Question about my first DIY project.

I have been using Speaker workshop to design my first speaker and had a question about box volume. I am using the Vifa P13-WH-00-08 mid/bass (pair) in an MTM config. I got a box volume of about 1.265 cu. ft from speaker workshop which seems a bit large and two ports 2" diameter.

My question is whether I can go with box volume. I have already built the boxes to about this dimensions (1.29 cu.ft) are they are looking quite huge for the drivers which are supposed to go in. The response graph for the box showed a flat response until about 52 Hz which may explain the size but I would like more input from experts. I know it is a bit too late to change the box dimensions but is there any way I can adjust other parameters or compensate for this, if indeed the box is too big for this set of drivers.

thanks.
 
Re: This is certainly......

Andy Graddon said:
...... a lot bigger than I have seen for a pair of P13WH before. If I remember correctly, they are usually about 2/3 cu ft or thereabouts. If you do a search for the Ariel ME2 you will find one example that is fairly well known.

I think you should re-check you calcs before you continue too much further.


thanks. Is there any possible way I can use the same box now by tweaking some other parameters (stuffing etc) or do I need to make a chamber which will cut the volume down by a little?

I will recheck the calcs and see what I come up with. I used a Chebychev alignment and went with a volume which gave me a sufficiently low bass response (of about 52 Hz or so).

Please let me know how I can fix this error.

thanks.
 
reducing volume

If you have already made the box, I would suggest that you need to reduce its volume to about half, what you have at the moment would indicate a nasty little peak at 52Hz then a drop to 100Hz, not good except for disco music.
I would try: Internal volume of 23Litres, tuned to 52Hz with a vent 60mm in diam and about 84mm long.
I work in metric, but you can find a converter by doing a web search

The only way to reduce volume is with solid objects, not wadding (which can actually increase the acoustic volume). ie timber partition, lumps of timber, bags of sand.

Good luck
 
Re: reducing volume

Andy Graddon said:
If you have already made the box, I would suggest that you need to reduce its volume to about half, what you have at the moment would indicate a nasty little peak at 52Hz then a drop to 100Hz, not good except for disco music.
I would try: Internal volume of 23Litres, tuned to 52Hz with a vent 60mm in diam and about 84mm long.
I work in metric, but you can find a converter by doing a web search

The only way to reduce volume is with solid objects, not wadding (which can actually increase the acoustic volume). ie timber partition, lumps of timber, bags of sand.

Good luck

Okay. I also have two ports each with 2 in. in diameter which I will not be able to partition out. Iwill have to calculate the freq response and see what I get. :(

Just curious, how did you get the freq response indicating a peak at 52Hz and drop to 100 Hz etc.

thanks.
 
pinkmouse said:
Hi Prash

Use Bricks!:)

They are easy to measure the volume of, add mass and stability to the cabinet, and are less fussy than sand or the various mass loading materials you can buy for this task.

Bear in mind, that you can have up to about +-10% volume without effecting response too much...


Since looks like I have to cut down the volume by a significant amt == a lot of bricks == weighs a ton! This could be good or bad depending on how you look at it I guess. Good for sound reproduction but could be hazardous if you have small children running around the house, well maybe not as it may not tip over that easily even on heavy stands...

Thanks for the suggestions but I'm sure I will have more questions later.
 
Re: ports

Andy Graddon said:
2 ports 50mm in diam indicate a length of 138mm each

I use BB6, when I input a 40L box for a pair of P13WH,(close enough to your volume) it gives a peak at 52 Hz then dips down about 4dB to 100Hz

Andy,

I am curious to know what the Thiele/small parameters you are using for the pair of Vifa P13WH that you said you found the peaks and drop at around after 52Hz- 100Hz.
According to my previous measurements, I have a set of those parameters which give me a box response graph which is clean and starts roll off at around 60-65Hz. I did not see the peaks that you mention. It is possible that my measurements previously made, were incorrect. I would just like yours for comparison.

thanks.

:)
 
Prash,

I'm trying to use Speaker Workshop as well. One problem I have is that when I do a simple filter for a woofer, (a series inductor), and plot the response curve of the network, I get a flat line, not one that curves down.

The low end is as expected meaning that the speaker itself seems to be modeled but the inductor has no effect. If I make the inductor value extremely high, it does effect the woofer, but down low; not on the high end.

Would you have any idea what I am doing wrong? I'm sure it's probably something I haven't initialized correctly but I don't know what.

TIA,
Phil
 
is the box veneered. if it is not i would brace the box. brainc can eat as much as 30% of box volume - atleast the way I do it :(

if the box is a thin tall box (say 3' x 0.5' x 1') then another way is to build a partiion at the bottom and fill the volume with a bag of sand. That means the box will have 2 parts a lower part filled with sand and a upper part for teh drivers and such.

in any case I would also parition the upper part so that the 2 woofers have independant boxes if you can work out equal volumes for each.

post internal dimensions and maybe we can think of other solutions.
 
Phil O.son said:
Prash,

I'm trying to use Speaker Workshop as well. One problem I have is that when I do a simple filter for a woofer, (a series inductor), and plot the response curve of the network, I get a flat line, not one that curves down.

The low end is as expected meaning that the speaker itself seems to be modeled but the inductor has no effect. If I make the inductor value extremely high, it does effect the woofer, but down low; not on the high end.

Would you have any idea what I am doing wrong? I'm sure it's probably something I haven't initialized correctly but I don't know what.

TIA,
Phil


Hi, I have not got to that point yet, still struggling with the enclosure volume etc. I will let you know once I figure it out. This will be pretty soon I'm sure.

Sorry.
 
navin said:
is the box veneered. if it is not i would brace the box. brainc can eat as much as 30% of box volume - atleast the way I do it :(

if the box is a thin tall box (say 3' x 0.5' x 1') then another way is to build a partiion at the bottom and fill the volume with a bag of sand. That means the box will have 2 parts a lower part filled with sand and a upper part for teh drivers and such.

in any case I would also parition the upper part so that the 2 woofers have independant boxes if you can work out equal volumes for each.

post internal dimensions and maybe we can think of other solutions.


Navin,

I rechecked with Speaker workshop and I got a more accurate reading this time. I wish I had waited until I double checked. This is a mess but I think I can get around it by adding partitions to it. Makes the box heavy but it is better for sound reproduction anyway. I reduced the width to 5.5 in from 8.5 inches. This has made the volume of the box about 1450 cu. in. which is more realistic for the Vifa P13WH.
 
navin said:
is the box veneered. if it is not i would brace the box. brainc can eat as much as 30% of box volume - atleast the way I do it :(

if the box is a thin tall box (say 3' x 0.5' x 1') then another way is to build a partiion at the bottom and fill the volume with a bag of sand. That means the box will have 2 parts a lower part filled with sand and a upper part for teh drivers and such.

in any case I would also parition the upper part so that the 2 woofers have independant boxes if you can work out equal volumes for each.

post internal dimensions and maybe we can think of other solutions.


Navin,

I rechecked with Speaker workshop and I got a more accurate reading this time. I wish I had waited until I double checked. This is a mess but I think I can get around it by adding partitions to it. Makes the box heavy but it is better for sound reproduction anyway. I reduced the width to 5.5 in from 8.5 inches. This has made the volume of the box about 1450 cu. in. which is more realistic for the Vifa P13WH.
 
navin said:
fill the gap between the 2 woods with sand.

regards
navin


When I use the T/S parameters to plot the box graph, it shows the -3dB point at around 110Hz. Does that mean that the speaker will practically have no frequencies below this freq or should I look at the freq response graph for the speaker? I am confused about the box graph. I am afraid that this box volume that I am using for this MTM config will have a freq response starting only at 110Hz.

If that is the case then I will have to fiddle around with other variables to see if I can get a response from say 70Hz or so. I am using Speaker Workshop and also checked with WinISD.