[tomlinmgt]

I built a pair of h-frames several years ago that used Eminence Alpha 15a's and fed them a little over 250wpc with a Soundcraftsmen amp. In a 20x23 room playing on their own they sounded fantastic down to the high-30's, but didn't have much authority any lower than that and lost composure when SPL's started coming up above a casual listening level.  When augmented with a pair of DIY sealed subwoofers using 12" Dayton Titanic drivers (positioned on the back wall and with DRC), the bottom of the first octave got filled in nicely and created a solid, robust, fast and musical low end.  However, I didn't have any way to high pass the Alpha 15a's so they continued to be the limiting factor when I wanted to push the volume up. 
The 15a's are long since gone, but I'm wanting to build X-Statiks...and later down the road NX-Oticas...and am wondering if I could recreate the OB sub/sealed sub scenario I had before, but instead use the 12" OB servo subs (one per side) with a goal of being able to play at higher output levels without any of the issues I had with the 15a's. Or, in a room the size of mine, will I need to go with two per side AND the DIY sealed subs if I want to achieve effortless and authoritative reproduction of low end down deep into the 20's at higher volume levels (say, up to the mid 90db range)?

[mlundy57]

I built a pair of h-frames several years ago that used Eminence Alpha 15a's and fed them a little over 250wpc with a Soundcraftsmen amp. In a 20x23 room playing on their own they sounded fantastic down to the high-30's, but didn't have much authority any lower than that and lost composure when SPL's started coming up above a casual listening level.  When augmented with a pair of DIY sealed subwoofers using 12" Dayton Titanic drivers (positioned on the back wall and with DRC), the bottom of the first octave got filled in nicely and created a solid, robust, fast and musical low end.  However, I didn't have any way to high pass the Alpha 15a's so they continued to be the limiting factor when I wanted to push the volume up. 
The 15a's are long since gone, but I'm wanting to build X-Statiks...and later down the road NX-Oticas...and am wondering if I could recreate the OB sub/sealed sub scenario I had before, but instead use the 12" OB servo subs (one per side) with a goal of being able to play at higher output levels without any of the issues I had with the 15a's. Or, in a room the size of mine, will I need to go with two per side AND the DIY sealed subs if I want to achieve effortless and authoritative reproduction of low end down deep into the 20's at higher volume levels (say, up to the mid 90db range)?

If you go with the full size NX-Oticas, go with three 16 ohm 12" drivers per side. You can use two but why? The third driver doesn't take up any more floor space and you get even better performance.

If you are going to go with the NX-Otica MTM then use two drivers per side with the MTMs on top of them, like my Avatar.

With your size room, you can go either way. It comes down to whether wou want two speaker cabinets or four. Either way you can get bass over 100dB down to 20Hz or lower (my duals are -3 at 14Hz). The four cabinet, full size 'Otica / triple servo subs will give you the most but the MTM / dual sub combo is no slouch. My room is much smaller (12 x 14) which is why I have the MTM / dual driver combo. And the bass rocks with these, even in the larger exhibit rooms at the Lone Star Audio Fest.

Mike

[tomlinmgt]

Thanks for the reply, Mike.  Sure, three per side would be the hot ticket, but I have a kid in college and a second not far behind...so budget is of some concern. Ideally, I’d be able get impressive performance and reach my goals with singles per side plus my DIY subs,  but I have no idea how the 12” servo subs perform as singles. I saw Danny tell another guy (who inquired in an older thread about using OB servo singles) that it would work for him in his 11x12 room, but clearly my room is quite a bit bigger and I’ve not been able to find any info that  states at what room volume singles per side will run out of grunt.  I’m thinking that when I build the Oticas I’ll want the four lower mid bass drivers because I’ve heard the NX-Tremes and I want to get as close to that experience as I possibly can. Which I suppose should tell me I need at least two drivers per side in the subs.   

[mlundy57]

Thanks for the reply, Mike.  Sure, three per side would be the hot ticket, but I have a kid in college and a second not far behind...so budget is of some concern. Ideally, I’d be able get impressive performance and reach my goals with singles per side plus my DIY subs,  but I have no idea how the 12” servo subs perform as singles. I saw Danny tell another guy (who inquired in an older thread about using OB servo singles) that it would work for him in his 11x12 room, but clearly my room is quite a bit bigger and I’ve not been able to find any info that  states at what room volume singles per side will run out of grunt.  I’m thinking that when I build the Oticas I’ll want the four lower mid bass drivers because I’ve heard the NX-Tremes and I want to get as close to that experience as I possibly can. Which I suppose should tell me I need at least two drivers per side in the subs.   

In your size room I would expect one 8 ohm driver per side to leave you underwhelmed.

The second driver isn't the big expense, the amp is. If you use one driver per side you still need two amps. Each A370 amp will drive up to two 8 ohm drivers or three 16 ohm drivers. If you start off with two 16 ohm drivers per side, you can add a third driver on top later on down the road very easily. If you start with one 8 ohm driver per side, the most you will be able to add later s one 8 ohm driver per side unless you want to replace the original 8 ohm drivers with 16 ohm drivers. In which case you would lose the money you spent on the 8 ohm drivers. While it may not be the least expensive up front, the most cost effective way to go is to start with two 16 ohm drivers per side. That's about $460 more than what singles would cost and about $460 less than what triples would cost. If you start with singles, it will save you $460 up front but starting with the 16 ohm doubles would save $920 down the road if you ultimately wanted triples.

It all boils down to what your goals and budget are. If budget is the factor between single driver and dual or triple drivers per side, I'd start by just using the sealed subs you already have. That's what I did when I went OB with the Wedgies a few years ago. I started with the open baffle Wedgies and used a sealed sub until I saved up enough for the OB subs. The sealed sub wasn't the best match but it worked and fit my budget.

Mike

[tomlinmgt]

In your size room I would expect one 8 ohm driver per side to leave you underwhelmed.

The second driver isn't the big expense, the amp is. If you use one driver per side you still need two amps. Each A370 amp will drive up to two 8 ohm drivers or three 16 ohm drivers. If you start off with two 16 ohm drivers per side, you can add a third driver on top later on down the road very easily. If you start with one 8 ohm driver per side, the most you will be able to add later s one 8 ohm driver per side unless you want to replace the original 8 ohm drivers with 16 ohm drivers. In which case you would lose the money you spent on the 8 ohm drivers. While it may not be the least expensive up front, the most cost effective way to go is to start with two 16 ohm drivers per side. That's about $460 more than what singles would cost and about $460 less than what triples would cost. If you start with singles, it will save you $460 up front but starting with the 16 ohm doubles would save $920 down the road if you ultimately wanted triples.

It all boils down to what your goals and budget are. If budget is the factor between single driver and dual or triple drivers per side, I'd start by just using the sealed subs you already have. That's what I did when I went OB with the Wedgies a few years ago. I started with the open baffle Wedgies and used a sealed sub until I saved up enough for the OB subs. The sealed sub wasn't the best match but it worked and fit my budget.

Mike

Great I go there, Mike.  Thank you for explaining the lay of the land.

Michael