Speaker box Design Help

[ralrigs]

what box should I make for a JBL m115-8a

Hello DIYers,
I'm starting those new topic because i rescently bought a pair of JBL m115-8a , wich looking not bad actualy for the try i made
So i would like to make my own speaker box , but i dont know which box design type is better
I would like to make those sort of box THIS or like THIS or like THIS
Do you guys have this sort of speaker box plan and do you think those sort of box is ok with th m115-8a speaker or should i go for another speaker box plan ?
Thank you for your help
Regards

 

[head_unit]

As a loudspeaker design engineer, I don't like ANY of those. Certain wacky designs, like from Danley or the Electro-Voice "manifold" technology, or the crazy stuff that Turbosound had, have strong design rationales and good performance.

BUT. A LOT of "PA" stuff, especially cheap stuff, is designed to look cool and/or copy previous successful designs but without the detailed knowledge. This stuff is junk.

I recommend a straightforward vented box, with a large unobstructed shelf port with radiuses edged.

But actually I recommend you start a totally different thread titled "what box should I make for a JBL m115-8a" (unless a moderator can kindly rename this one). Hopefully that would get you more specific help from those familiar with the woofer.

A very big note of caution about box design for PA speakers: you have to take operating temperature into account! Back in the day, you could run simulations on JBL Pro woofers, and realize that the "ideal box" would be smaller than the shipping carton! HOWEVER, with the speakers at full crank under power, the voice coil heats up tremendously and the parameters shift drastically, and therefore the box and tuning as well. This is not a concern with home speakers really.

So you need to consider at what volume level you will really be playing, how much power that will take, and try and find out what the parameters would be at that level.

Have you looked at JBL's site or asked them what box(es) THEY recommend?

 

[eriksquires]

Good points, all of them, but home speaker drivers can suffer from thermal compression effects fairly quickly. They won't melt, but they may also not sound very good.

Best,


Erik

 

[head_unit]

Good points, all of them, but home speaker drivers can suffer from thermal compression effects fairly quickly. They won't melt, but they may also not sound very good. Best, Erik

Oh, I'm not saying not to use PA drivers. I'm saying that you have to design for the actual use sound pressure levels, and the parameters will shift at higher SPL due to the input power heating the voice coil. Actually, the suspension parts change behavior, as does the magnet. So to really be picky you should have like a Klippel machine or use a LEAP simulator. But failing that it's possible to get some rough estimates to use as a guideline.

I'd never try any of the pictured designs without actual testing equipment, or a VERY sophisticated modeler like Akabak. And I rather doubt there is much true performance improvement-I think it's pretty much visual/retro appeal not based on science at all.

 

[ralrigs]

Ok thank you all , do you have any idea about a good speaker design that would work with those jbl then ?

 

[Ron E]

Vented box, roughly 150 liters tuned to 45-50Hz, use them with a subsonic filter that cuts everything below 45-50Hz. These are made to go loud, not low.

 

[ralrigs]

Vented box, roughly 150 liters tuned to 45-50Hz, use them with a subsonic filter that cuts everything below 45-50Hz. These are made to go loud, not low.

Ok thank you very much

 

[head_unit]

Here are designs from JBL themselves using this woofer:

JRX215 Products | JBL Professional
3730 Products | JBL Professional

I'd probably copy one of those. The box dimensions are listed, though you'd have to subtract some amounts from the specified dimensions to get internal volume. Someone with a simulator could help you with the ports-personally, I like shelf ports, but it depends if you have enough depth.