Help Calculating the speaker box size

Hi all,

I'm planning to embark on a DIY speaker build project and need help in calculating the size of the box I need based on the woofers I'd like to use:

2 x Peerless 6-1/2" Nomex Cone HDS Woofer
1 x tweeter
1 x super tweeter

Peerless woofer specs are as follows:

Qts: 0.37
V(as): 24.76 L

According to this chart, i'm getting a volume of 18.57 L or 0.65 cu/ft.

Multiplying 0.65 cu/ft x 2 Woofers = 1.3 cu / ft box.

If my calculations are correct, then I'm thinking on a 1.3 box, with a 2" x 6.5" long port, I should be getting low 30Hz?

Anyhow, please feel free to correct me on anything here, I'm doing this for the very first time.

Cheers all,

Rado

 

Best to consult diyAudio

They do this kind of thing routinely.

 

SUCKER!!!
...er, I mean, COOL!!!

I'll second @biggerdog that Multi-Way - diyAudio will help you more. Maybe too much! Also DIY Speakers and Subs - AVS Forum | Home Theater Discussions And Reviews
Anyway, among other things I'm actually a loudspeaker design engineer, so let me say/ask:
- Which model # woofers exactly? (To get more complete parameters, in particular Fs, also maybe Qms etc.)
- All those parameters and box volumes and port dimensions are all approximate. Don't get too hung up on simulations, they are all somewhat incorrect, unless you get into a full LEAP simulation with measured data, or maybe REW - Room EQ Wizard Room Acoustics Software . If you start worrying about the effect of changing some dimension by a small amount, you have gone down the rabbit hole.
- "Loudspeaker Design Cookbook 7th Edition Book" from www.parts-express.com! is a really really good book, you should get it and digest it.
- What are you using for a crossover? And where did the design come from?
- I'd prefer to see a larger port, like 3 inch. Yes, it becomes longer. Yes, it can become hard to fit in the box. Yes, that's why sometimes designs use slot ports. Or passive radiators.
- Ported boxes inherently have inferior time response compared to sealed. However, my personal experience has been that if they are somewhat undertuned, that is not problematic.
Have fun, I haven't built a speaker in a while and am getting the itch. My current project is to figure out how to make a fairly large yet lightweight speaker to hang from a ceiling grid, and look odd/funky.

 

If you can provide more info on your woofer I can run calcs thru WinISD and provide box size, port diameter and length. Model number would be good.

 

Thank you head_unit for the lengthy response. Really appreciate it.

Since I've not yet purchased the drivers, I'm now leaning more towards SB Acoustics SB17CAC35-8, 6" ceramic woofer, 8 ohms. Fs = 28 Hz, Qms = 4.46. You can see full specs here.

Really appreciate this recommendation. Will definitely get it.

I'm going to try to get Madison Audio to either give me an off-the-shelf solution based on the drivers, or design one from scratch.

Design was my own idea. I was inspired by a pair of old Dahlquist towers I had + a pair of cheap Sony bookshelfs: Dahlquists had very warm, deep bass from 2 x 6.5" and the Sonys have super crisp highs from the tweeter / supertweeters.

Thanks for the tip.

Woow.

 

Definitely @Gibsonian . Here is the full specs PDF.

 

The SB acoustics drivers are fantastic. I use the SB17MFC in MTM config with the HDS tweeter. 1.6 cubic foot boxes. Crossover is LR4 at about 1.8KHz. Profile pic is them.

Also, I would strongly advise against a strictly generic simulation based crossover design. The result will be nowhere near optimal and you will likely be disappointed in the sound. Average drivers with great crossover will sound really good. Great drivers with average crossover will not.

 

WinISD says, for 2 drivers:

2.078 cu/ft box
30.06 tuning frequency
F3 = 31 Hz
With 3.0" vent, 7.91" long
With 2.0" vent, 3.03" long
SPL at 3 ft, with 120 watt input = 109 dB

Great looking freq response on this driver. I think you've chosen well. How much are these?

 

If I plug in a 1.6 cu/ft box as MusicnBeer has, F3 is then 35 Hz

 

How can you get 30hz in an enclosure under 180L? Doesn't the science dictate you need an enclosure that big...

 

No. The ratio of moving cone area to volume is what matters. A small cone can make deep bass in a small enclosure. SPL will be limited though. It's a compromise you make in the design.

 

I like how thin your boxes are. I'm going for max bass in the smallest box size (aren't we all?)

Can you elaborate on what it means "The ratio of moving cone area to volume"?

 

Thank you @Gibsonian , really appreciate it. These drives are cheapest on eBay - $62 each, when you buy 4.

 

p.S @Gibsonian that's a great looking Denon turntable in your pic, right?

 

The simplist example, double the drivers, as in MTM, and it takes double the box volume to get the same bass response. The benefit is 6dB more SPL.

My boxes are thin because I needed them tall to do MTM and keep the tweeter at listening height. I could have made the boxes any volume but 1.6 cu/ft worked out best for my drivers.

Be careful not to make the boxes too big. The box won't load the driver enough and your power handling will be bad.

 

How did you figure out to use LR4 crossover with your SB17MFC? Like why not LR2 or LR8?

 

The goal to to have the crossover slopes as gentle a rolloff as possible with the drivers chosen. You cannot do LR2 with the drivers I used because the HDS tweeter cannot handle the lower frequency excursions required for the LR2 gentle rolloffs. The SB woofer is also borderline in being able to do LR2. I would definitely do LR4 with the driver you're considering because of the resonance peak.

You also want to keep the crossover frequency in a two way as low as possible, as long as the tweeter can handle it, to minimize the directionality differences between the woofer and tweeter at the crossover frequency. The best sounding speakers have the most even dispersion of sound emitted in all directions. This is called the power response. You can google it.

 

...and also, LR2, LR4, etc. refer to the measured acoustic response, not the electrical crossover filter. An LR2 crossover will most likely be very complex to shape the gentle rolloffs correctly.

 

I think that’s exactly my point. If we, as audiophiles, strive to get accurate reproduction of sound, how is a couple of 6 and a half inch drivers reproducing 50hz bass notes at -6db accurate?

 

I just started building a pair of speakers. I am using Building Speaker Enclosures by David Weems. It's a Radio Shack book from the 1970's. Gives all kinds of guidance on sizing the enclosure and selecting speakers. Has several speaker builds with plans and of course Radio Shack speakers.

 

These drivers are -3 dB at 31 Hz. Where are you getting -6 dB at 50?

 

Thanks! It is a JVC TT 101.

 

Might be worthwhile picking up the 4th edition. There have been some advancements in speaker design since then. Also check out Vance Dickson, Loudspeaker Design Cookbook.

jeff

 

I have a 1977 JVC QL-7, owned it for 10 years now, just had it fully serviced. Supper happy with it.

 

I wonder how good the bass is compared to a proper 15 inch woofer? Beyma 15lx60v2 cones to mind. I had a pair of them in square 20”x20”20” (131L) cabinets and the bass went down to 19hz WITH AUTHORITY AT HIGH SPL.

Are you claiming this little woofer can too? If so that’s amazing but I don’t really trust those measurements. Maybe one of these days I’ll take some time to build one and I’ll be blown away. (Not likely)