enclosure difference ?

[Aucosticraft]

I had enclosure with volume of 26 liters which was made of particle board 18mm thick. I kept 3 bottles filled with water,each one liter to attain 23 liters of volume. and tuned ports to my need. the woofer is down firing with front firing port.

Now keeping volume 23 liters I designed another box made of MDF 12mm thick. but this time one more change I made ie I changed port to down firing ( as read down firing ports give consistent performance.) but moment when I turned it on It was completely different to sound felt there is no bass. this stuff sounds like low bass with more mid. Now i am not clear what is making this difference ? Guys pls tell me what all corrections do I need to make.I am feeling totally lost. is the difference because of change from 18mm to 12 mm or switch from particle board to MDF or change in port placement.

[Inductor]

Maybe this new box prefers Coca-Cola.

I'm more inclined for the wood (Wood Strength Chart) materials and box construction (and also effective interior measurements).

[Aucosticraft]

Dear Inductor..... I guess u r right... for a trial i added bracings and surprisingly it worked to some extend. this made me clear that the thickness was the culprit. I should have used at least 18mm ply of MDF. I agree that still it doesn't sound like previous one but sure find some improvement. ( Thank God... Could save coca-cola for me... )

[neddludd]

You are doing non blind listening tests in a room with no calibration of input power or input material?

You have to be careful, your brain is not a measuring instrument but has its own
distortions and feelings ;-) We all know when a new system is heard it takes time to get used to it.

is this downfiring port exactly the same as the normal one?
I think you should read some loudspeaker design books. I used to get two from the local library. One edited by weems. Check amazon.

[Aucosticraft]

Neddludd, Thanks for reply.

I agree I am no measuring instrument also understand the the error that could result because of non calibrated environment. but I compared ( Listened) new and the previous one at the same time by listening. the difference is distinct. also the resonance was tuned using LIMP ( Trial). on graph they look much alike with difference of 2 db max. but yes one thing I noticed was that when i measured Fq response at port and driver there was a difference. the interception of the two curves ( port & driver) for older was at 50Hz where as for new its 80Hz.

Yes, the the downfiring port is exactly as the previous one except that of its placement (Previously it was frontfiring). I did some google to find if the placement of port makes any difference. but all said port can be placed any where. all you need to take care is the distance between the wall and port end must be at least equal to diameter of port.

[freddi]

the down-firing port is probably getting its boundaries lengthened and tuning lower killing upper bass punch - an impedance sweep of both enclosures would tell the story. 12mm might be stiff enough (?0

[neddludd]

Yep it sounds like the close boundary is detuning the port compared to the model. I would even compare thicker mdf or sand loading.

[Aucosticraft]

I am thinking of an experiment. Let me close the ports of both the enclosure pretending it to be sealed enclosure. Then both enclosure should sound exactly alike if its problem with port placement. Do you agree guys? Pls comment. in the mean while I will try it out and get back here.

[GM]

You changed more than one variable plus we don't know the full details of each build, so not much point in us speculating.........

I don't agree, it can be due to the cab's differing construction.

GM

[Aucosticraft]

Hey..... I changed the port place as you had suggested ( its front-firing now) but could not attain much of difference. still it doesn't sound like the model . Now whats different is the enclosure material and thickness. As I said the model material was particle board with 18mm thickness and now I am using MDF with 12mm thickness.