Looking for ideas for a small amplifer for a set of component speakers

[xtremerevolution]

I see an improvement!

 

you went from "I really don't care", to "Whatchu smokin'?", to "I am dying to know".

 

 

this is what I like to see.

 

 

two very high powered 18"s? sounds like something I would be into but that would obviously not be very practical in your car. w-7 in a sealed box would be your best shot. you can't JUST use wood though. the monoleaf is not strong enough and will soon break (even without all that weight) so I would suggest using a Birchmount steel spring, along with a fiberglass braced, thin walled, sealed box, with heavily fortified 2 to 3" faceplate (I use a 5" faceplate ). a clean transitioning sealed box relies on the air suspension to get that low. be careful with yours when you get it, some poor kid had his crappy particle board box explode inside his trunk.

 

 

 

now with the bass curve discussion going on, there seems to be a little confusion. the vocabulary term sharp roll off when talking 12 vs. 24 dB roll off's for the same given sub. 24 would be the sharper because the signal dropped 24 whole dB's in the same amount of time it took for the sealed to only drop 12. with ported you want it to drop sharply because without suspension the sub IS going to fart if you do not. and when it does it is NOT pretty. with a sealed box you want the opposite. the smoother the roll off, the better, because the shallower, the lower the bass extends to (glad you see that now, it is true with all subs, home or car). and the more you will experience if your amp actually plays that tone, and if the recording plays that tone.

 

now cabin gain is another topic that I do not find significant in the discussion of a sealed enclosure for a car. orientation of the sub does not matter at frequencies that low. the bass wave will not fully expand unless you open your windows/sunroof and let it. bass is non-directional and the cone just shoves air around. open the window and it will fluff up your girlfriend's hair and get you in trouble

 

Sometimes I wonder if you've even actually read what I've written.

 

I'll go from the top.

 

I have coilovers with either 300 or 400lb springs in the back. In fact, have one of the most modified cars on this board.

 

If you want to get technical, the word would technically be the sub would unload, and I'm quite aware of that. However, you also have to keep in mind that despite there being a port or otherwise open hole in the box, the port tuning does create a suspension of its own and keeps cone excursion controlled above the tuning frequency. Depending on the tuning frequency, you then have very little wiggle room below that before your sub starts unloading due to a lack of air suspension. You should do some more research on this topic before you tell me how sub boxes work. You've already proven you have no idea so I'm really not sure why you even came back for a second try.

 

Here, let me prove it to you:

 

 

That's a unibox modeling of a specific pair of subs in a vented (ported) box. You will notice that as the frequency decreases, the excursion increases. However, it suddenly drops to a very low excursion point right at the tuning frequency, after which excursion starts to rise very rapidly (as the sub starts to unload). You'll also notice that peak xmax is not reached until around 15hz, where the human ear cannot even detect sound. A high pass (infrasonic, subsonic, whatever you want to call it) filter solves that problem.

 

Here is a modeling of a sealed box:

 

You'll notice cone excursion rises gradually until it starts to plateu. Yes, it is more controlled, but output also decreases as the box's air volume starts to have more of an effect on excursion. Excursion increases as frequency decreases, and air suspension's effects increase as excursion increases.

 

The problem is that any rolloff is not desirable for a home theater sub. I mentioned this before and I'm mentioning it again. It actually doesn't matter at all how sharp or smooth the rolloff is in home audio, only in car audio, and the only reason it matters in car audio is because of cabin gain. Ideally, your rolloff would be inversely proportional to your cabin gain, if we are to assume that cabin gain is a linear function (which it likely isn't).

 

In home audio, you have no cabin gain, so you basically stuck with what you can model in a box. In home audio, you want linearity. You want a flat, neutral frequency response. You don't want to have any frequency louder or quieter than any other, and if you run a sealed box, that's exactly what you have. You have a rolloff with a slope that is directly related to the size of the box. The larger the box, the more shallow the rolloff, up to a point (with regard to sealed boxes). However, there IS a rolloff no matter what you do.

 

Now, the reason why ported boxes are recommended in home audio is because you can get a linear frequency response across the *audible* frequency range around and above 20hz, after the tuning frequency, yes, you will have a sharp rolloff, but with a well designed box like the one Matt Borgardt designed for my IDQ15, that rolloff will exist at a frequency range that the human ear can't even hear. With a car, you can get linearity with a sealed box due to cabin gain, so yes, it does in fact make a very big difference and it is very significant.

 

In fact, every frequency below around 70hz (the actual cabin gain turnover frequency varies based on the car) is affected by cabin gain. At frequencies as low as 20hz, you can expect around 20db of cabin gain. That's very significant. This is why linearity is bad for a car, because on paper you will have a very linear frequency response, but in a car, your output will rise by around 12db per octave for frequencies below the frequency at which cabin gain begins. Considering how large of an effect it has on sound quality and accurate sound reproduction, you can't possibly tell me (or anyone for that matter) that its not significant. It is significant.

 

By the way, a 5" baffle is a big excessive. I have a 1.5" baffle with a .9 net cubic foot box and there's no way in hell that thing is moving, and a W7 is not going to change that. I'd love to know, how do you keep the sub from choking at that point? 5" is basically the entire depth of the basket, so even if you flush mounted it, you'd still be severely restricting airflow. I can't say I've ever seen a 5" thick baffle with the exception of multi-sub arrays in SPL competition cars.

 

Hell, even JL Audio themselves recommend a 1" baffle, so I'm really not sure why you feel the need to use a 5" baffle.

 

By the way, there's no confusion here about rolloffs. I design crossovers for speakers. I design crossovers of different orders. In layman's terms, these are crossovers with varying slopes. I decide what slope I want at what frequency, and I model a crossover network that will allow a woofer's low pass and a tweeter's high pass to blend perfectly (depending on the slopes chosen) to create a perfectly linear frequency response. So no, no confusion here.

[Garrett Powered]

as if I don't do all that type pf shit too.

 

you know I Have built and chose crossovers and built my own cabinets from other thread discussions so why attack my credibility all the time?

 

yes they were "canned crossovers" but I have messed with a lot of stuff to make me competent to know what I like. just leave it alone.

 

If this is going to get into a rock throwing contest then I can't have any fun with it.

[xtremerevolution]

as if I don't do all that type pf shit too.

 

you know I Have built and chose crossovers and built my own cabinets from other thread discussions so why attack my credibility all the time?

 

yes they were "canned crossovers" but I have messed with a lot of stuff to make me competent to know what I like. just leave it alone.

 

If this is going to get into a rock throwing contest then I can't have any fun with it.

 

I usually try to be a nice guy but this time you've actually irritated me. You've come here with a blatant lack of knowledge on the subject and tried to tell me what the facts are.

 

Canned crossovers are worthless. Canned crossovers barely even take into consideration the impedance of the two drivers being used, let alone the phase alignment. They have absolutely no BSC (baffle step compensation) when used in home theater, no notch filters or proper zobel networks, no disregard for 2nd and 3rd harmonic distortions, and are usually comprised of 1st order slopes that "get the job done" at best with the cheapest variety of parts. Anyone can pick a crossover, try to match impedance, figure out the usable range of a particular driver, and match the crossover frequency to that. Its simple as pie and your speakers will make sounds after you're done that resemble music, but that's the extent of it.

 

Choosing a crossover is an entirely different matter than actually designing a crossover. Designing a crossover takes into consideration all of the above including off-axis response (something car audio seems to ignore to a great degree), phase alignment, combing/lobing, and a plethora of other concepts that I don't have the time to explain.

 

This will give you enough of an idea.

 

Q: Great. So now we're down to the crossover. Just buy one that matches the crossover points of the drivers, right?

 

A: Well, you can, but the end speaker still probably won't sound all that impressive.

 

Q: Why not? I'll just use really good drivers.

 

A: I wish I could say that building a speaker is like building a computer--that you just match up bus speeds and buy the latest high-quality gear you can and you've got a rip-roaring machine. Speakers are a strange analog animal, though, and getting high-quality performance from them is a delicate balancing act, where components are calculated, simulated, listened to, tweaked, measured, evaluated, and revised again and again until you have a speaker that is truly "transient" and transparent. And you'll know when you hear a speaker that gets this right. You'll hear depth and detail in music that you've never heard before, but the speakers will be non-fatiguing to listen to, and will just sort of effortlessly reproduce the music without using any sort of trickery on their own part. It is that sound that makes people pay thousands and tens of thousands of dollars for HiFi speakers. And yes, it is definitely possible for a DIY speaker to achieve that sound, but not with an off-the-shelf crossover.

 

Q: So what's so special about a "custom designed" crossover?

 

A: As I was saying, speakers present all sorts of strange analog quirks. A crossover designer almost becomes one of those "plate spinners" from the circus, as he tries to successfully manage several factors at once: filter order needed to attenuate the unwanted frequencies (aka: "stopband"), combining Acoustic Phase introduced by the filter and physical offset of the drivers, flat frequency response, gently-tapered power response, and keeping electrical Impedance and Impedance Phase safe for a given amplifier. Hopefully, when all those factors are in-check, the speaker will be sounding pretty good--but often there's still more tweaking to go until the speaker starts sounding "right" in terms of effortlessly reproducing a recording. Then, to really complicate things, changing the value of one component in a filter often cascades through the rest of the components in that filter. For example, a designer might increase the value of a capacitor, which may suddenly require the use a smaller-value inductor and perhaps a larger-value resistor... and so on down the line.

 

Q: Really? But in my car, I can just install better speakers and a better amp and I can hear an improvement.

 

A: You raise a good point, but the two worlds just aren't the same. In car audio, they say you can "throw parts at a problem," but HiFi speakers require a whole different kind of effort. As I said before, crossover design is a delicate balancing act.

 

Q: So making a speaker sound good is hard to do?

 

A: Yes, it is. The crossover in a HiFi speaker is like its brain. And as a result, a badly-designed crossover can make extremely expensive Scandinavian drivers sound like crap. Alternatively, a well-designed crossover can take "cheap" Chinese drivers and make them sound excellent.

 

https://sites.google.com/site/undefinition/diy-faqs-provendesigns

 

You've done nothing but argue with me in this entire thread in the face of blatant proof. Yeah I made a typo here and there, but I know my shit. I know exactly what works in car and home audio, and why it works. You set off the first big red flag when you tried to tell me that ported boxes do nothing but distort frequencies, and you didn't stop there, you kept going. You have the option of learning something, or arguing with me. You chose to argue with me, and that was your choice entirely.

 

Your JL W7 is on a short list of the best subs ever made, there's no doubt about that, and it integrates very well with the cabin gain of most vehicles in a sealed box, but building a 6 sided box to the manufacturer's spec and bolting in a sub doesn't make you an expert or authority on bass reflex box design, nor does experimenting blindly.

 

If you want to learn, arguing with someone who has a much deeper knowledge on the subject than you do isn't the way to go about it.

Edited June 5, 2011 by xtremerevolution

[White93z34]

I don't really see any reason to close this... yet. There seems to be a decent discussion/debate going on... However, I will not tolerate the personal jabs and insults that I see being casually thrown around.

 

I will request that the posters of such material edit their posts accordingly or I will have to close this. Thanks.

[gpgtp]

Gosh, all those years I spent learning FEA, building and testing drivers for tc sounds, winning sq contests, competing in spl contests (diff vehicle than the sq car), working with companies like xenon on amplifier development, etc. were wasted. I could have just came here and learned win-isd, and w7s were all I needed. As far as the comment about considering ported boxes distortion- when I was growing up, my younger brother always valued coins more than paper money. He called them "big monies", and would happily trade his dollar allowance for a quarter. Did that make him right? now, if you'll excuse me, I've got to go throw my lms 15's away and pick up some dub7's for next years comp car:thumbsup:

[xtremerevolution]

I don't really see any reason to close this... yet. There seems to be a decent discussion/debate going on... However, I will not tolerate the personal jabs and insults that I see being casually thrown around.

 

I will request that the posters of such material edit their posts accordingly or I will have to close this. Thanks.

 

All done. Let me know if I missed anything.

 

Now, I invite anyone to attempt to prove me wrong with regard to what I've said so far, or ask questions if you want me to explain or elaborate on something.

 

Sent from my HTC Awesome using Tapatalk

[alec_b]

xtreme, I won't ask you to elaborate because as interesting as all of this is (and I've read every word), it's way over my head! Boxes and xmax's and such. Wanna just come design me a box that will make my POS polk/momo 12" sound decent without me having to spend a ton! Ha.

 

Very interesting read though. I'd love to find time some day to really DESIGN a sound system for my car, not just build one. I will admit besides my sub amp, the rest of my system is crap. I miss my W6's.... If I hadn't made a 400% profit on them I would have kept them, and after reading this thread I probably could have made them into a killer SPL/SQL combo with a little time and a good carpenter friend.

[xtremerevolution]

xtreme, I won't ask you to elaborate because as interesting as all of this is (and I've read every word), it's way over my head! Boxes and xmax's and such. Wanna just come design me a box that will make my POS polk/momo 12" sound decent without me having to spend a ton! Ha.

 

Very interesting read though. I'd love to find time some day to really DESIGN a sound system for my car, not just build one. I will admit besides my sub amp, the rest of my system is crap. I miss my W6's.... If I hadn't made a 400% profit on them I would have kept them, and after reading this thread I probably could have made them into a killer SPL/SQL combo with a little time and a good carpenter friend.

 

All you have to do is ask. I took this from another forum because the guy said it better than I could:

 

"Xmax is the maximum linear travel of the voice coil/cone before it leaves the magnetic gap. Two factors determine this: voice coil winding length and suspension travel."

 

Xlim is the maximum excursion limit before the sub bottoms out. Basically, the voice coil slams against the back of the motor structure, and depending on how hard it does it, it can damage it permanently.

 

Xlim is usually considerably larger than xmax, but distortion goes up significantly once xmax is exceeded. There's generally a wiggle room of 10% with inaudible distortion, after which the distortion is very audible as the voice coil leaves the magnetic gap. In simple terms, the energy going through the coil is no longer producing the sound it should. Any time a signal is sent to a speaker and that speaker does not accurately produce the sound created by that signal, its called distortion, and the farther you exceed xmax, the more the distortion increases.

 

What this means for box design? Well, the box has an air volume. In a sealed box, that air volume acts as additional suspension that stiffens the travel of the cone on the sub, thereby allowing you to put more power to the sub while limiting the excursion, thereby keeping distortion low. In a ported box, this works essentially the same way though with a slightly reduced but still strong air suspension above the tuning frequency. Below the tuning frequency, the port tuning no longer controls the excursion and your sub basically starts moving freely, in which case there's no air suspension to control the cone movement and it will reach xlim (excursion limit, aka bottom out) and damage or destroy the cone. Its quite important to have a box that's sized properly to control excursion at the usable frequencies, and set a high pass filter on the amplifier to filter out any frequencies that are beyond the sub's excursion at xmax. Fortunately, I have software (which is readily available) to able to model all of this information to design a box that will sound great depending on the environment and intended purpose with all parameters considered.

 

Here's a picture of the cone I replaced on my IDMax shortly after I got it since the previous owner abused it. It might help you understand what I'm talking about. The cone was installed improperly from the factory and had a dust cap leak, and was replaced free of charge by Image Dynamics.

 

 

And here's the motor structure the cone goes inside:

Edited June 5, 2011 by xtremerevolution

[Garrett Powered]

its okay Xtreme mah brotha. I see your side of it too. you are very passionate at what you do and I recognize this. its fine with me, I like tossing ideas around and experimenting with this stuff when I got time. you take a very precise route thats by-the-book surgery which is admirable. I say go with it and use your knowledge that no one is contesting you have and take it to the next level.

 

I want to. I am thinking 4 18" sealed box built into the concrete foundation of a 4 story mansion out on a few acres right outside of city limits. 1/4" steel faceplate. lots of extra breakers on the panel. this is your life and you have the right to think big if you want, is what I say.

[alec_b]

Well all of that made sense to me, so that's a start.

 

And I must say, WHAT a sub that is. Looks like it's built to withstand a nuclear attack on your trunk. What are the specs on that thing?

[xtremerevolution]

Well all of that made sense to me, so that's a start.

 

And I must say, WHAT a sub that is. Looks like it's built to withstand a nuclear attack on your trunk. What are the specs on that thing?

 

Its a 10" IDMax with massive excursion and a surprisingly light cone. Its very articulate and accurate at moderate volumes, and digs very deep at louder volumes. 1000w rms. Its nearly (within 1-2db) as loud as white4d96's two 12" alpine r12's in similar box alignments.

 

And yeah, its built to take abuse. Very well vented coil and the entire dust cap assembly is a heatsink.

 

Sent from my HTC Awesome using Tapatalk

[xtremerevolution]

its okay Xtreme mah brotha. I see your side of it too. you are very passionate at what you do and I recognize this. its fine with me, I like tossing ideas around and experimenting with this stuff when I got time. you take a very precise route thats by-the-book surgery which is admirable. I say go with it and use your knowledge that no one is contesting you have and take it to the next level.

 

I want to. I am thinking 4 18" sealed box built into the concrete foundation of a 4 story mansion out on a few acres right outside of city limits. 1/4" steel faceplate. lots of extra breakers on the panel. this is your life and you have the right to think big if you want, is what I say.

 

I figure if you have the tools and know how to use them (hell, I could teach anyone how to use them), then you are that much better off. It gives you the power to get the most out of your sub, and gives you more precision than any amount of trial and error. You squeeze every last bit out of a sub.

 

If anyone wants me to teach them these design concepts and how to use this software, let me know.

 

Sent from my HTC Awesome using Tapatalk

[white4d96]

I'm looking into a new design, if you're willing to help me out that would be killer!

[xtremerevolution]

I'm looking into a new design, if you're willing to help me out that would be killer!

 

I'd be more than glad to. My 3rd sub was a single Alpine R12 in a ported box, and it was much too loose for my tastes. However, I have heard a pair of R12's in a sealed box and they sounded amazing. Very good SQ for that sub. I was truly impressed.

 

Actually, I don't have a whole lot to do so I'll model something up for you right now. Due to cabin gain playing a large part, I'd go with a sealed box instead of a ported one unless you want it to be just plain loud. One modeled sub design coming right up.

[white4d96]

I would prefer ported, but I'll try anything once. If I don't like it I'm out a sheet of wood and a day's work, no biggie.

[xtremerevolution]

Didn't get a chance to finish the modeling last night, but I did get pretty far with it and even modeled the predicted cabin gain, and even with a sealed box, you have a bit of an output in crease at certain frequencies. You will have a lot of difficulty integrating a ported box with the rest of your system.

 

Still waiting on your dimensions so I know how much volume I have to play with.

[Firen81]

Have you considered the alpine power pack? it sits behind the dash and is actually a 150w 4 channel amp. its actually pretty inexpensive, and works well. its the KTP-445. I was talking to an installer at work (Best Buy) and he was saying even if it was meant to be put inline with an alpine deck, apparently you can add it to any deck, factory or aftermarket.

[white4d96]

I don't believe that for a minute.

 

Besides, I looked into it once, and TBH, for the money you can get a good new amp online or a NICE used one.

 

Andrei, I forgot to take into account my trunk hinges, damn things take up half the sides =/ so whatever I PM'd you with, change the width to 36.

[xtremerevolution]

I don't believe that for a minute.

 

Besides, I looked into it once, and TBH, for the money you can get a good new amp online or a NICE used one.

 

Andrei, I forgot to take into account my trunk hinges, damn things take up half the sides =/ so whatever I PM'd you with, change the width to 36.

 

You will need to go sealed if you want any resemblance of sound quality. With the cabin gain I modeled, your car will sound like crap on a ported box.

 

To show you the difference, I'm bringing my two IDQ10 v2 subs in a sealed box to the meet. These were bought from a guy who won the MECA stock class A state sq championship with them. You'll see what real sq sounds like and how much of a difference there is between good sound and just plain raw spl.

 

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[white4d96]

I just thought of something and wanted your thoughts:

4th order. Make the area under the RSTB the sealed portion, and then I can take up the rear for the ported part. This way I should be able to have both spl and lows.

 

Honestly, I could care less about being loud, I just want the thing to be violent as hell on the lows.

[xtremerevolution]

I just thought of something and wanted your thoughts:

4th order. Make the area under the RSTB the sealed portion, and then I can take up the rear for the ported part. This way I should be able to have both spl and lows.

 

Honestly, I could care less about being loud, I just want the thing to be violent as hell on the lows.

 

That wouldn't sound very good. There's a reason why most people haven't tried it. If you want violent as hell on the lows, sell your subs and buy a used IDMax12. Otherwise, your best bet for good lows will be a sealed box.

 

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[Garrett Powered]

if you want violent as hell lows get something Fs3 technology wise. you will shit.

 

 

my idea of violent.

[white4d96]

Oh yeah I've seen those. Kcufing insane!

[xtremerevolution]

if you want violent as hell lows get something Fs3 technology wise. you will shit.

 

 

my idea of violent.

 

If SQ is home base, that's way out in left field. Hell, that's not even in the stadium. You cannot have both SQ and SPL at the same time. To think otherwise would demonstrate that someone has never really heard real competition winning SQ. The reason is moving mass, and a little thing called inertia when the driver cone is pushed in a direction. Once you reverse the current in a voice coil its still moving in one direction and it generates an opposing current and voltage. An object in motion will stay in motion unless stopped. The greater the moving mass, the greater the inertia.

 

10 yrs of testing speakers at panasonic.. same VC and magenet all we do is change cone mass and 99.9% of time the "faster" or more accurate speaker is identified as the one with the lighter mass and yes the spl change was accounted for.

want a good sub?? flat BL curve.. Low MM. low excurions!!! damn..

Its why Image Dynamics IDQ drivers win SQ competitions. Low excursion, very light cones, and very high efficiency. An IDQ12 will produce at 10W what a typical 12" driver will produce at 50-75W. It typically takes 2x the power to gain +3db of output. The IDQ15 produces 92.7db SPL at 2.83V. The IDMax12 has a 93.1db sensitivity.

 

The Dayton HO 10 in this thread happens to have a *very* good BL curve. Though it has a heavier cone than the HF 10, it will work better in a smaller box.

Edited June 14, 2011 by xtremerevolution

[Garrett Powered]

are you saying that JL and Boston have knocked a home run out the park? hitting low with massive excursion is what gives these woofers the SQ in the lowest frequencies with all that SPL. it is a competition that was won by the patent holder of the lightest and strongest cone design. would that be the maker of the W cone or ID?

 

http://mobile.jlaudio.com/products_subs_pages.php?page_id=37