Another cab build.....HELP ME PLEASE

[The Shrek]

[attachment=238159:basschatIMG_20170214_152534962.jpg][attachment=238160:basschat (2).jpg]

Hey guys, my aim is to build a smallish 2x10 to add some bottom to my little ashdown mi 12. I already have these two Eminence BP 102 - 4 OHM speakers. The dimensions of the cab I built work nicely to stack the little Ashdown. The internal measurements are:

H 610mm
D 295mm
W 355mm

some of the specs of the speakers are below, but I dont know if this helps or not.

Resonance: 35 Hz
Useable freq range : 40Hz - 2KHz
Sensitivity ; 92 dB

I am afraid that's as far as my ability gets me. I tried using the winsd program to work out what size and length of port I would need, but I am too stupid to work it out for myself. Is there a kind knowledgeable member who would calculate the port dimensions for me.... please please please.

Thanks Michael

Edited February 14, 2017 by The Shrek

[Bill Fitzmaurice]

[quote]The dimensions of the cab I built work nicely to stack the little Ashdown.[/quote]Doing that doomed the result. The BP102 needs at least twice the volume you allocated to work well. Stuffing two of them into that size box pretty much guarantees boomy response, with not much low end. You can salvage that box by leaving it sealed, which won't give a better result but at least it shouldn't be boomy. Otherwise it's back to the drawing board, I'm afraid.

[EBS_freak]

[The Shrek]

Oh crap!!. Thanks Bill.
would the box sound decent if I used it sealed? I can't believe I wasted all that time and money, The current cab sizes work really great to fit in my car and that what I based the sizes on. How much bigger would the cab need to be?

Edited February 14, 2017 by The Shrek

[Jack]

[quote name='Bill Fitzmaurice' timestamp='1487090198' post='3236953']The BP102 needs at least twice the volume you allocated to work well.[/quote]
[quote name='The Shrek' timestamp='1487096434' post='3237065']How much bigger would the cab need to be?[/quote]

Same cab, seal one hole and use 1 speaker??

I assume the 4 ohm load wouldn't be ideal for your combo though.....

Edited February 14, 2017 by Jack

[Bill Fitzmaurice]

[quote name='Jack' timestamp='1487097023' post='3237076']
Same cab, seal one hole and use 1 speaker??
I assume the 4 ohm load wouldn't be ideal for your combo though.....
[/quote]Agreed. OP, the purpose of speaker modeling software is to make sure of the result before you cut any wood, or order any drivers. Chalk this up to a lesson, albeit an expensive one, learned. Start from scratch, do it the right way, and see if you can sell the drivers to recoup some of your losses.

[Gottastopbuyinggear]

I have a feeling I'm going to regret asking this, but here goes... The dimensions of that cab aren't much shy of a quarter of an Ampeg fridge, and that has an f3 of something like 58hz. Also there's the SVT 210AV, which must be pretty close to those dimensions and is reckoned to have a similar f3 (I may be hugely mistaken here, but I think I read something written by Bill once that confirmed Ampeg's claims on that?).

Based on that you could conclude that putting a couple of suitable speakers in that cabinet, sealed, would give a similar result, but I've not found a speaker that models anywhere near that in WinISD. Is there some sort of magic involved in the drivers that Ampeg put in these cabinets?

[The Shrek]

Thanks guys. As you rightly say I need the cab to be 8ohms to use both. I thought this size of cab would be nice and compact and I based in on the size of a previous little Hartke 2x10 I previously owned.
I will finish the build as I am 99% completed. I even got metal speaker grille cut to size, I will try it as a sealed cab and If it is totally useless I will start a replacement build in the future after the sting of this wrong build wears off.

Thanks Michael

Edited February 14, 2017 by The Shrek

[Bill Fitzmaurice]

[quote name='Gottastopbuyinggear' timestamp='1487102554' post='3237183']
I've not found a speaker that models anywhere near that in WinISD. Is there some sort of magic involved in the drivers that Ampeg put in these cabinets?
[/quote]Model the Eminence Alpha 10, or B810. The cab will also need a fair amount of damping to get the Qtc down. They're not identical to the Ampeg driver, but they're close. They have high Qes, not good for ported, but fine for sealed. And they're cheap, with small magnets. That's why they have high Qes.
[quote]I thought this size of cab would be nice and compact and I based in on the size of a previous little Hartke 2x10 I previously owned. [/quote]The driver specs of the Hartke would have been different. The driver size alone doesn't dictate the required cab size.

[Beer of the Bass]

Just to play devil's advocate here, is the BP102 really such a disaster in this cab? I had a quick look a model of two BP102 in a 60l cab using WinISD (using a 40Hz port tuning); It looks undersized and boomy when compared to an optimally flat cab for these speakers, but it also looks as good as or better than many popular commercial cabs. So it really depends what you're comparing it to. It would go lower and have a smaller midbass hump than the 1x12" cabs I'm happily gigging with at the moment.
Am I missing something here, as I'm not seeing what's so bad about it?

Edited February 15, 2017 by Beer of the Bass

[The Shrek]

Thank you Beer of the Bass, at last a bit of optimism. Thanks guys and that's exactly what I have decided to do. It doesn't have to be the best cab in the world and if it adds a bit of support to the Ashdown then that will be fine for now. Loads of guys have built small cabs and against all odds they were pleased. Yes Bill I know I did everything wrong but I have learned my expensive lesson. So the question that remains is, do I port it and what size of port, and if the port makes it boomy I will simply remove it and block the port hole!

[stevie]

Two 75mm ports, 100mm long will tune the box.

[Bill Fitzmaurice]

[quote name='Beer of the Bass' timestamp='1487155110' post='3237522']
Just to play devil's advocate here, is the BP102 really such a disaster in this cab?
[/quote]It's not what it could be. The reason one would use a driver with the specs of the BP102 is to dig deeper than what the average driver will do, and that would seem to be the OPs intent, but in a box that's way too small it can't deliver on that promise. At this stage I would not port it.

[Beer of the Bass]

[quote name='Bill Fitzmaurice' timestamp='1487165434' post='3237686']
It's not what it could be. The reason one would use a driver with the specs of the BP102 is to dig deeper than what the average driver will do, and that would seem to be the OPs intent, but in a box that's way too small it can't deliver on that promise. [b]At this stage I would not port it[/b].
[/quote]

I don't know if I'm being spectacularly obtuse here, but would you care to go into your thinking behind that? Comparing models of a 40Hz ported cab to a sealed one (with this volume and these drivers), the ported cab shifts the F3 lower, increases power handling between 30Hz and 80Hz and only causes a bump of around 2dB at 100Hz. What is the factor that would make you lean towards sealed? The only thing I can think of is the possible challenge of fitting in enough port area.
I agree that one might not choose these drivers for a cab of this size if the project was fully planned out from the beginning, but it still looks like it could be a useable cab.

Edited February 15, 2017 by Beer of the Bass

[Phil Starr]

I don't see the problem either, a sealed cab will have a flatter response and may sound nicer, but that is to some extent subjective. putting these two speakers into a ported box that size won't get all the bass they could generate but it will still exceed them in a sealed box. You do get a 2dB hump at 100Hz so they will sound boomy (or punchy, choose your adjective based on your taste) but you will also get an extra 3db of bass down to 40Hz with a ported box. You maybe shouldn't have started here as Bill says, but it's not a disaster. Especially if you picked them up cheaply.


If you are happy to bodge the baffle or make two then try both and choose the one you prefer the sound of.

[Phil Starr]

Snap

[Bill Fitzmaurice]

[quote name='Beer of the Bass' timestamp='1487171301' post='3237744']
I don't know if I'm being spectacularly obtuse here, but would you care to go into your thinking behind that?
[/quote]IMO the difference between the two doesn't justify the added complexity of porting. If he had 60L net per driver it would be a different story.

[The Shrek]

Thanks again guys for the response. I have nothing left to lose with this box so I might as well try to port it. I was going to rear port it so what sizes will I use. One bigger port or two small ones as Stevie recommended . If it is a boomy box I will simply block the rear port holes again . I have a few old 100mm port tubes from previous cabs in my drawer, can I use them?

[stevie]

To use a single 100mm port, make it about 70mm long.

[EDIT] Just double checked this. Anything between 70 and 110mm would be OK.

Edited February 16, 2017 by stevie

[The Shrek]

Thanks Stevie, that saves me having to order new port tubes. Thanks to everyone for the help.

[xgsjx]

I think what Bill is saying is that it's like sticking a Ferrari engine in a Rover. The Rover might hold the engine, but you're not gonna get close to it's full potential.
Yes you can then modify the Rover, but it's still not gonna go like the Ferrari.

[stevie]

I'd hardly compare those Eminence drivers with a Ferrari.

[Beer of the Bass]

[quote name='xgsjx' timestamp='1487237956' post='3238214']
I think what Bill is saying is that it's like sticking a Ferrari engine in a Rover. The Rover might hold the engine, but you're not gonna get close to it's full potential.
Yes you can then modify the Rover, but it's still not gonna go like the Ferrari.
[/quote]

Aargh, car analogies! But if you could make the Rover work significantly better with about 20 minutes work using tools and parts you already had at hand, you'd do it, right?

[abar121]

Watching this closely, thinking of having a go my self, albeit with more modest speakers.

[stevie]

Just make sure you use a proven design or get some advice before you cut the wood. This thread - and I think the OP will agree - is a good example of how not to DIY.