Hi Chaps,
I'm about to revamp some Bass Bins that I bought a while ago. They are (so I have been informed in a previous post) W shaped Horn Loaded Bass Speakers - Whew! (Plz see my lovely hand drawn cross section diagram - attached)
They currently contain H&H 150W P.A. 12" cones at 16ohms each. Not only do the cones appear to be knackered, but my H&H amp doesn't like them either as it is 400W/ch into 4ohms or bridged is 800w into 8ohms.
I've now bought some nice Eminence Delta 12LF Low Frequency 400W drivers @ 4ohms which I intend to install into these bass cabinets.
It was mentioned in my previous post to the Loudspeakers forum, that I should remove the dense fibreglass stuffing from these drivers as it affects the 'reactance annulling of the chamber'
I don't exactly know what that means, but I want to get extra opinions that I should indeed be removing all the fibreglass from these speakers and leaving them hollow?
The reason I feel compelled to ask this is that these units 'claim' to have been built by H&H who were a British Pro-Audio manufacturer, but then they look a little home made as well - So I don't know where the stuffing decision came from!
Any help would be much appreciated!
thanks
Jonathan
I'm about to revamp some Bass Bins that I bought a while ago. They are (so I have been informed in a previous post) W shaped Horn Loaded Bass Speakers - Whew! (Plz see my lovely hand drawn cross section diagram - attached)
They currently contain H&H 150W P.A. 12" cones at 16ohms each. Not only do the cones appear to be knackered, but my H&H amp doesn't like them either as it is 400W/ch into 4ohms or bridged is 800w into 8ohms.
I've now bought some nice Eminence Delta 12LF Low Frequency 400W drivers @ 4ohms which I intend to install into these bass cabinets.
It was mentioned in my previous post to the Loudspeakers forum, that I should remove the dense fibreglass stuffing from these drivers as it affects the 'reactance annulling of the chamber'
I don't exactly know what that means, but I want to get extra opinions that I should indeed be removing all the fibreglass from these speakers and leaving them hollow?
The reason I feel compelled to ask this is that these units 'claim' to have been built by H&H who were a British Pro-Audio manufacturer, but then they look a little home made as well - So I don't know where the stuffing decision came from!
Any help would be much appreciated!
thanks
Jonathan
Attachments
The rear chamber acts like a simple sealed or ported enclosure (depending on if it's ported or not) The wadding makes the chamber artificially bigger improving the lf extension slightly and avoiding resonances in the cab.
Are the cabs dual drivers or singles? If they're doubles then you'll be better off running 8ohm drivers in parallel making a 4ohm load total for the cab.
Don't worry about the homemade nature - so long as the dimensions are accurate to the originals you should be fine - and don't forget that by changing the drivers you're completely changing the way the speaker works anyway!
Are the cabs dual drivers or singles? If they're doubles then you'll be better off running 8ohm drivers in parallel making a 4ohm load total for the cab.
Don't worry about the homemade nature - so long as the dimensions are accurate to the originals you should be fine - and don't forget that by changing the drivers you're completely changing the way the speaker works anyway!
Your original speakers have an impedance that suits your HH amps.
Two 16ohm speakers in parallel gives an effective load of 8ohms and your spec says HH can drive 800w into 8 ohms in bridged mode.
If you replace the drivers then 16 ohm replacements are a good choice (if you can find any).
Coupling drivers in parallel works well if your amp has the current ability to drive the lower load.
But most drivers do not perform well if coupled in series ( a dual voice works very well in series because it is the SAME driver).
Do not jump in and buy lots of 4 ohm drivers, your amps might struggle!
Two 16ohm speakers in parallel gives an effective load of 8ohms and your spec says HH can drive 800w into 8 ohms in bridged mode.
If you replace the drivers then 16 ohm replacements are a good choice (if you can find any).
Coupling drivers in parallel works well if your amp has the current ability to drive the lower load.
But most drivers do not perform well if coupled in series ( a dual voice works very well in series because it is the SAME driver).
Do not jump in and buy lots of 4 ohm drivers, your amps might struggle!
The H&H Drivers that are in the bins are completely knackered, hence I'm replacing them, the cones don't appear to move very freely, there appears to be corrosion probably caused by water on voice coils, and most importantly these speakes just seem to rattle. I've tried them in their cabinets and I've tried them out of their cabs - With just bass and with midtone and whatever I do to them they just sound rubbish.
(I originally wired the two bins in parallel to generate a mono 8ohm load on the amp, and tried them then - Unless I was playing something with very loud and very heavy bass, they just made a rattling noise)
They're only 150W each anyway so the Amp would punish them (which may be why they're knackered now as I bouth them all together second hand).
I went for the 4ohm drivers because I want to run these bins in Stereo. After a lot of investigation, I decided that stereo was the way to go with these. Bear in mind that I'll be running these up to something like 200Hz. I'm intending for them to take the stress of my smaller speakers in the bass region, but they're not going to be like the LFE channel on a home cinema system.
Given that the amp is specifically rated at 400W/ch into 4ohms in stereo, I opted for 4ohm drivers so that the two cabs are independant of one another.
What has confused me is whether or not there should be any stuffing in these cabinets - 'Centauri' told me in a previous post that it would affect the 'reactance annulling of the chamber' and should be taken out, but then 'pinkmouse' has advised to leave it in.
I think I'll leave it and then remove it if there's a problem - I really posed this question because these things are a pain to dismantle so I don't want to keep dis/re assembling them
Thanks for all your advice so far, and feel free to offer any other help
(I originally wired the two bins in parallel to generate a mono 8ohm load on the amp, and tried them then - Unless I was playing something with very loud and very heavy bass, they just made a rattling noise)
They're only 150W each anyway so the Amp would punish them (which may be why they're knackered now as I bouth them all together second hand).
I went for the 4ohm drivers because I want to run these bins in Stereo. After a lot of investigation, I decided that stereo was the way to go with these. Bear in mind that I'll be running these up to something like 200Hz. I'm intending for them to take the stress of my smaller speakers in the bass region, but they're not going to be like the LFE channel on a home cinema system.
Given that the amp is specifically rated at 400W/ch into 4ohms in stereo, I opted for 4ohm drivers so that the two cabs are independant of one another.
What has confused me is whether or not there should be any stuffing in these cabinets - 'Centauri' told me in a previous post that it would affect the 'reactance annulling of the chamber' and should be taken out, but then 'pinkmouse' has advised to leave it in.
I think I'll leave it and then remove it if there's a problem - I really posed this question because these things are a pain to dismantle so I don't want to keep dis/re assembling them
Thanks for all your advice so far, and feel free to offer any other help
pinkmouse said:
Reactance Annulling in horns is all about sizing the rear chamber to offset the reactance of the air load in the throat at the horn cutoff point. The horn itself will lower the Fs of the driver, and lowering rear chamber volume will push it back up. If you can get the driver/rear chamber resonance equal to the horn cutoff, then you maximise output down to that cutoff, but at the expense of any extension below that. If the rear chamber is too large (or accoustically too large due to stuffing), the horn will become less efficient at low frequencies.
An AES paper on this is available at http://www.aes.org/e-lib/browse.cfm?elib=3894
Cheers
Graeme
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