Phil Starr

[quote name='fryer' post='1039712' date='Nov 28 2010, 10:53 AM']Hi, I would like some help please. I have a TC RH450 head - 450 w at 4 ohm. I have bought two purple chili 1 x 12 cabs, which have Celestion 12" 300 w speakers. I want to upgrade these and was thinking of putting an Eminence 3012 LF, 450 w, in one cab, and a Beyma 605 ND, 125 w, in the other. They are both 8 ohms. I would seal the ports on the Beyma cab. The RH only has one speaker outlet, so you wire to one cab, then to the other. So if I took the output to the Eminence cab first, would I need a crossover or something to restrict the wattage to the Beyma ? Richard[/quote] You might be better off in the amps and cabinets forum, I'm not sure Alex has the time nowadays to answer a lot of questions other than those about Barefaced. there are some fairly experienced people there who won't answer on Alex's forum. Whether you want to re-post or continue here you need to give a lot more information before anyone can really help. What are the Celestion drivers you currently have in the cabs and what don't you like about their sound? What sound are you trying to achieve? Why have you chosen these two drivers, are they something you already have or do you still have to go out and purchase them? Are you up for selling the PC's and building your own cabs? If a cab has been optimised for a particular driver it is almost never optimum for another, so unless the cab is a real dog it is unlikely that you can upgrade the sound with a simple swap. Using two different drivers is 'interesting' rather than wrong as a few people in these forums will sometimes tell you, IMO. As well as the technical problems you always get with multiple drivers you get a subjective rounding down effect where the characters of both speakers seem to disappear a little leaving a more neutral tone. You might be able to achieve what you want by replacing one speaker only. Over to you. Are you open to other suggested drivers?

probably safer than bashing away at components (though I do this too) is to use a can of freezer spray, which will also help to locate any faulty components.

As Mr Foxen has pointed out the problem is with the 2x10 which potentially get 500W. However you can't strictly speaqking compare amp watts with speaker watts as they are rated differently. Amp ratings are the maximum they can reach without distorting. They are a peak rating, If you have a VU meter on your amp you'll see the signal going up and down. A thousand watt amp only produces a thousand watts for a fraction of a second at a time on the peaks. Speaker ratings are basically about heating 500W through a speaker coil has almost the same effect as 500W through an electric heater. Speaker coils get really hot and will potentially melt the glue holding them together or even the wires themselves and this is why they fail mainly. The rating is given by passing that much power in the form of filtered noise ,meant to simulate music, through the speakers for several hours. If none of the samples fail that is the rating. When you play bass though you don't play flat out all the time. You play loud bits and quiet bits and sometimes nothing at all. Even if you are hitting the strings really hard with a pick and pumping out a non stop 8-beat the front of each note may hit the amps peak but it will decay quickly and at the end of the song you will stop and the speaker starts to cool. If you play without compression you might have a dynamic range of 40dB and this means your average level could be 20dB less than your peak. This is a ratio of 100:1 so the thousand watt amp could be only producing an average of 10W! So long as you keep out of distortion and don't use a limiter/compressor you'll be way away from the limits of your speakers. If you look at the Eminence website you'll see that as well as the RMS (EIA) rating of their speakers they also give a program rating of double this and a 6dB 'crest' rating for short term peaks. There is one more hazard for a speaker though. The power rating is for general 'music' and you play bass which has a lot more low frequency. The speakr can only move so much before it hits the grille or the back of the magnet or moves out of the magnetic gap and this can definitely damage the speaker depending on it's exact design. Ported cabs are particularly prone to this sort of over-excursion as are certain speakers. There are 200W speakers that cannot handle 50W in the wrong cab at low enough frequencies. Really it is almost always worth filtering out very low and subsonic bass. If you use an over powered amp with a five string, no bass filter and use a lot of bass boost on your eQ then all bets are off. So. the answer is that if you avoid distortion, keep the volume down and either filter the subsonics and or go easy on the EQ then there should be no problems and by over-powering you should get a great clean sound. If not you may have to recone at some stage.

[quote name='Bill Fitzmaurice' post='1059750' date='Dec 15 2010, 05:14 PM']Perhaps the cab design pre-dates the woofer, and it was originally loaded with a driver that need a larger box. That, or Yamaha wanted to go lower than what 175L allows. IMO an eighteen loaded cab with a 50Hz f3 makes little sense.[/quote] I don't think it's the wrong speaker, though because I bought it second hand, I can't be sure. The original would be Eminence (it say's so on the badge) and they don't advertise a whole lot of 18's. I agree with you about the speaker making not much sense as a piece of design. It just seems lazy to me, but I might be missing something.With a magnet giving Qts of 0.29 there's leeway for lowering the response or using a longer voice coil as this thing is still excursion limited. Although the set up (s118's with s112V's) sounds pretty good it does seem like someone has said "we'll give them a big speaker in a big box" rather than starting with a design spec.

Anyone got any idea why the Yamaha cabs for this speaker are so big? WinIsd comes up with 175l and shows a pretty good response with 100l. My other modeller gives 140-156l for classic alignments. The Speaker is marked Eminence Sigma and eminence have this data [url="http://eminence.com/proaudio_speaker_detail.asp?web_detail_link=SIGMAPRO18A-2&speaker_size=18&SUB_CAT_ID=1"]http://eminence.com/proaudio_speaker_detai...mp;SUB_CAT_ID=1[/url] . Winisd has slightly different data (Vas slightly smaller). Are Yamaha trying to squeeze deeper bass out of this with an oversized cab or are they fitting a different version of this speaker? It is a fairly old cab. If anyone has any information I'd be very grateful

[quote name='Bill Fitzmaurice' post='1051192' date='Dec 8 2010, 12:40 AM']The only factor purely attributable to cone size is dispersion. Everything else is based on driver specs. Well explained here: [url="http://www.eminence.com/resources/data.asp"]http://www.eminence.com/resources/data.asp[/url][/quote] This was a really useful link for those late to the debate and well worth a read if you are new to this. There's a table of the upper frequencies which can successfully be reproduced in the piston zone of a loudspeaker which interestingly shows even a 4" speaker can't really reproduce the upper hamonics of a bass without compromise. A good steer this. [quote name='Mr. Foxen' post='1056163' date='Dec 12 2010, 04:27 PM']Can one of the experts confirm/disprove this?: the effect of the design of the box generally (unles you get horn loaded and suchlike) mostly affects 200hz and below, the mids are affected to an extend by the lining of the box and how reflective it is, but most of the upper stuff is down to the speaker's own properties. Which is why guitar speakers have their own sound since that low stuff isn't very relevant, but a bass cabinet is down to the box design relating to the speakers.[/quote] Most of my design and development experience has been with hi-fi designs until recently. There are lots of ways (I won't even attempt to list them all) that a box affects the sound apart from the box volumes and tuning issues we deal with in Thiele/Small calculations. For example any sharp surface on the baffle will reflect/refract sound and this will be frequency dependant being affected by the size of the irregularity and the distance from the speaker. This is why high end hi-fi has the speakers set flush into the baffles. The biggest refractions are usually at the edges of the cabinets. Many cabs have the edges rounded to reduce this effect and speakers are often mounted off centre so that all this effect doesn't happen at a single frequency. Then there are panel resonances, as well as major resonances there may be minor harmonic resonances well above the 200Hz limit. Most bracing doesn't just reduce resonances but also raises their frequency. All of these things are quite audible in A/B testing because we are so sensitive to tiny differences to changes in sounds especially those we are familiar with, like human voices. How important they are in instrument speakers is harder to judge. We listen to these sounds in usually dreadful acoustic environments with lots of other sound sources and at sound levels where our hearing becomes restricted by our bodies attempts to protect our hearing. In addition electric guitars and basses are entirely artificial sound sources, there isn't a 'right' or 'wrong' sound. Even a 'good' sound is entirely subjective. There is no doubt that the traditional square fronted 4x10 or 4x12 is all wrong for several reasons as far as fidelity is concerned and that the dispersal of higher frequencies is a total pain for the front of house engineer but if you like the sound then you have to work with this. I think the answer to your question is that it is mainly right. The cab design is fundamental to the reproduction of low frequencies but above the 200Hz limit it is the character of the speaker which will determine most of the sound if you are dealing with a single drive unit. Multiple drive units will affect each other as described above. I'm assuming we are not talking about horn cabs here.

The deltalite 2515 will give you a small bass lift, just noticeable and it has a small midrange peak centred around 2K. This peak is fairly broad and flat suggesting the breakup modes are well controlled. F3 is fairly high at 93Hz but you will still get 95 dB at 40Hz so I think you'll be happy with the bass. It has very similar characteristics to the Celestion and i think they would probably sound very alike, the only minuses are price £92 and it has an aluminium voice coil. It's a personal thing probably but I have had a couple of failures with Eminence and it has always been the aluminium coils corroding at the junction with the lead out wires. Always with quite old speakers though (10 Years)

Liking the Delta 10's is interesting, they have the pronounced midrange hump that is common to a lot of eminence speakers so I'd cross off the Fanes, they'll sound too polite for you. I wasn't thinking you'd do major surgery to the cab. If you want a 10 in the cab you'll have to make a new baffle ( the board the speaker fits on to). If you want to keep the original look or might want to go back to original then you could always cut a panel and screw it onto the back of the existing panel, then it could be easily removed if these ever become collectors items. You might like the sound of the Delta 15. The Pro would be similar to the sound of the 10's but louder than a single 10 and with noticeable extra bass in this cab, which is a bit big for a single delta10. I think the Delta15 might be a sound you'd love. If you can afford it the Celestion Neo looks made for your cab and is designed to be 'fast' sounding. It would be my choice. Do you want me to model the Eminence Neo 15's? It might be worth pm's to Stevie (another from this end of the country) and LawrenceH to get their suggestions, they both know at least as much as I do, probably more.

[quote name='Christophano' post='1054081' date='Dec 10 2010, 02:34 PM']Right then, the Multimeter is saying 7.1 when I touch the speaker connections. (The amp is now in bits so the speaker isnt attached to anything)... So i'm assuming it's an 8ohm speaker as I've read that most 8ohm speakers measure at about 7ohms? Measurements for the cab are 23 inches high, 22 inches wide and 8.5 inches deep. Take 5 inches off of the height for the amp gubbins that should be inside the cab, as I've have taken them out.[/quote] OK the speaker is probably a bit over 8 ohms but not by enough to worry the amp. So we'll go for an 8ohm speaker. The cab will have an internal volume of about 45litres, a bit small for a 15. Its probably got a huge bass hump and doesn't go too low with the fitted speaker. Speakers that would work in your cab might be Fane 15-500 £68 small bass hump, f3 74hz 112db output Fane 15-400 £54 nearly flat 115dB f3 91Hz Celestion BN 300S (neo so light weight) £75 Small bass hump f3 92 Eminence Delta 15pro £74.96 3dB bass hump, pronounced midrange hump f3 73 Hz Interesting and possibly not unlike the original as new, though I'm guessing here. Eminence Delta 15A loud with huge midrange and bass hump, wild and wooly Up to 120dB f3 73Hz. I'd go for the fane 15-400 for a cheap uncoloured sound or the Celestion Neo. Both would match a drummer but might need a little help from the PA in a medium sized venue. The Delta might be enough on its own for small and medium gigs. There's other alternatives especially if you want to pay more. Prices are from Blue Aran. Blue Aran you owe me. [quote name='Slipperydick' post='1054109' date='Dec 10 2010, 02:48 PM']Absolutely right, and a thoroughly nice bloke too. Helped me out a few times. Not sure if he's still getting the phone himself, must be knocing on by now. Website makes an interesting read, Hyde park with about 1500W for PA..wouldnt touch the sides now would it ?[/quote] When I was doing PA in the olden times the WEM PA anp was the most desirable thing going, 100W of pure transistor power and made for PA with a flat response instead of a borrowed guitar amp. Pink Floyd were so proud of theirs they put them on the album sleeve. Google Ummagumma

It's been a while since I worked on valve amps (30 years!) but the theory hasn't changed too much. If you run a mismatched speaker then this is less serious than running into open circuit for the reasons explained above. I don't think for example you would have any major problems running an 8ohm speaker off a six ohm tap in the output transformer. You might find that the output transformer has other unused taps. Some manufacturers in those days used standard, off the shelf OT's but most towns had people winding transformers so there were lots of custom built OT's as well. Whether these OT taps are identifiable or not if they do exist is another matter. It may be worth putting up another post here with 'valves' in the title. This post is probably only attracting the attention of speaker buffs rather than the valve experts, which I am not. What you do next is up to you. I'd measure the speaker to determine its DC resistance which should give an indication of its impedance. I'd also contact Watkins to see if they have any info or advice. I'd probably then just replace it with another speaker of the nearest impedance and not worry unless it starts eating valves. I don't think this will be a problem though, in the days when I used only valve amps I did from time to time run small mismatches with no real problems other than a slight loss of power. Axe Music in Axminster, quite near you, have a valve tech I think and are very helpful. If you get really stuck I could take a look as I am not too far away either. Meanwhile, have you measured the inside of the cab so we can start looking for a replacement speaker?

There are technical differences between 10" and 12" speakers but the overall sound of a speaker is the combination of many factors so there is no such thing as a 10" or 12" sound. Technical knowledge is, for me, fun and it might help you to home in on certain choices but to choose your perfect speaker you need only to use your ears. Bigger speakers move more air for the same excursion movement. They can potentially be louder than smaller speakers but lots of other factors also affect this; like coil geometry and magnet size. Big cones tend to be heavier so they tend to resonate at lower frequencies but this depends upon the stiffness of the suspension and how thick the designer has made the cone. Lighter cones can be made to track the music signal more accurately but again many other factors can affect this. All speakers start to have an irregular dispersion pattern and frequency response once they are producing sounds whose wavelengths are shorter than the cone diameter so high frequencies cannot be produced well by big speakers even if you lighten the cone. However speaker cones flex and most designs exploit this to produce sound well above the piston zone. There are so many variables for designers to play with that it is impossible to generalise on the basis of size alone. It's not true to say size doesn't matter but you could also say 'it's not the meat it's the motion'. Trust your ears

Just in case some of the posts have confused you I'll repeat the ohms thing. The impedance of a speaker is nominal, an approximation because the reality is that the impedance varies with frequency. It is made up of the DC resistance of the coil plus an extra bit of resistance due to the inductance of the coil which varies with frequency. If you want to go on Eminence's or Fane's sites and look up the specs of the speakers they both give a chart showing how the impedance varies with frequency and they give the DC resistance of the coils. The impedance of the speaker therefore is always higher than the DC resistance and multiplying the DC resistance by 1.3 is as good a rule of thumb as any. Since the impedance varies with frequency you can be happy that most amps will work fairly well and with no risk to the amp with a slight mis-match. You might not get every last watt out though. If the amp is looking for a 12ohm speaker (no longer available) then an 8 or 16 would both be acceptable. Give us the dimensions of the cab and how much you might want to spend and we can make some suggestions.

[quote name='Christophano' post='1049048' date='Dec 6 2010, 09:48 AM']Thanks for that info, Phil. I'm very green to this, but would like to learn as I find it all very interesting. I would like to enhance the Dominator as much as possible really without ruining it, full of beef, with a hint of chardonnay. I've been putting together a shopping list on tubeampdoctor.com New matched valves, pots and caps. Anything else you can suggest that I should look in to changing/upgrading?[/quote] If you are doing major surgery you might want to replace some of the old carbon resistors though make sure you get ones that can handle the wattage.

If you'd put the magic word 'Valve' in the title you'd have been swamped with answers. I love the sound of valve amps but wouldn't take on the running costs. The Orange amp sounds lovely to me whenever I hear it. It sounds like you need to budget for some good earplugs though as well as an amp.

Just so you are clear resistance and impedance are not the same but the impedance is always a little above the DC resistance depending upon the exact form of the voice coil. In practice an 8 ohm speaker usually measures around 6.3 ohms and a 4 ohm speaker will be half this. It will probably be 8 ohms. The Fane speakers of those days had great efficiency but like many speakers of that era high power melted the glue in the voice coil and distorted the former so they tended not to be reliable long term. If Watkins can't help then tell us what you want to achieve and the internal volume of the cabinet and we can suggest a replacement. Are you looking for the best sound possible or to restore the original sound?

[quote name='Bill Fitzmaurice' post='1043840' date='Dec 1 2010, 02:33 PM']That's the conventional wisdom, but it's not true. For every driver where that scenario does apply you'll find six where it doesn't. IME the only drawback to a vented box in general is the potential for driver over-excursion below the intended passband, and that's cured with a couple of capacitors in the signal chain to limit the LF bandwidth of the amp. [i]"would that be where sfx's Thumpinator would come in handy?"[/i] Or that. Not mentioned yet is that, while a sealed cab naturally controls below bandwidth excursion, it does nothing to relieve the amp of the load that amplifying below bandwidth content creates. Even with a sealed cab the sound will be cleaner and the amp will have more headroom when below bandwidth content is filtered. The main obstacle is the lack of suitable drivers.[/quote] I'm sorry to disagree with you but this is a bit silly. The differences between transient responses of different boxes (second order Bessel, second order Butterworth assorted Chebychev, QB3, BB4 etc) are all described perfectly adequately in the mathematical models and born out by measurement. Have a look in Dickason or a look at Gunther J Krauss, AES Mar1990. "Low frequency Transient Response Problems in Vented boxes". This isn't really a matter of opinion but of measurement. OK the worst sealed cab with a tiny magnet in a small box might have worse transient behaviour than a well designed QB3 but 6:1 in favour of ported cabs? The [u]only[/u] drawback? You've already said yourself about the noises associated with the ports but the real problem is that of ensuring correct alignment. Vas, fs and Qts are subject to manufacturing spreads QL is usually an assumed figure and there are problems with the pressure changes around the ends of ported tubes that lead to us using approximations in Thiele/Small calculations. As well as the transient, noise and tuning problems there are numerous other issues confronting the designer of a reflex system. All speaker design is a compromise as I am sure you know. I'm sorry if that comes across as a tetchy rant, but I am really interested in your ideas. Your 'Jack' for example uses a horn to boost efficiency (and transient response), but as you know it cuts off well above the bottom octaves. You reinforce this with a reflex port but this is going to be a lot less efficient than your horn in its pass band. You also advise using floors and walls to reinforce the bass but still your design depends upon the way we perceive sound. I'm sure your design sounds good with bass guitar because upper bass and lower mids are handled well and deep bass is less important and yet you don't allow the same leeway to sealed cabs. High efficiency has advantages. Flat frequency responses aren't a guarantee of good sound especially when talking about instrument cabs. Most of my designs are reflex designs for what I hope are good reasons. Ported, sealed and horn cabs have advantages and disadvantages which are all well known and I am hoping that you can add to the debate with your experience of how these theoretical problems work out in practical situations.

[quote name='4 Strings' post='1044469' date='Dec 1 2010, 11:07 PM']The Thumpinator sounds great but for that price I could buy a pretty good speaker. Is there a cheaper way to hit the rumble? If I wanted to put a cap in line I could solder something to the crossover board. Any ideas on values etc? Also, would it be in parallel across the speaker?[/quote] It is not sensible to try to put a filter in between the speaker and the amp, it needs to go earlier in the signal chain, either the effects loop or between the guitar and amp. It's not absolutely clear if this is a problem though, it is just one possibility, your amp may already be filtering out subsonics. Most do to some extent. If you turn down the bass control a little it will remove some of the subsonics, which is why I suggested it earlier. It will also change what you hear so you need to experiment to get the best out of this. If you have a graphic rather than conventional tone controls then just use the lowest one and the results should be fairly good. Lots of subsonics gone but not too much signal. Take all our techie squabbling with a pinch of salt. If it sounds good then it is good.

[quote name='Bill Fitzmaurice' post='1043214' date='Dec 1 2010, 12:51 AM']The downside of a vented cab is that excursion rises below the tuning frequency, and below bandwidth string thump noise can be a major problem. That's usually compensated for by a high pass filter in the amp, most have them, but not all. This thread explains: [url="http://www.talkbass.com/forum/showthread.php?t=714170"]http://www.talkbass.com/forum/showthread.php?t=714170[/url] With sealed cabs excursion decreases as frequency decreases, so high passing is seldom required. But sensitivity and therefore output also decreases, so it's not the best route to eliminating below bandwidth noise and driver over-excursion.[/quote] Hi Bill, as usual I agree with pretty much all that you say. The one word that I question is 'best' I'm not sure that there is a single engineering solution to the problems of amplifying bass guitar. We all know how to model the behaviour of cone speakers and the advantages and disadvantages of sealed versus ported are clear. Ported enclosures give an extra 3db at resonance and almost that around the bottom octave. Porting doesn't raise the resonant frequency in the same way as a sealed box. Below this the Ported cab cuts off at 18-24dB/octave depending upon the exact alignment and the sealed cab at 12dB/octave depending upon Q. All this is reflected in Stevie's graphs. I'll freely admit I'm trying to pick your brain here. Clearly sealed cabs offer better transient response and subsonic behaviour and, with a given driver, smaller size. The ports create problems of wind noise and manufacturing spreads in drive units mean that unless each driver is tested individually the tuning is a bit hit and miss. Despite all this most current bass speakers are ported designs. Add in the psycho-acoustics. We can't hear the bottom octave at all well and our brains construct what we hear from a partial pattern of information giving rise to auditory illusions similar to optical illusions. Then add in the effect of floors walls and ceilings and the rest of room acoustics and my question is how audible are these things in practice. Your own designs exploit all this of course, so why shouldn't another designer exploit the same things in developing a sealed design?

Sadly I find this interesting. Good result. If you get overwhelmed and your guitards are unable to find the volume controls try cutting the bass a bit before you turn up. Good luck

It could be so many things that it is going to be pretty nigh on impossible to diagnose over the net. Buy a can of freezer spray and systematically work along the signal chain. When you suddenly freeze the faulty component the fault will change and you have a culprit. There may be more than one. If it is a leaky cap then check any associated pot for pitting as it may have let in an unwanted DC voltage across the pot.

[quote name='Bill Fitzmaurice' post='1036418' date='Nov 25 2010, 02:46 PM']Loaded in 50L tuned to 50Hz excursion is at a minimum at 50Hz, and with 200w input only exceeds xmax below 43 Hz, so save for extreme drop tuning excursion is no concern. However, where excursion is at a minimum port output is at a maximum, seen in a port velocity chart, and that's what attention must be paid to where chuffing is concerned. All true from the standpoint of what you're hearing on stage, where more often than not boundary effects severely limit audibility below 60 Hz or so. Combined with the masking effects of the other instruments you can eliminate much, if not all, content below 60Hz and not notice the difference when the band's playing. But in the audience the situation can be very different. You can be totally unaware of high output in the lows where you're standing, whilst 40 feet away patrons are contending with drinks falling off their tables. It's the 40 to 60Hz bandwidth that large PAs pound out with authority that can define good concert sound, or for that matter ruin it when there's a ham-fisted idiot at the FOH console.[/quote] I've found that spurious sounds from sources other than the strings (such as banging the guitar) can creep into the signal chain and cause some alarming excursions with some set ups. Obviously I've no idea whether this is a factor or not in this case, its just a possibility. In any case this speaker is in an undersized poorly aligned cab so the situation will be worse. I absolutely agree with you about the PA but this speaker is for use in a practice room where I think the long slower tail off of the sealed cab could work well, especially since the sound is described as a bit boomy. [quote name='4 Strings' post='1036626' date='Nov 25 2010, 05:18 PM']Ok, first thing will be to put the tweeter back in and seal it for rehearsal next Monday and see what the difference is. I must admit it was a bit boomy, I rolled the bass back a bit. I'll give it a try for exhaustive comparison. But, I have played with some big, bassy cabs, I have the celebrated Monster even now, and the sound is affected throughout the fret board. Even playing up high on the 'G' sounds different with a big bottom end attached, it is fuller and, I think, more powerful. Its wrong to say that because I have a 4 string I don't need anything below the sine wave frequency of bottom 'E'. The strings give out frequencies across a wide band including rumbly lows and piercing highs (depending on your eq, string type etc) even if the majority of volume comes from the expected range. If I'm not happy with the sealed cab because the sound is not deep enough, then its butchery time![/quote] Good call, the physics of sound is pretty well worked out but the way we perceive it is complex and the language we have for describing it is inadequate so in the end the test that matters is how it sounds. Let us know how it works out. Cheers

[quote name='stevie' post='1035391' date='Nov 24 2010, 06:12 PM']You're not all that far from me, Phil. Sounds like an idea. I'd be very interested to hear what you've concocted. You can buy me a pint whilst we're at it [/quote] I'll pm you then, beer not a problem, bring a bass.

Stevie's graphs show just what you'd expect with the sealed box rolling off earlier and giving more power low down, below bottom E unfortunately. 5 stringers should be interested. For me the middle graph is significant. It shows extreme excursion below 50Hz at high power which I think may be part of the problem. Certainly this will be well beyond the excursion limit of the speaker if these frequencies get set off by room resonances/feedback. I also question the extent to which you will hear the differences at these frequencies. I've been experimenting with just this at the moment with a low Q driver in an optimum box a high Q driver in a smaller than optimum box and running A/B comparisons with and without ports. Playing recorded music through them you get to hear all the things you'd expect. Earlier roll off and slightly reduced but cleaner bass from the sealed cab and warm woolly bass from the undersized cab, but you have to choose the source carefully to hear this. With bass guitar I can hear a difference but my guitarist can't and with the full band playing I'd be dishonest to say it makes a whole lot of difference. We just aren't very good at hearing deep bass and if you can't hear it it doesn't matter. The other factor is the room acoustics, if the room is much less than 10 metres in it's longest dimension then it won't be possible to propagate sound at the frequencies we are worrying about and if you are trying to record deep bass is just going to be a nuisance for any mics you use. I think we all agree though. You've got a nice speaker which would work better in a bigger box, your port is too small and incorrectly tuned and you need to move the ports to get a bigger one in. You could simply try blocking the ports and will get the result shown in Stevie's graph which may give you a sound you'd like, or not.

You've been getting good advice so I'm not contradicting it, just suggesting an alternative approach. If the problem is port chuffing. (I also think it could be lack of loading below the cabinet resonance which is currently too high, this will cause the speaker cone to flap around like a plastic bag in the wind at the frequencies below the cabinet resonance) then get rid of the ports and make it a sealed cab. Since Thiele/Small and computer modelling made the design of ported cabs so easy we have forgotten the alternatives (OK BFM hasn't forgotten the hybrid/horn) Sealed cabs have better power handling and much better transient response than reflex cabs. With no ports there is no chuffing and no tuning problems. For a given speaker the cab will be smaller. The trade off is that the ported cab gives an extra 3dB of bass around the resonant frequency and the f3 roll off point will be raised in a sealed cab. Having said that there is often more deep bass from a sealed cab ie deeper but not so loud. You can try temporarily sealing the cab by blocking the ports with a bit of wood screwed on with a bit of mastic or a bit of draft proofing foam as a seal. If you like the sound hey presto! If not then just take it off. I haven't done the maths so I can't tell you what the Q would be for cab/speaker combination or how it might sound but it might be worth a try as it is so little effort. I've got some Beyma SM212's, lovely sound with bass but need a bigish cab for 12's.

Thanks Stevie. Before we make any recommendations a quick caution. Speakers and cabs form a tuned unit with the cabs optimised to match the speakers. This is quite important with sealed cabs and essential with bass reflex/ported cabs. Fortunately different speakers can be similar in their specs. and you can bodge together a good speaker system but not every speaker will match every cab. We'd need to know the internal volume of your cab and the size of any holes or ports. You may have to change the ports which is easy if they are tubes. Fane's are good value in the UK at the moment. I think what Stevie has said about Eminence is fair, there are some good ones there, but their design decisions are a bit haphazard at times. Celestion Truvox speakers are general purpose/PA speakers and they make a range of qualities in the range so don't dismiss them completely, you could upgrade by buying one higher in the range. Celestion Green and Orange speakers are clearly designed to be 'characterful' and 'musical' as are some of the Eminences. The rest are fairly neutral designs. Once you go beyond these manufacturers the prices go through the roof though there are some lovely speakers out there. Character speakers would be great for a practice studio but for recording you might want to have something more neutral and well controlled and use EQ to get the sound you want. If you get back with the dimensions of your cabs and the ports, if any, and tell us what sound you want and how much you want to spend we can start making suggestions. If you want some reading try this [url="http://www.ultimate-guitar.com/columns/gear_maintenance/choosing_speakers_to_drive_your_cabs.html"]http://www.ultimate-guitar.com/columns/gea..._your_cabs.html[/url] I apologise for the techie nature of the article though, I am such a nerd. Stevie, if you ever fancy a trip this way I'd love a second opinion on my cabs.