Sizing speakers to a room

[Rbrockman]

I have been doing quite a bit of research as I contemplate building my next set of speakers. One of the areas I need to better understand is how to correctly size speakers for a given room size.

My 2-channel setup is in a 28' x 30' x 9' room which is around 7500 cu/ft. The listening distance is 10' from the speakers. There is no HT usage in this room. The current setup includes the Modula MT speakers and a sub which I built to explore the sat/sub route. I have now decided I want to eliminate the sub and build a set of full range main speakers. I also want to significantly enhance the listening experience with improved dynamics and bass at a higher volume level (~90-105db)

Are there some basic criteria which can be suggested to ensure that the proper driver configuration and size are selected for a given size room? Additionally, what characteristics are more important in a music only rig than with a HT setup?

Thanks for any input and I'd really like to hear some discussion on this topic.

[cotdt]

That's a pretty decent sized room, perfect for the ModulaMT's as it is. You really only need to worry about the room when it is small like mine. My ModulaMT sounded boomy with a port and once I stuffed an old sock into the ports the sound was much more balanced. In a larger room I would have kept it ported.

[---k---]

It sounds like you're on the right path. I don't think there are any rules of thumb of what size drivers, how many, ect. you need. There are just to many varibles. You can have two speakers with 6" drivers, but one will have a small xmax and the other will have a big xmax. Big difference. Same with distortion, ect.

Looking at projects here, you might like the Statements.

[Rbrockman]

I guess what I'm hearing is that there is no magic bullet. I was hoping to hear some thoughts around driver configuration (MT, MTM, MTW, MTMW, etc.) and about woofer driver sizing. Perhaps I need to do some more research around fundamental pros and cons around these configurations.

Although sounding very good, my ModulaMT's have earned the nickname the "mini-me" speakers because they aren't able to fill the room they are in with the dynamics with which a much larger speaker would be able to.

For instance, here are 3 speakers which are quite different in configuration and approach:
Zaph ZRT - http://www.zaphaudio.com/ZRT.html
Troels Gravesen DTQWT - http://www.troelsgravesen.dk/JA8008_DTQWT.htm
Jim Holtz Mini-Statement - http://www.geocities.com/cc00541/MiniStatements.html

I'm sure these are all great speakers. However I would expect them to have some basic strengths and some weaknesses because of their inherent designs. In any given room, I'm sure they have a certain "signature" sound which separates them from each other.

It is this which I'm trying to better comprehend, and learn from those on this forum which much more experience than I.

[Jed]

If dynamics is a requirement, I'd imagine you'd want something that can move more air with multiple drivers- especially in the bass. A MT won't even come close to something like an MTMWWWW or WMTMW can do for dynamics.

[---k---]

As soon as I saw Jed had last responded, I thought, "why didn't I recommend his LineUp speakers in addition to the Statements."

[Rbrockman]

If I may continue to probe this topic for further discussion.

First of all, thank you for the input and specific recommendations. Much appreciated.

What I'd like to summarize so far is that moving air is very important for dynamics capability.

How this air is moved is what I'd like to discuss a bit more. For example;
- Jed's Tombstone uses a single large driver in combination with a MTM
- Jed's LineUp's use 4 much smaller WWWW drivers.
- Jim's Statements use 2 mid size WW drivers
- Zaph's ZRT uses 2 mid size WW drivers

I would think that perhaps what might be desirable for HT usage (excluding sub usage), and what might be desirable for 2-ch music would be somewhat different. I also think that room size would effect which configuration and format is best.

The goal here is not to seek a specific speaker recommendation, but to understand the driver configurations which work best in differing size rooms for 2-ch music listening.

[Jed]

The goal here is not to seek a specific speaker recommendation, but to understand the driver configurations which work best in differing size rooms for 2-ch music listening.

If your current speakers sound a bit small in your room, more than likely it is because they can't fill the room with enough sound to meet the dynamic requirements that you have. That's why I recommended multiple drivers originally.

The Tombstones use the highest quality drivers-Seas excel and a custom DXT tweeter, which may be getting replaced by a SS6600- but that's another matter. The goal in that system was to create a speaker with the most neutral midrange as possible. The midranges are in a dipole configuration, which IMO is responsible for the absolutely clean and coloration free sound. There is no box or midrange tunnel to reflect sound back through the cone, instead it augments the output in the room to create an even power response. The woofer was mounted low to avoid floor bounce cancellations, and in this case a 10" woofer is placed in a sealed box for the fastest transient response. Once you get used to sealed bass, you really can start to hear the slop in a lot of ported speaker systems. Even though the ported speaker will go lower, it's response does not match that of most rooms, thus creating a peaky bass response. A sealed box has a smoother rolloff in most room situations, therefore it creates a more natural sound. It takes some getting used to though, as many are used to ported box sound.

A speaker like my Dynamic 4T, which uses 4 RS180-s in series parallel will have more dynamic capabilities than the Tombstones, but the Tombstones are still my reference because of the tight clean bass they provide, large soundstage, and great detail on the top end. They are really expensive though- but I find the Excel drivers better than Dayton (at a point of diminishing returns? some question that, but it is a personal choice on how much the best sound is worth to you).

Using a bunch of woofers like used in the Lineup Series or Dynamic Series offers a few other advantages other than the output potential. The line of drivers help to smooth the bass response because there is more surface area radiating in a line that would otherwise influence room induced cancellations, and there is lower harmonic distortion because the workload of the drivers is split up. All of these factors lead to a better sounding speaker.

So, a design like a Scan Speak/Seas/Dayton 2way may sound absolutely killer at lower volumes, but add more power to get some slam and things start to fall apart much much quicker than a large woofer system MTMW or multiple woofer system WMTMW/MTMWWWW.

[---k---]

Jed's answer was great. To add to it, when you talk about moving air, you need to think in terms of displacement when comparing one configuration to the next. To calculate displacement, look at the effective surface area times twice the xmax. If you do this you can see whether a big 10 woofer displaces more than 2 or 4 5" drivers.

[Rbrockman]

Excellent replies, and thank you again for sharing.

I'm also led to believe that in general using less xmax to generate the same displacement will lead to lower distortion?

This is becoming much clearer now and adds to the interest in this hobby.

[Jed]

Excellent replies, and thank you again for sharing.

I'm also led to believe that in general using less xmax to generate the same displacement will lead to lower distortion?
.

Harmonic distortion is largely influenced by many factors of motor design. Xmax is only one. That being said, I'd check out some of the distortion measurements of various drivers at mark k's page, zaphaudio, and my site has some too- This will help you see the trends in various driver lines and their respective performance.

[---k---]

I'm also led to believe that in general using less xmax to generate the same displacement will lead to lower distortion?

That is correct. Drivers are not linear. The closer you get to a drivers xmax, the more the distortion. BUT, this does not mean that drivers with less xmax are better. Zaph has a page that say so, but it is specifically for woofers with xmax in the 20-30mm range.

JonW and I got together recently and listen to his 2-way TM with very expensive ScanSpeak drivers. In my opinion, his did somethings better than my big WMTMW w/ Dayton RS drivers (about 1/6 the cost, per driver), other things not so much. I think at reasonable volumes with not so complex music, his speakers were able to show off their very low distortion better sounding drivers, and it sounded better. But, as the volume was raised and the music more complex, I think his might have been getting pushed far enough that it became audible - still not bad. Mine sound better because I'm asking less of each of my drivers and they stay more linear. Jon has a thread where it got discussed. We're hoping to get together again around Christmas and do some side-by-side listening.