Hiya,

I have the choice to run my Boston GT40 (4x45W) semi-active or in bridged mode passive (2x140W) into my Polk SR5450 splits. The problem comes in that I have the tweeters in the a-pillar and the mids will be in the kicks.

Im worried that because there is a fair amount of distance between the tweets and mids, it will sound in a better term, weird. Will running the system semi-active help with time alignment issues or will it be a non issue? My head unit has no processing abilities (Naka CD45Z)

The other alternative (which im trying to avoid due to cost and system complexity) is to buy an extrenal processer such as an Audison Bit-One.

Any help would be appreciated.

Running semi-active will not help with time alignment issues. Lots of people run with large distances between the mids and tweeters. It doesn't sound as weird as you'd think, but really will never sound "right" at the crossover point.

As much as off-axis sounds worse as a rule, one compromise (car audio is full of them, get used to it) is to put your tweeters off axis, generally firing at the opposite headrests. This does wonders for pathlength differences, mostly pertaining to SPL of a nearby tweeter versus a distant woofer. You can actually achieve very acceptable staging with this setup, but the tradeoff is that it will be significantly harder to dial in the idea tonality.

Bi amping(semi active) them would be my first choice

Br85, thanks for the info, and yes, the tweeters are certainly off-axis.



Can you tell me why you would choose this over more power?

Cheers

Tuning preference over power, but in your case why not just try them both.
Ive bridged amps before and i didnt get the results i liked.Active was the better choice but ofcourse you need the H unit to do it so my second choice would be bi-amp through the passive crossover.

Thats a sweeping statement, and I would say it depends on the car rather than a hard and fast rule.

umm yes it would, you could set the time alignment for each speaker individually, rather than for each side when run passively

i bridged channels for the front stage and they sound better than ever.. and im chucking 360WRMS into each side. a bit of an overkill but they are loving it, and i didnt have a smaller amp. give it a go and if its average then you can biamp it

bi-amp, or semi-active is not really necessary unless you have the tuning ability, such as time-alignment.

stay passive, focus on your installation and tweeter positions/angles to get the right sound.

Get a pioneer P80RS and go fully active with all the tools you will need for tuning

If you have the processing tools to run active (not using the amps x/over, thats a joke) then it's a good idea to do so, if this allows separated time alignment, and better X/over control.

However more power does help dynamics, and quite often tweeters can sound much smoother
when there is no stress on the amplifier. (however sometimes midbass can sound worse when bridged on poorer amps because the amp has less control at the lower impedence.)

The other problem with bridging amps is, don't assume because the gain pots are in the same spot that the volumes are the same.

in fact 99% of amps are far from that. so the chances of getting left and right equal are very slim without using some test equipment.

There is a way of simply doing this, is by getting a AC Volt Metre, and play a single test tone through the amp (pink noise sorta works too) and measure the average voltage on each bridged channel and keep fiddling till you get them exactly even. Make sure the volume is high enough to give a accurate reading. Low volume readings won't be accurate enough.

kind regards
Juls

Thats interesting about the gains, i guess it make sense since its just a dial and its not exactly the most accurate way of getting this exact without some smaller 'steps' in adjustment.

What on earth is semi active? Either it is an active set up with an electronic pre-amp level crossover or it is a passive crossover. There is always losses involved in a passive crossover setup usually around 1-2dB so in the example above you would be better off going passive with loads of extra power, if you find that the tweeter is a bit too loud you can add an external L-pad to attenuate them some....

semi-active is when you are running the mid directly off an amp and still run the tweeter through the given crossover. that way if you are only starting out you dont exhaust the tweeter with frequencies it cant handle

So what cuts out the high frequencies from the mid??????

You usually put a bandpass on the mid.

This means, a low pass filter to filter any low frequencies you dont want the mid to play and a high pass filter to stop the mid playing any of the tweeters frequencies. So its effectively 2 filters are working on just the one speaker. Kind of like... trimming the ends of the frequency's played

If you do not have the tuning capabilities its easier to either stay passive or get a new headunit that can do it all imo.

This SEMI active caper still makes no sense it is either active or passive....

almost. As everyone else has pointed out...

the tweeters run "passive". That is, they use their own factory passive crossover block to filter the signal to them. They don't use the crossovers at the headunit or amp.

the midbasses run "active". that is, you set their crossover frequencies at the headunit or, if you dont have that sort of processing, at the amp. You bypass the factory crossover block which sits after the amp.

if you combine the two, you have a combination of active and passive...so.....

the reasons why you would do this are:
- it allows for more power to be directed to the midbasses than with a complete passive setup
- it allows the user to be secure in the knowledge that the passive crossover is designed for the tweeter, and is less likely to cause damage by selecting too low a crossover point or by overpowering the tweeter.
- it allows, similar to bi-amping, the user to apply time alignment to both tweeter and midbass, if they have that processing available.
- it is often a good way for n00bs who want to run active to start out, as there is less danger of damaging components whilst still retaining some level of tunability.

But, by all means mate, you can call it whatever you like.

and if you don't mind, the rest of us might stick to calling it "semi active".

cheers!

Seems like a strange way to do a simple job, why not just go active and that way it would be done properly not half arsed but I guess doing things properly is an odd thing to do for some people.....

well...thats one way of looking at it...

the other is that maybe, just maybe the speaker manufacturer knows a bit about the speakers it produces, and has the ability and the wherewithall to design a quality crossover. Who are you to say that you know better 'cause you can select a 3.15khz 12db/oct crossover on your new sony headunit?

Well if you look at it that way why would you ever go active as the manufacturer always knows best, they would never use cheaper quality components to keep the price down now would they?
I would never use a Sony either....

Because the passive units are made to fit everyone and everyone's car. So its made as a good all-rounder.

In the long run (if you know what your doing) its better to go active and tune for YOUR car according to YOUR install imo.

There's the safety of keeping the tweeter protected with the passives, but also there was some talk recently in a thread here that keeping the tweeter running off the passives has a positive effect with regards to the phasing and some other things I don't remember, but it was 'better' then running fully actively.

It's all preference really, if you want the extra safety of the passive protection go for it.

That's interesting... i might have to search for that thread your referring to Louie

Here's the thread

There's a lot of reading, but majority of it is pretty interesting.

nice threadmine Louie...i'd forgotten about that one

also, many tweeters do not have a smooth roll-off at the lower end, so using the passive crossover may employ some complex filter curve to compensate - I know Dyn do this.

also, there is the option of bi-amp.

To be honest, I tend to agree.

I guess a lot of people just use the crossovers on their amp with the crossovers on their head unit to bandpass the midbass. Then by using the passives for the tweeters, it saves the the need to buy a higher end head unit with inbuilt processing - so i guess it makes life a little easier in that way.

Aside from that, it allows people to keep the tweeter protection offered by the factory passives which helps avoid blowing up a tweeter.

Ultimately, for those with the knowledge to tune correctly I would suggest that full-active is the way to go over semi-active almost every time but for those who dont understand the concepts quite as well, it can be easier to just retain some of the passives' controls. Without prior knowledge of the context you're working with, tuning a fully-active system can be pretty much a hit-and-miss affair and that often results detriment rather then improvement.