Cabinet Design for Bass

[txstrat]

Or have a look at this. Another nice Weber application on the net to calculate a cabinet.

http://www.webervst.com/spkrcalc/port1.htm

[GregS]

Thanks, I haven't started cutting any panels yet so I am not committed to any particular design at the moment. Actually, I've decided on the speaker I'll get which is the Weber ceramic California 15. I'll need to get the T-S parameters in order to use the calculator.

Also, I notice the calculator also specifies a port length. I've heard of using plastic pipe for this but I assume you can only get this in certain diameters which likely won't be the diameter calculated. Is there another way to do this?

Thanks,

Greg

[txstrat]

You can buy the port(s) here and there in hifi audio equipment stores (yes, made of plastic). They (usually) have specific diameters used in those calculators and can be cut to the appropriate lenght. They are also crimped at one end to fix them. Easy stuff.

[txstrat]

I found the B-15N circuit is sort of lacking the highs and crispness after I'd build one. I even changed the bright function to B-15R specs (with an added resistor) to help that out. No such luck.
A 12'' speaker would only put out less deepness but not more highs IMHO.

Figured I have (or better the bass player in my band has) to live with it. It's got a gorgeous sound anyway. Not for slapping, though.

UPDATE
Got to correct myself. I built a second one and it's got all the high end our bass player needs, also for slapping. Very deep low notes as well.
Must have been a difference in the circuit. Can't get my hands on the other amp anymore to compare.

[Glass Snuff]

For bass, I would prefer a properly tuned cabinet to a detuned one any day. Regardless of what internet experts say about its "huge bottom end", the detuned cab doesn't load the speaker properly, and risks over-excursion of the cone even with low power.

Guitar players are weird. Most spend all their time on the bridge pickup which doesn't have solid bass fundamentals. A "detuned" cab for bass is a bad idea, IMO. The last thing you want is a huge hole in the baffle that lets the back wave cancel the bass frequencies. Either a really big closed cab, or one with a properly tuned port is the way to get a solid bottom end.

And yes, you probably need tweeters.

Keep in mind you can fine tune the cab's volume (make it acoustically bigger) by adding insulation. And while it's a pain in the butt, it's worth it to try slightly different port lengths. Speaker specs are never right on, and calculations can only get you close. Also, you need to break the speaker in before going nuts with the tuning. But in the end, a custom tuned cab will whomp a mass produced cab any day of the week.


Ack! Just noticed that date. Greg, how did things work out?

[GregS]

Ack! Just noticed that date. Greg, how did things work out?

It's fine for playing by yourself where volume is not an issue. I find practicing with the band I have the amp turned up to the limit of its headroom and I'm still not loud enough. This is obviously partly due to the low power (25W) of the amp but I could be heard more with the commercial ported cabinet at the same volume settings.

The detuned cabinet seems more responsive in the lower mid-range than at the very low end of the bass. The low F note seems particularly un-responsive - not sure why.
The commercial cabinet was louder in the low end but was also very muddy sounding in this range.

I suppose I could try out putting another speaker in the upper port hole and convert it into a 2x15 and see what happens.

[GregS]

UPDATE
Got to correct myself. I built a second one and it's got all the high end our bass player needs, also for slapping. Very deep low notes as well.
Must have been a difference in the circuit. Can't get my hands on the other amp anymore to compare.

Is the second one from a different stock B-15 circuit or did you make some of your own changes to it to get this result?

[txstrat]

Same circuit, slightly different layout (currently changing the layout to the old version). Must have done something wrong in the first build. The second one I built exactly like this: http://www.schematicheaven.com/ampeg..._portaflex.pdf, except I left channel two out completely and instead of the tube recto I used a diode bridge 4x1N4007.
The OT is rather heavy (specs are 50-60W @ 2xEL34 or 2x6L6GC). Biased it at around 48ma with 425V at the plates (using 6L6).
This amp has LOTS of headroom. We tried it with a guitar cab (2x12 Celestion) first and now it's running on a Behringer 2x10 cab with a tweeter. In a basement reheasal with a hard drummer we don't need to turn it up more than 3-4 (of 10). Great circuit.

[GregS]

The circuit you used is a newer version of the B15 than the one I built. It would have more power and headroom with fixed bias and that plate voltage. Mine is cathode bias with about 387V on the plates. I could get a bit more headroom by using a smaller value cathode resistor and working the tubes a little harder which I might do. Anyway, sounds like a great amp you've got!

[Glass Snuff]

I suppose I could try out putting another speaker in the upper port hole and convert it into a 2x15 and see what happens.

Since you're not loud enough with the band, that's what I'd recommend. There's a chance the internal volume might be too small, but that's when you add a port.

[txstrat]

I've found that I almost like it better as a head. Unless you wanna build it like the genuine one.
Since a purchased cabinet, say a Behringer that we've used, doesn't cost much more than the wood, speakers, glue and tolex you would need for a DIY cab. It has a well balanced design with two 10s and a tweeter. It's got a heavy punch in the lower mids and crisp highs.
I don't wanna talk you into this but before you spend a lot of time calculating and finding out by try and error this might be it. I'm very pleased with it. Maybe you can try your amp with a different cab somewhere? Music stores over here sometimes loan things to try in a rehearsal.
EDIT
I've read the harmony central reviews for this cab. Many complaints. You might think about it, although our cab sounds fine with no issues so far.

[GregS]

The lack of volume/power isn't a major problem. If the band practices at a reasonable volume it's ok. Gigs don't seem to be a problem as the stage volume tends to be lower than at practice. The cab is miked into the board so I have the PA to get as much power as I need. Still it would be nice to have more power in store from the amp alone.

Although I'm sure I can get some more volume from a different cabinet I still think the amp could use some more power and headroom. I think it's more difficult to do a DIY bass cabinet and get it right than a guitar cabinet so a commercial bass cabinet may be something I'll consider for the future.

At the moment I'm absorbed with a guitar amp design/build so I'll have to revisit this at a later time.