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Multi-Way Conventional loudspeakers with crossovers

comlicated port/driver combo question. (long read)
comlicated port/driver combo question. (long read)
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Old 29th July 2005, 09:03 PM   #1
exhausted mule is offline exhausted mule  Canada
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Default comlicated port/driver combo question. (long read)

since several years ago... i've been in search of a speaker that could reproduce the intensity of a strings assemble (cellos, violins, pianos...) with flutes, trumpets, baritones and the like.

but most notibly, organs.

however, still have the capability of reproducing modern movie soundtracks with ease at high decibals.

Now i understand that most speakers have difficulty in doing this (especially with most loudspeakers in the 3000-8000 range being directed to hometheater and general music reproduction)

I've been modeling some cabinets and doing some calculated measurements with winisd. Seems as though the larger the cabinet, the smaller the port can be. Makes sense right? in order to reproduce a given frequency, the soundwave has to travel a certain distance before exiting the port. (top of my head correct me if i'm wrong pls...)

so with a smaller box, you would need a longer port for a given hz.

ok, so onto my question. I'm trying to design a port/cabinet combo that will give me an above average gain in the hz that the port/tube is tuned at, however i dont want any "boom" in the reproduction. will having an absurdly long port create this? if not, is there a limit to how long the port can be?

what i'm trying to create, is an exceptionaly musical cabinet/port/driver combo but still have a high tuned gain.

assume that the box volume is equal to the port volume, and you'll the idea of what i'm trying to achieve. The would be true for all drivers in the cabinet excluding those allready tuned by the driver manufacter (tweeter, some midranges. however, i would like to tune those myself where possible).

if this doesn't make any sense to any of you, pls let me know. Looking around the net at the more knowledgable group of entusiast/diy'ers, seems as though you guys would know best and hoping the combined knowledge of the few who might understand this would be able to help out with an experienced answer.

thanks in advance.

wish me luck in the woodshop.
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Old 29th July 2005, 09:54 PM   #2
simon5 is offline simon5  Canada
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Hi, the port is shorter with a bigger box because you have more air in the box so the airmass in the port need to be smaller to tune at the same frequency. Why? I don't know exactly, but it's not because the soundwave has to travel a certain distance before exiting the port. If it was like that, port placement would be crucial, but in a vented enclosure, you can place the port anywhere.

You want to use a small box with a very long port. You must be careful with 1st port resonance frequency. If you use WinISD Pro, you'll see the 1st port resonance frequency in the "Vents" tab. For example, a 50 liters box tuned to 16.4 Hz (most of the time, the lower organ note) need a 68 inches long port if it's 4 inches in diameter. That port will resonate at 100 Hz, if your crossover is at 80 Hz, that resonance will not be attenuated enough and will mess up the sound a bit.

If you go too extreme with long ports, you might end up with a Transmission Line box I guess. Correct me if I'm wrong on that. Maybe it can limit how long the port can be, because you won't have any gain over a sealed box when you go too far I guess. The airflow might be restricted.

I also want to add that a big box with a short port is not boomy if you design it correctly. Because the box is big, you can also use more port area, so longer ports, since you can have longer ports easily in a big box.
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Old 30th July 2005, 05:55 AM   #3
exhausted mule is offline exhausted mule  Canada
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thanks for the help.

your right about the soundwave not having to travel a certain distance... i think its something to do with air moving in and out of the cabinet. like blowing into a beer bottle.

i didn't know, however, that ports them selves had a resonant frequency... i just downloaded winisd pro (had the beta without a vent mach) and well see what frequencies i can pull. cause the port i have here is the most complicated to build.

i'm hoping i dont have to croos my front speakers over though. so far, the lowest dip is at 32hz -3.5 db.

my 3 ports are 72 cms long at 6 cms wide in a 100 liter box. 3x8 inch woofers. i'll read up a bit more and model a bit more

and some more and some more....

and then build it to see how it performs.

then... onto the midbass to get rid of that dreaded "dead" feel to cellos!
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Old 30th July 2005, 08:05 AM   #4
simon5 is offline simon5  Canada
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I want to tell you BTW that three 8 inches drivers won't be enough if you're heavily into organs, unless you use JLaudio W7 line which is too expensive IMO.

Better to go with a single 12 or 15 inches driver.
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Old 31st July 2005, 07:53 AM   #5
exhausted mule is offline exhausted mule  Canada
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yeah i was thinking about this... because the drivers i'm using are the dayton audio ref series for this system and the drivers dont seem to have much in the way of xmax.

so... was thinking either three times 10 inches. the originall design i had for these was a 160 liter box with 8cm diameter wide ports. basically the same idea but in a double bass reflex with a port in the main chamber as opposed to all three in the bottom. (or rear)


with this (if i can remember correctly) i was getting much better numbers with two tunable regions. so one at 16hz and the other where the woofer dips. howover... 10 is probably the biggest i want to go as "more material, heavier woofer"

so with a 10 inch woofer. i'd have to change the design of the top cabinet and incorperate another 6 inch or figure something out for midbass.

and that just gets even more expensive.

keep in mind though.. the two subs that will be accompanying these will be two times double 12inch subwoofers built into an isobarik design.

quick and musical but has the displacement to achieve good spl as low hz.

again we'll see. i'm hoping to build a few of these if the triple 8's turn out. if they do i'll sell those and build another along with the tens and go with the top/center cabinet. and cross compare them.

but yeah. so far so good on acad and winisd.
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Old 31st July 2005, 08:07 AM   #6
simon5 is offline simon5  Canada
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Oh, you got two subwoofers to go with these triple 8.

You don't need triple 10 then.

Forget what I said hehe!
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Old 31st July 2005, 06:37 PM   #7
BassAwdyO is offline BassAwdyO  United States
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Here's the basics

Ported enclosures are helmholtz resonators. An air mass(the port) and a spring(the air inside the enclosure not including the port). They resonante the same as a mechanical mass and spring.

If you make the spring tighter(smaller internal volume) you need to make the mass heavier(longer port). Making the port of larger cross section also increases the "tightness" of the airspring, hence a longer port is needed.

I always wondered if a TL could be modeled as a ported enclosure but I dont really think its possible... There is no airspring in the TL it's simply a 1/4 wavelength pipe.

The port itself has resonances like a 1/4 wavelength pipe. Bends I believe will attenuate these somewhat.
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Old 1st August 2005, 04:20 AM   #8
exhausted mule is offline exhausted mule  Canada
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it wont be a tl. it'll be closely resembling a dbr box.

i'm currently looking for a programs that could model how a sound wave reacts with soundwave.

the port... will work like a "flute" in that in itself will produce a hz. just like a dbr but in a smaller tighter setting with the main box being tuned as a normal dbr with a single large port.

two "vortex" type spiraling ports will feed a parralelogram type chamber (where i need the wave modeler to see what happens when the sound wave comes into the chamger) and what i can do with another port from there.

i dont even know if this is possible but i'm wiling to try.

i figure i would need to tune that chamber according to the tune of the main chamber because we'll... it'll be feeding this secondary chamber.

it'll be almost exactly as the fostex type box but with a slight (but huge difference in tune) difference.

just curious really... if anybody has done something similar. the fostex type box is the closest thing to this and can't find anythign else.
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Old 1st August 2005, 04:32 AM   #9
soongsc is online now soongsc  Taiwan
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Quote:
Originally posted by exhausted mule
it wont be a tl. it'll be closely resembling a dbr box.

i'm currently looking for a programs that could model how a sound wave reacts with soundwave.

the port... will work like a "flute" in that in itself will produce a hz. just like a dbr but in a smaller tighter setting with the main box being tuned as a normal dbr with a single large port.

two "vortex" type spiraling ports will feed a parralelogram type chamber (where i need the wave modeler to see what happens when the sound wave comes into the chamger) and what i can do with another port from there.

i dont even know if this is possible but i'm wiling to try.

i figure i would need to tune that chamber according to the tune of the main chamber because we'll... it'll be feeding this secondary chamber.

it'll be almost exactly as the fostex type box but with a slight (but huge difference in tune) difference.

just curious really... if anybody has done something similar. the fostex type box is the closest thing to this and can't find anythign else.
I'm looking for that kind of tool too! The commercial tools are really expensive and involve finite element modeling. Some people recommend tools used for mold flow analysis, but I'm not sure if it works with air as the medium.
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Old 2nd August 2005, 09:03 AM   #10
exhausted mule is offline exhausted mule  Canada
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never thought of that actually ( and i did mechanical engineering in school)

if you could find a modeler where you can either change the properties of the material being casted (to exact specifics of air) or just select the combonation in relative parts or airs composition...

you'd be set.

but yeah, these programs cost 1200+ canadian.

we'd need something that could calculate the inflow of air also. cause in a cabinet, you have different pressures at any given moment (due to the sound "wave")

a flow gen (that i know of) doesn't calculate both ways, just the positive.
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