Speaker sizing question

[accuab]

So I have a buick with the monsoon factory setup that I will be rewiring to be powered off an aftermarket head unit. The rear originally had 4" for highs and a 6X9" for subwoofers. I have since removed the 6X9s because I added a sub. So what size speaker should I put for my rear fill. I obviously don't need all 4 just for rear fill. I was thinking changing the 6X9 hole to either a 5.25 or a 6.5. I would think that the 6.5 would get better mid bass and if I got a two way I could get some highs out it as well. Is this my best option to do what I am after?

[accuab]

Any ideas here?

[CHEMMINS]

I wouldn't even run rear fill. Invest in some better fronts and keep the sub and let er buck. You will probably be much happier with the soundstage anyway. You are not watching movies in 5.1 so surrounds/rears are not a necessity.

[zako]

If you have some kind of coaxial speakers that can fit the 6x9 holes with an adapter, you can always give them a try. In fact, why don't you wire the 4 inch speakers to the stereo? Audiophiles usually run them attenuated, so the brand/size/amplifier does not make a big effect on the result.

For some time I am have been using cheap coaxials as my rear speakers. They were time delayed (20ms or so), high passed at 250Hz, and attenuated to extent where they did not draw the sound stage to the rear. If I was running the same setup, I might have added an inline inductor to each one of them to create a bandpass setup from around 250 to 2500Hz. The added ambiance effect wasn't bad, but since I have switched to running 2-way active front I have lost the ability to send signal to the rear speakers. I think I might try running rear speakers again once I have an advanced sound processor like JBL MS-8 or BitOne/BitTen. One common recommendation is to have the rear speakers made by the same company from the same kind material, etc. I don't know if matching brands for front/rear is that important.

On the other hand, if you want the rear fill primarily for bass, I would say get a decent 6x9 speaker, bandpass it 60-200Hz or so. The fact that you have a stereo powering it could be a problem though. I am personally not a big fan of rear mounted midbasses. (note how my rear fill was high passed from 250Hz). Besides the sound staging issues, I think this could make the midbass frequency response worse or color it in some way. Bass frequencies are a lot more sensitive to phase coherency issues than higher frequencies. With 5 speakers playing midbass frequencies (2 front, 2 rear, and subwoofer) you now need to worry about creating a phase coherent setup with five speakers! The complexity seems not to be worth it. There exist several 6.5 round and 6x9 oval speakers that could provide adequate bass if installed in front with good sound proofing and power running to them.

[keep_hope_alive]

agreed with Zako, as usual.

in my dad's car i've installed rear 6x9 subwoofers that had a natural roll off above 200Hz. 4x6 in the dash. 1990 Caddy. it's weird, i mean, you have the full range replicated, and even off an aftermarket deck you get plenty of output, but when i listen to it i'm disappointed that i can completely located all midbass behind me. he loves it, and that's what matters.

so really, it depends on your expectations.

back in the day we had tiny dash speakers and huge rear speakers - so we just put everything behind us and didn't care. now we have the opposite - hell, i want to stash a sub under my dash. but we were just as happy back then as we are now and the systems are totally different.

if you have subs in the trunk they will distort the rear speakers. enclosing rear speakers works well, but you lose bass up front since those holes are the main pathway for air from the trunk. leaving the holes open results in more bass. most of these cars don't have front door speakers, but have plenty of room for a 6.5" speaker. even if you surface mount a pod and cut through to the door cavity (which i've done) you can get decent midbass up front.

[VWBobby]

Great posts above.

I personally would run either 4" speakers from 200-500hz or so.....or modify the 4" holes to 6.5" and run around the same range. Leave the 6x9 holes open as a blow-through from your trunk for your sub.