6.5 vs 5.25 in MTM

[augerpro]

Hi everyone. I need some advice. If I were to build a 3way MTMWW or MTMW what would be the tradeoffs of using 6.5" or 5.25" as the mid?

This speaker will be used for 2ch music and HT, sometimes at higher volumes, thus the multiple drivers. I've been reading some of Dr. Floyd O'tool's (sp?) findings concerning power response and it's effect on SQ, and some of the drawbacks concerning the MTM layout and it's off axis lobing around the wavelength between the mids' acoustic centers. Smooth power response and minimal cancellation between mids will be a design goal with these. Given that, I decided to use 5.25" for better HF off axis dispersion and the ability to have closer acoustical centers, minimizing off axis lobing.

So what am I losing by going this route? Low distortion even at higher volumes is important to me. Obviously the 6.5" would keep distortion lower at any given SPL. I assume power compression would be lessened at any given SPL with the larger woofer. So what else should I consider?

[Paul W]

To keep excursion low, you'll likely use a little higher xo frequency with the 5". A higher xo places higher demands on overall woofer quality (high breakup frequency, low distortion etc etc). Music "lives in the mids" so the 5" is a good choice but, especially with a higher xo, consider matching quality in the woofers.

You didn't mention budget, but the Seas MCA-15 offers excellent price/performance.

[augerpro]

Thanks Paul. The woofer section will be either two 6.5"s or one 8", so either should be able to cross well with the 5.25" between 300-400 Hz correct?

My budget price is about $40-60 per driver. Currently I plan on doing a roundup of drivers to see which one I like. On the shortlist: Aurum Cantus F1 or MK2 series (or both), Peerless HDS Nomex, Seas L series, and one or two others I haven't decided on yet.

[Paul W]

Another possibility for the mids would be the smaller Peerless Exclusive. I haven't tried them yet, but they look great on paper.

6.5 or 8" woofers will certainly do 400...but, playing loud, the woofers could easily run out of headroom before the mids. 10" (better yet a pair) should take care of the bottom end.

[augerpro]

I was curious about the Peerless Exclusive, but every measurement I've seen doesn't suggest that it performs any better or is any easier to work with than the HDS Nomex. I believe all the HDS use the same motor? Anyway considering I find it pretty ugly the lack of extra performance took it off the short list. But I'm open to more info on the difference between the Exclusive and Nomex.

I should mention that <60 Hz will be handled by a sub. So I think two 6.5' or one 8' should be fine? Still not sure of the pro/con there either. That will be a another thread in the future.

[ThomasW]

I was curious about the Peerless Exclusive, but every measurement I've seen doesn't suggest that it performs any better or is any easier to work with than the HDS Nomex. I believe all the HDS use the same motor? Anyway considering I find it pretty ugly the lack of extra performance took it off the short list. But I'm open to more info on the difference between the Exclusive and Nomex.

I wonder what's posted here?

http://www.htguide.com/forum/showthread.php4?t=11700&page=2&pp=35

[augerpro]

I wonder what's posted here?
http://www.htguide.com/forum/showthr...0&page=2&pp=35

Thanks Thomas. That thread is now favorited! So the 830883 is a very good performer, with the 882 possibly a little better as afar as HD and CSD? As far as the comparison with the 830875/832873 Nomex driver there were just a couple comments but no actual measurements. But I beleive the gist of it is slightly higher HD, but smoother FR with the Nomex?

I really wish the Exclusive wasn't so ugly, so I could just go with that and be done with the whole argument. Maybe I could just paint the flange black, the phase plug wouldn't really bother me much if the rest was black.

Regardless, this thread is more about the size of the mid. Once I figure that out I will buy a number of drivers for my own testing. Maybe even buy an Exclusive AND Nomex just to satisfy my curiousity.

[mmoeller]

I would love to see some Peerless Nomex 830875 comparisons. I too dislike the look of the Exclusive. If the measurements are comparable, then the Nomex would be a good one.

You might want to try out the 6.5" and the 5.25 Nomex to see the difference your looking for here.

I think it may be a matter of preference once again. I heard the RS three ways with the RS150 and the RS180. My personal choice was the 150. Not that it applies here, but you get the idea.

[Paul W]

Gotta agree Exclusive performance looks a lot better than the LOOKS!

Suggestion for the woofers...run down SL's "SPLmax" spreadsheet on his site and then run the numbers. That spreadsheet is quite easy to use and does both monopole and dipole. I was assuming a sub, so still recommend 10" to reduce excursion/distortion. (Last night, I listened to a pair of 18" crossed to an IB at 50Hz...clean headroom is good :W)

[augerpro]

Paul I know what you're saying, but I just can't see building a box big enough to accomodate a 10". I'm envisioning either a tall slender mtmww baffle or a tall slender trapazoid baffle if I use an 8". Looks are somewhat important here, I just don't see a 10" fitting in. However, I'll be crossing that bridge after i've done the mid and tweet shootout and I'll be posting for some advice on woofers. if you know a 10" that would require a small box, by all means let me know. i'll crunch the numbers and see just how big the speaker box would be.

mmoeller i'd love to buy one of everything for testing but I have to stop somewhere I have a budget of $250 TOPS for the mid testing. Then it's tweet testing. I can't justify to myself spending $1000 on test speakers when the actual speakers will only cost $1000. At that point i could have just as well bought Seas Excels or Revelators in the first place! I do want a wide variety to test, but I can only do that if I stay with one size, either 5.25" or 6.5".

[augerpro]

Well I think I'll go ahead with the 5.25". I think it's the right compromise for what I'm trying to do. Currently i plan on getting the Aurum Cantus 130MK2, Peerless 803882, and Seas L15. Any other woofers <$60 I should consider?

Also I plan on building a 2way bookshelf for each for comparison listening. What would be a cheap tweeter to use for them? Must be fairly flexible as far as XO frequency, and not bring any attention to itself. I was considering the Seas 27TDC or maybe the Vifa D26NC55.

[augerpro]

Added the Audax AP130Z0 to the list.

Paul: I've been thinking more about what you've said. i'm starting to think the woofer portion is going to be a headache. The first big problem I see matching sensitivity. I hate to use two mids for more headroom just to pad the hell out of them just to match one 8" or 10". Am I wrong?

However, I was planning on biamping since i already have a decent 7 channel amp with two channels unused. It's a Boston Acoustic A7200, basically a rebadged Sherwood Newcastle A965. So I started thinking I could solve the BSC and only having one woofer by using some gain on that channel. That way I wouldn't have to pad the mids as much (I may not anyway, but just kind of thinking ahead). How can i do this? I figured the DCX2496 is an obvious answer, but that brings in active crossovers and the whole project quickly gets out of my skill level. Any advice?

[Paul W]

You can generally use mids in series rather than parallel. That'll get you the SPL headroom with little/no padding. With drivers in series, cap values go down so you can upgrade quality. Inductor values go up, and you can use higher R air cores as part/all of the padding.

The DCX is a really good option because you can make small adjustments without a phone call to Mad or PE...BSC or basically anything else you want to do. The delays etc are valuable functions that are very difficult with passives. In the long run, the DCX can be easier than custom passive networks. (The only time I use passive anymore is when I run out of xo channels.)
Paul

[augerpro]

Thanks Paul. Still kind of confused. If I go from one woofer to two, I gain 3 dB. But then if double the impedence I lose 3 dB. So how does wiring them in series help? As compared to just running one woofer? I suppose for any given SPL each woofer would be doing less work with two woofers, so distortion would be lower. Hmmmm...

One other question: does the DEQ2496 do EVERYTHING the DCX2496 does, just with a couple extra features and supposedly better internals? I thought I read that, but partsexpress makes no mention of a crossover function in the DEQ2496.

Thanks everyone for being patient with my silly questions. I'm a pretty quick fellow just getting into the hobby so I'm in that strange situation of understanding complex concepts but totally unaware of simple details h:

[Paul W]

You are 99% there! Sensitivity to a given voltage input is different than maximum SPL output. Maximum SPL output is the same whether series or parallel. It takes more amplifier voltage swing with series drivers, more current for parallel; power delivered to each driver is the same either way. Assuming an adequate amplifier, in both cases maximum SPL output is limited by driver displacement.

The DEQ and DCX are quite different. The DEQ is basically a parametric equalizer with a very nice RTA function, the DCX is a crossover.

The DCX is more capable for your purpose because, in addition to the xo filters, it has PEQ and delay functionality for the individual driver outputs...that allows notching breakup peaks, trimming driver response, etc, etc.

Both boxes are useful...the DCX for driver adjustments, DEQ for room compensation. The DCX can be used for both, but it can run low on DSP horsepower. Buy the DCX first and then decide if you want/need the DEQ.