Help!! Ive made it too small!!

[johndory]

I have just attempted making my first set of speakers and I have gone and f**ed it up.
I have purchased a set of speakers that came with everything set up - crossover, ports and plans for constructing the cabinet. Easy!
So I go about cutting the wood out and all that, then I realise that the speaker cabinet will not fit in the space that they need to be. They are about 100mm (4inches) too tall. Because I have already cut the wood, and It was quite expensive wood, I was wondering if i can salvage it.
Could I just reduce the height, keep the remaining width& depth dimensions, and change the port length?, add another one? something?

If not and I have to start from scratch, Woud it make a difference if i change the shape of the pre-designed box, as long as i keep the original volume?

Thanks
John dory

[johninCR]

The easy way will probably. What percentage of total height does that 4" represent? The ports can be changed to get the same port tuning. The system Q will increase. Whether the effect will be of significance depends on the size of the box to begin with. Adding fiberfill can increase the effective size of the box to some extent to offset the lost internal volume. Which kit are we talking about?

[Lusso5]

Easiest fix would be to line the port with some polyfill (decrease diameter). As your box gets smaller you either need to decrease the diameter of the port, or increase length to keep the same tuning frequency.

What kit did you build? Can you provide any details?

[GM]

Just shorten the cab. Any BSC in the XO design is dominated by the cab's width. Worst case is that it will sound a little 'boomy' from being too underdamped. If so, you can 'stick a sock in it' as they say, i.e. experiment with damping the vent to roll it off and accept the slight rise in F3 using either stuffing, drinking straws, or stretching expanded weave material over it. Or you can install the vent part way and seal it around the edges and experiment with longer vents cut in 1" increments.

FWIW, I prefer damping the vent since it improves transient response due to making the cab semi/full aperiodic depending on how much damping is used.

GM

[johndory]

Sorry I cant provide any more info on the Speaker kit.
But the cabinet was meant to be 1100x230x323 mm ( 43x9x12.6)
external dimensions with 16mm MDF (3/5)
So making the port longer, adding more polyfill and polyfill the port? Would that be enough to counter the effect of reducing the height?

Thanks For everyones imput
Johndory

[johninCR]

Originally posted by johndory
Sorry I cant provide any more info on the Speaker kit.

What, is it top secret?

[johndory]

Originally posted by johninCR


What, is it top secret?

YES IT IS!!!
No, I dont have any more information to give - bought from Ebay.

[johninCR]

Originally posted by johndory



YES IT IS!!!
No, I dont have any more information to give - bought from Ebay.

In that case, you should measure the T/S parameters of the drivers yourself. Then model the cab to see if the kit models well to begin with.

[Jimmy154]

Originally posted by johninCR
What, is it top secret?

Originally posted by johndory
YES IT IS!!!
No, I dont have any more information to give - bought from Ebay.

Rats, I was hoping it was top secret. BTW John, there's no such thing as a photographic memory it is a myth, no body has film in their brain

What I would do is add bracing to the box make it stronger. Figure out how much volume you gained; you need to do this incase you didn't know. If you don't want to add bracing. Add 60% plastic roofing cement and 40% sand mixture to the inside of the enclosure, anywhere you think it might help. Both of these things could only help to deaden your enclosure. Having a enclosure that's too small, now that's a problem. Note: Loudspeaker Design Cookbook said that the roofing cement/sand mix is messy and time consuming. Well it is messy, but I found it fun and I hope it did a lot to deaden my enclosure. It's easier than cutting wood and adding bracing, in my opinion.

Also another thing you can do is move the bottom of the enclosure higher; so you will have a 3" high empty hole on the bottom. That's where you can put your x-over, this should also improve the sound.

[johninCR]

Jimmy,

His thread title is wrong. He cut the wood for a cab that is too Tall for the space, so he needs to make it smaller than the plans, not bigger.