Amp/Speaker Weirdness...

[edski]

I got a Trace BLX 80 from Evil Bay in the spring. The speaker was replaced and it was VERY boomy in the low register, and the volume all but disappeared by the time you got to the 9th fret of the G string...

I tested the amp with other speaker and it was fine, so I assumed the speaker (a Jensen of some sort with no identifiable model info) was ****.

Then I had a hair-brained idea: what if I reversed the leads to the speaker? No I talked to seem to think it would make a difference, but I tried it nonetheless.

It worked. While the D note at the 19th fret of the G string is still a little thin, there is good presence elsewhere. In fact, the low A and the E at the 9th fret of the G are live spots - not sure it's due to the bass (my J Bass) or the amp, but clearly this wasn't happening before.

Any ideas why this seemingly insignificant change would make a dramatic difference in speaker response?

I suppose that if I never get a good explanation I'll be OK. Whereas before I thought I had a junk piece regarding the speaker enclosure, now I have a very decent practice amp and don't have to lug my main rig to and from rehearsal. The guy who's house we play at will love that!

[jps]

Isn't that the amp with the modified Karlson type of enclosure? If so, you might want to try a "normal" type of speaker cabinet with the head and see if that produces a smoother response.

[edski]

Oh I have...and it does. But the simple act of switching the leads in the combo cab took from being unuseable to being a decent little combo.

I'll have to look up "Karlson Enclosure"...or if you'd explain that a bit more, Jeffery...I'd know what to say.

Basically it's a ported cab (slot port on the bottom) with a vertical slot port instead of a grill...

***************

OK, I looked up a couple of things...

Karlson enclosures look interesting. The Trace I have could be said to be a modified Karlson, except the from port is linear as opposed to exponential, and the speaker is not angled up. I saw one frequency response curve of a real Karlson, and it had some noticable spikes. Far form the theoretical flat response...

The Jensen XS speaker is freaking car stereo speaker. So I'm sure that isn't helping matters. I'll have to play the thing some more, but I think getting a real bass amp speaker in there will help, but it may just have response spikes at ~160 Hz and ~55 Hz...approximately the 9th fret E on the G string and the low A...

If I get a real speaker in it, I might just look to sell it. A lot of Trace enthusiasts would probably overpay for it. At leat now it plays decently, and I don't feel I was ripped off getting it for $220.

[gshadoan]

Take a 9 volt battery, and touch the + side to the tip of the speaker lead and the - side to the sleeve. If you have an NL type connetor you will have to remove the wires and touch them bare to the battery. If the speaker excurds outward, it is in phase. If the speaker excurds inward it is out of phase. The former should be true. If the speaker has been run out of phase for too long and too hard, damage to the spider may have occured. This is bad. They are designed for outward excursion. You may need to replace it. When shopping for a bass guitar speaker it is important to get one that has the correct freq response. A guitar speaker is not a great idea, nor is an SR speaker. Too many gaps in freq response from either of those. A home or car audio speaker are ALWAYS bad ideas. 50-5000 is about right for a bass. This really only applies to a single speaker system. If you have mulitple speaker system, it is fine to have different types to cover different freq areas. Entwhistles rig is a good example of this. Also, some like to add a piezo to get above 4000. Its also important that you get the correct Ohm speaker for your head. If you have a 4 Ohm min head, and you use an extra cab from time to time, 8 ohm cabs are what you need. 2 8 Ohm cabs(speakers) equel a single 4 Ohm load. 2 4 ohm cabs(speakers) equel a 2 Ohm load. Your amp will not like that. Peizos (for some reason) have no reactive load so you can use them with ease. A cap and an attinuator are good ideas for horns, for mixing the highs to the lows and protection. YMMV. Good luck.