I heard of something today that I've never heard of before, maybe I'm out of it, or maybe this is a new deal, or maybe its total b.s.

The guy called it iso-mounting subwoofers. He said that you could get a sub mount in normally into an enclosure, then get a second sub and mount in onto the face of the other, but backwards. Then, wire them up 180-degrees out of phase. He said that this would be louder than Heck. What do you guys think?

 

Yea, your talking about an isobaric system. Better yet, instead of fitting a 2nd driver flush with the first, put a cylinder in between the two, or a box whatever. Now, screw around with the vol of the box inbetween. Now, maybe port one or both boxes. All sorts of configs can be done. But being louder?!? Well, thats not really a given, it will have more power and more sensitivity. Kinda like stick a second engine on a car, but still have only 4 wheels. You still have only so much speaker area. So, it can only be so loud.

They are ok for space limited settings and a fatwallet dude, but if I shell out for another driver, I'm porting it in a separate enclosure.

There are lots of ways to load a speaker, isobar is one, horn is another. You must take so many variables into account, I won't go into it unless someone asks.

 

[updated:LAST EDITED ON 19-Dec-02 AT 07:48 PM (EST)]I'll ask, I'm always looking for a better way to get more SPL without spending moolah on extra woofers, amps, etc. I have a full size bronco, so what do you suggest? Oh, and I'm using 2 RF HE2 DVC 12" subs, and an 1100w amp (2 channel with phase controls and built in xover). Right now I'm running a bandpass box. I also have a couple of RF 10" punch z's in their own full range ported truck boxes (for higher frequency bass- I don't like where my 12's cut off)... but they're not important because I disable them for competitions.

here's a link to the box I'm using to help you out...

http://www.crutchfield.com/cgi-bin/S-nuhzZyGrCEk/ProdView.asp?s=0&c=10&g=65700&I=04412BP4++

OF COURSE, If you don't feel like getting into it, you don't gotta.

EDIT: I also may need to state that I have the subs mounted backwards (in order to fit in the box)

 

Ah, I can't resist. Give me a moment to formulate some kind of response.

 

I had those exact same subs. I blew the surrounds off 4 of them then got a 3 JL w6's. Seized only one in nearly 5 yrs. I pound them with a PPI 2350 (old number - they call em something else now - same thing tho). Its about the best amp made for a 4ohm load. Puts out 1400 watts rms into 4ohms.

I would loose the bandpass UNLESS you put in the required time to examine each speaker and optimize the box for them. OR, if you don't give a hoot about sound quality and just want to be the loudest. Consider porting both chambers of the bandpass. Get lots of pvc pipes cut to different lengths and spend a few days trying to tune it by interchanging pipes. It is possible to tune a box this way to play only one note, no matter what signal is feed into it (hence the term "boom box"), but it will do it very loud! This may not work at a frequency you like, you may to make one or both chambers larger. You can go here http://www.linearteam.dk/winisd.html and download WinISD and play around.

Also, is that amp 1100 watts max or rms? I'm guessing max. How are you hooking up those 12's and 10's. I'm almost ready to bet there is phase problem between them. Get some good boxplot software off the net that gives you a phase plot for box designs and try to get enclosures that complement each other. Hard to do really, different drivers in diff boxes with diff port freqs almost always require a separate circuit to line phase up. I had to make one out of radioshack parts to get my vegas in line with the w6's. I had to learn this the hard way.

The more crossovers you add the more screwed up you get. I like the 24 db/oct Linkwitz-Riley, it handles the phase shifts better than all except a simple 1st degree crossover (which is best for quality).

What I like about the w6's, is each VC is 6 ohm, so wire each sub in series for 12 total, then parallel all 3 for 4 ohm. That way you don't get the 15 degree phase shift between subs. I hope you got the 4 ohm DVC and wired the VCs together for 8 ohm and then paralleled from there for 4 and bridged your amp. Actually, DVC's should be powered with 2 amps so they don't have to deal with the 15 degree phase shift either. But I'm not buying 6 amps for this.

Some easy cheap mods for you would be to paint the inside of your box with some good poly sealer. Try the porting thing I was talking about above (if dont work you can always seal the hole up). Build a horn looking thing for over top of the ports. Kinda like the guys with hatchback cars always put the port in the back firing up at the glass. And get a cheap spl meter from radioshack or somewhere, give you an idea if something really got louder. And get a setup disc from Iasca online, they used to be about 15 bucks or so. That way you can play a "bark" or "warble" and use the meter to see how loud things got.

 

SO far, I haven't had any problems with the HE2's. I have the VC's wired (+) to (+), (-) to (-) (sorry about the way I described it, but its been a LOOOONG day and I just can't think in terms of series/parallel right now - man I hate the 6am to 4:30pm shift). Then, I have each speaker on its own channel, or in better terms 2ohm stereo. I haven't thought about it until now, but I bet it would work better if I brought a separate set of leads to each voice coil (2 leads of equal lenght and what not per channel).

The amp is 1050w rms, and is exactly 1123w peak. I'm not sure if its the subs or the amp, but it doesn't sound a whole lot louder than my 550w Kicker zr360, of course I know that after a point - loud is loud.

Now I'm not all that scientific with speaker design, so I'm gonna ask for a little help here. The box has a 1.84cuft sealed chamber for BOTH subs. It has a .94cuft ported chamber for EACH sub. My subs have a 2.0cuft recommended ported volume and a 1.25cuft recommended sealed volume. What should I do to optimize here, because once I start mix and matching ported and sealed chambers (ie bandpass with common sealed chamber) I get fuzzy? Should I just modify the box to have 2cuft ported chambers and a 2.5cuft seal chamber, or a 1.25cuft sealed chamber, or leave it or what? About the mounting style, you're just recommending playing around to see, right?

ALSO, I've heard that those db meters that you can get at radio shack aren't worth the money because they aren't accurate. They say not to use them to tell how loud you are, I assumed that it meant that it wouldn't help you tell if you have gotten louder either. Am I wrong here?

Lastly, what should I do about the phase control on my amp (RF power 1050s). Could that help the overall spl level, or just the spl level at the specified mic location? THANKS! I can see that I've become rusty on certain areas, and you've been a big help.

 

I don't mind helping. Those shifts do bite.
Lets see, you got your DVC's in parallel (++, --) for a 2 ohm load and hooked to to one channel on the amp, that SHOULD be fine. Only one thought there comes to mind. Since both drivers fire into a common chamber, I would tend to think running the drivers mono would be better. Try as an experiment, hooking VCs in series (+-, +-) and then hooking both drivers in parallel (++, --) at the amp BRIDGED. This should be 4 ohms, make sure you can bridge on that amp, I think you can. This will combine the signals of left and right to make a mono signal to power the sub that fire into a common chamber. The only trouble here is the 15 degree phase shift between the VCs I was going on about earlier.

About the cheap meters, I think you are right about not being accurate, but they good for relative loudness. Did it get louder? If the meter said it did then I guess it did. Also, there are different scales (a,b,c) for measuring spl. The competitors use the one that makes the number higher (not really any more loud). Kinda like MPH and KPH speeds on a highway. 200 KPH sounds fast but is only around 125 MPH or so. The radioshack model may say ur at 130 and you compete and find you are really 150, maybe the meter is bad, maybe the scales are different or both, who knows. They max out at 130 anyway.

Did you make a typo when you said "The amp is 1050w rms, and is exactly 1123w peak". Usually the max is about twice the rms. However max can be almost anything. Maybe an amp rated at 500 max could put out 1000watts for a 1/10 of a second before dying. Who knows, RMS is all we really can know for sure, and all that really matters. Thats what it can put out for a specified period of time before dying.

Another reason it my not sound louder may be due to the nature of power to spl. IE. 95dB at 1W, 105 at 10W, 115 at 100W, 125 at 1000W, 135 at 10,000w and so on. So, its easy to see that there is really not that much difference between 1000w and 500w in terms of spl. Maybe a few dB is all, and certainly not from 1000 to 2000 watts. Buying more subs is a more economical way to make noise. I just like to have plenty of power to the subs so they don't blow, gotta keep it all under control and that takes power.

I would like to ask, before we go churning numbers, are you willing to build a box yourself? There's too much involved with tuning a bandpass. I suggest pointing those speakers at each other in an angle and a simple but strong ported box. Adding some horns to the ports too.

As far as phase control goes. It is BETTER to keep it simple with properly built boxes, but if this can't be done, the AudioControl 24XS may help. Similar devices exist, but because of the lack of education on phase, not many places sell them. I got one and took it back (like $200 and the only one the place ever sold in 20 yrs!) and built one myself after months of research, never perfected it tho, got some noise in it, but it works. I can make the sound sound like its coming from anywhere in the car, erie actually. I just need some good IC's and never got around to getting them, like Burr-Brown, not radioshack.

 

first, do you want loud crappy sound or quiet nice sound?
if you want it loud and dont care about crappy, then what frequency do you want?
To get anything under 100hz out of a bandpass, you'll will need a bigger box on both ends, thats my bet.

Somebody around here threw away most of my manuals, so I don't have the specs for the DVC's anymore. I guess I could look them up on RF's site.

 

Okay, now explain this 15-deg of phase shift. I've been assuming that its the difference in signal arrival to each coil based on the fact that the wire is hooked to one coil first then another wire connects it to the other coil (depending on how you have it wired). Is this where the shift comes from?

I don't believe its a typo but as I've said it has been a long day. I'll quote my manual and info sheet that came with my amp and let you interpret. The manual says "2ohm stereo - 1050w rms @ 14.4v". The info sheet (personalized to this amp) says "Actual Total Power - 1123w @ 2ohms stereo 14.832v". I just took this to mean peak power, but it may be actual rms wattage, who knows.

About the box. I JUST got this one, so I'll keep it for at least this coming competition season (just to see what it'll do). BUT, I do plan on a completely custom design for the future, so those #'s will be very helpful.

I'm planning on trading up to the Punch HX2's. They are rated for 500/1000w instead of 400/800w but the sensitivity goes up 2 dbs. If I keep my amp the way it is, would they be louder? I think they should, but long day yadda yadda...

Well, I'm done for tonight, gotta catch up on some sleep!

 

Yep, you got it. There is a delay that takes place when a signal is sent thru one driver and then another. For reasons as obvious as wire length and resistence and for reasons of reactance. Ordinary resistence presents no phase shift of its own, only reactance, which is the resistence of a capacitor or inductor at a certain freq.

 

If the driver itself is more sensitive, there should be more sound per watt. However, in a box, this is not always so. I remember reading an artcle by the well known Mr. Clark, that elaborated on this. He claimed to be able to produce more spl with a less sensitive driver. I don't remember what he actually had in mind, but have found this to be so for the most part. What is really of importance here though, is the sensitivity of the box/driver combo. If THAT sensitivity goes up, then it WILL be louder.

If you need a real world example, go to a place that carries Legacy speakers. They have a sub that is 500/1000 I think it was and has a sensitivity of 95 or 96 and sells for about 50 bucks. Now, do you think you will be winning much with that? My JL's have about 87 or 88 I think, they are ten times louder than those Legacys. By the way, I do have a set of those Legacys and have no idea what to do with them, right now they just sittin in a dual horn loaded box collecting dust in the garage. Even the horns couldn't bring the deep bass out of them.

Get some software off the net and play around with different drivers. Most are freeware, perfectbox, winISD, boxplot, etc.
LEAP is really useful, but not free.