Built not bought…. In just 9 days!
The UK distributor of Crunch at the time ProPlus LTD who also took care of brands like Precision Power, MB Quart, Soundstream and Cerwin Vega Mobile to name a few asked me to design and build a really quick sound system in under two weeks with absolutely no budget for materials or a vehicle for.
The brief was simple, The brand chosen, the car picked and the rush started.
Lets get into some Hardware pictures and specs
Picking what eqipment to use from the range of Crunch Audio proucts was easy, They clearly thought out a few steps ahead and made a range which works well together. Unfortunately they didnt have a single mono amplifier capable of what i needed so an old school Atomic 3000D was used for the bass.
I was impressed by availability of the two channel 3500 being able to drive an array of midbass drivers, Way ahead of the game of many top end manufacturers back then who have only in the last couple years now caught onto the need for high power 2ch full range amplifiers.
The ten P1 12″ Subswoofers were chosen for their power handling and xmax which worked great in the clamshell design and hit my target bandwidth, The tweeters although very common over many brands, A generic design from china but work great for their ability in high SPL and easily replaceable diaphrams, Great projectivity and low crossover point, There was the option of 6″ or 8″ drivers for the screamers but nothing smaller to fit the bandwith i was looking for so a set of components were picked. They were wired so i could swap between the onboard silk domes for daily driving and the Titanium Screamers for playing at shows.
I used my Volkswagen Golf GTi mk2 as it was just sitting around at that point and we obviously needed a car for the project
I managed to bag a high output alternator via another friend that came from Mark Smith’s crazy Orion Golf, it was already modified with the correct pulley and was an easy swap. I also managed to blag a pair of Optima Red top AGM batteries from my good friend Lenny, thank you!
If this large case Mercedez alternator kept 20kw+ of current hungry Orion Audio gear going then we have no issues with supplying the small amount of current needed to run this system, I never saw voltage drop below 13.6 even when really driving the system hard for long periods of time.
I designed the clamshell to be efficient, Using the Soundstream MBQ 7-B EQ i was able to get a solid 5v peak down to the Audiocontrol DQS which then drove it up to a further possible 7v. The DQS provided me with the tools to balance the amplifers even before touching the gains, on these cheaper amplifiers i didnt have the confidence in the input boards so i bypassed all the onboard filtering and gain circuits. Having that reliability and flexibility from the DQS is key, Driving the amplifiers input boards at their optimal levels is crutial to be confident in turning up your system to the max without worrying about distortion or power compression killing equipment.
Sound System Equipment List
|Crunch Audio Crunch P1-12D4 Subwoofer||12″ Stitched Surround|
Dual 4 ohm VC
3000 wrms @ 1ohm
2000 wrms @ 2ohm
1000 wrms @ 4ohm
18db crossover network
|Crunch Audio CS4CX Coaxial|
Crunch Audio CR4BT Super Tweeter
|1″ Neo mylar tweeter|
Kapton Voice Coil
|Crunch 1200.4||150 wrms x 4 @ 4ohm|
300 wrms x 4 @2ohm
600 wrms x 2 @ 2ohm Bridged
|Crunch Audio CRSS8.4 Midrange||8″ Pro midrange|
Poly Cotton Spider
|Crunch 3500.2||900 wrms x 2 chan @ 4ohm|
1750 wrms x 2 chan @2ohm
3500 wrms x 1 chan @2ohm
The Door Builds
The idea of having an array of drivers along the bottom of the door gives the possibily to blur the point source of midbass, this does three things: Minimizing localisation, Provides higher SPL from the increased radiating area and helps mask distortion. Not something those that lean towards Sound Quality over SPL would try to attain but in this intance they worked very well in keeping up with the 10 “12 subwoofers.
The frame was built from the door out as oppposed to how its usualy done. I used threaded rod to ensure i could really pull the doorpod to the metal doorframe as tight as possible. The top section of twin mid and tweeters was built as an afterthought sadly, The plan was to work the mids and tweeters up higher but time and funding wouldnt allow for it.
Enter The Clamshell!
The enclosure was designed for low power around 100 to 150 watts per Crunch P1 subwoofer, With 10 at my disposal and 3kw on tap i could have designed for power handling, a narrower passband and more efficiency at the cost of extended sub bass and a big loss in percieved depth. It had to be loud for shows but also be able to give demos for long periods on a very limited power supply and not destroy this entry level gear every week! The idea was clear, the execution wasnt.
I thought about various safe designs whilst going through playlists deciding what kind of sound i was looking for.
Most designs i concieved of where typical half cabin height enclosures subs up with the port running across the back window using the cabin length to be able to generather longer wavelengths, Ideas came in various configurations i just was never happy with the bandwidth available and the issues in phase running multiple subwoofers, I could have opted for more the more powerfull range of larger diagphram sized drivers on the Crunch lineup but to achieve something cheap to play loud cone area and efficiency is king.
I went back to basics and decided that a sealed enclosure might work better for the style of music id be playing, It would give me the softer roll off i was looking for with a natural transition up into the 80-125hz region i knew i had most likely over 1kw of headroom to play with on the Atomic 3000D so a shallow 6db 60hz LPF was programmed into the AudioControl DQX and a fair bit of gain was applied to bring the levels back up.
After designing several iterations of sealed enclosures, building test boxes and plotting these outside and inside the Volkswagen Golf’s cabin it was clear to me that a Clamshell could give me not only the space to fit 10 subwoofers in a sealed enclosure but help reach the bandwidth goals in mind.
A clamshell design has certain features and rules to be followed, Somewhat like all orders of enclosures they require some undersanding of the space outside of the enclosoure. This is something i see very well documented and understood in the HiFi community, Well practiced in the music studio and have godlike status in the PA industry.
Understanding and evaluating the enviroment that a speaker is playing in is as important if not more important that the enclosure itself in respects.
A clamshell as its described generaly features a wide open mouth with the subwoofers opposing eachother. This clever enclosure style when designed badly can casuse a lot of phasing issues but done right can be smooth as silk.
Generaly when trying to fit lots of subwoofers in a car you can come across phasing issues where the deepest subwoofers are slightly out of time alignment with the ones right at the front of the mouth, pressure across all drivers needs to be equal, when you burry drivers deep into an enclosure problems can occur. The hardest design challenge (see the image below) can be for this particular issue is the Tunnel arrangement.
You can clearly see the subs at the front have less airspace immediately behind them than the ones at the back. The opposite is true of the mouth, The net result should be equal pressure across the entire bank of subwoofers.
The clam can also be ported down the middle at the throat or ported outside like a 6th order bandpass.
The Donated & Scrap Wood Build
There was no financial resources available for buying the kind of quantities of MDF and mateials i would normaly use for a build of this type, Even though it would be quite low power oscilation of 10 subwoofers at 100-150wrms each would cause some vibration. Tripple baffle’s…? No chance… Very little materials for bracing or dampening material.
I had to scrimp and scrape and find bits here and there, Get seriously Creative, Organised and Methodical with offcuts too! I had no time to digress or work problems, They had to be solved on the spot.
I have to say a massive thank you to the The Beulah Spa Harvester manager for donating a couple of old 6″ fence posts which made for great internal bracing.
I spent some money on sound deadening for the doors and boot and bought a box of expanding foam to fill up all the cavities i could find ensuring i could solidify the rear end as much as possible within budget. It also seemed fit to use some red fur for the enclsoure and give the install a somewhat respectable finish to represent the Crunch Audio brand.
It got featured on TalkAudio
After a short while the car was (total suprise to me) featured on the Talk Audio website by the LEGENDARY, Larger than life Mr Adam Rayner, God bless you sir for this feauture and trying to break the stigma, The great chats on the phone and all you do for the car audio community!
VIEW IN PDF
As if that wasnt enough for two weeks!
The car was not in or ever would get to the state of show worthy vehicle, It was never meant too, But it did make for some serious bassing fun!
I did make the effort of refreshing the engine with new seals, A freshly reconditioned gearbox and i ported and skimmed the head, With all the added weight i wanted things to be reliable.
I also went to the length of painting the entire car over and fitting coilovers. It was some rush job for sure!
I never thought id make it but it was done in just 9 days, I guess it shows but it did sound mean! Shocked alot of people that you can get savage with just about any gear, its how you use it and set it up that counts. I still remember peoples laughing faces not expecting to be hammered. It was never something i would build for myself but it was sure fun to have for a while and hurt some peoples egos aswell as breaking alot of stigma!