REL high Level + Class D amp help pls !

[noiwk1991]

hey guys i really need help !
so i own 3 REL subwoofers right now and i ordered this class D Amp from apollon audio (purifi) 5ch

Purifi 1ET7040SA Multichannel Amplifier (3-5 Channel) | Apollon Audio Hypex Purifi Premium Amplifiers

apollonaudio.com

REL is saying that its not a problem to connect high level with class d amps and that all you have to do is simply not connect the black wire to the negative (black ) binding post
however they mention and i understand that doing so may / likely result in humming noise/sound due to lack of grounding? (which im not sure what it means)

Rel suggest if that happens to then connect LFE into unused RCA /into sub in/out?
does that really solve the problem? because i see some reports in forums that it doesnt . .i even saw someone mention something like "high level digital cable" which agian i dont know what it is.. some others speak about making the black wire have RCA connection and connect to unused RCA? again will it solve?

and also i see some mentions about connecting both LFE and low level instead of high level? but what is this low level? how it different from the high level? and i saw it connect to RCA how does it differ from LFE? also my preamp(avr runing preamp mode) only have 2 subwoffer input ? what do i do then? how can i even connect 2 subs with both LFE +low level? do i use RCA splitters stuff? do they even help? do low level take signal from speakers? please explain to me and help me find solution and way to connect my subs with the new amp ive ordered ! thanks alot !

 

[jsilvela]

hey guys i really need help !
so i own 3 REL subwoofers right now and i ordered this class D Amp from apollon audio (purifi) 5ch

Purifi 1ET7040SA Multichannel Amplifier (3-5 Channel) | Apollon Audio Hypex Purifi Premium Amplifiers

apollonaudio.com

REL is saying that its not a problem to connect high level with class d amps and that all you have to do is simply not connect the black wire to the negative (black ) binding post
however they mention and i understand that doing so may / likely result in humming noise/sound due to lack of grounding? (which im not sure what it means)

Rel suggest if that happens to then connect LFE into unused RCA /into sub in/out?
does that really solve the problem? because i see some reports in forums that it doesnt . .i even saw someone mention something like "high level digital cable" which agian i dont know what it is.. some others speak about making the black wire have RCA connection and connect to unused RCA? again will it solve?

and also i see some mentions about connecting both LFE and low level instead of high level? but what is this low level? how it different from the high level? and i saw it connect to RCA how does it differ from LFE? also my preamp(avr runing preamp mode) only have 2 subwoffer input ? what do i do then? how can i even connect 2 subs with both LFE +low level? do i use RCA splitters stuff? do they even help? do low level take signal from speakers? please explain to me and help me find solution and way to connect my subs with the new amp ive ordered ! thanks alot !

Hi there,

I made a thread as I was similarly baffled by the REL high level connection. See https://audiosciencereview.com/foru...ends-on-amp-topology-how-can-that-work.40684/

Now, the TLDR;

In your REL, the high level and the low level connection (RCA driven) go through the same filters/phase control/gain control.
Since you seem to have an AVR or be capable of using RCA outs, those are totally fine.

REL favor the high level because their view is to skip AVR bass management, and "integrate by ear" to think of the sub as an extension to your mains.
They keep the LFE input for the AVR use-case though, and their advice there is to go for loud.

If you can use RCA out, I'd use that for the low level input and bypass the high-level cable.
On leaving the black wire out in the high level cable: this should be fine. It's not a given that you'd have ground issues in your case.

Oh, and since this seems to be your first post, Welcome!!

 

[noiwk1991]

Hi there,

I made a thread as I was similarly baffled by the REL high level connection. See https://audiosciencereview.com/foru...ends-on-amp-topology-how-can-that-work.40684/

Now, the TLDR;

In your REL, the high level and the low level connection (RCA driven) go through the same filters/phase control/gain control.
Since you seem to have an AVR or be capable of using RCA outs, those are totally fine.

REL favor the high level because their view is to skip AVR bass management, and "integrate by ear" to think of the sub as an extension to your mains.
They keep the LFE input for the AVR use-case though, and their advice there is to go for loud.

If you can use RCA out, I'd use that for the low level input and bypass the high-level cable.
On leaving the black wire out in the high level cable: this should be fine. It's not a given that you'd have ground issues in your case.

Oh, and since this seems to be your first post, Welcome!!

thank you both for your replay and for welcoming!

well im clueless about low level imput so i do have some questions how to do it..
1:do you mean i connect only Low level imput or both low level and LFE? as i would with high level?
2: where do i connect the low level imput to in the avr? do i connect it to the sub out? or do i connect it elsewhere?
3: if i only have 2 subwoofer out in my avr (denon x3700h) and i need to connect 2 subwoofers with 2 RCA each (low level+LFE) how do i do that?
4: but then low level unlike high level doesnt take singal from speakers right? this mean i can not have a subwoofer for the center channel am i correct? or maybe im not?
5: so its possible i could just connect high level to the speakers with the black wire out and have 0 problems and 0 risk for the sub/amp?
thanks alot !

 

[jsilvela]

1:do you mean i connect only Low level imput or both low level and LFE? as i would with high level?

Only the low level, instead of high level + LFE

2: where do i connect the low level imput to in the avr? do i connect it to the sub out? or do i connect it elsewhere?

Sub out, yes

3: if i only have 2 subwoofer out in my avr (denon x3700h) and i need to connect 2 subwoofers with 2 RCA each (low level+LFE) how do i do that?

You only need one RCA into your sub, as per previous answer. You could simply get an RCA splitter (of course this means the AVR can't set different delays)

4: but then low level unlike high level doesnt take singal from speakers right? this mean i can not have a subwoofer for the center channel am i correct? or maybe im not?

This is a bit of a voodoo area from REL. A good modern amp will not have a "signature", so the logic of making the REL "an extension" of your speaker is not clear. In any case, driving the REL via the low level RCA works just fine.

5: so its possible i could just connect high level to the speakers with the black wire out and have 0 problems and 0 risk for the sub/amp?

The black wire in the speaker would still be at the same potential as the black binding post in the amp, so would be similarly problematic.

BTW if your class D amp is Hypex based, those are not offset vs ground, so the high-level *should* be OK.
That said, I've switched to using the RCA low level in, and this is what I would recommend.

Luck!

 

[noiwk1991]

Only the low level, instead of high level + LFE

Sub out, yes

You only need one RCA into your sub, as per previous answer. You could simply get an RCA splitter (of course this means the AVR can't set different delays)

This is a bit of a voodoo area from REL. A good modern amp will not have a "signature", so the logic of making the REL "an extension" of your speaker is not clear. In any case, driving the REL via the low level RCA works just fine.

The black wire in the speaker would still be at the same potential as the black binding post in the amp, so would be similarly problematic.

BTW if your class D amp is Hypex based, those are not offset vs ground, so the high-level *should* be OK.
That said, I've switched to using the RCA low level in, and this is what I would recommend.

Luck!

hey again thank you !

1:tho rel suggest that you can use LFE+low level ? but ill trust you on that.
4: the point is.. right now i have 3 subwoofers 2x Rel t/9x both are connected via high level to the front speakers left/right and LFE to sub connection
the 3rd subwoofer is a REL t/5x which is connected directly to the center channel to improve the sound of my center which ill be honest and say it actually works.. it makes the center channel sound less thin and more like a larger speaker. but to the center it is connected via high level only to the back of the center .. assuming i change all connections to low level RCA i can not do anything similar to that to improve the sound coming from center can i?

my amp is Purifi based amp the new purifi 7040 . but i think the power supply is Hypex 3k i think? i linked the amp that i ordered in the link here.. idk if you mean power supply hypex based or the model ..


another thing id love to ask you about.. . what is the different between the Low level and LFE then? would you use low level for both music 2CH and HT movies? or would you use LFE for HT movies and low level for music only? how they are different? thank you !

 

[jsilvela]

hey again thank you !

1:tho rel suggest that you can use LFE+low level ? but ill trust you on that.
4: the point is.. right now i have 3 subwoofers 2x Rel t/9x both are connected via high level to the front speakers left/right and LFE to sub connection
the 3rd subwoofer is a REL t/5x which is connected directly to the center channel to improve the sound of my center which ill be honest and say it actually works.. it makes the center channel sound less thin and more like a larger speaker. but to the center it is connected via high level only to the back of the center .. assuming i change all connections to low level RCA i can not do anything similar to that to improve the sound coming from center can i?

my amp is Purifi based amp the new purifi 7040 . but i think the power supply is Hypex 3k i think? i linked the amp that i ordered in the link here.. idk if you mean power supply hypex based or the model ..


another thing id love to ask you about.. . what is the different between the Low level and LFE then? would you use low level for both music 2CH and HT movies? or would you use LFE for HT movies and low level for music only? how they are different? thank you !

Will give short answer this time, hope other REL owners can share their experience.

tho rel suggest that you can use LFE+low level

So, the "REL way" is to bypass the typical AVR's low-pass filter and bass management for music. This is where they claim they have the secret sauce.
This is the reason they push the high level connection. If using it, you set your left-right as Large in the AVR, send full-range bandwidth to the subs, and integrate by ear.

The reason they have a separate LFE input is on the assumption that if you are using your AVR with mains set Large, but you still want to have the LFE effects the AVR can produce, then you get the LFE channel input into the sub.
You'll notice the LFE has its own gain knob, but no phase switch.
If you watch John Hunter explaining, he says that you set the gain on the LFE as high as possible without getting distortion.
In other words, for the LFE only, they propose that you go for the boom.

If you use the low-level input, you should likely take advantage of bass management in your AVR, set left-right Small and tweak the crossover.
If you do this, then the separate LFE no longer has any utility.

On a side note. I've done REW readings, and the FR of the LFE seems to match the FR of the low level with the crossover knob set to max.

Hope this clarifies...

 

[noiwk1991]

Will give short answer this time, hope other REL owners can share their experience.


So, the "REL way" is to bypass the typical AVR's low-pass filter and bass management for music. This is where they claim they have the secret sauce.
This is the reason they push the high level connection. If using it, you set your left-right as Large in the AVR, send full-range bandwidth to the subs, and integrate by ear.

The reason they have a separate LFE input is on the assumption that if you are using your AVR with mains set Large, but you still want to have the LFE effects the AVR can produce, then you get the LFE channel input into the sub.
You'll notice the LFE has its own gain knob, but no phase switch.
If you watch John Hunter explaining, he says that you set the gain on the LFE as high as possible without getting distortion.
In other words, for the LFE only, they propose that you go for the boom.

If you use the low-level input, you should likely take advantage of bass management in your AVR, set left-right Small and tweak the crossover.
If you do this, then the separate LFE no longer has any utility.

On a side note. I've done REW readings, and the FR of the LFE seems to match the FR of the low level with the crossover knob set to max.

Hope this clarifies...

it does alot. . however 1 thing remain unanswered and thats how the LFE is different from the low level if they both connect from RCA to the AVR subout and both are managed by the AVR ? also the side note i didnt understand so much.. sorry i dont have much knowledge about these things. ty

 

[jsilvela]

it does alot. . however 1 thing remain unanswered and thats how the LFE is different from the low level if they both connect from RCA to the AVR subout and both are managed by the AVR ? also the side note i didnt understand so much.. sorry i dont have much knowledge about these things. ty

The side comment is where I was trying to answer that

If you're going to connect via an RCA cable:
- The low level input is controlled by the gain knob, phase switch and crossover knob
- The LFE input only has a gain. Without the phase, the time alignment is left to the AVR

The FR (frequency response) of the LFE is similar to the low-level with crossover set to the max.
So, they're pretty similar, but the low level leaves more control in your hands.

Other sub brands have a single crossover knob, with one position for LFE to mean: flat response to the widest set of frequencies, leave it to the AVR to determine the low pass frequency to apply to the sub.
REL subs don't really go for a flat FR. This is in keeping with their philosophy of not using DSP.

Oh, before you asked about Purifi vs Hypex. Don't know there, others at ASR should be able to help you find if Purifi modules are ground-offset or not.
Until you're sure, if you're going to use high-level cable, I would leave the black wire floating just in case.

 

[jsilvela]

By the way, going to mention:
do you have a calibration mic to measure your system response?

If you plan to connect the RELs via RCA and leave the integration to your AVR, then AVR setup should do OK.
If you plan to connect via the high-level, you'll likely follow the REL manual to help you tune by ear.

In this second case, and even in the first, I would advise that you buy a calibrated mic so you can take measurements with REW.
Especially in the "tuning by ear" route, you're kind of flying blind without measurements.

Amir's REW tutorials are easy and useful.

Room Measurement Tutorial for Dummies Part 1

There are few more things transformative in audio than learning how room acoustics works. You never look at any system the same again. Like moving from film photography to digital, measurements give you instant feedback on what your system is doing. Even if you choose to not make any changes...

www.audiosciencereview.com

It's a journey

 

[noiwk1991]

By the way, going to mention:
do you have a calibration mic to measure your system response?

If you plan to connect the RELs via RCA and leave the integration to your AVR, then AVR setup should do OK.
If you plan to connect via the high-level, you'll likely follow the REL manual to help you tune by ear.

In this second case, and even in the first, I would advise that you buy a calibrated mic so you can take measurements with REW.
Especially in the "tuning by ear" route, you're kind of flying blind without measurements.

Amir's REW tutorials are easy and useful.

Room Measurement Tutorial for Dummies Part 1

There are few more things transformative in audio than learning how room acoustics works. You never look at any system the same again. Like moving from film photography to digital, measurements give you instant feedback on what your system is doing. Even if you choose to not make any changes...

www.audiosciencereview.com

It's a journey

thank you.. i still dont know how i will connect to be honest.. and i get the feeling that ill most likely need to let go of the center channel subwoofer because the lowlevel connect to sub out and not to the specific channel rca

 

[jsilvela]

thank you.. i still dont know how i will connect to be honest.. and i get the feeling that ill most likely need to let go of the center channel subwoofer because the lowlevel connect to sub out and not to the specific channel rca

haha, don't despair.

For your information: if you use bass management on your AVR (which I recommend that you do), you'd set the left, right, and center speakers as Small.
This would mean you should definitely use the RCA inputs to your subs.
In this case, the AVR will route the bass for the Left/Right/Center to your subs.

On having individual signals (left, right, center) for the subs.
Not an expert here, pretty good people at ASR to ask about that.
But there's quite a bit of consensus that for low frequencies, we don't localize sound, and "stereo sub" isn't really a thing.

Your 3 subs will still be useful to give a better response across your room, but they don't need to have "identities".

 

[noiwk1991]

haha, don't despair.

For your information: if you use bass management on your AVR (which I recommend that you do), you'd set the left, right, and center speakers as Small.
This would mean you should definitely use the RCA inputs to your subs.
In this case, the AVR will route the bass for the Left/Right/Center to your subs.

On having individual signals (left, right, center) for the subs.
Not an expert here, pretty good people at ASR to ask about that.
But there's quite a bit of consensus that for low frequencies, we don't localize sound, and "stereo sub" isn't really a thing.

Your 3 subs will still be useful to give a better response across your room, but they don't need to have "identities".

but my denon only have 2 subwoofers out .. but let me ask you a specific questions. .
what would happen if i connect a y RCA splitter into my avr Center Pre. (where i connect the RCA from my exteranl class D amp) and then connect another RCA /subwoofer cable from there (the other center Pre RCA from the split) into the subwoofer Low Level imput? will it get signal from the center as if it were connected with high level to the center ? or not? would it cause problems?
another thing is.. you are basically suggesting using normal LFE for the 2 t9/x subwoofers yes? not the lowlevel? which im still failing to understand what makes low level better than LFE ty

 

[jsilvela]

what would happen if i connect a y RCA splitter into my avr Center Pre. (where i connect the RCA from my exteranl class D amp) and then connect another RCA /subwoofer cable from there (the other center Pre RCA from the split) into the subwoofer Low Level imput? will it get signal from the center as if it were connected with high level to the center ? or not? would it cause problems?

Agree: this would be equivalent to the high level connection. I don't think it would cause problems.
But, you'd need to set your center as Large in the AVR, and then you'd need to do the sub integration by ear.

another thing is.. you are basically suggesting using normal LFE for the 2 t9/x subwoofers yes? not the lowlevel? which im still failing to understand what makes low level better than LFE ty

I was trying to suggest using the low level RCA outs for the 2 t9/x. The LFE is similar but has less control. I have seen REL owners suggesting to use the LFE though, so you would not go wrong.

but my denon only have 2 subwoofers out

Many AVR's do.
Depending on your model of Denon, those 2 connectors may actually give out the same signal.
Or, the AVR may "see" 2 subs and be able to configure delay individually (if so, all the better).

If you used an RCA splitter out of one of the two sub-outs, that should be OK, but the AVR would not be able to set the delays differently for the subs connected there.

 

[noiwk1991]

Agree: this would be equivalent to the high level connection. I don't think it would cause problems.
But, you'd need to set your center as Large in the AVR, and then you'd need to do the sub integration by ear.


I was trying to suggest using the low level RCA outs for the 2 t9/x. The LFE is similar but has less control. I have seen REL owners suggesting to use the LFE though, so you would not go wrong.


Many AVR's do.
Depending on your model of Denon, those 2 connectors may actually give out the same signal.
Or, the AVR may "see" 2 subs and be able to configure delay individually (if so, all the better).

If you used an RCA splitter out of one of the two sub-outs, that should be OK, but the AVR would not be able to set the delays differently for the subs connected there.

hey thank you.. im more leaning toward the option of using Y splitter for the center pre RCA and use low level.. i will contact REL to ask if this will work.. if not i think ill sell my t/5x

 

[Chrispy]

Your model of Denon can do the three subs, but only set independent level and delay for two....but if you have two subs that are equidistant from your seat (as I imagine those positioned with your L/R speakers are), just use those with one pre-out with an rca cable splitter, and use the other sub on the other sub pre-out. I wouldn't bother with high level inputs, that's just really for old two ch gear that has no bass management. The use of "LFE" is misleading somewhat, as it only means the .1 channel in content that has it really, but some subs do have an "LFE" input that will bypass the subs' own low pass filter so as to not interfere with the avr's bass management (may be mislabeled "crossover"), but generally just set it to max value. The avr will only output an actual LFE signal from the pre-outs, and depending on your bass management setup in the avr, it may also include redirected bass from other channels and send it to the sub along with any present LFE content.

 

[noiwk1991]

Your model of Denon can do the three subs, but only set independent level and delay for two....but if you have two subs that are equidistant from your seat (as I imagine those positioned with your L/R speakers are), just use those with one pre-out with an rca cable splitter, and use the other sub on the other sub pre-out. I wouldn't bother with high level inputs, that's just really for old two ch gear that has no bass management. The use of "LFE" is misleading somewhat, as it only means the .1 channel in content that has it really, but some subs do have an "LFE" input that will bypass the subs' own low pass filter so as to not interfere with the avr's bass management (may be mislabeled "crossover"), but generally just set it to max value. The avr will only output an actual LFE signal from the pre-outs, and depending on your bass management setup in the avr, it may also include redirected bass from other channels and send it to the sub along with any present LFE content.

thank you ! so you think low level from 1 sub to the RCA center Pre with Y splitter wont work? also.. based on what you saying if i use LFE wont lose alot of bass that isnt LFE signal?

 

[jsilvela]

I think Chrispy's proposal, with which I agree is:
- 1 sub out connected to one sub
- 1 sub out connected to a Y splitter, connected to 2 subs. Especially if those subs are the Left-Right and located symmetrically.

LFE gets to be a confusing term as it has two meanings:
- in the AVR, LFE is a *channel* that contains movie effects like explosions, rumble etc.
- in the sub, the LFE input in your REL, and in other brands the LFE setting in the "crossover" knob, mean: let the AVR handle the low-pass filtering.

In your AVR, you should set the bass as: Main + LFE.
In that way, your subs connected via the sub outs will get the LFE channel PLUS the low frequencies of regular content in the L/C/R *channels*

 

[Chrispy]

thank you ! so you think low level from 1 sub to the RCA center Pre with Y splitter wont work? also.. based on what you saying if i use LFE wont lose alot of bass that isnt LFE signal?

No, I'm saying use low level rca pre-outs on the avr and rca inputs on your avr, and yes a splitter works fine (I use two splitters on one of my setups, as I have four subs on that system). If you use high level inputs to the sub only, you will not be able to get LFE content at all.

PS personally I don't use the avr's LFE+Main setting (I use LFE) as it tends to double up on some frequencies, but many do like to do that.

 

[Chrispy]

LFE literally stands for Low Frequency Effects and is a channel in multich audio formats. The term can easily be misused (or misunderstood without reading the manual for the sub perhaps).

 

[noiwk1991]

No, I'm saying use low level rca pre-outs on the avr and rca inputs on your avr, and yes a splitter works fine (I use two splitters on one of my setups, as I have four subs on that system). If you use high level inputs to the sub only, you will not be able to get LFE content at all.

PS personally I don't use the avr's LFE+Main setting (I use LFE) as it tends to double up on some frequencies, but many do like to do that.

im confused? please explain again