Newbie Questions about cab design (sorry guys!)

[Darren Orr]

Hey, I'm looking to build a couple of cabinets.
I have built a detuned cabinet before, I can do all the physical work, however my problem is the design/theory side of things.

I have downloaded winisd pro, the speakers I have aren't in there and I can't find enough specs to enter to a point where the program is happy.

The speakers are a 15" celestion 1525e and a bag end 12" from an swr cab (don't have model number on hand). Looking to build a cab for each that match in appearance.

Is there a "generic" cab design that may work?

Anyone know where I may find the information or a design for these speakers?

Thanks, Darren

[Enzo]

You have not told us just what you want to know, but you could probably get the T-S parameters from the speker manufacturers, I assume that is what you are "plugging in."

[soundguruman]

The manufacturer usually will provide free cabinet plans. Contact Celestion...
When a speaker is installed in a cabinet, the cab must have the correct internal volume, and the correct port size.
Otherwise a lot of the efficiency is lost. The bass frequencies are lost.
That's why there are no "generic" cabinets. Unless the cabinet is open back.
An open back cabinet is popular, but has very poor bass response. It works OK for guitar, but not for bass.

[tedmich]

often you can estimate the T/s parameters from the cab the drivers were originally in, or just copy the internal volume and port dimensions. I commonly design cabs where I take a typical port (say 4" dia 7.5" length) and change the diameter until I can just use the material thickness (usually 0.75") as the port length. Then I don't have to sweat cutting ABS etc.

I suspect most guitar speakers are unsuitable for real vented bass reflex alignments and are made for open backed high SPL designs with little bass response. You can also suss out the TS parameters yourself as few guitar speaker Mfg. ever generate or provide these numbers. There is even an affordable test system (Dayton Audio DATS ) which lets you do this for under $100. And the perfect alignment (B4 say) is not carved in stone, compromises are often made to avoid too big a box etc. Bass just suffers but is often not needed. A cab with a -3db response to 40Hz is not needed for a guitar amp cause its got very little at that frequency.

[Darren Orr]

Thanks for the replies.
I have emailed Celestion and Bag End about speakers and potentially cab designs. No reply from Celestion yet and Bag End definately dont give out their cabinet designs (which I think is fair enough).

The information I have currently is:

Celestion - LF Pressed Chassis / Ferrite - TF1525e - Celestion - Guitar, Bass & Pro Audio Speakers

Bag End - http://www.bagend.com/bagend/s12-d2.htm

I have tried entering the T/S parameters into Winisd for the celestion and It keeps coming up with errors. Am I really that inept with the program? or am I missing something here?

The Bag End data sheet has the cabinet measurements and volume, is this enough for me to backwards engineer a cabinet? It doesn't mention port size.

Ideally I would like the 2 cabinets to be the same width so I can stack them, however I am not adverse to having an extra compartment beside the 12" cab for storage.

Thanks again!

[soundguruman]

Thanks for the replies.
I have emailed Celestion and Bag End about speakers and potentially cab designs. No reply from Celestion yet and Bag End definately dont give out their cabinet designs (which I think is fair enough).

The information I have currently is:

Celestion - LF Pressed Chassis / Ferrite - TF1525e - Celestion - Guitar, Bass & Pro Audio Speakers

Bag End - s12-D specifications

I have tried entering the T/S parameters into Winisd for the celestion and It keeps coming up with errors. Am I really that inept with the program? or am I missing something here?

The Bag End data sheet has the cabinet measurements and volume, is this enough for me to backwards engineer a cabinet? It doesn't mention port size.

Ideally I would like the 2 cabinets to be the same width so I can stack them, however I am not adverse to having an extra compartment beside the 12" cab for storage.

Thanks again!

Did you follow these specs?
LF Pressed Chassis / Ferrite - TF1525e - Celestion - Guitar, Bass & Pro Audio Speakers
Be patient. Building the right cab with correct port is more than worth it.

[tedmich]

WinISD may want a lower Qts value for a B4 alignment, bassbox or Eminence designer allow for more flexibility and will point you toward a C4 alignment if your Qts is too high. Speakers designed for open backed cabs often have Qts values >0.5 and these do not work well in vented (or closed) boxes. The Bagend is definitely vented, just reproduce their internal volume and vent and you'll get a similar response. The celestion can be made to work with a more flexible program (free versions are available) but will never have as good a bass response.

On a side note, Bagend has a Linkwitz transform system (Infra) capable of a flat response to 20Hz for a small sealed sub...cool! Probably spendy though...

[Darren Orr]

So Celestion came back to me with a cabinet design.
In fact 3 and a couple of pdfs on cabinet building. Props to their customer service.

So with the bag end, as long as the internal volume is the same and the vent dimensions are the same, then I can effectively make it whatever dimensions I want? (within reason of course).
I've worked out that the bag end cab has a 2" vent. Is a vent the same as a port? Or is a vent just the thickness of the cabinet material vs a port with an internal extrusion?

I really feel like I'm asking you all quite simple tedious questions. Is there somewhere I should be looking for newbie instructions?

Thanks again for all your help.

[Darren Orr]

"Did you follow these specs?
LF Pressed Chassis / Ferrite - TF1525e - Celestion - Guitar, Bass & Pro Audio Speakers
Be patient. Building the right cab with correct port is more than worth it."

Yep. Those are the specs I put in.

[kg]

when in doubt, you really can't have a sealed cabinet that's too large. most of them are waaaaay too small.

[tedmich]

So Celestion came back to me with a cabinet design.
In fact 3 and a couple of pdfs on cabinet building. Props to their customer service.

So with the bag end, as long as the internal volume is the same and the vent dimensions are the same, then I can effectively make it whatever dimensions I want? (within reason of course).
I've worked out that the bag end cab has a 2" vent. Is a vent the same as a port? Or is a vent just the thickness of the cabinet material vs a port with an internal extrusion?

I really feel like I'm asking you all quite simple tedious questions. Is there somewhere I should be looking for newbie instructions?

Thanks again for all your help.

the typical cabinet design software calculates port tuning frequency and then you define the diameter desired and it spits out a length. The volume of the port (usually a cylinder) is subtracted from the box volume and if you are anal the volume of the driver assembly (usually <5% of the box internal volume) can also be subtracted. And its just volume so yes you can make a odd skinny box which fits under your coffee table. The geometry of the vent is more constrained as with certain dimensions it can have an audible movement of air that sounds BAAD. Vent = port yes!

Many a car subwoofer web site has a good intro to using Thiele Small parameters to design bass reflex (ported or vented) cabinets.
heres one
Audio Speaker Design Calculators - KBapps.com

[Darren Orr]

Right, so I have been doing some more digging about the bag end speaker and their cabs. I've discovered their port is just a 2" hole in the back of the cab with a round over inside and out.
I cant find any T/S specs for the speaker at all.
Thinking I will just replicate the original cabinet volume and hope for the best.

Thanks for all your help!

[tedmich]

its likely undersized for an optimal B4 alignment but thats the compromise Mfg. make to decrease material and shipping cost. You can't really go "wrong" just sub-optimal and unless you are OCD this shouldn't trouble you. Its best to make real things that work rather than plan to make perfect things that never actually do, IME.