Looking to build a 3.5 way speaker system

[dmm]

I have 2 JBL 2231H 15" woofers that I would like to use in a 3.5 way speaker. I plan a seperate box for the JBL's, a seperate box for a 7"-8" mid bass, topped off with a seperate box for a 4" mid and 1" tweeter. JBL's will be side firing, with dual venting on front face, all others stacked on top. Everything I see in the 3.5 way systems uses 7" - 8" double woofers which is not where I am. I thought I could just adapt someones top end and then make what adjustments are necessary. Not so easy. Tony Gee has an open baffle top end over similar bottom but his speaker choices are all scanspeak and too expensive for my first attempt at this sort of thing. Any help would be greatly appreciated. I have a complete woodshop so the end design will be interesting.

[cjd]

So, ho far in do you want to go?

We can help you with driver choices (I already have some thoughts ) and such, some of us can/will even take good data and work up crossovers, but the difficulty is in GETTING that data.

If you're willing to pick up some equipment to measure, we'll get you there no problem, whether you want to do your own crossover work or have someone else. Check out the Spassvogel thread for someone else who started with no background (some theory) and worked his way through to a superb pair of speakers.

C

[Dennis H]

I have 2 JBL 2231H 15" woofers that I would like to use in a 3.5 way speaker. I plan a seperate box for the JBL's, a seperate box for a 7"-8" mid bass, topped off with a seperate box for a 4" mid and 1" tweeter.

That would be a 4-way. A 3.5-way uses the same drivers for the bass and midbass, rolling the bottom one off at a lower frequency.

You might look at some of the 3-ways in Missions Accomplished. You could use an active crossover and 2 amps to cross any of them to the JBLs.

[looneybomber]

Hmm, 1" dome,
4" cone mid,
2, 7-8" midbass,
2, 15" woofers.

I like the sound of this. But, could a ribbon tweeter work and how much $$ were you thinking of spending? Fountek makes a nice tweeter that goes by the name of Neopro 5i, look it up It might be a bit overkill though.

[cjd]

Why would you want a ribbon tweeter? :P

And yeah, you're right - this would be a 4way.

[looneybomber]

Why would you want a ribbon tweeter? :P

Well, in case he's looking for a very high (SPL) output driver?

[Operandi]

How about find a 2 way (or small 3 way design) you like, turn the JBLs into bass bins and integrate the two? Sounds a little more sane to me sine the JBLs are unknown quantities.

[dmm]

I started out by creating a graph of the drivers Tony Gee used for the "Progress" speakers. Thought was to find some drivers tha had similar specs. Have researched all of the recommendations from the "Zaph" site and thought I would go with his highly recommended drivers. Then see where it led to the crossovers. My plan at this time is 1" dome tweeter, (cloth or metal?), 4" or 5" mid range with good overlap with the tweeter, 7" or 8" mid woofer, crossing over the very bottom at 80 hz since the JBL"s work well down there.

[dmm]

Here is the list of drivers I have selected to be in the running for my speaker. Tweeter, either Peerless HDS 810921 or SEAS 27 TDF. For the Mid Range, either Dayton RS 100-4 (new driver), Dayton RS 125 - 4, TangBand W4 - 10525D, or TangBand W5 - 704D. For the Mid Woofer, either Peerless HDS 830883, HiVi F6, or the Dayton RS 180 - 4. I already have the Woofers, JBL 2231H. Any experience with these drivers or which ones to group together would be helpful.

[bluewizard]

I don't claim to be an expert on this, and only just recently began investigating the subject I'm about to address. So, if I get it wrong, really, feel free to jump in and correct me.

Let's examine why we want to implement a 'half way' system. By 'half way' I mean a 3.5-way system rather than a 3.0-way system. Let's look at the purpose and need for the 0.5 aspect.

When ever you build a speaker, any speaker, there is a point based on the width of the front of the cabinet (baffle width), where the bass begins to drop out. This point is called the baffle step. And this drop out usually occurs well below the low-to-mid crossover point.

I won't get into why this downward step is there, you can look that up on line by searching either 'baffle step' or baffle step correction'. For now, we just accept that it occurs.

So, let's say this downward baffle step occurs at 300hz, and the low to mid crossover is 800hz, and the mid to high crossover is 4000hz.

So, one way to compensate for the drop in low frequency levels is to bring all the other levels down to match that which is below the baffle step.

But, how about instead of bring everything else down, we bring this weak low end up?

How about if we use two identical woofers, below the baffle step we have both woofers kicking out sound. Then as we reach the baffle step, one of the woofers fades out, and the other carries the sound up to the low to mid crossover point.

Woofer-1 = 20hz to 300hz ...(this is the 0.5-way aspect)
Woofer-2 = 20hz to 800hz ...(this is the first part of the 3-way)
Midrange = 800hz to 4000hz ...(this is the second part of the 3-way)
Tweeter = 4000hs to 20,000hz ...(this is the third part of the 3-way)

That second woofer that only plays below the baffle step is the 0.5-way aspect of the system. This is very different in both design and concept than a subwoofer. This second woofer raises the output level in the otherwise weak area below the baffle step.

So, it is with this in mind that you want to approach a 'half-way' system, whether it is 2.5-way or 3.5-way.

I've only seen 'half-way' systems that use identical woofers. I suppose if you needed addition levels below the baffle step you could use a 10" below and an 8" above, as an example. I speculate that, but I've never actually seen it.

Now, how does that information fit into your plan for the JBL 15" woofers?

Keep in mind, that this 'baffle step' is determined by the width of the front of the speaker cabinet in the area of the woofer.

I'm sure that doesn't help much, but it is important information to keep in mind as you design your new speakers.

Steve/bluewizard

[Dennis H]

I think you're really underestimating how hard it is to design a good crossover. Add more drivers and it gets waaaay harder -- a passive 4-way ranks about a 12 on a 1-10 difficulty scale. Even the experts would cringe at attempting it.

I strongly suggest you build an existing 3-way design and use the JBLs as bass bins / speaker stands. Other than the ribbon tweeter, the Statements Monitors are very close to what you are looking for for the top 3 drivers. They are a proven design and their sound has been highly praised. Build them according to the plans, use a $100 Behringer active crossover to bring in the JBLs somewhere below 100-200 Hz and you're stylin'.

http://www.htguide.com/forum/showthread.php4?t=29605

Edit: if you insist on designing from scratch, get ready to spend several hundred bucks on measuring gear and design software and spend several months learning to use it all.

[dmm]

Thanks to Bluewizard and Dennis H for your comments. I have been toying with this project for a long time and not afraid to put more time in. I have no interest in a ribbon tweeter at this time, can't exactly say why, just don't like the look I guess. I have about 4 differst drawings for the cabinet at this time, although final size will be determined by the different speaker volume needs. My research indicates that having a midrange and midwoofer thru the vocal range is highly desirable. I thought having the JBL's on the bottom makes the woofer crossover a no brainer. I guess the artist/designer in me wants to make something unique. I really like Zaph's detailed evaluation of speakers and thought his list would give me the imput to choose what would sound the best. Is there a way to link the midbass and woofer together and run it all as a three way? Again I appreciate all the help.

[bluewizard]

Take a look at the ZAPH ZDT3.5 to get an idea of the design concepts behind a 3.5 way system, and look at the complexity of the crossover.

http://zaphaudio.com/ZDT3.5.html

I believe there are ported and closed versions of this as well as a center version.

This is actually a pretty nice speaker system to build. Several in the various audio DIY groups have built this and been very pleased with it.

If nothing else, if you insist on a completely original design, this design will give you a framework to work from.

Notice on the picture of the ZDT3.5 crossover, at the bottom, L22 with R23 and W24 are the 0.5 way aspect of this system. Also note that the 0.5-way aspect is an extension of the low pass woofer section.

Also, keep in mind that because both woofers are in play below the baffle step, this is a 4 ohm speakers system, despite the fact that for most of the frequency range it is 8 ohms.

Steve/bluewizard

[cjd]

If you have two drivers covering the same frequency range (i.e. "sharing" a crossover leg so it's just a 3-way) they're sharing *all* that range, and had better have near identical impedance and response characteristics over that range and far enough out past for the crossover to work right.

Choosing drivers is half the art of getting a truly seamless system. Crossover is half the art. Enclosure design is quarter.

If you were to actively cross the JBL's you *might* be able to get away with .5-ing a driver we'd have to treat as a separate entity in a 4-way, but it's really not a value proposition - if you need extra displacement and your midrange isn't up to the range, it's not going to suddenly have no problem by halving in another driver for part of it... it'll struggle, the other driver might sorta cover, so you'll have more mucked up sound, AND you'll have lower impedance.

[dmm]

You guys are spot on. I have all the specs and drawings for the Zaph ZDT 3.5 and the Tony Gee "Progress". They are why I thought it was a possibility. I just put together a list of all the projects I have saved from the web, trying to see if there was a trend in driver matching I might be able to use as specific segments of my design. I feel I am getting close to picking my drivers so you can give me your sense of whether I am in the right direction or not. Can anyone tell me how I put my idea sketches up for view? It might help everyone understand what is on my mind.

[cjd]

If you use the "Advanced" reply option there's room to "manage attachments" (though file size is controlled I believe...) you can upload some image files that way.

C

[dmm]

I have been pondering the driver question for some time now. Her's what I have in mind. The SEAS 27TDF tweeter, the Dayton RS125, either the 4 or 8 ohm mid range, the Dayton RS180, again, not sure which to use, either the 4 or 8 ohm mid bass, with the JBL 2231H on the very bottom. I am starting to calculate volumes for a vented system. The tweeter and mid range in one vented box, the mid bass in it's own vented box, and the woofer in a dual vented box. Is it worth purchasing the duo of BassBox Pro and Xover Pro? I have been using KBapps for vented enclosures for now.

[cjd]

IMO that's not a software package worth purchasing.

In almost every case I will recommend the RS150 over the RS125 - box volume is almost the same, but the RS150 is a better sounding driver IMO. If you want the smaller size, go with the TB W4 driver everyone likes so much (though the 27TDF isn't quite as good a match in this case...)

Of course, I'd also recommend stepping up to the RS225 instead of the RS180...

Ahh snap. See, that's practically a Khanspire with the Seas 27TDFC (already measured, never crossovered... yet...)

Another way of looking at this: RS180, but instead go with something like the RS52 for midrange and a nice cute tweeter for the top end. Rather like Zaph's project.

Venting the midrange enclosure is probably not going to buy you anything other than larger boxes. Even the mid-woofers, this is true.

If you have MS Excel check out Unibox. Otherwise I think a lot of folks are using WinISD.

[spentit]

Another Option

Another option that is close to what your looking for with a xover designed by someone well respected, would be Dennis Murphy's 3 Way using the RS225,RS150, and either Seas 27TBFC/G or RS28A. The drawings and xover schematics have been posted on this forum. If I remember correctly the sealed version plays down to 60hz, so they would work great crossed over to your subs in separate enclosures.

Although I haven't seen a build thread for these, apparently Dennis did build one for voicing and was very happy with the xover. I am hoping to build 4 for L/R/Surround along with the Dayton RS Center it as soon as $$ saved.

Spencer

[Curt C]

Here is the list of drivers I have selected to be in the running for my speaker. Tweeter, either Peerless HDS 810921 or SEAS 27 TDF. For the Mid Range, either Dayton RS 100-4 (new driver), Dayton RS 125 - 4, TangBand W4 - 10525D, or TangBand W5 - 704D. For the Mid Woofer, either Peerless HDS 830883, HiVi F6, or the Dayton RS 180 - 4. I already have the Woofers, JBL 2231H. Any experience with these drivers or which ones to group together would be helpful.

When you pick drivers, its first good to look at the woofers to determine the sensitivity requirements of the other drivers.

My initial research indicates the 2231 wants a BIG sealed box, like 5 cu. ft. -And according to JBL's scanty literature, they will have an f3 of only 50 Hz in that big box. There are no published T/S parameters for the 2231H that I can find, so you will need to measure yours to utilize any box program.

The published sensitivity of the 2231 is 94 dB, so you will need a woofer of similar sensitivity to mate with it at your intended crossover frequency. -Speaking of crossover frequency, designing a usable passive low-pass crossover at 80 Hz will be highly improbable. The crossover inductor reacts with the driver to exhibit a large resonant peak, generally right where it will be the most difficult to deal with. Better to treat these like subs, and actively drive them with plate amps. This initially appears to resolve both the sensitivity issue and the crossover problems. In addition: should you go active, then your possibilities for companion drivers are substantially increased. As others have already noted, build one of the already documented 3 way designs to mate with the JBL's.

-But please note that you will end up with bass bins that while being quite large in stature, will not provide the low-end reinforcement of a typical sub driver, or even a typical 6" driver, for that matter. A Linkwitz transform could possibly provide both increased extension and a smaller enclosure, but I don't see the advantage when there are so many other, more capable drivers available.

The big advantage of the 2231's are their sensitivity and wide range, -up to 800 Hz according again to the JBL documentation. I would think their forte would be crossed to a pro-sound midrange as a high sensitivity 3 way system.

C

[cjd]

Were I to be tasked with putting a system together with the JBL's I'd be looking at an 8" midrange and a compression driver/horn to go with them... So yeah, I agree with Curt.

[dmm]

What I seem to be hearing is that basing a design on the JBL's as the foundation isn't the most optimum way to design the system. I hate the thought of having them and then not using them. As for the box, the original "Belle Klipsch" they were intended for were very large. I do have a box question. Bullock says that most designs err by designing on the small side and that an increase of up to 10% from the box program dimensions is a good way to go. Elsewhere I learn to expect apparent box volume increases by the inclusion of dampening material. How far should I adjust the original box design to accomadate the dampening change and still err on the positive side if possible?

[ThomasW]

Programs like WinISD Pro Alpha or Unibox are accurate so no need to design for any 10% error. Design using heavy fill and you're good to go.

The T/S parameters for the 2213H are on page 4 here....

https://www.jblproservice.com/pdf/Thiele%20Small%20Parameters/Theile%20Parameters.pdf

I'll echo what others have said, there's no need to be married to those woofers unless you need a high output PA type system for your home.

[cjd]

Designing around the JBL's isn't an issue - just actually DESIGN around them rather than trying to find a way to shoehorn them in.

[bluewizard]

I think, given the woofers you have (15" JBL), you might be better off just making them into some stereo subwoofers. The difference between a 4-way and a 3-way with a subwoofer, is the the subwoofer has its own amp and crossover.

I've always been interested in the idea of independent stereo subwoofers, though you could certainly use one Sub Amp, and combine both JBLs into one subwoofer cabinet.

Essentially do as you originally suggested, two 8" 3-way each in its own cabinet, and the 15" each in their own cabinet. Then add a subwoofer plate amp to each of the bass cabinets, and you have one sweet SMOKIN' system.

If you only have a pair, and you insist on using them, then I think this is the best choice. Prices on Sub plate amps vary, but you really don't need to spend a fortune on them. You could probably get by with $150 or less per amp, though if you have the cash, you can certainly jump up to the +$300 per amp range. (BASH 300 watt @ $150, Dayton 240 watt with bass boost @ $140, Dayton 500 watt @ $325, etc...)

Another nice aspect is that, in general, the passive 3-way and the Sub don't have to be tonally matched. That is, you could use Dayton speakers in the 3-way and JBL in the Sub with no problems. The frequency response of the Sub is very limited, so, within reason, tonality doesn't come into play.

Also, while most video subs strive for ultra low sub-audible frequencies, there is nothing wrong with a sub that goes down to the 25hz to 30hz range. In fact, that is the lower limit on many commercial subs.

I think a passive 3-way combined with an active Sub, is probably the least expensive and most effective way to use those speakers.

But then, that's just my opinion.

Steve/bluewizard

[Curt C]

Designing around the JBL's isn't an issue - just actually DESIGN around them rather than trying to find a way to shoehorn them in.

Couldn't agree more, Chris. I suspect dmm was just unaware of what a proper design for these legacy drivers would be.

Using the published parameters provided by Thomas :T I came up with two possible alignments for this driver:

Sealed in 2.75 cu ft. Qtc .7 w/ medium stuffing. The f3/f10 models 65Hz/35Hz.

Vented in 4 cu. ft. tuned to 25 Hz using a 4" x 11.5" flared port. Expect f3/f10 of 40Hz/25Hz. –This would be my preferred choice.

Max SPL with either alignment: 114 dB at 100 watts. Yes, this qualifies as insanely loud, but consider it takes only 10 watts to get to 104 dB. This could be the foundation for a nice (but large) high efficiency design.

C

[cjd]

I think, given the woofers you have (15" JBL), you might be better off just making them into some stereo subwoofers.

They're not subwoofers...

They're woofers.

[dmm]

I really appreciate everyone's help and thoughts. It's nice to have a dialog after working on this project alone. this is kind of what I envision for the speakers. The top and middle box can be joined together as a single unit. The top box is .359326 cu ft. The middle box is 1.147973 cu ft. The bottom box is 4.426003 cu ft. I drew the speakers to their real size. I don't have a side view of the JBL at this time but will add it. I have some ideas about beveling the front of both the top and middle boxes to improve diffraction at the edge of the speakers. Overall height is 64" with the mid bass centered at approximately 48". There are 2 vents on the front of the bass box. Both upper boxes will be 1" mdf with the bottom box 2 layers of 3/4" mdf and a layer of grace rubber membrane glued between as deadening material. I have not given a thought to bracing, it will come in it's own time.
I can't seem to get the pdf file to attach so you can see the drawing. Help!!!

[Jed]

DMM, go to webshots.com and get an account. You can upload your pics there and insert it in the forum in different size formats.

[cjd]

You know, this looks a lot (in some ways) like the big RS 3-ways I did with dual RS270's on the bottom, except you can get away with a single 15" driver. And I'm sure the crossover wouldn't work. If these're out in the open we start to include baffle step and such, the sensitivity numbers drop into more "normal" territory.

I'd still not immediately pick any of the current projects to integrate with, but look seriously at driver selection to match these JBL's.

[ThomasW]

They're not subwoofers...

They're woofers.

Correct, and they were probably used in ported boxes with a Fb around 40Hz

I can't seem to get the pdf file to attach so you can see the drawing. Help!!!

To cut down on our server load attachments are limited to a file size of 70k.

[Curt C]

I really appreciate everyone's help and thoughts. It's nice to have a dialog after working on this project alone. this is kind of what I envision for the speakers. The top and middle box can be joined together as a single unit. The top box is .359326 cu ft. The middle box is 1.147973 cu ft. The bottom box is 4.426003 cu ft. I drew the speakers to their real size. I don't have a side view of the JBL at this time but will add it. I have some ideas about beveling the front of both the top and middle boxes to improve diffraction at the edge of the speakers. Overall height is 64" with the mid bass centered at approximately 48". There are 2 vents on the front of the bass box. Both upper boxes will be 1" mdf with the bottom box 2 layers of 3/4" mdf and a layer of grace rubber membrane glued between as deadening material. I have not given a thought to bracing, it will come in it's own time.
I can't seem to get the pdf file to attach so you can see the drawing. Help!!!

If you are still thinking passive crossover on the JBL's, you will need to front mount them, as you will end up crossing them much higher than the 80 Hz you are thinking.

Here is a link to exojam's JCW 3 ways: They may give you some ideas, as the woofers have similar functionality as the JBL's. -And as Chris and I have suggested, utilize pro drivers for the mid and tweeter.

http://www.avsforum.com/avs-vb/showthread.php?t=1061558&highlight=

C

[dmm]

I created a webshots account and loaded the jpeg of the drawing. It shows regular boxes stacked one on top of the other on the left, and my tapered design on the right. There are multiple side views of different configs.
The webshot account is under my name dmmolner, it is a public folder, subtitle is speakers. It is 204kb so it won't fit here. I may try to split it in half and serve up as 2 posts.

[ThomasW]

You're making this much more difficult than it needs to be. Either compress the images to make them 70k, or post the URLs of the Webshot pictures in the message reply box.

[bluewizard]

They're not subwoofers...

They're woofers.

And your point would be...?

Yes, I know, but that doesn't mean they can't be used as subwoofers, if you don't expect ultra-low sub-audible frequency response.

I made a note of this in my reply, acknowledging that they won't go that low.

But if you can pull them down in the 40hz range, or better, the 30hz range, they will still do the job they were intended to do in this 4-way bi-amped system.

Regardless of how they are used, there are going to be limitations. But when people start talking about using multiple amps and a complex set of active crossovers, it seems to be driving the price up ridiculously high just to use two spare JBL speakers.

I still say the shortest and cheapest way to the best end result, is to put the JBL's either in stereo bass cabinets with individual Sub amps, or to combine them together into one big bass speaker with a sub amp. That's dirt cheap compared to some of the other suggestions.

Then set those under the passive 3-way speakers that the original poster was going to build anyway.

In a sense, don't think of it as a Subwoofer, think of it as a self-powered low bass speaker.

Steve/bluewizard

[exojam]

The JCW's are also shown on this forum in case no one wants to venture to the other forum.

http://www.htguide.com/forum/showthread.php4?t=31102&highlight=jcw

[dmm]

I am trying to do this again. Here are my first design ideas. Stacked plain boxes. Design more the way I want to go.

[cjd]

Design concept is fine, but that JBL really should be front fired so I'm not sure how well suited to the drivers you have on hand. On the other hand, it wouldn't take TOO much fiddling with the designs in the second image where you have a tapered lower box to get it big enough to fit the driver out front.

Very definitely a 4 way would be required.

C

[Curt C]

I'll suggest the 8" upper bass driver will integrate better with the woofer if it is sealed rather than vented. Vented will provide a 4th order acoustic transfer function, and whether you go passive or active on the JBL's, you likely will want 2nd order acoustic for both the JBL LP filter and the upper bass driver HP filter. It will allow you to reduce that enclosure volume as well.

The designs look quite good, otherwise.:T -The truncated pyramid shape of the 2nd design in particular…

C

[dmm]

The idea behind side firing woofer is that it allows me to have a narrow front profile. I have seen several designs showing side firing so I felt it just fit my concept. As for venting the mid bass, I thought it would be more effecient when I cross the woofer at a lower 80 - 300 hz range. Having followed this thread and all the responses, I have been considering maybe the upper should be an MTM design, resulting in a 3 way. My original idea was to create the broadest and complete mid available. I'm feeling that the project is way too ambitious for my abilities, especially in the crossovers.

[ThomasW]

Sell the 2231's, put the money toward building one of the proven designs posted in the Missions Accomplished section of the forum

[exojam]

Dmm,

Have you ever made speakers and crossovers before? The only reason I ask this question is, if you have not than you were in the same boat as myself awhile. I had been constantly reading forums like this where folks were knocking out design that really caught my attention for a considerably less cost that the big brand companies and figured, hey this is DIY maybe for me.

My process was probably a** backwards since I had picked the drivers I wanted to use before anything else. I had-have no measuring equipment or knowledge on what the heck I would be looking at if I could measure something. In discussion with someone I trust from this site he basically laid it out as, you will need measuring tools, possibly multiple cabinets attempts, plus possibly about a year in time doing all of this with no guarantee that I would have anything other than a bad design.

Have you thought about moving this to a three way and active for the crossover? I would like to believe that could make things easier for you (but more knowledgeable folks may correct this). Than with measurements and assistance from the folks here you may be able to produce what you are looking for.

James

[cjd]

You'll not even get an octave out of the JBL's crossing at 80Hz is all...

This gets back to what I said before: you can design with the JBL's as a starting point, or you can design with other desires and find drivers to meet those goals. Right now, you're working on two separate projects.

Port the JBL's and you'll nudge below 40Hz on the bottom. Cross them up top to an 8" midrange at ~200Hz perhaps. Midrange choice and some will dictate how it works above that, but a waveguide loaded compression driver (see Isiris) or possibly even something like the tweeter Dan is using in his new open baffle project could work out here (not sure the total efficiency on the JBL's all said and done but I'm guessing it'll be into the low 90's and that tweet will be a good match).

Or, build the concept you hav here, which I think is slick. 15" RS sub side fired, RS225, RS150, RS28A or your preferred tweeter flavor... Cross ~70Hz, 250Hz, 1800Hz. Or perhaps you prefer other driver choices, depending on budget and desires... One of the Seas Mag cone mids not the RS150, a nice Scan 6600 tweeter perhaps. Or... yeah. Lots of options for your box concept.

C

[Curt C]

Chris has already covered most of this, but since I've already written it, I'll post it just in case it will be of some benefit. :Z

I can understand your concern about the narrow front baffle, as that woofer has a mighty big ‘footprint’.

The issue with side firing woofers is the psychoacoustics of how the brain localizes the sound. Below about 100 Hz, the brain is incapable of determining the direction the sound is coming from. Above that point it is pretty easy. The result of crossing side firing woofers higher is that the imaging is adversely affected, and the position of the various instruments and voices ‘move’ on the soundstage depending on the frequency. Most listeners want to have a solid soundstage and stereo image, so this is why we have been suggesting the front mounting with the JBL’s. -That and the higher crossover point mandated by the passive crossover you indicated you were considering.

Going the other way: Crossing the woofers at say, 100 Hz will require active equalization, (think plate amp) and result in a woofer passband of slightly over one octave. This is kind of a waste for such an otherwise capable driver, -like putting ketchup on beef wellington, but after all, this is your design, and you should be able to build it the way you want it.

Venting the upper woofer: Yes, it would allow a smaller driver to reach lower, but most 7 or 8” drivers will reach down below 80 Hz in a sealed configuration. There is no reason to vent them when the high pass filter will limit the passband anyway, and any increase in ‘efficiency’ will not be utilized.

Another option would be a Sat/Sub combo:
If you are determined to use the JBL’s and want a narrow front profile, don’t put them under the rest of the speaker at all. Build a couple of subwoofer cubes, and put them in the corners of the room. Use plate amps and cross them over at 100 Hz or less, along with picking out one of the DIY designs published here or elsewhere and build them. Now you will have your narrow profile, and very likely better bass as well, since you will have some flexibility in placement of the ‘subs.’ Lower bass extension (and much smaller enclosures) could be gained by replacing the JBL’s with drivers dedicated for sub performance.

Another possibility: If these are truly NIB JBL’s they will fetch a nice price on Ebay, and would likely finance a significant portion of your speaker project. Certainly you could then afford to purchase true subwoofers, and a couple of nice plate amps, which would reduce the woofer cab volume requirements resulting in a more elegant looking design.

C

[dmm]

I have to say I am really enjoying this. Okay, I didn't want to go front mounted woofers, mostly because I'm not a conventional guy. The design of the cabinet is as important to me as the drivers, you spend a lot of time stareing at these things you know. anyway, I kicked around the front mounted idea and here it is. Also, I beveled the upper cabinets to add dispersion. What say you now?