I just got the yen to experiment with a subwoofer out
on my Yamaha receiver.

There's a couple 8 inchers I haven't built Voigt pipes for yet.
I'm wondering if I can do a quick and dirty build with one
or both.

I have the RP U100 book out in front of me, but sure can't see
anything about a cutoff frequency or what goes on inside the Yam.

Oh yeah, no spec sheet on these 2 Roland 8 inchers either.
They were sold as closeouts from Roland pianos on Ebay.

Would it be a waste of time to mount these? Play with
isobarik maybe?

I'm on my way to do one of Fitz's Tuba 18's eventually.

IMHO
Bill W.

I have a spare box that I can make a front baffle for
just to see what the sub output of the little Yamaha
would do-- for grins, as we say. In my general ignorance
of things, I wanted to try the isobarik technique to get
that constant pressure volume mentioned in Ray Alden's
book Speakerbuilding 201.

But yes, I want to do the Tuba 18 and am enthused about
it.

I have never used a sub system before, so this is
just daydreaming.

The Roland 8 inchers have pretty small magnets too.

I'm wondering what one of those cheap plate amp subs
woudl so in such a rig?

--> The thing I want to avoid at all costs is any sort
of rumbling, wall shaking thud that may be a cause for
gee-wiz, but sound like shite on music-- in other words,
what most people experience as home theatre. :-/

I'm pretty happy with my single driver MLTL boxes using
Fostex 127e from a design at Single Driver Forum. It is the
best scratch build I've done, but still doing some tuning
stuff on those.

This is a comparison of a tuba 24 with EV 18 subs. The 18 inchers are shown in blue and the tuba is orange. If you listen to a bass note progression on the EV speaker, you'll hear every note about the same volume level.

The tuba hits 40hz and 80hz real loud, but 50hz is 4 times lower than 40hz and about 50 times lower than 100hz(!) In terms of musical notes, this means D(37)and E(41) are blasting, but then F(44) and G(49) are much lower. Notes A(55) through C(65) grow gradually louder and when you hit D(70) again, the sound is getting pretty loud. E(80) is booming one note bass with F(87) and G(98) very loud too. Loudness falls off after that again. In the span of one octave, D(37) to D(70), loudness starts very high then drops to a low and rises to a huge 15dB peak again. I don't know about you, but two huge peaks in a single octave is unacceptable to me.

I'm sorry, I just couldn't let this go unnoticed. I don't mean to be a nag but I couldn't remain silent any longer. I was told this site was choosy and quality oriented but then I see tubas with whatever woofer will fit and dr horns with 50 cent knock off piezos. They may be good for garage bands on the cheap but I don't think you can call them hi fidelity.

• Frequencies of Musical Notes

All speakers have strengths and weaknesses. Single drivers, with and without subs, multi-way speakers, planars, horns - All have their strengths and weaknesses. Remember that the Tuba horns were designed for environments where EQ is generally available and response peaks can be smoothed out.

Bill's plans are illustrated and detailed. They are good quality plans. Bill is also a sponsor here, paying to support the website and helping to make it possible for us to have this discussion. He gives of his money and time to host his forum here, and to provide support to people building speakers using his plans.

I wouldn't call that "cheap." What I think is cheap, is manufacturers of audio products that pop into discussion websites like these for free plugs or to bash their competitors. If an audio kit manufacturer or DIY company doesn't host a support forum, that's cheap. If manufacturers or dealers go into open discussion sites just to plug their products, that's cheap. And if they send in sockpuppets to attack competitors, that's not only cheap but also low. I see a lot of bottom feeders like that popping into various audio discussion forums.

Don't think they'll make it as subs. Courtesy of 'Zene':

Fs = 78.76 hz
Vas = 24.5 L/0.8652 cu ft
Re = 7.309
Le = .2462 mh
Qms = 5.772
Qes = 1.977
Qts = 1.473
Sd = 21.4 sq cm/3.317 sq in
BL = 0.4477 N/A (calc'd)
Spl 89.65 1w/1m
Pe = 30W

Here's an Alpha TL (end loaded straight pipe) I did for someone, but if they built it they didn't let me know how it performed. Looks good in a sim though:

L = 39.25"
SO/SL = 166"^2
recommended stuffing density = 26 oz of polyfil

GM

Well, back on topic, and me being the cheapest of all with
no test gear I'm going to start cutting holes in wood and make up a
small isobarik.. maybe play it with no mains just see if it is
doing anything.

Far as I know this will be plug and play and whatever cutoff will
be handled by the receiver. With a phono plug connection I'll
prob'ly buy a phono plug one end and bare on the other rather
than fooling with tinning and such.