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Cabinet Port Sizes.


B.Flat
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A 102mm port has an area of 8167 square mm, two 50mm ports a combined area of 3925 square mm, so the answer is no. For the same Fs the 50mm ports would be much shorter. However, they also might chuff. Your speaker modeling software should show you port velocity at maximum excursion, which you want no more than 20 meters per second within the cab pass band. It will also show you what port area and length you can get away with to meet that requirement.

Edited by Bill Fitzmaurice
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I cannot, because an easy calculation won't tell you port velocity. If it's too high, because port area is too small, you'll have chuffing noise. If the port area is larger than required to prevent chuffing the ports will be larger than necessary, making the cab larger than necessary. The speaker modeling software I use for ported cabs is WinISD 0.7.950
http://www.linearteam.org/

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If you want something really simple to use then this https://www.ajdesigner.com/speaker/ will design a vented box for you. It isn't very flexible however as it will simply calculate a single box size optimised to give the flattest response. This often means the box is impracticably large for bass guitar. What it will do is just tell you the port is too small.

Win ISD that Bill is recommending is much more flexible, you can change the tuning and box sizes and it will show you how that affects the frequency response and it will allow you to make the ports any size you want too, recalculating the length to keep the same tuning. It will pay you to learn to drive this software if you want to do any serious speaker building or modification.

As to the OP request, give us a lttle more detail. Why are you wanting to do this? What speaker are you using? what size is the box? How much power will you be putting into the speaker? It is unlikely that you'd get chuffing at low power but if you are trying to match a monstrous drummer with a single speaker....

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Hi. Thank you Bill, Phil & Dan. Advice taken on board.
To answer your question Phil I have a sealed 2 X 10" Deltalite 2510 cab, the drivers are in separate chambers but at 33 ltrs total volume per chamber this is not good.
Using some internet info I calculated one 100mm dia port between 116 & 125mm long in each chamber. However I do not trust my own calculations!
Since starting the thread I have realised smaller dia ports are not required as I can put them (10mm dia) in the back of the cab.

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The 2510 shouldn't be used in a sealed cab, the specs aren't suitable. Your f3 will be around 95Hz. That's fine for guitar, NFG for bass. A 33L per driver cab is much too small for the 2510. The ideal volume is 60L per driver, and that's not inclusive of the port. You can get a good result with as little as 45L per driver, but again, that's net, not including the volume of the port. In short, the cab size you have would be suitable for one 2510, but not two.

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I haven't got time at the moment to optimise what you have but you might like to have a look at Eminences own designs for this speaker https://www.eminence.com/pdf/DeltaliteII_2510_cab.pdf If you scroll down you'll see their recommended cab for a bass 2x10. It's getting on for 85litres. There are loads of other designs too.

Is this a cab you've built or have you installed the speakers in a commercial cab? They are perfectly decent speakers so if you are up for a bit of woodwork well worth building a suitable cab for.

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Thank you for your reply Phil.
Unfortunately I am the wrong side of 75, have no workshop facilities and little disposable income!
I was given the cab to supplement a 1 X15". I have an old YAMAHA pb1 preamp which has bi-amp outputs.
I was hoping to use the 2 X 10" as a mid/high box. I thought putting vents in it would improve its performance enough for this. Maybe crossed over at around 85 to100 Hz

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Thanks again Bill, but tell me as the volume per chamber appears to be around double the Eminence advised max is this putting the speakers at risk or reducing their efficiency?
And finally wlll a port not have any beneficial effect over 100hz?
I appreciate the time you, Phil & Dan have taken to help me.

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[quote name='B.Flat' timestamp='1505817955' post='3374482']
Thanks again Bill, but tell me as the volume per chamber appears to be around double the Eminence advised max [/quote]That's how small a cab they may be used in, not how small they must be used in.
[quote]wlll a port not have any beneficial effect over 100hz?[/quote]None.

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One of the keys to getting an active crossover to work properly is making sure that the drivers are flat an octave either side of the crossover frequency. At the moment, your 2x10 cab is rolling off just below 200Hz. This will produce a phase shift which in all likelihood will result in an unwelcome suckout in the very important 100 to 200Hz region when you pair it with your 15. This will happen whether or not you use an active crossover (unless you use asymmetrical slopes, but let's not get into that). The OP can get a good idea of what this sounds like simply by running both cabs together as they stand.

I think the original suggestion was best. Although it's true that these drivers need a larger cabinet, if the OP ports the 2x10s as originally planned, he'll extend their frequency response down another octave or so, which will allow the crossover to work (more or less) as intended. It will also give him the opportunity to run both cabs together without a crossover. I am assuming you have a stereo power amp. (You shouldn't have any chuffing problems with two 4" ports).

Using a crossover on your 2x10 means that you are potentially reducing system power handling by half because the tens are not handling any bass. Carrying a 70-litre midrange cabinet around with you is just silly. ;) Plus, you would have the added flexibility of using the 2x10s on their own and taking the 15" cab along for the occasions when you need the extra oomph.

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[quote name='Bill Fitzmaurice' timestamp='1505747774' post='3373974']A 33L per driver cab is much too small for the 2510. The ideal volume is 60L per driver, and that's not inclusive of the port. [/quote]

But if we took a driver out, filled in the gap and then ported it, we'd have a 66l, ported 1x10" cab?

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OK how old are the Deltalites? Are they marked as Deltalite 2510-II or just as Deltalite 2510?

I've been trying to keep it simple because I think B.flat just wants to get on with something that sounds OK, to get the best out of what he has. To be honest Stevie I don't think the phase issues will necessarily be that serious as the OP isn't trying to get a cab with a flat full range response. As he has the gear all there and he can try it without any expense or speaker surgery he might as well try it. (for the OP the phase issues will result in a bumpy frequency response through the crossover range) The thing is it is difficult to say what the combination would sound like when we don't know what the 15 is. Unless the sensitivity is in the region of the 2x10 then driving them all in parallel might not work. There are still too many unknowns to be

I do agree with Stevie that porting the cab will give some extra bass and may make the 2x10 more useable on its own. yes it'll be bass light but that may still be OK. If they are the older generation Deltalites then they should be fine, WinISD shows them as being flat +-1db down to 80Hz with the cab tuned to 60Hz

The other issue is impedance, I'm assuming the Deltalites are 8ohms and so is the 15. That's not an issue with a stereo amp but a single amp would struggle to drive all three speakers.

I'd suggest the OP try the cabs with his crossover as they are. If he likes the sound that's great. If he wants to port the cabs after that with a bit more detail we can calculate the ports for him.

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[quote name='Jack' timestamp='1505847881' post='3374771']
But if we took a driver out, filled in the gap and then ported it, we'd have a 66l, ported 1x10" cab?
[/quote]Since the OP intends on bi-amping with a 1x15 for the lows and the 2x10 for the mids and highs there's no reason to change the 2x10 from what it is. If he wanted to spend some $$$ to create a useful 2x10 or a pair of 1x10 then ported is the only way to go with his tens, but he doesn't want to.

Edited by Bill Fitzmaurice
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Hi Phil.
The drivers are Deltalite 2510 II. Bill is correct on the info I have given so far, but on balance, I would like to go ahead and port the cab.
I would be grateful if you could calculate the port for me. I have bought some reflex tubes 110mm internal dia. The chambers in the cab are 33ltr total without deduction for speaker or port.
Once again I must thank you for the advice and assistance, I am trying to understand the physics but the old grey matter I finding it hard going !!

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