Ported box volume question

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As said above, it varies by degree.

If your box is way too small, you will get a big bump in the response, the smaller the box, the higher the bump. If the box is only slightly too small, the bump will be one or two decibels, which isn't too bad.

An example of manufacturers using this to create "better" sound is this:

A bump around 40Hz will improve the "kick" of a bass drum, 60-100Hz will create the more disco style "thud thud thud" which occurs in the dance/club music.

Personally, I prefer sealed boxes, as they are so much easier to make and use, and the driver's excursion is very predictable.

Chris
 
chris661 said:
What kind of set up are you going for? PA or home-use? [/B]

Chris
Home system, using two dayton 18s I got used for a super cheep price, so I thought I would work work them as eventual bass bins for a front horn full range from maybe 200 hz or 250hz up for the horns.

Thanks for help so far to all reply's!

Ed
 

GM

Member
Joined 2003
Of more importance is the horn/woofer vertical spacing than woofer/floor spacing, so working backwards from the desired 'FR' driver height makes sense to me. ;)

Conventional theory dictates the vent(s) be as close as practical to the driver(s) due to its relatively high mid-bass/mids BW output, but this assumes a ~uniform particle density within the cab (golden or acoustic ratio dims) in its pass-band, so for high aspect ratio cabs it's better to take advantage of any pipe loading to increase vent damping, ergo near/at the floor placement is desirable.

GM
 
GM

As I understand your reply, I should keep the bass bin short enough to mount the mid/wide range horn above and keep the driver close to listening height.

I should place the bass driver up off the floor, maybe mid way or above and the ports close to the floor.

The cabinets they came with were made fairly close to the right volume but i plan to build new cabs to optimize things.

Thanks
Ed
 
if there were such a thing as a mid bin then that is what should be placed right next to the treble horn mouth.
The bass bin should be right next to the boundary, be it floor or wall, if you are assuming 2Pi loading.

But many a PA style speaker only have a horn and bass/mid driver. Compromise becomes the rule.
 
Well, you could make it a long MLTL tuned such that when folded in half in an inverted 'U" it puts the woofer near/at its physical 'top'. I did some ages ago and all concerned were very pleased with the results, but Panomaniac is well along on a large Altec VOTT components loaded set, so AFAIK a current assessment is in the near future. Hopefully, it will be positive enough to spur other 'hornies' to try it where a low tuning is desired.

Regardless, yes, that's the idea, with the vertical spacing between the horn and woofer center-lines ideally being < 1/4 WL long of the XO's -12 dB point, so for 250 Hz/2nd order this equates to ~13560/4/(250*2) = 6.78", which of course can only be done in a Unity concept horn or funky 'V' shaped horn/woofer placement plus reflector, so neither is a trivial pursuit. A <1 WL of the XO point is considered the max acceptable, so you get them as close as physically practical, then line them up in phase at the XO point and 'it is what it is'.

Note that placing the horn somewhat above ear height, putting the woofer at face/chest height, is desirable when trying to reproduce that ~'live' experience in a HIFI/HT app. Ideally, there's also the room height to consider as to where the horns will work best overall. This gets a bit complex to figure, but I've found that for a typical nominally 8 ft height, a large screen TV's optimum 2/3 screen height for the HF driver of ~48.81" works well.

GM
 
AndrewT said:
if there were such a thing as a mid bin then that is what should be placed right next to the treble horn mouth.
The bass bin should be right next to the boundary, be it floor or wall, if you are assuming 2Pi loading.

But many a PA style speaker only have a horn and bass/mid driver. Compromise becomes the rule.

Andrew,

I am talking a two way system with this bass box and a wide range driver in round front horn for the upper frequencies. What would to me be mid-high driver. I see your comment as maybe a three way idea? Or maybe i miss understand.

Ed
 
AndrewT said:


that's the problem.
A two requires the mid to be close to the horn but the bass to be close to the floor. You cannot win. You must compromise.

OK....the horn is the mid....no high frequency driver involved here, no bass horn, only a ported box.
Two drivers only, 1 bass bin under 1 front horn wide frequency range driver. There are thousands of these in used in the world.

Ed
 
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