passive radiators for midrange

[Cousin Billy]

I am building a 3-way. The midrange will be the Accuton C158-8-085.

I notice that the frequency response is a little down below 500Hz.

Would a passive radiator help?.

 

[tinitus]

usually the opposite
pad down whats too much

but you say its used as mid driver
Vas is pretty big for a 5" midrange, with 35liter

how did you calculate it ?
crossover ?

 

[Cousin Billy]

Hey Tinitus, I haven't calculated anything yet. I just had a thought?.

I will look further into what a passive radiator can do.

 

[AllenB]

I'd probably consider using the upper crossover to cut above 500Hz.

 

[tinitus]

I will look further into what a passive radiator can do.

its calculated like vented BR port

you are not using vented BR midrange, are you ?
(impedance peak, phase issue, xo problem, etc etc)

but without knowledge and experience nothing will ever work properly
even with, its difficult enough

I suggest to start with cheap drivers
and simple 'straight forward' design (if there are any)

 

[AllenB]

I just noticed what speakers you are using .link.. Very nice by the way..

Can I assume the mids aren't attenuated? yet they are a little quiet for the woofer. I'd use a second amp for the woofers to allow you to make up the difference in level and roll off the highs as needed with the mid.

 

[tinitus]

ahh, sorry, I have misunderstood
sounded like a theoretical project
(thanks Allen)

but that impressive looking speaker you have there is not a 3way
or at least not in common sense

it is '3way', sure ... but basicly more like a 2way with sub woofer


btw
why say you are building a speaker ?
looks like you already have
or are you going to rebuild it ?
(its confusing not getting all info)

 

[Cousin Billy]

Tinitus and AllenB, thank you for your response'.

I will be building a second pair for the cottage.

The woofer is DSP controlled, with a 1500 watt plate amp. The midrange uses a notch to lower the bottom octave's. I found this to sound better than to put a cap in the signal path.

If I build a pair for the cottage, I can always face the woofer forward, and cross higher.

Any thoughts on the sound quality of a passive radiator system for the mids vs. my sealed version?.

Billy

 

[AllenB]

I can't see it sounding better than a closed box, or necessarily easier to work with, to design or to implement. Just my opinion. Anyway, since this low end is being discarded by the crossover it won't be the dominant effect, the filter will.

By the way, how do you notch the low end without source impedance or a capacitor in the signal path, do you use a current amplifier?

 

[Cousin Billy]

AllenB, yes I use a current amplifier. It is the Atma-Sphere MA-1. It has an output impedance of 2.3 Ohms.

When I was designing the speakers, I worked on the mid to tweeter filter first. Once this was finished, we listened for a few weeks. It was amazing, though I have always preferred a 2-way over a 3-way. When I started adding caps to cross to the woofer, every variation, be it in value or manufacturer, caused a loss of midrange clarity. It was at that point I thought, try a notch. I had a 12mH inductor on hand, did some calculation, and voila, it worked.

The natural roll-off of the midrange (9 liter volume), the notch, and the fact that the slope of the woofer was tweaked with the DSP (digital sound processor), made the cross from woofer to mids quite easy.

I just had a thought. Most of my store bought speakers have been ported. Maybe I only perceive there is a lightness below 500Hz. When I measure, it's about 1dB down. Would I be able to hear this slight drop?, or do I just remember the ported sound?.

 

[AllenB]

1dB may not seem to do much on some systems but when a system is good, it can make a fair difference. The octave below 500Hz is quite important for feeling the weight of certain sources such as voices.

It looks as if this region may be crossing the 'baffle step' though and this can complicate matters as you'd need to go through it in the time domain and at various angles to make sure what you see is what you hear.

As you get it balanced above and below 500Hz the speakers may sound a little more dull, but press on and get it right and you'll probably want to keep it that way.


By the way, have you thought about a first order shunt highpass filter?

 

[tinitus]

since you know how to handle a DSP ...
why not ad another woofer, and try real 3way
with the sub crossed lower

or do real 3way, and use EQ to get the woofer down
it might not be so good for loud SPL, and strugle with the EQ
but that's just a choice

 

[tinitus]

btw, why can't the DSP take care of the 'missing midbass' 😕

ahh, sorry, you only have DSP on low woofer
and use tube amps for the top
tricky stuff

adding another 5", having two in series

and btw, tube amps can do weird things when presented to impedance variations from a passive crossover
maybe that is your real problem

or you could have phase problems around the missing frequency ... or both

 

[head_unit]

Passive radiators work at low frequencies. As a speaker engineer, to be honest I cannot directly say why it wouldn't work, but a lot of intuition alarm bells ring in my mind. I have only ever seen Electro-Voice implement a vented mid-range...a passive radiator would be a whole other layer of difficulties. Plus your rolloff will be so much faster, and excursion at low frequencies uncontrolled...you'd have to totally rework your crossover. My educated guess is you will do a lot of work and suffer for not great results.

I might suggest instead a small passive shelf filter for the upper section? Like a 1-2 dB step just with a couple of resistors and a capacitor.

 

[Cousin Billy]

Thanks guys.

Looks like a shelf for the 500 Hz + region is going to work. First few listens aren't bad.

Bill

 

[sreten]

Hi,

PR's don't do midrange. Baffle step can be addressed by
a passive filter pre power amp and is a lot more than 1dB.

In a 3 way the slope of the bass can be manipulated to
provide the BSC for the mid unit. Seems to me there
is a fair amount of waffle and no hard details here.

rgds, sreten.

 

[tinitus]

Hi,

PR's don't do midrange.

no, it won't

but if the problem is too early rolloff in closed box, 'porting' might help
could be like rolling off closer to 100hz, instead of 200hz
just random number, ofcourse 😉

but I have always suggested to be very cautious porting a 2way when using subs

 

[sreten]

no, it won't

but if the problem is too early rolloff in closed box, 'porting' might help
could be like rolling off closer to 100hz, instead of 200hz
just random number, ofcourse 😉

but I have always suggested to be very cautious porting a 2way when using subs

Hi,

I don't disagree, but I can't see the relevance to good 3 way design.

Here we've got general details and no specifics, like why a notch
filter is really better than a high pass, giving an elliptic function.

Its used much more often on low pass than high pass due
to inevitable distortion issues for the high pass variant.

rgds, sreten.

 

[tinitus]

The natural roll-off of the midrange (9 liter volume)...

with closed 9liter calculation does in fact show a very nice smooth rolloff at 100hz

around 5liter seem to gives 1db more output around 150hz

not something I would consider for a final design
but you could still try in the one you have playing
stuffing with closed cell foam might do it

I still suspect your worst problem right now might come from a phase problem

 

[Cousin Billy]

Tinitus

Please help. Where would my phase problem come from?.

I am using a first order crossover, with a notch to help the low end roll-off.