Speaker Testing Question--Acme Low B 4

[knigel]

Hello all,

I recently came into possession of a used Acme Low B4 at a very good price. I knew going in that I would have to replace the speakers--the question was how many. I was aware it came with one stock speaker still in the cab (plus the mid and tweeter), and the seller was able to find a second speaker that appears to be a new stock speaker (I have sent an email to Acme to confirm).

(Now, what did the previous owner do to cause the other speakers to be MIA? Yikes. This is a pretty robust cab!)

My plan is to replace the speakers with what the manufacturer recommends, which I believe are the original speakers from Eminence and are a fair price. My quandary is if I have to replace all 4, the project is probably not financially feasible. But only replacing 2 speakers would be fine and I would have a great cab to leave at my practice space.

My question is, what is the best way to test the speakers I have? Is it the battery test and cross my fingers? Try playing with the two I have hooked up?

Thanks in advance!

 

[agedhorse]

There are many kinds of damage, some easy to detect, some very difficult.

What we do in the lab is difficult to do without test equipment, but close visual examination is a first step.

Generally, when a speaker (or two) is blown in a multi-driver cabinet, the remaining drivers are also usually damaged. That’s a warning that there may be hidden damage.

 

[Old Garage-Bander]

Battery test will confirm that the voice coil works. It will also confirm polarity.
You can also, VERY GENTLY, push on the cone to move the voice coil and see if you get any scratching/rubbing noise.
An Ohmmeter will help determine impedance if you need to know it.

None of these tests are dynamic. You'll still have to play em to see how they do.

 

[knigel]

There are many kinds of damage, some easy to detect, some very difficult.

What we do in the lab is difficult to do without test equipment, but close visual examination is a first step.

Generally, when a speaker (or two) is blown in a multi-driver cabinet, the remaining drivers are also usually damaged. That’s a warning that there may be hidden damage.

All speakers being damaged is what I'm most afraid of. Maybe I'll post some pictures of the speakers later and maybe someone will see some damage that I am missing. They seem in good nick, but...

Battery test will confirm that the voice coil works. It will also confirm polarity.
You can also, VERY GENTLY, push on the cone to move the voice coil and see if you get any scratching/rubbing noise.
An Ohmmeter will help determine impedance if you need to know it.

None of these tests are dynamic. You'll still have to play em to see how they do.

I did try the pushing test on the "new" speaker that wasn't in the cab, and it seemed ok. But again, who knows for sure? Might try starting with buying two new ones (after confirming the other two look ok and are the proper speakers) and just hoping for the best.

Thanks for your thoughts all!

 

[Wasnex]

The Acme Low B cabs have low sensitivity ratings. I believe the Low B4 was rated 96dB 1W/1m with 700W RMS power handling. Also the mechanical power handing was 600W at 30hz.

The lowish sensitivity rating means more power is required for the cab to get loud. With 700W the calculated SPL would be about 124.5dB. The measured SPL will be a bit lower due to power compression. I think this would be loud enough for me, but some players require more SPL.

I believe Acme recommended powering the B4 with 800 to 1000W. This is more than the cab's RMS rating and also more than the cabs mechanical power handling, so it's necessary to use some degree of judgement and restraint to avoid blowing the drivers when using an amp with the recommended power. Many players ran even higher-powered amps with these cabs, so it's not a surprise to find damaged drivers.

Years ago I owned one of the original Low B2s. Calculated SPL at 350W comes to 118.4dB. This cab was barely loud enough for many gigs, and it felt pretty compressed when it was pushed. At some point it seemed like turning up the amp did not really result in more volume. Also, at some point as the power was increased, the drivers would clack their voice coils, which is a good way to destroy speakers. AFAIK the resulting damage would likely be internal, so you may not be able to see it.

The Low-B cabs are unique and desirable, but they trade extended low end for efficiency. If extended lows is a priority, it may be worth replacing the drivers. If you want the cab to perform as new, your best bet is probably to replace all four woofers. Installing two worn/weak woofers with two new woofers may be more expensive in the long run, especially if you push the cab relatively hard.

IMHO, carefully weigh the cost against your expectations and requirements. A free cab is not necessarily a good deal. Unless you want the specific characteristics these cabs are known for, you are probably better off putting the money towards a new, modern cab that better meets your needs.

 

[agedhorse]

Another option (IF the cabinet is in nice condition) is to do the math to see if there might be other driver options with higher sensitivity that would work out better. I don't know the answer without doing the math because it's possible Acme used a driver that requires a lower tuning frequency than typical.

I caution you against assuming that the remaining drivers are good, and sometimes a cabinet is not worth repairing (especially if the cabinet itself is not is good condition).

 

[Wasnex]

Another option (IF the cabinet is in nice condition) is to do the math to see if there might be other driver options with higher sensitivity that would work out better. I don't know the answer without doing the math because it's possible Acme used a driver that requires a lower tuning frequency than typical.

I caution you against assuming that the remaining drivers are good, and sometimes a cabinet is not worth repairing (especially if the cabinet itself is not is good condition).

I do believe the cab is tuned rather low as the response is supposed to be -6dB at 30hz. Probably fairly easy to retune cab for a different driver since is has tubular ports...it may be possible to shave down the ports.

If the OP decides to retune the cab, he is still on the hook for 4 new woofers. Additionally, the mid and tweeter in this design are also rather inefficient and have limited SPL capabilities...I doubt they would work well with more efficient drivers. In fact, IMHO they are not even loud enough to really balance out the OEM drivers.

I would either buy OEM drivers or part it out.

 

[knigel]

I think this would be loud enough for me, but some players require more SPL.

I believe Acme recommended powering the B4 with 800 to 1000W.

If extended lows is a priority, it may be worth replacing the drivers. If you want the cab to perform as new, your best bet is probably to replace all four woofers. Installing two worn/weak woofers with two new woofers may be more expensive in the long run, especially if you push the cab relatively hard.

IMHO, carefully weigh the cost against your expectations and requirements. A free cab is not necessarily a good deal. Unless you want the specific characteristics these cabs are known for, you are probably better off putting the money towards a new, modern cab that better meets your needs.

Totally agree with your thoughts here. I'm a 4 string player exclusively, so massive low end isn't a priority, and this will live at my small rehearsal spot so extreme volume is not required (I have a pair of TE 2x8 cabs for gigs--again, volume isn't required for the band I play with these days.) My goal is to have a functional cab that is basically static. 4 new drivers from the manufacturer would only be around $400, so only slightly more than I could sell it for on the used market.

Another option (IF the cabinet is in nice condition) is to do the math to see if there might be other driver options with higher sensitivity that would work out better. I don't know the answer without doing the math because it's possible Acme used a driver that requires a lower tuning frequency than typical.

I caution you against assuming that the remaining drivers are good, and sometimes a cabinet is not worth repairing (especially if the cabinet itself is not is good condition).

Thanks for that info--I follow your posts carefully, and know that original drivers are likely to be the best fit. Besides the internal volume, what other information would someone need to find a suitable alternative? I'm willing to do the research, just not sure what to look for.

Also, thanks so much everyone for their help. Talkbass is such a nice resource for people to interact and ask questions!

 

[knigel]

Here are some pics of the speaker that came with the cab but was not installed. Looks jankier than I remembered (what's up with that crease around the cone?) but hey, it was free. Any thoughts? Also, google says this is an Eden driver--could it have been used by Acme as well? I will dig out the driver in the cab later tonight (I mean, I should be working right now!)

 

[Popps]

That looks like what happens when an Acme cabinet is under powered
and over pushed. I believe you will find that speaker is no good.
Also, I can't speak to the 12's, but, Andys 10" speakers are OEM.

 

[knigel]

That looks like what happens when an Acme cabinet is under powered
and over pushed. I believe you will find that speaker is no good.

Nuts. Had the same feeling though!

 

[logdrum]

Between what Wasnex and AgedHorse have said, I will abandon this project if it was me. If you buy 2 only and the tow have hidden damage then it may also take out the new 2. And new drivers will need some modifications and 4 new OEM drivers may still not work with the tweeter.

I think the unloaded driver is also beat.

 

[Wasnex]

Here are some pics of the speaker that came with the cab but was not installed. Looks jankier than I remembered (what's up with that crease around the cone?) but hey, it was free. Any thoughts? Also, google says this is an Eden driver--could it have been used by Acme as well? I will dig out the driver in the cab later tonight (I mean, I should be working right now!)

View attachment 4903583
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That's a totally trashed OEM driver for the Eden XLT line. My last touring rig included a D210XLT and a D410XLT...way different design concept. Very efficient but not a lot of extension down low.

Looks like you need four new drivers.

 

[knigel]

That's a totally trashed OEM driver for the Eden XLT line. My last touring rig included a D210XLT and a D410XLT...way different design concept. Very efficient but not a lot of extension down low.

Looks like you need four new drivers.

It sure is looking like it ha ha. Still going to dig out that other speaker. Kind of a fun mystery!

And the people of New England are animals--if I need the space back in my garage, I can certainly get what I paid for it ($15).

 

[Wasnex]

It sure is looking like it ha ha. Still going to dig out that other speaker. Kind of a fun mystery!

And the people of New England are animals--if I need the space back in my garage, I can certainly get what I paid for it ($15).

If the cab is in decent condition and the mid and tweeter are in working order, I might spend $400 on a set of new OEM woofers. I think this is pretty close to the breakeven point, and I would not be willing to invest very much more.

 

[knigel]

If the cab is in decent condition and the mid and tweeter are in working order, I might spend $400 on a set of new OEM woofers. I think this is pretty close to the breakeven point, and I would not be willing to invest very much more.

That is EXACTLY what I'm thinking. OEM drivers and just call it a day. The manufacturer has been very responsive to my queries. Any other alternative driver I have found is more expensive except one, these Faital Pros. And for what would amount to $80 is it worth the risk? Probably not.

https://usspeaker.com/faital pro 10fe200-1.htm

 

[agedhorse]

That looks like what happens when an Acme cabinet is under powered
and over pushed. I believe you will find that speaker is no good.
Also, I can't speak to the 12's, but, Andys 10" speakers are OEM.

No, that's the classic case of when a driver is mechanically overpowered, way overpowered.

I don't think that is the correct driver either, looks like an Eden driver, it's going to have completely different parameters than what's needed for the OP's cabinet.

That's a totally trashed OEM driver for the Eden XLT line. My last touring rig included a D210XLT and a D410XLT...way different design concept. Very efficient but not a lot of extension down low.

Looks like you need four new drivers.

That was my thought too, wrong driver for the application.

That is EXACTLY what I'm thinking. OEM drivers and just call it a day. The manufacturer has been very responsive to my queries. Any other alternative driver I have found is more expensive except one, these Faital Pros. And for what would amount to $80 is it worth the risk? Probably not.

https://usspeaker.com/faital pro 10fe200-1.htm

I don't think the Faital drivers would be a good choice without retuning the cabinet, and even then the driver is good for about 100 watts RMS mechanically at ~40Hz.

I think you are better off with the OEM drivers, and you will need to pay close attention to the wiring details, that's also probably screwed up.

 

[knigel]

I don't think the Faital drivers would be a good choice without retuning the cabinet, and even then the driver is good for about 100 watts RMS mechanically at ~40Hz.

I think you are better off with the OEM drivers, and you will need to pay close attention to the wiring details, that's also probably screwed up.

That’s what I’m thinking too. Keep it OEM and be done with it. I only briefly considered the Faital based on the price—wasn’t much of a consideration either.

Thanks to you and everyone else for your help! Very informative all around!

 

[micguy]

Generally, when a speaker (or two) is blown in a multi-driver cabinet, the remaining drivers are also usually damaged. That’s a warning that there may be hidden damage.

You have 4 identical drivers that have been given the same rough treatment. One of them has blown. What's the chance that the others are likely to go? Probably darn close to 100%

 

[byacey]

No, that's the classic case of when a driver is mechanically overpowered, way overpowered.

Exactly. The cone reached the end of it's mechanical excursion limit, and the coil tried to push it yet further. Something has to give.