Not necessarily. There are many ways to deal with BS and the filter is a last resort to my mind.
Baffle Diffraction Step (it needs a bit of updating).
An ML-TL or ML-Voigt gives another tool in the fight.
The other thing to keep in mind is that baffle step compensation is always a compromise. As one artificailly raises the lower levels to flatten on-axis response, one is raising the room response above flat by that amount. It is a problem with many dimensions.
dave
Baffle Diffraction Step (it needs a bit of updating).
An ML-TL or ML-Voigt gives another tool in the fight.
The other thing to keep in mind is that baffle step compensation is always a compromise. As one artificailly raises the lower levels to flatten on-axis response, one is raising the room response above flat by that amount. It is a problem with many dimensions.
dave
I've been thinking of building a bipole ML-TL instead of an MTM. TM on the front and the other M at the back, this to fight BSC. What are your thoughts on this idea? I guess you need to low pass the rear midwoofer to avoid rear midrange?
Bipoles solve BS in a different way. And one has to be aware of the bipole dip.
One can move the 2nd driver to the side (or the top if end loaded — check for Castle microTower for an example.
Or if you cross low enuff put the biple drivers on the sides where there is no bipole dip.
dave
One can move the 2nd driver to the side (or the top if end loaded — check for Castle microTower for an example.
Or if you cross low enuff put the biple drivers on the sides where there is no bipole dip.
dave
Does the bipole dip occur when the driver radiations do not overlap at a specific frequency?
P.S. I just read in your article that it occurs due to the delay of the rear to front speaker. It is stated that a wider to depth baffle ratio (3-4) to 1 minimizes the effect. What is the wavelength relation of the dip?
P.S. I just read in your article that it occurs due to the delay of the rear to front speaker. It is stated that a wider to depth baffle ratio (3-4) to 1 minimizes the effect. What is the wavelength relation of the dip?
Last edited:
It is. The dip is caused by different path lengths between the back driver & the front driver at those frequencies just below the transition from 2π to 4π.
Offset Bipolar MLTL with CSS EL70 Drivers--Part 1
dave
Offset Bipolar MLTL with CSS EL70 Drivers--Part 1
dave
Thanks Dave! There's a bit of a problem that some people say about bipoles though - room placement. The speakers will have to be placed 2ft close to a roof angled ceiling.
Yes room placement can an issue, but if you are crossing low not near as much.
In FR bipoles the top part of the rear driver is rolled off. One gets the advantage of push-push but minimizes bipole dip and room issues.
dave
In FR bipoles the top part of the rear driver is rolled off. One gets the advantage of push-push but minimizes bipole dip and room issues.
dave
Primarily, anything you would prefer not to do with a normal speaker, you would do the same with a bipole or 2.5 way. Either way you choose to compensate your baffle you'll find wide radiation at lower frequencies and more narrow at higher frequencies.
I agree, that walls spaced away from the speakers can be a problem.
I agree, that walls spaced away from the speakers can be a problem.
What would be your opinion on biamping, current driving the fullrange part of the MTM? Might current drive result in a fuller, less harsh sound for many fullrangers? What about another driver I got hinted on the Bulgarian audio forum, Beyma 3FR30?
As long as the impedance over the driver’s bandwidth is flat it makes no difference what an amp’s Rout is.
If the impedance is not-flat and you are using a current amp then a fraction* of the impedance will be imposed on the frequency response.
As a midTweeter you can mostly ignore the bass resonance and you end up with a rising impedance with frequency, it can be a near zero rise to a BIG rise. A copper polepiece is used to flatten the rising impedance — hence often the case w cheaper drivers with no copper.
This can be used to advantage where the rising impedance causes the top to tilt-up the response to compensate for a natural fall-off.
*this effect starts on the “voltage” amp side of the divider with amplifiers of ~1Ω Rout into 8Ω. As the Rout increases so does the effect of the impedance on FR.
A variable transconductance amplifier that lets you dial in the Rout lets you use this to dial in the response of the loudspeaker by changing the amplifier’s Rout.
Worth trying if you have, or are itching to build, a current amp.
dave
If the impedance is not-flat and you are using a current amp then a fraction* of the impedance will be imposed on the frequency response.
As a midTweeter you can mostly ignore the bass resonance and you end up with a rising impedance with frequency, it can be a near zero rise to a BIG rise. A copper polepiece is used to flatten the rising impedance — hence often the case w cheaper drivers with no copper.
This can be used to advantage where the rising impedance causes the top to tilt-up the response to compensate for a natural fall-off.
*this effect starts on the “voltage” amp side of the divider with amplifiers of ~1Ω Rout into 8Ω. As the Rout increases so does the effect of the impedance on FR.
A variable transconductance amplifier that lets you dial in the Rout lets you use this to dial in the response of the loudspeaker by changing the amplifier’s Rout.
Worth trying if you have, or are itching to build, a current amp.
dave
It makes sense about the rising impedance Dave, but what about distortion? I've seen publications where distortion seems to get lower with current drive. Some claim that current drive can give a more transparent kind of sound.
I'm using own DIY tube amplifiers and was thinking - a high power CFB tube amp for the midbass section and a low power and DF DHT pentode section for the midrange.
I'm using own DIY tube amplifiers and was thinking - a high power CFB tube amp for the midbass section and a low power and DF DHT pentode section for the midrange.
The effects of amplifier impedance are very loudspeaker dependant, it's best to suck it and see Variable Amplifier Impedance
That is indeed the thots from some, a speaker is a current device. The jury is still out, but i think there is a good chance something more than anecdotal information will come. In the meantime we just try and see what happens. I have had good experiences with current amps on the right speakers,
dave
Already have it, i.e. draws less current for a given power 'demand', hence [potentially] lower distortion due to VC coil heating, ditto power wiring if it's used as a series resistor.
GM
GM