# Why don't amp gains and HU preout voltages match?



## grampi (Jun 29, 2007)

Have you ever wondered why if a HU has 4v preouts, you can't just set the amp's input gain to 4v and be done with it? My 9887 has 4v preouts and if I set my amp's gains to 4v, I would have little to no output from the comps, and absolutely no output from the subs. Hell, I've got the gain set at 2v now for the comps and it actually probably needs to be turned to 1v because I know I'm not getting full power from the amp to my comps, and the sub gain has to be set at .2v, and this is an Alpine amp. Why do they even bother putting voltage settings on the amp's gain controls? They apparently don't mean anything.


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## MuTT (Apr 4, 2007)

grampi said:


> Have you ever wondered why if a HU has 4v preouts, you can't just set the amp's input gain to 4v and be done with it? My 9887 has 4v preouts and if I set my amp's gains to 4v, I would have little to no output from the comps, and absolutely no output from the subs. Hell, I've got the gain set at 2v now for the comps and it actually probably needs to be turned to 1v because I know I'm not getting full power from the amp to my comps, and the sub gain has to be set at .2v, and this is an Alpine amp. Why do they even bother putting voltage settings on the amp's gain controls? They apparently don't mean anything.


Wondered the same myself for years. As well as, why cant they have a module on an amp that auto detects input voltage and adjusts itself.....if this already exists, then please disregard. (sorry if you consider this a post dump.)


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## Whiterabbit (May 26, 2006)

grampi said:


> Have you ever wondered why if a HU has 4v preouts, you can't just set the amp's input gain to 4v and be done with it?.


That's exactly what I do. What's the problem? 

You can always buy a bigger amp...


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## owdi (Apr 4, 2008)

grampi said:


> Have you ever wondered why if a HU has 4v preouts, you can't just set the amp's input gain to 4v and be done with it? My 9887 has 4v preouts and if I set my amp's gains to 4v, I would have little to no output from the comps, and absolutely no output from the subs. Hell, I've got the gain set at 2v now for the comps and it actually probably needs to be turned to 1v because I know I'm not getting full power from the amp to my comps, and the sub gain has to be set at .2v, and this is an Alpine amp. Why do they even bother putting voltage settings on the amp's gain controls? They apparently don't mean anything.


Voltage ratings on preouts are less important than most people think. An HU with 4v preouts should only output 4v at maximum volume, with source material that is also at maximum volume. Most of the time it outputs much much less. 

When you set the gain on your amp to 4v, it will need 4v to reach maximum output. Since most of the time your HU is outputting much less, you can safely set the gain to a lower voltage on your amp. However, if you set the gain on your amp to a lower voltage setting than what your HU can output, you can push the amplifier into clipping before your preouts clip.

Dan


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## grampi (Jun 29, 2007)

Whiterabbit said:


> That's exactly what I do. What's the problem?
> 
> You can always buy a bigger amp...


That's dumb. I've got a better idea. How about making preout voltages and amp gains so the full output power of a given amp can be used? Doesn't that make more sense than having to buy much more expensive amps only to use a portion of the power it'll actually make? To me, that's just a waste.


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## grampi (Jun 29, 2007)

owdi said:


> Voltage ratings on preouts are less important than most people think. An HU with 4v preouts should only output 4v at maximum volume, with source material that is also at maximum volume. Most of the time it outputs much much less.
> 
> When you set the gain on your amp to 4v, it will need 4v to reach maximum output. Since most of the time your HU is outputting much less, you can safely set the gain to a lower voltage on your amp. However, if you set the gain on your amp to a lower voltage setting than what your HU can output, you can push the amplifier into clipping before your preouts clip.
> 
> Dan


Can you explain why I have to have the gain on my Alpine amp turned all the way up (.2v) to get any decent output from my subs? If I set the amp gain at 2v (which is double where it should be set for a 4v preout, which is what my HU has), I have no sub output at all. I could certainly understand things being a little off, but when you have to set the gain 20 times higher than it should be set, that's just not right.


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## placenta (Feb 2, 2008)

grampi said:


> Can you explain why I have to have the gain on my Alpine amp turned all the way up (.2v) to get any decent output from my subs? If I set the amp gain at 2v (which is double where it should be set for a 4v preout, which is what my HU has), I have no sub output at all. I could certainly understand things being a little off, but when you have to set the gain 20 times higher than it should be set, that's just not right.


one cause of that for me is having the sub in the trunk. thats why im doing two ports thru my rear deck to let air pass through


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## grampi (Jun 29, 2007)

placenta said:


> one cause of that for me is having the sub in the trunk. thats why im doing two ports thru my rear deck to let air pass through


I removed my factory rear speakers, so I have my ports, but still I have to have sub gain all the way up.


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## jrwalte (Mar 27, 2008)

First off, it's much easier to hear highs over lows. They travel farther and are easier to determine where they're coming from. It's also much easier to hear the highs that are right next to you than lows that are far away in your trunk. You have gains on your amps to attenuate and resolve this situation. That's what they're for. It has nothing to do with matching up with what the HU can output.


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## grampi (Jun 29, 2007)

jrwalte said:


> First off, it's much easier to hear highs over lows. They travel farther and are easier to determine where they're coming from. It's also much easier to hear the highs that are right next to you than lows that are far away in your trunk. You have gains on your amps to attenuate and resolve this situation. That's what they're for. It has nothing to do with matching up with what the HU can output.


But with the way I have my amp configured, I'm pushing double the power to my subs (500) as compared to the power my comps are getting (125 per side). That in itself SHOULD be enough compensation to make up for the difference in the different freqs and speaker locations. I SHOULDN'T also have to have the amp gain set twice as high for the subs as I have it set for the comps. That's the part that doesn't make sense to me.


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## Abmolech (Nov 2, 2006)

Actually low frequency have far more energy, than higher frequencies.
Logically thats why you have 500 plus watt amplifiers for the subs, and a 50 watt for the tweet.

Problem is that the sensitivity on a tweeter is often around 96 dB at 8 ohm, versus a sub woofer, around 83 dB at 4 ohm.

Thats a huge difference. Combine that with equal loudness curves and you no longer question the requirement for multiple subs and large power amplifiers.

Quite simply, you don't have enough power for your sub woofer. Either consider multiple subs, or higher sensitivity.

First I would try to maximise output by trying different positions for your enclosure. The sub woofer is effectively situated in the mouth of a wave guide (your car body), changes in position can greater effect the acoustic loading. 
(No not standing wave, your car is to small a length)

Other choice is to have a higher acoustic load with the use of a bandpass enclosure. These will maximise the output, at the cost of enclosure size.


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## jrwalte (Mar 27, 2008)

What makes you think 100 watts to a speaker playing highs should get the same amount of output from a speaker that plays lows? They don't. Not only is it easier to hear highs, but it takes less energy to push them through the air.

Think about it. Would something as small as a tweeter or even the small magnet of a mid driver require nearly as much power as a massive magnet on a subwoofer? No. Therefore they require less energy to produce Db.

I run 175RMS to my comps and I currently have 2 12" in my trunk with 800RMS. My comps can still out power my subs in terms of loudness.


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## GenPac (Oct 29, 2007)

Abmolech said:


> Actually low frequency have far more energy, than higher frequencies.
> Logically thats why you have 500 plus watt amplifiers for the subs, and a 50 watt for the tweet.
> 
> Problem is that the sensitivity on a tweeter is often around 96 dB at 8 ohm, versus a sub woofer, around 83 dB at 4 ohm.
> ...


 
Not to detract from what Abmolech is trying to teach us here, but... It's really subjective at the same time.
Case in point: I have a 92.5dB sensitivity 4ohm tweet and a 92.2 sensitivity SVC 4ohm sub. 
65w on the tweeter and 350w on the sub.
The sub has over 5 times the power, but to MY ears, the sub runs out of steam at just about the same time as the tweeter is at it's volume max w/slight noticible distortion.
So, in IME, my sub to tweeter power ratio is roughly 5:1 when sensitivites are closely matched.

(NOTE: also, this is in an extended cab 'truck' so the sub sits roughly 3feet from my head which accounts for alot.)


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## t3sn4f2 (Jan 3, 2007)

Also head units don't always put out what they claim. 

Here's a quote from Andy at JBL talking about using higher preout voltage head units on the MS-8 which can only support 2 volts of input.

"*We've tested a bunch of headunits that claim to have 4V out. Guess what...?*

In the event that you really do have a 4V head unit, then in the setup routine you'll be instructed by the MS-8 to turn up the head until it reaches the max input with the setup CD. Whatever that volume control setting is will be the max that you can use without clipping the input. If that's the case, you can use the MS-8's volume control or the head unit's, up to that point.

*In nearly every case (we haven't tested EVERY headunit on the market), the inputs will be just fine.*
__________________
Andy Wehmeyer
Product Marketing Manager
Harman Consumer Group
Mobile Systems Division


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## grampi (Jun 29, 2007)

Abmolech said:


> Actually low frequency have far more energy, than higher frequencies.
> Logically thats why you have 500 plus watt amplifiers for the subs, and a 50 watt for the tweet.
> 
> Problem is that the sensitivity on a tweeter is often around 96 dB at 8 ohm, versus a sub woofer, around 83 dB at 4 ohm.
> ...


I'm currently running 2 Sundown SD-1 v1 10's, which are supposed to run very nicely off of 150 each, and I'm feeding them 250 each. I don't think my problem is a lack of power.......not directly anyway. It is a lack of power, I believe, because of too low of a preamp signal to the amp, which in turn is not allowing the amp to deliver full power. Once I install the line driver, I think the amp will then be getting enough of a preamp signal to deliver full power. I do like the idea of using a bandpass enclosure though. I've used them in the past and I really like the sound. Not only do they hit hard, they sound good doing it. Does anyone sell pre-made band pass enclosures that'll work with these drivers?


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## chad (Jun 30, 2005)

Do not look at the numbers on the amplifier. It may say .2V but does it specify what that .2V does ?

4V is not a nominal output, it's 0DbFS, balls out, running down hill.

Shall I post my standardization rant? Rant? It's not pretty


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## grampi (Jun 29, 2007)

Would this enclosure work with my subs?

http://www.crutchfield.com/App/Product/Item/Main.aspx?g=178750&i=044QB2104&c=3&tp=128

That might solve my subs not playing deep problem too, as I would guesstimate they'd play much deeper in this enclosure than they do in my small sealed enclosure.


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## ViperVin (Mar 15, 2008)

MuTT said:


> As well as, why cant they have a module on an amp that auto detects input voltage and adjusts itself.....if this already exists, then please disregard


i have wondered the same thing. it cant be that difficult to implement an auto-sensing module and auto gain from there. this would help prevent clipping from users wrongly settings their gains.


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## 60ndown (Feb 8, 2007)

im guessing yur sytem is still working grampi 


_*woot!*_


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## 60ndown (Feb 8, 2007)

grampi said:


> Would this enclosure work with my subs?
> 
> http://www.crutchfield.com/App/Product/Item/Main.aspx?g=178750&i=044QB2104&c=3&tp=128
> 
> That might solve my subs not playing deep problem too, as I would guesstimate they'd play much deeper in this enclosure than they do in my small sealed enclosure.


oh-oh.................. 

duck grampi 

here it comes


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## GenPac (Oct 29, 2007)

grampi said:


> Would this enclosure work with my subs?
> 
> http://www.crutchfield.com/App/Product/Item/Main.aspx?g=178750&i=044QB2104&c=3&tp=128
> 
> That might solve my subs not playing deep problem too, as I would guesstimate they'd play much deeper in this enclosure than they do in my small sealed enclosure.





Crutchfield said:


> is made from 5/8" fiberboard for strength


This is a reason I would not recommend this enclosure to anyone.


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## 60ndown (Feb 8, 2007)

grampi,

1.set all your eqs and setting to flat.
2.put some well recorded music on you know well.
3. set volume on hu to 75%
4.adjust sub and speaker amps so things sound balanced.
5.sit in drivers seat and adjust eq to get sound as good as possible.

now your ready to start tuning.


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## chad (Jun 30, 2005)

grampi said:


> Would this enclosure work with my subs?
> 
> http://www.crutchfield.com/App/Product/Item/Main.aspx?g=178750&i=044QB2104&c=3&tp=128
> 
> That might solve my subs not playing deep problem too, as I would guesstimate they'd play much deeper in this enclosure than they do in my small sealed enclosure.


That thing is ****, the bandpass enclosure needs to be *VERY SPECIFICALLY *designed for the driver, you just can't pop any-old deriver in an arbitrary sealed enclosure with a tube hanging out it's ass and expect anything more than a burp machine, if it does not shread the driver first 

BUILD a vented enclosure to try out first, you may be just fine.


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## jrwalte (Mar 27, 2008)

Sealed enclosers can create excellent base response. You may have a box that isn't the correct cubic feet for your sub. I prefer the SQ of a sealed over bandpass (which i mistakenly bought as my first sub back in 98 when I got my first car). But to each his own.


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## grampi (Jun 29, 2007)

60ndown said:


> grampi,
> 
> 1.set all your eqs and setting to flat.
> 2.put some well recorded music on you know well.
> ...


I did that, and when I get to step #4, the gain for the sub has to be all the way up for a balanced sound.


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## DiamondFanatic (Dec 26, 2007)

I run my Diamond Audio D6600.4 with the gain bypassed (for a 4V input) on my Morel Supremos and Elate SW6's active and it SCREAMS off the output from my DEQ-P9. However, with my Alpine 9835 I couldn't run it with the gains bypassed, there wasn't enough output. I think Alpine has issues with their rating system on pre-outs, but also on inputs on amplifiers based on my experience.


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## chad (Jun 30, 2005)

grampi said:


> I did that, and when I get to step #4, the gain for the sub has to be all the way up for a balanced sound.


With the amp pinned?


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## GenPac (Oct 29, 2007)

Recommended enclosure sizes for SD-1v1



Sundown website said:


> 0.5 ft^3 - 0.75 ft^3 sealed
> 1.00 - 1.25 ft^3 tuned to 30 – 35 Hz ported


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## 60ndown (Feb 8, 2007)

grampi said:


> I did that, and when I get to step #4, the gain for the sub has to be all the way up for a balanced sound.


if thats true, (even with the speaker amp turned all the way down), i dont really see a problem.


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## 60ndown (Feb 8, 2007)

chad said:


> With the amp pinned?


wtf is pinned supposed to mean?

(layman audio filter on please)


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## grampi (Jun 29, 2007)

chad said:


> That thing is ****, the bandpass enclosure needs to be *VERY SPECIFICALLY *designed for the driver, you just can't pop any-old deriver in an arbitrary sealed enclosure with a tube hanging out it's ass and expect anything more than a burp machine, if it does not shread the driver first
> 
> BUILD a vented enclosure to try out first, you may be just fine.


The reason I'm looking at pre-made boxes is because I don't really have the tools I need to build my own. I used to build my own all the time when I was still in the Air Force because I had a limitless access to all the tools I'd ever need at the wood hobby shop. Maybe that's why the sealed enclosure I have now sounds like ass, because it's a pre-made, but it is the correct volume. And if I'm going to go to the trouble of building my own enclosure, I'm building either another selaed or bandpass enclosure. I prefer either of those to a regular ported box.


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## 60ndown (Feb 8, 2007)

grampi said:


> The reason I'm looking at pre-made boxes is because I don't really have the tools I need to build my own. I used to build my own all the time when I was still in the Air Force because I had a limitless access to all the tools I'd ever need at the wood hobby shop. Maybe that's why the sealed enclosure I have now sounds like ass, because it's a pre-made, but it is the correct volume. And if I'm going to go to the trouble of building my own enclosure, I'm building either another selaed or bandpass enclosure. I prefer either of those to a regular ported box.


you can buy all the tools you need to build speakers for the next 10 years for $100.

jigsaw = $45
cordless screwgun=$50
caulk gun =$5


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## 60ndown (Feb 8, 2007)

where and how exactly is your subwoofer located / aimed in the vehicle?


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## grampi (Jun 29, 2007)

chad said:


> With the amp pinned?


What does that mean, pinned?


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## chad (Jun 30, 2005)

Wide open as sensitive as it will go.


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## grampi (Jun 29, 2007)

WHAT THE HELL AM I SAYING? I live near an Air Force which I'm sure has a wood hobby shop. Being retired Air Force, I can use it! Also, the bandpass enclosure I'm talking about is isobaric. I built one once using a pair of MTX Blue Thunder 12's and it sounded fantastic! If I build an enclosure, that's what I'm building.


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## khail19 (Oct 27, 2006)

Alpine decks are known to have weak preouts in general. When I changed out my 9835 and put in the Pioneer 860mp, everything was way louder. I had to lower all my gain settings.


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## grampi (Jun 29, 2007)

chad said:


> Wide open as sensitive as it will go.


Yes, the gain is maxed at .2v.


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## chad (Jun 30, 2005)

It holds two drivers facing each other? That's not isobaric, it's just two drivers sharing a common sealed chamber.


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## 60ndown (Feb 8, 2007)

grampi said:


> WHAT THE HELL AM I SAYING? I live near an Air Force which I'm sure has a wood hobby shop. Being retired Air Force, I can use it! Also, the bandpass enclosure I'm talking about is isobaric. I built one once using a pair of MTX Blue Thunder 12's and it sounded fantastic! If I build an enclosure, that's what I'm building.


your gonna be sorry you got your sytem working  

welcome to hell


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## 60ndown (Feb 8, 2007)

chad said:


> It holds two drivers facing each other? That's not isobaric, it's just two drivers sharing a common sealed chamber.


its called

'bearded clam'


shell.


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## grampi (Jun 29, 2007)

60ndown said:


> where and how exactly is your subwoofer located / aimed in the vehicle?


It's in the trunk, located right behind the rear seat with the subs facing the front of the vehicle.


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## chad (Jun 30, 2005)

grampi said:


> Yes, the gain is maxed at .2v.


HEHE welcome to my world a year ago 

This is why I ended up purchasing an Audio Control Matrix  It's since sold as i now have an amp that is sensitive enough to allow for my setup goals.

If you search Matrix and my name you will see that we have/had the exact same issue.


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## 60ndown (Feb 8, 2007)

grampi said:


> It's in the trunk, located right behind the rear seat with the subs facing the front of the vehicle.


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## chad (Jun 30, 2005)

dupe


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## chad (Jun 30, 2005)

60ndown said:


> lmao


You are running out of A to LO


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## grampi (Jun 29, 2007)

chad said:


> It holds two drivers facing each other? That's not isobaric, it's just two drivers sharing a common sealed chamber.


No, I'm talking about when the subs are mounted together face to face, with the air sealed between the two cones, and one wired out of phase. That's isobaric and they sound fantastic.


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## 60ndown (Feb 8, 2007)

chad said:


> You are running out of A to LO ;P


edit^

more a


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## chad (Jun 30, 2005)

Right, but in a bandpass? Seems like too many variables and uncertaintys.


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## grampi (Jun 29, 2007)

chad said:


> You are running out of A to LO


???????????


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## 60ndown (Feb 8, 2007)

read this grampi for gawds sake, chads lost is mind
http://www.teamrocs.com/technical/pages/aiming.htm

$50 sais you dont need to do anything but aim your sub in the RIGHT direction


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## chad (Jun 30, 2005)

60ndown said:


> read this grampi for gawds sake, chads lost is mind
> http://www.teamrocs.com/technical/pages/aiming.htm
> 
> $50 sais you dont need to do anything but aim your sub in the RIGHT direction


Or shove it WAY in the very rear of the trunk and load it up.


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## grampi (Jun 29, 2007)

chad said:


> Right, but in a bandpass? Seems like too many variables and uncertaintys.


I don't think isobaric enclosures are referred to as bandpass, though they are a form of a bandpass enclosure. All I remember about them is they are very efficient and they sound very good. I just didn't build many of them because I don't like pissing around with ports. But the ones I did build sounded phenominal.


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## 60ndown (Feb 8, 2007)

chad said:


> Or shove it WAY in the very rear of the trunk and load it up.


filter chad, filter.

what do you mean 'load it up'


mutaphuka.

its every post now, can you please keep the cryptic posts for foxy.


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## 60ndown (Feb 8, 2007)

read it grampi

http://www.teamrocs.com/technical/pages/aiming.htm


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## GenPac (Oct 29, 2007)

khail19 said:


> Alpine decks are known to have weak preouts in general. When I changed out my 9835 and put in the Pioneer 860mp, everything was way louder. I had to lower all my gain settings.


A little OT but, when I went from an 860MP to an 880PRS, I noticed a drop in 'preout voltage' - Compensated by having to bump up the gains. When I installed my DRZ9255, I had to lower the gains to right about where they were for the 860MP because it seemed 'too loud' at low HU volume...

Strange, but it just worked out that way.


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## grampi (Jun 29, 2007)

60ndown said:


> read it grampi
> 
> http://www.teamrocs.com/technical/pages/aiming.htm


I'll move it back and face it back after work today and see how that sounds. Of course it would sound best located where it's most inconvenient.


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## energizedsbs (Dec 11, 2007)

grampi said:


> It's in the trunk, located right behind the rear seat with the subs facing the front of the vehicle.



try turing the subs around. you might get a little suprise


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## 60ndown (Feb 8, 2007)

grampi said:


> I'll move it back and face it back after work today and see how that sounds. Of course it would sound best located where it's most inconvenient.


lemme guess, you want amazing sound and convinience?


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## grampi (Jun 29, 2007)

60ndown said:


> lemme guess, you want amazing sound and convinience?


Silly me!


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## jrwalte (Mar 27, 2008)

60ndown said:


> you can buy all the tools you need to build speakers for the next 10 years for $100.
> 
> jigsaw = $45
> cordless screwgun=$50
> caulk gun =$5


Forget the jigsaw. You can get a special 'router bit' that you can connect to your drill that can cut round holes up to 18" for around $40.


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## jrwalte (Mar 27, 2008)

grampi said:


> It's in the trunk, located right behind the rear seat with the subs facing the front of the vehicle.


That's the single most worse bass response location you can pick  Others already suggested where you should place them.


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## placenta (Feb 2, 2008)

khail19 said:


> Alpine decks are known to have weak preouts in general. When I changed out my 9835 and put in the Pioneer 860mp, everything was way louder. I had to lower all my gain settings.


man.. youre gonna have everyone second guessing the 9887 now... even me. Tho i guess a TRU line driver is cheaper than a new deck.


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## Whiterabbit (May 26, 2006)

grampi said:


> That's dumb. I've got a better idea. How about making preout voltages and amp gains so the full output power of a given amp can be used? Doesn't that make more sense than having to buy much more expensive amps only to use a portion of the power it'll actually make? To me, that's just a waste.


Take a note from industry. Devices like smart washing machines and smart toasters, smart ovens used to be powered with pentium 166's. Was it more power than they needed? You bet! So why overkill it? Because it was a known reliable configuration.

Because maxing out your capabilities is asking for unreliable performance. Even fatigue failure.


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## chad (Jun 30, 2005)

grampi said:


> I don't think isobaric enclosures are referred to as bandpass, though they are a form of a bandpass enclosure. All I remember about them is they are very efficient and they sound very good. I just didn't build many of them because I don't like pissing around with ports. But the ones I did build sounded phenominal.


Oh, hit clear, we were on different pages 

An isobaric is only more efficinet interms of enclosure size but is LESS efficient than 2 drivers in an appropriate enclosure by a bunch. Iso was cool before the small box woofers came out, but there really is no need to do it these days now that we have easy and affordable access to drivers with monster excursion, high power handling, and very powerful motors isobaric configs ahve pretty much fizzled out.




60ndown said:


> filter chad, filter.
> 
> what do you mean 'load it up'
> 
> ...


My bad Buttercup.

A subwoofer enclosure is largely omnidirectional as shown in Eddie's tutorial, by placing the enclosure against a boundary you eliminate the mixing of the waves, you "load up" the enclosure into a corner and cause it to act like a waveguide, there is little to no modal interaction thus causing a large gain in efficiency. Look up free space, quarter space and half space loading.

Chad


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## dtviewer (Dec 18, 2006)

jrwalte said:


> First off, it's much easier to hear highs over lows. They travel farther and are easier to determine where they're coming from. It's also much easier to hear the highs that are right next to you than lows that are far away in your trunk. You have gains on your amps to attenuate and resolve this situation. That's what they're for. It has nothing to do with matching up with what the HU can output.



 Please everyone pretend you didnt read this post...............


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## owdi (Apr 4, 2008)

GenPac said:


> Not to detract from what Abmolech is trying to teach us here, but... It's really subjective at the same time.
> Case in point: I have a 92.5dB sensitivity 4ohm tweet and a 92.2 sensitivity SVC 4ohm sub.
> 65w on the tweeter and 350w on the sub.
> The sub has over 5 times the power, but to MY ears, the sub runs out of steam at just about the same time as the tweeter is at it's volume max w/slight noticible distortion.
> ...


Your sub may be 92.5db sensitive at 1khz, but at the frequencies you actually use it sensitivity can easily dip below 80db. 

Sensitivity itself is a useless spec for an active system, efficiency is much more important. Efficiency below 100hz is what you really need to look at when determining how much amp you need.

Dan


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## A8AWD (Mar 6, 2008)

"An isobaric is only more efficinet interms of enclosure size but is LESS efficient than 2 drivers in an appropriate enclosure by a bunch. Iso was cool before the small box woofers came out, but there really is no need to do it these days now that we have easy and affordable access to drivers with monster excursion, high power handling, and very powerful motors isobaric configs ahve pretty much fizzled out."

^^^Chad has this right....isobaric is having 2 drivers with identical parameters mounted face to face out of phase with some space in between...in a sealed application it will typically 1/2 the enclosure volume that one speaker would require, but also becomes VERY inefficient as you need to power to motors to push one cone. An isobaric setup can actually be adapted to any type of enclosure if built correctly including bandpass...


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## vactor (Oct 27, 2005)

grampi said:


> Can you explain why I have to have the gain on my Alpine amp turned all the way up (.2v) to get any decent output from my subs? If I set the amp gain at 2v (which is double where it should be set for a 4v preout, which is what my HU has), I have no sub output at all. I could certainly understand things being a little off, but when you have to set the gain 20 times higher than it should be set, that's just not right.


cuz your subwoofer out from your alpine headunit is not maxed out ... which then matches the voltage output from the main L/R channel outputs of the headunit. the alpine sub out is only a cut circuit, not a boost, as it would seem from the way it is setup in the interface


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## Abmolech (Nov 2, 2006)

Some interesting replies.
Sensitivity is mainly driven by the cone mass to air mass ratio. Since the difference between various cones composites is rather small in terms of mass, you would possibly be looking at around 3 -5 dB maximum.

If the cone mass to air ratio is mainly "fixed" where do the other differences come from?

Compliance.
Motor strength (BL)

The compliance is how much force to more it. A highly compliant suspension therefore require less force than a low compliance suspension. (QMS)
If you observe the VAS, this is a ratio of how compliant it is compared to the compliance of air. Normally 2 times VAS for an enclosure, means the compliance is dominated by the actual suspension, and air contribute little or nothing to to the compliance.

Point
High compliance = higher sensitivity, = Large enclosure.

Motor strength (BL)
No free lunches. The stronger the motor the less sensitive the network. (QES) The total Q of the driver therefore is the sum of QES + QEM = QTS

If you put it into an enclosure, you can change the Q of the system by using air for compliance.
Therefore the total Q of the system = QTS + air compliance.

If you have a sub of 92.5 dB you have a weak motor, with high compliance, designed for a very large enclosure.
If this is not the case, the sensitivity is rated outside the expect frequency range. (Most likely 250 -4 KHz Average)

*Marketing and head unit output voltage.*

Most of these head units can do what they suggest, however you need to have your EQ etc maxed out.
Welcome to the marketing department.
Hint your not going to get above 4 volts without a switching supply.

Most likely your going to have around 3.3 volts without the EQ.

So what does it mean if you set your power factor gain on your power amplifier at 3.3 volts and it is not loud enough?

Assuming the marketing department has not been near the power amplifier "specifications", then, you will max out the power amplifier at 3.3 volts input. (IE it won't clip)

It is possible to tolerate some clipping, so don't get too anal retentive over it.

If this is not loud enough, then you system is at fault.

Like I said, higher wattage, more sub woofers (run at lower impedance), better sub sensitivity or better placement of the sub woofer in your car are the usual solutions.
Top SPL enclosures over the range?
Depends a bit, but approx in this order.
Acoustic lever
Bandpass
Reflex
Passive radiator
Transmission line
sealed
Infinite baffle.
Isobaric

As Chad said,
Your sub woofer is in the mouth of a waveguide, and it is highly sensitive to placement.
*IT HAS NOTHING TO DO WITH STANDING WAVES.*

It is acoustic impedance mismatch, IE what most call "transfer function". That is, how much difference the mass of the cone to the mass of air ratio.


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## chad (Jun 30, 2005)

OK, after that, here's my rant from another forum.....



> Disclaimer, I'm from pro audio, I think in those terms, but because it's EASIER at times and STANDARDIZED, please bear with me, Also this can get profane if I get wound up.
> 
> First off I don’t give a flying jellybean f**k what you think your head unit puts out in volts while running downhill with the wind against it’s back, I care less about what it says in the shiny brochure or on the front panel in gold print. I want to know its NOMINAL operating voltage. Let’s get this **** out, here’s the skinny and here’s how it works.
> 
> ...


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## 60ndown (Feb 8, 2007)

i bet grampi is busy enjoying his bass now he has his sub in a good location 

tuning bass gains down even?

cancellation s a bi-hatch.


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## FoxPro5 (Feb 14, 2006)

Preamp voltage is driven my the waveform of the music track. Put in a track from 1980 or earlier, turn you gains all the way down, get some ballsy amps in your car, crank the mafakin volume to the max and shut up!!!!!!!


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## chad (Jun 30, 2005)

60ndown said:


> i bet grampi is busy enjoying his bass now he has his sub in a good location
> 
> tuning bass gains down even?
> 
> cancellation s a bi-hatch.


Nope, it happens even with corner loading.


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## Abmolech (Nov 2, 2006)

> cancellation s a bi-hatch.


Do you want to do the calculation for cancellation in a car for sub 80 Hz waves?
Clue
Unless your driving a bus, it is not going to happen.


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## 60ndown (Feb 8, 2007)

Abmolech said:


> Do you want to do the calculation for cancellation in a car for sub 80 Hz waves?
> Clue
> Unless your driving a bus, it is not going to happen.



http://www.teamrocs.com/technical/pages/aiming.htm


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## chad (Jun 30, 2005)

nope it ain't gonn happen, BUT since a sub is omni, Would you rather couple the whole car... or 2/3 of it with a good portion of the rest causing IM issues?


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## chad (Jun 30, 2005)

Hold on, ...Fawk can I call you luke? Is that yer name from the old UN?

I'm gonna get you a calculator..

BRB


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## chad (Jun 30, 2005)

60ndown said:


> http://www.teamrocs.com/technical/pages/aiming.htm


Here ya go bud, play with this...

http://www.mcsquared.com/wavelength.htm


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## Oliver (Jun 25, 2007)

Horn loading and corner loading work in big rooms?


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## Abmolech (Nov 2, 2006)

Even easier... 

http://www.sengpielaudio.com/calculator-roommodes.htm


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## chad (Jun 30, 2005)

Abmolech said:


> Even easier...
> 
> http://www.sengpielaudio.com/calculator-roommodes.htm


I use a very similar calc from Syd-Aud-Com that's excel based. VERY, VERY handy when walking into a club that's a box. Walk it out, see what the dimensions are, plug it in, use it as a reference if you think there are low-end room issues and "sacrifice" from there.


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## Abmolech (Nov 2, 2006)

Cheat, you should be able to do it in your head by now.  

Is the car large enough to create standing waves from a sub woofer?

Not if we obey physics.

Still I have been assured that "physics" doesn't work inside a car. 
I am desperately trying to use the inside of a car for a cold fusion power source, unfortunately it still seems to obeying the laws of physics, what am I doing wrong?


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## jrwalte (Mar 27, 2008)

dtviewer said:


> Please everyone pretend you didnt read this post...............


So I got the first part wrong. But the fact it takes more energy to produce the same amount of Db for low frequencies over high is true. This is why you may have to set the gain of your sub near max when your highs are turned all the way down.


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## Abmolech (Nov 2, 2006)

> This is why you may have to set the gain of your sub near max when your highs are turned all the way down.


The power factor gain is used to match the power.

One more vote for Pro industry standards (including XLR balanced line cables, bye bye RCA "magic" cables .)


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## grampi (Jun 29, 2007)

60ndown said:


> i bet grampi is busy enjoying his bass now he has his sub in a good location
> 
> tuning bass gains down even?
> 
> cancellation s a bi-hatch.


Right after work I turned my box around and slid it all the way to the rear of the trunk, then spent 5 hours listening to CD's on my way home. I definitely think this location is an improvement, but it didn't make enough of a correction to be able to turn the gain down. However, tcguy is selling me his PG line driver and THAT should allow me to turn my gain down.


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## 60ndown (Feb 8, 2007)

grampi said:


> Right after work I turned my box around and slid it all the way to the rear of the trunk, then spent 5 hours listening to CD's on my way home. I definitely think this location is an improvement, but it didn't make enough of a correction to be able to turn the gain down. However, tcguy is selling me his PG line driver and THAT should allow me to turn my gain down.


damn thats a long commute 

glad you got some bump at last.


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## grampi (Jun 29, 2007)

60ndown said:


> damn thats a long commute
> 
> glad you got some bump at last.


In case you didn't figure it out, I only make that commute on the weekends. It's still a lot of driving, but you can see why I want a nice system........it'll get lots of use!


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## tcguy85 (Oct 29, 2007)

grampi said:


> Right after work I turned my box around and slid it all the way to the rear of the trunk, then spent 5 hours listening to CD's on my way home. I definitely think this location is an improvement, but it didn't make enough of a correction to be able to turn the gain down. *However, tcguy is selling me his PG line driver* and THAT should allow me to turn my gain down.


yessir! she will be on her way shortly. it will fix your problem. the pre-outs on the sub channel is just weak on the alpines.


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## grampi (Jun 29, 2007)

Whiterabbit said:


> Take a note from industry. Devices like smart washing machines and smart toasters, smart ovens used to be powered with pentium 166's. Was it more power than they needed? You bet! So why overkill it? Because it was a known reliable configuration.
> 
> Because maxing out your capabilities is asking for unreliable performance. Even fatigue failure.


I'm not talking about running my amp at full power, I'm talking about being able to use more of the amp's power potential, which is completely different. Right now with the weak preamp signal, my amp is probably running at about 1/3 of its max power when I'm honkin' on it, and peak transients are probably taking it a little over half power. Once I get a strong preamp signal going to the amp, I'll probably be able to get 2/3 of its power and between 3/4 to full during transients, but keep in mind, this would require extremely loud volume levels to get this much power from the amp, which I will probably rarely do. So I won't be overtaxing the amp, I'll just be able to use more of its potential.


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## grampi (Jun 29, 2007)

A8AWD said:


> "An isobaric is only more efficinet interms of enclosure size but is LESS efficient than 2 drivers in an appropriate enclosure by a bunch. Iso was cool before the small box woofers came out, but there really is no need to do it these days now that we have easy and affordable access to drivers with monster excursion, high power handling, and very powerful motors isobaric configs ahve pretty much fizzled out."
> 
> ^^^Chad has this right....isobaric is having 2 drivers with identical parameters mounted face to face out of phase with some space in between...in a sealed application it will typically 1/2 the enclosure volume that one speaker would require, but also becomes VERY inefficient as you need to power to motors to push one cone. An isobaric setup can actually be adapted to any type of enclosure if built correctly including bandpass...


Not quite following you. When you say you need to power two motors to push one cone, what do you mean? I an isobaric configuration, there's two motors and two cones, how are you using two motors to push one cone? Also Chad mentioned that isobaric configs went away because of high excursion, high power handling, and powerful motored drivers. The subs I have have none of those. I have the Sundown SD-1 v1 10's and they're made to be effecient in low power applications. Plus my amp is only pushing 500wrms to the subs. I'm certainly open to enclosure suggestions, but it's been my past experience that sealed (which is what I'm using now) sounds the best, but they're not the most efficient, ported are more efficient, but I generally don't like their sound as much as sealed, and isobarics have kind of been the best of both worlds; the efficiency of ported with the SQ of sealed. If there are better enclosures, I'm all ears.


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## Abmolech (Nov 2, 2006)

Efficiency could be measured by an increase in temperature. An isobaric enclosure cancels out odd order harmonics, at the cost of producing extra heat.

Aperiodic turns the rear wave to heat.
Packing (stuffing) an enclosure turns some of the rear wave to heat.

Ergo the most efficient enclosures are rigid structures with a blocker above 12 dB of attenuation. These structures reduce the mechanical loss of the reciprocating voice coil to vibration and use reflection of the rear wave back through the cone. 

There is only so much available acoustic power from a woofer. By using an acoustic lever device or bandpass enclosure you restrict the total frequency bandwidth, and therefore you have the ability to increase the SPL by summing that acoustic power underneath the "saved frequencies".

In the case of sealed, reflex or passive radiator, these restrict the REAR wave roll off, and that acoustic power underneath those frequencies can be summed onto the output.
VIZ 
Sealed 12 dB roll off
Reflex 24 dB roll off
Passive radiator 29 dB roll off.

As you see the passive radiator has the most potential to sum the rear wave.
The advantage with a bandpass enclosure is is can sum the front wave as well.

Highest output over a limited band width therefore is a bandpass. Next is passive radiator, then reflex.

Acoustic levers have the highest potential of all, but it is a complex subject.


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## grampi (Jun 29, 2007)

Abmolech said:


> Efficiency could be measured by an increase in temperature. An isobaric enclosure cancels out odd order harmonics, at the cost of producing extra heat.
> 
> Aperiodic turns the rear wave to heat.
> Packing (stuffing) an enclosure turns some of the rear wave to heat.
> ...


Your knowledge about enclosures is obviously way beyond mine, but isn't an isobaric configuration also considered a bandpass? Is it possible to build a BP enclosure that offers excellent SQ? If so, is there a certain I would want to consider? Thanks.


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## grampi (Jun 29, 2007)

Just for ****s and grins I just went out and pushed my enclosure to the front of the trunk (with the woofers still facing to the rear) and it seems to sound the same as it did when it was all the way to the rear of the trunk. It must have something to do with the sound traveling to the rear of the trunk and then being forced towards the front of the vehicle (is this the same theory as corner loading)?


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## ClinesSelect (Apr 16, 2006)

Some articles on isobaric:

http://www.mtx.com/caraudio/education/enclosureDesign.cfm

http://www.the12volt.com/caraudio/boxes4.asp

http://www.the12volt.com/caraudio/boxes2.asp

http://en.wikipedia.org/wiki/Isobaric_speakers


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## grampi (Jun 29, 2007)

Also, are there different order BP enclosures, and if so, which one should I consider. Thanks.


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## jrwalte (Mar 27, 2008)

If your sealed box is on the low end of the recommended cubic footage, you could try stuffing poly fill in it. Even if your box is to specs, might as well give it a try for a few bucks. The bass response may increase.


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## placenta (Feb 2, 2008)

Grampi, I just found out this for my own sub weak output. Check it. Make sure you are on system 2.










My problem is I had to go to volume 20-24 to get good sub output. With system 2, you only adjust your sub with that 1-15 setting. Volume has no effect! So you will have sub at all low volumes also.


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## ClinesSelect (Apr 16, 2006)

Set up correctly, there is no need to use system 2. Personally I could not stand the overpowering bass at low volume levels.


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## placenta (Feb 2, 2008)

ClinesSelect said:


> Set up correctly, there is no need to use system 2. Personally I could not stand the overpowering bass at low volume levels.



thats why it has a level setting.


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## ClinesSelect (Apr 16, 2006)

placenta said:


> thats why it has a level setting.


Having the level of the sub remain constant while the level of the other drivers change with the volume knob is not a substitute for correctly designing, installing and tuning a system. Its a band-aid fixing a much larger problem. But that is just my opinion. 

People, and I am speaking in general, tend to buy a sub and _then_ hope it reaches the desired level of output instead of figuring out up front how much output is needed/desired and then designing a system around those needs/desires.


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## placenta (Feb 2, 2008)

ClinesSelect said:


> Having the level of the sub remain constant while the level of the other drivers change with the volume knob is not a substitute for correctly designing, installing and tuning a system. Its a band-aid fixing a much larger problem. But that is just my opinion.
> 
> People, and I am speaking in general, tend to buy a sub and _then_ hope it reaches the desired level of output instead of figuring out up front how much output is needed/desired and then designing a system around those needs/desires.


ya i should really have double the sub power i have now in a correct system.

i run 100x2 fronts, 300x1 sub.. 600x1 sub would be just right.


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## grampi (Jun 29, 2007)

grampi said:


> Also, are there different order BP enclosures, and if so, which one should I consider. Thanks.


Anyone?


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## Oliver (Jun 25, 2007)

Here is one at Crutchfield
http://www.crutchfieldadvisor.com/S-gzlD1tNY79x/reviews/20040713/subs_comparison.html?page=3

Here is a sixth order program
http://www.carstereo.com/help2/Articles.cfm?id=32

Here is another bandpass designer program
http://www.ajdesigner.com/speaker/bcb.php


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## Oliver (Jun 25, 2007)

Sonic has some boxes
http://www.sonicelectronix.com/item_3357_Dual+15-+Bandpass+Enclosure.html

http://www.sonicelectronix.com/cat_i97_bandpass-enclosures.html


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## 60ndown (Feb 8, 2007)

grampi said:


> Anyone?


the 'best' one is @

www.decware.com

main page has a 'speaker' section,

scroll down about 8 items to

'the death box'

read the design notes about it, ive used several of them,

they are excellent


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## 60ndown (Feb 8, 2007)

a$$hole said:


> Sonic has some boxes
> http://www.sonicelectronix.com/item_3357_Dual+15-+Bandpass+Enclosure.html
> 
> http://www.sonicelectronix.com/cat_i97_bandpass-enclosures.html


please


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## grampi (Jun 29, 2007)

placenta said:


> ya i should really have double the sub power i have now in a correct system.
> 
> i run 100x2 fronts, 300x1 sub.. 600x1 sub would be just right.


Maybe 3x the power on the subs as compared to the comps is the ticket. I've kind of always gone by doubling the power, which may not be enough.


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## Dillyyo (Feb 15, 2008)

grampi said:


> Your knowledge about enclosures is obviously way beyond mine, but isn't an isobaric configuration also considered a bandpass? Is it possible to build a BP enclosure that offers excellent SQ? If so, is there a certain I would want to consider? Thanks.


BP and SQ?! Thats like ****z and cookies.....just don't mix. Also, the voltage you actually see out of a HU is also dependent upon the HU's output impedence. You can have ~4V outs, but if the impedence is like 1000 or so, you get dribble


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## Dillyyo (Feb 15, 2008)

grampi said:


> I'm currently running 2 Sundown SD-1 v1 10's, which are supposed to run very nicely off of 150 each, and I'm feeding them 250 each. I don't think my problem is a lack of power.......not directly anyway. It is a lack of power, I believe, because of too low of a preamp signal to the amp, which in turn is not allowing the amp to deliver full power. Once I install the line driver, I think the amp will then be getting enough of a preamp signal to deliver full power. I do like the idea of using a bandpass enclosure though. I've used them in the past and I really like the sound. Not only do they hit hard, they sound good doing it. Does anyone sell pre-made band pass enclosures that'll work with these drivers?


Don't look at the stated numbers. You need to measure if you want to make this argument. I.e. You would think with all Zapco BLT, that they would let one keep amp gains as high as possible since they are supposedly giving 12+V of signal, but I still have to turn my gains lower to make them match the actual incoming signal. You are only taking the stated voltage and not accounting for any system impedance (load).


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