4x8" Speaker Cabinet...Anyone?

[printer2]

Originally Posted by StephaninMelb

I ran through the enclosure calculations and filled in the missing values.The bottom line is that speaker type won't work in a sealed enclosure. The speakers motors aren't strong enough. This means is that the QMS (4.53), QES (1.17), and QTS (0.93) is too low a value. They need to be electrically & mechanically stronger. There are three ways to fix this. (1) Get stronger speakers or (2) Open the back or (3) Use ports. Ports are kind of silly for quitar, but in your case the enclosure needs to be opened somewhat. The necessary enclosure volume is 59.8148 cubic feet or 3.91 x 3.91 x 3.91 feet. You can adjust the sides to suit. You will need four ports 2.5" in diameter with 5.6" port length (pipes). If necessary these don't have to be on the front, but ideally they should be.


QMS......4.53
QES.......1.17
QTS......0.93
Fs........45
QES.....1.17
QTS.....0.97
QTC.....0.707
VAS.....0.93 ft3

Sealed Enclosure
3dB Down Point (f3) 34.2165 Hertz
Resonant Frequency (f3) 34.2097 Hertz
Enclosure Volume (Vb) -2.2508 cubic feet <--- this negative value indicates that the
QMS, QES and QTS values are too small (the speaker isn't strong enough)

Ported Enclosure
3dB Down Point (f3) 13.382 Hertz
Resonant Frequency (f3) 19.1485 Hertz
Enclosure Volume (Vb) 14.9537 Ft3 x 4 = 59.8148 cubic feet <-- calculation for 4 speakers
Box = 3.91' x 3.91' x 3.91'
Port Diameter 2.5 Inches
Proper Port Length 5.5977 Inches
Reference Efficiency 0.19977 %

I am a little confused. The speaker will not work in the enclosure? Does that mean they will not make any sound? While I probably would not have picked a foam surround speaker for guitar I think the software is assuming that the speakers will be used for hifi purposes. I was under the impression that a smaller enclosure will move the low frequency cutoff up the frequency range (and since we are dealing with guitar a speaker going down to 34Hz would be a detriment). As a further consequence we would get a bump in the bass response which we might be able to tame with a bass control.

Now operating a speaker with a loose cone that is expecting to use the air in the back of the cabinet to limit its excursion in an open back cabinet seems to be a recipe for disaster. Well maybe the spider is stiff enough to keep things in check.

[printer2]

Originally Posted by StephaninMelb

Every additional 3dB SPL (decibels of Sound Pressure Level - the true indicator of volume) doubles the apparent volume of a sound. Therefore a speaker rated at 97dB SPL will be "twice as loud" as a speaker rated at 94dB SPL and half as loud as one rated at 100dB SPL (all common ratings for guitar speakers). You can make an amp louder or quieter just by changing the speaker to one with a greater or lesser sensitivity. You get the most volume out of your amp by buying the highest rated speaker you can afford. This is also the cheapest way to maximize sound volume. The alternative is to disregard speaker SPL and sink more money into a more powerful amp.

As a rule of thumb doubling the number of speakers adds 3 dB, which doubles the volume. Note that an inefficient pair of 8 / 10 / 12 inch of guitar speakers with 3 dB less in SPL compared to a higher rated 2 x 12 is equal to only a single better quality speaker. With the less efficient cab (rated 3 dB lower SPL) you are carrying around one speaker of "dead wood" in a 2 x 12 or two speakers of "dead wood" with a 4 x 12. A 2 x 12 with high SPL rated speakers can be as loud as a 4 x 12 with average speakers. When there is an SPL difference greater than 3 dB the advantage increases.

Excursion Limit or Xmax
Quite simply this is the range the coil can move without leaving the magnet (blown speaker). Excursion limit is the Xmax figure and measured in mm. The total travel is double the Xmax. 0.8mm Xmax is OK for a guitar speaker and will support a low E note. For bass guitar or full-range PA the Xmax should be at least 4mm

Hate to disagree but 3dB is not a doubling of volume or loudness. More like 10dB. Three dB is perceivable but not a great increase in sound. Put a stereo pair of speakers beside each other and if you can run a mono signal. Turn one speaker off then on again. Does not sound twice as loud, does it? The doubling of sound, namely adding the second speaker's output to the first adds 3dB to the sound. It does not make it sound twice as loud.

[Jammin'John1]

"Every additional 3dB SPL (decibels of Sound Pressure Level - the true indicator of volume) doubles the apparent volume of a sound."

NOT TRUE !
All things considered,it takes twice the power to raise the volume 3db on a given speaker.

It takes TEN TIMES THE POWER to DOUBLE the volume.

3db is the smallest NOTICEABLE volume increase that the human ear easily notices.

JJ

[Joe-Bob]

Originally Posted by Jammin'John1

"Every additional 3dB SPL (decibels of Sound Pressure Level - the true indicator of volume) doubles the apparent volume of a sound."

NOT TRUE !
All things considered,it takes twice the power to raise the volume 3db on a given speaker.

It takes TEN TIMES THE POWER to DOUBLE the volume.

3db is the smallest NOTICEABLE volume increase that the human ear easily notices.

Yes, 3dB is twice the power. For instance, a signal splitter should have a 3dB boost for unity gain.

And tests show that most people will notice a difference of about 1.5dB.

[SamClemons]

If you want to give 4x8's a try, old 4x8 PA columns are cheap. Fender made some with Jensens. I bet they would be fabulous with a guitar.

[StephaninMelb]

Most 8" speakers sold these days are pretty low performance. As mentioned using PA column speakers as donors would be worthwhile looking into. You will probably be disappointed with four inexpensive 8".

There should be a good market for a high quality / high performance 4 x 8 and 2 x 8. Phil Jones builds terrific bass & guitar cabs using three / five & six inch speakers.

[Joe-Bob]

Originally Posted by StephaninMelb

There should be a good market for a high quality / high performance 4 x 8 and 2 x 8.

I'm not so sure about that. I think most guitarists would rather go with a 2 x 10 or a 4 x 10. The new Neo speakers are light enough to make 4 x 10s practical. Also, a 4 x 8 has less than 15% more area than a single 15.

[StephaninMelb]

I've had good results with the large Phil Jones cabs and their small ones have great sound too. The interesting tone feature about high-quality small speakers is they have very fast response - they sting like a bee! I use them with a large bass rig..... which was the original PJB market.

[mrz80]

Originally Posted by Joe-Bob

Updates?

Stereo/mono switching 1/4" phone jacks just got here, and I'm still waiting for the Parts Express order with the screws for mounting the speakers (wouldn't you know, none of the hardware stores or bigbox places in my hick li'l ol' Gator Country town carry black pan-head screws ). Once the screws get here, it's mount 'em up, wire 'em up, and start playing with stuffing. Oh, and grilles, I'm looking for a better bracket for the round grilles than those clunky plastic things I got from P-Exp.

[mrz80]

Got the drivers mounted in the cabs and wired up. Propped the backs up against the cabs and jury rigged some connections to a cheap old Radio Shack stereo amp and fired it up with my semihollow into the GT-8. Didn't sound half bad, if kinda muffled (it's after midnight and everyone else in the house is asleep :) ). Need to stuff some poly in, screw the backs on, and lug the critters to church next band practice to see how they do. Pix later; I'm exhausted and so is my phone (wherein are the pics). zzzzzzzzzzzzzzzz

ps - yeah, really good drivers like Jensens or Celestions or so forth would probably produce better results, but the Peaveys ain't half bad for now

[tele salivas]

This is one of the craziest, and most enlightening threads I've ever read.

[mrz80]

The craziness moves into the dining room! I finished up the wiring, put the backs on, and lugged the cabs into the house for some playtesting. The loud stuff'll have to wait for the wife to go to quilt group, but a few chunky chords and a couple quick melodies convinced me I'm On The Right Track (tm).





I'm carting everything to church on Friday to scare everyone to dea... er... give 'em a try in a band environment. :)

[steadyriot]

I'd love to see an update on this! =D