Ruds

Xmax : Excursion limit before distortion (speaker "farting"). Xlim : Excursion limit before damage.

If you're willing to consider a ported cab, the Oberton 10B200 seems like an excelent 10". It should perform very well in a small cab. The Eminence Basslite S2010 also does fine in small volumes.

Ok, this discussion can be basically about design philosophy. Mine tend towards Phil's premise that the fundamental is not of much importance when it comes to bass tone, so I also favour 60Hz and up. But I have the impression that in this case it's exactly when you set your design goals that you can have an optimal way of achieving it (and not so good ways too). Even if that's not the case, at least so far nobody pointed to any critical flaw in my reasoning and "experiment", so maybe its a valid approach. I'm going to think more and try to elaborate this idea further, just to see how far it can go. And of course doing some practical experiments would be very nice too. Thank you Bill and Phil for your comments!

I'm aware that different rooms can change bass response dramatically. But in my case I just took into consideration the rehearsals with my band, which are always in the same room, with the cab always in the same position. Unless temperature and humidity have much influence, room acoustics were pretty much the same. So I think it was a fair comparison. Of course you could argue that I had expectations, and this wasn't a blind test. That's probably the case. I'm definetely not convinced by my subjective experience either. That was just the incentive to my study. What would convince me is objective data and measurements. That's why I started this discussion. I modeled my case in WinISD. Just for the record, Selenium is very shy on their Xmax ratings, so I added (magnetic gap)/4 to Xmax in my WinISD. This is what I got: It's very similar to the 3012HO case. Here's what I did: Using the SPL chart, I adjusted system power for both tunings so that between 60Hz and 100Hz the output was roughly the same. After all, output is what really matters in the end, so that must be the reference for comparison. The 4th column shows that the output in that frequency band is aprox. the same. In the 3rd column you can see that for the same bass output, system power was 175W and 140W for 48Hz and 55Hz tuning, respectively. Then I started to "measure" excursion, both at the fundamental and the 2nd Harmonic. Look at the excursion for 31Hz. For 55Hz tuning it's a tad lower than for 48Hz! Anyway, I'm more interested in the last column, which uses the 6th and 7th columns as "weights" for calculating the total excursion. Considering a signal in which the fundamental is just 3dB below the 2nd Harmonic (the difference is usually higher for bass) I arrived at those numbers for total exc.. As I said before, their absolute value is arbitrary, but the comparison is valid, since they are based on the same output level. So in this particular case, for the same output level at the 60Hz-100Hz range, using 55Hz tuning results in less excursion than 48Hz tuning for reproducing the lower notes of a 5 string. It also requires less input power, so easier on the amp. This would suggest that at their limits (just before distortion), 55Hz would be louder at the low B than 48Hz. Of course 48Hz tuning would be louder at the fundamental compared to 55Hz tuning. But that would be -10dB or even lower relative to the 2nd Harminc. If you aply that -3dB difference I assumed for bass guitar signals, then you end up with -13dB. It seem to me that the fundamental is not of much importance to output. That's why I chose 60Hz to 100Hz as the range for comparing bass output (the "usable" bass output). OTOH, Using only the maximum SPL chart, I got the following: 55Hz tuning would be 2,4dB higher at 62Hz. At 31Hz, it would be 3,7dB lower (-3,7dB). Both compared to a 48Hz tuning. Only based on that, what would one conclude about the capacity of the box for reproducing the low B? I'm not sure, because I wouldn't know how to correlate that chart to the actual signal being reproduced. I know my signal reaches as low as 31Hz. So I could say that the 48Hz tuning would be capable of higher output, because it has higher maximum SPL at 31Hz. Even if I take into account that the signal at 31Hz is 3dB below 62Hz, 31Hz is still the limiting frequency and the conclusion is the same. But that's the oposite conclusion from the other analysis I conducted before. Which conclusion is right? (I really mean it. I don't care about being right or wrong. I wanna know what's the best tuning for my cab.)

[quote name='Phil Starr' timestamp='1415635456' post='2602220'] Here's to stubbornness! Test your thoughts to destruction then hand them over to someone else to destroy if they can, it's the only way to find anything out. (I'm an ex science teacher)[size=4][/quote][/size] [size=4]It's so good to be understood![/size] [size=4][quote name='Phil Starr' timestamp='1415635456' post='2602220'][/size]I just noticed you'd used twice the square rt of 2 in your calculations. You have to make some assumptions and yours tie up with the TKS data and I've no experience to argue with them either so it all seems to be reasonable.[size=4][/quote][/size] [size=4]Now I see I may have misunderstood your question, so let me add to my earlier response.[/size] The absolute value of the numbers I used in this operation are irrelevant and arbitrary. What's relevant and not arbitrary is their relation, which in this case is 1,414. This represents the 3dB difference I refered to in my other post ( 20*log10(1,414) = 3 ). In that last column, I chose to use values instead of just the relation because then I get a simple number as a result. I thought it would make it easier to read the table. So that last column is only good for comparing Xmax under the same bass output, but the absolute numbers don't mean anything [i]per se[/i]. That could be changed by adjusting the master knob on an amplifier. About your comments on sealed and ported cabs, I was thinking that maybe the question is where should the dip in Xmax be placed so as to result in the least excursion when reproducing a signal composed of a weak 31Hz and a strong 62Hz. Oh, and I already compared sealed and ported. Very interesting, indeed. [size=4][quote name='Phil Starr' timestamp='1415635456' post='2602220'][/size]Like you I want to know where the excursion is taking my speaker but I think this is more significant for reliability than it is for the 'sound' if you want undistorted 120dB bass from a fiver you really need two 12's not one. [/quote] No doubt for big bass output, the larger the cone area the better (or the larger the horn the better, right Bill? [size=4] ). But I don't think I'm trying to get huge lows from a single 12 in this "thought experiment". Only to get the most physically possible from a bass reflex. And my hypothesis is that that would be achieved if the tuning was somehow "optimized" for bass guitar (eventually considering psychoacoustics too).[/size] [quote name='Bill Fitzmaurice' timestamp='1415655806' post='2602502'] It's not that xmax isn't important, it's that you don't have to consider it along with the thermal power rating, frequency response and sensitivity in a juggling four specs scenario when the maximum SPL chart wraps it all up in one neat package. It also helps to know that you don't need for a cab to have consistent maximum SPL down to the lowest fundamental. Where you run into a compromise situation with respect to a design that anyone can use is not knowing if the end user has a four string, five string or a drop tuned six string. [/quote] I agree with you that if we don't know much about what the cab is going to be used for, then the maximum SPL chart is our best tool for evaluating the cab's output capabilities. Let me just tell you guys the reason why I started to think about all this. I have one 1x12 cab, arpox. 55l, with a Selenium 12PW5 in it. I had it for a long time tuned to 48Hz, but some weeks ago I changed the tuning to 55Hz. After that I noticed that, on average, I was EQing a little less bass on my amp. And I can't say for sure if I noticed any loss in "fundamental" or "bass extension". I know from theory that the cab lost bass extension, but that didn't seem to affect the tone in a much negative way. OTOH, the gain in what we use to percieve as bass response was very noticeable. Then I started to wonder if using that bit less of bass in my EQ was compensating the increase in excursion on the fundamental. It probably wasn't. But I know the excursion caused by the 2nd Harmonic was lower because of the new tuning, and even a bit more reduced because of my new EQ setting. So to what extent do that compensate the suposedly larger excursion caused by the fundamental. I also know that the 2nd Harm. has way more energy than the 1st. About thermal power, I don't give that much attention to it because, unless heavily compressed or distorted, electric bass signals have a huge crest factor. So the cab has to deal with a big low pitched peak at the attack of the note, and for that the limit is Xmax. I suppose 95% of the times, the real limit to a bass cab's (clean) output is Xmax, not heat dissipation. At least for good quality drivers. That's not to say I don't consider it. Its just that I think its second in importance in determining maximum SPL for this particular application, compared to Xmax.

[quote name='Phil Starr' timestamp='1415608759' post='2601821'] You've probably been following the 1x12 design diary [url="http://basschat.co.uk/topic/227904-1x12-cab-design-diary/"]http://basschat.co.u...b-design-diary/[/url] and together with the link to TKS above tht's probably most of the background on this site.[/quote] Yes, that 1x12 design diary is an awesome topic! But I read it before October, so tks.se's posts were new to me. His measurements and experiments seem to agree with my speculations here. [quote name='Phil Starr' timestamp='1415608759' post='2601821'] This is further complicated by the possibility of wind noises in the ports. [...] [/quote] In my designs, I always try to use a port large enough to simply prevent compression/chuffing. Especially since I learned from practice how important a well designed port is. But I guess I understand very well the idea of compromises. [quote name='Phil Starr' timestamp='1415608759' post='2601821']OK a question for you, how did you derive the fundamental/2.83 second harmonic/2 figures? Was this on the basis of some experiment or just derived from the maths?[/quote] I have some experience with musical instrument signals, since I've done some research in audio signal processing during my graduation. Electric bass signals and their characteristics are not alien to me since then. I also remember reading here and there about electric bass timbre eventually. And more recently, when the problem of box tuning started to bug me, I did a bit more measurements. I plugged my 5 string (35" scale with 2 EMG 40DCX), directly in my PC and used SciLab to analyse its spectrum (no EQ or any ohter signal shaping used). I did some plots and calculations to try and understand especially how the first and second harmonics behaved on the B and E strings. I Recorded with just the bridge PU, bridge+neck and just the neck PU. My methodology was not careful, after all I was just doing it "for fun", but it was not difficult to see the pattern even then. So, without entering in further detail, for electric bass, I'd say its very safe to assume that the fundamental is always below the second harmonic, and the 3dB difference I used in that operation to "measure" Xmax is conservative, so to speak. That is the basis of my assumption. [quote name='Phil Starr' timestamp='1415608759' post='2601821']My contention, without any data to be fair, is that the proportion of cone movement down to fundamental/second harmonic would vary between basses and between neck and bridge pickups. Essentially the further the pup is up the string the nearer it is to the antinodal point for the fundamental and the louder this will be. Where you pick/pluck will also affect this.[/quote] I agree 100%. But from my experience, even the most "bassy sounding" bass still has less energy in the fundamental than in the second harmonic. At least if it still sounds like a bass. I may be wrong, but if I'm not, this information could be useful in bass cab design. [quote name='Phil Starr' timestamp='1415608759' post='2601821']Another factor is that of using Xmax as the sole basis for decision making. [...] [/quote] You are absolutely right. But the exact value of Xmax ou even Xlim is not an issue to this analysis. Independent of the limit you choose to "impose" on your design (mathematical Xmax, measured Xmax, Xlim...) the question is how to get the maximum usable bass SPL before reaching this limit. In a practical situation, the player is going to raise the volume knob or the bass EQ knob until he reaches his desired level of SPL. At this point, is the cone excursion the minimum it could be (at the worst case scenario, usually the open B string)? If not, I'd consider that the cab is not optimised. I couldn't make the last citation work, so about your last paragraph: I respect BFM and really take what he says very seriously. Maybe I'm just overthinking, and in practice this is not important, or I'm overlooking something. But unfortunately one of my flaws is stubbornness. So until I get convinced I'm wrong, I will "feed this bug". And I still have some things in my head, but this post is already too long as it is, so I'd better keep it for another one. Thanks for your support Phil! Let's hope this topic can be of some use.

Thanks, Allie and madshadows!

[quote name='Bill Fitzmaurice' timestamp='1415549375' post='2601359'] I don't. I look at SPL, Maximum SPL and port velocity charts. I don't worry about excursion per se, as it's just a means to the end that's seen in the Maximum SPL chart. Looking at the excursion chart shows only one dimension of a three dimensional result. The main benefit to looking at the excursion chart is in learning how it fits into the overall result, including how tuning affects excursion, but after a few decades of designing speakers that's second nature. [/quote] I'm sure I still have a lot to learn from practical experiences. I'll keep your advices in mind. [quote name='Musky' timestamp='1415554245' post='2601418'] This is way beyond me, but there was a discussion in another thread recently that may be of some interest. [url="http://basschat.co.uk/topic/227904-1x12-cab-design-diary/page__view__findpost__p__2566219"]http://basschat.co.u...ost__p__2566219[/url] If it were me I'd invest in an HPF like the Thumpinator or F-Deck, assuming your amp doesn't already have an HPF. [/quote] I'll take a look at that topic, thanks. As for the HPF, I already use one I built specifically for the cabs I currently use. No doubt it helps protect my speakers when I need to crank up the volume. But even using such filters, I'm interested in optimizing the cabinets I design.

I really appreciate your participation in this topic, Bill. I thought about what you said, ran some more simulations, but am still not convinced (one way or the other, that's why I opened this topic [size=4]).[/size] I understand that the Maximum SPL chart takes into account excursion, thermal power and sensitivity. But it doesn't show the relation between these factors, only the end result: maximum SPL for a pure sine wave. For example, I could be reaching maximum SPL because of thermal power on one specific frequency, but still have plenty of headroom excursion-wise. This would allow me to "spend" this excursion on other frequency that may be playing simultaneously. This chart alone wouldn't allow me to know that. I understand the maximum SPL chart applies directly to pure sine waves, white noise or if you don't know anything about your input signal. But, if I know the cab is going to be used mostly for electric bass, and I know something about this signal, wouldn't it be more precise to use this information to estimate the limits of the enclosure on a more practical situation? That's what I tried to do in my analysis.

I've been thinking lately about port tuning and its effects on excursion, specifically in the case of electric bass. At first, I thought that if I wanted the cab to handle a bass' low B better, I should use a lower tuning. Say, for instance, 55Hz for a 4 string bass and 48Hz for a 5 string. That seemed correct, since taking the "unloaded driver" zone lower should help against over-excursion at the low B's fundamental (31Hz). But then I thought a little more about all the implications of lowering the tunning frequency, and realized it might not be that simple. So I ran a WinISD model and collected some data. I modeled a cab I just intend to build for myself in the future, using a Kappalite 3012HO in a 56l enclosure. This is what I retrieved from WinISD: The meaning of the columns from left to right: 1) The note being analysed; 2) port tuning; 3) system input power; 4) SPL at the 2nd Harmonic frequency; 5) SPL at the fundamental frequency; 6) Excursion at the fundamental frequency; 7) Excursion at the 2nd Harmonic frequency; 8) (exc. Fund.)/2,83 + (Exc. 2nd H.)/2 The last column means 1/4 of the system input power on the 2nd Harmonic and 1/8 on the fundamental. This 3dB difference seemed apropriate, at least for this theoretical approach. My idea was that for real bass signals (not sine sweeps) all frequencies contribute simultaneously for excursion. But above the 2nd harmonic, tunning would have too little influence on excursion (or SPL) to be of importance for this study. That's why I only considered tne 1st and 2nd. I experimented with two different tunings, 55Hz and 48Hz, and analysed the behaviour of the box for 3 different notes. I wanted to "measure" excursion in both tuning cases when the box was producing roughly the same SPL on the bass region (under 90Hz). I assumed the 2nd Harm. was a good "loudness" indicator for bass, so I chose this as reference. Input power for 48Hz tuning was always 240W. In the case of 55Hz tuning, power was set in order to produce the same output SPL on the 2nd Harmonic for each note being analysed. So, after studying this table, my conclusion was that, at least for this case, tuning at 55Hz is better than 48Hz if I want to use this cab with a 5 string bass. On the low B, for a 55Hz tuning, I got 6,38mm of excursion, which is a lot better than the 8,01mm for a 48Hz tuning. Both situations at roughly the same usable bass output. Now, my intention with this topic is to put this purely theoretical "study" I conducted to the test (or peer review). I know there are people more experienced in this bass cab business than me, so I want to know if I made any mistakes. Another way to put it is this: Would it really be better to tune this box to 55Hz, instead of 48Hz, if I want better over-excursion protection when using my 5 string bass?

Hi, everybody! I know Basschat for a while. I've already followed (not as a member) some very interesting topics. I decided to join now because I have something I'd like to discuss about bass cab design. And hopefully I can also help with the little I know. Ruds.