HT Sealed Mains with Vented Center?

[diesel_88]

I'm looking at Zaph's BAMTM (sealed) for a combo music/home theater setup. WAF is a high priority, and a big speaker hulking over the TV Is Not Acceptable. Had a crazy idea....

I understand that for HT, it's a good idea to have identical left-center-right speakers for "seamless" front sound effects. What if I were to design a smaller center channel speaker (using, say, the DA135, cousin of the DA175), and make it a vented alignment so it could reach as low as its bigger siblings. Then tweak the box alignment and maybe put in a high-pass filter so the center speaker matches the low-end rolloff of the mains.

WinISD suggests this is possible, with transfer functions matching pretty closely down to about 50 Hz and -6 dB. My receiver supposedly starts the rolloff at 80 Hz anyway, so that would push the "mismatch" level down even further. The power handling would of course be different, but I listen only at modest volumes, so that's probably not a biggie.

What other issues would I face doing this? I am a relative newbie...wisdom, please?

[Hezz]

It would be better to have the right and left mains as vented since they will carry more bass information. THe main purpose of the center is voice quality and for this a vented is not really the best option. Although it can work well if designed properly but this usually requires a larger not smaller box. Tuning a small box puts the vent tuning up near the vocal range which is not good for natural sound reproduction in that frequency range.

You can make the center channel smaller and use an aperiodic vent which is my preference and there is less box resonance to mess up the vocal range. Or get drivers that can be nearly critical Q sealed alignment in a smaller box. Having identical drivers across the front is not that important unless you are trying to put together a state of the art system. In which case you will need to forego most of the WAF to do that. But having drivers with a similar cone material across the front is a good idea.

[diesel_88]

When you say "tuning a small box puts the vent tuning up near the vocal range," do you mean the "organ pipe" resonance of the port?

So identical speakers across the front are not required, but similar material is a good idea. I assume that holds for tweeters as well?

I think maybe I need to put down WinISD and take a deep breath. Thanks!

[sreten]

Originally posted by diesel_88

I understand that for HT, it's a good idea to have identical
left-center-right speakers for "seamless" front sound effects.

Hi,

Often quoted and likely in the context of garbage.
Different but similar balance quality speakers will work together.

Venting the center will double its box volume and it not particularly
desirable if filtering at 80Hz, the same applies to left and right, the
larger vented boxes only make sense if used unfiltered IMO.

http://www.eldamar.net/audio/RS150MTM/

Will work with the BAMTM and you can use the same tweeters.

/sreten.

[Hezz]

Originally posted by diesel_88
When you say "tuning a small box puts the vent tuning up near the vocal range," do you mean the "organ pipe" resonance of the port?

So identical speakers across the front are not required, but similar material is a good idea. I assume that holds for tweeters as well?

I think maybe I need to put down WinISD and take a deep breath. Thanks!

Yes, often a small box reflex will have tuning in the 50-60hz range. Since male voice can reach down to around 80Hz and the port (vent) operates over a range that will go up a little higher than it's tuning this can give a somewhat unnatural resonance to male voices. With a larger bass reflex the tuning is quite a bit lower and less of a problem.

The thing is that stuffing speakers into the smallest box you can and venting is usually less than desirable for a center channel. Since bass response is not really that important for the center channel it's best to focus on designs with better timbre and lower group delay properties. Like low Q sealed and aperiodic designs.

Keeping the drivers across the front with the same material helps to some degree to insure uniform timbre between the speakers but still the crossover and overall design of the speaker is probably more important than this. For a first time builder, unless you are following an established design it is a good idea to use forgiving drivers like mineral filled poly woofers and mids and linen dome tweeters.