6" Guitar Speaker

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#3
mozz said:
If you can use 6.5", can't beat this price.
Eminence 6-1/2" Guitar Speaker 20W 4 Ohm
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Thanks for the tip!! Indeed, that is a GREAT price for the speaker; however, one purchaser reports:
"This one is not as warm is the 620H and this speakers resonant frequency is around 140hz where the 620 H is around 55.5 which is much more friendly sounding for guitar., this speaker is more harsh, would work Better as a harmonica speaker. The 620H is a superior speaker with a hemp cone."

Indeed the Parts Express speaker is ~$13 shipped; the 620H from Eminence is ~$70 shipped. I guess you get what you pay for. Eh?
 
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#6
Among the user questions and answers for that 6.5" Eminence, I found this:
I would also like to know the T/S parameters of these. I purchased 4 just because they are so inexpensive (and interested in more). I understand they will likely have a high "Q" and high FS but would still like to know what can be done with them.
kipakoo on Aug 26, 2015
BEST ANSWER: A sweep on the WT3 shows the parameters below.

Re: 4.01 ohms
--> Fs: 108 Hz <--
Qts: .966
Qes: 1.04
Qms: 14.2
Le: .48 mH
Mms: 5.59 g
Vas: .378 cuft
SPL: 93 dB
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I recently built a small guitar amp using a pair of 6.5" speakers with an Fs at about 103 Hz. Bass was not lacking, as long as SPL is kept within the speaker's abilities. I would say a resonance frequency of 108 Hz for these little 6.5" Eminences should work quite well for electric guitar.

-Gnobuddy
 
#8
I also asked the manufacturer for the specs on the Weber Ceramic Signature 6S 6" speaker. First for the sensitivity, the reply was:
"It’s going to be in the very low 90's."
OK. What about the rest of the Thiele/Small parameters:
"I am afraid I do not have that info to give you. I would if it existed, but it doesn’t. I’m sorry."
What? A manufacturer that can't (or won't) make the effort to measure their own speakers?....Perhaps I'll put my $$ elsewhere......
 
#11
dotneck335 said:
"I am afraid I do not have that info to give you."
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For what it's worth, the crucial Thiele-Small parameters that let you design for an accurate bass response go flying out of the window as soon as you drive the speaker with pentodes, and put it in an open-backed enclosure.

Because of the high output impedance of tube guitar amps, the damping current that normally flows in the voice coil (due to back-emf from the coils motion in a magnetic field) is unable to flow. Result, no magnetic damping to speak of. Result, mechanical Q of the speaker soars to nearly Qms (instead of being down around Qts.) Result, big bass hump, soggy bass response. Partial fix: open-back cabinet which heavily cuts deep bass, sweeping the big bass hump under the carpet.

Since those Thiele-Small parameters become useless anyway for guitar amp use, there isn't much point to the manufacturer measuring or providing them.

The story is different for bass guitar speakers, and P.A. speakers, and, of course, Hi-Fi speakers.

-Gnobuddy
 
#12
Gnobuddy said:
...the crucial Thiele-Small parameters that let you design for...
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Oh, they are still there, and when used properly still give accurate results.

The main change is that damping (usually mostly electromagnetic) must be modified for, as you say, the non-Zero amplifier impedance. Say we take a big old Altec with Qt of 0.33. On a typical classic Fender this becomes 0.7 or so. On a no-NFB pentode we have nearer Qt(eff)= around 3, except now we must break-out the several parts of Qt because only Qes changes, Qms and the other one don't change.

Knowing the new Q (even roughly) we can make predictions. Say open baffle. Q of 3 means a 10dB bump. But the open baffle has a 6dB/oct bass cut. If we size the baffle so this cut hits 9 or 10 dB where the speaker resonance is up 10dB, we have a fair (not perfect) flatness for 1.5 octaves below where we'd expect that size baffle to loose thump. This (plus the bi-di throw of an open baffle) is marvelous size efficiency. One of E-V's papers points out that it is comparable to a good vented box, except it is big and flat not semi-cube like good furniture. And tends to flap; this is a Large-Cone(s) system. This is the Fender Twin. (But oddly no Stack seems built this way.)

Also: Qt(Qes) and Fs and diameter directly tell you the power efficiency in the flat range, above where a box matters and below beam forming. This power efficiency is the base for adjusting back-box for the bottom octave, and can be used to quick-predict power response when horn loaded.
 
#13
dotneck335 said:
I also asked the manufacturer for the specs on the Weber Ceramic Signature 6S 6" speaker. First for the sensitivity, the reply was:
"It’s going to be in the very low 90's."
OK. What about the rest of the Thiele/Small parameters:
"I am afraid I do not have that info to give you. I would if it existed, but it doesn’t. I’m sorry."
What? A manufacturer that can't (or won't) make the effort to measure their own speakers?....Perhaps I'll put my $$ elsewhere......
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Don´t be harsh with Weber. 😡
They are not a 2 city block sized factory like Eminence or Celestion with 400 employees but a very dedicated small custom builder who makes them one by one, and offers a bewildering array of options, with typically 6 or 8 cone options (straight - curved - shallow - deep - smooth - various ribbed ), 6 or 8 voice coil options (paper - kapton - Nomex - fiberglass - etc.) , 3 or 4 doping ones (no-light-medium-heavy), different dustcaps , for *¨*each** speaker size.
You want him to measure TS parameters for all of them and keep them available? 😱

besides, 2 points:

1) TS parameters are NOT used to design Guitar cabinets anyway, period.

2) most respected Guitar speaker makers (Jensen, Celestion, even Altec or JBL) did NOT supply TS parameters (which by the way had not even been invented) for about 50 or 60 years.
Did that stop Leo or Jim from using them and getting killer sound?
I guess not.

But ... but .... now large manufacturers supply them!!!! 😕

Well, why not, they make thousands of each type, they already measure and publish them for the Hi Fi crowd , so telling the dedicated employee to also pick one from the production line and measure it is easy.
Why not? ... the guy is getting his salary anyway and the anechoic chamber is already set up.

But just *try* to have any large Manufacturer to make you *one* , say: "6" speaker, light cone, 4 ribs, lightly doped, 1" Nomex short voice coil, 4 ohm, 15W, large cloth dustcap" 😉
 
#15
The NFB that our amps have do a decent job of bringing the dampening factor down to give a little control over the speaker. And the SS amps that have more than enough dampening we throw in some current feedback to get more of a tube sound. Funny world huh?
 
#16
For most small speakers, you will not go wrong with this:

Advertised diameter. Times 1.1. Calculate a Cube. Figure the volume. Now sketch a NON-cube, and twiddle to get the same internal volume. 20% error is nothing, 40% error is hardly-anything. Build.

So-called 6-inch speaker. Times 1.1 is 6.6. And 6.6*6.6*6.6 is is 287 cubic inches.

"6 inch" boards are really 5-1/2 inches. If we cut 4 sides from such boards, the front must be 52 square inches. Which would be 7.23" square, but we prefer non-square. 6"*9" is 52 sqin (near enuff).

This is internal dimensions. The outside will be thicker by the thickness of the boards. Board thickness/length should be 20-30 (use 3/4" for an 18" side). Our small box suggests 3/8" stuff, though if 3/4" is on-hand and weight is not critical, use it.

Plan-ahead for corner overlaps, rebates, insets. Classic Fender cabs are top/bottom/side boards with speaker board inset a bit. For home use, face-nailing 3/8" plywood to stock shelf-boards is easy and functional. Drivers smaller than 12" really should be totally-enclosed, though of course you should try your Six open-back just to see how gut-less it can be.
 
#17
I figure the volume of my Micro Cube to be ~319 cubic inches, allowing for subtraction due to circuit boards. WinISD suggest that adding a 2" dia x 2" lng port will provide ~ 3db more bass (@131 Hz---low 'C' on my lap steel) with the Eminence 620H driver, albeit with a bump-up at ~ 250 Hz. Port would also have to be on the side or back, no room on front baffle. Hmmmmm......
 
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#19
PRR said:
...287 cubic inches.
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My experience is that small open-back cabs like this sound extremely "boxy". Because of the smaller linear dimensions, all those internal acoustic resonances move up into a frequency range where our ears are quite sensitive. The result sounds a lot like holding a 5 litre bucket (or a 1-gallon jug) up to your face and speaking / singing into it.

In my experience, people vary widely in their tolerance to this sort of sonic colouration. It doesn't bother some at all, and it drives others nuts.

I owned a Blues Junior briefly, and the boxy sound was one of several reasons why I didn't warm up to it, so it went on Craigslist. I owned a VOX AC4 TV even more briefly - that was so boxy I couldn't stand it, so it got immediately returned to the music shop I bought it from. My Super Champ XD has some audible boxiness, but not enough to make it unpleasant - I have learned to live with it, and I like other things about this amp.

To my ears, an open-back cab about the size of a stock '65 Princeton Reverb (which is a little bigger than a Super Champ XD) is the minimum size at which audible boxiness stops being much of an issue.I no longer build open-back cabs significantly smaller than this, even if the plan is to put a smaller speaker in it.

IMO, if you must go smaller than that, and if there are no valves in it (requiring ventilation), a sealed box is the way to go. Small sealed boxes still tend to sound boxy, but not as much so as an open-back box of the same (small) size. You can lightly stuff it with acoustic stuffing, foam rubber, or the soft insides of a cheap pillow, to reduce the boxiness a little.

Fuch's is the only manufacturer of electric guitar amps I know of that has left 1950s speaker cab "design" behind - they put acoustic wool inside their speaker cabs.

-Gnobuddy
 
#20
Gnobuddy said:
My experience is that small open-back cabs like this sound extremely "boxy". ...
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Well, yes. That is why I proposed a closed box.

Open-back has some real advantages but mostly only when it is bigger than the acoustic instrument it is reproducing. Foot-wide is marginal for band guitar. Twin was better in days when electric Bass was not the authoritative thing it is today. A 4-foot baffle is about a minimum for "full range" all-sorts music. And you note that nobody seriously makes open-back bass speakers. (OK, I know a bass virtuoso who used a Twin, but he was the star, and another bassist bottomed the sound with a closed Ampeg.)
 
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