Re-designed Sub

[MGrant1957]

Just wanted to get any comments/thoughts/suggestions?
thanks for any input.

Finished the re-design of the sub-woofer box today. Over all dimensions are 24x19x11.5 inches. Will be using a pair of SD215-88s in each chamber with the smaller chamber stuffed around 60% and the larger chamber stuffed about 80% with 2 2inch I.D. vents at 12.5 inches long, ported section is tuned to 31.8Hz.

I wanted to ask: since I will be wiring all 4 voice coils in parallel to get a pair of 2 Ohm loads in each enclosure, Is there some way to calculate a proper Zobel net work that will work accross each pair of drivers? and if I do put a Zobel network accross one drivers voice coils do I have to half or double the values of the resistor and or the capacitors?

[Chris Roemer]

Just wanted to get any comments/thoughts/suggestions?
thanks for any input.

Finished the re-design of the sub-woofer box today. Over all dimensions are 24x19x11.5 inches. Will be using a pair of SD215-88s in each chamber with the smaller chamber stuffed around 60% and the larger chamber stuffed about 80% with 2 2inch I.D. vents at 12.5 inches long, ported section is tuned to 31.8Hz.

I wanted to ask: since I will be wiring all 4 voice coils in parallel to get a pair of 2 Ohm loads in each enclosure, Is there some way to calculate a proper Zobel net work that will work accross each pair of drivers? and if I do put a Zobel network accross one drivers voice coils do I have to half or double the values of the resistor and or the capacitors?

So, this isn't really a band-pass? It just looks like an isobaric closed box siamesed to an iso vented box. Why?

[Wolf]

Yeah- I'm with Chris- Why?

Another thing- if this is to be a subwoofer with a plate-amp, just avoid the zobels altogether. All they do is waste power in a sub anyway If you're trying for a passive sub in a 3-way, you're going to need a lot mre than just a zobel...
Later,
Wolf

[AMC]

I have always been told that mixing sealed and vented in the same range is a very bad idea. Exactly what is the point / goal of this?

[MGrant1957]

Two words: Car Audio
Two of these will be mounted (mirrored) where my back seat used to be. The original box was a 4th order bandpass, but the output just was not there. Since I already had the boxes built, I thought I would re-design them to make use of the available volume. Since PE put these up for cheap, I decided to go Iso and minimize the volume requirements. Modeling them in WinISD, I was concerned that the high impedance would be a factor, I can run the 2 sealed drivers by themselves, the two ported drivers by themselves, or I can run all 4 sets together. With an 80w input the amp load drops to less that 15w around 50Hz, and again down around 28Hz. I do listen to a lot of Bach, Beethoven, Mozart, and others as well as a lot of Floyd. A lot of these tunes have a fair amount of information in the 25-40Hz range that I would like to be able to here while driving on a long trip. These will be crossed over the mains between 80 and 120Hz, I will have to play with to see where is sounds best.

The problem I was having is what do I have to do to the zobel network if I end up running all 4 speakers, since each V.C. is 8 ohms I will end up having 4 V.C.s in parallel, so do I double/half the values of the inductor or resistor?
Should I just forget the Zobel?

[Wolf]

Use an amp with active xover, and forget the passive network for the sub altogether. That's the easy way.
Later,
Wolf

[MGrant1957]

It has an active crossover in the HU. The amp is being fed the subwoofer pre-amp out. the high-level/speaker outs are sent through a pair of line-level converters to a pair of separate amps, one for the front pair and one for the rears.

All 3 amps have built in LP/FR/HP filters built in, and all are adjustable. I was just concerned about the big change in impedance of the drivers restricting the amps effective power in differing parts of the bandwidth of the subs.

[Wolf]

Then why are you asking about coil value and zobels? That's passive stuff. Just use them on the LP'd active amp and be happy as long as the cabinet alignments are sound.
Later,
Wolf

[MGrant1957]

I was concerned that the impedance load that the amp sees will not vary from 2ohms up to as much as 25ohms. just wanted to flatten the curve a bit so that the amp sees a more constant load. I don't have the software to calculate a proper Zobel for a load that has 4 voice coils on each channel.

[Chris Roemer]

I was concerned that the impedance load that the amp sees will not vary from 2ohms up to as much as 25ohms. just wanted to flatten the curve a bit so that the amp sees a more constant load. I don't have the software to calculate a proper Zobel for a load that has 4 voice coils on each channel.

A Zobel flattens the upper curve impedance RISE, it won't affect your single (sealed) or double (vented) humps resulting from the Fs being altered by your box design(s). So . . . you'll cross below the "rise" (most likely even below the Zmin, which might be around 200 Hz - typical), and a Zobel can't help your curve around Fs, so that's that.

Chris

[fusseli]

I have always been told that mixing sealed and vented in the same range is a very bad idea.

This is true, a sealed and a vented won't play in phase with eachother. Even with variable phase adjustment that would only get them in phase for the frequency of wherever you put the test tone at. You can almost gaurantee mixing vented and sealed for the same passband isn't going to produce a very flat response...

[MGrant1957]

Guess I'll just have to bridge it down to 2 ch and put in the DPDT 15A switch mounted on the front of each enclosure.

Through it one way and the amp sees 2 ohm in 4 voice coils in a sealed enclosure with a Q of about 0.72 on each of 2 ch.

Through it the other way and the amp sees another 2 ohm load in 4 voice coils in a ported enclosure tuned to 30.3 Hz in an SBB4 alignment with about 60% fill of acoustastuff.

[MGrant1957]

So you think I should just split this enclosure in half and put in 2 sets of isobaric drivers in each box?

[isaeagle4031]

What is the desire for Isobaric? There is very little to gain going this route. No gain in depth or SPL. Only gain is a smaller enclosure and slightly less audible distortion (though this is subjective)

[MGrant1957]

mostly to reduce cabinet size. two of these will be going into my 1995 Honda Civic CX Hatchback where the back seat used to be. I have limited space to do this. And since I already have all the drivers, I figured that doing the iso thing would be the best way to keep the box size down.

[spasticteapot]

Have you considered infinite baffle?

[MGrant1957]

In a Hatchback?