Double Bass Speaker cab resurrection

[timobee4]

Hi fellow DB pluckers! I have a speaker cabinet I want to resurrect to use in small duo gig situations. It is no fancy birch just an old PA cab. At the moment I have a FAITAL PRO 10PR300W - 10" 4Ohm SPEAKER (NEODYMIUM) specs are Faital Pro 10PR300 10" Speakers - Faital Pro 10PR300 10" speaker and that has a lightweight neodymium magnet - Faital Pro 10PR300 600 watt 10" high efficiency of 98dB SPL woofer for all high power bass applications. Faital Pro
I had a blown 8 Ohm tweeter in the box that I had to bin. So should I replace it with a 4 Ohm tweeter? If so what sort of wattage/type? Do I need to have a crossover? I'd like to ad a tweeter volume control. Do I need to block the vents? Do I need to install some sort of sound dampening material to avoid standing waves (??) Resurrecting a box is possible I think but totally clueless when it comes to this subject Please give me some ideas. I want it to be a 4 Ohm cabinet to pair it with a Wizzy 10 for bigger venues. Thank you thank you thank you!!!!!

 

[iiipopes]

Nah. Instead of replacing the tweeter, make it into a tuned response port with the proper diameter and length of PVC pipe.

 

[drurb]

Is there a crossover in there now? There sure ought to be even if it is simply a capacitor in series with the tweeter to form a high-pass filter. If that's all there is, then you can likely dump the tweeter but keep in mind that, depending on how the system was wired, the nominal impedance of the box will change. If you like the bass response of the cab, then plug the hole where the tweeter was.

Attempting to make a tuned port, given the presence of the other ports (presumably designed as part of the cab) would not be a good idea at all. You are not likely to end up with anything satisfactory.

If you liked the response with the tweeter, then replace it... with an 8 ohm driver that matches the one that was there. A level control can be added reasonably easily. You'll need an L-pad.

 

[iiipopes]

Drurb is, of course, correct that porting is a complex issue. The reason I mentioned it is because most PA cabinets are ported to drop sharply off below 50 Hz or even a tad higher, to limit speaker excursion (and warranty claims) which could cause the bottom end to sound lacking when used for bass.

Francis Deck has some great material on proper speaker cabinets for bass application on his website:
Invalid Link Removed

 

[timobee4]

I'm sorry but I totally failed to mention that the original driver was an 80W 8Ohm driver I replaced with a more powerful nice 4Ohm driver thinking that happy days, problem solved, except the dead tweeter is 8Ohm 20W and yes it has a capacitor on it's side that acts as a crossover (To me that was just an orange colored thingy untill Les told me that "There sure ought to be even if it is simply a capacitor in series with the tweeter to form a high-pass filter") can I salvage the capacitor and use it the same way again (I dont have a multi meter that does farad or ESR meter) if I get a more powerful tweeter or better get a different one and how am I going to ad a control to turn the tweeter off or up & down? So if the original driver was 80W 8Ohm and the tweeter was 20W 8Ohm should my 300W driver be coupled with a 75W tweeter? To some of you this is a simple task but to me is a nightmare, I like that little cab even bought smart little side handles has lovely grill i resprayed and it can be mounted on a pole too. I am learning something by doing this. I decided to keep the vents since I saw the crazy 8 has similar vents. In all an all I am trying to jazz up a PA cabinet here keeping it 4Ohm so when its paired with 4Ohm Wizzy boy it will be 2Ohm system my AI can handle that. Speaker making should be left to experts but I figured if I can get an idea I just order the parts and done and dusted

I found this fantastic free smart calculator but buggered if I know how to use it! http://www.apicsllc.com/apics/Misc/filter2.html

 

[DoubleMIDI]

The crossover frequency for the tweeter will change if the load of the tweeter changes but the capacitor in series does not change!

I also think that (if there is no inductance in series with the main speaker) the load for higher frequencies is less than 4 Ohms, so if you put one more 4 Ohms speaker in parallel your amp might blow up (probably not immediately but earlier or later).

 

[drurb]

The capacitor in series with the tweeter forms a simple first-order high-pass filter. The cutoff, f (in Hz), is:

f = 1/(2πRC)

where R is the nominal impedance of the tweeter (here, treated as resistance) and C is the capacitance. From this, you can see that going from a 4-ohm tweeter to an 8-ohm tweeter (changing R from 4 to 8) halves the frequency of the cutoff. Thus, with the 8-ohm tweeter, more low-frequency content will reach the tweeter if C is held constant. This might be why you blew your tweeter.

 

[fdeck]

There's a decent chance that the speaker is already ported OK. You could seal the tweeter hole and find out the port tuning by putting a couple grains of rice in the cone and adjusting the frequency of a sinewave generator until the rice stops bouncing around. There's a convenient frequency generator in the free WinISD program.

 

[timobee4]

Must say that you guys are walking encyclopedias possessing knowledge that I just can't fully grasp. I guess to simplify the whole thing I should put it in a simpler way that is indicative of just how much everything you guys say goes over my head. So if you were given a cabinet with a hole where the tweeter once was and just a 4ohm 300w driver in place and you took a fancy to the cabinet how would you go about choosing a tweeter? The wires all there I just need to hook it up. Is there a small shopping list? If not I probably better off plugging the hole put the grill back and leave it at my friends house were we jam (less stuff to carry) I really appreciate your help just don't forget that what you take for granted is completely Chinese to me cheers

 

[DoubleMIDI]

I doubt that the tweeter was blown because of drurb explanation since only the woofers impedance has changed, not the tweeters. But if a 4 Ohms tweeter will be used what drurb expects might happen.
So, timobee4, if you want to change the tweeters impedance too, you need a new capacitor with this tweeter with approximately half the value of the one you use now (if the frequency range is the same, of course).
For a different frequency you could use the formula drurb showed (where n means PI=3.1415...).

If you don't understand what we are talking about, the best you can do is
1. either go back to a 8 Ohms woofer and get a 8 Ohms tweeter as a replacement using the existing capacitor or
2. seal the hole of the tweeter and live without it keeping the 4 Ohms woofer.

 

[timobee4]

If you don't understand what we are talking about, the best you can do is
1. either go back to a 8 Ohms woofer and get a 8 Ohms tweeter as a replacement using the existing capacitor or
2. seal the hole of the tweeter and live without it keeping the 4 Ohms woofer.

So you saying my 4 Ohm driver is no candidate to be paired up or accompanied by a tweeter of any kind to make a functioning cabinet?

 

[drurb]

I doubt that the tweeter was blown because of drurb explanation since only the woofers impedance has changed, not the tweeters.

There seems to be some miscommunication. Here's what Timo told me via PM:

I have my sweet 10" box with a 4ohm neo speaker but the tweeter died, when I pulled it out I noticed that it was 8ohm!

I thought he replaced an original 4-ohm with an 8-ohm but his post in this thread indicates that he replaced a dead 8-ohm with a 4-ohm and the 4-ohm is now dead. I think I have that right. Yes, indeed, going from 8-ohms to 4-ohms will raise the corner frequency of the high-pass filter by an octave leading, if anything, to less likelihood of blowing the tweeter as a result of feeding it less low-frequency content.

Double, it is not true that "only the woofer's impedance has changed." In fact, the impedance of the woofer has been a constant throughout Timo's adventure.

So, let's see. Timo blew two tweeters. One of the most common reasons for blowing tweeters is the use of an underpowered amp. When an underpowered amp is driven into clipping, large amounts of energy are splattered to high frequencies. This is one of the surest ways to fry tweeters. Timo, what amp are you using?

Edit: I see now from Tim's post below that you're right, Double. When he said he replaced "the driver," he meant the woofer! So, I'll try again. Timo has had one blown tweeter in a box that originally had an 8-ohm woofer, which he swapped for a 4-ohm woofer. Okay, I think I got it now.

Timo, here's my advice. IMO, tweeters are generally a waste when it come to amplifying DB. Plug the hole and go about your business. If you absolutely want a tweeter, replace it with something comparable to what was originally in the box. The reason you keep blowing tweeters lies outside the box.

 

[timobee4]

There seems to be some miscommunication. Here's what Timo told me via PM:

I have my sweet 10" box with a 4ohm neo speaker but the tweeter died, when I pulled it out I noticed that it was 8ohm!

I thought he replaced an original 4-ohm with an 8-ohm but his post in this thread indicates that he replaced a dead 8-ohm with a 4-ohm and the 4-ohm is now dead. I think I have that right. Yes, indeed, going from 8-ohms to 4-ohms will raise the corner frequency of the high-pass filter by an octave leading, if anything, to less likelihood of blowing the tweeter as a result of feeding it less low-frequency content.

Double, it is not true that "only the woofer's impedance has changed." In fact, the impedance of the woofer has been a constant throughout Timo's adventure.

So, let's see. Timo blew two tweeters. One of the most common reasons for blowing tweeters is the use of an underpowered amp. When an underpowered amp is driven into clipping, large amounts of energy are splattered to high frequencies. This is one of the surest ways to fry tweeters. Timo, what amp are you using?

Timo, here's my advice. IMO, tweeters are generally a waste when it come to amplifying DB. Plug the hole and go about your business. If you absolutely want a tweeter, replace it with something comparable to what was originally in the box. The reason you keep blowing tweeters lies outside the box.

Yes my sweet old cabinet had a blown tweeter and 8 Ohm 80W woofer. I use an AI Clarus for a head and I thought I can keep the box replacing the guts of it,
so I got a ripper neo driver 4Ohm 300W when I installed it and tried it out noticed that the tweeter dead, I didn't blow it it was blown. I took it out and started a thread. Now I have an extra hole I wanted to fix. Got the best handles, neutrik inputs, new more powerful driver but I am stuck with the tweeter. Drurb is 100% correct about the plugging of the hole as it is pretty useless for DB. I used to have a 210 box with a tweeter with a dial and I used to turn it right off!!!!! So that is settled!!!!!!! One more question though should I put insulation inside???? Its going to be my jamming cab permanently stationed at my friends studio! Wizzy for gigs although I am very interested in that crazy 88 cab. Bless you all and thanks heaps!!

 

[drurb]

Yes my sweet old cabinet had a blown tweeter and 8 Ohm 80W woofer. I use an AI Clarus for a head and I thought I can keep the box replacing the guts of it,
so I got a ripper neo driver 4Ohm 300W when I installed it and tried it out noticed that the tweeter dead, I didn't blow it it was blown. I took it out and started a thread. Now I have an extra hole I wanted to fix. Got the best handles, neutrik inputs, new more powerful driver but I am stuck with the tweeter. Drurb is 100% correct about the plugging of the hole as it is pretty useless for DB. I used to have a 210 box with a tweeter with a dial and I used to turn it right off!!!!! So that is settled!!!!!!! One more question though should I put insulation inside???? Its going to be my jamming cab permanently stationed at my friends studio! Wizzy for gigs although I am very interested in that crazy 88 cab. Bless you all and thanks heaps!!

If you were happy with the cab before, then just plug the hole. You can "cap it" with a piece of wood, etc. The cabinet building folks would likely have good ideas about what to use. Then again, you can cap it with the dead tweeter!

 

[DoubleMIDI]

Yes, some misunderstanding, but timobee4 made it clear now, I think.

And drurb is absolutely right with his explanation why the tweeter might have been fried. The speaker combinations are dimensioned for normal musical signal frequency mixes, not for highly disturbed signals.

An extended range woofer might be a better option than a tweeter to get a bit more midrange for better hearing of yourself, but I haven't tried it yet. I'm afraid there might be a few drawbacks with extended range speakers, but at the moment I can't nail them down.

Timobee4, if you mean damping material inside the box by mentioning insulation, then yes, one (or two) sheet(s) of damping material on every surface might help to avoid or at least reduce resonances of standig waves inside the box. But it depends on the construction of the box. If there are a lot of parallel surfaces it will help. You even can calculate the resonances. The distance between the parallel surfaces is half the wavelength of the resonance frequency.

BTW, a 300W, 4 Ohms speaker is still a bit less for what your amp can deliver (400W at 4 Ohms or 250W at 8 Ohms for a Clarus 1). Better get a 300W, 8 Ohms speaker if you want to use it with the AI Clarus to avoid killing the speaker if it gets loud. (It might even happen if you have a damaged cable that will have a faulty contact generating clackling noise.)