I don't remember what dims I posted, but the basic T/S max flat comes closest to what you built though the vent is 1.5" diameter x 1.125", not 1" diameter, which dramatically lowers Fp so LF output should be minimal. I assume it sounded 'muddy' because the driver/vent was being severely overdriven at even modest SPLs. With no damping there's also some comb filtering with the vent up beyond 1 kHz.

With the recommended vent there's much more mid bass, but less LF extension, and the comb filtering is much higher in amplitude with no damping.

With a 2" x 6" vent, Fp is down where the 1" x 1.125" vent put it, though it's better damped due to the greater vent air mass and now the comb filtering is truly excessive due to its length so little wonder it sounds 'clear', what with the high amplitude 'spiked' harmonics. Like BB opined, accurate reproduction it ain't, but you seem to need to hear the kind of dynamics that separates a speaker system from sounding 'accurate' to one that sounds more 'live'. To get both requires a much more serious system than a couple of small FR drivers.......

Anyway, based on your apparent performance preferences, an optimized (but unstuffed) Voigt pipe may be the 'best conclusion' for this speaker project.

WRT the Tuba, I have a super slow dial-up so didn't wait for the link to load, but I gather it's a folded radial design with too small a mouth, like Tom Danley's LABhorn. If so, then without a corner or at least a wall/floor junction to load it, then significant EQ will probably be required to shape its FR. Also, the long pathlength will probably require digital TD to get it ~in step with the mains.

Still, with the advent of small, high linear excursion drivers, reasonably compact upper LF/midbass horns can be realized, so assuming you're more interested in a 'fast' upper LF/mid-bass system to fill in below a FR system rather than a true sub system, then I imagine the Tuba will get the job done.

'Thump test'? Do you mean 'click' test? If so, it's just a little 1.5V battery powered ckt. using a DC rated SP-DT toggle switch to make/break the driver. With a typical minimally lined or stuffed vented cab it can still be somewhat underdamped (peaking at Fb, or worse, higher up if severely underdamped) so when the driver is switched it will tend to 'boom' (AKA 'ring') to some extent. Damping the vent till all you hear is just an amplified 'click' means it's critically damped, i.e. make it somewhat aperiodic, so any more just rolls it off more (overdamped). Note that a resistor equal to whatever the amp's output resistance is required between the switch and speaker for best results. I don't know who originated it, I first saw it in a mid '60s DIY speaker building book written by a couple of Altec employees.

GM

I would love to hear a set of lowthers, so will someone PLEASE bring a set to GPAF!!!???
thanks
-akhilesh

Greets!

I don't remember what dims I posted, but the basic T/S max flat comes closest to what you built though the vent is 1.5" diameter x 1.125", not 1" diameter, which dramatically lowers Fp so LF output should be minimal.

--
Dims are given at FRDF.
I was just going through my hand notes on that stuff... lessee:
my hole borer is 1.5 inches and that was the port I played with. I re-measured and it's 1.5 diameter with various lengths tested. What would moving the port do-- front, back?
--

I assume it sounded 'muddy' because the driver/vent was being severely overdriven at even modest SPLs. With no damping there's also some comb filtering with the vent up beyond 1 kHz.

With the recommended vent there's much more mid bass, but less LF extension, and the comb filtering is much higher in amplitude with no damping.

--

With a 2" x 6" vent, Fp is down where the 1" x 1.125" vent put it, though it's better damped due to the greater vent air mass and now the comb filtering is truly excessive due to its length so little wonder it sounds 'clear', what with the high amplitude 'spiked' harmonics. Like BB opined, accurate reproduction it ain't, but you seem to need to hear the kind of dynamics that separates a speaker system from sounding 'accurate' to one that sounds more 'live'. To get both requires a much more serious system than a couple of small FR drivers.......

--
No doubt. Playing at low levels all the time might be
a problem too and the 'listening room' leaves much to be desired.
I had stuff 'dry clamped' for quite a while and can hear slight
differences now that the glue-up is complete. Inside seams are
caulked, no special wire. The 2x6 ports are not glued in. I
can still monkey with that as needed.

One of the problems I'm dealing with may be solid state amplification
equipment and source material that varies widely. Or I might be going deaf.

--

Anyway, based on your apparent performance preferences, an optimized (but unstuffed) Voigt pipe may be the 'best conclusion' for this speaker project.

--
I yes, I've wanted cut a Voigt for almost a year: tools
and materials preventing a lot of progress: I want to do Poplar
carcass. And I bought 2 of those full range Rolands from Ebay.
Those are 8 in. I want to put those in Voigts. Nobody over at FRDF
has made specs for those but the magnets are pretty small.

--

WRT the Tuba, I have a super slow dial-up so didn't wait for the link to load, but I gather it's a folded radial design with too small a mouth, like Tom Danley's LABhorn. If so, then without a corner or at least a wall/floor junction to load it, then significant EQ will probably be required to shape its FR. Also, the long pathlength will probably require digital TD to get it ~in step with the mains.

--
I started that project yesterday. It's something I can do
with what I have in tools and material costs. I wanted the
experience of doing this construction.

Do you have an opinion on SonoTube sub woofer constructions?

--
Still, with the advent of small, high linear excursion drivers, reasonably compact upper LF/midbass horns can be realized, so assuming you're more interested in a 'fast' upper LF/mid-bass system to fill in below a FR system rather than a true sub system, then I imagine the Tuba will get the job done.

--
Yes, I'm thinking that is ideal. Low level and almost nearfield listening is the way this setup looks. Not looking for seat-shakers.
The driver used for the Tuba has the highest excursion I'm aware of:
16mm. It's the MCM #55-2421 8" : Claimed Fs of 25hz, Qts .18, Vas 39 ltr, SPL 87db, 120 w power rating and 16mm Xmax. Link below... but the unit is out of stock.

--

'Thump test'? Do you mean 'click' test? If so, it's just a little 1.5V battery powered ckt. using a DC rated SP-DT toggle switch to make/break the driver. With a typical minimally lined or stuffed vented cab it can still be somewhat underdamped (peaking at Fb, or worse, higher up if severely underdamped) so when the driver is switched it will tend to 'boom' (AKA 'ring') to some extent. Damping the vent till all you hear is just an amplified 'click' means it's critically damped, i.e. make it somewhat aperiodic, so any more just rolls it off more (overdamped). Note that a resistor equal to whatever the amp's output resistance is required between the switch and speaker for best results. I don't know who originated it, I first saw it in a mid '60s DIY speaker building book written by a couple of Altec employees.

--

That must be it. I couldn't imagine rapping my knuckles
near the driver to get any sort of result. The only battery
test I've used is for polarity.

Thanks for answering all my (maybe inane) questions. I mentioned to
Bill that what I have to work with is the equivalent of a quote from
the Time Portal episode of orginal Star Trek which said "I'm working with stone knives and bearskins."

We've spoken of comb filtering which is (from my recently purchased "Speakerbuilding 201" book) are dips and peaks very close together which look like the tines of a comb. But what does this represent as audio reproduction? What do my deaf ears hear?

Lastly, it may be time to learn some measuring techniques. I know there's a measuring forum on here at ART, but what would you say is a good minimal measuring setup?

lon

--

GM

• MCM 55- 2421

I've had this discussion any number of times, although usually in the context of baffle step correction filters.

IMO Reflections off of the back of the cabinet through the cone are in the 1-2kHz range. The reflections put a bump in the frequency response of the speaker in this range. People like the effect.

--

Must be so. As I described to bernie it gives the effect of listening to the speaker as an instrument-- if that makes any sense.

--

It gives sparkle to the sound of the speaker. Removing the reflections give a sound more true to the recording. It lacks the extra sparkle. It lacks "life". The same happens with. By cutting the treble to match the bass, you remove the exaggerated mids and the sound then lacks "life".

--

Our original discussion was about 'muddiness' at lower musical
instrument ranges: string bass plucking on jazz solos in poarticular.

But I also use organ recitals as a test of performance. I'd like to
have 1.) sharp and noticeable string decay on plucked upright bass and (perhaps) boomers from the organ recitals. I haven't gotten a happy medium for that.

--
Don't get me wrong. If you like the extra "life" in the sound of your speakers, by all means go for it. Just understand where it is coming from.

Bob

Thanks Bob. I appreciate these dialogs, but many of these threads get buried over time. Sorry if my response was slow. Maybe Wayne can
be persuaded to upgrade the forums. I noticed that some Linux discussions have a personal profile that contains 'my discussions' so all thread answers are grouped together under the thread started and can be indexed that way at login.

Two valid concerns were expressed about using the 8" driver in a 2.5 ft bass reflex enclosure: 1) These drivers are so new that no one has reliable T/S parameters, spl vs frequency measurements, or personal experience with them, and 2) If the published T/S parameters are correct then they are not a good candidate for a bass reflex enclosure. I will try to address both of these concerns.

First, they do come with a published spl vs freq graph, and it's important to know something about this graph, which I assume is correct. In simple terms, there's a subatantial rise in spl up to 1khz, after which the response is fairly flat except for the kinds of squiggles you see on the Fostex graphs. A few sample points taken directly from the published graph are: 40hz:82dB, 100hz:88dB, 200hz:91dB, 1.2khz to 14khz:100dB average. So the published
95.4dB/W(m) is an average, and it doesn't describe these drivers' sensitivity anywhere on the graph except at 800hz.

I first listened to them connected direct to the amp with no bsc, and to my ears they sounded bright and fatiguing. Then I tried several bac values and finally settled on a 1.5mF 15 ga inductor with a parallel 6 ohm resistor (mostly because those values sounded best of all the parts I already had in the bin). With the bsc, to my ears the 3dB peak at 70hz and the 2dB null at about 140hz are inconsequential. Given the fact that this alignment has no output below 60hz, the small peak at 70hz actually adds a nice warmth to the sound. Of course the bsc reduces the sensitivity above 1khz, but since the reduction is from 100dB and above, they still are sensitive enough to play loudly with my 3.5 watt Paramours and to be driven to sounding a bit congested with my 300B.

I'm not sure how to describe the overall sound except that it resembles the Fostex FE-166EE's in the Voigt pipes I built, but with more midbass punch and a bit more brightness in the 4-8khz range. The soundstage and imaging are definite strengths of these speakers and are comparable to other single driver speakers I have heard. I will need to hear them side by side with some other single driver speakers to comment in more detail.

These speakers are fun to listen to, and I plan to keep them for now and alternate with other types of speakers in the smaller listening room. They are the best match of all my speakers for my 3.5W 2A3 Paramours. I'll bring them to the June Lone Star Bottlehead meeting in Dallas, and hopefully a few members of the Great Plains Audio Community can carpool down to join us and hear what I am struggling to describe accurately.

• Audio Nirvana Spec Sheet