Rega RS5 active crossover filtering

I am toying with the idea of running an analogue active 2 way crossover at about 90 to 100 Hz in order to free up the RS5's of bass load and split it off to my dual Rel T5i subs.

Has anyone done this?

The setup would be:
Pre amp out > active 2 way crossover > above 90 Hz goes to power amps feeding the RS5/below 90 Hz running into the Rel T5i's RCA input.

I love the RS5's but they are at heart a 2.5 way therefore the 5 inch mid is running full range into mechanical failure which just happens to coincide with the roll off of the 7 inch woofer (no crossover components between) and even the 7 inch woofer while ive seen claimed specs of 45 Hz i doubt it.

I am hoping that by running the active crossover i will get even better sub integration as its not relying on guesswork blending the T5's crossover with the Regas roll off. Plus hopefully ridding the tube amps and the RS5's of sub 90 Hz freq they can operate more efficiently.

PS: Please no comments saying Rel recommends speakon high level connections. I know, i am currently doing it but its not possible with the use of the active crossover which should offer greater improvement. I will be moving to bigger subs eventually so wanting to future proof a bit.

Cheers.

 

I think that you are relying on stray thoughts vs real experience here. You can over-analyze almost anything very easily without feedback from experience, so asking is a good first step. While there are certain applications and rooms where bi-amping with active crossovers is better or even essential, it is unusual for a typical stereo set-up in a typical room. It isn't practical for one, it is more expensive, and it often doesn't sound as good for the last, which is the strongest point.

I'll start off by suggesting a situation where you would likely want bi-amping and active crossovers. For a huge space, where you want crazy loud dynamics or you have very inefficient speakers which are tough to drive but still sound very good. These are unusual circumstances for a home system.

The Rega RS5 and RX5 go pretty deep and although I am not sure how deep, it does depend upon the room and placement. You can measure your in-room response and have a better idea at what frequency a sub might best be integrated. My experience with these shows that the bass is very high quality, while maybe not as deep as you'd like to go by adding the power of a sub, you are perhaps substituting quality for quantity. You'd need a very special pair of subs in a stereo configuration to even attempt to reach the performance of the Rega system from midbass into the midrange. Your crossover idea of 90hz is way too high. Even Dolby doesn't recommend anything above 80hz, and those surround systems generally suck in their two channel performance as compared to most high end stereo systems. Also you are using a term that might confuse some folks here about the Rega speakers capability, when you say "mechanical failure" as they will certainly not fail. You correct that later with roll-off, which I am sure is what you meant before as well. Let's just say that you measured and got an in-room response of your RS5 system to have a low frequency roll-off of about 45hz. I would not want to cross-over at anything above 60hz, even if I was to use an active high pass crossover and biamp the system. I think that you'll find through simple listening tests that you can set the subs crossover to integrate into your room pretty well at 50 hz or so depending upon how your speakers are positioned. This running the mains full range and allowing the subs to fill-in below their natural roll-off. Another thing to consider about active crossovers is that they are essentially preamps and they will add the level of noise and colorations associated with preamps in their quality range into the system. You likely have a better sounding main amp already and you would be placing the crossover in front of that, which you might find to sound inferior. So most systems that I have assembled have used a mains that runs to it's low freq. cut-off and then a sub or a pair of subs is added to supplement bass beyond that frequency. That keeps bot the top end and the bottom end as pure as possible.
-Bill

 

Thanks @KT88, ill detail a bit of what im thinking longer term below (although it will probably make you cringe).

The Rel T5i subs do integrate rather well between 60 and 80 Hz and they go down to 32 Hz at -6 db which isnt super low but i favour my bass notes to have a bit of a leading egde to them, pleanty of snap and instant decay, especially when listening to funky bass lines and double kick drumming.

I guess what im trying to say is that i essentially want bigger fuller sounding speakers but i love the midrange and treble performance of the RS5 that much im not willing to part with them. I also love the bass performance too but i want more therefore have added the Rel T5i subs and its helped a lot and i am essentially "happy" with my setup.

I have however been doing a fair bit of reading recently on larger 3 and 4 way speakers with active crossovers and i am itching for a DIY project for the holidays. Then i saw a set of active crossover modules come up for sale and its got me thinking of eventually doing something like what the great aussie speaker designer Greg Osborn does with his Epitome 3 way range.

Basically its a 3 way 3 driver floorstander but you can add optional bass towers to the setup. Im not sure what sort of extra crossover componentry is used to make this happen but it is a passive system i believe. I dont have the knowhow to build passive crossovers but i can build a cabinet and i love a project (even if it doesnt pan out). Therefore when i saw these xkitz 2 way actives for sale cheap with optional 90 and 50 Hz crossover modules i thought that maybe i could have a crack, but initially i would just run them using the Rel subs until the build was done.

Im thinking of either dual 8 inch or single 10 inch scanspeak woofers, not specifically a subwoofer driver but something that specs down below 30 Hz and running them in a large sealed cabinet with a volume control power amp. Keeping in mind i would have the option to change crossover frequency from 50 to 90 Hz so if i moved up to Rega R9 or RS7 speakers as i intend to (if i ever find a set) i could run the lower crossover as the transmission line Rega's spec a bit lower.

Below is a pic of the Osborn Epitome speakers with bass towers, this is essentially what i want with my Rega speakers.

 

Right, we agree here. I pretty much do the same thing. I like the arrangement that the photos show. I sometimes place the subs on the inside depending upon the room. The RS5 allow you to also move those woofers facing inside or outside, so there is a lot of fine tuning available. I simply don't like the idea of the active preamp and higher crossover points that you are suggesting adding to the system. You should be able to get better sound with what you have, running the mains full range and utilizing all of the placement options to find the best positions for bass response in your room.
-Bill

 

Another option is a simple passive crossover between the preamp and main amp, thus avoiding a potentially poor sounding active crossover with added amplifier stages in the path. The simplest would just be first order, so just one good sounding capacitor in series with a value chosen based on your amplifier input impedance (typically 47Kohms) and the crossover point. I agree with Bill, if you go that way, go as low as you can. When I've done something similar, I usually set the crossover point around the rolloff point of the mains, and use the added crossover to keep the extreme lows out of the mains, as you propose. You can increase the high pass filter slope to second order if the losses aren't a problem (they shouldn't be here if you have plenty of gain), but that's about all you can realistically do with just capacitors and resistors.

Some places like Harrison Labs also sells inline second order low pass and high pass filters in a variety of frequencies for about $25 pair that could also be used, but again, I would keep the frequency low as possible, around 50 Hz if possible, for best integration. I haven't heard them or seen what the internal parts quality is like, I wouldn't expect too much, but they could be used for testing with the intention of building your own better sounding units later if it works the way you want. Not much DIY potential for the holidays with that approach, though

"Harrison Labs FMOD Inline Crossover Pair 50 Hz High Pass RCA" from www.parts-express.com!

 

Yep good info guys ill sit back for the moment on the active crossovers just got a bit excited when i saw a set for sale. I really need to measure the -6 db low frequency of the RS5's and then if i go down the passive sub bass tower route have a low pass filter at -6 db on them at that frequency.

I would still like to filter the lows out of the tube amps ive got running the RS5's and looking again at the Osborn Epitome speakers the first 10 inch woofer on the main tower is crossed over with the 6.5 inch mid at 125 hz and 12 db per octave. The bass/sub tower is crossed over or low passed at 60 hz but it doesn't specify if its just simply low passed or whether there are extra crossover components between the 2 towers. The description makes it sound like its crossed over but its impossible to know for sure.

So basically i have 3 options. Option 1 would be as stated first up above and running the tube amps and RS5's full range, then applying the appropriate low pass filter to the subs. Should i do that at speaker level after the power amps running the subs or line level so the power amp only sees the lows? I am thinking line level. Option 2 if i decide to do this instead of just continuing with the Rel T5 subs is to measure the freq response of the RS5's and then run passive 2 way first order crossovers after the pre-amp between 50 and 60 hz or whatever the measurements say. Option 3 again measure the RS5's then line level passive high pass filter the tube amps and RS5's and passive line level low pass the bass towers ( i can do this as my pre amp as dual pre outs).

What is the general feeling on line level passive crossovers and high/low pass filters? Is it ok given the low level signal? Maybe i should forget the whole thing and just measure the RS5's and blend the Rel T5's accordingly. My main goal if i was to go down this route would be to try and implement the woofers as if they were part of the RS5's hence the desire to actually cross them over with the main speakers, if this is ok at line level then it sounds like a goer.

I was thinking 10 inch scanspeak classic series woofers in sealed marine ply 80 - 100 liter boxes, the woofers have a very hard carbon fiber reinforced paper cone and were used in the Dunlavy SCIV/A speaker which they delivered 25 Hz in and were the main reason that the revised SCIV was so much better than the original.

 

Passive high-pass filters can color the sound a bit also by lowering the SNR. Passives are best implemented at speaker level. The Rel subs do all of this for you for the low-pass section. If you have a pair of the T5 subs, then you should be golden. Adding active subs at the low frequency cut-off point of any speaker system allows deeper bass as well as control of level and phase of it for matching into a particular room. The deep bass will have their own amps and crossover, and so you are effectively creating a very cost effective bi-amped system that doesn't intrude on the integrity of the main amp and speaker set. You shouldn't worry about the amps powering to the mains down to their lowest regions. The little bit below that isn't being as wasted as you might think as the Rega speakers do not attempt to draw too much power at levels below their range. If you really wanted to cut the very lowest of frequencies to the main amp without harm to the sound of the mains, then you might look into a very high quality passive LF filter, such as a subsonic filter for tit. Some preamps include this on the phono input, if you have that option, you should use it there. most Preamps also have some level of AC coupling to the main outputs which effectively cuts output which is below a certain level, usually subsonic, to the power amp. I think it's covered well enough not to be a concern.
-Bill

 

Once again @KT88 your logic is infallible. I will continue with the T5i's and just try and measure the low Freq roll off of the RS5 to gain better integration. The integration is already very good, i just hate not acually knowing a number.

I think moving up to the RS7 or R9 if i can ever find a set will give me what im missing in the RS5 while still giving me that glorious mid and treble i love from the RS5. I would also like to swap out the T5s for Rythmik F12 subs eventually. So ill forget about extra amps and crossovers and work on acquiring an RS7/R9 and dual F12 setup.

 

In fact it is the passive crossover that is the potentially poor sounding option. The main speaker woofer will have some of its most challenging parts of the impedance response curve below 100Hz, just where you want to cut out the sub-bass. This can make an "80Hz" capacitor value act like a 200Hz crossover at 100Hz but act like a 40Hz crossover at 50Hz.

Additionally, passive crossovers are much milder than you might imagine - an 80Hz single order only reduces 12dB at 20Hz, leaving substantial content from the main speakers in the two octaves the subwoofer needs to do its work.

With active crossover, you can have very steep slopes, ideally 24dB/octave (or 48dB/octave done digitally) for zero phase shift.

Fortunately our ear isn't acutely sensitive to the quality of audio in the subwoofer ranges. We only perceive the quantity. Strange cancellations are just detected as one bass note being louder than another.

 

The passive crossover we were discussing in this context is at line level between the preamp and amp, not between the amp and the speaker.