"Houston we have a problem" Isobarik Sub

[Fearlessleader1]

I hope some one can answer this for me I am building a Isobarik sub using 2 Dayton Part # 295-185 dual VC sub. I thought I found a real good deal on 4 of these so I bought them. I was using Bass Box 6 for design and thought I had a real winner OPPS I made a big mistake I did not see bass box had set up as individual VC instead of parallel VC. At first I thought nothing of it untill my I reset Bass Box and seen my F3 went from 28 Hz to 52 HZ. I am a bit of a newbie at this home DIY, I have done many car subs just using the air space for the box for a sealed box and all was good. So what has happened here when I reset and started over the suggested air space went down to .64 from 1.489 Why would my Vb get cut 60% just by changing VC wiring to match the ohms for the amp I want to use? I can't see any way to use individual VC's in a isobarik sub but now I own 4 of these subs and really don't want to build a single sealed box that I have done a bunch of times before. Is there any way to get this sub to to flatten its response, or am I wrong to think this is a problem at all?

[Volenti]

Ignore the individual wiring option in bassbox, it appears to plot the response you would get with only one voice coil connected, unless of course you prefer that response and can deal with halving the power handling of the drivers.

[Fearlessleader1]

I see what your saying but but this explains very little as to why I am losing 8.5 DB @ 29 Hz when before I only lost 3 Db at 29 Hz. I have tried every possible combination of VC's but only individual seems to have a good response and that seems a bit crazy. I also see a great amount of system impedance increase between 60 hz and 30 hz and this seems to go with my loss of low bass response. I would think one VC would carry all the load causing the coil to heat then 2 VC's would split the load and heat less? The other thing I don't get is why should my Box Vb change no matter what VC combination I would use?

[Volenti]

I'm going to re-test a dual voice coil sub I have here using just one voice coil to see if the change in Qes and Qts is comparable to what we see in that dayton sub...

[Volenti]

My test results are consistant with the change in the Dayton parameters and the subsequent change in system response.

ahh I see where you are seeing the large difference, you're using normalized Amplitude response, which I've found to be pretty useless, use Custom Amplitude response, and you'll see there's far less difference between the different configurations when compared with the same power input.

[Fearlessleader1]

Then if all the data here is correct then I must conclude that this sub just does not perform well in sub frequency range in a closed box or at least using both VC's as a compound isobaric sub, because even while the graph looks better the actual numbers still look bad. I still see a loss of at least 8.5 Db at 30 Hz. Was your data also constant with the Vb. being .64 Cf. for the dual VC’s and 1.489 Cf. for the single VC? I did test parameter changes and box configurations last night till my eyes bleed. Nothing I did helped, I did different Isobaric configurations mag. to mag. and facing the same direction, round isobaric chamber and square and all still seems to be the same only the single VC works well. Even this came at cost gaining so much Vb. I ended up with a 24.75” long and a 14.25 X 14.25 W/H. I can get the size down some with a round isobaric chamber but then the cabinet work get more difficult using sono tube for the isobaric chamber. I just was hoping I could get a good test box with little work as this was intended for final use in the bottom of a pair of bi-amped loudspeakers. I really am grateful for your help in this matter. I am just bit beside myself yet with this. Do you think some real world test could be fruitful?

[BassAwdyO]

You need to up the enclosure size of the simulation with both coils to the same size as single coil. This will probably change the response significantly. As much as 8db at 30hz I'd guess

[simon5]

Do you need an enclosure that small? You know you'll get some room gain.

If the response isn't good enough, you could port your isobaric box or use a passive radiator.

[Fearlessleader1]

I just tried to increase my Vb to the same as a single VC and still my frequency response remains almost the same, I have a 3 Db drop at 51 Hz and no matter the size of the box the response remains the same right down to the point the driver will no longer fit the box Vb .64 and then I went all the way up to Vb 2.5 and the same thing. I even tried to increase and decrease The Isobaric chamber Vb and still nothing changes. Change the set up for single VC and abracadabra the frequency response flattens out and I am not getting a 3Db drop until 29 Hz and everything looks great. Well all most great because then I just cut my power handling from 1200 watts to 600 Watts. Opps and one more thing it just don't make any sense!!! If I did not buy these Daytons already would have looked for a single VC sub and saved you all from my crazy questions *LOL*

[Volenti]

Originally posted by Fearlessleader1
Do you think some real world test could be fruitful?

With that thought in mind I used the same DVC sub I tested earlier in both individual and paralell with some music I know well, I used the same 50L test box that I have for testing driver parameters.

I did notice a difference between the two configurations that was consistant with the model in Bassbox.

I would suggest a real world test would indeed help you a great deal in deciding on what configuration would be most suitable for you.