Sub/amp separation?

[joshua43214]

So I started pulling interior parts out of my car so I could plan the installation of the stereo that formerly lived in my Saab.

After looking it over and talking to the Kicker tech people, I have decided to build a sub enclosure that will fit behind the backseat. The enclosure will span the entire back of the seat and be just as deep as needed to give the sub 1" clearance, then internaly blocked up to give the desired volume.

Mounting the amp is the next issue, the thing is rather large, 21"x12"x3" and weighs a fair amount. I can either mount it directly to the bottom of the parcel shelf upside down, or I can mount it to the back of the sub enclosure.

Inverted mounting gives me better access to the amps controls and wiring, but this stuff is not touched once the system is running properly so maybe not such a big deal. I just like the idea of the sub, amp and EQ all being in one nice clean assembly. Not to mention better heat disipation if its not inverted.

I like the idea of it mounting to the enclosure since I would not lose any vertical space that way, but it would put the bottom of the amp less than 2" from the magnet on the 10" sub. Is there a problem with an amp being so close to a large magnet like this? and is there any thing I can do to sheild it if so?

[Rustam]

So I started pulling interior parts out of my car so I could plan the installation of the stereo that formerly lived in my Saab.

After looking it over and talking to the Kicker tech people, I have decided to build a sub enclosure that will fit behind the backseat. The enclosure will span the entire back of the seat and be just as deep as needed to give the sub 1" clearance, then internaly blocked up to give the desired volume.

Mounting the amp is the next issue, the thing is rather large, 21"x12"x3" and weighs a fair amount. I can either mount it directly to the bottom of the parcel shelf upside down, or I can mount it to the back of the sub enclosure.

Inverted mounting gives me better access to the amps controls and wiring, but this stuff is not touched once the system is running properly so maybe not such a big deal. I just like the idea of the sub, amp and EQ all being in one nice clean assembly. Not to mention better heat disipation if its not inverted.

I like the idea of it mounting to the enclosure since I would not lose any vertical space that way, but it would put the bottom of the amp less than 2" from the magnet on the 10" sub. Is there a problem with an amp being so close to a large magnet like this? and is there any thing I can do to sheild it if so?

I don't think you will be able to shield the magnetic field. I would move the amplifier away.

And, then if I understand you correctly you want to mount the amplifier to the subwoofer enclosure - the enclosure may be subject to some vibration, depending on design. So I would possibly stay away from mounting anything to it.

[Rustam]

So I started pulling interior parts out of my car so I could plan the installation of the stereo that formerly lived in my Saab.

After looking it over and talking to the Kicker tech people, I have decided to build a sub enclosure that will fit behind the backseat. The enclosure will span the entire back of the seat and be just as deep as needed to give the sub 1" clearance, then internaly blocked up to give the desired volume.

Mounting the amp is the next issue, the thing is rather large, 21"x12"x3" and weighs a fair amount. I can either mount it directly to the bottom of the parcel shelf upside down, or I can mount it to the back of the sub enclosure.

Inverted mounting gives me better access to the amps controls and wiring, but this stuff is not touched once the system is running properly so maybe not such a big deal. I just like the idea of the sub, amp and EQ all being in one nice clean assembly. Not to mention better heat disipation if its not inverted.

I like the idea of it mounting to the enclosure since I would not lose any vertical space that way, but it would put the bottom of the amp less than 2" from the magnet on the 10" sub. Is there a problem with an amp being so close to a large magnet like this? and is there any thing I can do to sheild it if so?

Why not mount the amplifier in place of the original amp? Is it too large?

[stargazer_61]

Build something to mount it in the trunk either under the parcel tray or better yet behind the back seat panel or by the well where the old one is. The amp needs room to breathe and for heat dissipation. Like Rustam said, keep it away from the magnetic field on the sub. Isolate all of your hardware with rubber so that you don't get the rattles. Easier to show off a custom installation job, too!

[pingu]

The amplifier will internally use negative feedback to ensure that it's output signal is a faithful reproduction of the input signal.

Although there are some theoretical reasons for keeping an amplifier away from the magnet of the sub, in the real world these reasons won't be an issue. It's worth remembering that the distortion of a loudspeaker (at normal listening sound levels) is roughly about a thousand times greater than the distortion of the amplifier. No matter how much you spend on loudspeakers, the loudspeakers will be the weak link in the chain - they distort far more than any reasonable amplifier. It is, however, important to make sure that the volume of the sub enclosure is suited to the parameters (known as Thiele-Small parameters) of the subwoofer.

[Rustam]

The amplifier will internally use negative feedback to ensure that it's output signal is a faithful reproduction of the input signal.

Although there are some theoretical reasons for keeping an amplifier away from the magnet of the sub, in the real world these reasons won't be an issue. It's worth remembering that the distortion of a loudspeaker (at normal listening sound levels) is roughly about a thousand times greater than the distortion of the amplifier. No matter how much you spend on loudspeakers, the loudspeakers will be the weak link in the chain - they distort far more than any reasonable amplifier. It is, however, important to make sure that the volume of the sub enclosure is suited to the parameters (known as Thiele-Small parameters) of the subwoofer.

You don't think that the amplifier potentially can have problems with Hall Effect being in magnetic field?

[genphreak]

Sounds like a good plan, a sealed enclosure from my experience sounds best. Keeps weight more forward too.

I put my amp under the shelf. It's kinda long but it fits fine. Lost 56mm of storage height but it is easy to do and keeps the connections near to the trunk's wiring loom. Use good self-tapping screws with both a flat and a spring washer to avoid it coming loose.

If you mount to your woofer enclosure the screws will vibrate out faster than anywhere else so you have to cover this more carefully. The problem with magnetism on your amp may be real or immaterial; however if it vibrates with the woofer the PCB ideally needs to be mounted on damped supports (which it won't be) and regardless the transistors bolt to the heat sinks so you will see fasteners loose in the amp after a while or even worse dry joints cracking earlier than they normally would (so try not to do it).

:) Nick

[joshua43214]

Thanks for the feedback every one.

There are 3 large lugs under the parcel shelf that I can bolt an amp mounting board to, I presume they are for mouning the rear power shade. They should easily support the weight of the amp. As for the sub, The enclosure will rest on the floor of the trunk and I will bolt it through from the other side.

Once I start actualy cutting parts, I'll post some pics.

[genphreak]

There are 3 large lugs under the parcel shelf that I can bolt an amp mounting board to, I presume they are for mouning the rear power shade. They should easily support the weight of the amp. As for the sub, The enclosure will rest on the floor of the trunk and I will bolt it through from the other side. Once I start actualy cutting parts, I'll post some pics.Do you have the new style amp? Let us know when you post how you are wiring everything- if only we had a away to use the old crossover in the later model booster amps, the sound would be guaranteed. I am still marvelling over mine, it is tight and perfectly balanced, like BMW did it all perfectly in the first place for a high power setup but forgot to any hardware to reproduce signals below 100Hz and install the correct amps... of course I'll probably blow a tweeter or two soon, but the highs are not distorted or dirty in any way, even at full blast.

[joshua43214]

I doubt I would bother to upgrade the OE system in my car. It plays music nice and clearly, but any upgrade would just be maintaining the same poor imaging the system came with. I have lived with it for 2 1/2 years since it does the job reasonably well and its a pain to install the new system. I just can't stand being able to pick out each individual driver in the system with out even listening closely.

The only parts of the OE system I will be using is the power to the head unit and the antenna, the rest will be a clean install.

[pingu]

No. Hall sensors internally have 4 electrodes in order to measure the Hall effect (most Hall sensors also have integral electronics, which means that they end up having 3 rather than 4 connections to the outside world). Transistors internall have 3 terminals and so aren't really suitable for measuring the Hall effect. Also, the amplifier would only get a DC magnetic field from the subwoofer magnet - I don't think I've ever seen an audio amplifer that will amplify DC.

[Rustam]

No. Hall sensors internally have 4 electrodes in order to measure the Hall effect (most Hall sensors also have integral electronics, which means that they end up having 3 rather than 4 connections to the outside world). Transistors internall have 3 terminals and so aren't really suitable for measuring the Hall effect. Also, the amplifier would only get a DC magnetic field from the subwoofer magnet - I don't think I've ever seen an audio amplifer that will amplify DC.

I did not relate to measurement of Hall Effect. I related to presence of Hall Effect. Whether there are sensors or not, Hall Effect takes place when current passes within magnetic field...

[genphreak]

I doubt I would bother to upgrade the OE system in my car. It plays music nice and clearly, but any upgrade would just be maintaining the same poor imaging the system came with. I have lived with it for 2 1/2 years since it does the job reasonably well and its a pain to install the new system. I just can't stand being able to pick out each individual driver in the system with out even listening closely.Have you heard the OE system properly driven? Car interiors have terrible imaging, period- glass and various objects like people's legs help destroy it in all sorts of ways too.

I personally don't thnk they got it wrong in the e34 at all, the placement is as good as I can imagine it being without sticking speakers on the windows, and although I can also pick where the sound is coming from the crossover frequencies between the drivers is execllent, as far as I can tell. The front Tweeters and Mids are angled and the rear deck drivers make perfect use of the window angle. The only way I can imagine it being any better is if the OE speakers do work out to have inadequate power limitations (mine doesn't seem to yet) or if they had therefore used larger drivers (and accordingly better amplification) in the rear shelf which was a long way from the norm at the time (and would bias the bass delivery).

If you replace all the drivers, you may be able to improve performance, but you could encounter some niggling sonic issues that they had ironed out very well in the original system. The more complex of the aftermarket eq and crossover systems can help; but more adjustments always means more fiddling. This mic setups I've seen so far that baseline the actual response curves within the cabin are kinda dinky, I haven't heard one that actually true gets results the way they do with PA systems in concert halls- I guess there are too many channel and frequency overlaps in the cabin area- and perhaps small changes in mic location yield big change in response.

As much as I like decent speaker manufacturers, the reality I have found is that composite cones and titanium tweeters (etc.) make for expensive purchases but deliver stuff-all difference when placement, enclosure, size are far more important and must be brought together well if one wants to get the kind of response curves necessary to reproduce music (esp. that made with natural instruments) faithfully. Acheiving this in a car is a hard task. It always works for doof doof music, but with an e34 I have found one can have the best of both worlds- but that is just my opinion. I fear the day when I have to replace an OE driver, cos I am almost 100% sure a nice replacement (say a polk or JBL split system of the same size) would not work as well (though would be better units).

For most people the basic 'tuning' is considered fine tuning so they (ultimately) live with the default result. I've no doubt you can acheive this better than most people but I just am surprised to hear you can the stock system- but do understand. (I also canned it and was considering driver replacements as well until I got a big amp driving the crossover and the sub integrated properly).

It runs great flat with almost no eq at all, no bass or treble enhancement. The only thing I can say is that the highs may not be pronounced enough. Maybe I like it brighter than most, so maybe I should boost the treble just a tad.

However I say all this without seeing the newer premium sound systems, I bet they do a far batter job- but that's for consideration on another day. Tread well and good luck in your quest for good sound!

[joshua43214]

Genphreak--

I pretty much agree with every thing you said. This has been most of the reason I have not bothered to install a new system in the car. Though after reading your post, I am tempted to dig into the original amp and see if I can decipher the Xover's in it and experiment a bit. There is a real issue with SPL between the tweeters and the kick mounted mids that I assume the factory amp dealt with. Or perhaps the factory system never dealt with the SPL problem since at the time car audio philosophy was to always place the tweeters as high as possible regardless of the position of the mids. So if it doesn't look too ugly, I may see what it sounds like with a big amp running the factory crossover system, but my EQ is only 1/2 octave so it may not be able to tune the drivers more than roughly.

One of the reasons I went with compression drivers in the first place is that they high pass at 800Hz. This puts the majority of the frequencies that need to be well directed into one driver. The downside of course is major installation hassles if you want a clean look.

Back in '99 when I put this system together, I spent alot of time researching and talking to car audio people and understood it much better than I do now, since most of the fine points have fallen from my memory. When the system was in the Saab, the sound seemed totaly sourceless. I really have only heard the same quality of staging on high end custom installs where you feel completely imersed in the music. I assume this was partly luck and partly the interior design of the 900 combined with a bit research. Hopefuly I will get similar results in the 540i, Since I already have every thing, it will cost almost nothing to install and if nothing else will make an interesting post for some people.