Check my math please?

[BKr0n]

Making a DIY speaker and want to make sure I have my sensitivities right before I make any purchases. Going to be going active with this one with a hypex fusion amp. Drivers:

https://www.madisoundspeakerstore.com/ribbon-tweeters/raal-70-20xr-am-extended-range-ribbon-tweeter/ sensitivity 93db/2.83V

https://purifi-audio.com/document/share/16/6b6d90f3-b9db-4eaa-9f36-9d424bd2adba sensitivity 86.8/2.83V (2 of these making it 89.8/2.83V)

https://www.daytonaudio.com/images/resources/295-104--epique-e180he-44-spec-sheet.pdf sensitivity 83.8/2.83V (4 of these so +6db bringing it to 89.8/2.83V) (before you ask these will be 2 sets in isobar perpendicular to the main drivers)

https://www.hypex.nl/products/amplifier-families/fusion-amplifier-family/fusionamp-fa253 if all my math is right, then this should be the optimal choice to go with... did I get everything?

 

[alex-z]

You will lose 6db at low frequencies to baffle step loss, make sure to account for that if you have a particular SPL requirement in mind.

True isobaric drivers need to be mounted cone to cone, to minimize the lossy air volume that is coupling them together. If you are doing side mounted woofers in a tower that is a completely different application and the E180HE-44 is not a good choice.

Something like a Peerless 830667 will give you 57% more cone area at less than half the cost, and it has less mounting depth as you have a narrower front baffle. The only thing you lose is high frequency extension.

Peerless by Tymphany 830667 8" Paper Cone SLS Subwoofer

The Peerless SLS Series combines high quality performance with an affordable design. The SLS drivers are ideal for use in systems with high power handling requirements, and are a logical choice for use with the SDS line of transducers.

www.parts-express.com

 

[BKr0n]

For starters, thank you for responding

You will lose 6db at low frequencies to baffle step loss, make sure to account for that if you have a particular SPL requirement in mind.

Not so much SPL as much as lowest distortion possible while still not absolutely breaking the bank (aka purifi). Resolution and accurate representation is the goal here.

True isobaric drivers need to be mounted cone to cone, to minimize the lossy air volume that is coupling them together. If you are doing side mounted woofers in a tower that is a completely different application and the E180HE-44 is not a good choice.

The design choice there was for force cancelation. KEF Blade does something similar, but I'm using MTM instead of a coaxial. I figure if I want bass response I would need a separate driver. Additionally, at bass frequencies you're omnidirectional anyway so placing the drivers on the side won't hurt anything.

Edit: the only thing the Daytons will be doing is handling 20-200hz or so. The rest can be handled by the purifis and the raal.

 

[BKr0n]

@NTK this is what i came up with instead of using those KC62 drivers

 

[Holmz]

… Resolution and accurate representation is the goal here …

What is resolution?
(I see it spoken about a lot, but am failing to understand what people mean.)

 

[BKr0n]

What is resolution?

In this circumstance I meant it literally (to resolve) not the concept of resolution in audio.

THAT resolution has more to do with the way data is interpreted by the electronics that do the conversion to analog or digital.

 

[Holmz]

I have read the term elsewhere, and it always sounded (to me) like the driver could only output when there was enough of a signal to make it output.
And below that it would be stuck.
Sort of like a quanta unit of sound.

However the drivers are essentially friction free and not sticking, so I am wondering what is “a resolution limit”? Or a “Resolving speaker”?

They should play down to 0, 10, 20 phon, or 0 dB(A) in SPL.
I suppose that whether we can hear it above the noise, could be cured with some anechoic room.

And if there are harmonics, or other distortions, that are masking the low level sounds… then I can see that as making it difficult to resolve the low level sounds in the presence of higher level sounds. But that lowering of distortion would likely fall into your “Accuracy” category. (I think??)

 

[BKr0n]

However the drivers are essentially friction free and not sticking, so I am wondering what is “a resolution limit”? Or a “Resolving speaker”?

Like I said, in this this circumstances it's literal. So it's saying that it will "resolve" it's input signal with as little distortion as possible. Remember: when talking hifi, you're typically talking about getting the most accurate interpretation of whatever you're listening to in regards to whatever media (music, movies, etc)

They should play down to 0, 10, 20 phon, or 0 dB(A) in SPL.
I suppose that whether we can hear it above the noise, could be cured with some anechoic room.

And if there are harmonics, or other distortions, that are masking the low level sounds… then I can see that as making it difficult to resolve the low level sounds in the presence of higher level sounds. But that lowering of distortion would likely fall into your “Accuracy” category. (I think??)

This is more in the electronics realm than the acoustic. Speakers are still a type of transducer. A transducer is something that turns one type of energy into another (this is a gross oversimplification, but for our purposes go with it). When you run current into a speaker, you still need to put in enough to create a big enough magnetic field in order to make that object (the driver cone) move. After that, then you worry about the acoustic properties.

 

[Holmz]

Like I said, in this this circumstances it's literal. So it's saying that it will "resolve" it's input signal with as little distortion as possible. Remember: when talking hifi, you're typically talking about getting the most accurate interpretation of whatever you're listening to in regards to whatever media (music, movies, etc)

Ok - I suppose we can call low distortion as resolving.

This is more in the electronics realm than the acoustic. Speakers are still a type of transducer. A transducer is something that turns one type of energy into another (this is a gross oversimplification, but for our purposes go with it).

yep - it is a transducer.

When you run current into a speaker,

Most are designed to be flat with respect to voltage.
But I agree that the current is what is producing a magnetic field.

you still need to put in enough to create a big enough magnetic field in order to make that object (the driver cone) move.

We are back to this idea of “stiction” and the speaker not being able to have some fields that are a 100 dB down being able to produce the field.
And on top of that the cone does not really have to move in a velocity sense… it only has to apply pressure in an acceleration sense.
There are drivers with 15” cones or larger, and they really hardly move, and still are able to pressurise the air.
We usually cannot even see the MR or the tweeters moving, as the distance they move is astonishingly small..

After that, then you worry about the acoustic properties.

Yeah but I am not even sure how to quantify “resolving”.
We can quantify distortion though.

If it is NOT resolving in terms of a signal on its own, and only “resolving” in terms of a signal in the presence of other signals, then it is distortion.

 

[BKr0n]

We are back to this idea of “stiction” and the speaker not being able to have some fields that are a 100 dB down being able to produce the field.

It's still a transfer of energy. Decibels can be defined as watts and watts can also be defined as voltage times current. It's not going down that far because there's not enough force generated at -100db to move that cone. There will still be a field. There will still be power running through the speaker. Just not enough.

And on top of that the cone does not really have to move in a velocity sense… it only has to apply pressure in an acceleration sense.
There are drivers with 15” cones or larger, and they really hardly move, and still are able to pressurise the air.

That has more to do with the sensitivity and the size of the diaphragm. More mass means you don't need to move the cone as hard to move the same volume of air. The sensitivity has to do with its efficiency. If a 15" speaker is efficient enough it can easily match a smaller driver built for higher frequencies (not tweeters).

We usually cannot even see the MR or the tweeters moving, as the distance they move is astonishingly small..

That and the fact it's moving too fast for us to really recognize its moving.

 

[voodooless]

Isobaric will not give you better efficiency, only needed less volume for the same response. It will also not go louder. In current day and age of DSP processing, it’s a waste of resources. Just add the woofers in a smaller enclosure and make sure you have enough Xmax and power handling to compensate.

 

[BKr0n]

Isobaric will not give you better efficiency, only needed less volume for the same response. It will also not go louder. In current day and age of DSP processing, it’s a waste of resources. Just add the woofers in a smaller enclosure and make sure you have enough Xmax and power handling to compensate.

Not going for loudness. Isobaric is mostly for the force cancelation it provides. Although 7 drivers IS a lot for one speaker...

 

[KSTR]

Isobaric is mostly for the force cancelation it provides.

Isobaric is not force-cancelling.

The idea is to free the inner speaker cone from the front-side air load, which is handled by the outer driver (load sharing), running in phase wrt cone motion, and vice versa. Its cone must be mechanically coupled to the inner driver, and the smallest possible coupling air volume between cones is the best we can do here.

It's a rather ineffective and brute-force method.
The additional volume for the second driver plus the trapped air volume enforce a larger cabinet so that the net volume benefit (comparing total occupied outer box volumes) is not that great.

Isobaric action can still be realized with force-cancellation, with two isobaric cells mounted back to back, 4 drivers total.

 

[alex-z]

Not going for loudness. Isobaric is mostly for the force cancelation it provides. Although 7 drivers IS a lot for one speaker...

In an isobaric config there is no force cancellation. Both drivers are wired to have the same polarity so that the air volume that couples them together does not change with excursion.

The type of build you are talking about is just called "opposing drivers" aka pull/pull or push/push. There is merit to using such a config to aid in controlling low frequency directivity, cancelling cabinet vibrations is secondary because frankly it isn't that difficult to build a well damped cabinet in the first place.

The big selling point of high-end drivers like the E180HE is that it can play deep bass while still having enough extension to reach a tweeter crossover. You don't need that extension, so you should purchase cheaper drivers with more cone area. It doesn't matter how much you engineer a 6" woofer, even a cheap 10" woofer will offer higher SPL at low frequencies before audible distortion.

 

[Holmz]

It's still a transfer of energy. Decibels can be defined as watts and watts can also be defined as voltage times current. It's not going down that far because there's not enough force generated at -100db to move that cone. There will still be a field. There will still be power running through the speaker. Just not enough.

I would like to see some proof that there is a magic level where the driver stops making a sound, it still am reading it like a quantum unit of sound which it cannot go below.

That has more to do with the sensitivity and the size of the diaphragm. More mass <diameter/area> means you don't need to move the cone as hard to move the same volume of air.

I am not sure what “hard” means?
A bigger area will need less force per area, than a smaller area would need… but by the time we multiply it by area, that force should somewhat be the same.

Then you also have to make some compromise about the beam width and the driver size.
So if we want the angular dispersion to be relatively constant, then we need drivers that get smaller and smaller as their frequency ranges go up.

The sensitivity has to do with its efficiency. If a 15" speaker is efficient enough it can easily match a smaller driver built for higher frequencies (not tweeters).

You can pump in whatever frequency you want to any driver.
Yeah a sub will have a lot of inductance that makes it playing at tweeter frequency pretty difficult.
A bigger problem is that the cone breakup modes are a real thing, and that has a clear impact on performance in terms of nice sound.

That and the fact it's moving too fast for us to really recognize it’s moving.

A tweeter probably never moves more than a mm.
At lower volumes that very quickly gets to be less and less… probably micrometers or nanometers would be the right units.

If it was moving a mm,, we would see it as a blur, and not a tweeter dome that appears to be in a static position.
It is just a fact that at nominal levels (say 90dB(A)) the cones of a MR and tweeter are not “moving” very far.

 

[voodooless]

If it was moving a mm,, we would see it as a blur, and not a tweeter dome that appears to be in a static position.
It is just a fact that at nominal levels (say 90dB(A)) the cones of a MR and tweeter are not “moving” very far.

A 1” tweeter will move about 55 µm at 90 dB and 2.5 kHz.

 

[Hayabusa]

https://purifi-audio.com/document/share/16/6b6d90f3-b9db-4eaa-9f36-9d424bd2adba sensitivity 86.8/2.83V (2 of these making it 89.8/2.83V)

These are 4 ohm, so you can't put them in parallel to get to your 89.8dB

 

[BKr0n]

The type of build you are talking about is just called "opposing drivers" aka pull/pull or push/push. There is merit to using such a config to aid in controlling low frequency directivity, cancelling cabinet vibrations is secondary because frankly it isn't that difficult to build a well damped cabinet in the first place.

I thought dampening low frequencies was difficult in a small space? Since it's active it will be sealed so no porting would make it more difficult wouldn't it?

These are 4 ohm, so you can't put them in parallel to get to your 89.8dB

...well that sucks lol A shame fusion amps can't run 2 ohm loads. Then again for what they are they're fairly capable.

 

[BKr0n]

In current day and age of DSP processing, it’s a waste of resources. Just add the woofers in a smaller enclosure and make sure you have enough Xmax and power handling to compensate.

Could you elaborate on this a little more please? I thought a 3 way crossover was preferable to a 2 way?

 

[Holmz]

Could you elaborate on this a little more please? I thought a 3 way crossover was preferable to a 2 way?

I would be using a 3 way…
You could also do 4 way with the 3 way trailing off under 80-100 Hz.

If you want some evenness in angular dispersion then a 3 way gives that more easily, and each driver can play in a more limited range…
So either less distortion, or cheaper drivers, or lower order slopes and good drivers.

Then the subs playing in opposition can do the lowest registers.

A 1” tweeter will move about 55 µm at 90 dB and 2.5 kHz.

We are literally splitting hairs
So it is about 1/40 of a hair, and it should be lower excursion at say 10KHz.

But any subwoofer moving can easily start competing with that 55 microns, and start to add in Doppler distortion, etc.
So having them cancelling each other out, and in a stiff and dampened cabinet would be worthwhile to prevent small movements that start to compete with the micros of tweeter movement.
It does not take much movement to start making those tweeters more a long ways in phase, if the cabinet is “floppy.”