mikel

As above, what type of enclosure do you have for the two 12" subs - you may have serious "suck out" where the ouput from each is cancelling the other. Try switching the phase on one of the subs and see if it makes it better or worse.

In reality your front 6.5" will be rolling off above 55Hz even though that's what the box says. Having the sub take over from around 80Hz is fine. You only want to apply a single stage of filtering which will result in a matched (ie the same cutoff frequency) high and low pass signals. The high pass to drive the front and rear splits and the low pass to drive the sub. Based on your descripton you can do it at either the head unit or at the amps, but you don't want to do it at both. Two cascaded filters (eg one in the head unit and one at the sub amp) set at the same frequency will double (or there abouts depending on the "order" of the filter 1st order 2nd order, 3rd order etc) the slope of the rolloff. Eg a 4th order filter (24db rolloff per octave) is built by cascading 2x 2nd order filters set at the same frquency (each being 12db rolloff per octave). In other words, if there's already a low pass output at the head unit for the sub, you don't need to apply another low pass filter in the sub amp. The same goes for the additional Sony amp. You don't need to set a high pass at the Sony amp if the head unit drives it with a high pass output. If you can't disable the additional filters because they're in built, separate them as much as possible. For example set the head unit high pass/low pass combination at 70 Hz and the low pass at the sub as high as possible eg 140Hz and the high pass on the Sony amp as low as possible eg 35Hz. That way in effect the low pass at the sub, and the high pass on the Sony amp are doing as little as possible. To minimise the filter interaction of cascaded filters, ideally the crossover frequencies should be at least 2 octaves apart (one octave above 70Hz is 140Hz, 2 octaves above is 280Hz, one octave below 70Hz is 35Hz etc). This may not be possible in your application, but your idea of setting the low pass of the sub at 90Hz is on the right track (ie higher than the head unit). The other option is to disable the filters at the head unit and use the high pass in the Sony and the low pass at the sub. Set the crossover at the same frequency (or as close as possible, 10Hz won't make much difference) cheers

old thread but... as Alex said that driver is better suited to a ported box. Suitability Factor = Fs/Qes = 32.7/0.317 = 103 Anything >100 is better ported Anything < 50 is better sealed Anything in between can be used for either. A ported box will give lower bass but require a larger box

if you want to save on space go for a sealed enclosure. a ported enclosure will give lower bass for a given driver but be much bigger

You would need to make sure you had a selectable phase switch on each amp/sub, otherwise you could experience major "suck out", where the subs essentially cancel each other out instead of adding to each other. It's also not easy to predict in advance as it depends on the crossover frequency and how far apart the subs are. If you don't have a phase switch you can just reverse the polarity of your speaker wires on one driver. Worth doing if you don't have enough bass, but not just to fill a hole in the boot.

I read in a recent Zoom or HPI an article by Martin Donnon discussing how over boosting is a significant issue for internal gate turbos when you put a free flowing exhaust on and reduce back pressure significantly. Basically the internal wastegate is not free flowing enough to allow sufficient exhaust to bypass the turbine (ie with a free flowing exhaust, a component of the exhaust finds it easier to keep going through the turbine rather than going through a restrictive wastegate). If you're making boost with the wastegate fully open then the wastegate is clearly not able to flow enough exhaust. The answer in the magazine was some trimming around the wastegate port and increase the size of the flap. If I remember I'll have a look tonight to find the article.

Just got mine installed (everything except the strut braces which I already had). I had to get the rear guards rolled as the tyres scraped with the softer suspension (rear tyres 265 x 35 x 18, rear wheels 18" x 9.5" 38mm offset). The difference between the old suspension (cusco coilovers 10kg/mm front and 8kg/mm rear) and the new is fantastic. I can't wait to try it on the track again. Thanks Matt and Gary for answering all my stupid questions.

Skyline model = R33 GTST front Starcorp rim Wheel diameter = 18" Wheel width = 8.5" Wheel offset = 38mm Tyre size = 235 x 40 x 18 Modifications to fit = nil - plastic insert still installed. Height of the car is ~355mm centre of wheel to guard (SK's kit) rear starcorp rim Wheel diameter = 18" Wheel width = 9.5" Wheel offset = 38mm Tyre size = 265 x 35 x 18 Modifications to fit = needed to roll the rear guards to prevent scrape. Height of car ~345mm centre of wheel to guard standard brakes front and rear. interesting that even when it was 15mm lower than the current height it never scraped with the Cusco coilovers (8kg/mm rear), it's just that all my fillings fell out. cheers

old thread, but I was curious to see what the theoretical response calculated to. I wish Alpine would publish the specs on their drivers, but I found the specs for the 12" SWR 1241D on this website: http://www.thielesmall.com/database.asp Vas =58 litres, Qts= 0.43 Fs = 28Hz building the box at 32 litres gives a theoretical Qtc of 0.72 and an F3 of 46Hz. If you weren't short on space this provides a very good response shape if you're prepared to put up with a small amount of peaking at the expense of some transient response (still way better than a ported box) you can drop the box size to as low as 13 litres which gives a Qtc of 1.0 (as high as I would ever go) and an F3 of 51 Hz - so lose 6Hz of response, but a get little boost in bass so that the ear could never tell and have a much smaller box cheers,

Hi Gary, just had my Cusco coilovers taken out: coil ID 70mm wire OD 13mm # coils 8 on the long one ( is this front or rear? - obviously I'd know this if I took them out myself) # coils 7 on the short one cheers, Mike

80 Hz is as good a place to start as any. It depends a little on whether there's a corresponding high pass filter for the main speakers, ie you have a crossover pair (high pass filter feeding the main speakers and low pass feeding the sub). If you don't then the best place to set the sub crossover is where the main speakers naturally start to rolloff. Then you'll minimise a hump in the frequency response with your sub playing the same frequencies as the main speakers. If you set the frequency too low you'll have a hole in your frequency response in between where the main speakers get down to and where the sub starts. Setting levels between sub and main speakers depends on amplifier gain and driver efficiencies. Do it by ear and if you can get it to sound good that's fine. If not you really need a test tone CD and an SPL meter. This can also show you where your main speakers start to rolloff so it makes setting your sub crossover frequency easier. I assume your bass control is like a tone control? If that's the case try 0 to start until the gain and crossover frequency sounds good and then increase bass if you feel like it. You'd typically set gain and crossover frequency once and forget it once it's right and adjust bass from the head unit. Be careful of having high gain/high bass levels set and playing low tones on a test CD. Unless your sub has a high pass filter set at an appropriate point where your port unloads (say 20 - 25Hz) you can get very high cone excuresion and damage your driver. Normal music typically doesn't have program material down that low, but most test tone CDs go down to 20Hz. Mikel

yes, but assuming both drivers have the same wattage rating, the one with the higher efficiency will produce more SPL at a given rms output of the amp. I completely agree that you shouldn't choose a driver on efficiency alone. Efficiency is just one of the valid specs to look at when choosing a driver, as is size, rms wattage, Vas, Fs, Q, Xmax, etc. Efficiency is important if electronically assisting rolloff (eg using a Linkwitz Transform) as otherwise massive gain is required to achieve the desired response shape. If two drivers met my needs but one was more efficient, I would choose the more effcient driver (assuming similar cost), otherwise you may need bigger amps, with more power drain etc to get the SPL you're looking for.

agreed it completely depends on efficiency of the drivers an 83db driver will be twice as loud (in sound pressure level - SPL) as an 80dB driver at the same power. Your ear may not "perceive" the SPL increase as twice the volume however - psycho-acoustics being what it is

not necessarily simple. a clipping (ie overdriven) amp can easily damage drivers that said a 20 watt rms amp driven into clipping will probably never kill 250 watt rms woofers (tweeters can always be damaged by clipping amps). 800 watts is a very big number for a driver, and it sounds more like total system power or some combination of system power and peak music power (PMPO) - these specs are meaningless. You need the rms ratings of the individual drivers to make sensible judgements. A good rule of thumb is to have power amps above the wattage of the driver. If you hear distortion it's likely to be the speakers and you turn the volume down to prevent damage. In this way your unlikely to be driving the amps into clipping. Judge maximum volume by the sound, not the position on the volume dial. Without knowing the rms ratings on your drivers, go for a bigger amp per channel than eachspeaker can handle, and turn the volume down if it starts to sound like sh1t

your problem won't be easily (or cheaply) resolved I agree completely with the posters above - the sound inside the car is all that counts, but... install more subs, preferably poorly designed ported enclosures for that "boom box" sound - just expect that the sound inside the car will begin to be compromised (that boomy sound is terrible)

If you can fit a small sub in the cabin it will perform better than one in the boot. If you want to install one in the parcel shelf you'll need to build an enclosure beneath it. If you want the lowest bass then 6.5" ain't gonna really cut it - they can't shift enough air - but two (or four) would help. Driver selection is critical - go for the driver with the most excursion (Xmax) possible. For the same driver, a ported enclosure will give lower bass than a sealed enclosure, but the ported enclosure will be much larger. A ported enclosure requires less driver excursion than a sealed enclosure (provided you don't go below the tuning frequency of the port, in which case you unload the port and suffer massive excursion - the reason why many ported subs run a high pass filter set just below the port frequency to prevent damage to the driver) Sealed enclosures enjoy far superior transient response to ported enclosures, so even though they lack the low bass (for the same driver) they have great impact (rock concerts cut off at around 40Hz, but they still have amazing bass). Don't think that because you can't get below 45-50Hz you can't have great bass, you just can't get low bass. Don't build a ported enclosure yourself, unless you're prepared to experiment. Don't get a ported enclosure/driver combo installed unless it's well known and has a good reputation - building good ported speakers requires lots of R&D to get it right - it's very easy to build a badly tuned ported speaker that sounds terrible. Never buy a pre-built ported enclosure and install a driver - ported speakers need the enclosure to be designed around the driver - even manufacturing tolerances can impact the sound of a ported speaker. Sealed subs are far more tolerant of variations in box volume and driver specs. As a home builder of speakers, I only build sealed enclosures, as I can't be bothered endlessly experimenting with box sizes to suit a particular driver. I'm happy to sacrifice the lowest bass for the tightest bass at a higher frequency.

depends on the box size a back of the envelope calculation based on my memory of how big the space is in the back of my R33 says I could fit something around the size of 30cm tall x 20cm wide x 20cm deep - this could be way off but gives a volume of 12 litres. plugging that volume and the specs for the 10" driver from the Jaycar web site into the spreadsheet gives a response of: The F3 (or 3dB cutoff point) is around 48 Hz, not exactly sub woofer territory but not bad. The efficiency is ordinary, and you'll need a big amp to drive this speaker. The Jaycar 12 " is 2dB more efficient, which means it would need a bit more than half the power for the same volume (every 3dB more efficiency means you need half the power to make the same volume or SPL) I'm happy to send the spreadsheet to anyone who wants it - I didn't create it. I'll need your email address, as I can't upload an excel spreadsheet. Mike ps I'm not a car audio guru - my knowledge is all in home audio, but the principles of speaker, amplifier and crossover design remain the same

It appears I can't upload an excel spreadsheet. PM me your email address and I'll send it directly Mike

Can't wait to see it - odd shaped boxes are superior to a normal box as they damp standing waves inside the box - just make it as rigid as possible. If anyone is interested I have a great spreadsheet for modelling what the response will be like depending on the driver. You will need to know the volume of this enclosure and key parameters of the driver you'll be using (Fs, Vas and Qtc). Assuming it's a sealed box a driver with a large excursion is preferable (Xmax should be >8mm), as the cone excursion on a sealed speaker is bigger than a ported speaker. The very best 12" driver for a sealed woofer I've found to date is the NHT1259 - do a search on the web for the specs and plug them into the spreadsheet. It blows just about anything on the car audio sub woofer market away. Unfortunately the only source I've found is Madisound in the US. For a sealed box look for woofer drivers with low Fs (say lower than 35Hz), high Qtc (say greater than .4), large Xmax (say greater than 10mm) and reasonable efficiency (pref >90dB for 1W @ 1m) so you don't need a power station to run it. I also have some simple rules of thumb equations for when a driver is better suited to a ported enclosure than a sealed enclosure pm me if you'd like the spreadsheet and/or the rules of thumb. cheers, Mike

only problem with that is you're trying to work on a hot engine unless you do it over several days. btw when I got mine fixed, my mechanic recommended that I put new exhaust manifold studs in - this may be BS, but while it's all apart...

mine made a whistling noise that was a dodgy exhaust gasket. Still made good power, but frustrating. Unfortunately lots of stuff has to come off to replace the gasket

Matt, transfer completed at my end, PM sent. Mike

Gary, are the bank details in the original post still current? I'd like to put an order in cheers Mike

Famous fully comprehensive cover all mods have been stipulated on the policy $760 per annum being old has some advantages Mike

I tried Mobil 1 on my crunchy gearbox (R33 GTST) and when it didn't make any difference I put a tube of Nulon in which made a marginal difference for about 100km. Just put in Redline shock proof light weight and had an instant improvement - still a bit notchy but not a single crunch yet after about 200 km and a track day.