New design possible problems?

[Theli]

Hi all,

I'm looking for some feedback/comments on a possible new design, basically anything bad that I may have missed. I've thought of BSC, and resonances at the moment. This will be my first design, so be gentle

Construction will be with 1" or thicker MDF sandwiched and glued together. I work in a shop with a CNC router AND being the only CAD/CAM guy there gives me some priviledges.

EDIT: Dimension are about 36" tall, 6" wide at the widest, 24" deep. Volume is approx 62ltrs. I'd like to use 6.5" for woofers.

And for some reason I don't think its unique design, I'm sure I've something similar somewhere.

[Theli]

so more views...

[Theli]

front

[Theli]

rear

[sdclc126]

Looks like a cool idea - a bipole? You've got either 2 woofs facing opposite directions or a rear-facing port. If it's a bipole you'll just need to keep it away from walls to get the proper effect - you need a relatively large listening room.

The design is essentially almost baffleless, so you may want to be mindful of diffraction issues, but I'm no expert there.

Do you have drivers in mind? You might get some more input once you do, as drivers, crossovers and cabinets must all be part of the design "equation." You state the volume to be approximately 62 liter, but that should be calculated based on the woofer you are going to use and how you want to tune the enclosure - deciding on a volume beforehand is really putting the cart before the horse.

From pure aesthetics though, it's a beautiful design.

[Theli]

Originally posted by sdclc126
Looks like a cool idea - a bipole? You've got either 2 woofs facing opposite directions or a rear-facing port. If it's a bipole you'll just need to keep it away from walls to get the proper effect - you need a relatively large listening room.

Its setup as a bipole right now, but that can always change. Especially if my future listening room is too small. ( will be buying a house in the very near future).
Maybe a BSC circuit will be a better solution..?

The design is essentially almost baffleless, so you may want to be mindful of diffraction issues, but I'm no expert there.

this was something I hadn't thought of.

Do you have drivers in mind? You might get some more input once you do, as drivers, crossovers and cabinets must all be part of the design "equation." You state the volume to be approximately 62 liter, but that should be calculated based on the woofer you are going to use and how you want to tune the enclosure - deciding on a volume beforehand is really putting the cart before the horse.

well, the dimensions were there just give a sense of scale. It will all vary depending on the drivers I choose in the end. At this point its just an idea.

From pure aesthetics though, it's a beautiful design.

Thanks!!!

[morbo]

looks very nice, aesthetically speaking. The bipole idea is great, assuming you can have it 3 feet out into the room. I'd estimate that puts the baffle 5 feet or so from the rear wall?

What I would worry about is how you are going to do the crossover. That is the most important part of the speaker, and the most difficult to develop from scratch, but most noobs treat it as an afterthough, secondary to enclosure design and poring over the minutae of driver specs and differences (not saying you are, just most, self included when I started out).

Since you have a non-standard baffle, you won't be able to find any other design that matches it, so you will definately be developing your own XO. Hopefully you have access to measurement and modelling gear, or better yet, to someone who has both and a wealth of experience using them

Not trying to rain on your parade at all, just want to be realistic about what you're getting into, you may already be aware of all this but it doesn't hurt to check

[Theli]

Originally posted by morbo
looks very nice, aesthetically speaking. The bipole idea is great, assuming you can have it 3 feet out into the room. I'd estimate that puts the baffle 5 feet or so from the rear wall?

How is that determined?

What I would worry about is how you are going to do the crossover. That is the most important part of the speaker, and the most difficult to develop from scratch, but most noobs treat it as an afterthough, secondary to enclosure design and poring over the minutae of driver specs and differences (not saying you are, just most, self included when I started out).

Since you have a non-standard baffle, you won't be able to find any other design that matches it, so you will definately be developing your own XO. Hopefully you have access to measurement and modelling gear, or better yet, to someone who has both and a wealth of experience using them

Not trying to rain on your parade at all, just want to be realistic about what you're getting into, you may already be aware of all this but it doesn't hurt to check

Yah, it's quite the challenge. Right now I'm building some existing designs to help me understand different concepts. I can only read so much until I have to actually do it to see cause and effect. A reverse engineering type of thing...But I do appreciate the suggestions. Sometimes one needs a boot in the right direction!

So, choose my drivers, finalize enclosure, then suffer through crossover design?

[sdclc126]

"So, choose my drivers, finalize enclosure, then suffer through crossover design?"

Well yes, but there other baffleless designs out there; for example this new one at PartsExpress:

http://www.partsexpress.com/projects...lar/index.html

The designer doesn't go into any detail regarding baffleless problems, or if he designed the crossover in any way to deal with it, but you can probably contact him at PE and pick his brain a little.

You might even consider adapting the design to your enclosure - this will save you a ton of work and headaches, and maybe some money too. The woofers are inexpensive and some of the best available at their price point, and you can do a single or dual woofer design.

A similar design is here:

http://www.zaphaudio.com/BAMTM.html It uses a different tweeter but one considered to be one of the best at any price.

Worth considering.

[morbo]

How is that determined?

Well I'm just eyeballing it, as I understand 'rule of thumb' for dipoles is rear driver 3 feet out from the backwall at the minimum, and it looks like the enclosure is about 2 feet deep, so...

So, choose my drivers, finalize enclosure, then suffer through crossover design?

Yup. Although, a few things about the design will have an impact on your driver selection. You will want a midbass that is about 6db less efficient than the tweeter in a monopole (to allow for baffle step compensation), but in the bipole (if I understand it correctly), you want it to have the same or slightly lower efficiency than the tweeter, since the rear driver will do the BSC. Of course it can be lower still but you'll have to pad down the tweeter to match.

The center-center distance from tweeter - midbass will also have an effect on your XO frequency, slopes, and the size of your drivers. Assuming you keep the drivers as close to each other as possible, you will probably not be able to get into anything larger than an 8" midbass, generally 6-7" is more common. If you go with a larger midbass, you will need a very robust (read: can crossover low) tweeter and/or steep slopes in the crossover.

Personally, I think the safest bet for you, if you do your own crossovers, is to go with a 6-7" driver that is easy to work with (read: not a metal cone which will need to be crossed low or have notch filters on the top end), something like Peerless Nomex/Paper, Seas Paper, Vifa/Scanspeak Paper, Adire Extremis, etc. This leaves you open to a lot of tweeters, I would suggest something that is both a great performer and very robust like the Seas 27tdfc or tbfc (depending on whether you like metal or silk domes better). IMHO, this would be a hard design to screw up, give a pretty high margin for error (by that I mean, you could find a lot of ways to do this 'right') and still sound very good indeed.