15" speakercabinet

Johan Jansen · Post by **Johan Jansen** » 21 Feb 2003 6:21 am

Hi,
I'm trying to build new cabinets for my 15" blackwidow-speakers, , and I want them as compact as possible!!!!
So, if I build a cabinet 17" wide, 17" high, how deep should it be? I don't mind open or closed back, just compact!!!!
Thanks,
Johan

Scott Swartz · Post by **Scott Swartz** » 21 Feb 2003 7:36 am

Do you have the Theile-Small parameters for the speaker? These are measures of the mechanical characteristics of the speaker.

With these in hand, there are easy to use calculators on the net for optimum bass performance, ie not boomy or mushy sounding.

Otherwise just check specs of popular 15 inch speaker cabs and copy them.

Here's an example, let's assume a sealed cab.

Speaker = EVM12L
Qts = 0.2
Vas = 12.4 ft3
Fs = 52
Qtc = 0.71 (optimal smooth rolloff at resonance)

The box calculates to 1.05 ft3 for the above

Go here for the calculator I used
http://www.carstereo.com/help/Articles.cfm

The hard part is finding the T-S parameters for your speaker.

Tommy Detamore · Post by **Tommy Detamore** » 21 Feb 2003 8:15 am

I believe Peavey lists the TS parameters for all of their speakers somewhere on their website....

Mike Brown · Post by **Mike Brown** » 21 Feb 2003 11:22 am

Thanks Tommy. Here is a link to that page off of the Peavey website;http://www.peavey.com/support/technotes ... kwidow.cfm

Scott Swartz · Post by **Scott Swartz** » 21 Feb 2003 12:36 pm

Its cool that Peavey has the data available, a lot of times it isn't.

Speaker = 1501-4DT
Qts = 0.34
Vas = 6.64 ft3
Fs = 46.7
Qtc = 0.71 (optimal smooth rolloff at resonance)

The box calculates to 1.98 ft3 for the above. That would be internal volume, of course. You can go 10-20% smaller on volume by lining the box with 4 inch R-19 insulation and keep the Qtc at 0.71.

Tom Hodgin · Post by **Tom Hodgin** » 21 Feb 2003 12:54 pm

Johan, I just bought a speaker from Avatar Speakers for a 15" JBL..$79.95..18H x 18W x 151/2 D....perfect...IMHO........tom ps..www.Avatarspeakers.com

Terry Downs · Post by **Terry Downs** » 21 Feb 2003 6:46 pm

Johan,
If you desire a small cabinet, a ported design will give you much more bass than a closed or open back design. I ran the numbers on my Excel spreadsheet. I assumed an 18x18x15.5 outside, approx 17x17x14.5 inside (2.4 cu ft). I assumed the use of insulation will increase the effective volume enough to keep from subtracting the speaker magnet and structure volume.

Closed back -3dB freq: 97Hz
With a 4.5" circular port 1" deep -3dB freq: 77Hz

Low C note on C6 neck fundamental frequency is 65Hz. (55Hz for boo-wa) The ported cabinet would need to be 3.5 cu ft to get to 65 Hz. It would hardly be worth making it that big as you need mostly harmonics of the low C6th string anyhow. So 2.4 cu ft would be fine.

Steel guitar allows you to have a small cabinet. It's those darn bass players that need to have the large volume cabinets. E string on a bass is 41Hz and 30Hz for a B on 5 string. That is a big difference!! It would require 15 cubic feet to get the -3dB point down to 30Hz. (31x31x31in)

I will send you my spreadsheet if you want it.

Regards,
Terry Downs

Jeff Peterson · Post by **Jeff Peterson** » 21 Feb 2003 9:58 pm

Here's a formula....make it open back, and make it any size you want. If it's open, it's infinite baffle. You want more bass, turn it up.

Gene Jones · Post by **Gene Jones** » 22 Feb 2003 11:06 am

....(Johan)...So, if I build a cabinet 17" wide, 17" high, how deep should it be?....

The closed-back-ported cabinets that I built were ll" deep at the bottom and 9" deep at the top, i.e., the side panels were cut 18x11x9
www.genejones.com

Terry Downs · Post by **Terry Downs** » 22 Feb 2003 11:29 pm

An open back speaker cabinet is NOT an infinite baffle. It is a dipole speaker. An infinite baffle would be a board big enough to not disallow dipole cancellation within audible range. That would be a 28 foot wide cabinet. Another example of an infinite baffle is in a car trunk. When a sealed enclosure volume gets large enough with respect to the volume of air equal to the speaker’s compliance, Vas, the sealed volume of air does not add to the suspension stiffness of the woofer. An average "rule of thumb" for determining when the volume of air in the trunk equals or exceeds three times of the Vas total of all the woofers. Even with the large size of many trunks, it is still possible to use woofers where the relationship between the total Vas of the woofer and the volume of the trunk leads to a situation where the air in the trunk does affect the mechanical operation of the woofers. But it is still a closed space. Waves from the back don't cancel out the waves in the front. Much different than a dipole speaker.

The corner frequency of an 18 inch square cabinet is 376Hz!! An Evans FET 500 at 25 inches has a corner frequency of 270Hz.

Jeff makes a good point however. For most steel guitar music, really low frequency response from a cabinet is not necessary. Depending on your system, you can just turn up the bass to compensate for a small open back cabinet.

I interpret the post as a question of how to make the most compact speaker cabinet possible and not suffer any more bass loss than necessary.

Johan Jansen · Post by **Johan Jansen** » 23 Feb 2003 10:39 am

Thanks for all your replies, guys!
I hope to have some new, lighter cabinets very soon now!

Johan

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Click on the pic!

John Russell · Post by **John Russell** » 24 Feb 2003 6:22 pm

Johann:

I built a cab for my EV-15 speaker some 15 years ago. It measures 11" x 19" x 22". I worried a lot about the correct diminsions at first and then did what I suspect most audio mfgrs. do, just built something that was portable and not too bulky. It's roughly the size of a Peavey Nashville 400 amp.

At first it was open back to emulate the Fender amp sound. Then, a few years ago I insulated the inside, and built a back cover for it, then mounted to 2" tubes on the front as bass ports. A very noticeable improvement. Much better bass response though it is more directional but that's not an issue as I usually mike the speaker or angle it direcly at my ears.

The box is made of 1/2" plywood, reinforced all the joints with wood molding and metal corners. Works for me and easy to move around.

--JR

Johan Jansen · Post by **Johan Jansen** » 8 Apr 2003 8:12 am

So, if I conclude from different threads and emails, I can build closed-back cabinets with 15"black-widows from 1/2 " plywood,inside measures 17x17x11", front-ported by 4 2"-holes in the corners,all glued and screwed very well, some dampingmaterial inside, is this right?
Johan

James Quackenbush · Post by **James Quackenbush** » 9 Apr 2003 6:10 am

Johan,
At a smaller sized box that you want to make, you won't have a lot of meat in the front of the cab for ports...You can put your ports on the back of the cab....Jim

Donny Hinson · Post by **Donny Hinson** » 9 Apr 2003 9:44 am

I think an 18" square cabinet for a 15" speaker is far from optimum, but if the depth is kept over 11", it will suffice. It may sound "peaky", but it'll work.

Big speakers like big enclosures.

Buck Dilly · Post by **Buck Dilly** » 10 Apr 2003 9:58 am

Look around for the EV design. It is a baffled cabinet that is modifiable, in that it includes a front port that can be covered or uncovered according to taste. Small simple and designed by pros for amateurs to build.

Jeremy Steele · Post by **Jeremy Steele** » 10 Apr 2003 10:14 am

I built a "Thiel" design cabinet for a 15" speaker from plans I got from EV. I play bass through it, and it puts out an amazing amount of sound for its size. Not sure if it would work so well for steel, though.