Slot port problems

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10 years 4 months ago #21213 by Laurence
Slot port problems was created by Laurence
So its been a while designing my cabinet, its a very simple design but is proving a little complicated as i do not have the specs for the driver of hf units. The lf driver is eminence but i dont know what model it is as there are no markings on the back so i am going on the specs of the eminence Alpha and Beta models thus making it quite hard to model the thing in WinSD. Ive been trying to calculate the slot port length and height through online calculators and im getting some weird results as the port seems extremely high for this enclosure and if i make it any lover i hardly have a port at all and it seems weirdly short. The original port is about 1.25" high and 18.75" across and roughly 5.5" long, however using the calculators i have ended up with a port 3" high, 15.9" across and 7.77" long. Does this seem too big for this sort of enclosure? Ive heard something about an 8.1 ratio but not quite sure what is meant by it. Here are some pictures:
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10 years 4 months ago #21214 by bgrade
Replied by bgrade on topic Slot port problems
Your problem is common, and Eminence will help you. Here, from their support page, they tell you what identifying marks to look at and who to contact for T/S parameters.

www.eminence.com/support/faq/

See especially:
"The Eminence speaker that I have is not on the website. What's its model number?"
and
"I need the T/S params for one of your custom-manufactured speakers."

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10 years 4 months ago #21215 by Laurence
Replied by Laurence on topic Slot port problems
Ahh thanks, however, the fact remains that the port still seems pretty large for the driver size, and the parameters cant make that much of a difference. The reason im doubtful is because when i see other loudspeakers with a slot port at the bottom they are often not very high, maybe 1" and then are quite wide which seems to go against the 8:1 ration that many people seem to think is important.

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10 years 4 months ago - 10 years 4 months ago #21216 by bgrade
Replied by bgrade on topic Slot port problems
You would want the T/S parameters to know if the box volume and vent area and vent tuning are appropriate. Otherwise it is gambling against the odds that this driver will work optimally with this design. The proportions of the vent are within the 1:8 ratio, which I agree is fairly important to get the vent to work correctly. The area seems pretty big, but it depends on the x max and the tuning. I doubt it has a very big xmax, as that is really more of a sub trait than a mid driver trait. If it were a 5mm xmax 12 inch driver tuned to 60hz, I get a minimum area of 16.5 in^2. That does not mean that the vent can't be bigger, just that if it were smaller there would be an increase in port noise. This vent area could accommodate up to nearly 12 mm xmax before that became an issue. I guarantee that driver is not moving that far.
Last edit: 10 years 4 months ago by bgrade.

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10 years 4 months ago #21225 by Laurence
Replied by Laurence on topic Slot port problems
Well this driver is 10", i also too doubt the Xmax will be that big, probably more around 3-3.2mm, and i put the box tuning as 50Hz. The specs cant be THAT off though, im going by the specs on an Eminence Alpha & Beta drivers which are probably pretty close to this one so im not sure why im getting such strange results. I'll take out the driver and see what markings there are.

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10 years 4 months ago #21226 by bgrade
Replied by bgrade on topic Slot port problems
Is there any acoustic dampening material in there? Could be standing waves. I had to put a bunch in my mids to stop that problem.

Yeah for a 10 inch driver that vent does seem huge. It is nearly as large as the cone area. I usually shoot for about somewhere around 1/3 of the SD, give or take, depending on x max and tuning.

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10 years 4 months ago #21227 by Laurence
Replied by Laurence on topic Slot port problems
I havent built the enclosure yet, want to make sure i have the design right before buying a load of wood, its just all the slot port calculators give me this weird result and im wondering if i should just treat it as a vent rather than a slot as then i could use WinSD to calculate the port length.

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10 years 4 months ago #21228 by bgrade
Replied by bgrade on topic Slot port problems
Sorry to beat a dead horse, but there is no way to be really accurate without the specs on the driver. If you are not going to find those and recalculate, then your next best method is to just build the cabinet and see if it is satisfactory, but you won't know whether it could be operating better until you try it in another enclosure. Really, the whole point of the T/S parameters is to save a lot of trial and error builds. It will give the best guess simulations, and safest box volume to keep you from blowing the driver. It may seem like it is not worth the effort to find out, but if you are anything like me, you will be forever bothered by the fact that you did not build a custom box for the actual driver, and you will always wonder if it could have been better.

Personally, I would say it would be worth it to buy non-custom drivers, with all the specs readily available, because if you decide to build more, you can just buy more drivers instead of making a bulk custom order. Keeping that in mind, if you build based on Alpha or Beta, then you can always upgrade to one of those later, but if you have a driver that is closer to a Delta or Kappa, that would be a downgrade.

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10 years 4 months ago #21229 by Laurence
Replied by Laurence on topic Slot port problems
Indeed, will get the parameters as soon as and then see what the port size comes out as

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10 years 3 months ago #21382 by Tony Wilkes
Replied by Tony Wilkes on topic Slot port problems

Laurence wrote: Well this driver is 10", i also too doubt the Xmax will be that big, probably more around 3-3.2mm, and i put the box tuning as 50Hz. The specs cant be THAT off though, im going by the specs on an Eminence Alpha & Beta drivers which are probably pretty close to this one so im not sure why im getting such strange results. I'll take out the driver and see what markings there are.


I would have thought that 50hz was way too low for any Emmi 10" unless you are using an exotic alignment. Would have thought 70 hz would be closer and reduce any port length dramatically. For a 10" driver with limited Xmax I would normally use a 64mm tube port.

Tony

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