Bi-amping

[alexclaber]

I'm currently in the midst of a personal biamping debate. Do I use an active crossover (24dB @ ~1kHz) and get 550W into one 15" (or 900W into two) on the lows and 300W into the mid/high horn on the highs, or do I build a passive crossover and then bridge my amp for 2000W shared between single 15" and mid/high horn (or 3000W into two 15"s and mid/high horn)?

Hmmm...

I would not recommend biamping with standard bass cabs, they simply aren't designed right for it. Fullrange on one cab and lows only on another could work well though.

Alex

[Bill Fitzmaurice]

[quote name='MoJ' post='12657' date='Jun 5 2007, 02:58 PM']If its any help Bill, I play 4 string tuned down to low B so I was swinging toward the omni 15 for its lf (correct abbreviation?) and I know that that has internal 3 way crossover in it for the differing speakers. Would a Titan and Omni 10 bi-amped be feasible?[/quote]
The O15 can easily be bi-amped, and doing so eliminates a lot of costly and from what I understand hard to find in the UK crossover components. T39 and O10 can go either way as well, and again, bi-amping would save a lot on the crossover parts. I'd only go with an O10.5 with a T39, two tens aren't necessary.

[MoJ]

[quote name='warwickhunt' post='12702' date='Jun 5 2007, 09:47 PM']I'd certainly try before you buy with regard to bi-amping as I've tried it numerous times over the years and I've 'never' been satisfied with the results.

Tried it with the stand alone heads (GK 800rb) to preamps and separate power, with a variety of cabs (2x10 & 1x15 to 4x10 & 2x15 and all combinations in between), none ever did it for me as they all lacked something in the range that the crossover was set.

I believe that Bill, Alex and various knowledgeable bodies were able to explain why this was but the upshot was still that I disliked the sound of bi-amping with typical bass cabs. That isn't to say that specifically designed cabs wouldn't do a better job but if it were me I'd want to give it a try before I built or bought cabs. If the intention is to use this rig on a large stage with a quality PA you do have to ask yourself what's the point? The PA will be doing all the bi/tri-amping you require. If we are talking pub/club gig... will you or the audience get the true benefit?

Simply an opinion and observation![/quote]

And a valid observation it is!
Well, Im reading through the Pod XT Pro manual that BOD2 was kind enough to email me and its got me GASing for it, if only for what it does, but I need to sleep on that (not that Im rushing into buying) as there are few things it doesnt make clear.
However, should it be the case that I dont like bi-amping, it still leaves me the ability of a full range putput without extra gear going to waste. Then again I may just not like the XT Pro altogether!
The only point in large gigs that I can see is this; the monitors Ive played through (or at least the sound guy operating them) never seem to have enough of me in them and have to rely on my rig for monitoring or they have too much and even then,no bottom end to the sound, still leaving me to rely on my rig behind me. Who knows whats goiing on in the FOH mix! By having a sound Im happy with on stage, in theory the sound guy would here my bi-amped sound during soundcheck and try to replicate that.
In theory.
And of course, I could be being naive here!

[quote name='alexclaber' post='12716' date='Jun 5 2007, 10:32 PM']I'm currently in the midst of a personal biamping debate. Do I use an active crossover (24dB @ ~1kHz) and get 550W into one 15" (or 900W into two) on the lows and 300W into the mid/high horn on the highs, or do I build a passive crossover and then bridge my amp for 2000W shared between single 15" and mid/high horn (or 3000W into two 15"s and mid/high horn)?

Hmmm...

I would not recommend biamping with standard bass cabs, they simply aren't designed right for it. Fullrange on one cab and lows only on another could work well though.

Alex[/quote]

Im wondering how to go about getting a low pass filtered sound and full range sound togeher though, without investing in the Aguilar preamp (and although the XT Pro has a model based on an Aguilar I doubt it imparts any of its features other than tone).
With an external active 2 way crossover, like an amp with its volume up but no speakers attatched, would I do damage to the crossover by taking say the low out and go to a power amp, and then the full range signal from a preamp to the same poweramp (assuming its dual channel obviously)? I guess in the same way, I could keep the volume of unused channel of the crossover at zero.
I would then of course need a stereo preamp. So,is there any other way of bypassing a the crossover to get the full range signal to a power amp?

[quote name='Bill Fitzmaurice' post='12723' date='Jun 5 2007, 10:40 PM']The O15 can easily be bi-amped, and doing so eliminates a lot of costly and from what I understand hard to find in the UK crossover components. T39 and O10 can go either way as well, and again, bi-amping would save a lot on the crossover parts. I'd only go with an O10.5 with a T39, two tens aren't necessary.[/quote]

Well,this at least tells me that its possible to do with your designs Bill.
On the O15, I would assume then that 2 speakon connectors would be put on the back of the cab, and thus connected to the different speakers internally? And the HF horn,would that be connected to the same speakon as the mid driver?
The O15 would certianly appear to be the easier build and also easier for transportation too if it can be externally crossed over. The band hasnt quite gotten round to employing roadies or a tour bus yet....
Oh, and in the case that I do veer toward a T39 and O10.5, are they he same impedance? I guess with a seperate power amp it wouldnt be of as greater importance having seperate controls for volume per channel. I know the O10.5 is 8ohm, but even if the T39 is 4ohm,that would possibley of use for low end frequencies anyway right?Due to the higher energy requirement for low bass frequencies. Again, merely questions to matters of which I have no real concept!

Hmm..so many questions..so many options....

I really do appreciate all your input and opinions guys. This is really food for thought!
I think Warwickhunt has given me the most to think about in that is it really going to be worth it for all that effort, but Im still liking this idea of full range/low frequency-amping and now the O15 possiblity.
Still, I will forge on and investigate all my options.
Thanks
Andy

Edited June 5, 2007 by MoJ

[BOD2]

[quote name='MoJ' post='12736' date='Jun 5 2007, 11:03 PM']Im wondering how to go about getting a low pass filtered sound and full range sound togeher though, without investing in the Aguilar preamp (and although the XT Pro has a model based on an Aguilar I doubt it imparts any of its features other than tone).[/quote]

I'm not trying to sell the XT pro here - it's quite a big step to go over to that for a live rig. But...if I'm interpreting the manual correctly you can setup the biamp on one pair of outputs while having the full range signal on another pair of outputs. As I mentionbed earlier in this thread, the manualsuggest that the baamped outputs are only available on the "Unbalanced Analog Out" jacks. The "Balanced Analog Out" XLRS always have the full range signal (or so it would appear). This should give you what you want, but I would recommend confirming this first.

And you'd still need to check that the XT Pro can produce the quality of sounds that you want.

[Bill Fitzmaurice]

[quote name='MoJ' post='12736' date='Jun 5 2007, 06:03 PM']Well,this at least tells me that its possible to do with your designs Bill.
On the O15, I would assume then that 2 speakon connectors would be put on the back of the cab, and thus connected to the different speakers internally? And the HF horn,would that be connected to the same speakon as the mid driver?[/quote]
The usual method employs a 4 pole speakon, with poles 1+ 1- for lows, 2+ 2- for highs, a single cable/jack. For electric bass a dynamic tweeter is often too sensitive, so an option is a pair of piezo tweets instead. This lowers driver cost considerably, and eliminates the need for any passive crossover at all in a bi-amp rig, as the mid and tweeters can be simply parallel wired.

[MoJ]

[quote name='BOD2' post='12743' date='Jun 5 2007, 11:14 PM']I'm not trying to sell the XT pro here - it's quite a big step to go over to that for a live rig. But...if I'm interpreting the manual correctly you can setup the biamp on one pair of outputs while having the full range signal on another pair of outputs. As I mentionbed earlier in this thread, the manualsuggest that the baamped outputs are only available on the "Unbalanced Analog Out" jacks. The "Balanced Analog Out" XLRS always have the full range signal (or so it would appear). This should give you what you want, but I would recommend confirming this first.

And you'd still need to check that the XT Pro can produce the quality of sounds that you want.[/quote]

Reading the manual so far it doesnt imply you cant do this. In fact, if you look at the beginning of the manual it has a signal flow diagram explaining points specifically. For the bi-amp feature it goes on to say
[quote]...the 1/4 inch outs are both sent a freqency-split version of the Model signal... The XLR outs take their signal just after the Dl/Mdl mix, before the frequency-split...[/quote]
so that would appear to be correct Alan.
The next thing to do would be to figure out which jack gives you the low frequency to take to the power amp.
So far as working out if the XT Pro is something Im happy with goes, as I mentioned earlier I have acces to the XT Live so would be able to make a judgment based on that.

[quote name='Bill Fitzmaurice' post='12748' date='Jun 5 2007, 11:23 PM']The usual method employs a 4 pole speakon, with poles 1+ 1- for lows, 2+ 2- for highs, a single cable/jack. For electric bass a dynamic tweeter is often too sensitive, so an option is a pair of piezo tweets instead. This lowers driver cost considerably, and eliminates the need for any passive crossover at all in a bi-amp rig, as the mid and tweeters can be simply parallel wired.[/quote]

So thats good news all round then Bill. A cheaper way to buil the cab and still get the bi-amped features of it. Eliminating the internal crossover would also mean a greater flexiblilty in what frequencies to choose via an external one too.
So Im guessing Bill, that with your designs (if only the O15), bi-amping (of sorts) is something you feel is a viable option for bass guitar?
Although I greatly appreciate all the views expressed so far I also understand that this is your area of expertise and also that you are top of your field too.
Having said that though, its all down to individual prefences, needs and opinions I guess.
Thanks
Andy

[Bill Fitzmaurice]

[quote name='MoJ' post='12780' date='Jun 5 2007, 07:18 PM']So Im guessing Bill, that with your designs (if only the O15), bi-amping (of sorts) is something you feel is a viable option for bass guitar?
Andy[/quote]
Definetely. I don't make a big deal about it because bi-amping bass heads are so rare, but nearly all of my designs are bi-amp friendly.

[MoJ]

[quote name='Bill Fitzmaurice' post='12804' date='Jun 6 2007, 02:46 AM']Definetely. I don't make a big deal about it because bi-amping bass heads are so rare, but nearly all of my designs are bi-amp friendly.[/quote]

Good to know Bill. Of course buying seperates opens the options up some what.
Does the O15 give a pretty natural sound bi-amped, if its all in one cab and with 3 drivers? What type of crossover would you suggest if using an external active one? All I remember is 1st, 2nd, 3rd and 4th order so the name wouldnt be of much use right now and it maybe a case that the majority of crossovers are 4th order to get the most efficiency.
Just that people talk about not getting a good sound out of bi-amping and am wondering if this maybe down to the point of crossover and its cut-off rate i.e. 24 dB per octave being too steep or 12 dB allowing too much of the other frequencies through.
Thinking about about it, having a dual channel power amp would also allow greater fine tuning of an O15 rather than having an internal passive crossover.
All seems like a very good route indeed.
Just, again, thought Id ask. Its most likely these are just things I need to experience myself.
Andy

Edited June 6, 2007 by MoJ

[Kiwi]

[quote name='Jack' post='12715' date='Jun 5 2007, 10:29 PM']The GK heads have an inbuilt 'boost' circuit that adds quite a bit of growl and dirt, this is located AFTER the crossover on only the woofer amp. The result is overdriven speakers and a pristine clean tweeter.

In other words, it was designed specifically to combat what you mentioned: drive sounding harsh on tweeters.

Of course, you can only use the inbuilt boost, which you may or may not like. The effects loop is full range.[/quote]

I first tried a GK RB400 combo at a gig and it was pretty much love at first listen. There was an integrity to the sound that I hadn't heard in any other amps I'd played up until that point. I can't hear any missing frequency bands either. When I added a 2x10" it just got growlier. I could really hear the upper mids of my Smith basses - particularly the thup of my fingers leaving the string.

To some the amps may sound fairly aggressive but as I've said in the for sale ad for a GK RB700, I have to decide what to take away from the sound with these amps, not get frustrated at what is missing. If I want to soften the sound up I can use the contour control to dip the mids. I can also actively control the [i]volume[/i] of the tweeter and the woofer independently.

I'm not going to comment on how effective the biamping system is in terms of efficiency, but I don't find myself wanting for volume, clarity, quality or warmth. I don't like the look or the marketing of the amps but after 6 months of using them in a variety of gigs, I still feel my money's been well spent.

[The Funk]

A lot of very helpful comments.

Having seperate volume controls for each cab is great when they have different frequency ranges. Bi-amping at its simplest.

Did you say you have a Pod and a crossover? If you don't bother with the built-in bi-amping function and just send
- the Left Out to Channel 1 of your power amp full range and then
- the Right Out to your crossover and then send just the lows to Channel 2 of your power amp, and then Channel 2 to the bassier cab,
you should have basically the same kind of set up as me.

Edit: I have a GK400RB as a back-up. Lovely little head.

Edited June 6, 2007 by The Funk

[MoJ]

[quote name='Crazykiwi' post='12881' date='Jun 6 2007, 09:54 AM']I first tried a GK RB400 combo at a gig and it was pretty much love at first listen. There was an integrity to the sound that I hadn't heard in any other amps I'd played up until that point. I can't hear any missing frequency bands either. When I added a 2x10" it just got growlier. I could really hear the upper mids of my Smith basses - particularly the thup of my fingers leaving the string.

To some the amps may sound fairly aggressive but as I've said in the for sale ad for a GK RB700, I have to decide what to take away from the sound with these amps, not get frustrated at what is missing. If I want to soften the sound up I can use the contour control to dip the mids. I can also actively control the [i]volume[/i] of the tweeter and the woofer independently.

I'm not going to comment on how effective the biamping system is in terms of efficiency, but I don't find myself wanting for volume, clarity, quality or warmth. I don't like the look or the marketing of the amps but after 6 months of using them in a variety of gigs, I still feel my money's been well spent.[/quote]

Well, I do like an agressive tone. I tend to 'thwack' the strings on my Ric so as I get that upper mid aggressivness. Trouble is, to get the amount of bass and lower mids Id like it seems to over power the upper mids and all that work is pretty much for nothing. I could be clutching at straws with thei bi-amping lark but it sounds on paper like it would work and would be for me.
Of course, the Ric has stereo outs which allows for bi-amping in a way, but that then requires two pre amps as well, and isnt really a line that Id like to go down. However, I do like the idea of being able to apply say overdrive to the treble pickup but with all Rics since the 80's (except for those being made since last year) having the .0047 cap taken out there's plenty enough bass in that signal already, and its only a mild fascination.
If GK heads lend themselves to an agrresive sound then they may be worth looking at, although I do find my favourite part of my tone that I boost a little is below th 5 kHz crossover that GK set, mine being around 1 and 2 kHz. I would assume though that you would need to have GK cabs (or at least someone's expensive bi-amp cabs) to facilitate this?

[quote name='The Funk' post='12888' date='Jun 6 2007, 10:05 AM']A lot of very helpful comments.

Having seperate volume controls for each cab is great when they have different frequency ranges. Bi-amping at its simplest.

Did you say you have a Pod and a crossover? If you don't bother with the built-in bi-amping function and just send
- the Left Out to Channel 1 of your power amp full range and then
- the Right Out to your crossover and then send just the lows to Channel 2 of your power amp, and then Channel 2 to the bassier cab,
you should have basically the same kind of set up as me.[/quote]

Indeed The Funk, a LOT of helpful comments. But thats why we like Basschat and all its former guises
At the moment, no, I dont have any of the components as of yet, but yes I think that having a seperate crossover sounds like it allows for this kind of set-up much more easily, reagardless of preamp. Though Id still need to find a way of getting two signals out of one preamp if I werent to get an XT Pro.
Im definitley considering this as in theory there would be no loss of a partcular area of frequencies but would enable me to have more control over the bottom region of my sound.

I enquired with Dave Hall recently about tube power amps and he said that to make one powerful enough for bass he would have to do it stereo. How good would this be????
Thanks
Andy

Edited June 6, 2007 by MoJ

[The Funk]

Stereo's great. It just basically gives you two sets of controls, inputs and outputs - perfect for bi-amping. I don't really see how bi-amping would be possible without a stereo power amp.

What equipment do you have at the moment? If you could adapt bits of your rig to a new bi-amped rig with a minimum of expenditure, that's always a good thing.

[obbm]

Lets get the terminology right.

Stereo is Left/Right

Bi-Amp is Hi/Lo

for either you need a 2-channel power amp or 2 single channel power amps.

If you Bi-Amp in Stereo you 2 x 2-channel power amps.

I used to run a Trace GP12SMX using the crossover outputs into a 2-Channel 300W+300W power amp into a 1x15 and a 2x10. Total waste of time. It was much better running a full bandwidth output into each channel and each cabinet. Clearer and more focussed.

Edited June 6, 2007 by obbm

[MoJ]

[quote name='The Funk' post='12899' date='Jun 6 2007, 10:26 AM']Stereo's great. It just basically gives you two sets of controls, inputs and outputs - perfect for bi-amping. I don't really see how bi-amping would be possible without a stereo power amp.

What equipment do you have at the moment? If you could adapt bits of your rig to a new bi-amped rig with a minimum of expenditure, that's always a good thing.[/quote]

Most power amps that Ive been looking at are stereo (dual channel) so that bits not the problem. If I [i]were[/i] to run with a full range signal and a low pass signal, Id need a stereo pre amp so as I could bypass the crossover with one of the signals and send the other via the crossover.

[quote name='obbm' post='12907' date='Jun 6 2007, 10:35 AM']Lets get the terminology right.

Stereo is Left/Right

Bi-Amp is Hi/Lo

for either you need a 2-channel power amp or 2 single channel power amps.

If you Bi-Amp in Stereo you 2 x 2-channel power amps.

I used to run a Trace GP12SMX using the crossover outputs into a 2-Channel 300W+300W power amp into a 1x15 and a 2x10. Total waste of time. It was much better running a full bandwidth output into each channel and each cabinet. Clearer and more focussed.[/quote]

Woah there, we're moving a bit too fast here. A stereo bi-amped system for me is just way too much to think about let alone the extra equipemnt needed. As you say a 2nd power amp and then twice as many cabs too!
I realise that you're just stating facts but thought Id grind that thought to halt quickly.
It'd be a monster rig though!

Appreciate your opinion though OBBM. Thats the reason I set this thread up
Do you find that bi-amped, your sound is missing anything, or is just a case that it sounds clearer and more focussed?
Thanks
Andy

Edited June 6, 2007 by MoJ

[Kiwi]

If you wanted to get a custom made valve power amp, it would be relatively easy for one to be built. However you'd risk end up paying through the nose on an hourly rate if there were a lot of bugs that needed fixing.

You would probably be better off in the long run looking for a Mesa Boogie Strategy 400 power amp for about £600 off Ebay or somewhere (assuming you are happy to load/unload it - a stereo valve power amp is a very heavy lump).

Re: the eq for your rick, you'd be best off going to a music shop or coming along to the Bass Bash and seeing if the upper mid control on an RB400/700/1001 head is centred on the frequencies you like. You can run them with full range cabs from other manufacturers but can't use the biamp facility without some modification to the cabs (assuming the speakers are the right rating etc.).

[The Funk]

[quote name='obbm' post='12907' date='Jun 6 2007, 10:35 AM']Lets get the terminology right.

Stereo is Left/Right

Bi-Amp is Hi/Lo

for either you need a 2-channel power amp or 2 single channel power amps.

If you Bi-Amp in Stereo you 2 x 2-channel power amps.

I used to run a Trace GP12SMX using the crossover outputs into a 2-Channel 300W+300W power amp into a 1x15 and a 2x10. Total waste of time. It was much better running a full bandwidth output into each channel and each cabinet. Clearer and more focussed.[/quote]

I prefer the term dual mono but if someone says a stereo power amp (as opposed to a stereo bi-amp rig), I take it to mean 1 x 2-channel power amp. I don't think anyone was actually asking about a stereo bi-amp rig.

[MoJ]

[quote name='Crazykiwi' post='12934' date='Jun 6 2007, 11:31 AM']If you wanted to get a custom made valve power amp, it would be relatively easy for one to be built. However you'd risk end up paying through the nose on an hourly rate if there were a lot of bugs that needed fixing.

You would probably be better off in the long run looking for a Mesa Boogie Strategy 400 power amp for about £600 off Ebay or somewhere (assuming you are happy to load/unload it - a stereo valve power amp is a very heavy lump).

Re: the eq for your rick, you'd be best off going to a music shop or coming along to the Bass Bash and seeing if the upper mid control on an RB400/700/1001 head is centred on the frequencies you like. You can run them with full range cabs from other manufacturers but can't use the biamp facility without some modification to the cabs (assuming the speakers are the right rating etc.).[/quote]

Thats the aim if I can find somewhere that has any GK heads in stock and I can get the time to do it. Or as you say get myself to a Bass Bash.

[quote name='The Funk' post='12946' date='Jun 6 2007, 11:46 AM']I prefer the term dual mono but if someone says a stereo power amp (as opposed to a stereo bi-amp rig), I take it to mean 1 x 2-channel power amp. I don't think anyone was actually asking about a stereo bi-amp rig.[/quote]

Yes, sorry, I should stick to one set of terms for clarity's sake. Think I may have misunderstood the point OBBM was trying to get across there. Sorry OBBM.

Thanks
Andy

[Bill Fitzmaurice]

[quote name='MoJ' post='12865' date='Jun 6 2007, 04:26 AM']Good to know Bill. Of course buying seperates opens the options up some what.
Does the O15 give a pretty natural sound bi-amped, if its all in one cab and with 3 drivers?[/quote]
As I noted above, the main reason why bi-amping generally doesn't work well when using two commercial cabs is that those cabs aren't optimized for narrow bandwidth operation. It's a very different story when using two cabs that are bandwidth restricted, or a single cab that has multiple drivers that are bandwidth restricted.

[MoJ]

[quote name='Bill Fitzmaurice' post='13034' date='Jun 6 2007, 01:59 PM']As I noted above, the main reason why bi-amping generally doesn't work well when using two commercial cabs is that those cabs aren't optimized for narrow bandwidth operation. It's a very different story when using two cabs that are bandwidth restricted, or a single cab that has multiple drivers that are bandwidth restricted.[/quote]

Excellent news Bill!
Looks like I may be buying some of your plans in the hopefully not too distant future!
One thing I would like to ask, and you'll have to forgive me for my dimness on this (hey,we all gotta start somewhere!),is that you mention that the 'normal' way to do this is with a 4 pole speakon/single cable cable arrangement. This I assume would be per channel of crossover/power amp output?
Ive just looked at the online manual for a particular power amp (Peavey PV2600) and it says that unless in bridge mode, the speakons connections are arranged 1+ and 2+ for the outs, and 1- and 2- are the grounds. Is this still what you were getting at?
Thanks
Andy

[MoJ]

Bill, just thought Id ask a second question, and please let me know if this better suited to your forum, but you suggest the T39 to go with the O10.5.
Having just had a look at the main page for the different cab designs the T39, even loaded wioth a 12" driver doesnt seem to have a great response below 30 Hz. As you already know, my knowledge on these things is limited (which is one great reason for coming to Basschat as its a mine of information given by some very knowledgeble folk) but as I understand low B on bass guitars is someting like 30 Hz. Is there someting Im missing? I gather that the human ear doesnt always need the fundamental to know the note, but surely having the fundamental and being able to reproduce it clearly is a good thing?
I know that there must be something Im missing.
Thanks
Andy

[Bill Fitzmaurice]

[quote name='MoJ' post='13104' date='Jun 6 2007, 11:13 AM']Ive just looked at the online manual for a particular power amp (Peavey PV2600) and it says that unless in bridge mode, the speakons connections are arranged 1+ and 2+ for the outs, and 1- and 2- are the grounds. Is this still what you were getting at?
Thanks
Andy[/quote]
That's normal for a stereo amp, where you'd have separate cables to separate speakers. To run a single cable to a bi-amped speaker you'd make up a dedicated cord with two plugs at the amp end.
[quote]but as I understand low B on bass guitars is someting like 30 Hz. Is there someting Im missing? I gather that the human ear doesnt always need the fundamental to know the note, but surely having the fundamental and being able to reproduce it clearly is a good thing?
I know that there must be something Im missing.[/quote]
You wouldn't want a cab that runs flat to 30 Hz. The bulk of sonic content, and power demand, for the lower notes lies in their 2nd and 3rd harmonics, 60-100 Hz. Fundamentals only exceed the harmonics in strength once the string length is at least 1/4 wavelength. With a 34" scale bass that's from just about 100 Hz.

[Stewart]

[quote name='MoJ' post='13234' date='Jun 6 2007, 07:18 PM']Having just had a look at the main page for the different cab designs the T39, even loaded wioth a 12" driver doesnt seem to have a great response below 30 Hz. As you already know, my knowledge on these things is limited (which is one great reason for coming to Basschat as its a mine of information given by some very knowledgeble folk) but as I understand low B on bass guitars is someting like 30 Hz. Is there someting Im missing? ...[/quote]

It looks very reasonable to me - those graphs would change out of all recognition in a room anyway...

The thing is - that graph is always going to nosedive below around 50Hz to bugger-all at 20Hz or so (at which point you're not so-much hearing anyway...)
Reproducing low B is always going to be a struggle for any loudspeaker, regardless of cabinet.

[MoJ]

[quote name='Bill Fitzmaurice' post='13260' date='Jun 6 2007, 07:53 PM']That's normal for a stereo amp, where you'd have separate cables to separate speakers. To run a single cable to a bi-amped speaker you'd make up a dedicated cord with two plugs at the amp end.

You wouldn't want a cab that runs flat to 30 Hz. The bulk of sonic content, and power demand, for the lower notes lies in their 2nd and 3rd harmonics, 60-100 Hz. Fundamentals only exceed the harmonics in strength once the string length is at least 1/4 wavelength. With a 34" scale bass that's from just about 100 Hz.[/quote]

Fair point Bill!
Although I wouldnt expect any SPL chart to run flat that far down, it just looked like the T39 was a little weak round that area. Again, not doubting the wisdom you posess Bill, but needed clearing up in my head. I may still go for the O15 as has all I want in one conveniant cab, which leads me onto...

I may just have to purchase the plans for O15 to fully appreciate and understand whats going on internally, but with one cable with two plugs at the amp end, the wiring must be intergrated at the cab end with the -1 from the lows and -2 from the highs (or whichever way it is) going to ground and then the two + connections feeding the drivers?
I may just have to sweet talk OBBM into making something up for me.

Still, only in the planning and investigating stages as yet but all this is useful to know.
Thanks
Andy

[Bill Fitzmaurice]

[quote name='MoJ' post='13291' date='Jun 6 2007, 03:51 PM']the wiring must be intergrated at the cab end with the -1 from the lows and -2 from the highs (or whichever way it is) going to ground and then the two + connections feeding the drivers?[/quote]
The way it's done in pro-sound PA is to take the amp outputs to a separate jack panel on the rack for the Speakons that actually connect to the cabs via 4 or more conductor cables. Bad idea to use two sets of jacks on the cab both wired 1+1- to the same config on the amp via two cables, as a mix up will give you toasted MF/HF drivers in a literal flash.

[MoJ]

[quote name='Bill Fitzmaurice' post='13376' date='Jun 6 2007, 11:33 PM']The way it's done in pro-sound PA is to take the amp outputs to a separate jack panel on the rack for the Speakons that actually connect to the cabs via 4 or more conductor cables. Bad idea to use two sets of jacks on the cab both wired 1+1- to the same config on the amp via two cables, as a mix up will give you toasted MF/HF drivers in a literal flash.[/quote]

Ok,thanks Bill.
If and when I should get to this stage, and with one of your cab designs (which is more than likely) then I shall probably get in touch about how to wire everything.
By the way, what if eveything was labeled up? So for instance I had channel one on the crossover marked as low, then channel one on the power amp as low, and the appropriate speakon connection on the cab (if it were th O15) labelled? Would make things clearer. Just a thought
Thanks for all your advice though Bill, most helpful!
Andy

Edited June 7, 2007 by MoJ