Zaph L18/27TBFCG question

[sangram]

Hi

I believe a few guys here are building this, and so am I.

My drivers and the better crossover parts (Goertz 14 AWG foil, Solen caps, Eagle films - all the series components) are reaching me early next week or today, so I shold start briefing woodworkers early next week.

A few Qs on cabinets, stands and ports, would be great if someone helps me out here. Thanks in Advance.

1. Box volume: How tolerant is the design to small changes in internal volume? Since the woodworking is local (shipping to India is killing) and my brief to the woodworker will be to use corner and front to back bracing above woofer, which will probably kill a bit of internal volume. I will increase the dimensions to compensate, but may go slightly off - how big of a problem is it?

2. Stuffing and damping: I don't have Sonic Barrier, Whispermat etc. available, so will be using local substitutes, someone help me with making a choice:

a. Car carpet (difficult to get but can try)
b. Generic yellow bedding foam
c. Recron - the Indian substitute to Dacron
d. Coir

3. Ports: I may not be able to get the exact port tube of 1.6" internal width. In which case I will need to plug the box dimensions to the closest I know, along with the T/S (I'll be using Zaph's average of two units, not manufacturer specs as I can't measure them myself) into WinISD to get a port length to find the length I'll need to tune the box to the 42 Hz required. Is this acceptable as a procedure?

Staying on ports, what would be a minimum acceptable width? I thought 1" would be way too small, and 3" too wide. Is there some way to determine port width WRT box/woofer size or air velocity?

4. Cabinet material: I will probably be using plywood and not MDF (easier to get). The stuff varies greatly in quality, so I'll have to figure a way to get good quality board. I may have to use 1" ply throughout, buying just one 4/8 sheet. Apart from increasing all external dimension by half an inch, anything else to watch out for? Like what glues, type of joints etc. should be used?

5. Stands: The application is for nearfield monitoring from my DAW at my home studio. I was thinking of buying a couple of inexpensive barstools and setting them up for the time being, and later figure out how to make the stands. Which is where I need the most help. I have no idea on how to make a good stand. Any pointers, link would help, as I have never used standmounts before.

I was thinking sand-filled PVC pipe with MDF platforms on top and bottom (absorbent), or a complete cast iron structure spiked to the floor (transmittive), or a combination (MDF platforms/cast iron rods or Cast iron plates/sand-filled pipe)... Which way to go?

Boy, this is surely my last try to get things from USA by courier. The delivery is quick, but $200 is what you should be prepared to spend, over and above the cost. $80 shipping, $120 tax. This thing had better be beating some high-dollar designs, which I am pretty sure it will do.

Thanks again.

[sangram]

Hi

The title may be misleading, I'm looking for any help at all, and not, as the title would suggest, only from Zaph.

So guys, help a noob out, please.

TIA.

[Zaph]

I don't see anyone helping you, so I'll just put out a few quick answers.

1. Not too critical but be sure to err on the larger side. Also be willing and able to adjust the port length to maintain tuning.

2. It's difficult to judge the consistency and effectiveness of any of those items. Dacron can work, but due to it's fluffy consistency, it's difficult to arrange in a vented enclosure so that the middle of the cabinet can remain open. If you can get it in denser sheet format that would be fine. Otherwise, consider 1/2" carpet padding, doubled up to 1" thick on all internal sides. This stuff is also variable in consistency. Your best bet is to search out items with proven acoustic properties from vendors who supply that type of thing. Good luck.

3. If you are not using a flared port, use roughly 50mm inside diamater and calculate a new length using WinISD. Anything much larger than that will not fit in the box, and anything smaller than that without a flare will have turbulence noise.

4. Plywood is fine, as long as it's void-free. Leave it to your woodworker for figuring out the corner types.

5. Stand construction is not critical. The issue bigger than mass, damping, coupling and all that is tip-over stability and speaker location. These need to be out from the walls a bit and the tweeters need to be at ear level. You mention these are for near field listening, however I hope they are still at least a meter away from your ears. Anything closer than that will make them sound a little on the warm side, along with some integration and imaging issues. These are not nearfield speakers by design, but should work fine at least a meter away.

Originally posted by sangram
This thing had better be beating some high-dollar designs

I almost regret posting my designs for fear that the design will not be liked, the expectations are too high, or the pain in building your own speaker is too much. (among other things) So, I hope it works out for you. If you have more questions, I'll let others answer them. I'm a little busy and won't be back to this forum for some time.

[sreten]

Hi,

You say the application is nearfield monitoring, the design as is is not suitable.

There is a reduced baffle step crossover available. However, it comes with a disclaimer.

From Zaphs article. This is what you need for genuine nearfield.

Dense padding (carpet type) etc... up to 1cm thick works best as
the first layer lining a wall, but its optional. To get vented boxes
working well the box walls should be lined with open cell foam
2cm to 3cm thick. In the tall thin box types you can add dacron /
BAF/Polyfill or similar to the airspace that is well way from the port.

There are two schools of thought with stands.
Lightwieght and rigid and massive and rigid.

Either works well IMO, I'd go all steel and simply copy a manafacturers product.

http://www.millennium-music.co.uk/ho...36&mode=detail



Is a nearfield stand.

/sreten.

[sangram]

Hi Zaph, sreten,

Originally posted by Zaph
I don't see anyone helping you, so I'll just put out a few quick answers.

1. Not too critical but be sure to err on the larger side. Also be willing and able to adjust the port length to maintain tuning.

Great, that's all I was looking forward to hearing. The baffle will also become a bit larger. I'm using 1" wood through and through, and trying not to have two sides of the same size. So almost all sides add 1/2", and the depth 1/4" more than the PE box, the volume also goes up a bit.

Originally posted by Zaph
2. It's difficult to judge the consistency and effectiveness of any of those items. Dacron can work, but due to it's fluffy consistency, it's difficult to arrange in a vented enclosure so that the middle of the cabinet can remain open. If you can get it in denser sheet format that would be fine. Otherwise, consider 1/2" carpet padding, doubled up to 1" thick on all internal sides. This stuff is also variable in consistency. Your best bet is to search out items with proven acoustic properties from vendors who supply that type of thing. Good luck.

Thanks, don't have those kind of vendors, but after reading sreten's post below, will be using open cell yellow foam. Think that should work out OK, or try for carpet padding.

Originally posted by Zaph
3. If you are not using a flared port, use roughly 50mm inside diamater and calculate a new length using WinISD. Anything much larger than that will not fit in the box, and anything smaller than that without a flare will have turbulence noise.

Just the answer I was looking for. I'll probably get someone to machine a 45-50 mm flare into the back panel and cut a tube to the length.

Originally posted by Zaph
4. Plywood is fine, as long as it's void-free. Leave it to your woodworker for figuring out the corner types.

Done, except if I leave to them they will just not do anything apart from regular glue. So maybe I'll specify corner braces and front-to back and side to side bracing.

Originally posted by Zaph
5. Stand construction is not critical. The issue bigger than mass, damping, coupling and all that is tip-over stability and speaker location. These need to be out from the walls a bit and the tweeters need to be at ear level. You mention these are for near field listening, however I hope they are still at least a meter away from your ears. Anything closer than that will make them sound a little on the warm side, along with some integration and imaging issues. These are not nearfield speakers by design, but should work fine at least a meter away.

I'll be about a meter away, just about. I guess I should have asked before I built. We'll see, or build another pair later for nearfield, or change the lowpass to suit.

Originally posted by Zaph
I almost regret posting my designs for fear that the design will not be liked, the expectations are too high, or the pain in building your own speaker is too much. (among other things) So, I hope it works out for you. If you have more questions, I'll let others answer them. I'm a little busy and won't be back to this forum for some time.

OK I had typed a really long reply to this.

That comment was directed at the frustration of paying almost double the original unit prices to get the units into the country. It had nothing to do with the design and whether the design was worth it.

I know you're probably not around to read this, but FWIW I really enjoy reading your pages, I think your designs are fantastic, and you're doing a great job for all of us in this little DIY community.

I for one would be really disappointed if this flow of info stopped, and would kick myself comatose if I felt my misplaced comment had anything to do with it. My apologies.

I don't think you quite realise how much it means to hear from you directly, Zaph, and how much more confident of my success this reply makes me. Thanks again.

Originally posted by sreten
Hi,

From Zaphs article. This is what you need for genuine nearfield.

Great, I can't see a way of emailing Zaph, but I seem to remember the crossover seemed have a 1.5 mH inductor instead of 2.2 mH on the woofer. Can't remember much else.

Edit: Forget it, I found the crossover on one of Zaph's earlier posts, the L-pad is also different, 3.3 and 5 ohms instead of 4 and 3.3 ohms. Maybe I'll try both.

Originally posted by sreten

Dense padding (carpet type) etc... up to 1cm thick works best as
the first layer lining a wall, but its optional. To get vented boxes
working well the box walls should be lined with open cell foam
2cm to 3cm thick. In the tall thin box types you can add dacron /
BAF/Polyfill or similar to the airspace that is well way from the port.

Awesome, I'll use up the surplus 2" foam sheet I have with me. And a layer of closed cell padding foam for the first layer.

Originally posted by sreten

There are two schools of thought with stands.
Lightwieght and rigid and massive and rigid.

Either works well IMO, I'd go all steel and simply copy a manafacturers product.

http://www.millennium-music.co.uk/ho...36&mode=detail

Is a nearfield stand.

/sreten.

Looks nice, and not too complex to make using steel rods and x-sections. I'll see what I can do.

Thanks a ton for the help!

[sreten]

Hi,

I would not use closed cell foam padding for the first layer,
it will reduce internal volume too much for little effect.
The first layer (up to 1cm) can be dense, but not closed cell.

Note that you can obviously EQ the baffle step, but building
with lower BSC gives you a liitle more monitoring headroom.

:0/sreten.

[sangram]

Hi,

I thought even the dense carpet padding would reduce the volume by a similar amount, maybe I could use a dense open-cell foam - if I can find it.

Thanks, I didn't remember about EQ, as I'm a bit of a snob about it. Maybe I'll put in these inductors (almost as expensive as the tweeters!!!) for now and bundle the reduced BSC components with my next speaker purchase, as I'm beginning to feel I should've gotten that crossover to start with.

Thanks sreten for your help. I look forward to a long and happy build.

[noah katz]

"I'll probably get someone to machine a 45-50 mm flare into the back panel and cut a tube to the length."

Ideally the end of the port inside the box would terminate with a small piece of wood so that it could be similarly flared.

Not only will there be less chance of port noise, but the air will flow easier in one direction than the other, with the possibility of the driver's center position getting offset, reducing effective xmax.

[sangram]

So flared on both ends, right?

Then I'll try to do as Zaph said, get two flared ports and join them back to back.

[noah katz]

"So flared on both ends, right?So flared on both ends, right?"

Yes.