I’m on the verge of buying another amp and because I only want to run two amps, it will determine what head unit I buy and whether I run the system passive, semi active or fully active. The gear I already have are Focal K3Ps, a Boston G512 DVC sub and a Boston GT-42 amp. If I go fully active I would go for a Clarion HX-D2 or otherwise a Pioneer P80RS.

I’m trying to decide between another Boston GT-42 (4ch) or a GT-28 (2ch)

If I get another Gt-42 I can go fully active but the sub will be a little underpowered, yet adequate. The GT-28 will be more than enough for the sub in fact enough for two if I want to add another later but I can only go semi-active or passive. The choices I have are as follows.

PASSIVE
I could bridge the GT-42 to run left and right (rather than front and rear) which can give me 350W each @ 2ohms to drive the K3Ps. The GT-28 will drive the sub 1000W @ 2ohms

PASSIVE or SEMI ACTIVE
Using the GT-42 for the front I would run the midrange and tweeters off the front channels and the mid-bass off the rear channels which gives me 75W each @ 4ohms. Once again the GT-28 will drive the sub 1000W @ 2ohms

FULLY ACTIVE
Using two GT-42 amps Each driver gets 75W @ 4ohms and the sub gets 350W @ 2ohms

My questions are:

If going fully passive I get the most power by bridging but I understand that bridging is not the best for sound quality but how much does it affect it?

If going passive or semi-active how much control would I probably have over the tweeters?

If going Fully active I won’t be giving the sub as much power but is that much of a big deal? I have tried the G5 off the rear channels of the GT-42 and thought it would be okay but if I heard it off 1000W it could change my mind!

Overall I would like suggestions as to which amp to buy and whether to go passive, semi-active or fully active.

Cheers


Doug

If it was me i'd go fully active.



Any well designed amp won't increase THD by a noticable amount when loading the amp down within spec, so you should be fine there.

Go Semi-active, and get Yanddy (Audio Art & Tech) to design you a custom passive for the mids and tweets. He is the best guy in the country for this (slight bias here, I havent heard anyone else... ). Thats what Im doing. Passive is alright but not that good, active is good (but personally, I dont think anyone can ever get the emotion of the music through, or warmth) and custom passive is ausome.

As to bridging, you prolly wont notice the increase distortion, so dont worry about it!!

Would the custom crossovers be better than the stock Focals?
edit: Sorry I just read what you said again and the answer is obviously YES

And what about the sub? I've never heard a big sub running off heaps of power for very long to make a comparison about that. The GT-42 drives it as I said "adequately" but would you guarantee I'd like it a whole lot better with more power behind it?

Most of the time I listen to the average music they play on the radio but sometimes I like that Bass & Drums stuff as on the "Two Tribes" CD

see ya


Doug

I've just been reading Shiny Car's thread from a while ago asking who's running active and it sounds like a lot of work, (very interesting read though) but I think I'll stay passive and get the GT-28.

Yep, should definitely go A&T and see Yanddy as he has a demoboard where you can compare (stock vs custom). It is not cheap to build one from scratch but its worthwhile to ask him and modify your stock crossover to see how you like it.

A vote for fully avtive

The custom passive sounds like a good idea but they're vehicle specific aren't they? I'm not sure I'll be keeping this vehicle all that long.

I've made up my mind to get the GT-28 but whichever HU I get will have the ability to go active. So I'm trying to nut-out how to go active with just those two amps, K3Ps and a sub. Would it be any good to run the mid-bass and midrange together instead of midrange and tweets?

That really depends on how much you spend on the Xover. The more expensive they are, the more tailored they can be to your vehicle. That being said, if you swap cars, you really only need to replace a few components at a really small cost to account for new vehicles (unless you go from a kombi to a convertible to a saloon!!). They are more tailored to your gear, and the placement inside the vehicle then the vehicle itself, and obviously to your taste and style of music.

No, not better. Worse. The reasons mids and tweets are run off passives is their need to 'blend together' to produce a nice sound. Fully active systems cant properly recreate a blend between the mids and the tweets that a good passive can recreate. For example, I have Harry Connick Jnr's 'She' album and was listening to it on a mates active system about 2 months ago (He has 3 way Dyn's in full active config). In one of the songs, there is a really nice trumpet playing in the background, to the left of the snare drum. On his system, the sound was quite distinct and seperate from the vocals, and so removed that 'warm' feeling when all the instruments blend nicely together.

The other reason is of course, cost. The lower the frequency, the more expensive (and larger) the coils, caps and resistors required to Xover a speaker. Therefore to custom Xover a tweet/mid combo will require smaller and cheaper parts then a woofer/mid combo (all parts of constant quality here). Passive Xover's for a sub are usually quite large (about the size of a high-tuned port in a box) and arent really worth it. Active here is more cost-effective. So the general rule is active for low-frequencies and passive for sensitive frequencies (vocal ranges).

Thanks for that

Yeah I will always have a van. I was just thinking it would be good to have greater control over the tweeters, like time alignment. Then it would be less of an issue where you put them (I imagine)

I was doing some more work in the vehicle last night and it just hit me if you go fully active, you need a lot more speaker cable going to the front. And considering that you have RCA's going from the front to the back as well, that's a LOT of cables.

I'm thinking about mounting the HU in the back. Then I could leave the old stocker in the normal pozzy, and that would be a good deterant for theives! But it would be a real pain bending round all the time to change discs. I don't know, coming up with all these ideas just makes for more decisions to be made.

cheers


Doug

Time alignment can be built into a passive if done properly. You first determine placement, and THEN mod a passive to suit. It does take time, but the results are definetly worth it.

Depending on the size of the passive (most customs tend to be quite large) the amount of cable vs active is negligble. This is because the passive is so big, its in the boot anyway. Attached is a photo of Yanddy's own car at the AutoTechnika. You can see the passive.

As with headunits in weird places, your only limit is your imagination there mate good luck!!

Holy crap

Very nice. Those look like bullets down the sides. Certainly looks ready for action.

You know I still can't make up my freakin mind about what to get next, if anything. I was on my way to Audioart today to see about the P80 and it hit me like a ton of bricks that the flip face would drive me nuts. I'm too old to get used to doing things differently.

Then later on I was going to go ahead with the HX-D2 but it's that extra grand, so that didn't happen either. So the struggle continues.

Thanks for your suggestions and I'll give the custom passive consideration

cheers


Doug

Bullets?? I think you are referring to the business cards there mate....

Good luck finding what you are after. The possibilities are infinte!!!