As a by-product of my thread asking for advice on building the Hi-Fi Answers August 1975 Transmission Line Monitor (HFA TLM) I have come up with two other issues on which I would like greater (in fact, any) basic understanding.
The HFA TLM uses the following crossover:
What I would like to understand is not the theory (which I suspect is beyond me) but what frequencies are fed to each of the drivers. I guess that the B139 is only fed frequencies below 375 Hz and the 4001G is only fed frequencies above 10 kHz but does the B110 only see frequencies from 375 Hz to 3 kHz and the T27 only see frequencies from 3 kHz to 10kHz? I accept that there will be overlap from driver to driver, not clean cut-offs. However, in general terms, is the result of this crossover much as I have described?
Secondly, each of the drivers has a DC Resistance value but the nominal resistance seen by the amp is (say) 8 Ohms - what would be the result if without changing the crossover in any way one was to disconnect one of the drivers - e.g. the B139 or the 4001G?
BI-AMPING:
As I understand it, bi-amping (or tri-amping come to that) involves using multiple power amplifiers to feed the drivers in a speaker - presumably avoiding the need for a crossover - is this substantially correct?
What does this do to the resistance seen by the amp?
How does one cater for the different efficiencies (output level) of the drivers?
For instance, if one were to take a bass driver (e.g. Kef B139) and a mid-range / high frequency driver (e.g. Celestion HF1300) and connect them to a CD player with a variable line output level via one Quad 303 each, how would this work? How would you adjust the levels of each driver such that you didn't get too much or too little bass? Incidentally, the choice of the B139, HF1300 & 303 is for illustrative purposes only. I am trying to keep it simple, I don't really want suggestions for other drivers or power amps
Any guidance targeted at a complete novice in both subject areas would be greatly appreciated.
- Crossovers
- Bi-amping
The HFA TLM uses the following crossover:
Secondly, each of the drivers has a DC Resistance value but the nominal resistance seen by the amp is (say) 8 Ohms - what would be the result if without changing the crossover in any way one was to disconnect one of the drivers - e.g. the B139 or the 4001G?
BI-AMPING:
As I understand it, bi-amping (or tri-amping come to that) involves using multiple power amplifiers to feed the drivers in a speaker - presumably avoiding the need for a crossover - is this substantially correct?
What does this do to the resistance seen by the amp?
How does one cater for the different efficiencies (output level) of the drivers?
For instance, if one were to take a bass driver (e.g. Kef B139) and a mid-range / high frequency driver (e.g. Celestion HF1300) and connect them to a CD player with a variable line output level via one Quad 303 each, how would this work? How would you adjust the levels of each driver such that you didn't get too much or too little bass? Incidentally, the choice of the B139, HF1300 & 303 is for illustrative purposes only. I am trying to keep it simple, I don't really want suggestions for other drivers or power amps
Any guidance targeted at a complete novice in both subject areas would be greatly appreciated.
Hi again - let's tackle the two separately
CROSSOVERS
Your description is correct. The components used in the crossover determine which frequencies go to which drive unit. Varying the components gives you the flexibility to move the frequency hand-over points from one driver to the next.
A passive crossover (as you've described above) is usually designed in conjunction with the specific drivers used (and ideally the cabinet to account for any effects that has). Removing a driver from the equation may upset a number of factors, including impedance, and can't really be assessed without measuring the effect.
BI-AMPING
Unfortunately this term has got a bit hijacked. The UK hi-fi press often uses to to refer to adding two amplifiers to a speaker but still driving the speaker via it's passive crossover. This gives you more available watts but no other benefit.
What we were talking about on the other thread was
ACTIVE CROSSOVERS
In this case, the amplifiers are connected directly to the drive units and the crossover comes before the amplifier.
The crossover itself usually comprises active, powered components like transistors or op-amps but it is possible - though less common - to use passive components. The crossover goes between the preamp and power amp stages, eg the 33 and 303 in a Quad set-up.
You shouldn't connect a power amp direct to (say) the HF1300 and connect it to a source because the tweeter will see all the frequencies, including bass. It will blow up at very low volume. So the active crossover does the same as the passive and filters the sound first, stopping bass frequencies from reaching the tweeter and stopping high frequencies from reaching the bass.
Why bother with active? Several reasons:
1. The amplifier is directly coupled to the drive unit. This enables it to control the driver better (increased damping) and means the amplifier sees a stable impedance. So the amplifier requirements are less - no need to provide such large current delivery.
2. The amplifier can be tailored to the drive unit. Got a huge 500w powerhouse? Stick it on the bass driver and use a lower-cost 25w amp on the treble. My commercial active uses 250w on the bass/mid, 75 watt on the treble.
3. Active crossovers offer more flexibility - crossover slopes can be steeper, for instance, making sure there is less overlap between the drivers. The latest development is digital crossovers - look on here or google MiniDSP - which offer crossovers which can be programmed via computer for immense flexibility.
4. More headroom. As I mentioned on the other thread, there are losses in a passive crossover arrangement and it is usually reckoned that if you add up the overall power in an active speaker, it would take double that to generate the same sound output in a passive. (It's a generalisation.)
5. It might be cheaper. High grade passive crossover components can get very expensive. An active crossover uses small value components, will be smaller and could be built for £15 (a firm on UK eBay offers ready-built ones for £30). The amplifiers can be smaller and don't need such large heatsinks (mine uses the metal back plate of the speaker and rarely gets warm). The power supply can be smaller. My actives have amplifiers, crossover, power supply built into the 10 litre speaker cabinet. The whole thing is very compact and you save on the cost of amplifier cases; most studio actives do it this way. But there's no disadvantage (other than having to buy more speaker wire) in having the power amps elsewhere if you've already bought or built them as stand-alone amps.
(Be aware that some commercial companies such as Naim, who offer add-on active crossovers, maintain you should use the biggest and best in their range to go active. This is because they want to sell you something.)
I hope that helps as a starter. There are lots of people on here building active speakers so I'm sure they can help in greater depth if needed.
- let's tackle the two separatelyCROSSOVERS
Your description is correct. The components used in the crossover determine which frequencies go to which drive unit. Varying the components gives you the flexibility to move the frequency hand-over points from one driver to the next.
A passive crossover (as you've described above) is usually designed in conjunction with the specific drivers used (and ideally the cabinet to account for any effects that has). Removing a driver from the equation may upset a number of factors, including impedance, and can't really be assessed without measuring the effect.
BI-AMPING
Unfortunately this term has got a bit hijacked. The UK hi-fi press often uses to to refer to adding two amplifiers to a speaker but still driving the speaker via it's passive crossover. This gives you more available watts but no other benefit.
What we were talking about on the other thread was
ACTIVE CROSSOVERS
In this case, the amplifiers are connected directly to the drive units and the crossover comes before the amplifier.
The crossover itself usually comprises active, powered components like transistors or op-amps but it is possible - though less common - to use passive components. The crossover goes between the preamp and power amp stages, eg the 33 and 303 in a Quad set-up.
You shouldn't connect a power amp direct to (say) the HF1300 and connect it to a source because the tweeter will see all the frequencies, including bass. It will blow up at very low volume. So the active crossover does the same as the passive and filters the sound first, stopping bass frequencies from reaching the tweeter and stopping high frequencies from reaching the bass.
Why bother with active? Several reasons:
1. The amplifier is directly coupled to the drive unit. This enables it to control the driver better (increased damping) and means the amplifier sees a stable impedance. So the amplifier requirements are less - no need to provide such large current delivery.
2. The amplifier can be tailored to the drive unit. Got a huge 500w powerhouse? Stick it on the bass driver and use a lower-cost 25w amp on the treble. My commercial active uses 250w on the bass/mid, 75 watt on the treble.
3. Active crossovers offer more flexibility - crossover slopes can be steeper, for instance, making sure there is less overlap between the drivers. The latest development is digital crossovers - look on here or google MiniDSP - which offer crossovers which can be programmed via computer for immense flexibility.
4. More headroom. As I mentioned on the other thread, there are losses in a passive crossover arrangement and it is usually reckoned that if you add up the overall power in an active speaker, it would take double that to generate the same sound output in a passive. (It's a generalisation.)
5. It might be cheaper. High grade passive crossover components can get very expensive. An active crossover uses small value components, will be smaller and could be built for £15 (a firm on UK eBay offers ready-built ones for £30). The amplifiers can be smaller and don't need such large heatsinks (mine uses the metal back plate of the speaker and rarely gets warm). The power supply can be smaller. My actives have amplifiers, crossover, power supply built into the 10 litre speaker cabinet. The whole thing is very compact and you save on the cost of amplifier cases; most studio actives do it this way. But there's no disadvantage (other than having to buy more speaker wire) in having the power amps elsewhere if you've already bought or built them as stand-alone amps.
(Be aware that some commercial companies such as Naim, who offer add-on active crossovers, maintain you should use the biggest and best in their range to go active. This is because they want to sell you something.)
I hope that helps as a starter. There are lots of people on here building active speakers so I'm sure they can help in greater depth if needed.
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re:'the T27 only see frequencies from 3 kHz to 10kHz' - no, all freqs from ~3Khz up, (3rd order HP)
this link may be useful:
BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1
this link may be useful:
BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1
Thanks Colin, that certainly helps. Thanks also to PeteMcK for the clarification.
I take it then that a typical passive crossover cuts off either at upper (bass) or lower (mid & treble) frequencies for each driver rather than at both ends which would give a true lower and upper frequency range (e.g. 375 Hz to 3 kHz or 3 kHz to 10kHz)? I guess that an active crossover can be cleverer?
Looking at this Bi-Amp block diagram taken from the WestHost.com article linked by PeteMcK
I imagine that you would still need some sort of level control following each of the amplifiers?
I have often been puzzled by advertising material for cheap(ish) speakers that include two sets of speaker cable binding posts, one for the low frequency driver and the other for the high frequency driver. I take it that these both still end up feeding the same passive crossover and in practice are little than a marketing gimmick and a way to sell more high margin speaker cable?
I take it then that a typical passive crossover cuts off either at upper (bass) or lower (mid & treble) frequencies for each driver rather than at both ends which would give a true lower and upper frequency range (e.g. 375 Hz to 3 kHz or 3 kHz to 10kHz)? I guess that an active crossover can be cleverer?
Looking at this Bi-Amp block diagram taken from the WestHost.com article linked by PeteMcK
I have often been puzzled by advertising material for cheap(ish) speakers that include two sets of speaker cable binding posts, one for the low frequency driver and the other for the high frequency driver. I take it that these both still end up feeding the same passive crossover and in practice are little than a marketing gimmick and a way to sell more high margin speaker cable?
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Usually the crossover part associated with an individual driver will cut off all the frequencies that driver doesn't need to see. For example, in my 2-way the bass unit gets to see nothing above 3kHz, the treble nothing below. In a two-way, you only need to cut-off one side of the frequency spectrum.
In a three-way, the mid-range crossover will cut off bass and treble frequencies.
Your HFA crossover isn't quite a four-way - it's more like 3.5-way in that the super-tweeter is run alongside the T27. It's more of a helper tweeter, rather than a complete hand-over, if you like. It's less usual and some would argue not needed.
In a three-way, the mid-range crossover will cut off bass and treble frequencies.
Your HFA crossover isn't quite a four-way - it's more like 3.5-way in that the super-tweeter is run alongside the T27. It's more of a helper tweeter, rather than a complete hand-over, if you like. It's less usual and some would argue not needed.
Re the westhost block diagram: The levels for the individual power amps will be set in the active crossover as part of the design process. Once set, they can be left alone. Overall system volume control will take part in the preamp as usual.
I think the confusion arises because the diagram is assuming source = preamp. (Or a source which has its own volume control, like an iPad or computer.) The diagram also shows a passive crossover between the mid and tweeter. So the diagram is showing a compromise system instead of a fully active system. A fully active three-way would have an active crossover feeding three power amplifiers.
I think the confusion arises because the diagram is assuming source = preamp. (Or a source which has its own volume control, like an iPad or computer.) The diagram also shows a passive crossover between the mid and tweeter. So the diagram is showing a compromise system instead of a fully active system. A fully active three-way would have an active crossover feeding three power amplifiers.
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Bi-amping
This is the definition we use in the UK.
It has existed for decades.
Some other countries have active speakers and use the term biamping to mean active.
That is not what we Britains do.
We have quite a few British manufacturers who produce active speakers. They call them, active speakers. They do not call them biamped speakers.
A few examples that I can remember: Meridian, Linn, Roksan, Tannoy .....
Bi-amping is using two amplifiers with the same gain to drive a single two way passive crossover speaker that has bi-ampable terminals.
This is the definition we use in the UK.
It has existed for decades.
Some other countries have active speakers and use the term biamping to mean active.
That is not what we Britains do.
We have quite a few British manufacturers who produce active speakers. They call them, active speakers. They do not call them biamped speakers.
A few examples that I can remember: Meridian, Linn, Roksan, Tannoy .....
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The term is in common use in the pro audio world. Here are a few examples
Event Electronics | Reference Studio Monitoring | opal
Latest Active Speakers - Products | AVI HiFi
Active Speakers and Speaker Systems from Genelec since 1978
And here is a good explanation from the Sound on Sound website (see Active Electronics towards the end of the page)
Choosing Monitors
Event Electronics | Reference Studio Monitoring | opal
Latest Active Speakers - Products | AVI HiFi
Active Speakers and Speaker Systems from Genelec since 1978
And here is a good explanation from the Sound on Sound website (see Active Electronics towards the end of the page)
Choosing Monitors
just to add confusion a crossover placed betwixt Pre Amp and Amplifier Needs Not be active.
Also note that crossovers before the Amplifiers (active or passive) are Not a Be all / End all solution.
Care/thought in design and execution is required.
Wayyy easier to say than to do.. well.
Just as many such setups sound no better than their replaced passives versions, as do ones that gave audible improvement.
Best path is to have a minimum possible number of crossover points, 1 is Great, Zero being the ideal.
G'luck
a crossover placed betwixt Pre Amp and Amplifier Needs Not be active.Also note that crossovers before the Amplifiers (active or passive) are Not a Be all / End all solution.
Care/thought in design and execution is required.
Wayyy easier to say than to do.. well.
Just as many such setups sound no better than their replaced passives versions, as do ones that gave audible improvement.
Best path is to have a minimum possible number of crossover points, 1 is Great, Zero being the ideal.
G'luck
I am British and purchased some British speakers in the early 2000s that were advertised as being able to be bi-amped. I had no interest at the time of purchase but a few months later I brought some hardware home from work one weekend to have a play running them active only to find I could not work out how to bypass the passive crossover. A phone call to the manufacturer to find out how to do this informed me that any attempt to bypass the crossover would void the warranty and biamping did not have the meaning every British person outside the audiophile world would assume. My question about why anyone would want to "bi-amp" in this way was not satisfactorily answered.
many manufacturers will use the term tomean passive bi-amoing, where the passive XO is seperated into 2 ormore parts and it is possible to drive each section of the passive XO with a different amplifier.
Real bi-amping requires "moving" the XO tp in front of the amplifiers driving the speakers directly, Best performance requires a custom XO designed, like the passive hopefully is, to deal with any driver "nigglies".
If the speakers are from the early 2000s hasn't the warranty long expired? What are they?
dave
Real bi-amping requires "moving" the XO tp in front of the amplifiers driving the speakers directly, Best performance requires a custom XO designed, like the passive hopefully is, to deal with any driver "nigglies".
If the speakers are from the early 2000s hasn't the warranty long expired? What are they?
dave
It would seem I have failed to make my point clearly. The term biamp is indeed used by audiophiles in the UK in the way Andrew states but it is not necessarily used in that way by non-audiophiles in the UK. At the time I tried to "biamp" the speakers I had taken effectively no interest in the home audio world since the 70s but I had a technical background.
Not sure it is relevant but the speakers were KEF Q1 coaxials which I had bought for the kitchen of the flat I was renting at the time. The exercise to "biamp" them was in order to gain experience with a measurement system that was new to me and not to permanently modify the kitchen speakers. The speakers would have been returned to passive crossovers on Sunday evening. I cannot remember what I did with my weekend instead but I do remember being peeved by my introduction to how audiophiles can misuse the meaning of words.
2way speakers with 2sets of terminals can be driven by a single amplifier if the supplied pair of shorting links are using across the 2sets of terminals.
The manufacturer will usually tell you how to bi-amp them; by removing the supplied shorting links and using 2 amplifiers with the same gain, one amplifier to drive one PAIR of terminals and a separate amplifier to drive the other PAIR of terminals.
This is Biamping. It does not void the Warranty. It is written into the manufacturer issued operating manual.
Very many 2way speakers are made with 2pairs of terminals. These are ready for bi-amping, if the user wants to go that way.
The manufacturer will usually tell you how to bi-amp them; by removing the supplied shorting links and using 2 amplifiers with the same gain, one amplifier to drive one PAIR of terminals and a separate amplifier to drive the other PAIR of terminals.
This is Biamping. It does not void the Warranty. It is written into the manufacturer issued operating manual.
Very many 2way speakers are made with 2pairs of terminals. These are ready for bi-amping, if the user wants to go that way.
This is passive bi-amping, and althou easy does not have near the benefit of active bi-amping (the default definition here at least) with a sorted active XO.
Sounds like the marketing people have done a thorogh job of pulling the wool over people's eyes in GB. Similar to how thoroughly was made best speaker panel material when in fact it is just cheap.
dave
Yup. And the magazines colluded very enthusiastically. Any manufacturer not offering the extra terminals for biwiring had to give a very good excuse for not doing so.
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Do both pairs of terminals end up feeding the same single passive crossover or are there actually two passive discrete passive crossovers inside the box, one for the HF driver and another for the LF driver? I am just curious, I do suspect that it is pure marketing nonsense since it seems commonplace, even on budget (e.g. Richer Sounds) speakers where I doubt they would ever actually be driven by two amplifiers.
Active speakers are those with amp(s) built-in. They can have active or passive XOs.
dave
Hi,
There's hifi bi-amping and there's hifi active biamping.
Hifi biamping means nothing other than being stupid
to the PA crowd, who do biamping and triamping.
Whatever, trying to keep it simple means you can't
discuss the subtleties of proper active bi-amping.
Which cannot be explored with the appalling
mismatch of a B139 / HF1300 Two way.
rgds, sreten.
There's hifi bi-amping and there's hifi active biamping.
Hifi biamping means nothing other than being stupid
to the PA crowd, who do biamping and triamping.
Whatever, trying to keep it simple means you can't
discuss the subtleties of proper active bi-amping.
Which cannot be explored with the appalling
mismatch of a B139 / HF1300 Two way.
rgds, sreten.
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