stevie

I've re-checked one cabinet that I have here with a slot port, and my software is 100% accurate compared with the impedance measurement. I also recalculated the Cab Diary speaker and it's only 2Hz away from what we actually measured. Just for information, really, as what matters is the actual measurements on the cabinet.

Yes, I think you're right, Phil. See my comment in the Beyma thread that's currently running.

Looks OK. I get 89 litres tuned to 44Hz, although since my recent failures with my tuning software I'd take the latter figure with a grain of salt. The limiting factor is the size of the ports. Increasing them to 4" diameter (by 5" long, but perhaps someone would double-check) would help, if that's possible. The low end response is 15dB down at 40Hz. Excursion-limited power handling would be close to 500 watts, which is pretty good.

[quote name='Phil Starr' timestamp='1475523712' post='3146671'] I think he may be as old as we are Stevie [/quote] Sounds like it, Phil.

Inches? Really?

BoB said earlier that they have a "proper" crossover and not just a high pass filter. If it's a 2nd-order crossover designed for 4 ohms, connecting it to an 8-ohm load will cause a nasty peak in the midrange and pull the impedance down below nominal. If it's just a 1st-order (inductor only), it will lower the crossover frequency and depress the mids. Either way, not good.

Really appreciate this. Thank you.

Fascinating! John, I just re-entered the numbers in your last post into my software and get 57Hz for the slot port, which is still quite a bit off. My software is actually deducting volume for the port and the driver, which should make it more accurate, but there's obviously something wrong that I can't quite figure out yet. I did the same with cab no. 2 and get 55Hz compared with your measured 61Hz. That's also rather disappointing. Bassbox Pro is usually spot-on with round ports, as we found when we meaured Phil's prototypes. When I have a bit more time, I'll have a fiddle with WINisd, although I believe Phil uses WINisd and he got the same figures as I did in our earlier calculations. I really like your side-ported version, by the way, as it leaves space for an optional tweeter or midrange driver. Phil originally built a slot ported cab, but with the ports at the end of the box. We discarded that because of a nasty standing wave that was not present in the box with round ports. We assumed at the time that this was because the slot port had made the internal dimensions square . This thread would indeed make a useful addition to the Cab Diary. Maybe one of the mods could pick it up and stick it on the end. [Edit] I would just add that your measurements demolish my theory that cab mis-tuning was the cause of your damaged driver.

It seems to be a common problem with DJs. Otherwise, I agree: it's not as common as it used to be.

That's not correct, Bill. You're assuming that the driver is matched to the cabinet, which it isn't. A QB3 cabinet for a Beta 10 is nearly 100 litres. Even Eminence suggest using a 64-litre cabinet per driver, and it still peaks then. To try to prevent this from becoming really confusing, I've modelled the driver using 90 litres as the internal volume for the Peavey cab - that's probably not too far out. This is what the frequency response looks like: The yellow curve is the sealed box and the pink one is the vented one. Personally, I'd take the sealed curve anyday, but some people like the peaked response and that's their choice. I also modelled power handling. The sealed cabinet reaches the driver's 3mm xmax at 50 watts input, the vented cabinet at 75 watts. So the choice is between a 200-watt sealed box or a 300-watt vented box. Having said all that, Bigwan needs to take it one step at a time, and the first thing to do is to connect the drivers directly to the input, bypassing the crossover. That could be the real problem.

Very good point, BoB. I agree, there will definitely be some weirdness going on if it's a proper crossover (you don't come across those very often). Better to try it with the crossover bypassed first. To convert the crossover to 8 ohms, double the size of the inductor and half the size of the capacitor going to the LF drivers. In the unlikely event that there is a resistor in the LF circuit, you can probably leave it as it is.

That's how those drivers sound in that cab and there's probably very little you could do to the porting to change that. The Beta 10s are suitable for used in sealed cabs. How well they will work in the Peavey depends on its internal volume. Why not simply close up the port by stuffing some cloth inside, and have a listen? If it sounds promising, take it from there. Sealing the cab will reduce the amount of low bass. If the problem you are experiencing is excessive, boomy bass, sealing the cab could be a good solution.

I wouldn't rely on Xlim too much, Phil. There is a myth going around that Xlim is the maximum excursion a driver can take before it gets damaged, but that's plain wrong. Xlim is a short-term physical limit that relates more to the suspension, cone and coil former rather than to the voice coil. When you go past xmax, power compression starts to kick in with a vengeance and you put power into the coil that has nowhere to go. The magnetic gap provides an important path for cooling the voice coil. Push the coil too far out of the gap, and it doesn't get cooled properly. The voice coil can reach its thermal limit well before it reaches Xlim, as I'm sure many on this forum will testify. My guess is that this is what has happened here, but like anything else, it's impossible to be sure at a distance. If overheating is the cause, the voice coil will be discoloured. Here's a useful diagram showing xmax and xlim: [url="http://www.subwoofer-builder.com/xmax.htm"]http://www.subwoofer...er.com/xmax.htm[/url]

I'd say it's likely you drove the speaker past its limits, but you'd need a post mortem of the driver itself to know for sure. If you have it reconed (a good idea!), the reconer will be able to tell you. The port provides valuable support for the speaker around the tuning frequency. To tune a bass guitar cab for maximum power handling your tuning frequency should be around 50 Hz. There are times when you might want to tune lower, but I wouldn't ever tune higher. I've lost count of the number of times people on this site have said you can always hear a speaker complaining. I've never bought into that one. Anyway, you're welcome and please let us know what you find.

John, I think you'll find your cabinet is tuned too high. My calculations say you've tuned to around 60Hz. With that tuning, you'll be exceeding xmax at 40Hz with an input of 200 watts. As you have also applied bass boost, this figure could easily drop to 100 watts or less. Tuning to our recommended 50 Hz will give you an extra 3dB at 40Hz, perhaps making bass boost unnecessary. The speaker will then also handle an input of 350 watts without exceeding xmax (at least in theory). You might like to check the tuning frequency using the rice grain test. Use your good driver obviously. This works on the principle that driver movement is greatly reduced at the cabinet tuning frequency, because that's where the port is doing most of the work. Turn your speaker on its back and sprinkle a few grains of rice in the centre of the cone. Then go to this site (or something similar): <http://onlinetonegenerator.com/subwoofer.html>, play the frequencies and you will see the rice dancing up and down along with the movement of the cone. As you approach the tuning frequency, movement will slow down. The point at which the rice moves least is your tuning frequency, and this will be shown on your display. Then get back to us. PS Try this with your good cab with the round ports first. You should get a tuning frequency of 54Hz.

I wasn't suggesting putting the whole bass signal through it, MoonBase. The Phil Jones box has two 2.5-inch drivers in it and that's not going to go very loud without highpassing. In fact it only works from about 1kHz up. The active version of the Titan I linked to has tone controls - so you would just adjust the bass control as needed.

That's true. So when you're ready to have a bash, let me know and I'll send you the capacitor and inductor.

While Bill is perfectly correct about the need to custom design crossovers, have you had a look at what bass speaker manufacturers are actually fitting? The last commercial speaker I measured was an Eden and it looked like the crossover had been designed by the tea boy. There will eventually be a two-way 12" design with a proper crossover in the Cabinet Diary thread, as I'm starting on one at the weekend. Don't hold your breath though. I'd give it a go, BoB. Try a 3.3uF film capacitor and a .35mH inductor in a second order circuit and stick an L-pad on the end. Switch the polarity of the HF unit to taste. It's not going to be optimal, but it will probably work. The P.Audio HF units are unbeatable for the money.

It's a bit Mickey Mouse. IMO. A little active monitor like this would likely do a much better job: https://www.andertons.co.uk/p/TITAN8BLACK/active-pa-speakers/b-stock-wharfedale-titan-8a-powered-pa-speaker-in-black

The Monacor piezos are not bad, with sensitivities of between 94 and 96dB. Thomann stocks them. They all have bad resonances at between 4 and 5kHz though, which should ideally be tamed with a crossover. And if you're going to do that you'd probably be better off with a good, cheap tweeter. Having said that, if the OP can get a couple from Phil for the cost of postage, that would certainly be worth trying.

With such a huge list of positive recommendations, this contribution is probably superfluous. However, I'd just like to thank Mike for the Behringer amp he recently *gave away* because he wasn't able to check if it was working. In fact it seems to be fine - so I'm feeling a bit guilty about having it. Not only did he not want any money for it - he dropped it off at my house as well. What can I say? Thanks Mike!!

I agree with those who have replied already - cutting up an expensive cabinet will reduce its resale value and might not give you the result you're after. Another option would be a box with a small tweeter that would fit on top of your existing cab(s). Google Greenboy Head Case for the general idea. If you use one of these tweeters: <http://www.bluearan.co.uk/index.php?id=PAUPHT416&browsemode=manufacturer> the whole thing should come in at well under £50 and is likely to sound better than most commercial tweeters. Apart from the box, you'll need a couple of Speakons, some speaker cable, a capacitor, inductor and L-pad.

I had the 15" version. It was not a quality piece of kit in my opinion, but built down to a price. It sounded OK until you turned the volume up a bit. I do have to say that mine was one of those they built in China. I sold it on eBay after only a few days because I didn't want to foist it on a Basschatter. I'd advise caution. Not in the same class as the Markbass, I'm afraid.