MA FR HT project

[jonedd]

I apologize that this is long, but I tried to anticipate and answer some questions upfront. If you read this, thanks!

I'm ready to try my hand at building some speakers and was hoping to get some advice from those who have heard a number of different designs. I've read quite a bit over the past few decades but have been too poor and itinerant to be able to invest in the hobby, or even to listen to more than my headphones (which actually are pretty sweet). I've never actually heard a full range speaker or even heard the effect of different box designs, and I live in the boonies, so it's a bit difficult to audition commercial designs. That said, based on theory and philosophy, I would like to build some FR speakers for my new home, but I am wavering on some design options.

The ultimate goal is to outfit a new room (18' x 14'front with a 10ft open back wall) with a 7.2 surround system for music and HT. I don't need astonishing volume. I plan on driving the front 2 ch with a 60wpc SS amp(1st G Densen Beat B100, owned) and the surrounds with an NAD C245BEE (not currently owned), though other thoughts and input would be welcome. The source will be an HTPC which unbuilt, but I think I'm going to use a Xonar Essence card for output. Having the computer as the source is not optional.

My original thought was to use the Alpair 10 G2 all-around, but I have no idea when those will be available or if they'd even be suitable. I've read about the fellow who used the Mark Audio Alpair 12 for a similar purpose, so copying that is a possibility. The room is pre-wired through the walls, so I would like to build wall-mounted surrounds if they would work. Which brings me to my barrage of questions:

1) I've seen the CHR70 sealed wall-mount designs--has anyone heard these? Would they produce adequate SPL, 6 ft from the listening position?

2) How about an Alpair 7 in a similar sealed wall-mount for the surrounds? Overkill for a surround channel?

3) Understanding it would be theoretically easier for the driver and the amp, has anyone heard if adding a sub/woofer audibly improves the overall sound quality, over just supplements the low end? Or, stated differently, should I cut the off the FR somewhere (200hz?--probably needs 2 woofers; 80hz?--too low but could maybe use one sub)? I'm a bit afraid to build a big horn.

4) Probably better asked elsewhere, but if I use a woofer/sub, does anyone know using the LFE cutoff on the soundcard would be an adequate crossover? My impression is that, for bass frequencies, it doesn't really matter.

[planet10]

4/ for HT bass is usually <120 Hz. When dealing with room modes a minimum of 2 subs (running mono) are indicated

3/ HTPC should have bass management, allowing you to cut off the mains/surrounds at 80-100 Hz or so. Freedom from expending themselves producing bass, this sweetens the FR's capacity to produce mid & top.

2/ Alpair 7 is definitely better than CHR on absolute grounds, but will show the warts on a lesser amplifier. Further, surrounds have a daunting task when it comes to optimum dispersion. For surrounds 2 CHR per surround probably win out over a single A7 because of this. (see the splayed sealed surround in the microTower Home Theatre appendix document)

1/ not those specific designs but the milliSize sealed box they are based on. Simple, with outstanding performance at very low cost. The mMarS produce ample volume (for me) in my room at 12' distance.

0/ Madisound is selling CHR70 for an obscenely low price. I suggest grabbing a pair and stuffing them into anything handy that is 5-7 litres and get a feel for the sound.

dave

[jonedd]

Thanks for your reply. I had actually already downloaded your mMarS plan (thanks for publishing all of those designs BTW), but was worried about exceeding the power limit of the CHR70. I was planning on buying some of those drivers anyway while I experiment and build some woodworking skills. I'll try and share my experience, but it could be a while (in addition to a driver, I have to choose a saw).

I noted you're building a 2-way with 4x SDX-7 for the low end. Can you explain your decision. I assume you chose the 7 so that it can cross high, but why do you feel you need four? I had been thinking of using one SDX-10 per side. Any thought on or experience with that?

[planet10]

Originally Posted by jonedd

I noted you're building a 2-way with 4x SDX-7 for the low end. Can you explain your decision. I assume you chose the 7 so that it can cross high, but why do you feel you need four? I had been thinking of using one SDX-10 per side. Any thought on or experience with that?

Actually, SDX7 doesn't go all that high for its size... it starts falling at 1-1.1k. Something i use to advantage. Once treated they do well up to there and roll off smoothly.

I really like the woofer (once at least simple mods are performed), it performs on par with larger drivers, and works very well in a simple sealed enclosure.

But the real reason is pragmatic (and overkill -- but to hit 20 Hz with authority, some subwoofers probably still needed). I ended up with quite a few and they are a hard sell.

I want to make this design a statement... like the cost of a house commercial offerings (but better )

Althou all of the concepts in the design were coming together already, the KEF Blade and a loonngg listening session with the Alpair 7 really gelled what had been a loosly defined project.

I'd like to present both ative & passive XOs. If it works out i know 2 vendors stitting on drivers that would enable a <$1k parts investment (a bit more fully tarted up) to get parlayed into something that would cost 5, maybe 6 figures at your local hifi emporium.

dave

[jonedd]

Well, now that I'm doomed to remain covetous and dissatisfied with anything I build...

I ordered some CHR70s--I think I'll try some mMarS, Castle-Micro-Tower and Pensil R70

I hope this isn't addicting.

[planet10]

Originally Posted by jonedd

I hope this isn't addicting.

Remember the story of the cookie... it is awefully hard to eat just 1... and it sounds like you already have 3 on your plate

dave

[GM]

Greets!

Your Qs imply that you're not 'up to speed' on what it takes to design a successful HT, so FWIW here's a response I made to another recently:

>>>The original 5.1 specs limited the center/surrounds to ~100-7 kHz with, but nowadays all channels are supposed to be 20-20 kHz. Browsing THX certified cinema or consumer systems tells a different story though with ~80-20 kHz being required to meet the top of the line THX Ultra with ~42-20 kHz for the mains.

Anyway, depends on what level of performance you want: Consumer Home Entertainment Home Theater THX.com

Of more interest to the serious DIYer is the Dolby tech library where you can find all the recording/playback details for the various formats: http://www.dolby.com/professional/technology/index.html<<<

GM

[jonedd]

I'm not really interested in designing an actual home theater at this time, 'though maybe a few years in the future. Trying to keep up with THX specifications, I feel would just add complexity and ruin the fun. Anyway, for this room I didn't want side or rear speakers anywhere but on the wall, so (and maybe I'm wrong) I didn't think I'd be able to get decent bottom range without cutting them off to the front.

[giantstairs]

Originally Posted by planet10

0/ Madisound is selling CHR70 for an obscenely low price. I suggest grabbing a pair and stuffing them into anything handy that is 5-7 litres and get a feel for the sound.

dave

Isn't the price the same at CSS?

[planet10]

Originally Posted by giantstairs

Isn't the price the same at CSS?

Looks like indeed they are.

dave