Planning for my some-day reference system

RockLeeEV

Member
2010-09-24 9:40 pm
Disclaimer: I don't know much about speaker building, and I don't plan on building this anytime soon for financial reasons, but I want to get started on some general plans to make a modified design based on an RBH T-30LSE. Why rip it off? because it looks amazing; but it's limited edition! By the time I ever have money to buy one of those, they'll be long gone! If I ever do DIY this, then I can't make cost an object. I mean if a pair of T-30LSEs retail for around 15000 a pair, i guess that can be the "budget" for a 3-speaker front stage, give or take.

By modified, the differences I'm leaning towards are

-taller, wider cabinet, maybe like the T-3 configuration over T-2 configuration. I still plan to use the same height from the ground for all the drivers, just add some extra cabinet space, and maybe passive radiators up there. The dimensions of the T3 are

91.75" H
13.25" W
18" D

and the dimensions of the T30LSE are

60.5" H
15.5" W
18" D

So given these factors, I think the dimensions for my box, with 3/4 HDF as the cabinet material, will likely be somewhere around

92" H
16" W
20" D

-Dual 12" subwoofer drivers instead of a pair of 10s, and maybe passive radiators instead of a port - with the larger cabinet i think this could work

-a front stage of 3 matched speakers instead of a L/R pair + Horizontal center (note: I'm not sure how to go about this, since the L/R are a mirror pair.


General configuration

Tweeters - The T30-LSE uses a trio of scanspeak 9500 lined up on the inner baffle. Hey, it's DIY, why not go with a step-up from that!? 9x[3 per speaker] ScanSpeak D2905/9700 in a truncated line array (ahem "dispersion averaging array). Who knows, I might even go with the scanspeak revelator, although the price for 9(possibly 15 if you factor in surrounds) of those sounds like they're overkill - is it?

M/T Crossover:

I'm leaning towards using a close or same crossover design to what the T30lSE already does, which means I need a woofer that'll blend really well around the 2.2 khz range). I'm also considering active crossovers and bi (er... tri?) amping.

What should I look into? The key is being well spaced, and with HQ parts all over the place for max linearity. How was DIY crossover making the first time you did it?

MidWoofer:

12x [4 per speaker] 6.5" woofer with genuine phase plugs. I don't neccessarily need the aluminum that RBH used in theirs, but comparable speed, power, precision, and power handling are a must. What kind of impedance woofers should i be looking at in this scenario (let's assume the amplifier to be a trio of Emotiva XPA-1, one for each speaker's tweeter/mid sections. Or should I go with a built in class D amplification?)

M/W crossover

On the T-30LSE, there is no m/w crossover - it basically relies on the natural rolloffs but I'll probably go with a true crossover of some sort. maybe active.

SubWoofer section

I'm also unsure on this section. A couple general thoughts i've got include:

-Would a subwoofer section on the center compromise the sound? Most people seem to go with a horizontal T-1 to pair with the surrounds which makes sense in a lot of situations, but in my planned scenario it'll be behind an acoustically transparent screen

4x or 6x 12 inch subwoofer drivers (2 per speaker)
8x or 12x Passive Radiators at 12" (4 per speaker)

I'd have to model some drivers to see which 12 would work best. Undistorted extension down to 15 hz maybe, with a HPF at around 12 hz? Or is this simply too low?

And powered either by a plate-amp or pro-amp.

Again, the biggest difference between my DIY and the real thing is probably ported vs PR. I'm not sure if that's the way i'll ultimately go but it's just the way i'm leaning.

So on that note, give me a ton of recommendations for woofers to consider among the other questions i had. I have all the time in the world to make changes, this is more of like a dream project or something and it probably won't be my first speaker build by that time either on that note. I just want to have it written down what i'm aiming for. Any suggested design modifications are welcome as well including other tweeters i might want to look into. One other idea i've got floating around up there is a transmission line instead of a port or PR.
 
Disclaimer: I don't know much about speaker building, and I don't plan on building this anytime soon for financial reasons, but I want to get started on some general plans to make a modified design based on an RBH T-30LSE. Why rip it off? because it looks amazing; but it's limited edition! By the time I ever have money to buy one of those, they'll be long gone! If I ever do DIY this, then I can't make cost an object. I mean if a pair of T-30LSEs retail for around 15000 a pair, i guess that can be the "budget" for a 3-speaker front stage, give or take.

Have you heard them? My guess is probably not.

Just because something looks amazing, doesn't mean you should build it.

jeff
 
With a speaker like that this thread should be in the multi-way forum.

[IMGHTTPDEAD]http://www.rbhsound.com/images/products/t-30lse_grille_off.jpg[/IMGHTTPDEAD]

One would need to listen to make a proper judgement, but based on appearances one can make some general inferences.

0/ a big huge monkey coffin with lots of shiny drivers. That has a definite appeal to a certain part of the market.
1/ 3 widely spaced tweeters. If you use multiple tweeters, they should be VERY closely spaced, and as close to filling the space between floor & ceiling as possible. A distant listening position is required to get integration. It also needs to be accompanied by floor-to ceiling mids.
2/ optimum bass usually requires the (sub)woofers sited in a different position than the higher frequency components.
3/ given that you have 2 big (sub)woofers XOed at 80 Hz, below which everything is omni, one could get big advantage with mounting them push-push... this would really help with problems caused by ...
4/ a speaker this big made with 3/4" HDF and with minimal bracing and not well executed
5/ a passive 80 Hz XO... with the components needed for an XO this low, and all the issues with XOing where the driver impedances look like a roller coaster, it would probably be cheaper and certainly sound way better with active woofers.
6/ even with just a single tweeter the array of mid-basses is too widely spaced to support a cross-over as high as is used.

The way to approach this kind of project is piecemeal. Look at it as 2 powered subwoofers + 2 sattilites.

Since you are financially constrained, you start small and work up. What you learn during the journey will inform where you get in the end. And i bet it won't be where you think you'd like to be today. We all learn so much on the journey.

dave
 

mayhem13

Member
2008-09-22 4:37 am
While i agree with MOST of what you've posted Dave, a clever designer COULD pull off the top section with 2.5 way topology on the mid drivers and power tapering in the way of series wiring on the top and bottom tweeters. Lots of XO components and design time but it just might work.......really well.

Passively working in those two sub drivers.....that's not so good.

Either way, i wouldn't want to have to move those around at all!
 
First, you need to clarify your goals: do you want good sound, good looks, or to impress your friends? This might sound facetious, but it's a serious question. What do you want? If you don't know, you're unlikely to get it.

What sounds good to you - based not on looks, but extended listening sessions with your favorite music - might come from some rather unlikely systems. The more you listen, the more you should be ready for preconceptions to be destroyed. I often hear speakers at hifi shows that sound much better than they should, based on looks. And I also hear many speakers that have great reputations and top reviews, and sound just dreadful.

Second, I have to warn you: the complexity, difficulty, time, and expense is a square (or even cube) law of the number of crossovers in the speaker system. Translated to English, a full-range speaker is the easiest, consisting of driver selection and the right enclosure (and you could do a lot worse than check out the Planet10 site for some very interesting designs).

It takes anywhere from several months to several years to master designing a two-way system, depending on how good you want the final result to be. This requires getting some kind of PC-based measurement system, by the way. Off-the-shelf (or "textbook") crossovers do not work. You have to measure, and learn how to make an accurate and repeatable measurements. If you are not willing to do this, stick to kits or pre-designed systems with good reputations. If you go this route, build them exactly as specified - most important of all, do not swap drivers from the specified models.

Three-way systems: This is where the deep waters begin. I started designing speakers in 1975, and never really liked any of the 3-way systems I designed. My current system under design is essentially an augmented 2-way, with a subwoofer and a supertweeter. I find three-ways to be very, very hard to design - the big problem is a lack of coherency. By that, I mean the system sounds OK at one volume level, but the sound disintegrates when it is quiet or when it goes loud, drawing attention to all the different drivers, instead of sounding like a single, large driver. Just getting a three-way to sound as good as a single-driver table radio at quiet listening levels is not a trivial task - very few succeed.

Four-way systems: Speaking only for myself, I've yet to hear a four-way system that sounds coherent. They must exist - but I haven't heard one yet. Going the full-active route, with a stack of power amplifiers, a flexible active crossover, and a good measurement system is probably the only way to make this work. This is so ambitious that some people give up speaker design entirely after attempting a 4-way project.

Moving on, a passive crossover at 80 Hz is a very bad idea, particularly with the great choice of self-powered subwoofers we have today. Power amplifiers are not at their best below 100 Hz, and putting a crossover in that region creates ripples in the impedance that creates a very difficult load for nearly any power amplifier. If the impedance dips are severe enough (4 ohms or lower), it can threaten the survival of the power amplifier. You shouldn't have to buy a 1-kilowatt arc-welder amplifier just to compensate for poor crossover design. (A rather famous speaker, well-reviewed in the audiophile magazines, has just this design error, with an impedance dipping down to 2.5 ohms in the 80 Hz region.)

A self-powered subwoofer solves several problems at once; it relieves the main amps of delivering power at the lower edge of their working range, and removes the need for a very expensive, very large, and very heavy passive crossover. (Large inductors and large caps cost big money - more than the drivers, which is a hint there is a conceptual design error.)
 
Last edited:
Don't mean to sound negative, but crossovers have a steep learning curve. There are many well-reviewed audiophile speakers selling at quite high prices that have badly-designed crossovers, resulting in uneven frequency response, high driver distortion, and ragged polar patterns. A good crossover, by contrast, controls driver excursion (which lowers distortion), has flat response at the listening position, and smooth control of off-axis frequency response.

Referring to this forum, a single-driver system gets you from build to good sound the quickest way possible. Coherency is never an issue, but heavy-metal or full-concert sound levels require a sophisticated approach. The folks on this forum are here to provide guidance; this is probably one of the best sites in the world for single-driver speakers.

If you choose to go to the dark side and go for a multiway system, there is of course the "multi-way" forum. The hardest task isn't driver selection, even though that's the most fun part, but the hard slog of crossover design, diving into the theory of filter slopes, phase shifts, driver spacing, and the effect on polar pattern. The waters are pretty deep here, and the rarity of well-designed speakers, even at the high end of the industry, is a testament to the difficulty involved. Consumers don't look at the ugly crossover hidden deep inside the speaker cabinet, but it's the difference between a bad speaker and a good one.

These days, there are very powerful digital crossovers, combined with measurement systems, that let you twiddle with all kinds of crossovers, and hear the result for yourself in real-time. You do need a stack of amplifiers, but the power requirements are much more modest in a system with active crossovers, since each amplifier is only handling a limited frequency range, and clipping in one frequency range is much less audible than a full-range amplifier. 60 watts per driver is plenty in the real world, unless it's a PA system.
 
Last edited:
Why wait on an unrealistic budget, for a speaker you haven't heard, and probably wouldn't be all that great anyway.

You've gotten some excellent advise here already, and I would hurry over to the fullrange/single driver section and ask a few questions.
Once you've heard a good single driver speaker, you may decide that you've found your home, as so many others have.

I personally own, and have designed, both single driver speakers and multiways and can tell you that even a 2-way's crossover can be rather daunting to correctly design.

I concur with dave (planet10) on his general conclusions formed from looking at the picture.

Best Regards,
TerryO
 
Lynn,

Which brand digital x-over would you recommend for such an endeavor?


regards,

The ubiquitous Behringer DCX2496, combined with a PC-based measurement system. The opamps and associated electrolytic coupling caps are trash, but that doesn't matter much when tuning a speaker, and plenty of people have info on replacing them with decent modern types. It's even more convenient that the analog section is on its own board, separate from the main digital board, thus easy to modify.

The ADCs and DACs and digital processing section are excellent, and don't need to be tweaked.

The real danger with any multi-amped system are turn-on and turn-off transients destroying the tweeter. If you're curious, I'd move that question, along with any others relating to using the Behringer or any other of these digital wonder gizmos, to the multi-way forum. This is way off-topic for the Full Range forum.

The best advice for the OP is to spend some quality time listening to fullrange speaker systems using a variety of drivers and cabinet styles, and make a decision if that's his kind of sound or not. One Fostex or Lowther does not represent the universe of fullrange drivers - he should hear some of the big-driver full range systems too, which are a different breed of cat than the four to seven-inch drivers. I'm not much of a fullranger person myself, but if I went that way, it would be a big-driver type, like maybe an Altec Biflex or the 12" ToneTubby hempcone driver with a helper tweeter (crossed high, like a supertweeter, which is much easier to design). As for smaller fullrangers, I like the Feastrex a lot, but that is insanely expensive, even more than an Alnico Lowther or AER.

I should add that any speaker, not just fullrangers, that have seriously large magnet systems, combined with super high efficiency, are really meant for horn loading, whether front horn or rear horn. One of the best Lowthers I've heard used the Big Fun horn, which is a rear-loaded horn, but big, as claimed. Lots and lots of great designs on the Planet 10 site and elsewhere. The little guys come into their own with a big horn - not so little anymore! Plus, basshorns have a unique quality that has to be heard to be appreciated.

I have to admit that a horn-loaded Alnico-magnet speaker has a lot more entertainment value than those silly audiophile speakers with a zillion drivers, no matter how any of them measure. Plus, when you're spending money on an Altec, Lowther, AER, or Feastrex driver, you're putting your money where it counts, on the driver.
 
Last edited:
I'm with Lynn, Dave & Terry on this. If you've got yourself a decent budget, you can do a whole lot better than these. But as noted above, you first need to establish what exactly it is you are wanting from your speakers. There are a lot of options available, from single-driver based back-horns, through large dipoles, hybrid mono / dipoles, to 4 box (2 per channel) line arrays with separate subwoofer lines crossed to wideband lines + supertweeters if desired (think Infinity IRS with moving coil drivers rather than the original's ribbons, which had an unfortunate habit of breaking), to single lines of EQ'd wideband drivers... name your poison & it's possible.
 
Last edited:

RockLeeEV

Member
2010-09-24 9:40 pm
Ok, how about starting with something you could actually lift by yourself. Try cloning a Von Schweikert UniField 3.
You're totally right. If you had read all of my post you would have caught the part where I said "it probably won't be my first speaker build by that time either on that note." In fact The idea of crossing these over well is kind of intimidating just because of all the drivers. That's also why I someday want the challenge. I wanted to get a feel for this forum for starters, it was my first post here.

While i agree with MOST of what you've posted Dave, a clever designer COULD pull off the top section with 2.5 way topology on the mid drivers and power tapering in the way of series wiring on the top and bottom tweeters. Lots of XO components and design time but it just might work.......really well.

Passively working in those two sub drivers.....that's not so good.

Either way, i wouldn't want to have to move those around at all!
I wouldn't want to move them around either :p but anyways, the whole thing you said about design time etc is partially why i want to start planning now, and then do a simple 2-way, 2 driver design or two or eight, then work my way up to a simple 3-way.

Have you heard them? My guess is probably not.

Just because something looks amazing, doesn't mean you should build it.

Likewise, just because something looks different from the norm and possibly attractive, doesn't mean it's not going to sound great.

I've heard other lower end RBH speakers. In fact I own a pair of 3-way EMP e55ti speakers and they're certainly the speakers I've most enjoyed and prefered in the price range. I absolutely love their sound (when the grilles are off at least) - it's clean, it's neutral, the instrument separation is great, and the off axis response is nice. I'm not a reviewer or superlative throwing audiophile but from my experience with these, I have little reason to doubt that the flagship speaker designed by the same people that made it isn't "for me".

Even if I wouldn't have the exact same reaction as that reviewer, given my experience with the brand, even a fraction of that sounds fine by me. I already know they design great-sounding speakers. Their 800 dollar tower is audibly better than a lot of towers I've gone to audio dealerships to listen to. Is that based on preference? Sure it is. Guess what, I've already developed a preference for them.

There are many well-reviewed audiophile speakers selling at quite high prices that have badly-designed crossovers, resulting in uneven frequency response, high driver distortion, and ragged polar patterns. A good crossover, by contrast, controls driver excursion (which lowers distortion), has flat response at the listening position, and smooth control of off-axis frequency response.
Well, there's only been one or two reviews of this particular system... what did you think of this:

RBH T-30LSE Measurements & Analysis — Reviews and News from Audioholics

Plus I'm not saying reviews are the end-all be-all in any way - BUT if you've ever heard a speaker from the same designers before, you can generally get a feel for their capabilities. You may not have heard a speaker from that company, but I have, so if we're talking about the review, then maybe the review resonated with me in a different sense than it may resonate with you.

First, you need to clarify your goals: do you want good sound, good looks, or to impress your friends?
In a sense, I want all 3, in that specific order of magnitude.

I want great sound. I do want great looks. I do want to impress my friends with my ability to build it... although they can help me lift it (lol). In order to impress my friends I need it to look and sound great.
In order for it to sound good, it has to have incredible trebel detail and extension, neutral tonal response, detailed mids where instruments have a sense of air around them, a wide, deep, immersive soundstage, great off-axis response, and to be able to deal with both extremely quiet sounds and shift gears into amazing sounds the way only some speaker i've heard are able. And of course, powerful, accurate, stereo bass eliminating the need for a subwoofer in the corner.

0/ a big huge monkey coffin with lots of shiny drivers. That has a definite appeal to a certain part of the market.
1/ 3 widely spaced tweeters. If you use multiple tweeters, they should be VERY closely spaced, and as close to filling the space between floor & ceiling as possible. A distant listening position is required to get integration. It also needs to be accompanied by floor-to ceiling mids.
2/ optimum bass usually requires the (sub)woofers sited in a different position than the higher frequency components.
3/ given that you have 2 big (sub)woofers XOed at 80 Hz, below which everything is omni, one could get big advantage with mounting them push-push... this would really help with problems caused by ...
4/ a speaker this big made with 3/4" HDF and with minimal bracing and not well executed
5/ a passive 80 Hz XO... with the components needed for an XO this low, and all the issues with XOing where the driver impedances look like a roller coaster, it would probably be cheaper and certainly sound way better with active woofers.
6/ even with just a single tweeter the array of mid-basses is too widely spaced to support a cross-over as high as is used.
1) wouldn't that depend on the specific tweeter being used?
2) would you say this even if paired with a duo of matching subwoofers opposite of them at the other end of the room?
3) I'm also considering push-push on that end
4) Care to elaborate on "minimal bracing and not well executed"?
5) The original design doesn't use any real crossover components BTW
6) Again, doesn't that depend on the mid-bass component being used?

Anyways, Lynn, I appreciate your post. It was one of the few that didn't come across as overly patronizing.
 
Last edited:
1) wouldn't that depend on the specific tweeter being used?

Not really. To get to 20k, in theory, you need something like 38mm center-to-centre spacing. There are some tweeters that will let you get that close. but once you add the 2nd one, you usually want a floor to ceiling array.

2) would you say this even if paired with a duo of matching subwoofers opposite of them at the other end of the room?

Yes. Floyd Toole's book is a very cheap investment to have it well explained -- and not just woofs.

4) Care to elaborate on "minimal bracing and not well executed"?

Braces are far apart. Particularily for 3/4" material. A brace ideal ends up dividing a panel into subpanels with a higher aspect ratio than the original panel.

5) The original design doesn't use any real crossover components BTW

????

6) Again, doesn't that depend on the mid-bass component being used?

Same reasons as tweeters, althou opporating at lower frequency spacing can be further apart. Using the 4 driver array in a 2.5 way config mentioned in another post would be a way to have your cake & eat it to -- just one tweeter thou. And i'd look at one of the many very good ribbons available.

dave
 
Returning to the OP, really, it all depends on the goals of the project. If the OP is happy with a big, dramatic-looking speaker with a collection of expensive drivers, the quickest way to get from here to there is: an active crossover, a PC-based measurement system and the know-how to use it, a stack of amplifiers, and whatever drivers are currently in fashion this week in the high-end biz.

With the active EQ, he can make it sound any way he wants - indeed, the knobs can be twiddled for every record and CD. Every record be re-mixed to taste, just like the good old days when receivers had 5 and 10-band equalizers.

If the goals are different ... well ... the path is steeper. Much steeper. Passive crossovers are far more difficult to design, considering the bewildering array of interactions between drivers, driver spacing, crossovers, and amplifiers. The OP should buy a copy of Vance Dickason's Loudspeaker Design Cookbook and ponder on whether he wants to take on something like that - or not.

I would take the comments on Amazon seriously. Are you ready for something like this? Before you spend a dime on drivers, buy this book instead, read it, understand it, and then draw your own conclusions. Despite what the Amazon commenters say, I consider LDC a beginner's book. It's called a cookbook for a reason - it's only a starting point.

Cooking a fried egg for breakfast is not the same as opening a restaurant in the fashionable high-rent district of downtown. If you're thinking about opening that restaurant, first of all, you need to have a realistic assessment of your cooking skills. The learning curve for a (good) loudspeaker designer is similar to the learning curve for a professional restaurant cook catering to the gourmet market. Before you open that restaurant and order all that food, you might want to buy a cookbook first, and decide if that is what you really want to do.
 
Last edited: