choosing woofer speaker for bass amp(own build)

[fatecasino]

I built my first bass amp but I am facing a great problem with the woofer!
the preamp is the bass man:
http://www.diystompboxes.com/smfforum/index.php?topic=101898.msg905776#msg905776

and the amp is Taylor's tiny giant-20Watt solid state
http://www.musicpcb.com/pcbs/tiny-giant-pcb-only

I bought a woofer with these characteristics:
Replacement Speaker 10 "suitable for speaker
Power: 125W RMS / 250W max.
Impedance: 8 ohms
External diameter: Ø257 mm
Hole diameter: Ø237 mm
Diaphragm: polypropylene with rubber edge suspension
Coil: 2 1/2 ", ventilated
Magnet: 40oz
Frequency response: 25Hz - 6KHz
Sensitivity (1W @ 1m): 90db
It costed me 45 euros 
I added a tweeter and a typical first order crossover.
I first connected my mp3 player and the whole system played really nice and loud
I started getting distortion after 60-70% of amp volume.
Then I connected the bass and it was a total failure. The woofer goes crazy just after 20% of the amp volume. The speaker plays clear only for that low volume, after that point the woofer creaks and crunches.
Obviously I am missing some important piece of knowledge here.

Should I try to insert some kind of compression? Try another speaker?

[antonis]

Does it distort the same indepentently of various tone settings..

[tca]

Double post, sorry.

[tca]

Then I connected the bass and it was a total failure. The woofer goes crazy just after 20% of the amp volume. The speaker plays clear only for that low volume, after that point the woofer creaks and crunches.
Obviously I am missing some important piece of knowledge here.

Should I try to insert some kind of compression? Try another speaker?

Regular (read cheap) woofers do that, even for low power guitar amps. 20% you say... less than 3W, maybe 1W.

You will need to get a real bass cheesy speaker. Before that, try to cut bass under 40Hz.

[amptramp]

You have a 10 mm rim from the outside of the speaker to the speaker cone.  Are you hitting the cone on anything?  Are you using all the mounting holes?

Are you using a baffle or a ported enclosure or a sealed box?  A sealed box has to be big for bass and if it is not, it starts adding even harmonics due to non-linear compression.  Is the box structurally solid enough so enclosure resonances don't occur?

[PRR]

> I bought a woofer

Box?

As Ron implies, a naked cone without a box will NOT make bass waves.

The simplest box for a 10-inch is about a cubic foot sealed enclosure. Get 6 feet of foot-wide board. Cut four pieces 12" long and tack them together. Measure the inside and cut the rest of the board to fit. Cut hole in one for the speaker. Get some 1" square sticks and some Liquid Nails or other tough construction glue to back-up all 12 corners.

IMHO, a Bass Amp should use a Bass Amp Speaker, not a Hi-Fi woofer plus a tweeter. A Hi-Fi speaker is built to be "mellow", have no tone of of its own. A Bass Amp speaker should have some tone. It will also be tuned to handle Just-Bass, whereas a Hi-Fi speaker is tuned to handle the Whole Band (where the bassist is only a part of the total sound). Even at the 25 Watt level, a proper Bass Amp speaker may cost more than 45 Euro. Eminence Beta 10A may be suitable, play twice as loud as your hi-fi cone, and sells for US $69 (~~62 Euro, so may be above your budget).

Using the Tiny Giant, a 4-Ohm speaker will suck out twice the power of an 8-Ohm speaker.

[fatecasino]

Does it distort the same indepentently of various tone settings..

@antonis: yes, it distorts in  most tone settings, it's ok only when I turn down the preamp bass knob, but this has very few bass frequencies

Regular (read cheap) woofers do that, even for low power guitar amps. 20% you say... less than 3W, maybe 1W.
You will need to get a real bass cheesy speaker. Before that, try to cut bass under 40Hz.

@tca: how can I filter out frequencies under 40Hz? any schematic would be helpful!

Are you using a baffle or a ported enclosure or a sealed box?  A sealed box has to be big for bass and if it is not, it starts adding even harmonics due to non-linear compression.  Is the box structurally solid enough so enclosure resonances don't occur?

@amptramp: the woofer was behaving like this since the beginning, before I put it in any enclosure. Now I put it in a old hifi 10" speaker box just for testing. Same bad sound, especially on E string

@PRR

Eminence Beta 10A may be suitable, play twice as loud as your hi-fi cone, and sells for US $69 (~~62 Euro, so may be above your budget). Using the Tiny Giant, a 4-Ohm speaker will suck out twice the power of an 8-Ohm speaker.

First I would like to try to make it work as it is (cause I already ran out of budget ) even with some tonal compromise. Is there some filter/circuit that would make my woofer play?
If not, can you suggest a bass woofer around that budget (60-70 euros) that would definitely stand the power of tiny giant?that Eminence Beta 10A? I wouldn't stand one more failure on choosing woofer, I am already depressed!
I'll start building the proper enclosure after I am 100% sure I have the proper woofer

[Rob Strand]

I wouldn't stand one more failure on choosing woofer, I am already depressed!

I've been designing HiFi and Bass Enclosure for 30years and what PRR says is right on the mark.

Here's the problem:
- No box = *** Immediate fail  ***; and all the problems you mentioned
- polypropylene with rubber edge suspension  usually means it's s HiFi woofer, and that means...
- the bass response goes down quite low but the efficiency is poor (90dB hopefully at 1W 1m)
- Hifi Speakers sound a bit dead for guitar and bass but you can sometimes get away with it for bass

The solutions for current driver:
- add a box
- make the right size.  PRR's recommendation of a 1cu ft sealed box is right on the mark.
  You might be able to go 0.7 cu ft to 1.2 cu ft

The problem remaining is you have a small amplifier and an inefficient speaker:
- You can give-up some bass response by adding a high pass filter.   
  Try a simple filter to see how you go.
   Reduce R7 on your preamp from 1MEG to 22k.   
   Perhaps try 15k to 22k to suit your taste.  This should let you crank the amp up a bit.

Since the speaker is inefficient you are cranking-up the amplifier in order to get
more volume.  I'm pretty sure the amplifier is clipping and that's why is sounds crap.

It's possible to add a compressor around the power amp to prevent clipping.  Some small commercial amps do this.

What many commercial amps do is use efficient speakers.  Efficient single speakers usually mean the the low frequency response is poor.  It also means they use light paper cones on the speakers instead of the heavy poly-cones used for Hifi.

[fatecasino]

Since the speaker is inefficient you are cranking-up the amplifier in order to get
more volume.  I'm pretty sure the amplifier is clipping and that's why is sounds crap.

In my average understanding this tiny giant amp (I have made one more tiny giant but for guitar with 30W Vox guitar speaker) gives a nice and clean sound until at least the 50% of the volume knob. This level is very satisfying for my needs (practicing, small gigs, travelling with band, etc). In this bass case, just after 20% my woofer starts going crazy giving crap sound. I have tried other instrument too:

-mp3 player, good clean sound sound until 60% of the volume
-voice,  good clean sound sound until 50% of the volume
-electric guitar, good clean sound sound until 30% of the volume
-acoustic guitar(piezo) ,good clean sound sound until 40-50% of the volume

What many commercial amps do is use efficient speakers.  Efficient single speakers usually mean the the low frequency response is poor.  It also means they use light paper cones on the speakers instead of the heavy poly-cones used for Hifi.

did you mean to say "low frequency response is good"?

I will start building the box, but I still don't know what speaker I should put inside!!
I am a bit pessimistic for my current woofer because in the hifi box I am testing it, the woofer fails to play the bass guitar.

If you have any suggestions for 4/8Ohm woofers please tell.

[tca]

-mp3 player, good clean sound sound until 60% of the volume
-voice,  good clean sound sound until 50% of the volume
-electric guitar, good clean sound sound until 30% of the volume
-acoustic guitar(piezo) ,good clean sound sound until 40-50% of the volume

My guess is the TDA7240A is clipping at low frequencies and the woofer reacts badly. Note that as the frequency goes down the useful volume range also goes down. Regular music (MP3) is gentle with amps and speakers.

[Rob Strand]

I think your expectations are not realistic for this little amp even with a good speaker.

If you have any suggestions for 4/8Ohm woofers please tell.

Given your reference loudness levels is a guitar + 20W amp + 12" fairly efficient guitar speaker.
I'm pretty sure any 10" cabinet you build will be a disappointment!

A 12" guitar speaker has a sensitivity of say 96dB 1w 1m.    To get the same level as the 96dB  speaker you will need 4x20W=80W for the current 90dB 1w 1m speaker.   Adding to that you generally need about 5 times the power for bass amp the same effective loudness as a guitar.  The amp power you need is becoming well beyond the 20W amplifier.  Even if you used a 96dB 1W 1M speaker you would need around 100W to compete.

A 50W amp +  1x10" efficient speaker is likely to be more useable.

There's a few more issues here:
- you need to make sure you power supply can handle the power.
- the amplifier is 20W into *** 4 ohm *** you are probably only getting 12W into 8 ohm;
  and even then only if your supply voltage is high enough and it doesn't sag.

PRR already mentioned the Eminence 10A which is 97dB 1W 1m.  Which is quite high efficiency for a 10".

This one is 96.3dB 1W 1m,
http://www.usspeaker.com/legend%20ca10-8-1.htm

Many others are only 93dB 1W 1m,
http://www.usspeaker.com/guitar-bass-1.htm#EMINENCE

did you mean to say "low frequency response is good"?

The bass response for 10" bass guitar drivers is actually quite poor compare to hifi.
You basically trade low frequency response for better efficiency - it's comes from the physics of speakers.

[fatecasino]

Reading your posts, I realise that any successful project of mine of the last  2-3 years was just a matter of coincidence!
You increased significantly my understanding on amps 

If you have the patience, could you please explain 1-2 more things:
-a 20Watt commercial amp (an average quality one), what speaker does it have? what's the actual power of its amp?

-in my case, I realised by Rob's recommendation that tiny giant is little for my woofer. Does this simply mean that, tiny giant amp can play bass guitar only to that low volume generally? After that volume the amp (and not the speaker) clips/crunches/sounds crap?

just for the record:

- you need to make sure you power supply can handle the power.

confirmed, I tried a 120W power adapter, same results

[Rob Strand]

what speaker does it have?

In the old days I think the manufactures looked up speaker manufacturers, grabbed a number samples from candidate suppliers, then picked one.   I suspect a lot of these weren't anything more than guitar speakers. In more modern times speakers are custom made and built as a bass guitar speaker; eg. Crate,  Behringer and Peavey would be doing this.

Many of the speakers have very poor bass response and have a thin boxy sound.  They rely on speakers with high resonant frequencies to get efficiency.   (Cheap PC speakers are designed like this, that's why they sound loud but are only a few watts.)  These days companies tend to put compression in the power amplifier to stop the amp from clipping and sounding bad.

what's the actual power of its amp?

For cheap stuff probably 20W!  Some better models might put out a tad more.

Does this simply mean that, tiny giant amp can play bass guitar only to that low volume generally? After that volume the amp (and not the speaker) clips/crunches/sounds crap?

That's pretty much it.  I don't bother with less than 50W for bass.  If you look at any amplifier which isn't a "toy" they are rarely less than 50W for solid state stuff.

**** One thing I forgot.

If you use a tweeter there is pretty much zero tolerance for amplifier clipping as  the high frequency distortion components are clearly output by the tweeter!   If you use a guitar/bass speaker, with a not so extended frequency response,  and with no tweeter the high frequency distortion components are greatly attenuated.

[Rob Strand]

Here's the classical cheap speaker:
http://www.musiciansfriend.com/accessories/warehouse-guitar-speakers-g8c-8-20w-american-vintage-guitar-speaker?src=3soswxxa

Note resonant frequency is 148Hz  which is very high and very typical of cheap speakers.
(The 8" won't be as sensitive as a 10".)

Here's the specs
https://wgs4.com/g8c

sensitivity is quite high at 95.78 db (1W 1m?  I hope).  Tomorrow I will check.

[PRR]

The volume-knob setting is not very important. A "hot" instrument with high output may over-drive the amp on "2" when a less-hot instrument might need "4".

You have three systems: preamp, power amp, and speaker. The real problem might be in any of these.

First put your bass direct to the Tiny Giant (no preamp) to your speaker. Will it play loud? (Bedroom loud; the TG in a small speaker will never be stadium-loud.) Will it play deep? You might have to turn the TG full-up, that is OK.

Next find someone with a bass-amp where the speaker unplugs. Try it with your TG. It should play reasonably loud, though maybe half or a quarter of the loudness it gives with typical "real" bass amps (50 to 200 Watts). It should play deep.

The TG is intended to take electric guitar directly, as a low-gain amp (you have to turn-up and play hard to make it distort). Looking at that preamp, that is a LOT of gain added to the low-gain TG. Also R6 680K into TG is a lot of loss. My first quick thought is to remove C2 C6 to lower gain. My next quick-thought is to re-rig Q2 as a source-follower, directly feeding TG input through a coupling cap (no R6).

[Rob Strand]

While the those wgs drivers are efficient I doubt they will sound that great
For good efficiency use 10" or even 12" driver (which might be a bit big).

If you add not too expensive then

The beta 10A, which PRR recommended,
http://www.eminence.com/speakers/speaker-detail/?model=Beta_10A

or cheaper is, the alpha 10A,
http://www.eminence.com/speakers/speaker-detail/?model=Alpha_10A

For a typical modern amplifier which has a high pass filter and a limiter on the power amp, both helping you get more volume, check out

http://elektrotanya.com/fender_rumble_15_2010_schematic_rev-a.pdf/download.html

Under the pic, is the text
"Click the preview picture to see bigger size.
The preview is worse quality than the original pdf.

This file is downloadable free of charge: Get Manual               *******
(You are not logged in, only 2 downloads per day possible for you.)
"
Click on the "Get Manual" link ; you might have to wait for it to appear.

[fatecasino]

I started a step by step debugging process:

First put your bass direct to the Tiny Giant (no preamp) to your speaker. Will it play loud? (Bedroom loud; the TG in a small speaker will never be stadium-loud.) Will it play deep? You might have to turn the TG full-up, that is OK.

Nothing really special, same sound, just a bit poorer in quality, but same low volume

Next find someone with a bass-amp where the speaker unplugs. Try it with your TG. It should play reasonably loud, though maybe half or a quarter of the loudness it gives with typical "real" bass amps (50 to 200 Watts). It should play deep.

I borrowed a very cheap samick 10 watt bass  amp. I disconected it from its amp and connected it with mine, keeping it in its enclosure and...amazing!!! I finally got such a nice sound from a cheap 6.5" woofer!! I was amazed! It was simply that I was using a hifi speaker that would not even match for a bass guitar.
So now, whats the actual solution? should I find a second hand bass amp and take its speaker (perhaps a little bit bigger 8" or 10")
or...try to sell my woofer and buy the eminence beta 10A after I collect some money? I tend to try the second choice, but I am really afraid that a smaller speaker may play much better than eminence!! Then I will be again at point zero with a much more expensive woofer in my hands!!
What do you think?

[Rob Strand]

So now, whats the actual solution? should I find a second hand bass amp and take its speaker (perhaps a little bit bigger 8" or 10")
or...try to sell my woofer and buy the eminence beta 10A after I collect some money? I tend to try the second choice, but I am really afraid that a smaller speaker may play much better than eminence!!

You should definitely sell the HiFi speaker.

Beyond that it's not a simple choice.   

From a cost point of view you probably better off buying a second-hand amp and modding it.
You get the everything: speaker, amp, transformer, enclosure - probably for less than you could buy a new speaker!

[PRR]

> samick 10 watt bass amp. ...amazing!!! I finally got such a nice sound

The hi-fi speaker is "not right" for a stage amp, but it shouldn't suck that bad, so bad that a smaller but stage-tuned speaker is "amazing!!". I wonder if it is defective.

But also measure the DC Volts across the speaker. It should be "zero", less than 1 Volt (more like 0.1V). If you have a flaw in your TG build, you might have 6 Volts DC on the speaker. A stiff stage-amp speaker *may* tolerate this (at reduced performance). A soft hi-fi speaker will throw its voice-coil nearly out of the gap and suck bad. (However you say it was playing MP3s OK?)

[fatecasino]

Yes, mp3 sounded great on hifi woofer, I will measure the voltage today and I'll write back.