Bill Fitzmaurice

[quote name='Stylon Pilson' timestamp='1429274337' post='2749920'] If this was a Hollywood movie, the plucky bootsy666 would build his bass cab anyway. There'd be a montage scene with lots of screwing and glueing and tolexing. And then there'd be a final climactic scene where his bass cab would face-off with one of Bill's, and blow it out of the water, and Bill would admit defeat and pass the mantle to the spunky young underdog. [/quote]This scene would be more apropos, and I'm not the one with the sword: https://www.youtube.com/watch?v=anEuw8F8cpE

[quote name='bootsy666' timestamp='1429266251' post='2749786'] If there were two sets of four speakers in this cab, both same impendance and watts, but different frequencies. Four of the the same in the centre four holes, and the other four in the top two and bottom two, with a horizontal baffle inside dividing the eight speakers into two sets of four, would it sound better? [/quote]Please don't take offense, but posing questions like this one point out why you should not be trying to design your own speaker. One must learn to crawl before learning to walk, and where the science of acoustical engineering is concerned you're still in the pram. Whatever time and money you have invested in this project should be chalked up as a loss, the cost of a learning experience. Go back to square one and read, read, read. The sources are out there.

[quote name='bootsy666' timestamp='1429121886' post='2748301'] Celestion have told me that the tf1525 is for PA and electric bass. My other option is the 1530e? [/quote]You have literally dozens, if not hundreds, of options for drivers. But before you even think about designing your own speaker you have to start with the basics of understanding how speakers work and how they're properly designed. This resource is a good starting place: http://techtalk.parts-express.com/showthread.php?219617-The-Speaker-Building-Bible

To be brutally honest, nothing about that cab configuration is as it should be. It will put out a fair amount of low end, via sheer brute force with a sufficiently large amp, but the same low end output could be realized using two good fifteens in a properly engineered cab. The midrange dispersion will be horrid. My best advice to the OP is that if you haven't bought the TF1525 yet, don't. They're supremely unsuited to electric bass. Believe me, if I coud find any basis to lend encouragement here I would, but there is none.

[quote name='chrismuzz' timestamp='1429046239' post='2747434'] Apparently you can't if your amp has a valve power stage, but I don't know why [/quote]With SS if there's no speaker no current flows from the output devices, so no harm. With tubes current flows from the tubes to the output transformer primary windings whether there's a speaker or not. As current can't flow from the transformer secondary windings if there is no speaker bad things happen.

[quote name='leonardobass' timestamp='1428414103' post='2741039'] i can't really find any reviews for this brand on that particular use. [/quote]Reviews don't matter. T/S specs and measured response charts do. With those you can accurately predict results and cab compatability. Without them you have no way of knowing what you'll end up with. By the same token, when it comes to building a cab you can't just toss a driver into a box. No matter how good the driver is if the cab isn't properly matched to it, and if the cab isn't properly constructed, it won't work well.

[quote name='yondergo' timestamp='1428242799' post='2739481'] Thanks again Bill, that's made a big difference to the plan, I'm going to look at sealing the existing 4" baffle hole and porting the sides of the cab now, once I subtracted the volume of the ports and winISD recalculated the length of the ports I was almost butting up to the back of the cab. Should have done this work earlier, probably would have decided to buy a different cab and scrap the peavey enclosure. Oh well, we soldier on. [/quote]You can keep the ports behind the grill, just add 90 degree elbows to the ducts. The effective duct length is measured on the centerline.

[quote name='yondergo' timestamp='1428132343' post='2738273'] One other concern was how much clearance I would need inside the cab where the end of the port approaches the back of the cabinet, it's looking like i'll have probably an inch and a half between the port end and the foam damping, is there any negative effect to be expected from this? [/quote]You need approximately the port diameter distance to the back of the cab, otherwise the air mass between the cab back and port entrance can add to the air mass in the port, lowering the tuning.

[quote name='yondergo' timestamp='1428095685' post='2738133'] I was hoping to use 2 4" ports, would your point about 4" ports not being suitable apply to using multiple ports or is it 4" ports in general? [/quote]There's nothing wrong with 4" ports, but that's insufficient area to use with a 15" driver. Two would be OK.

Port velocity at 35Hz is moot with electric bass. You'll never put 450w at 35Hz into that cab. What happens between 50 and 60Hz is what's significant. That said, a 4'' round port is too small for a 15" long excursion driver. BTW, foam damping does not reduce the cab volume. If you're lining the cab with foam you can predict its influence in the Box window, using the advanced tab, changing the Qa value from the default 100, which is a bare box, to 50.

[quote name='ubit' timestamp='1427790603' post='2734159'] Why not raise it instead of tilting it? If it's tilted, the audience are going to be hearing the dull sound you encountered when you were outside its cone of pleasure. [/quote]Not necessarily, since the midrange and high frequency pattern is cone shaped. The picture below shows +/- 30 degree dispersion, which is about average in the upper mids from a bass cab. In the upper frame the cab flat on the floor puts the audience within the dispersion pattern, but not the player. In the lower frame with the cab tilted both the audience and player are within the dispersion pattern. The issue with lifting the cab is that if you lift a small cab high enough off the floor to hear the mids at close range you will lose boundary reinforcement in the midbass. That can be beneficial, if the room is boomy, as that will reduce the output in the boom frequencies. But in a dead room you may not want that reduction in the midbass. If you want to be ready for any contingency have the ability to either tilt or lift the cab to suit the room.

[quote name='bassmayhem' timestamp='1427654628' post='2732751'] Since the line array makes the sound spread more horisontal, you won't get that [i]rolling and tumbling low frequency rumble[/i] in the church, but a more focused sound that is easy to control.[/quote]The height of the Bose array makes it very limited in how well it works as a line array. It does not function the way the Bose marketing claims. As the bass modules are so small they don't function as line sources at all. Required reading: http://www.diy-audio.narod.ru/litr/nflawp.pdf

[quote name='ras52' timestamp='1427569249' post='2731874'] And do you lose any low end by not being in contact with the floor?[/quote]You would not, as being in contact with the floor has no effect on the low end anyway. You have to lift the cab a matter of a few feet to lose any boundary reinforcement, but that's caused by proximity, not contact.

[quote name='JTUK' timestamp='1426974363' post='2724408'] Dull.... ?? making a cab less dull by pointing it at your ears on tilt isn't going to remedy a dull sound going out to the audience [/quote]He did just as he should have, as with the cab on the floor aiming straight out the audience is within the cone shaped midrange and high frequency dispersion pattern, while he is not. Tilting it back both he and the audience will be within said cone.

[quote name='51m0n' timestamp='1426759768' post='2721563'] Yes but even then the mic and position can really affect how you hear all of them [/quote]+1. If one wanted to one could measure the same cab with the mic in three positions, get three different results, then pose the same poll question and see how many saw through the ruse.

A test of this sort will only tell you how the speakers you're listening to it on sound. If that's a full sized stereo system with flat response from 30-15kHz you might glean some benefit, but even then the gear used to make the recording is just as significant as the source. If it's a typical computer speaker the test is meaningless. Even listened to on a good system the test is of dubious value, as the main difference between how different drivers sound will be heard off-axis. A meaningful test would be done with the mic placed 45 degrees off-axis.

Read this. It cites PA subs, but with bass cabs the same physics apply. http://www.prosoundweb.com/article/in_search_of_the_power_alley/

[quote name='MOSCOWBASS' timestamp='1424943047' post='2702106'] I always keep my Barefaced Midget on the floor or somewhere you get boundary reinforcement. Experience of lifting up higher results in quite a lot of low end loss. [/quote]In order to lose acoustic coupling with the floor the cab must be lifted at least 1/4 wavelength. 1/4 wavelength at 100Hz is 2.8 feet, at 80Hz is 3.5 feet, so in most cases there is no meaningful loss of coupling. What's perceived as a loss of lows is actually hearing the mids and highs that you can't hear when the cab is on the floor.

Front port goes lower, because it's larger. The rear port has them on the back because there's no room for them on the front.

[quote name='krispn' timestamp='1424101852' post='2692603'] Any thoughts? [/quote]Don't. The main issue isn't the driver or amp, it's the size of the enclosure. Google 'Hoffman's Iron Law'. If you did this the additional output would be modest at best.

[quote name='Animalbeats' timestamp='1423874523' post='2690086'] I've come across a page of WEM vintage columns with 10" drivers. I'm hoping to pair them with Selmer treble and bass. Do you think they'll be suitable for bass speakers? [/quote]Back in that era they would have used generic musical instrument drivers, good for guitar but not for bass. Using enough of them they would be tolerable, just as the original '69 SVT was tolerable. But they had to use two 8x10s to handle the 300w head. BTW, I saw [i]Ten Years After[/i] the summer before last, but without Alvin Lee it wasn't the same band I saw back in 1969 at a farm in upstate New York by any means.

There's far more to a bass cab than just using drivers intended for bass guitar. For one thing done correctly a bass cab will have roughly twice the internal volume of a guitar cab using the same size drivers. IMO don't throw away good money after bad, use it as is, when you're able to afford it get a proper bass cab.

The result is as unpredictable as mixing drinks. It might be OK, like gin and tonic. It might be disastrous, like Bailey's and lime juice.

[quote name='alexclaber' timestamp='1423345789' post='2683826']even the drummer! [/quote]Now you're stretching the bounds of incredulilty.

[quote name='Mykesbass' timestamp='1423212539' post='2682177'] Hi Bill, If I can borrow this thread for a moment, if you are using good quality leads does the length make any difference - just thinking the lower cab will need a long lead, whereas if you daisy chain you can use two shorter leads? [/quote]Assuming you're not using seriously undergauge cables you're not going to have an issue with the six feet or less for a bass rig. It's with the long leads to PA speakers that you have to be wary.