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Discussion Starter #1 (Edited)
Kinda in that I have worked at a car stereo store in the past, but never got into construction.

For some reason, I thought it might be fun to build some of my own subs for my HT. FWIW I recently picked up a used pair of SVS CS-Ultras with matching amp (500+ watts to each @ 4 ohm). I love them and not sure why I even want to try to better them.

Whatever I decide to try to make, I will make a pair of them. When I got the idea, my first thought was to try something along the lines of 2 10" instead of 1 15". They are about the same surface area, and I figured 2 10s would be more responsive (I know with a big enough amp and fancy enough large sub, they can be "just as quick"). I installed WinISD and started playing with configurations using 10" Dayton subs I found on PE (RSS265HF-4 & RSS265HO-4).

here are some quick results I am trying to understand better



The green line looks pretty good, and is the "RSS265HF-4" in a ported box, 1 or 2 drivers didn't vary significantly. the pink line, which is much worse IMHO is the "RSS265HO-4". The 2 subs are very similar, the HO handles nearly double the power and has a QTS of 0.35 instead of 0.45 with the HF. I then read that if the sub has a QTS over .4 it should be in a sealed box, not ported. The yellow line is what I am getting from pretty much any sub I put into a sealed box... completely unacceptable to me.

The best looking result by far is the green line, but that is apparently a configuration that shouldn't be built... (QTS 0.45 ported box)

I just started playing with this a few hours ago, so I have lots to learn, but can someone help me on what I am seeing.


Thanks,
Brad
 

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Discussion Starter #2
I was thinking of getting a rack mount amp of about 1000 watts X2 @ 4 ohm. 1000 watts for each side, Maybe Samson SXD7000 or something.
 
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Discussion Starter #3
Clearly I must be missing something. I was looking at others builds online and even with an 18" driver, the bass graph was worse than the above yellow line. We want more or less flat from 100Hz down to hopefully below 20Hz, so how do you get flat when even an 18" is -20dB at 20Hz...

What is it I am not getting here....
 

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You may or may not need flat to 20Hz, it all depends upon your situation. For example, HT and 2 channel music have different requirements; the former demands very deep bass, while the latter not so much. For music, 20Hz output is almost unnecessary

Unless you have a gigantic room there will be boundary reinforcement, so if the room you're building these for is where the subs will be for a while you will be able to design them and use that to your advantage. In my case I start to get reinforcement at 25Hz, so were I to go the DIY route I would be concentrating more on the response above that and let the room help me below it. I wouldn't forgo sub-20Hz performance of course, just that I would be more concerned on the area where the sub won't be getting any help.
 

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Discussion Starter #5
You may or may not need flat to 20Hz, it all depends upon your situation. For example, HT and 2 channel music have different requirements; the former demands very deep bass, while the latter not so much. For music, 20Hz output is almost unnecessary

Unless you have a gigantic room there will be boundary reinforcement, so if the room you're building these for is where the subs will be for a while you will be able to design them and use that to your advantage. In my case I start to get reinforcement at 25Hz, so were I to go the DIY route I would be concentrating more on the response above that and let the room help me below it. I wouldn't forgo sub-20Hz performance of course, just that I would be more concerned on the area where the sub won't be getting any help.
Thanks, I guess what is confusing me is there are plenty of sealed subs that are +/- 3db flat from below 20Hz up. I just sold a pair of sealed Velodyne's that were flat into the teens (and that's in an anechoic chamber). But every sub I throw into the WinISD program, if I select sealed, is nowhere remotely close to flat and are in the -10 dB or worse in the 30Hz and below range. Even with ported subs, the 10 inch looks pretty good, but the bigger the sub I put into the program, the worse the low end extension is...?

I have a fairly high end system, I want it to be as "flat" as possible. It is for HT and music. Right now, the 2x10" (per sub) looks like the best option for a flat curve and reasonable cost point.
 

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But every sub I throw into the WinISD program, if I select sealed, is nowhere remotely close to flat and are in the -10 dB or worse in the 30Hz and below range.
That suggests to me the wrong driver/enclosure combination, or perhaps not enough of a low-end boost.

Pretty much every subwoofer today has tuning applied using DSP (Digital Signal Processing), which is basically a fancy way of doing EQ. In order to achieve a flat response into the lowest octave sealed designs are often boosted quite heavily using a Linkwitz Transform as their natural tendency is to roll off rather early. If the driver is not the right type for a sealed enclosure, or if the enclosure is too small, you could also see a high roll off point.


I have a fairly high end system, I want it to be as "flat" as possible. It is for HT and music.
Have you ever heard a sub with a truly flat response? The reason I ask is that's claimed by many to be the holy grail, but in reality most people actually don't like the way it sounds. Systems configured that way tend to come off as a bit flat to most ears, and in response a lot of people will apply a 'house curve' to compensate (which basically means they boost the output or the EQ applied).
 

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Discussion Starter #7 (Edited)
That suggests to me the wrong driver/enclosure combination, or perhaps not enough of a low-end boost.

Pretty much every subwoofer today has tuning applied using DSP (Digital Signal Processing), which is basically a fancy way of doing EQ. In order to achieve a flat response into the lowest octave sealed designs are often boosted quite heavily using a Linkwitz Transform as their natural tendency is to roll off rather early. If the driver is not the right type for a sealed enclosure, or if the enclosure is too small, you could also see a high roll off point.
OK, thanks, that answers the question. I Googled and studied "Linkwitz Transform" and it makes complete sense to me. I didn't realize that was how that was handled/fixed. Ideally, I would think, you would want the LwT circuit before the amp, but in my situation, I want rack mount amp and passive subs. But I think ported is going to be the right answer for me.


Have you ever heard a sub with a truly flat response? The reason I ask is that's claimed by many to be the holy grail, but in reality most people actually don't like the way it sounds. Systems configured that way tend to come off as a bit flat to most ears, and in response a lot of people will apply a 'house curve' to compensate (which basically means they boost the output or the EQ applied).
After using my Emotiva PrePro PEQ to flatten out a large 10+dB spike at about 50 Hz, My SVS' are flat +/- 3dB from below 20 Hz to above 80Hz. The sound was better to me after flattening it out. Most people enjoy "more bass" and will run their subs higher than what is technically correct. Mine are 0-2 dB above. But it litterally shakes the entire house and sounds fantastic.

I want to aim for flat, I can tweak that afterwards if needed.
 
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