinets I have in mind aren’t too deep and I thought 66ml was a trade off. Will port noise be an issue?

To recap, what box and port measurements would work well for a flat, low-end response and will 66ml ports be too small vis-à-vis port noise?

Thanks for your time. If you have any advice please feel free to contact me!

Cheers,

Tim :)

markkanof 22nd January 2002 05:05 AM

You could try using winISD to design your box.

www.linearteam.org

kelticwizard 22nd January 2002 06:53 AM

Tim:

The 260's are nice speakers. They are still for sale. No longer cutting edge, still a nice woofer.

What kind of box? Well, how deep do you want to go? A nice arrangement is a 2 cubic foot box tuned to 27 Hz or so. Your F3 should be around 32 Hz.

Your 6.6 cm vents should be 21.6 cm long. I usually use 3 inch vents-the 260 has a fairly long excursion-9mm. I would use a 3" diameter vent 11 5/8 inches long. This is to tune the box to 27 Hz.

Lower cutoffs are possible with bigger boxes. If this 2 cubic foot box is not satisfactory, let me know what size of box you are planning, or how low a cutoff, and we can proceed.

Tim Buchanan 22nd January 2002 11:54 AM

Thanks guys
 
I've had a poke at WinISD and it gives a good forecast for the 260's in a 60 litre box - cheers markkanof! It's quite a nifty program.

The only hitch is that the port sizes in the program aren't easily availiable in electronics stores over here (Victoria, Australia).

kelticwizard - I'm thinking a 60 litre box (2.1 ft^3) is best. I've found an 85mm (3.35") diameter port that has the tube angled at aproximately 30 degrees which will help with the depth issue (port has a fixed 'elbow' type bend). It has a maximum length of 320mm (12.6").

I've tried numerous formulas and java based calculators but they give very different results! If possible, could you try the 60L box with the 85mm port to see what the length should be? That'd be fantastic, but don't put yourself out - I'm aware that this is very easy stuff and if it weren't for the conflicting measurements I wouldn't ask at all.

Thanks again for the advice. Have a good one.

Tim

Tim Buchanan 22nd January 2002 12:25 PM

Is this a stupid idea?
 
I almost forgot - is it possible to set up a mic in front of the port, send a 26Hz sine wave to the woofer and adjust the length of the port untill the output reaches a maximum? Is that how ports are tuned? I hope it is because that's something that can easily be done! Thanks again.

Tim

markkanof 22nd January 2002 03:44 PM

Just a note on winISD in the window where the port tube length is calculated you can use the preset diameters, or you can just type in your own in the list box and then it will calculate the length.

Also don't know if you noticed but all the boxes that have a unit of measurement next to them, for example the port tube size is by default meters (m) you can click that unit and it will change to another unit that you might rather use. Also any numbers that you have already input in the corresponding box will be converted.

Hope these tips were helpful, they were stumping me for a while.

Mark

kelticwizard 22nd January 2002 04:25 PM

Tim:

Your question: "is it possible to set up a mic in front of the port, send a 26Hz sine wave to the woofer and adjust the length of the port untill the output reaches a maximum?"

Your answer: Absolutely!

In fact, here is a nice tone generator you can download off the internet. Set it to "sine wave". You don't need to accept the preset frequencies. Just highlight the frequency box in blue and write in your own frequency.
http://www.world-voices.com/software/nchtone.html

Just about any port calculator is accurate. The difference in results stems from the fact that air has different densities at different heights above sea level. Air has different densities depending on the weather. If one speaker program designer writes his program in Colorado on a sunny day, and another speaker program designer writes his in New York on a rainy night, there are going to be two different calculations. Nothing to worry about-it is unlikely to vary more than 1 Hz-not enough to make any difference.

kelticwizard 22nd January 2002 04:45 PM

Tim:

I ran an 8.5 cm port in a 2.1 cu. ft box through Boxplot.

32.36 cm tunes the box to 25 Hz.
26.84 cm tunes the box to 27 Hz.

As long as your length is somewhere between those two numbers, you cannot be that far off. A centimeter here or there doesn't mean anything.

Tim Buchanan 24th January 2002 04:01 PM

Cheers guys
 
Many thanks to kelticwizard and markkanof for the excellent, easy to understand and informative advice. I've been surprised at the generosity of people on this forum. It is a credit to you all.

Mark - I hadn't notticed the added functionality of WinISD. That program is excellent, I find myself staring at graphs in my free time! I'm not sure whether that's a good thing or not. I like the look of an isobaric configuration, don't like the price.

Kelticwizard - the tone generator works a treat. I've had trouble with the one in WinISD, this one is quick and effective. Many thanks for the simulations also, they were perhaps the biggest help and give me an idea of where I should be headed. I was expecting much smaller port lengths (last boxes using Vifa drivers had 8.5cm long ports) and would have been stumped had I not thought that 33cm port lengths were acceptable.

Cheers guys, I feel much more confident about building these boxes knowing what to expect.

Tim

kelticwizard 24th January 2002 08:04 PM

Tim:

Just thought I would clue you in on this free program. It is a full scale speaker testing program. Apparently, all you need to do a full scale test is a decent sound card and a microphone to plug in it.

For some reason, I have been unable to get this program set up right. Perhaps I should re-download and try again. But everyone speaks so glowingly of this program, that I feel safe in saying it is worth a try:
http://www.audua.com/

Good luck!


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