help me choose a bass amp 10" speaker(driver)

[fatecasino]

I am about to build a bass amp using this amp module
http://www.ebay.com/itm/2x50W-Digital-AMP-Amplifier-Board-with-Radiator-TDA7492-D-Class-High-Power-Hot-/291639327649?hash=item43e70efba1:g:wxcAAOSwrklVOKIJ

I intend to use a single speaker and use the second amp output for external speaker (just in case).
Can you please suggest a bass speaker which would match to this amp? I would say something until 70-80€

[anotherjim]

What sound are you going for? By speaker, do you mean a complete cabinet or a driver to go in your own box?

[fatecasino]

 I mean just a driver to go in my box, which I forgot to mention it is 10"
I play ska/reggae, I don't really know which speaker would fit most for this sound, Hartke?

[anotherjim]

Eminence Legend.
http://www.eminence.com/guitar-bass/bass-guitar/
You need to have the supply voltage for that amp module settled before choosing speaker impedance. Higher supply voltage then higher speaker impedance as per the sellers info.

[fatecasino]

There are two things I do not understand
1. Should the bassguitar loud speaker frequency response start from 40Hz? Most bassguitar loudspeakers start higher than this
2. Supposing I take an 8 Ohm speaker for this 50W amp, what RMS wattage should the speaker have in order to have a "normal" function when the volume goes to 70% or more? I have done some experiments in the past and I never got a good match.Either the speaker couldn't stand the power of the amp either the amp didn't have enough current for a high wattage speaker!

[Nasse]

Eminence BP102 might be suitable

[R.G.]

There are two things I do not understand
1. Should the bassguitar loud speaker frequency response start from 40Hz? Most bassguitar loudspeakers start higher than this

That's what you want. It is expensive to get that in terms of both the speaker and the enclosure it goes into. Most basses don't produce much 41hz fundamental though. Best advice: find a store that will let you try various loudspeaker cabinets, read the user literature and try to find two comparisons, one with 40Hz pass and one with 60-80. Listen.

2. Supposing I take an 8 Ohm speaker for this 50W amp, what RMS wattage should the speaker have in order to have a "normal" function when the volume goes to 70% or more? I have done some experiments in the past and I never got a good match.Either the speaker couldn't stand the power of the amp either the amp didn't have enough current for a high wattage speaker!

There is a lot of complexity there.

This board has two "50W" amps on it. Examining the datasheet for the chip, it's more like a 20W amp at 8 ohms, 35W at 4 ohms, per channel. It's not clear from the applications literature whether you can run it in bridged mode. Maybe.

If you use a speaker rated at less than the actual power it puts out, the speaker manufacturer is telling you that their speaker can be burned out by your amplifier's output. Wattage ratings on speakers are a statement that the speaker can get rid of the heat put into it by X watts of audio without burning out.

I personally wouldn't use a speaker (or series/parallel speaker combination) on this rated at less than 30W. A 30W speaker could be burned out by it when driven by a continuously overdriven signal, which pushes the amplifier into heavy clipping and making it put square waves at max voltage into the speaker.

I'm not sure what you mean by " not have enough current for a high wattage speaker". High wattage speakers are designed to get rid of heat. Speakers are famously inefficient. Probably 95-98% of all the audio that goes into a speaker stays there as heat. The actual sound coming out is 1-5% of the electrical audio power in. High wattage speakers don't necessarily have less audio output  per watt in, although that can happen. The current the amplifier can provide isn't a good measure of whether the amp can drive the speaker well.

An amplifier produces a signal voltage. The speaker's impedance lets a certain amount of current flow from that voltage. How much listenable audio you get per electrical watt in is specified by the speaker's efficiency, usually expressed as sound pressure level (SPL)  at one watt rms, 1 meter in front of the speaker, on axis. This is normally 85-100db for moderns speakers, usually 95-100 for musical instrument speakers.

The amp either can provide enough current to the speaker or not. Usually, this is determined by the amplifier's power supply, not the amplifier itself.

So can you expand on what you mean by amplifiers not driving high wattage speakers well?

[PRR]

> response start from 40Hz? Most bassguitar loudspeakers start higher

A speaker flat to 40Hz and enough efficiency to deliver high sound level without insane power is Frikkin BIG.

A ten-inch doesn't begin to go there.

A Ten will work fine down to 70Hz. 1 to 3 cubic foot sealed box is fine. Vented box may give you another couple low-notes, or less slap on the same notes, but isn't a huge improvement despite intense calculation.

Do your Watts specs carefully. The sales headline claim is often misleading. If R.G. reads that amp at 20 Watts in 8 Ohms, you may as well stay home. IMHO, "real bass" starts at 50 Watts in a 15-inch. As a sound guy, I see a bassist show up with 50W 15", I expect he will need a lot of help from the PA system. When I see 400W in several 15"s I relax, throw a wire to it but only pot it up for solos.

[PRR]

> not clear ...whether you can run it in bridged mode.

FWIW: "Mono BTL power 100W / 4 Ohms". "BTL is not "bacon tomato lettuce", but bridged.

However no Ten will make BIG (stage size) bass at the 100W level. (They do in cars, because all efficiency and much output is sacrificed for the smaller quieter space.)

[R.G.]

A ten-inch doesn't begin to go there.

Well, OK, but what if Xmax = 2 meters? And a non-tapered labyrinth enclosure?


OK, OK, so it won't. 

There were some articles in the old speaker builder magazine about bass-i-cizing speakers by gluing rings of solder to the junction of the cone and voice coil to mess with the low frequency resonance.

There is a way to get there with this amp and 10" speakers: modular amps. Make the best-effort 10" speaker and cab you can be sure to replicate. Add to this the sub-$20 amp and power supply. Iterate this amplifier+speaker until you run out of money, space, and/or time. Somewhere along the way to a wall of speakers, you'll get good response down to 40Hz. Or 20, or 10 even. 'Course, that violates the OP's unstated wish to get a $10 amplifier and then pair it with some unstated speaker to have a cheap bass amp.

@OP
People have heard so much about amplifiers that they think that with a power amplifier circuit, they're in business. This sadly neglects the power supply  (as expensive or worse than the amplifier circuit) and speaker (not cheap for a good one) and the enclosure.

[fatecasino]

Well, I really thank you for your advice, you made me understand much more about the relation amp-speaker. Further research was made much easier now

So can you expand on what you mean by amplifiers not driving high wattage speakers well?

I don't know how to describe this. Increasing the master lever, I get louder and louder sound. After a certain level lets say 70%, the speaker start vibrating in and out at a constant rate, could be 2-3 times per second, giving a sound which is like when you breath in strongly with your lips almost closed. This vibration stops only when the level I turn down the volume level below 70%. Some people told me that this could be that the speaker is not provided enough current (too big loudspeaker?). I tried the same experiment with other loudspeakers, crappier loudspeakers gave me the same vibrating situation in much lower volume levels. I thought that it could be the power supply , but I use a 3A laptop power supply. Between The power supply and the amp I have put a 1.2A fuse which never gets burnt. I could be totally wrong with this thinking. This experiment took place when I had a Y148 amp module
http://www.dx.com/p/y148-audio-amplifier-module-93121#.V1bB7GF95cY

As I understand a very good choice is Eminence Legend BP102-4. Would it there be any real disadvantage if I use the 4 Ohm instead of the 8 Ohm version?
http://www.thomann.de/gr/eminence_legend_bp1024.htm?ref=search_rslt_Eminence+BP102_224814_0

I couldn't find any cheaper option in Thomann. For European shippings you can't really find any bargains like the ones from US web stores.

[R.G.]

So can you expand on what you mean by amplifiers not driving high wattage speakers well?

I don't know how to describe this. Increasing the master lever, I get louder and louder sound. After a certain level lets say 70%, the speaker start vibrating in and out at a constant rate, could be 2-3 times per second, giving a sound which is like when you breath in strongly with your lips almost closed. This vibration stops only when the level I turn down the volume level below 70%. Some people told me that this could be that the speaker is not provided enough current (too big loudspeaker?). I tried the same experiment with other loudspeakers, crappier loudspeakers gave me the same vibrating situation in much lower volume levels. I thought that it could be the power supply , but I use a 3A laptop power supply. Between The power supply and the amp I have put a 1.2A fuse which never gets burnt. I could be totally wrong with this thinking. This experiment took place when I had a Y148 amp module
http://www.dx.com/p/y148-audio-amplifier-module-93121#.V1bB7GF95cY

The problem is not the speaker, or not just the speaker anyway. It's the amplifier, or possibly the amplifier/power supply combination. The setup is oscillating at very low frequencies, which used to be called "motorboating". The change with different loudspeakers was because the slightly different speaker load changed the motorboating frequency. It is also possible that the power supply is hitting its own current limit on current peaks, lowering its output voltage, then re-starting when the current drops because of the lower voltage. Note that this is different from the loudspeaker being too big.

There are a few hundred different ways to go from here. To advise you on those, I need to know what your final goal or objective result is. If you want to build the cheapest possible small amplifier for practicing in a small room, that is one path. If you want to have an amp suitable for practicing with a few friends in a garage or basement, that's another path. If you want to have an amp you can play small gigs with, that's yet another. And finally, if your objective is just to enjoy tinkering and turning out something useful for fun, that is many, many paths.

As I mentioned in my earlier post, people get the wrong idea about what is hard and needs the most effort and money in dealing with amplifier setups. There is a popular idea that once you have a functioning amplifier *circuit* complete on a PCB, then you have an amplifier. That is not accurate. You need an amplifier circuit, you need a power supply, you need a case to put the amplifier and power supply into, you need a speaker and you need a speaker *enclosure*.  Unless your path is to just have this thing live on your workbench, with wires running here and there, you're going to have to add some of the rest of this stuff.

That's why I put it the way I did: think about where you are going to be (that is, imagine that you have been successful) and describe what that looks like. Write down the things you have in that scenario, and the processes, labor and money you had to spend to get therm, and then start adding up what the costs in money, materials, and time was.

The reason I'm blathering on about evaluating costs is that you're asking the wrong question. You're asking which ~US$50 loudspeaker to use with a ~US$10 amplifier circuit board. In terms of end results, it would make more sense to pick a good-sounding loudspeaker, then accumulate an amplifier to drive it. 


As I understand a very good choice is Eminence Legend BP102-4. Would it there be any real disadvantage if I use the 4 Ohm instead of the 8 Ohm version?
http://www.thomann.de/gr/eminence_legend_bp1024.htm?ref=search_rslt_Eminence+BP102_224814_0

I couldn't find any cheaper option in Thomann. For European shippings you can't really find any bargains like the ones from US web stores.

[PRR]

> what if Xmax = 2 meters?

Red herring. We trying to make waves. A 10" piston moving 80 inches, or even 10 inches, the air just slides around the side, wave formation is terrible.

That's even before you consider the layout and magnet cost of such a long displacement.

Yes, we can get Xmax (maximum cone displacement) over 1" in car subwoofers. (But not 10".)

A problem with that is that with multi-tone full-range music, the higher partials are intermodulated by riding on the large bass excursions. Like the trumpet player on the train: plays sharp when he comes and plays flat when he leaves. If the train is going back/forth at 42/whatever Hz, the upper partials are all smeared.

A guide for clear speech is to hold Xmax down around 0.050". Single instrument with few important high partials can exceed this. But rarely over 0.25" max for MI speakers.

> rings of solder ...to mess with the low frequency resonance.

The resonance per se is a side-effect. What the added mass does is drop the midrange response to match some selected point on the size-limited bass response. Bass does cover 42Hz to well over 1KHz. Is it worth a 6dB or 10dB loss of sensitivity on everything over 70Hz just to make it "flat" with the 50Hz output? Some older PA/theater woofers in small domestic rooms with hi-power amps, it did make sense. Filling a club and paying crowd, you probably don't want to slug-down any of your response.

> modular amps....Iterate ... ... ...

That's how modern big-arena sound is done. You do the auditorium on Thursday, bring 1/3rd your rig; Friday at the football stadium you bring the whole rig. Also appears to allow optimum directivity (however there is much potential for phase-nulls). Interestingly there is some optimum size for any given amp/speaker combo. In smaller rooms you will favor smaller modules. However I guess this thread is not about such big-venue theory.

[12Bass]

A number of people on TalkBass have had a similar idea:

https://www.talkbass.com/threads/low-cost-diy-practice-coffeehouse-tweeterless-110-long.736360/

https://www.talkbass.com/threads/another-diy-cab-thread-loud-small-and-cheap-22-pounds-that-pounds.1095329/

https://www.talkbass.com/threads/diy-class-d-practice-amp-and-8-cabinet.1105507/

[anotherjim]

When I was a kid, bass cabs were just like sealed guitar cabs, only the drivers were bigger, otherwise same construction (and Fane was the dirt cheap poor boy brand). If you were wealthy, you might have 30 to 50watts more than the guitar amps had. We never missed the lack of fundamental, because we never heard it on the records we liked either. I now know the bass guitar was relying on the strong 2nd & 3rd harmonics of the bass guitar to sound lower.
I do miss the tight/controlled sound of those sealed cabs, but not the total absence of top end. But lack of top didn't matter when everybody used flat-wound strings, which were the default until the '70's. These days, making roundwound sound like flats isn't easy.
Those early Ska records had a middy/honky bass tone with zero top end and weak fundamental. Later Reggae brought earth moving bass which will need a big speaker. A tight cab is still important, because the groove relies on clean note mutes in the gaps. Bop-bop, not boomboom.

[fatecasino]

There are a few hundred different ways to go from here. To advise you on those, I need to know what your final goal or objective result is. If you want to build the cheapest possible small amplifier for practicing in a small room, that is one path. If you want to have an amp suitable for practicing with a few friends in a garage or basement, that's another path. If you want to have an amp you can play small gigs with, that's yet another. And finally, if your objective is just to enjoy tinkering and turning out something useful for fun, that is many, many paths.

My scenario is to play in small gigs of 100-150 people in small venues, bar, etc. What would the solution be in that case for "motorboating"? try another power supply?

[anotherjim]

Try a 1000uF capacitor on the power supply input to the power amp. The capacitance onboard will probably be "only just enough".
You don't say what voltage your power supply puts out. That is important. If 12 or 18V, a 4 ohm speaker will be better match.