Considering Purifi vs Hypex MP but don't want to overpower LS50's

[john61ct]

> LS50s require an amp with both high Damping factor AND high Current to overcome voltage drop, due to the fact that their "nominal" impedance in reality can drop down to 4Ω or even a bit lower.

If that's true, that in fact a respectable Damping factor is not at all needed

is it just a coincidence that those amps handling varying impedance loads well at high SPL by delivering high Current levels

tend to also have high damping ratings?

Or is there an inherent connection between those two factors?

calling @harkpabst

 

[terryforsythe]

Apparently thereabouts is the right place for LS50s specifically, many say even higher.

It depends on numerous factors. The following two are fairly significant in my view:

1. SPL - The THD of the LS50s below about 160Hz or so starts to get a bit high at SPLs higher than 86dB. Handing off the lower frequencies to the subwoofer below 150Hz certainly will help.

2. If crossing over at 150Hz, the subwoofer location will be audibly detectable. In my experience, that degrades soundstaging and imaging. The lower the crossover slope on the subwoofer, the more the degredation. One way to reduce the issue is to place the subwoofer between the two speakers, but not off into a corner and certainly not behind you.

How far will you be sitting from the speakers and how loud do you plan on listening to them?

If sitting within 2m or so from the speakers, assuming you do not play them really loud, I think a 100Hz crossover frequency will be preferable, especially if the subwoofer is not located between the two speakers. If sitting farther away from the speakers, you like your music loud, and the subwoofer is placed between the two speakers, perhaps the 150Hz crossover frequency is the best choice. But, you won't know for sure until you actually put it together, start listening, and tuning with whatever means you have available.

 

[Sokel]

Thanks for actually addressing my text.

Yes I am aware a good DSP may well be superior, but 1. I can't afford a good one yet, may be years away and 2. my preference / bias is for analog simplicity especially for my LS50s channel, at least until measurements show more sophistication is required.

The LS50s are also the given in my system for now.



> 150 and 200Hz are a little high for a subwoofer/satellite configuration.

Apparently thereabouts is the right place for LS50s specifically, many say even higher.

You are correct that testing is needed. If 120Hz is high enough I can try using my Outlaw ICBM-1 to handle more of the crossovers.

There's a really nice thread here about subs, who digs deep about it.
Best place to form your views.

Adjusting an x-over to an inherent weakness of a speaker is not the right way.
Regarding subs, x=over and cut-freqs and configuration, I would start from the very experts here, I quote:

Floorstanders come with benefits, beyond headroom and low frequency extension. However, the main advantage has been somewhat kept a secret; due to a stubborn and detrimental simplification of reproduced sound in engineering literature: Disregard for inter-aural time domain coherency at low frequency. In case LF inter-aural time and magnitude differences have been recorded across channels, and made it safely through a reproduction chain, it is such a pity to kill Auditory Envelopment (AE) at the last stage, by using mono sub(s) with bookshelf/nearfield monitors. That’s game over before even started.

Floorstander-users expect at least some ability of a room and system to convey AE, possibly the most universal and enjoyable dimension the human auditory system is able to declare. The topic has been discussed before on ASR, and we will report from new studies in 2025. To the questions:

Genelec 83 series monitors include extensive per channel frequency domain and time domain adjustment capability. The GLM application can be used to adjust those parameters automatically, manually or in a combination of both. You might also make adjustments upstream instead, or partly upstream and partly in the 83s. Anyway, settings may be stored and set in stone per monitor. Settings will stay the same despite power-down; until GLM is connected again and deliberate changes made.

Building your own subs, for instance into walls, or buying a different brand, is therefore also fine. Because of AE, I would *always* use at least two sub channels. If later movement of subs will be impossible, consider listening to AE test samples before committing to placement. If two subs are not possible, I would not cross-over higher than 40 Hz.

Regarding hearing safety, with an average listening level of 105 dB(A), according to the clinical gold standard, adults should be listening for no more than 2 minutes per day (risk of material hearing loss ~1%).

It applies to any rig, even if the stereo sub subject is divided.

 

[john61ct]

It depends on numerous factors. The following two are fairly significant in my view:

1. SPL - The THD of the LS50s below about 160Hz or so starts to get a bit high at SPLs higher than 86dB. Handing off the lower frequencies to the subwoofer below 150Hz certainly will help.

My goal is "max safe" SPL across audible range, with the LS50s being the weakest link


> 2. If crossing over at 150Hz, the subwoofer location will be audibly detectable.

Sorry if it was not clear enough, but that crossover is handing off to the STEREO MBM pair collocated with the LS50s.

The "true sub(s)" if needed, will indeed be mono, only handling non-localized frequencies and placed to tame any room modes, or with the Center channel if that works.

And yes both types of testing will go into both placement and specific xover points.

 

[john61ct]

Best place to form your views.

Thanks for those references, will study

> Adjusting an x-over to an inherent weakness of a speaker is not the right way.

I plan for the MBM pair to give wide flexibility so I can experiment, go even higher if needed (300+?), or stay with the more usual lower ranges, if the midbass LS50 distortion issue is not an audible issue for me.

If that MBM pair give me "deep/loud enough" bass, and timing / room modes are not a problem then I may put off "true sub(s)" for some time, to rebuild family budget reserves.

I think it likely that when I do add to below-40Hz capabilities, it will be with more than one box.

But for now, that's getting ahead of the scope I want to get into detail with here.

 

[terryforsythe]

Sorry if it was not clear enough, but that crossover is handing off to the STEREO MBM pair collocated with the LS50s.

OK. That gives you a lot more flexibility with the crossover frequency and crossover slopes, which should enable you to keep the LS50s operating above the frequency range where they struggle at higher SPL. You will need some way to level match the SPL of the LS50s with the MBMs, which you probably already know.