Speaker enclosure building advice needed

**solid7** · **05-06-08, 11:43 AM**

I'm a newbie to building speakers. (other than subs) I have ordered a copy of the Loudspeaker Design Cookbook, and will be educating myself from there. In the meantime, I would like to pose several questions here.

First off, I have been researching a build for a high quality wall mount speaker. While not acoustically optimal, it is, aesthetically necessary. (for me, anyway) I have seen several suggestions for building MTM's, or similar designs, and I like them, but not the box geometry. I would like to build a somewhat tear drop shaped enclosure, with the the drivers mounted on the big end of the tear. While not a typically feasible design, I have some resources available to me that are not normally associated with DIY, and I intend to use them to the fullest. Which brings me to the first question: If I design a tall enclosure, can a I transfer the ports (in the case of a typical MTM or similar arrangement) from the front or back, to a top/bottom firing arrangement? Secondly, is the box volume the most important consideration, or the box geometry?

I am able to make rounded back enclosures. In fact, I do not plan on having any square corners in my enclosure at all. I plan on using somewhere between 4.5" to 6.5" drivers. I would like to use high end drivers in this design, although if I can get great performance out of a smaller driver, I will consider it. It must also look great.

My final question pertains to selection of drivers - can anyone please point me to a resource which lays out all of the key fundamentals to driver selection?

I will post pictures of my proposed design in subsequent posts.

Thank you for your time.

**Anthony** · **05-06-08, 12:58 PM**

I'm sure others will address your other questions, but I'll tackle the design/volume one.
You are fighting two different design challenges with box design and volume.

Box design (mainly the width) determines the baffle step. An on-wall or in-wall speaker will have a minimal effect here, otherwise, the narrow speakers have a very high frequency rolloff, whereas a wide speaker would reinforce the bass more, but then lead to diffraction effects. The corners of a cabinet can act like re-radiators of the sound. For a narrow cabinet, the path length differences are small, so this does not affect things much. For a wide cabinet, you can get a certain degree of comb filtering in the higher frequencies. So you end up designing the narrowest cabinet that you can while trading off the bass reinforcement.

(note: you can get that bass back by using the shelving filter or BSC circuit in the crossover to trade efficiency for bass extension -- basically lowering the efficiency of the higher frequencies to match the lesser bass output)

With volume, you are trying to tune the "air spring" behind the woofer to smooth out its extension. This will be dependent on the number of woofers, which models (and their T-S parameters), and whether the speaker is sealed, ported, or passive radiator (or .5 way design).

Sorry if I raised more questions than I answered -- this is a complicated hobby

**BoomieMCT** · **05-06-08, 01:00 PM**

Quote:

solid7 wrote:

If I design a tall enclosure, can a I transfer the ports (in the case of a typical MTM or similar arrangement) from the front or back, to a top/bottom firing arrangement?

Yes you can move them but they aren't all quite the same. Since the vents tend to play the low frequencies their location can change the amount of room gain they pick up. This is one of the reasons so many designs use rear ported vents. The other thing to consider is port noise. Front ported designs may have port chuffing be more noticeable.

Quote:

solid7 wrote:

Secondly, is the box volume the most important consideration, or the box geometry?

See p-112 (section 5.30) in LDC for info about enclosure geometry. Since it sounds like you are going vented box volume is very important as it will greatly affect the tuning of the speaker.

Quote:

solid7 wrote:

My final question pertains to selection of drivers - can anyone please point me to a resource which lays out all of the key fundamentals to driver selection?

Since you are going vented check out p-61 (section 2.40) in LDC. Beyond what is there I can say there is no substitute for building test baffle and testing drivers yourself.

**solid7** · **05-06-08, 04:54 PM**

Quote:

Anthony wrote:

Sorry if I raised more questions than I answered -- this is a complicated hobby

I'm eagerly awaiting the arrival of my LDC. It's all appreciated, though. I'll take plenty of time to pour over what you've written, and let it lead me down other paths of research.

Quote:

BoomieMCT wrote:

Since it sounds like you are going vented box volume is very important as it will greatly affect the tuning of the speaker.

Since you are going vented check out p-61 (section 2.40) in LDC.

I have not settled on a ported design. My question came about due to the fact that so many designs that I see are ported. I can see pros/cons in both methods. Most likely, I'll end up with a sealed design, but you never know.

Thank you for the page references.

**solid7** · **05-06-08, 05:12 PM**

These are 2 designs that I really like. The one with 4 drivers uses 4.5" drivers, with 2 tweeters, and the one with 2 drivers uses 6.5" drivers.

Both designs are 30.5" tall and 5.5" deep. The smaller enclosure measures approximately 7" across the face, and the larger is approximately 10" across the face. I really prefer the assymetrical look of the larger enclosure. However, I have no idea if either design is practical at all. Still learning...

**BoomieMCT** · **05-06-08, 05:18 PM**

Quote:

solid7 wrote:

These are 2 designs that I really like. The one with 4 drivers uses 4.5" drivers, with 2 tweeters, and the one with 2 drivers uses 6.5" drivers.

Any reason why you are using 2 tweeters? It seems like you may be asking for comb filtering effects - especially since they are side-by-side instead of on top of each other.

**solid7** · **05-06-08, 05:27 PM**

Quote:

BoomieMCT wrote:

Any reason why you are using 2 tweeters?

Just plain ol' ignorance

I like the way they look. I saw a design somewhere that had 3 in a horizontal row, and I thought was sharp. To be honest, I'd really prefer a ribbon tweeter, but it only takes 10 seconds to model the round cutouts...

**BoomieMCT** · **05-06-08, 08:00 PM**

Quote:

solid7 wrote:

Just plain ol' ignorance

I like the way they look. I saw a design somewhere that had 3 in a horizontal row, and I thought was sharp. To be honest, I'd really prefer a ribbon tweeter, but it only takes 10 seconds to model the round cutouts...

If you really wanted to use a ribbon try the NG Neo3. there are two faceplates (a flush mount and surface mount) you can use with it that are round.

**solid7** · **05-06-08, 08:41 PM**

Does the asymmetrical placement of the larger enclosure violate any conventions?

I don't know why, but I really like these types of arrangements.

**BoomieMCT** · **05-06-08, 09:44 PM**

Quote:

solid7 wrote:

Does the asymmetrical placement of the larger enclosure violate any conventions?

I don't know why, but I really like these types of arrangements.

Normally (but not all the time) you try to put drivers as close together as possible. The more spaced out they are the more likely you'll get comb filtering. The only possible advantages I can see to an assymetrical arrangement is if you intend to listen to it off-axis or if you are trying to pick up some bass off the bottom woofer.

**avaserfi** · **05-06-08, 10:09 PM**

Quote:

BoomieMCT wrote:

Normally (but not all the time) you try to put drivers as close together as possible. The more spaced out they are the more likely you'll get comb filtering. The only possible advantages I can see to an assymetrical arrangement is if you intend to listen to it off-axis or if you are trying to pick up some bass off the bottom woofer.

Just to expand on driver placement i.e., the "not all the time."

The distance between each transducer need not necessarily be as close as possible, but rather as close as required by crossover point in relation to wavelength. Thusly, the shorter the wavelength (higher the frequency) the closer together transducers should be placed to avoid comb filtering issues.

Also, it is important to note that the flush mount item for the Neo3 tweeters offered by Parts Express will act as a waveguide. For a true flush mount unit something like this would be needed*. I purchased two from here (the only place I am aware that sells them. They won't make instillation much easier though since they are square as well.

*Do note the person who built the speakers did not flush mount the units, but it can be done with this plate.

**Anthony** · **05-07-08, 07:01 AM**

Or you can go my route for the Neo3 and carefully route out the back so that everything sits flush with the front. You have to end up with a roundover or chamfer to act as your own waveguide (little one) otherwise there is not thickness for the screws to grab onto!

It was a pain and required a lot of hand tool work to get everything right. If I was making a production run using this method, I would definitely take the time to make some templates.

Round holes are so much easier

**solid7** · **05-07-08, 09:02 AM**

I have some nice equipment at my disposal. I will most likely opt to make a template, as it's very easy to and cheap to make routing templates out of sheet metal. I will make templates that achieve my entire layout, whatever that ends up being. Chances are, I may also make my own faceplates. Some research will be necessary, as I'm not sure if the faceplates are an integral part of the acoustics of the speaker, itself.

After achieving the countoured enclosure, the cutouts will be a piece of cake, no matter what shape!

**BoomieMCT** · **05-07-08, 09:09 AM**

Quote:

solid7 wrote:

Some research will be necessary, as I'm not sure if the faceplates are an integral part of the acoustics of the speaker, itself.

The tweeter faceplate will most certainly affect it's low-end performance as well as off-axis dispersion. For example in my tests between the flush mounted and surface mounted BG Neo3 faceplates I found the surface mounted one (which has a deeper waveguide) boosts the low end response (just below 2kHz) a bit.

**solid7** · **05-07-08, 09:28 AM**

I was referring to the contour geometry of the faceplate - not necessarily so much the mounting depth or method. Whatever method I use would mimic the original mounting, although I prefer a rectangular flush mount face. The circle really isn't bad, though. What material are the faceplates made from?

**BoomieMCT** · **05-07-08, 09:34 AM**

Quote:

solid7 wrote:

I was referring to the contour geometry of the faceplate - not necessarily so much the mounting depth or method. Whatever method I use would mimic the original mounting, although I prefer a rectangular flush mount face. The circle really isn't bad, though. What material are the faceplates made from?

Not exactly sure what you mean by "contour geometry". What I'm saying is that no matter whether you buy a pre-fab faceplate or make your own the shape of the area around the tweeter will affect it's low-end response and dispersion. What this means is that you will really want to test the tweeter with it's final baffle/faceplate before you begin crossover design.

The BG faceplates are plastic. No idea about the rectangular ones.

**solid7** · **05-07-08, 09:46 AM**

Quote:

BoomieMCT wrote:

Not exactly sure what you mean by "contour geometry".

I meant that the front side and mounting side of the faceplate are not parallel to one another. There is a contour on the front side. Not sure if that matters, at all...

**mayhem13** · **05-07-08, 01:30 PM**

I believe you are talking about the waveguide design itself. Yes, different geometries such as overall depth, mount surface area and the rate of taper will have different effects on the performance but at the depth of the commercially available plate, it's not much different from flush mounting. You could probobly measure the differences but i doubt you could aurally locate them.

**solid7** · **05-09-08, 09:08 AM**

Based on my initial UniBox calculations, I have decided to go with 2 Scan-Speak 15W/8530K01 for the Bass/Midbass, and I am unsure what I need to compliment it. Does this design want a tweeter, or a wide/full range driver between these 2? I am basing my design on the KEF KHT9000's.

This is a sealed enclosure, measuring about 11.5L. It's a large wall mount to be sure, but it works OK for the space that I have.

**Jay_WJ** · **05-10-08, 06:42 PM**

11.5 liter enclosure is way too small for two SS 15W/8530K01!

If you want a small sealed enclosure and SS Revelators, the lower Qts 15W/8530K00 version will be better suited. Even with that, 11.5 L is a bit too small.

BTW, consider my offer I made in your "wall mount speaker" thread. I initially thought you were looking for a "in-wall" design, but it seems that it's actually "on-wall." Anyway, if this is your first DIY build and your SQ standard is not extremely high, using the SS drivers is, in my opinion, somewhat risky unless this is cost no object. The Dayton or HiVi drivers I recommended can also make a great sounding design.

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