Building a high-end audio system for top sound quality in the Boxster

[newBgeek]

In the late 80s I was deep into car audio and built a DIY competition system in a 280ZX turbo, which consistently won the best sound quality award at car audio events. I also had a chance to listen to dozens of other competition vehicles and I would like to share some of my personal secrets and opinions for fellow Boxster owners who would like to achieve the highest levels of sound quality in their vehicles. It's actually quite simple and there are only 3 main points that are really required for high sound quality.

#1. You must select the best sounding component speakers. While this may sound obvious, I can't stress enough that the speakers must take first priority above everything else. Do a lot of careful listening before selecting your component speakers and forget coaxials. There are no coaxial speakers that will get you to that top tier of sound quality, and only a small percentage of component speakers would qualify. It's also a mistake to think that more speakers are better. Ninety percent of the sound energy from the best sounding competition vehicles came from the front component set.

#2. Speaker location and enclosure design. While it's impossible to get great sound from poor quality speakers, it's easy to screw up the sound quality from great speakers with a poor installation. The best enclosure in my opinion is a sealed enclosure to stop back waves from cancelling front waves or adding harmonic distortion. Avoid using the door cavity as an enclosure unless you like boomy, distorted music. The tweeters should be located within line-of-sight, and as far away from you as possible for the best imaging and to minimize side-bias. In low-seated cars like the Boxster, my favorite location is the kick panels. If you think it's weird to install tweeters by your feet, sit in you Boxster and point to the dash speakers, then point to the kick panels. The 20 degrees or so of angle difference is insignificant compared to the extra distance you are going to get. The first question that every person who sat in my 280ZX was "where are your speakers?" because with proper imaging, you can't localize the sound.

#3. Plenty of clean power. While the internal head-unit power is fine for the average car stereo, it should not be used in a high sound quality vehicle. Head unit power is rated at a different standard than external and is always over-rated, while high quality external amps are always under-rated, so that competition vehicles can "cheat" by producing more power than their power class. The Alpine amp that I selected comes with a certificate of actual measured power, which is always going to be higher than the rated power. You will need this power to handle the dynamic peaks of music and to overcome road noise.

When done right, it's possible to achieve a level of sound quality which is comparable to a very good home audio system. When heard in a car, it is such a surprise because that level of sound quality is so unexpected in that environment. Imagine driving a lonely mountain road with your favorite opera playing with true-to-life sound quality, in perfect harmony with the singing flat six engine. It sounds like a commercial, but it can actually be quite an amazing experience.

[newBgeek]

When selecting the component speakers, I first turned to Google and found the #1 rated speakers were the Hertz HSK165XL, so I found where they were sold and went for a listen.

I first listened to their top-of-the-line speakers, the Mille MLK2TW components that retailed for $1400, but at the time was on sale for $800. They were horrible. No musicality and extremely harsh. Cars with these types of speakers are what I like to call Torture Chambers.

Next were the HSK165XL. These were much better than the Milles, but I still found them overly harsh to my ears. These were $500 at that time.

The next speakers at $400 were the HSK165 (without the XL) and these were much better. It had the same dynamic punch as the XLs but a much more natural and smooth presentation, and very balanced. I briefly compared these to the Alpine R series component speakers and there was no comparison. The Alpines weren't even in the same class. They also had a cheaper Hertz component set from their Dieci line for $200. There was a notable drop in quality. These sounded cheap, hollow, but inoffensive, similar to what you would find with typical component speakers in factory systems. So I decided to go with the HSK165.

I also decided to replace the dash speakers like so many others have done. These would only be used for top fill only, so I didn't want to spend a lot of money. I compared the Alpine SPS410 with the Hertz Dieci DCX1003. They were both awful, but the Hertz had a more natural sound so that's what I picked. The Alpines had peaky highs and mid-bass, typical of many coaxial speakers, sounding like you had already hit the "loudness" button on the receiver.

[newBgeek]

I initially thought about creating a custom sub box in the space used by the rear storage cabinet, but after examining the space, I realized I'm never going to get a decent sub in that tiny space. Any space saving sub, even the factory Bose sub, is going to be a compromise. So I decided the best way to get decent base is to use the existing sub enclosures in the doors, but replacing the drivers with the ones from the component set. While plastic isn't the ideal enclosure material, there was no other way to get a decent sized enclosure in such a tight space.



Here is a comparison of the existing door sub, and the speaker that will replace it.

There are other threads which detail the modification the existing door enclosures, so I won't get into the details. I used 3/4" MDF to create the baffles. These baffles will be screwed into the enclosure since I don't trust any glue to withstand the constant pounding of such a large magnet. They are shaped to be as large a possible, while still fitting inside the door panels.



I used the trim piece as a template for the screw holes.



Here is a photo of the attached baffle, with plenty of Goop to ensure that it is airtight.



Here is the right-side enclosure with the wiring connector attached. I just pulled it from the front and re-drilled another hole in the side. This allows me to snap the connector back into the existing socket in the door. I used the existing wiring in the doors after I realized it is virtually impossible to run a new wire in the existing door harness without pulling out the door and harness, which would have been too much work.



Here is the finished right-side speaker enclosure installed. Note that the trim ring, which is not shown here, is used to dampen the sub enclosure. Since the baffle used up 4 of the screw holes, I cut the trim ring and attached the last 2 remaining screws to get at least some dampening.

I was a little worried that I wouldn't be able to fit the tweeter in the driver's side kick panel due to the fuse box location, but it actually doesn't get in the way. You do need to cut into the door a bit, but the space behind is empty. This was cut with a hole saw with the kick panel out of the car, but the fuse door still attached.



I used a dremel tool to slowly expand the hole until the tweeter just snapped in. The fuse door can still be removed easily without the tweeter popping out.



Here are the finished driver's side speakers.



The passenger side kick-panel didn't come out as easily, so I just pulled it back and cut the hole in-place, putting a piece of wood behind to ensure I don't drill into the wiring harness behind the panel.

Dash speakers are one of the worst locations for speakers, because the back waves reverberate through the dash producing virtually 100% harmonic distortion.



I attempted to dampen the back waves by cutting up some old T-shirts and stuffing them around the dash speakers.

[newBgeek]

I chose the Alpine MRV-F300 4-channel amp for it's flexible configurations and small size, so that it will fit beside the existing factory amp. My plan was to bridge the Alpine to power the component set at 150W per channel, and use the factory amp at 40W per channel to power the dash speakers.

While there are slight differences in sound quality between different amplifiers, I personally wouldn't worry about it, just buy a quality brand and as much power as you can afford while still fitting in the space that you have available. And avoid buying amps that are designed for subwoofers to drive your component speakers.

For the head-unit, I chose the Pioneer DEH-X8700BS for it's ability to play FLAC files and HD radio. Call me old school, but I still wanted a CD player as well. I also like how quickly Pioneer seems to connect to Bluetooth devices.



Here is the wiring run for the RCA cables and speaker wires for the tweeters, into the very convenient grommet behind the battery, all nicely loomed.



Here is the finished install of the amp and crossovers. I pulled the door wires from the factory amp harness using suitable sized drill bits to push the pins out and wired the door speakers up front. The tweeter speaker wires were sent to the cabin in the loom. I used a dremel to open up some space to sneak the wiring through the plastic case behind the spare tire, and up through another grommet behind the amp where there is a convenient grounding bolt for the amp ground. I used some left-over 8-gauge power wire from my car audio days to wire the power for the amp and a 40-amp in-line fuse that is connected close to the battery.

With the spare tire in place, there is zero loss of storage space, and no lost space in the passenger compartment. So there is no compromise in driving pleasure or usability.

[newBgeek]

I hooked up the amp and head unit first and did some preliminary listening as I was replacing the speakers.



The factory dash speakers, I would classify as junk. Comparing those with the replacement, there was a huge improvement. I can certainly understand how most people would be pleased with replacing the dash speakers. There is finally some bass where there was none before and much clearer highs. However, in hindsight, the dash speakers were a totally unnecessary step as they are trounced by the component speakers and add very little to the overall sound quality of the final product.

In comparing the door speakers, which are just a subwoofer in the stock system, I was stunned at just how good they really are with proper power delivery and matched with the component tweeters and component crossovers. I believe it is due to the large voice coil and magnet for the small size of the speaker, and that they were specifically designed for that enclosure. They are 2 ohm speakers, which will draw a little more power from the amp, but modern amps should handle them with no problem. The sound was a bit shallow in the upper bass, but punchier in the lower bass. However, at this point I had already converted one side so I was committed to do the other. The component woofers from the kit are very good as well, not as punchy in the lower bass as the factory subwoofer, but have a much broader sound. Anyone who wants the most bang-for-buck might consider only the HT25 tweeters and component crossovers that came in the kit and save themselves a bunch of work by not replacing the subwoofers.

Overall, the final product has met with my expectations. The bass is very good for a system without a true subwoofer. Playing DJ Magic Mike's Ultimate Subwoofer Test won't rattle the windows, but you will feel it in your chest, and it will find anything that vibrates in your car. The drum beats from Fanfare for the Common Man from the IASCA test CD are very powerful and very convincing.

The tweeters are wonderful, and I don't heap praise lightly. They are among the best that I have heard. Very clear, bright, detailed, and without a trace of sibilance. Female vocals really come to life. The trumpet attacks on John Williams Duel of the Fates is spot on and will have you grinning. You will be searching your music collection for high quality recordings.

Regardless of the genre of music that you enjoy, jamming to Stevie Ray, Country, or Classical, a system that is musically accurate will be able to play it back as the producers intended. It's not that hard or expensive. It just takes some very careful planning and your Boxster can have the sound quality that is as luxurious as the brand deserves.

[flaps10]

Great write up.

[Prelude Guy]

Awesome write-up!

I am an audiophile as well. I have always enjoyed creating SQ setups in my car. Before the Internet, I used to build the best system I could with popular name-brand products. Now that the Internet has allowed us to research lesser-known brands that are higher-end, the experience is even better.

I just recently built a system in my 1997 Accord wagon. It was some-what of a budget-build but I was looking to try new products. Given the low front speaker location in the front doors, it was hard to get a good-sounding speaker. I was introduced to Focal so I tried them. They are coaxial speakers. I was still blown away by them!

Ill definitely check out Hertz!

Do you think a custom box for a small sub like a Kicker 40CWRT672 or JL Audio 6W3v3-4 could work in the passenger side footwell under the "glove box"?

I wish I could hear your setup.

Keep the updates coming!!

[Smallblock454]

So your high end system has tweeters that entertain your feet. Nice, but definetely not high end for the ears . maybe in the 80ties. Sorry.

Today we have electronic x-overs, time alignment, phase correction, multi band eq's. No need to entertain feet anymore.

Regards, Markus

[newBgeek]

Originally Posted by Prelude Guy

Awesome write-up!

I am an audiophile as well. I have always enjoyed creating SQ setups in my car. Before the Internet, I used to build the best system I could with popular name-brand products. Now that the Internet has allowed us to research lesser-known brands that are higher-end, the experience is even better.

I just recently built a system in my 1997 Accord wagon. It was some-what of a budget-build but I was looking to try new products. Given the low front speaker location in the front doors, it was hard to get a good-sounding speaker. I was introduced to Focal so I tried them. They are coaxial speakers. I was still blown away by them!

Ill definitely check out Hertz!

Do you think a custom box for a small sub like a Kicker 40CWRT672 or JL Audio 6W3v3-4 could work in the passenger side footwell under the "glove box"?

I wish I could hear your setup.

Keep the updates coming!!

I wouldn't really consider myself an Audiophile. Maybe an audio enthusiast of perhaps audio realist? I'd take solid state over tube any day and I believe a skilled producer will do far more for sound quality than whether it was recorded in 16 or 24 bit. In other words, let your ears be the judge.

While it is amazing how a clean bottom octave can transform a car audio system, I don't think you can get there with a compact sub without serious intrusion. In the words of Scotty, "I can't change the laws of physics!" In order to get clean, deep bass, you really need to be able to move a lot of air, which means a lot of area, a stiff cone, a very long throw, and a big strong magnet and voice coil for precise cone control. I would say that even 1" of lost leg room would be too much of a compromise, since we buy these cars for driving pleasure above all else, and the leg room is tight as it is.

That said, the bass from the stock sub enclosures is pretty darn good, clean and well controlled, and that's either from the stock subs (note that I had the enhanced audio with the larger sub enclosures) or the upgraded components woofer that I replaced it with. It's not a boom car by any means, and I personally am not interested in boom cars, and this from a guy who used to have a 15" sub with a 20 lb magnet in the hatch!

[newBgeek]

As a teenager, my first car was a beat up station wagon that I picked up for a few hundred bucks. I was an audio enthusiast even back then, so I did my best with what little funds I had. I put a couple of Radio Shack Minimus-7 speakers (very well rated compact speakers back then) and screwed them to the roof by the tailgate. I had an old home-made house speaker with a blown midrange and tweeter, but a working 12" woofer and threw that in the back to use as a sub. Bought a cheap amp and threw that into the spare tire well. What I got was simply outstanding! Amazing sound quality that would blow away most car systems even today. So what did I learn from that experience? Just carry house speakers in your car!

But seriously, when you think about it, if you took the compact speakers that you listen to at home and shrunk your listening room, all of a sudden those small speakers that sounded OK in a large room will sound a lot better in a much smaller room, because of the smaller space you need to fill. Bass response improves, and the energy level of the speakers is much higher. If you took high-end bookshelf speakers, and put them in a small, carpeted listening room, they would sound fantastic. When you look at what I did with the Boxster, they are basically sealed bookshelf speakers turned on their side.

As far as tweeter placement, what I always do is to put the tweeters on extra long wires before I install them, then use double-sided tape to stick them in various locations and do very careful listening tests. I believe the spot that I picked is the best location because you get the greatest distance and minimize the delta between the left and right tweeters, improving imaging. It also helps to surround tweeters with carpeting for a slightly cleaner sound. But listen for yourself and stick them wherever you want.

[Topless]

There are two obstacles to getting great audio in a car environment. One is creating a well designed sound system that puts music into your ears. The other is overcoming the inherent noise floor of a sports car. Limited space hinders the first. More importantly a sports car is pretty damn loud at highway speed, in some cases exceeding 80db. If you develop a system that produces clean audio up to 110db (rock concert levels) your effective dynamic range is only 30db. That doesn't rate HiFi in my book.

My solution won't appeal to everyone but works great for me:
ipod with lossless music library and these:
Westone UMPro 20 - Clear | Sweetwater.com

Full range, flat response, reference monitor quality IEMs that attenuate the noise floor by 25db when properly fitted. This brings the background noise level down to a typical living room so I can listen at normal levels while still getting good dynamic range, and eliminates all the standing waves and resonant frequencies found when measuring the sound space in a Boxster interior. Definitely not a fun car project but if reference quality sound is your goal, this is a good way to go. Just another option to consider.

[newBgeek]

My competition car scored 116db in the SPL tests which was on the low side since I was tuned for sound quality. The average was about 118-119 with the loudest cars hitting 125. I'm running the same power in my Boxster and from general impressions, I'm probably hitting very close to the same levels.

With the top down and the windows up, the Boxster cabin is an amazingly quiet and refined place to be, and you can enjoy your tunes at moderate listening levels, and still be able to have a conversation with your passenger or be able to hear sirens. On a busy freeway, the noise from other vehicles becomes a problem and you really need to crank it to overcome the noise, so it's nice to have that flexibility.

Also, the decibel scale is logarithmic, so every 10db gain has 10X the sound intensity, so a 30db gain actually has 1000 times more sound intensity which qualifies as hi-fi in my book.

While I don't think it's ever a good idea for a driver to wear headphones, I'm also a headphone junkie and got my start in real hi-fi with a pair of Sennheiser HD430 headphones which were an amazing headphone in it's day and still one of my favorites to this day. Headphones are great to use as a reference sound due to their very low distortion levels and high quality per dollar spent. A very good reference headphone to use to setup car audio systems is the AudioTechnica ATH-M50x. They are very clean with strong, extended bass that is slightly on the heavy side, but is what you want in a car environment. If you can setup a car audio system to sound like these, you have done very well.

[TrumpyAl]

Originally Posted by newBgeek

stick them wherever you want.

Personally, I'd have made a very specific suggestion where

Thanks for the write up, a very welcome one with some useful information.

[alm001]

Originally Posted by newBgeek

Also, the decibel scale is logarithmic, so every 10db gain has 10X the sound intensity, so a 30db gain actually has 1000 times more sound intensity which qualifies as hi-fi in my book.

While this information is not incorrect, I believe you misunderstood Topless's comment regarding dynamic range.

With an 80db noise floor (his example, not mine. But I can measure it next time I take the car out) you lose a lot of information because you only have a 30db "window"

From a quick search, here are the dynamic range capabilities of various media;
78 RPM Phonograph = 40 dB quickly reduced to 30 dB and worse due to wear
Compact Cassette = 50 dB
Digital 16 Bit Audio = 96 dB
24 Bit Audio = 144 dB

So while a snare may measure 116db at your ears, a soft piano key may fall below the 80db floor, and get lost. You can overcome this with equalization and compression, but you end up with stifled dynamics.

Probably not helpful, I just wanted to clear up dynamic range vs max spl.

[newBgeek]

Originally Posted by alm001

While this information is not incorrect, I believe you misunderstood Topless's comment regarding dynamic range.

With an 80db noise floor (his example, not mine. But I can measure it next time I take the car out) you lose a lot of information because you only have a 30db "window"

From a quick search, here are the dynamic range capabilities of various media;
78 RPM Phonograph = 40 dB quickly reduced to 30 dB and worse due to wear
Compact Cassette = 50 dB
Digital 16 Bit Audio = 96 dB
24 Bit Audio = 144 dB

So while a snare may measure 116db at your ears, a soft piano key may fall below the 80db floor, and get lost. You can overcome this with equalization and compression, but you end up with stifled dynamics.

Probably not helpful, I just wanted to clear up dynamic range vs max spl.

Yes, I get what he meant. I was just making the point that 30db is actually a lot more dynamic range than what the numbers might suggest. We want a 90db or greater noise floor in our music source so that we can have absolute silence when the music isn't playing. Gone are the days when we could set our music volume by the noise we hear before the music starts playing! True, we are going to lose some of the nuances of the music due to road noise, especially during quiet music passages, but that is true with any car. Is it still worth doing a decent stereo in the Boxster? If you have a stock or mild aftermarket exhaust, then absolutely. If you have a racing exhaust, it's probably not worthwhile.

Most of us drive the Boxster because it makes us feel special. Sometimes we just want to put our foot in it and hear the song of the engine, which is great. Other times we just want to cruise and turn on some cruising tunes. It's nice to have a sound that is rich, lush, and wraps around you like a warm blanket. It just gives the Boxster that extra-special feeling of refinement.

[alm001]

I agree, always worth it to upgrade the stereo.

I'm making slow progress in my current car, but all my previous cars have had extensive work done.

[Topless]

Yep, most of my audio experience is in pro sound, not car audio so I do have an appreciation for excellent music and and understanding of the relationship between dynamic range and SPL. The other half of this topic not yet discussed is the effect of driving around in a car every day with music at 110-115 db. Hearing damage is pretty certain and once they are gone, they are gone. Choose wisely gents.

https://www.google.com/search?q=osha+spl+chart&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari#imgrc=NADVANC4d8NHeM%3A